ICG2022-10

ICG2022
Fluvial Geomorphology 

Fluvial forms and processes are crucial in shaping the landscape, as rivers are widespread on most of the Earth's surface. Fluvial systems bear enormous importance due to their consequences on sediment connectivity from uplands to oceans, on available water resources, on stream ecology, on natural hazards scenarios, and on ecosystem services for humanity. The purpose of this session is to gather contributions that highlight the role of geological and geomorphological aspects in understanding, modelling, and predicting, the past present and future behaviour of rivers. We warmly encourage contributions on the following topics, which are not exclusive:
i. Long to short-term geomorphological evolution of fluvial landforms and hydrographic basins induced by climate change, tectonic activity, and base-level variations;
ii. Channel evolutionary trajectories and influences of natural and anthropic driving factors;
iii. Sediment cascade, in channel-hillslope coupling and effects on channel morphology and dynamic on transitional environments;
iv. Geomorphic processes during floods and related hazards;
v. Basin management and river restoration projects;
vi. Interactions between fluvial morphology and ecology;
vii. Methodological advances in fluvial geomorphology (remote sensing, sediment transport monitoring, numerical modelling…).

Public information:

oral summary of posters will be possible during gaps of the oral program following abstract withdawal

Conveners: Vittoria Scorpio, Ana Lucía-Vela, António Martins, Ekaterina Matlakhova, André Salgado, Frédéric Liébault
Orals
| Mon, 12 Sep, 14:30–16:30, 17:00–19:00|Room Sala Mondego-C2A, Tue, 13 Sep, 09:00–10:30, 11:00–16:30, 17:00–19:00|Room Sala Mondego-C2A
Poster
| Attendance Tue, 13 Sep, 10:30–10:45 | Display Mon, 12 Sep, 09:00–Tue, 13 Sep, 19:00|Poster area, Attendance Tue, 13 Sep, 16:30–16:45 | Display Mon, 12 Sep, 09:00–Tue, 13 Sep, 19:00|Poster area
Public information:

oral summary of posters will be possible during gaps of the oral program following abstract withdawal

Orals: Mon, 12 Sep | Room Sala Mondego-C2A

Chairpersons: Vittoria Scorpio, Emmanuèle Gautier
Fluvial systems in the Long-term
14:30–14:45
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ICG2022-33
André Salgado, Eric Rezende, Rodrigo Paixão, and Paulo Castro

This work research fluvial piracy processes between two of the fifty largest catchments in the world: the Paraná and São Francisco ones, in South America. The study area comprises the Furnas Lake of the Furnas Hydroelectric Plant, in the south-west portion of Minas Gerais State, Brazil. In this region, the Paraná River is called Grande River and its catchment forms a large "amphitheater" facing north, towards the São Francisco catchment. The research method was based on: remote sensing, in order to identify drainage anomalies; the use of the Seppômen computational tool, to reconstruct paleotopographic evolution; and by field work, to confirm/improve remote sensing interpretations and to also obtain sedimentary and geomorphic data. Nowadays, the drainage divider between the two catchments is characterized by a series of mountain ranges and plateaus. However, in the region of Furnas Lake, near the village of Pimenta, there is an anomalous low divider between the two catchments. This anomalous low divider is located 25 km north of a 90° elbow that changes the direction of the Grande River from north (towards the São Francisco catchment) to west (towards the Paraná Sedimentary Basin) and corresponds to an expressive morphological record of paleo-valley that seems to have connected the two hydrographic basins currently separated. In the region of the low divider, on the top of a hill located in the paleo-valley on the São Francisco catchment side, next to the current headwaters of its tributaries, a pebbly fluvial Pleistocene unit (deposit of ancestral river before the beginning of the incision stage or being and old terrace) indicates that a major river flowed by the actual divide, in the past. In addition, the elbow that changes the direction of the Grande River makes it cross a quartzite mountain range through a series of river gorges, before entering in the Paraná Sedimentary Basin. The obtained Seppômen maps demonstrate that near the drainage elbow point the relief was about 400 m higher than it is now, configuring an old drainage divider along the quartzite mountain range. Furthermore, in the northern portion of the elbow, the topographical reconstruction maintained the valley morphology indicating that the Grande catchment had a connection with the actual São Francisco catchment. These evidences indicate that a major drainage rearrangement occurred between the two catchments, where a paleo-Grande (Paraná) River captured the ancestral upper São Francisco River catchment. This fluvial piracy was responsible for a capture of more than 50000 km2 and by the fact that the former source of the São Francisco River is now the current source of the Paraná River.

How to cite: Salgado, A., Rezende, E., Paixão, R., and Castro, P.: Large drainage rearrangement in South America: the capture of the high São Francisco catchment by the Grande (Paraná) River, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-33, https://doi.org/10.5194/icg2022-33, 2022.

14:45–15:00
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ICG2022-156
Arved C. Schwendel and David J. Milan

Post-glacial evolution of upland floodplains has been influenced by temporal changes in vegetation, sediment supply and hydrological regime. Channel-floodplain morphodynamics over the Holocene were conditioned by glacial deposits, lateral interaction with slope processes and fluvial sediment reworking, changes in flow and sediment supply regimes driven by climatic change, and more recently direct and indirect anthropogenic activities, e.g. deforestation, floodplain land use and channel modification. Current drives towards river re-naturalisation, often use floodplain topography as a guide to appraise such a planform state, however reconstruction of former channel state is often restricted to surface features visible on historic maps and aerial photographs. This research focuses upon the floodplain of the upper Swindale Beck, Lake District, UK, that was recently restored to a planform design based on the recent meander pattern visible in the floodplain topography. We investigate the potential of Ground Penetrating Radar (GPR) to reconstruct past channel pattern and evolution, and present findings from 40 intersecting GPR survey lines with a total length of over 3.2 km, covering >51000 m2. A centre frequency of 100 MHz allowed reliable imaging of the stratigraphy above the glacial diamict and was supported by 19 soil cores for ground truthing. An outcrop of an andesitic sill just downstream the study site provides a local base level and several alluvial fans constrain the floodplain laterally but also provide sediment to the system. Upstream of the site Younger Dryas glaciation extended into Swindale and the deposited moraines present a source of sediment to Swindale Beck.

Analysis of GPR data revealed several stratigraphic units, including gravel/ cobble plains, small multi-channel systems, several levels of larger channels incised in diamict or fluvial deposits, layered channel fill and floodplain deposits. These were interpreted as braided systems, dynamic wandering planform and single-thread meandering systems with spatial transitions conditioned by tributaries and valley slope. GIS analysis of valley slope, channel gradient and local valley floor aspect allowed the interpretation of individual evolutionary stages of river and floodplain development at Swindale and provides links to processes in the wider environment such as the influence of alluvial fans and bedrock outcrops. Such information can be particularly valuable for restoration projects to aid design of channel dimensions, planform configuration, channel gradient, substrate characteristics and connection with tributaries. While restoration generally aims to resemble a more natural reference state, specific targets may seek to improve a particular set of functionalities (e.g. ecological, flood and sediment management, recreational) which should be resilient to the consequences of ongoing climatic changes and should be achieved sustainably (e.g. locally sourced gravel). Here, GPR-based floodplain analysis provides a non-invasive approach to understand possible evolutionary trajectories and to appraise a wider range of restoration options and sustainable resources.

How to cite: Schwendel, A. C. and Milan, D. J.: Spatio-temporal floodplain evolution over the Holocene under the influence of valley constrictions, lateral fan input, and reworking of glacial deposits and the implications for river restoration., 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-156, https://doi.org/10.5194/icg2022-156, 2022.

15:00–15:15
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ICG2022-283
António Martins, Pedro Cunha, Margarida Gouveia, Alberto Gomes, Christophe Falguères, Martin Stokes, Pierre Voinchet, João Cabral, Jean-Jacques Bahain, and Gerardo de Vicente

The Lower Mondego Valley (LMV), located in the Western Iberian passive margin which is under compressive tectonic reactivation since ca. 80 Ma, is used for deciphering long-term landscape evolution during the Quaternary and the control played by active tectonics, eustasy and climate.

The elaboration of a detailed geomorphological map allowed the establishment of the spatial and temporal distribution of the different geomorphological units and morphogenetic systems operating in the LMV. The culminant unit of the Mondego Cenozoic Basin (allostratigraphic unit UBS13, recording an Atlantic fan-delta and adjacent shallow marine siliciclastic environments) and terrace levels (river and marine) are used as geomorphic markers to quantify fluvial development and tectonic activity. The main stages of evolution are a transition of endorheic to exorheic (Atlantic base level) drainage in the Mondego Cenozoic Basin, ca. 3.7 Ma ago, followed by onset of the fluvial incision stage (valley entrenchment) by ca. 1.8 Ma.

Electron spin resonance (ESR) dating is used to improve the chronological framework for the terrace staircases of the LMV and to decipher the response of the river to the regional uplift and other long-term controls (resistance of the substratum to erosion, eustasy and climate). Six river terrace levels (T1, the older, to T6, the younger), inset in the UBS13 and previous to the modern alluvial plain, were characterized and correlated with marine terraces represented at Cape Mondego, near the river mouth. The fluctuating eustatic and climate controls are superimposed on a long-term crustal uplift.

The data show marked compartmentalization of fluvial system behaviour with changes in incision rates (acting as a proxy of uplift rates) from east to west, creating distinctly different sectors. Differential uplift is inferred between the valley sides and between the four main reaches in which the LMV is subdivided by major faults. Differential uplift is mainly related to regional fault sets trending N-S to NNW-SSE, NNE-SSW, ENE-WSW, and E-W to WNW-ESE. Using as geomorphic references the topmost deposits of the UBS13 unit and river terraces located above the alluvial plain, average long term incision rates were estimated ranging from 0.03 to 0.16 m/ka, depending on the response of the Lower Mondego River to coupled regional uplift and differential uplift due to active faulting. Estimated average rates for the vertical slip component on the inferred active faults is ca.0.04 m/ka. This study demonstrates the applicability of river archives to assess not only the timing of uplift on a regional scale, but also the relative uplift of individual smaller tectonic blocks.

How to cite: Martins, A., Cunha, P., Gouveia, M., Gomes, A., Falguères, C., Stokes, M., Voinchet, P., Cabral, J., Bahain, J.-J., and de Vicente, G.: Geomorphic markers of Quaternary tectonics in Westernmost Iberia: insights from the Lower Mondego River terraces (central Portugal), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-283, https://doi.org/10.5194/icg2022-283, 2022.

15:15–15:30
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ICG2022-322
Pedro Proença Cunha and Augusto Pérez-Alberti

The drainage basin of the Atlantic Sil River is located in the central-eastern sector of Galicia (NW of Iberia) (Fig.1). The Sil and its tributaries, especially the rivers Xares, Bibei, Quiroga, Navea and Cabe, flow through a contrasting relief. Here, the transverse drainage is characterised by an alternance of tectonic depressions preserving Cenozoic sedimentary infills and incised meanders/canyons across montains of basement [1, 2]. The main tectonic depressions crossed by the Sill River are those of Valdeorras, Quiroga and Monforte (Fig.1). The mountains crossed by the river are mainly located the Ribeira Sacra sector. The Sil and tributaries mainly run cross basement areas, which mainly consists of Palaeozoic metamorphic rocks with minor granites, that are intensely faulted with main directions NNE-SSW, NO-SE and WNW-ESE.

In this work we present a characterization of the geomorphic and sedimentary units recording the geological evolution of the study area during the Cenozoic, under an intraplate compressive tectonic setting, leading to drainage re-organization, development of the Atlantic drainage and later stage of fluvial incision.

In the tectonic depressions, several sedimentary units are preserved: 1) two sucessive allostratigraphic units (unconformity bounded sequences; UBSs) of arkoses (Paleogene and Miocene); 2) two successive units of alluvial fan deposits, with endorheic drainage, probably recording the upper Tortonian to lower Zanclian (UBS11 and UBS12); 3) an uppermost unit of ocre heterometric alluvial fan deposits (UBS13), the first episode with exorheic drainage, tributary of an ancestral Atlantic river (the Sil River, conected with the Minho River) and with sedimentar record probably comprising the Upper Piacenzian to Lower Pleistocene (ca. 3.7 to 1.8 Ma) [2]; 4) a staircase of fluvial terraces (strath and sedimentary) produced during the later stage of fluvial incision (probably, the last ca. 1.8 Ma), recording the alternance of episodes of down-cutting, dynamic equilibrium and eventual sedimentary aggradation.

Regarding the NW of Iberia, our model for the transition of endorheic to exoreic drainage and the development of transcontinental drainage to the Atlantic Ocean is similar to the one proposed for the genesis of the Douro [3, 4] and the Tejo/Tajo (Tagus) [4, 5] rivers, involving as main mechanism an overspill induced by a major climatic change of increasing humidity by middle Pliocene.

 

How to cite: Proença Cunha, P. and Pérez-Alberti, A.: Discussion of the transition of endorheic to exoreic drainage of Cenozoic Basins in Galicia (NW of Iberia), the development of the ancestral transverse drainage to the Atlantic and the later stage of fluvial incision, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-322, https://doi.org/10.5194/icg2022-322, 2022.

15:30–15:45
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ICG2022-335
Geoffrey Houbrechts, Tomasz Kalicki, Paweł Przepióra, Bastiaan Notebaert, and François Petit

This research has two objectives: (I) to improve the methodology of using small-sized iron slag (microslag) as a stratigraphic marker to reconstruct the centennial-scale floodplain evolution and (II) to study the geomorphic evolution of the Ardennian rivers using the evaluation of the concentration of microslag in alluvia. In addition, 14C dating, topographic surveys and sedimentological analysis were carried out. Using these data, floodplain processes have been quantified in several Belgian rivers (Ardennes massif): fine floodplain sedimentation, lateral mobility rates and channel incision phases. A major hillslope erosion episode occurred during the Bronze Age. Archaeological data and historical sources indicate Roman and High Middle Age occupations in the area but no evidence of erosion or increased floodplain sedimentation have been observed. Several peat layers have been dated in the Chavanne floodplain to approximately 1000 BP and probably indicate very low anthropogenic activity and a high level of groundwater. Before 1000 CE, the fluvial style of the Ardennian rivers was probably different, characterized by a low-level forested floodplain, which explains the presence of frequent peat layers within the alluvial sequences and abandoned channels. From the eleventh century onwards, a generalized increase in sedimentation rates occurred, coinciding with a higher concentration of charcoal in the alluvium and also the formation of colluvial deposits. Analyses of slag concentrations allowed us to reconstruct the evolution of the floodplain topography. In Ardennian rivers, the mean floodplain aggradation over the last several centuries is between 3 and 20 cm/century, depending on the study site. Such differences in floodplain sedimentation rates can be explained by several factors such as the distance to past cultivation areas, the degree of woodland clearance, flow velocities during floods and the incision of the riverbed during last centuries, which reduces the frequency of inundation and, therefore, sedimentation on floodplains.

How to cite: Houbrechts, G., Kalicki, T., Przepióra, P., Notebaert, B., and Petit, F.: Microslag as a stratigraphic tracer to quantify floodplain processes during the last centuries, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-335, https://doi.org/10.5194/icg2022-335, 2022.

15:45–16:00
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ICG2022-420
Rodrigo Paixão, Marcelo Freitas, André Salgado, Luiz Guilherme Silva, Pedro Cunha, Antonio Alberto Gomes, António Martins, Julio Almeida, Miguel Tupinambá, and Marcelo Dantas

Endorheic drainage systems are rare in humid tropical areas and/or near the coast. However, in the passive margin of southeastern Brazil, in a region close to the Atlantic Ocean, is located the hydrographic basin of the Paraíba do Sul River, which has a humid tropical climate and presents landforms typical of endorheic drainage systems. The present work examines the possibility that Paraíba do Sul River Basin was endorheic during the most of the Neogene. It was based on morphological analysis of the drainage system, field work and on the interpretation of paleotopographic maps prepared using the Seppômen method. Five drainage convergence areas were identified along the main axis of the Paraíba do Sul River Basin, separated from each other by structural highs and each one associated with a Cenozoic graben. The drainage convergence areas appear to be endorheic hydrographic paleobasins, separated from each other by structural highs that would constitute their paleodivisors. The most probable mechanism for the transition endorheic-exorheic is overspill, leading to the progressive incorporation into the exorheic system and followed by headward erosion advancing inland from the gorge developed at each overspill area Atlantic Ocean. Two processes often occur concomitantly and both contribute to the same result: the expansion of an exorheic basin by the incision of a permanent channel into the endorheic basin infill. No numerical dating has been yet obtained for the proposed endorheic-exorheic transition; nonetheless, regional denudation rates suggest that this transition occurred sometime in the interval 8 to 4 Ma (end of the Miocene to mid-Pliocene), probably by 4 Ma. This transition was marked by a decrease in subsidence within the aforementioned grabens and by a much wetter climate that promoted the overspill and connection to the Atlantic. According to the interpretation of the evolution of headward erosion pulses in the Paraíba do Sul River basin, surfaces that dissected and sculpted the relief at different times during each tectonic and/or climatic event were interpreted.

 

How to cite: Paixão, R., Freitas, M., Salgado, A., Silva, L. G., Cunha, P., Gomes, A. A., Martins, A., Almeida, J., Tupinambá, M., and Dantas, M.: From endorheism to exorheism: The Atlantic draining Paraíba do Sul River Basin (Brazil) transition, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-420, https://doi.org/10.5194/icg2022-420, 2022.

16:00–16:15
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ICG2022-497
Fabiano Pupim, Caio Breda, Carolina Leite, Ian Del Rio, Sebastian Gómez, André Sawakuchi, and Mauricio Parra

Alluvial fans and terraces are well developed and preserved in the foothills of the Eastern Cordillera of Colombia, being potential archives of tectonic uplift and climatic variations in a poorly studied tropical region. The main aim of the work is to investigate the evolution of fluvial terraces and alluvial fans in the upper Caqueta river basin. We used Landsat imagens and Copernicus digital elevation model (DEM; GLO-30) to map landforms and optically stimulated luminescence (OSL) dating in quartz grains to estimate burial ages. Our results show that most landforms have an alluvial origin, organized in wide fluvial fans with distinct lobes, at least two terrace levels (7 and 13 m above the river level), and connected incised floodplains along the landscape. The sedimentary facies of the fluvial fans and terraces are dominated by clast-supported massive gravels, with thin layers of coarse-grained sandstones. The modern floodplains are related with braided-like to sinuous channels from up to downstream; gravels dominate their sedimentary facies, but fine sand and mudstones are frequent. This sediment finning from terraces/fans to modern floodplains suggests a significant sediment-to-water discharge ratio change through the late Quaternary. New OSL ages will allow us to estimate the burial ages of the mapped landforms and give new insights into the timing and driving factors related to changes in the fluvial dynamic and landscape evolution of the tropical Andean piedmont. (FAPESP #2020/11047-1)

How to cite: Pupim, F., Breda, C., Leite, C., Del Rio, I., Gómez, S., Sawakuchi, A., and Parra, M.: Fluvial fans and terraces in the foothills of the Eastern Cordillera of Colombia: morphology, sediments, and luminescence ages, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-497, https://doi.org/10.5194/icg2022-497, 2022.

16:15–16:30
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ICG2022-610
Renato Villela Mafra Alvesda Silva, Nelson Ferreira Fernandes, Carolina Coelho do Vale, and Lucia Maria da Silva

The river system plays a very important role in denudation processes and, consequently, in relief evolution in non-glacial landscapes. Several theoretical and empirical studies have contributed to a better understanding of how rivers change after modifications in their boundary conditions, such as tectonics or climate. The region of the Middle Valley of Paraíba do Sul (MVPS) has important records of recent drainage captures, which show a state of transition of the landscape and, consequently, a reorganization of the drainage networks. This region is in the Southeast of Brazil, topographically characterized as an area with escarpment of passive continental margin, where, close to the coast, the Serras do Mar and Serra da Mantiqueira stand out. The relief of the PSMV area and its respective drainage network had its evolution conditioned to the tectonic and climatic events that occurred during the Cenozoic. The oldest tectonic event is described as a NW-SE (E1) stretch, of Paleogenic age, followed by an E-W sinistral transcurrence (TS) event in the Neogene and a dextral transcurrence (DT) event, which occurred in the Pleistocene-Holocene. Finally, the extension event (E2) in the Holocene was associated with generalized reactivations of NE-SW structures, locally related to the generation of grabens, such as the Rio Bananal graben.Although of great importance in studies involving relief evolution, there are still few works that use river profiles and fluvial gradient indices such as χ and ksn to analyze the role of river captures in the reorganization of drainage networks and their relationship with neotectonics. Thus, the present study aims to investigate the causes of the reorganization of the drainage network in the MVPS region and its relationship with the evolution of the relief and its respective neotectonic activity. The E1 event was responsible for the consolidation of the hemi-graben configuration of the sedimentary basins in the MVPS. The normalized steepness index calculated for the main rivers demonstrates that this configuration possibly established a greater erosive power for the basins that drained the active fault, represented by the basins of the northern sector of the study area. During the Neogene, the TS event occurred, responsible for the inflections of the main channels to N-NW. These inflections are marked by knickpoints and sudden changes of χ and ksn in the fluvial profiles of the main channels. The paleotension analysis showed that structures associated with the TD event may be related to the filling and clogging of valleys with alluvium-colluvium ramps. The E2 event generated a system of normal transcurrent faults associated with a NW-SE Holocene extensional regime, responsible for captures oriented preferentially to SE and secondarily to NW. In the field, the relationship between TD and E2 was observed: the first related to NW-SE triangular facets and filling by valleys with alluvial-colluvium ramps and then, the fluvial capture promoted by E2. The Chi-z fluvial profiles and longitudinal profiles corroborate this model, indicating migration of the dividers compatible with the main capture directions observed.

How to cite: Villela Mafra Alvesda Silva, R., Ferreira Fernandes, N., Coelho do Vale, C., and Maria da Silva, L.: The drainage reorganization during the Cenozoic in the Middle Vale of Paraíba do Sul: the influence of tectonic and neotectonic controls on drainage captures, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-610, https://doi.org/10.5194/icg2022-610, 2022.

Coffee break and poster session
Chairpersons: Frédéric Liébault, Arved Schwendel
17:00–17:15
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ICG2022-634
António Gomes, Pedro Proença Cunha, António Martins, Martin Stokes, and Rui Fernandes

The Douro River, is ~900 km long and has a drainage basin of ~97,600 km2, crossing most of the Iberian Peninsula from east to west. The evolution of the Douro system documents an outstanding example of a continental-scale drainage reorganization, reflecting a transition from endorheic to exorheic conditions. By the middle Cretaceous, the passive Western Iberian Margin was tectonically reactivated by an increasing N-S to NW-SE compression, leading to intraplate deformation. This deformation peaked at ~9.5 Ma (middle Tortonian) resulting in differential uplift of crustal blocks. Until ~3.7 Ma (middle Pliocene) the regional drainage was routed east into the endorheic Douro Cenozoic Basin (DCB).

The Lower Douro River Section (LDRS) is limited upstream by a pronounced knickzone called the Arribas do Douro developed into resistant basement bedrock. Along the LDRS, the Douro incises into hard granitic and metamorphic rocks crossed by active fault zones, before reaching the Atlantic coast. The main valley along the LDRS displays a fluvial staircase configuration of 11 levels, with the upper levels occurring as erosional bedrock straths and the 3 lowest levels as straths with a fluvial sediment cover.

Recent work has indicated that capture-related re-organization via headwards erosion of a small Atlantic draining system was unlikely due to the high resistance of the basement bedrock and instead overspill is a more plausible explanation (Cunha et al., 2019). Although the endorheic-exorheic reorganization leading to an Atlantic system, has recently been investigated, the fluvial incisional stage of the main river and tributaries is less understood along the LDRS.

In this work, the characterization the transient landscape relief of four distinct sectors along the LDRS, in terms of: valley floor width-height ratio, degree and rates of incision, uplift rates, migration of successive erosion waves and knickpoint propagation, preservation of old plateaus of the regional planation surface, influence of lithology on the relief evolution, and the staircase arrangement along the main course considering the presence/absence of aggradational levels. The LDRS can be divided in four sectors separated by two major NNE-SSW strike-slip fault zones, which are represented morphologically as river gorges along the uplifted blocks between pull-apart basins (e.g., Régua and Vilariça-Pocinho). The less uplifted areas are also where the aggradational strath terraces are well expressed.

The 4 sectors are: I) from the river mouth till the confluence of the main northern tributary, the Tâmega River – adjacent to a wide littoral platform with inland hills (top surface <500 m); II) from the Tâmega confluence to the Mesão Frio-Régua tectonic corridor, corresponding to the uplifted relief of the Occidental Mountain Range; III) from Régua to the Pocinho-Vilariça pull-apart basin, corresponding to the High Plateaus region of Northern Portugal; IV) from Pocinho to the river elbow that marks the DCB margin, the old erosion surface of the Iberian Meseta.

Cunha, P.; Martins, A.; Gomes, A.; Stokes, M.; Cabral, J.; Lopes, F.; Pereira, D.; de Vicente, G.; Buylaert, J-P.; Murray, A.; Antón, L. 2019. Mechanisms and age estimates of continental-scale endorheic to exorheic drainage transition: Douro River, Western Iberia. Global and Planetary Change, 181, 102985.

How to cite: Gomes, A., Cunha, P. P., Martins, A., Stokes, M., and Fernandes, R.: Patterns and controls on fluvial incision in the lower Douro River (Western Iberia) following endorheic-exorheic drainage reorganization, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-634, https://doi.org/10.5194/icg2022-634, 2022.

17:15–17:30
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ICG2022-650
Piotr Gębica, Anna Michno2,, Mateusz Sobucki, Agnieszka Wacnik, and Sławomir Superson

Reconstruction of fluvial style changes in the San River in the Subcarpathian Basins is based on
geomorphological and sedimentological analyses. The time control of alluvial fills and temporal
changes in the river channel are derived from radiocarbon and optically stimulated luminescence
dating combined with independent pollen-based biochronostratigraphy. The results showed that the
alluvial plain of the braided (BR) or braided-meandering (BR-M?) river was abandoned before
12,800 cal BP. Large meanders (LM) were cut off in the older part of the Younger Dryas (YD; ca.
12,600 cal BP), and in the younger part of this period (ca. 12,450 cal BP). The small meanders (SM)
developed at the end of the YD and were abandoned at the onset of the Preboreal (PB; ca.11,550
cal BP). The erosion phase at the YD-PB transition, reported from many valleys in Central Europe,
was not confirmed in the study area. The full cycle of San River channel transformation (BR (BRM?)->
LM->SM); was estimated to be approximately 1200 years. According to the palynological data,
open pine forests with birch that survived from the end of the Allerød dominated the landscape of
the river valley during the YD cooling and did not undergo major changes during the warming in the
early PB. Therefore, we assume that the influence of vegetation changes in the San River channel
pattern transformation was nonsignificant. The location of the studied palaeochannels in the
floodbasin filled with silty clayey deposits may have influenced the formation of relatively narrow
and deep channels, than that of much the wider and shallower meanders from the YD, situated
several kilometres downstream of the surveyed sites.

How to cite: Gębica, P., Michno2,, A., Sobucki, M., Wacnik, A., and Superson, S.: Chronology and dynamics of fluvial style transformation in theYounger Dryas – Holocene transition (lower San River, SEPoland), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-650, https://doi.org/10.5194/icg2022-650, 2022.

17:30–17:45
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ICG2022-710
Eduardo Morais and Otávio Cristiano Montanher

The avulsions cause intense transformations in the fluvial landscape of meandering rivers. However, the morphometric and sedimentological adjustments during this process are still poorly understood. The Peixe River, located in the southeastern region of Brazil, has a partial avulsion, established with an avulsion channel of 14 km long, which remains for more than 48 years. In this study, we investigated variations in the sinuosity and width channels with remote sensing, as well as sedimentological features in channel banks of the parental channel with sampling in fieldwork. The sinuosity analyses showed between the years 1985 and 2020 a subtle increase in the avulsion channel (1.11-1.15), followed by a decrease in the parental channel (2.00-1.67). The decrease and increase in the mean width in, respectively, the parental channel (40.7-33.6m ±0.5m) and the avulsion channel (26.4-31.1m ±0.5m) between the years 2011 and 2020 resulted in a recent and approximated equivalence of width between the channels. The bank channel deposits in a segment, which includes the parental channel, were discriminated in the top and bottom layers. The top layer, which has coarser sediments and a lower concentration of organic matter than the bottom layer, showed a significant increase in muddy sediments and organic matter in the avulsion reach (t-test, homogeneous variance, p-value = 0.0013 and 0.048, respectively). Therefore, morphometric and sedimentological parameters evidence recent reorganizations of the drainage network and in the depositional model of the floodplain due to the development of partial avulsion.

How to cite: Morais, E. and Montanher, O. C.: Geomorphological adjustments in a partial avulsion: the Peixe River, Brazil, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-710, https://doi.org/10.5194/icg2022-710, 2022.

17:45–18:00
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ICG2022-738
Baotian Pan, Zhenbo Hu, and David Bridgland

The Yellow River originating from the Tibetan Plateau, flow eastward through the Chinese Loess Plateau and North China Plain, thus offers a favorable setting where fluvial response to the tectonic uplift, climatic change, and landscape evolution can be evaluated individually. Its formation and evolution process has attracted worldwide attention from geoscience. A series of continuous fluviolacustrine deposits with a chronological framework of >8.3-3.7 Ma were accumulated on the northeastern Tibetan Plateau and the west front of the Luliang Mtns, and regarded as correlated sediments of a Planation Surface leveling the eastern Asian. The statistics of gravel fabric and lithology in these fluviolacustrine sediments reveals that lots of paleo-lakes fed by local streams dominated the Yellow River catchment in this period. Two sets of fluvial gravel layers with local provenance, covered by Red Clay, were distributed discretely on this Planation Surface, along the northern Jinshaan gorge. They were dated prior to 4.9 Ma and 3.7 Ma respectively, indicating a northward flowing stream, which is different from the current Yellow River. The dramatic surface uplift initiating prior to 3.7 Ma not only interrupted the fluviolacustrine sedimentation, but also leaded to uplift of this Planation Surface. The hypsographic relief was enlarged, resulting in drainage re-organization. Previous fluviolacustrine systems were pirated by the river in the southern Loess Plateau and the North China Plain, creating the main part of the middle and upper Yellow River during the period of 1.2-1.8 Ma. Subsequently, an episode of uplift initiating at 1.2 Ma forced the Yellow River to continuously excavate and extend into the interior Tibetan Plateau. The current drainage pattern of the Yellow River was probably fixed prior to ca.10 ka. 

How to cite: Pan, B., Hu, Z., and Bridgland, D.: Origin of the Yellow River, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-738, https://doi.org/10.5194/icg2022-738, 2022.

Remote sensing and fluvial geomorphology
18:00–18:15
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ICG2022-15
Gustavo Nagel, Steve Darby, and Julian Leyland

Rivers and floodplains are hotspots of biodiversity that support a large and growing number of people with food, water, nutrients, and transportation 1. In these floodplains, processes of erosion on the outer-bank and sedimentation on the inner-bank drive lateral channel migration that can produce highly sinuous, intricate, meandering river landscapes. A key question in river meandering research concerns the debate about whether lateral river migration is driven initially by outer-bank erosion that induces local inner-bank deposition (bank pull), or whether inner sedimentation instead initially diverts the flow and subsequently forces outer-bank erosion (bar push). So far, studies exploring these mechanisms have been based on data from only a relatively few locations, producing divergent and inconclusive results 2,3

Here we propose a methodology in which a long time series of remote sensing imagery is combined with cloud computing to identify the prevalence of bar push versus bank pull across large expanses of the global river network. In our methodology, each image is analysed to identify the timing of pixels undergoing erosion and/or sedimentation. This was achieved by combining the algorithm LandTrendr, which identifies change detection in a time series, with the Modified Normalized Difference Water Index (mNDWI) extracted from Landsat imagery during the period 1984-2020. For the Amazon region, we created a time series of mNDWI for the dry season (August to October) to have a higher availability of Landsat images and to detect the point bars that would otherwise be submerged during the high-water season. Then, we extracted and polygonized the river shore for different periods of the time series. For every river mask, we analysed the erosion years that intersect the outer-bank polyline and the sedimentation that intersect the inner-bank polyline. Then we compared the mean of the two distributions (Δmean_1990 = mean erosion – mean sedimentation) and used the Z-test to identify if they are distinctive. Positive values of Δmean discriminate episodes of ‘bar push’, while negative values discriminate ‘bank pull’. By repeating this analysis for different years and across multiple Landsat tiles, we were able to extract a distribution of Δmean and Z-test values for a large number of river bends.

Extending this methodology for different rivers along the Earth will enable us to test the bar push versus bank pull theories systematically on a wide range of real environments. This will help to identify whether rivers have a predominant mechanism or if they shift between both processes thoughout the years, as suggested by Mason and Mohrig 2. This unprecedented scale of bar push versus bank pull analysis will improve our understanding of meandering rivers.     

 

1             Junk, W. J., et al. A classification of major natural habitats of Amazonian white-water river floodplains (várzeas). Wetlands Ecology and Management 20, 461–475 (2012).

2             Mason, J. & Mohrig, D. Differential bank migration and the maintenance of channel width in meandering river bends. Geology 47 (2019).

3             Van De Lageweg, et al. Bank pull or bar push: What drives scroll-bar formation in meandering rivers? Geology 42, 319-322 (2014).

How to cite: Nagel, G., Darby, S., and Leyland, J.: Towards a Global Assessment of Bar Push Versus Bank Pull using Remote Sensing and Cloud Computing., 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-15, https://doi.org/10.5194/icg2022-15, 2022.

18:15–18:30
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ICG2022-208
Robert Williamson, George Heritage, and Neil Entwistle

Naturally functioning gravel-bed rivers are dynamic, highly biodiverse, well connected to their floodplains. They provide valued services to mitigate downstream flood wave propagation and storage of supplied sediment. Human-altered environments, whether urban, agricultural or otherwise, have severely degraded channel form and function and have all but destroyed natural fluvial processes. They have been trained, straightened and dredged, with embankments further restricting flood waters, and management maintains the status-quo. These interventions have often resulted in an armoured plain river bed devoid of physical complexity to support stream metabolism, ecosystem productivity and biochemical function. Effective and sustainable river restoration; primarily through the structural alteration of channel form, requires an advanced mechanistic understanding of how flow and sediment transport regimes affect biota and ecosystem processes. Here we critically examine the 2021 restoration of Goldrill Beck, Cumbria, UK, using repeat drone based orthophotography and DTM outputs to quantify system response. Coupled with HEC-RAS 2D modelling we provide an insight into different river controls on the composition, structure, and dynamics of flow, sediment dynamics, habitat; and system resilience to a geomorphologically effective flood events.  The recorded changes are used to critically assess current approaches to river restoration and we suggest that a process-based approach to river restoration utilising improved scientific understanding of natural flood functioning and sediment dynamics is needed to address the challenges for ecosystem management that lie ahead.

How to cite: Williamson, R., Heritage, G., and Entwistle, N.: Effective and sustainable river restoration: 4D monitoring of a large upland gravel-bed river , 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-208, https://doi.org/10.5194/icg2022-208, 2022.

18:30–18:45
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ICG2022-35
Giulia Iacobucci, Michele Delchiaro, Francesco Troiani, Andrea Titolo, and Davide Nadali

The Barada River that originates in the Zabadani valley, within the western Anti-Lebanon Mountains (Syria), is the major watercourse within the Damascus Basin at the south-eastern sector of the Palmyrides chain. Since the early-mid Holocene, several human settlements have appeared in the area thanks to the water resource guaranteed by the Barada River, some ephemeral streams developing over a series of alluvial fan bodies fringing the piedmont zone at the margin of the Damascus Basin, and the  Al-Ataibeh Lake, in the eastern part of the basin, nowadays rarely reached by the Barada River outside the spring and the flood periods.

The importance of fluvial processes in the development of the active and relict landforms within the Damascus basin, as well as for the development and distribution of historical human settlements, is noticeably pointed out by the occurrence of several alluvial fans and associated deposits in the piedmont area. Their characterization of the piedmont processes and landforms in this specific zone can benefit from a remote approach based on Digital Elevation Models (DEMs) because of the large extension of the area preventing the exclusive field-based mapping and, moreover, in this zone as in the whole Syrian territory, the foreign research has been significantly restricted with the only exception for the archaeological ones. In this work, the interferometric 1-arcsec SRTM and the optical SPOT DEM with 8 m of ground resolution have been adopted for measuring morphometric variables useful to discriminate the prevailing fan feeding processes, considering that the construction and the development of fan deposits can be the results of fluvial processes (fluvial dominated fan), mass movements (debris-flow dominated fan) or by their combination in either space or time (composite fan). Unravelling the principal constructional process can be helpful for deciphering the main factor, amongst climate, tectonics, and human activities, influencing fans formation and their space-time development

The main aim of this study is the mapping and classification of the main alluvial fans along the south-eastern margin of the Anti-Lebanon mountains, distinguishing which kind of constructional process prevails in the area starting from a land-surface quantitative analysis. Eight alluvial fans have been selected, among which the most extensive is the westernmost one, developed by the Barada River. A series of morphometric variables have been computed using GIS useful for describing the surficial expression of the fan deposits, the upstream catchment morphology, and their relationship This work presents the preliminary results of the study and, for the first time, a preliminary geomorphological scheme of the piedmont zone along the northern margin of the Damascus Basins. Here, the occurrence of several archaeological settlements seems to be strongly influenced by the geomorphological framework of the area, suggesting a key role of the fans development in the spatial distribution of the early human settlements.

How to cite: Iacobucci, G., Delchiaro, M., Troiani, F., Titolo, A., and Nadali, D.: Land-surface quantitative analysis of the alluvial fans along the northern margin of Damascus Basin (Syria): preliminary results and geomorphological mapping, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-35, https://doi.org/10.5194/icg2022-35, 2022.

18:45–19:00
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ICG2022-709
A new look to an old problem: using Gaussian Mixture Models and topo-bathymetric LiDAR data for morphological classification of large lowland rivers
(withdrawn)
Alex Andréault, Stéphane Rodrigues, and Corentin Gaudichet

Orals: Tue, 13 Sep | Room Sala Mondego-C2A

Chairpersons: Frédéric Liébault, Vittoria Scorpio, Ronald Pöppl
Human impacts on channel morphology and sediment transport: managing and restoring altered channels
09:00–09:15
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ICG2022-62
Hanna Hajdukiewicz and Bartłomiej Wyżga

The Biała is a gravel-bed river in the Polish Carpathians that was severely affected by human activity over the last century. To restore the river, establishing an erodible corridor in two river sections was proposed. We analysed changes in planform river geometry over the last 130 years to determine hydromorphological river degradation and thus verify a need of river restoration. The belt of historical river migration on the valley floor was subsequently identified to help delimit boundaries od the erodible corridor. Finally, the degree of narrowing of the contemporary river in relation to its historical width was determined to predict the river potential for future bank retreat in the erodible corridor.

The study used topographic maps from 1878, 1935 and 1962, aerial photos from 1967, 1977 and 1987, and orthophotos from 1998 and 2009. For each date, boundaries of active river zone and river geomorphic units were digitized and their average width in 8 river reaches was determined. Overlays of an extent of active river zone from all analysed dates indicated the belt of river migration during the last 130 years. A comparison of contemporary river width with the largest river width recorded during the study period indicated the degree of river narrowing caused by its channelization and channel incision.

Between 1878 and 2009 the Biała experienced a marked reduction in width: three-fold in the upper study section and more than six-fold in the lower one. The river narrowing was associated with a reduced occurrence of channel bars in the river and nearly complete elimination of islands. These changes did not reflect a river metamorphosis that would require a substantial increase in channel sinuosity, but they were accompanied by deep channel incision with nearly unchanged river sinuosity, hence demonstrating hydromorphological degradation of the Biała.

The belt of the river migration over the last 130 years was 4.9 times wider than the contemporary river in the upper section of the proposed erodible corridor and 5.3 times wider in the lower section. This allowed for delimiting an erodible river corridor on a substantially larger area of the valley floor than the area of the river from 2009.

The contemporary river is narrower than the largest river width recorded between 1878 and 2009 along nearly the whole length of the investigated river sections, more than twice narrower along three-fifths of the upper section of the erodible corridor and two-thirds of the lower section, and more than four times narrower along one-fifth of both river sections. These values indicate that the concentration of flood flows in the narrow channel increasing their unit stream power is a factor markedly increasing the future potential of the river for bank erosion and channel widening in the erodible corridor.

This study demonstrated that analysis of historical channel changes is useful for diagnosing hydromorphological river degradation, delimiting an erodible corridor and predicting the river potential for future widening in the corridor.

 

This study was completed within the scope of Research Project 2019/33/B/ST10/00518 financed by the National Science Centre, Poland.

How to cite: Hajdukiewicz, H. and Wyżga, B.: Use of data about past river activity for delimiting an erodible river corridor: the Biała River, Polish Carpathians, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-62, https://doi.org/10.5194/icg2022-62, 2022.

09:15–09:30
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ICG2022-66
Anne-Julia Rollet, Romain Reulier, Guillaume Fantino, Simon Dufour, and Arthur Glais

In the search for good ecological status of watercourses, the restoration of sediment transport is today the subject of particular attention. The removal of transverse structures (weirs, dams) is often advocated, even though the real effect of small weirs on the transport of the bed load has not been demonstrated in all types of context (particularly medium and low energy rivers). This paper will present the results of a study on two highly anthropised rivers in Normandy (Vire and Orne Rivers, N-W France) to (I) document the real effect of weirs on the dynamics of coarse sediment transfers (> coarse gravel), (II) quantify the morphological effect of this interruption on the morphology/granularity of the channel, and (III) discuss the relevance of the removal of these structures for the restoration of sediment continuity in these systems. To this end, an annual sediment tracing system (848 RFID tracers) was set up in 2017 upstream of 6 structures of different types (micro-power stations, weirs, breached weirs) as well as on two recently restored sites in order to test different configurations. These tracers were placed in transects perpendicular to the flow, at different levels in the reservoirs in order to understand in detail the contribution of the water bodies and the structures as such in the modification of the mobility of coarse sediments. This monitoring was completed by measurements of morphological parameters (granulometry and geometry) upstream and downstream of these structures as well as by bathymetric measurements in the reservoirs in order to determine their filling levels. We were thus able to highlight the existence of coarse sediment mobility between structures despite modest powers (< 30 W.m²) as well as the significant effect of the hydraulic slowing of the reservoirs on the mobility of coarse sediments, regardless of the size of the structure considered. Since 2017, no tracer has been able to pass unrestored structures, which leads us to believe that these structures really affect sediment dynamics. Nevertheless, this sediment load interruption does not seem to induce any morphological adjustment downstream. These results thus question the interest of structure removal operations for the physical restoration of rivers in which the importance of solid flow seems to be a secondary control factor.

How to cite: Rollet, A.-J., Reulier, R., Fantino, G., Dufour, S., and Glais, A.: Weirs effects on the sediment continuity of two lowland rivers (Orne et Vire rivers, France) : implications for river restoration., 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-66, https://doi.org/10.5194/icg2022-66, 2022.

09:30–09:45
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ICG2022-79
Emmanuèle Gautier, Clément Virmoux, Charlie Hureau, Ségolène Saulnier-Copard, and Tristan Douillard

The new French regulation concerning the management of flood zones makes it possible to lower dikes that protect less than 30 inhabitants. Many dykes in rural areas fall into this category and can therefore be removed or lowered. In this context, we studied a long rural dyke (7 km) in the Loire valley (France). The dyke has created a “triple fluvial bed”, composed by a floodplain protected from frequent floods, a currently active bed and between the two parts, a floodplain occupied by a riparian forest - the active bed and the proximal floodplain being protected (Natura 2000). The objectives of this work are therefore i) to analyze the long-term trajectory of the embankment system in order to understand evaluate the potential effectiveness of the dyke removal; ii) the precise study of the alluvial forest aims to build a modelling of the future evolution. We developed a pluri-disciplinary approach combining history, earth science (geomorphology, sedimentology, geophysics and hydrology) and biology (study of the alluvial forest mainly by dendrology).

The historical study based on archival maps shows that the dike was built in several stages from the mid-18th century to the 1810s. The dyke has led to a fluvial metamorphosis marked by a strong reduction of the sinuosity and fluvial bed simplification. The river channel narrowed by two thirds. The alluvial vegetation progression not only reflects the fluvial form evolution, but also economic practices. On the one hand, pioneer vegetation growth was delayed by the agro-pastoral practices that ended at in the 1970’s. On the other hand, the dyke and the proximal floodplain were planted with hay and fruit trees, in order to protect the engineering work from erosion. Thus, different generations of fluvial forms are identified.

The precise study of the vegetation distribution allows to precisely determine the readjustment of the bed and the environmental drivers. The dendrochonologic analyses of the alluvial trees (hardwood and softwood forest) are good proxies to identify controlling factors at an annual time scale: hydrology (mainly frequency/duration of floods and of low water levels), climate and fluvial form evolution. The approach reveals a recent change (at the beginning of the 1990’s) that is mainly induced by the fluvial bed entrenchment and by the increasing duration of low water level. Finally, the study suggests that the dyke removal will not drastically modify the biogeomorphologic dynamics.

How to cite: Gautier, E., Virmoux, C., Hureau, C., Saulnier-Copard, S., and Douillard, T.: Long-term trajectory of an embankment fluvial system – the Loire River (France), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-79, https://doi.org/10.5194/icg2022-79, 2022.

09:45–10:00
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ICG2022-126
Antonia Foley and Luca Mao

Anthropogenic and climatic events continue to affect river systems despite restoration action. Flooding events are increasing across the UK and placing additional pressure on Local Authorities to mitigate flood risks River restoration remains a key focus of conservation by the UK government, particularly as anthropogenic activities and the changing climate continue to degrade river systems at all scales. The increasing risk of flooding events across the country puts pressure on Local Authorities to mitigate flood. Flooding causes high degrees of sediment transport along the entire fluvial system and has negative ecological and chemical consequences. Under further threat are chalk streams, where the calcium concentration allows for tufa to deposit under varying hydraulic conditions. Chalk streams are heavily degraded by anthropogenic and human activities; however, their consistent flow from grounder aquifers provide ecological opportunities. Tufa naturally occurs within chalk stream environments and creates step barrages within the UK, providing hydraulic conditions such as degassed oxygen which provide ecological benefits and microhabitats. These barrages have been removed in some chalk streams such as the Upper Witham in Lincolnshire and encouraging their restoration may have hydraulic and ecological benefits.

There remains limited understanding of the physical factors controlling tufa deposition and no local understanding of the deposition rate within Lincolnshire. Consequently, the focus of this work is to explore the physical and chemical factors influencing tufa deposition and monitor its growth. The aim is to quantify the tufa deposition rate at Dunston Beck, Lincolnshire, and the role of flow velocity, flow depth and substrate on deposition rates. These aims will be met by measuring the tufa growth on the 14 sandstone and wooden plates that have been placed along a small reach of Dunston Beck that emulate different hydraulic conditions. The tufa growth will be measured using a handheld 3D scanning device monthly and samples of tufa grown on these plates will be taken and scanned using a Scanning Electron Microscope to categorise morphology and substrate. This is extremely important for classification of tufa as its categories can be caused by varying physical factors including flow rate. The results can be used to inform restoration practices as flow rates and microbial activity have a known relationship with tufa deposition. This work will inform the second phase of the Dunston Beck restoration and inform the Environment Agency with further information for restoring and classifying these sites.

How to cite: Foley, A. and Mao, L.: Can we make tufa grow? Understanding the hydraulic conditions affecting tufa growth. , 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-126, https://doi.org/10.5194/icg2022-126, 2022.

10:00–10:15
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ICG2022-291
Sayoni Mondal and Priyank Pravin Patel

The inclusion of the term 'Hydromorphology' in the Water Framework Directive by the European Union has altered earlier perspectives of stream health analysis. Rivers are now viewed from integrative standpoints of channel morphology, hydrology and ecology for framing and sustaining long-term restoration goals. The scant examples of such analyses, especially from the Indian subcontinent, has spurred on this study to be undertaken in an eastern Indian river along which the ambient stream geomorphic condition was examined using an integrated, multi-metric framework that places due importance on morphological functions and hydrological attributes while also considering the riparian ecological structure as an essential element in judging the overall stream health. The enumerated Morphological Quality Index (MQI) deftly highlighted the causes of geomorphic and hydrological disconnectivities within the stream reaches while the site-specific Horton's Water Quality Index (WQI) revealed the direct influence that channel morphology and water quality have on in-stream biota. These results were further validated using vegetation indices like the Qualitat del Bosc de Ribera (QBR), Riparian Strip Quality Index (RSQI) and Normalised Difference Vegetation Index (NDVI) to provide greater objectivity of assessment and to gain a holistic insight into the overall stream health status. With anthropogenic pressures being the main triggers of stream health deterioration along this river, all the above indices pointed towards mostly degraded channel conditions, except in some relatively inaccessible reaches. Finally, the overall channel quality rating obtained by combining all these indices, identified the middle and lower courses as experiencing the highest degree of impairment, which equates to just over one-fifth (21.37%) of the entire river course. The adopted methodology was proven to be a rational framework for addressing the hydromorphological disturbances faced by a channel, in addition to pointing out sites that need management and restoration on a priority basis.

How to cite: Mondal, S. and Patel, P. P.: Multi-parameter based Channel Health Assessment for Reach Prioritization along the River Silabati in Eastern India for Stream Restoration, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-291, https://doi.org/10.5194/icg2022-291, 2022.

10:15–10:30
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ICG2022-336
Katarina Pavlek, Sanja Faivre, and Ivan Čanjevac

Since the end of the 19th century, river channels across Europe have been noticeably modified by human interventions and climate change. In Croatia, rivers are most significantly altered by the construction of hydropower plants and flood management measures, which often involve hard engineering strategies such as river straightening and channelization. This study investigates changes in channel morphology on two Croatian rivers from contrasting environments (the Karst Dinarides and the Pannonian Basin) since the end of the 19th century, based on the analysis of historical topographic maps and aerial images in GIS.

The Cetina River, located in the Mediterranean basin, has a composite valley characterised by an interchange of narrow carbonate canyons and zones of lateral valley widening. Its channel morphology has been strongly affected by the construction of hydropower plants since the 1950s. Therefore, we analysed changes in active channel width and the occurrence of fluvial bars and islands in the pre-dam phase (1880s–1950/60s) and the post-dam phase (1950/60s–2010s). Partial channel narrowing and drying of marsh zones recorded in the pre-dam phase were attributed to the natural changes in humidity and discharge following the end of the Little Ice Age. Agricultural intensification most likely had an influence on the increase in sediment supply, as evidenced in particular by a considerable river delta progradation of 500 m by the 1960s. In the post-dam phase, severe reductions in discharge due to water diversion resulted in channel narrowing by about 50% along one third of the river length. Moreover, we observed a reduction in the bar area and an increase in the island number. These changes can also be related to land abandonment and natural reforestation in the catchment.

The meandering Orljava River, located in the Pannonian basin, is distinguished by its dynamic morphology due to frequent flash floods. The river has not been extensively channelized unlike most lowland Croatian rivers. Nevertheless, its morphodynamics has been under significant human impact due to removal of riparian vegetation, artificial cut-offs, and the construction of weirs. Preliminary results suggest that the acceleration of lateral channel migration after 2011 is strongly related to the combined effect of recent engineering works, particularly removal of riparian vegetation, and a major flood event in 2014, since higher discharges were not followed by such high channel migration rates in the previous decades. Recently increased erosion of river banks leads to the loss of adjacent agricultural land, demanding a shift in approach to river management.

How to cite: Pavlek, K., Faivre, S., and Čanjevac, I.: River channel adjustments in contrasting environments from the analysis of historical maps and aerial images: the Karst Dinarides vs. the Pannonian Basin, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-336, https://doi.org/10.5194/icg2022-336, 2022.

Coffee break
Chairpersons: Vittoria Scorpio, Anne-Julia Rollet, Tomáš Galia
11:00–11:15
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ICG2022-414
Manel Llena and Damià Vericat

Human disturbances may alter the dynamic equilibrium state of a river system, which infers a balance between processes and forms. Within the human disturbances, instream gravel mining is one of the most widespread impacts in intermontane fluvial corridors since these systems have been historically used as: (i) preferential pathways for accessing and bypassing mountain barriers; and (ii) sources of local and available gravel for building industrial and transportation infrastructures. Instream gravel mining has a rapid and localised impact on channel morphology that may cause subsequent channel adjustments upstream and downstream. Traditionally, the classification of fluvial morphology of in-channel units has been centred on field-based and planimetric identification approaches, but these involve subjective interpretation of unit type and unit boundaries. In response of these limitations, fluvial taxonomy approaches based on the objectively and consistently delineation of geomorphic units from high-resolution topographic data, are presented as a more consistent approach to mapping geomorphic units. At the same time, these approaches has potential for assessing changes in geomorphic units as part of quantitative instream gravel mining monitoring, allowing testing gravel mining actions design hypotheses. In this context, the aim of this work is to quantify the short-term effects of instream gravel mining on the geomorphic unit diversity of an intermountain river. To pursue this objective, we use pre and post-gravel mining high-resolution topographic surveys of the Upper Cinca River (Southern Pyrenees) to systematically map changes in the geomorphic units by the application of the Geomorphic Unit Tool (GUT).

How to cite: Llena, M. and Vericat, D.: Quantifying the short-term effects of instream gravel mining on the geomorphic unit diversity of an intermountain river, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-414, https://doi.org/10.5194/icg2022-414, 2022.

11:15–11:30
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ICG2022-505
Sumantra Sarathi Biswas and Padmini Pani

Anthropogenic activities are one of the extrinsic factors that significantly alter the fluvial processes. The stream power is the primary agent of a river that controls the natural processes of a channel. It is influenced by hydrology, natural configuration and artificial constructions of a river. The Damodar River runs through the plateau, plateau fringe and plain region of eastern India has been selected for the study. It is altered by several anthropogenic activities such as dam and barrage constructions, sand mining, industries and coal mining, landuse changes etc. The upper and middle sections (~180 km) of the river have been taken for the study as stream power variation is significant in these sections. The flow velocity is measured from eleven sites from the upper and middle sections of the river to estimate stream power. The Integrated Anthropogenic Index (IAI) has been generated for the identification of the natural and anthropogenic dominant reaches. The IAI includes various types of indices such as artificial water surface ratio (AWSR), road along river ratio (RARR), road density (RD), artificial river ratio (ARR), artificial coal mining ratio (ACMR), and bridge along river ratio (BARR). The anthropogenic controlled reaches are characterised by the drastic increase of stream power with some exceptional knicks. The multimodal stream power distribution of the river is associated with energy alteration. It reflects in the development of various types of bars which are inversely related to stream power. Innumerable human activities produce slope irregularities resulting in stream power and eventually, it reflects on the processes and landform development of the river.

How to cite: Biswas, S. S. and Pani, P.: Indices Based Approach Appraisal of Anthropogenic Activities and its Impacts on Stream Power of a Plateau Origin River in India, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-505, https://doi.org/10.5194/icg2022-505, 2022.

11:30–11:45
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ICG2022-582
A national catalog and an assessment tool for hydromorphological characterization of French rivers (Carhyce)
(withdrawn)
Frederic Gob, Nathalie Thommeret, Clelia Bilodeau, and Karl Kreutzenberger
Biogeomorphology of rivers
11:45–12:00
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ICG2022-93
Janet Hooke

Presence of vegetation in channels has major effects on hydraulics and on erosion and deposition dynamics, especially in ephemerally-flowing channels in drylands where plants may grow on the channel bed as well as on the banks.  The plants can alter the flow velocities and patterns of flow, including the location of erosion and deposition. The plants themselves provide resistance through both aerial parts and roots and they interact with the flows to increase sedimentation.  Levels and frequencies of flow vary markedly in dryland channels and plant species commonly demonstrate distinct zonation related to these flow dynamics, channel bed elevation and substrate.  Channel flow and availability of water may encourage growth, but large flood events may damage or destroy vegetation by various mechanisms, including removal and burial.  Quantitative data are needed on the conditions for growth, the effects of differing flows on a range of species and the thresholds for destruction. In addition, rates of regrowth after damaging floods are required to provide the basis for modelling and the timescales of recovery. Evidence and measurements from a series of sites and monitored plots on channels in SE Spain over a period of 25years are analysed to quantify these dynamics and interactions. The implications for the functioning and management of such channels are discussed.

How to cite: Hooke, J.: Vegetation dynamics and interactions with flows in dryland channels, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-93, https://doi.org/10.5194/icg2022-93, 2022.

12:00–12:15
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ICG2022-398
Quintia Vaessen, Jean Van Campenhout, Geoffrey Houbrechts, and Alain Hambuckers

Since decades, rivers have undergone numerous alterations that have led to disturbances in flow regimes, sediment transport, and water quality to name a few, leaving freshwater fauna facing among the highest risk of extinction. The thick shelled river mussel (Unio crassus) is a European endangered freshwater mussel. As an “umbrella” species, its preservation benefits the whole river ecosystem. However, it remains uneasy to establish a direct causal link between a specific factor of alteration and a decline in the mussel populations. Indeed, in Belgium, this species is unevenly distributed, and its decline is equally uneven. This study explores the link between the species and its fluvial habitat to identify which parameters of the abiotic and biotic environment are responsible for the current distribution of the thick shelled river mussel in Belgium. To test the ability of environmental variables to predict the presence of the species, hydro-geomorphological characteristics of the streams (e.g., return period of the bankfull stage, substrate grain size, land cover, local slope, stream power at bankfull stage…), physico-chemical parameters (water chemistry and pollutants), and host fishes’ abundance of the mussel were compiled. A regularized linear regression technique was used to select the relevant variables to the presence of the species. After selection, logistic regression was performed on the selected parameters to determine which variables have the greatest impact on the species distribution. Our analysis indicates local slope as the most impacting parameter for the presence-absence of the thick shelled river mussel in the studied rivers. Other parameters could be significant, especially at a more local scale. The ecological significance of river longitudinal profile in the existing distribution patterns of the species could be useful to river managers to optimise species habitat and helps establishing target actions to be undertaken to improve their conservation.

How to cite: Vaessen, Q., Van Campenhout, J., Houbrechts, G., and Hambuckers, A.: How fluvial habitat variables shape the regional distribution of a threatened freshwater mussel, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-398, https://doi.org/10.5194/icg2022-398, 2022.

12:15–12:30
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ICG2022-362
Naoko Nagumo and Shinji Egashira

River flow, sediment transport and channel width influence one another, and channel width generally changes toward the equilibrium state in sediment transport. When the tidal range is large with the water level fluctuating periodically, the sediment transport capacity of the river channel increases in the river mouth due to the drawdown effect during low tide, whereas the backwater effect becomes dominant during high tide. Therefore, the channel width is determined by the flow discharge during low tide and tends to be wider toward the mouth. On the other hand, when the channel in the river mouth is submerged during the rainy season in tropical regions, the channel width is defined by the flow discharge during the transition period from the rainy season to the dry season. This presentation explains a mechanism that determines the channel width in the river mouth by taking rivers in Japan and Southeast Asia as examples.

How to cite: Nagumo, N. and Egashira, S.: Effect of water level variation on the channel width in the river mouth, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-362, https://doi.org/10.5194/icg2022-362, 2022.

Lunch break
Chairpersons: Frederic Gob, Daniel Vázquez, Frédéric Liébault
Sediment transfers and connectivity in the river channels
14:30–14:45
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ICG2022-28
Ronald Poeppl, Kirstie Fryirs, Jon Tunnicliffe, and Gary Brierley

Globally, fluvial systems are under considerable and increasing threat from a plethora of anthropogenic stresses. These include different types of indirect (e.g. land cover/use or climate change) and direct human impacts (e.g. river engineering) that alter water and sediment dynamics. It is widely known that (dis)connectivity relationships in river and catchment systems determine the source, timing and rates of water and sediment flux and thus their geomorphic sensitivity and response to disturbance. However, most river and catchment management plans overlook the role of sediment (dis)connectivity. Here we use examples from different environmental settings with different sediment-related problems to show how understandings of sediment (dis)connectivity can inform catchment-based management. Specifically, we focus on concerns for river conservation and recovery, using examples from Austria, New Zealand and Australia. Moreover, we present questions for practitioners to appropriately contextualise (dis)connectivity concepts in system-specific place-based management applications. 

How to cite: Poeppl, R., Fryirs, K., Tunnicliffe, J., and Brierley, G.: Why is managing sediment (dis)connectivity in fluvial systems so important?, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-28, https://doi.org/10.5194/icg2022-28, 2022.

14:45–15:00
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ICG2022-77
Lukáš Vaverka, Adriana Holušová, Zuzana Poledniková, and Tomáš Galia

From a general point of view, river sediment is gradually fining the downstream direction, which is mainly a product of abrasion and selective transport. Downstream fining is not constant, and certain disturbances, such as sediment supply from tributaries or erosion connected with lateral and vertical shifts in the channel, can abruptly change sediment size. The main goal of this case study is to analyse discontinuities in the downstream fining of sediment size and link these variations with possible sources, i.e., lateral inputs. We focussed on the 75-km-long Odra (Oder) River reach in Czechia. The Odra is a relatively preserved meandering river with dominant gravel sediments. The supply of sediments is realised from two contrast geologically distinct mountain ranges, namely the Nízký Jeseník Mts. (generally offals and slates) in the Bohemian Massif and the Moravskoslezské Beskydy Mts. (flysch-based) in the Outer Western Carpathians. Analysis of the surface layer of 15 gravel bars was performed by the Wolman method, by which we randomly measured 100 clasts on each gravel bar. Additionally, we collected subsurface samples for sieving analysis. In the composition of the subsurface samples, there were dominant gravels and sandy gravels. Only four sites were muddy sandy gravels, which may be caused by the predominant slow flow in that part of the Odra River reach. The data of the coarse-grained material (≥ 2 mm) from the surface layer showed downstream fining only in the approx. first third of the river reach (27 km). The downstream part of the reach did not show significant fining, but rather a gradual increase in grain size of the surface bar layers. The most apparent fluctuation in grain size showed the 25th and 75th percentiles (14 - 29 mm and 25 - 42 mm, respectively), while the median indicated lesser variations. The discontinuity in fining can generally be linked to the influence of tributaries that carry coarse gravel from mountainous areas, but in this case the samples near tributaries do not show abrupt changes in sediment calibre. It is reasonable to assume that the coarse sediment was supplied to the river by lateral erosion of alluvial deposits in active meander bends, as indicated by the presence of coarse gravels in the architecture of the eroded alluvium.

How to cite: Vaverka, L., Holušová, A., Poledniková, Z., and Galia, T.: Downstream fining of bar sediments in a meandering river: variations and influence of lateral inputs in the upper Odra River, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-77, https://doi.org/10.5194/icg2022-77, 2022.

15:00–15:15
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ICG2022-80
Virtual velocity of fluvial sediment using mine tailings as a tracer in a gravel-sand bed river in the Ozark Highlands (USA)
(withdrawn)
Robert Pavlowsky and Scott Lecce
15:15–15:30
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ICG2022-128
Tomáš Galia, Václav Škarpich, and Stanislav Ruman

Many mountain streams across Europe are managed by grade-control structures (e.g., check dams or boulder ramps) and embankments with the aim to increase the lateral and vertical stability of the channels and to reduce bedload transport rates. We conducted a field experiment in the flysch Carpathians, Czechia, to assess sediment fluxes in a managed and untreated pool-riffle stream of similar characteristics (channel width ≤5 m, bed slope ~2 %) to evaluate the impact of rigid stream management on coarse sediment connectivity. The fieldwork included the tracking of PIT-tagged gravels and cobbles (four-year monitoring between 3/2018 and 2/2022), the analysis of the grain size of the surface and subsurface bed sediments, and geomorphic mapping. After three bankfull flow pulses, we found large disproportions in bedload transport activity between the managed and the untreated stream, when much longer travel distances of the PIT-tagged particles up to 500 m by skipping of seven consolidation check dams were recorded in the first case, whereas the most PIT-tagged particles were deposited in gravel bars and riffles relatively close to the release site in the latter case. Lateral sediment supply and vertical bed material exchange were markedly reduced by the presence of artificial bank stabilisations and a forced bed armour layer (d50surf / d50sub ~ 4) without noticeable development of gravel bars in the managed stream. This also led to overall degradation of the channel and loss of geomorphic complexity, when uniform plane beds without variable bedforms were separated by individual check dams. On the contrary, the frequent presence of bank failures on the outer banks of bends and the low difference between the grain sizes of the surface and subsurface sediments (d50surf / d50sub ~ 1.5) suggested strong interactions in the vertical and lateral dimensions of the sediment (dis)connectivity in the untreated pool-riffle stream. These findings have implications for sediment-transport processes and sustainable management of wider gravel-bed channelized rivers, when one may expect rapid flushing (relatively low incoming rates) of bedload particles and intensification of bed armouring processes accompanied by a loss of habitat heterogeneity.

How to cite: Galia, T., Škarpich, V., and Ruman, S.: Mountain managed streams as highways for reduced bedload transport, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-128, https://doi.org/10.5194/icg2022-128, 2022.

15:30–15:45
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ICG2022-472
Suspended sediment budget in the Bananal Plain tropical wetlands, Araguaia River basin, Central Brazil
(withdrawn)
Edipo Cremon, Daniel Araujo Ramos dos Santos, and Gabriel Pereira
15:45–16:00
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ICG2022-480
Askoa Ibisate, J. Horacio García, Alfredo Ollero, Carles Ferrer, Daniel Vázquez-Tarrio, Juan Pedro Martín Vide, Iban Sánchez-Pinto, Xabier Herrero Otero, and Josu Ortiz

Dams, weirs and other transversal obstacles limit sediment transport. River restoration seeks the recovery of river processes and functions. Rivers need water, sediment and space. In this work we present a couple of examples of sediment transport recovery and monitoring. One of them was implemented through the removal of a dam and the second one through sediment transfers downstream a dam.

Dam removal allows the recovery of the longitudinal connectivity of rivers, facilitating water and sediment transfer. In Leitzaran River (Basque Country, Spain) bedload sediment transport was monitored from 2016 to 2022 in a reach of river affected by the Oioki dam, 7-meters high. The removal, funded through a LIFE project, started in 2018 with the first 3 meters of the dam, and was completed in 2019 with the remaining 4 meters. RFID technique was used for the monitoring. 300 tagged particles were introduced each year, 100 in each subreach (control, upstream the dam and downstream), 1800 in total. Each summer an intensive field work campaign searching these tags has been conducted. This long monitoring has given results of the sediment transport in different conditions, before removal, during partial removal and after complete removal. Once the dam is completely removed an important increase of the volume of mobilized sediment both in the upstream and downstream reaches is given. The mobilization of sediment is more a question of availability and change of river conditions, opening of a barrier and base level change, more than flows, as it was registered in the most discreet hydrological year of all the monitoring period.

In active hydroelectrical stations,, where removal is not an option, sediment transport recovery could be implemented differently. In Viar River, a tributary of Guadalquivir (Spain), is a completely clogged counter reservoir where the electrical company (ENDESA) needs to withdraw sediment to increase volume and pump it back to El Pintado reservoir for reversible hydroelectrical generation. Guadalquivir basin authorities require giving it back to the river instead of bringing to a dump. In 2021 autumn 700 m3 of sediment were withdraw from a deposit and located upstream the counter reservoir dam, terrain characteristics are difficult and do not allow downstream mechanical transfer. The clogged reservoir would allow the auto-transfer by the river. The goal is to propose an auto-transfer system, studying the critical flow and creating flow conditions from upstream reservoir to allow sediment movement and transfer, recovering environmental conditions and avoiding reservoir clogging.

How to cite: Ibisate, A., García, J. H., Ollero, A., Ferrer, C., Vázquez-Tarrio, D., Martín Vide, J. P., Sánchez-Pinto, I., Herrero Otero, X., and Ortiz, J.: Sediment mobility recovery experiences: dam removal and sediment transfer through dams, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-480, https://doi.org/10.5194/icg2022-480, 2022.

16:00–16:15
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ICG2022-530
Julián García-Comendador, Núria Martínez-Carreras, Josep Fortesa, Jaume Company, Antoni Borràs, Edwin Palacio, and Joan Estrany

Soil properties' conservative behaviour is essential in sediment tracing research. To compare suspended sediment and soil samples, it is necessary that soil properties remain stable or vary in a predictable way during its transfer from sources to deposition areas. Conservative behaviour of soil properties has been largely focused on the differences in particle size and organic matter. However, in-channel biochemical alterations are also known to occur, but further research is needed considering the wide variety of fluvial regimes. Here is presented an experiment to investigate variations of in-channel soil properties' by using the most common soil properties used as tracers in sediment fingerprinting studies; i.e., colour, fallout radionuclides and geochemical elements. Twenty-eight soil samples collected from different land uses were introduced in an intermittent stream channel of a small Mediterranean catchment. Samples were extracted at different time intervals (i.e. 7, 30, 60, 90, 150, 210, 270 and 365 days) during one year. Results showed that changes on soil properties -average coefficient of variation 8.1 ± 8.8%- were generally lower than its spatial variability within the catchment (average coefficient of variation 16.3 ± 18.5%); being the colour properties the most stable tracers with an average coefficient of variation 2.6 ± 2.2%. The general low variability observed in the investigated soil properties and its strong correlations with specific surface area and carbon content seems to emphasize the role of particle size and organic matter in the conservative behaviour of soil properties. The exploration of in-channel soil properties variability can improve the selection of tracers in future suspended sediment fingerprinting studies in Mediterranean catchments.

How to cite: García-Comendador, J., Martínez-Carreras, N., Fortesa, J., Company, J., Borràs, A., Palacio, E., and Estrany, J.: Sediment Fingerprinting Tracer Conservativeness: Exploring the In-Channel Soil Properties variability, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-530, https://doi.org/10.5194/icg2022-530, 2022.

16:15–16:30
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ICG2022-597
Joan Estrany Bertos, Julián García-Comendador, Jaume Company, Miquel Febrer, Miguel Molina-Rotger, Adolfo Calvo-Cases, and Josep Fortesa

Sediment discharges quantify the pace of landscape evolution and provide a baseline for assessing the impacts of land use changes on soil erosion and sediment discharge. Estimates of the long-term sediment discharge from catchments are important because they provide a measure of basin-averaged erosion rates considering the understanding of erosion and sediment transport is crucial for the sustainable management of water and soil resources. Geomorphologists have currently a significant understanding of sediment delivery in catchments, but there is still a lack of comprehension of how these processes are coupled or decoupled in different types of catchment cascades. Besides, catchment monitoring is complicated by the fact that the relevant processes operate at different temporal and spatial scales. This requires that a nested approach is adopted and that catchment data are collected on the micro to macro scale. This approach has been applied in three gauging stations (3.4, 52.6, and 145 km2) of the Sant Miquel River, a Mediterranean mountainous catchment (151 km2) highly shaped for the human activity (i.e. intensive agriculture, terracing, check dams, channelization) and land abandonment (i.e. revegetation processes). It has an intermittent hydrological regime due to the predominance of karstic processes, despite groundwater from these karstified formations contribute with large water volumes in the middle and downstream part of the catchment. This communication aims to assess the runoff and suspended-sediment transport as well their dynamics (hysteresis) at different time-scales during a 7-year study period for these three nested catchments where water and sediment fluxes were continuously measured and recorded to evaluate the sediment cascade at annual, seasonal and event scales. A discharge (Q; m3 s−1) and suspended sediment concentration (SSC; mg l−1) database with 56 (3.4 km2), 36 (52.6 km2), and 99 (145 km2) events was used to perform a hysteretic analysis using the h index developed by Zuecco et al. (2016). Results showed an annual average suspended-sediment yield of 7.5, 40.8, and 26.2 t km-2 yr−1 from headwaters to downstream, evidencing transmission loses between the middle and downstream part of the catchment. Clockwise Q-SSC hysteresis loops (with the suspended sediment peak leading the discharge peak) were recorded most frequently (~50 %) at the two headwater sites, being only 31 % in the downstream site where the figure-of-eight pattern (clockwise and anti-clockwise) predominated with 62 % of the events involving that sediment concentration continued to rise despite the falling hydrograph; pattern promoted by the sediment contribution from different tributaries and sources. The need to obtain long-term monitoring programmes provides the key value of this communication to reach a comprehensive understanding about the sediment cascades on catchments at different scales. For this reason, it is necessary to continue exploring the sediment origin dynamics in the future, like an opportunity to reach the scalar integration between processes and techniques to better understand and validate erosion models in Mediterranean catchments.

How to cite: Estrany Bertos, J., García-Comendador, J., Company, J., Febrer, M., Molina-Rotger, M., Calvo-Cases, A., and Fortesa, J.: Quantifying suspended-sediment cascade and dynamics in a Mediterranean mountainous river, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-597, https://doi.org/10.5194/icg2022-597, 2022.

Coffee break and poster session
Chairpersons: Janet Hooke, Askoa Ibisate, Vittoria Scorpio
17:00–17:15
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ICG2022-737
Menghao Li, Zhenbo Hu, and Baotian Pan

The Yellow River is one of the rivers in the world with the largest sediment runoff, with the middle reaches of the Yellow River being an important link between the Qinghai-Tibet Plateau and the North China Plain, and even the Bohai Sea and the Yellow Sea for material transport. Understanding the material transport pattern of this section of the Yellow River is crucial to solving the problems of sediment accumulation in the lower reaches of the Yellow River, which is prone to breakouts and diversions. Detrital zircon U-Pb spectrum is widely used as an important provenance tracer in the river sediments of the world. Previous studies of coarser sediments (>40um) in the modern riverbed of the middle and upper Yellow River suggest that the modern Yellow River can barely transport material from upstream to downstream. This study extends the range to >20um grains and uses sediment source tracing on the geomorphic surface combined with chronology to reveal the formation process and material transport pattern of the Yellow River from the Jinshaan Gorge to the Sanmen Gorge section.

The study shows that the main source of material in the Jinshaan Gorge section of the Yellow River has been from the surrounding mountains and the bedrock within the gorge since its formation. Since the Holocene, increased surface erosion within the Chinese Loess Plateau and headward erosion by local rivers have brought material from the western part of the Chinese Loess Plateau. In the Sanmen Gorge section, the discrepancy between the ancient eastward-flowing rivers and the modern Yellow River material source reveals the formation of a pattern in which headward erosion of local rivers cut through Sanmen Gorge and led to the eastward flow of the Yellow River into the sea.

How to cite: Li, M., Hu, Z., and Pan, B.: Detrital zircon U-Pb ages from geomorphology surfaces in the middle reaches of Yellow River, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-737, https://doi.org/10.5194/icg2022-737, 2022.

Channel response to extreme events and flood hazard management
17:15–17:30
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ICG2022-87
The role of extreme events and human activities in the transformation of the Himalayan river corridor (Darjeeling Himalayas, India)
(withdrawn)
Pawel Prokop
17:30–17:45
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ICG2022-125
Steve Darby and the EVOFLOOD Team

Flooding is the deadliest and most costly natural hazard on the planet, affecting societies across the globe. Nearly one billion people are exposed to the risk of flooding in their lifetimes and around 300 million are impacted by floods in any given year. The impacts on individuals and societies are extreme: each year there are over 6,000 fatalities and economic losses exceed US$60 billion. Moreover, these problems will become much worse in the future: There is now clear consensus that climate change will, in many parts of the globe, cause substantial increases in the frequency of occurrence of extreme rainfall events, which in turn will generate increases in peak flood flows and flood increased areas of land.

Faced with this pressing global challenge, reliable tools are required to predict how flood hazard and exposure will change in the future. Existing state-of-the-art Global Flood Models (GFMs) are now widely used to simulate the probability of flooding across the Earth, but in some instances the predictive ability of current models is constrained by a fundamental limitation. Specifically, current GFMs treat rivers and their floodplains essentially as 'static pipes' that remain unchanged over time. In reality, river channels evolve through processes of erosion and sedimentation, driven by the impacts of diverse environmental changes (e.g., climate and land use change, dam construction), which lead to changes in channel flow conveyance capacity and floodplain connectivity.

In this paper we demonstrate the extent to which flood model predictions of flood inundation are sensitive to altered representations of channel morphology, across large spatial scales. In our GFM the channel bathymetry is inverted from bank elevation given an assumption of bankfull discharge (typically 1 in 2 year). By changing the bankfull discharge and recomputing the bathymetry it is therefore possible to simulate the impact of conveyance changes, driven by channel erosion and sedimentation, on flood hazard. Here we conducted a suite of simulations for test sites within the Mississippi River basin, at which long term change or variability in bankfull conveyance have been constrained by direct observations at gauging stations.    

Our results clearly indicate that in-channel changes are significant in driving altered flood hazard. It follows that until GFMs are able to fully account for morphological changes predicting the evolution of future flood hazard, understanding its underlying causes, or quantifying associated uncertainties, will remain very challenging.

How to cite: Darby, S. and the EVOFLOOD Team: Large-Scale Flood Model Simulations Reveal the Significant Role of Changing Channel Conveyance Capacity in Driving Altered Flood Hazard, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-125, https://doi.org/10.5194/icg2022-125, 2022.

17:45–18:00
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ICG2022-236
Frédéric Liébault, Guillaume Piton, Gabriel Melun, Margot Chapuis, and Paul Passy

Documenting and interpreting channel responses to catastrophic floods help understanding how rapid fluvial metamorphosis can propagate in a catchment under sediment cascading effects. The recent example of the October 2020 Alex storm in SE France (~500 mm of rain in 24 h) provides a unique opportunity to investigate the sudden formation of a braided channel along 35 km of a confined alpine valley (Vésubie) and to link the morphological response with sediment wave initiation and propagation. GIS-based analysis of remote sensing data (high-resolution ortho-imagery and airborne LiDAR data) acquired before and after the flood allowed combining channel changes with sediment erosion and deposition along a 35-km reach of the Vésubie, including the most impacted portions of the valley. Archives of aerial imagery and old pictures were also used to integrate the storm impact in the historical trajectory of the river. Comparison of the Alex storm effect with past major floods that occurred in the valley shows that active channel widening after the storm was one order of magnitude higher than during the 100-yrs flood of November 1997. Dramatic channel aggradation was observed, with net bed-level change exceeding 10 m in some proximal reaches. This case study allows us to discuss the critical role of floodplain and terrace erosion in the formation of the post-flood braided channel, and to compare the geomorphic impact of the storm with similar reported cases in the literature.

How to cite: Liébault, F., Piton, G., Melun, G., Chapuis, M., and Passy, P.: Channel change during catastrophic flood: example of the Alex storm in the Vésubie valley, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-236, https://doi.org/10.5194/icg2022-236, 2022.

18:00–18:15
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ICG2022-350
Sedimentation from extreme summer 2021 flooding along the Maas River, Netherlands: The role of flood duration
(withdrawn)
Paul Hudson
18:15–18:30
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ICG2022-260
Gerardo Benito, Noam Greenbaum, Alicia Medialdea, Mikel Calle, Yolanda Sanchez-Moya, Maria Machado, and Juan Pablo Corella

The Duero River is one of the three major rivers in the Iberian Peninsula, draining a catchment area of 98,073 km2 (20% in Portugal and 80% in Spain) to the Atlantic Ocean. Extreme flooding in the western Duero River is associated with winter Atlantic fronts leading to some of the highest specific discharges to be found in European rivers. A paleoflood record in the Duero canyon, at the Spanish-Portuguese boundary, provides evidence of magnitude, frequency and timing of such extreme phenomena during the last 15 ka. Slackwater flood deposits (SWDs) are preserved in thick, high-standing benches in canyon expansions and tributary mouths. Fourteen high-resolution stratigraphic profiles were studied in two reaches, next to Bemposta and Saucelle dams, at the Arribes Natural Park. The paleoflood chronology was established using optically stimulated luminescence (OSL) and AMS radiocarbon dating. Flood discharge associated with each flood bed was estimated from hydraulic modelling (HEC-GeoRAS v.5).

The most complete record is found at the Duero-Tormes river junction (Bemposta reach), which comprises five inset SWD benches at elevations between 15 m and 25 m above river water level (arwl). The highest bench comprises six flood units within four sequences, dated to 13.8ka, 8.4ka, 2.4ka and post-2.4ka. At 23.5 m arwl, the second flood bench recorded 23 flood units organized into four sequences separated by well-developed paleosols, and dated to 11.6ka, 9.5ka, 4.4ka, 2.2ka and <0.5ka. The third inset bench (20 m arwl) comprises 19 flood units dated between 11.6ka and 10.5ka, whereas in the fourth inset bench (17.5 m arwl) 17 flood units were dated to 14.9ka, 12.6ka and 11.5ka. About 1 km downstream, a flood bench deposited at a channel expansion records 14 flood beds over the last 1.8ka with discharges >5000 m3/s.

The composite stratigraphic record comprises 62 floods over the last 15ka grouped into 10 flood phases (FP1 to FP10) with minimum discharges ranging between 4000 m3/s and 11,000 m3/s. The hydroclimatic analysis of the flood events, supported with historical flood analysis, shows a good temporal correlation between the occurrence of catastrophic floods and the existence of anomalous negative NAO index phase. The Duero’s palaeoflood record correlates in timing with flood episodes recorded in other Iberian rivers (e.g. Tagus, Guadiana) and lake sediments (e.g. Lake Sanabria), which highlights the impact of atmosphere-ocean hemispheric coupling conditions on extreme floods in the region. These findings suggest a response, at centennial scale, between climatic factors and the outcome variability in the magnitude and frequency of floods.

How to cite: Benito, G., Greenbaum, N., Medialdea, A., Calle, M., Sanchez-Moya, Y., Machado, M., and Corella, J. P.: Magnitude and frequency of palaeofloods of the Duero River (Spain and Portugal) in the context of climate variability during the last 15 ka, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-260, https://doi.org/10.5194/icg2022-260, 2022.

18:30–18:45
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ICG2022-659
Anna Kidová, Artur Radecki-Pawlik, Miloš Rusnák, and Karol Plesiński

The contribution evaluates the impact of river training works designed to address problems associated with flooding on the braided-wandering Belá River in Slovakian Carpathians. This impact was investigated after the flood event in July 2018 on 11 river reaches where the river engineering and management intervention was applied. We analyzed its impact by spatio-temporal variations in river morphology (12 channel parameters) and changes in cross-section and hydraulic parameters (flow velocity, shear stress, stream power, W/D ratio) between pre- and post-flood management periods. The research hypotheses related to decreasing geodiversity in managed river reaches, a rapid increase in flow velocity during an extreme flood in river reaches where there is no sufficient floodplain inundation due to artificially high banks built by river training works, and increasing erosive force in the channel zone thanks to river management intervention were confirmed. The intervention in the braidplain area of the Belá River resulted in an undesirable simplification of the river pattern, loss of geomorphic diversity, loss of channel–floodplain connectivity, and disturbance and restraint of hydromorphological continuity. Identification of main conflicts of the Belá River management is important for clarifying the different approaches of stakeholders in the study area and aims to provide an objective illustration of their consequences. The presented analyses could help in future management issues as well as in the more critical decision-making process in vulnerable and rare braided river systems on the present when we are losing so many natural rivers by human decisions. This research was supported by the Science Grant Agency (VEGA) of the Ministry of Education of the Slovak Republic and the Slovak Academy of Sciences (02/0086/21).

How to cite: Kidová, A., Radecki-Pawlik, A., Rusnák, M., and Plesiński, K.: Morphological and hydraulic response of the braided-wandering river to human intervention (the case study of the Belá River, Slovak Carpathians), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-659, https://doi.org/10.5194/icg2022-659, 2022.

18:45–19:00
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ICG2022-676
Peter Labaš, Anna Kidová, Šárka Horáčková, Milan Lehotský, and Miloš Rusnák

The multi-thread Belá River runs through the Liptov basin in the north part of Slovakia representing a braided-wandering river system. Flood events and a large volume of sediment transportation are crucial to keeping the braided processes, supported by the multiple channels re-division and formation of gravel bars. However, environmental changes in the last decades had been affecting the river system. The former braided river pattern had been gradually transformed and simplified to the braided-wandering river system. These morphological changes provide space for floodplain preservation, including benches formation and maintenance, landforms with a lack of attention in fluvial geomorphological research in the mountain gravel-bed rivers. A local incision of the river channel restricted the floodplain development limited only to ledges formation. The river landscape monitoring, based on a combination of the Earth observation data (on 11 time horizons) and field surveys allowed monitoring and evaluation of the response of the river systems to environmental changes (discharge decreasing, extreme floods reducing, land cover changes, anthropogenic interventions). Research on lateral shifting and incision of the river channel, as well as the research of the multiple floodplain levels, preserving benches as fine sediment storage, separated from the river, were carried out. Based on these results a process-oriented hypothesis of the recent lateral and vertical development of the floodplain will be formulated. This research was supported by the Science Grant Agency (VEGA) of the Ministry of Education of the Slovak Republic and the Slovak Academy of Sciences (02/0086/21).

How to cite: Labaš, P., Kidová, A., Horáčková, Š., Lehotský, M., and Rusnák, M.: Geomorphological evolution of the floodplain in mountain environment as a response to environmental changes (case study of the Belá River, Slovak Carpathians) , 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-676, https://doi.org/10.5194/icg2022-676, 2022.

Display time: Mon, 12 Sep 09:00–Tue, 13 Sep 19:00

Poster: Tue, 13 Sep, 10:30–10:45 | Poster area

Chairpersons: Frédéric Liébault, Vittoria Scorpio
P42
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ICG2022-579
Maria Pilar Rabanaque, Vanesa Martínez-Fernández, Mikel Calle, Carles Sanchis-Ibor, Francisca Segura-Beltrán, Yolanda Sánchez-Moya, and Gerardo Benito

Since the 70s, Mediterranean ephemeral rivers in Spain have been subject to large-scale in-stream gravel mining. In the 90s, this activity ceased to a large extent, although nowadays new controlled in-stream gravel extraction pits have continued. The decreased on gravel mining activity, together with the longitudinal transport of sediment generated by flooding, has allowed these streams to begin to recover their alluvial landforms although their development and continuity is controlled by channel entrenchment and limited by sediment supply.

This study aims to quantify the spatial-temporal changes generated along the river in order to characterise the transmission of sediment longitudinally.  For this purpose, remote sensing methods offer efficient and powerful techniques. Particularly, a supervised classification with SVM (support vector machine) was carried out annually from 2018 to 2021 in the Rambla de Cervera, an ephemeral stream at the Castelló province in eastern Spain. Orthophotographs from the Institut Cartografic Valencia with a resolution of 0.25 m/pixel and RGBI bands were used for the classification. In this classification, three landforms have been differentiated: bedrock (exposed at riverbed), channel (channel gravels and unvegetated gravel bars) and vegetated gravel bars (gravel bars with vegetation cover). Subsequently, an automatic segmentation along the river corridor was performed every 100 m. Finally, the classification values for each segment were extracted and data analysis was performed.

Preliminary results show that river recovery is controlled longitudinally by geological and structural controls. On wide alluvial reaches lateral river supply from bank erosion contributes to forming lateral gravel bars within a narrower alluvial active belt. Conversely, on confined reaches with structural control, gravel bars in the channel bed are discontinuous and alternate with erosional stretches indicating supply-limited conditions. At the most depleted sediment transmission conditions, dense vegetation is stablished decreasing the alluvial longitudinal continuity. The diachronic analysis of the orthophotographs (2018-2021) indicates an incipient recovery of the alluvial landforms at the most downstream reaches which were subject to the most extensive in-channel gravel mining. In summary, the combined use of high-resolution orthophotography with machine learning algorithms provided an effective technique for monitoring spatial-temporal stream recovery and the identification of river sectors where management and restoration efforts are urgent.

How to cite: Rabanaque, M. P., Martínez-Fernández, V., Calle, M., Sanchis-Ibor, C., Segura-Beltrán, F., Sánchez-Moya, Y., and Benito, G.: Monitoring channel response and recovery of ephemeral Mediterranean streams using diachronic orthophotography analysis with machine learning (Rambla de Cervera, Spain), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-579, https://doi.org/10.5194/icg2022-579, 2022.

P43
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ICG2022-41
Rosana Menéndez-Duarte, Daniel Vazquez-Tarrio, Jesus Ruiz-Fernandez, Jose Maria Fernández-Fernández, and Gabriel Goyanes

In this work, we present preliminary data on grain size, morphometry, and sediment transport for the lower sector of a stream located in the South Bay of the Hurd Peninsula (Livingston Island, South Shetland Archipelago). This stream flows close to the Spanish Antarctic Base ‘Juan Carlos I’ (BJCI) and has a length of roughly 300 m, representing a small proglacial channel draining the front of the Hurd Glacier. 
To characterize channel morphometry, we based on high-resolution topographic measures collected in the field with a dGPS (Trimble-R8S) and a 4-cm resolution photogrammetric DEM, built using aerial images taken with a drone. These data, together with field observations, allowed us to define three different sectors along the longitudinal profile of the studied stream. The most upstream sector flows through a raised beach, where the channel shows a typical braided morphology with a gentle slope (0.6º). The channel evolves downstream into a steeper (average slope 4º) and straight single-thread channel, which is incised through a series of successive raised beachs. The channel finally ends and flows into a small coastal lagoon, where it deposits its load and generates a fan-shaped sediment lobe. The lagoon is formed by the damming effect of the upper bar of the modern cobble beach.
We also sampled for grain-size characterization in four different sections: 1) a braided reach, located in the upstream sector of the channel: we observed there a highly heterometric and matrix-supported deposit, likely suggesting the influence of debris and/or hyperconcentrated flows; 2) a single-thread reach, incised into the beach terraces located in the middle sector of the channel: there, we documented a coarse, paved and clast-supported deposit that we interpreted as a basal lag; 3) the upper sector of the fan-shape lobe deposit in the coastal lagoon: we observe a coarse, but heterometric grain-size distribution typical of bedload transport; and 4) the lower sector of the fan-shape deposit: we reported a sand-rich grain-size distribution, typical of fluvial sediment transport. The observed downstream trends in grain size suggests a change in the rheology of the flow during the dominant channel-forming floods from hyperconcentrated to stream flows.
Moreover, we have launched a monitoring study of sediment transport processes in this stream. To do so, we seeded 50 PIT-tagged stones (tracers) for RFID tracking along two different cross-sections located in the single-threaded, middle sector of the studied channel. The tagged cobbles were collected from the riverbed, drilled and sealed with resin, after inserting PIT-tags into them. All these tasks were carried out at the BJCI facilities during the 2018-19 Antarctic campaign, and we are planning to return there in the 2022-23 campaign in order to track and document the tracer displacements.

How to cite: Menéndez-Duarte, R., Vazquez-Tarrio, D., Ruiz-Fernandez, J., Fernández-Fernández, J. M., and Goyanes, G.: Grain-size, morphometry and sediment transport in an Antarctic stream located close to the Spanish Antarctic Base ‘Juan Carlos I’ (Livingston Island, South Shetland Archipelago)., 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-41, https://doi.org/10.5194/icg2022-41, 2022.

P44
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ICG2022-74
Daniel Vázquez-Tarrío, Rosana Menéndez-Duarte, and Raquel Martínez Álvarez

Plenty of sediment-transport equations and models have been proposed for the estimation of bedload volumes and rates in mountain streams. Some of the more ‘modern’ equations incorporate explicit considerations of complex phenomena (e.g., hiding/exposure effects, armour breakup) and provide reliable bedload computations based on section-averaged hydraulic parameters. However, due to the strong non-linearity of sediment transport, bedload equations are highly sensitive to the input parameters. Then, some doubts appear when facing poorly gauged river reaches, which is a common situation in many mountain rivers, i.e., gauging data are usually scarce and incomplete for mountain streams, as well as the availability of robust rating curves is rare.

In this work, we evaluated the uncertainties inherent to the application of bedload equations in the case of poorly gauged mountain streams, and we test a workflow to follow in such situations. This workflow involves three steps: (i) first, using the available gauging records from neighbouring basins to reconstruct the flow duration curve of the ungauged stream; (ii) then, using a flow-resistance equation to solve the hydraulic geometry relations; and finally, (iii) computing bedload volumes based on a sediment transport equation. This workflow was tested with a database of 33 Idaho (USA) mountain streams, and we documented that it could potentially approximate annual bedload volumes in an ungauged situation.

Then, we posed the following question: could this observation be extrapolated to 'similar' mountain streams located in other regions? To approach this question, we selected the Coto river, a gravel-bed stream located on the Cantabrian Mountains (NW Spain). Bedload data derived from particle tracking (tagged stones) were available for this river, so it was possible to compare the field measurements with the outputs obtained from bedload equations. First, we based on available data for 27 gauging stations located across the Cantabrian mountains to reconstruct the flow duration curve of the Coto river. Then, we measured Coto river’s cross-section, bed slope and grain-size in order to apply a flow resistance equation and to solve the hydraulic geometry relations. Finally, we applied a bedload equation, and we estimated an annually averaged bedload volume of 900 m3/year. The estimated bedload volumes are coherent and in good agreement with those derived from tracer observations.

How to cite: Vázquez-Tarrío, D., Menéndez-Duarte, R., and Martínez Álvarez, R.: Estimating bedload in a poorly-gauged mountain river: Coto river (Cantabrian Mountains, NW Iberian Peninsula) , 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-74, https://doi.org/10.5194/icg2022-74, 2022.

P45
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ICG2022-109
Wesley Rodrigues and André Salgado

In the last decades, there has been progress in understanding the importance of tectonic activity and climatic oscillations for the relief evolution of semi-arid regions. However, little is known about the role of drainage rearrangements in the morphogenesis of semi-arid areas. The semiarid region of Brazil, particularly in its northern passive margin, exemplifies this lack of studies. The configuration of the drainage network in the region is interpreted as a passive inheritance, given by superimpositions on Precambrian structures reactivated during the opening of the Equatorial Atlantic Ocean in the Cretaceous. Thus, this research aims to understand the current hydrographic configuration of the northern Brazilian semi-arid region, investigating geological and geomorphological evidence of possible fluvial reorganisations. Those evidences were identified on a regional scale, from the analysis of diagnostic morphologies of drainage rearrangements (e.g. capture elbows, anomalous drainage patterns, low divides and dammed river deposits) in geological maps and in data extracted from remote sensing (e.g. MDE SRTM 1 arc-second). Among the results, the following stand out: (i) dense drainage network formed by parallel exorheic rivers, in which only two very asymmetrical catchments – Jaguaribe and Piranhas-Açú – comprise about 73% of the regional flow; (ii) transverse tributaries marked by gorges that break the regional structural fabric; (iii) 4th order (or higher) river channels with sudden inflexions and reversals, especially orthogonal elbows, generally close to flattened divider sectors; (iv) concentric drainage patterns coincident with areas of natural damming of Neogene fluvial deposits, and areas with inactive pediment levels and; (v) surface dissection levels with differences of about 200 m high, with transitions limited by Precambrian structures reactivated during the Neogene-Quaternary. This evidence suggests that the region's drainage network has undergone recent and complex reorganisations, with fluvial incorporations carried out by the Jaguaribe and Piranhas-Açú catchments, probably on endorheic systems. The apparent expansion of the Jaguaribe and Piranhas-Açu catchments indicates that these rivers had their erosive power increased to the detriment of adjacent rivers, reordering regional watersheds through captures and overflows. This fact indicates that drainage rearrangement processes in semi-arid areas may have been more complex than previously thought and show the need for more research on the topic.

How to cite: Rodrigues, W. and Salgado, A.: Drainage rearrangements in a semi-arid area: a case study on the Brazilian northern passive margin, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-109, https://doi.org/10.5194/icg2022-109, 2022.

P46
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ICG2022-114
Massimo Rinaldi, Rafael Baena-Escudero, and Inmaculada Concepción Guerrero-Amador

This study describes the morphological changes occurring upstream a dam along a low energy alluvial river having cohesive banks, low bed slope, and high flow regulation within the catchment. Based on the observed changes, a channel evolution model is developed.

A multitemporal analysis of aerial photos and topographic survey comparison of the channel bed upstream a run-of-the-river dam along the lower Guadalquivir River (southern Spain) were used to document the morphological changes within a temporal interval of about 60 years and to derive the channel evolution model. For different cross-sections located along the reservoir channel, the trajectories of channel changes and the development of riparian vegetation were documented in relation to magnitude and frequency of floods and to the functioning of the dam.

Morphological changes mainly consisted of bed siltation and channel narrowing, terrace formation in the channel reservoir, and expansion of riparian vegetation. These changes induced significant effects on flooding of the adjacent alluvial plain, consisting of a reduction of the discharge necessary to start the inundation. Information on morphological changes in different locations along the reservoir within the investigated time interval were summarised by a space-for time evolutionary model consisting of a sequence of stages of channel evolution.

How to cite: Rinaldi, M., Baena-Escudero, R., and Concepción Guerrero-Amador, I.: Morphological changes and development of a channel evolution model upstream a dam, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-114, https://doi.org/10.5194/icg2022-114, 2022.

P47
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ICG2022-115
Dan Dumitriu

 

Flood events as geomorphic thresholds for river channel change

Dan Dumitriu

“Al.I.Cuza” University of Iaşi, Faculty of Geography and Geology, Department of Geography, Carol I Bd, no 20A,Iaşi, 700505-RO, Romania

E-mail address: dndumitriu@yahoo.com

 

Abstract: River channel are highly dynamic in time and across space, constantly adjusting under the influence of natural and anthropogenic controls. The aim of this study was to assess the role of flood events recorded between 1994 and 2020 in the Trotuș River (Eastern Carpathians) channel changes. The response of the channel to these floods consisted of discontinuous spatial adjustments in the channel width and channel bed elevation. The assessment of the channel aggradation/degradation rates was performed based on the evolution over time of average multiannual discharge levels and channel survey data (cross-sections). Prominent changes in the channel occurred in the Târgu Ocna–Căiuţi sector (30 km long, nearly 20% of the entire length of the river), where, between 1994 and 2020, the channel planform have widened significantly and channel bed deepened by an average value of 1.15 m (2.2 cm y-1). In terms of their geomorphic impact, the 2005, 2010 and 2016 flood events can be considered severe floods, even catastrophic in certain sectors. The recovery time for changes triggered by major flood events ranged between one and nearly 10 years, whereas in the case of shifts generated by high frequency, low magnitude events, the recovery time was maximum one year. Over short term flood events drive the direction and intensity of channel bed elevation adjustments.

Keywords: Flood; channel bed level change; channel planform change;  recovery time; geomorphic impact

How to cite: Dumitriu, D.: Flood events as geomorphic thresholds for river channel change , 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-115, https://doi.org/10.5194/icg2022-115, 2022.

P48
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ICG2022-147
Camille Fraudin, Eva Mercier, François Petit, and Geoffrey Houbrechts

Significant hydrological and morphological changes occur with the construction of hydropower plants. The main modifications are related to changes in the hydrological regime and disturbances of the sediment continuity.

This study is based on the Warche River in the northern Ardennes (Belgium), on a 7 km stretch downstream of the Bütgenbach dam built in 1932. During the winter months, the hydroelectric power plants release a flow of 10m³/s almost every day, which corresponds to the morphogenic flow (0.6 bankfull discharge).

A study carried out in the 1990s (Assani and Petit, 1997) showed that, following the construction of the Bütgenbach dam, a general incision of the entire 7 km stretch took place in about 30 years, followed by a doubling of the channel width. Other changes such as a reduction in the number of riffles and pools, an increase in the number of gravel banks and islands and an increase in rock outcrops in the channel have also taken place.

In our study, the question is to quantify the rate of propagation of this incision. For this purpose, RFID tags implanted in pebbles were used. As the morphogenic discharge is reached almost daily, surveys were conducted directly in the days following the deployment of the PIT tags. In a second step, more spaced surveys were also carried out according to the hydrological events.

A second part of our study consists of analysing the morphological evolution since the 1990s by comparing past surveys with the topographic data of 2022. Thanks to these data, we can observe whether a new morphological equilibrium has been reached or whether the canal continues to widen.

How to cite: Fraudin, C., Mercier, E., Petit, F., and Houbrechts, G.: Long-term impacts of hydropower plants on the sedimentology and morphology of the Warche riverbed (Belgium), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-147, https://doi.org/10.5194/icg2022-147, 2022.

P49
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ICG2022-182
Noam Greenbaum, Uri Schwartz, Paul Carling, Nati Bergman, Amit Mushkin, Rami Zituni, Gerardo Benito, Rafi Halevi, and Naomi Porat

Direct measurements of boulder entrainment in desert wadis are not available. The 2004 flood (peak discharge - 470 m3 s-1; recurrence interval - 120 years) in the hyperarid, ungauged Nahal Hatzera ephemeral stream (45 km2), which drains the Small Erosional Crater (SEC; Makhetesh in Hebrew) in the Negev Desert Israel, transported and deposited 0.85-2.1 m concrete boulders and slabs detached from infrastructure upstream as well as natural boulders. EDM and drone air-photographic surveys documented the geometry of the study reach and the location of boulders. Analyses of flood slackwater deposits established a paleoflood record of 23 floods with peak discharges of 200-760 m3 s-1, during the last 600 years. 1-D HEC-RAS hydraulic analysis provided water surface profiles, discharges and hydraulics, along the study reach and velocity, shear stress and stream power for each boulder Xsection.. MAX program and Pearson 3 distribution were used for flood frequency analysis. Most of the concrete boulders were deposited in the sub-critical backwater of channel constrictions where velocities were 1.5-2.1 m s-1. The largest boulders were deposited in super-critical flow where velocity was 8-9.2 m s-1. The sandy alluvial channel enables to transport these concrete boulders, reflecting the unstable, active sandy layer of the channel bed over which the boulders moved. The maximum flood shear stress and stream power characterize medium-large floods with return period of 20-120 years rather than the largest floods, which produce larger extension of backwater ponding upstream of constrictions. The combination of the flood frequency analysis and the hydraulic parameters of the flood enables to reconstruct the frequency of the tractive forces that transported these boulders. Boulders <2.1 m and weighing <15 tonnes can be transported at least once in 120 years. The shear stress and stream power indicate that the moderate-large floods are the most geomorphically effective floods rather than the largest floods in Nahal Hatzera basin. Nevertheless, the 'geomorphic effectiveness' of the 2004 flood – a typical desert flash flood, was small based on the minor changes along the channel and banks indicating that their resistance thresholds were not exceeded and energy expenditure was mainly on boulders entrainment and transport. 

 

How to cite: Greenbaum, N., Schwartz, U., Carling, P., Bergman, N., Mushkin, A., Zituni, R., Benito, G., Halevi, R., and Porat, N.: Frequency of Boulders Transport during Large Floods in Hyperarid Areas using Paleoflood Analysis – An Example from the Negev Desert, Israel, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-182, https://doi.org/10.5194/icg2022-182, 2022.

P50
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ICG2022-191
Daniel Vazquez-Tarrio, Rosa M. Mateos-Ruiz, Virginia Ruiz-Villanueva, Sergio Iglesias-Asenjo, and Andres Diez-Herrero

Mountain rivers can convey significant amounts of coarse sediment (gravel, cobble), and large wood pieces; both recruited from river margins and valley slopes. The erosion, transport, and deposition of this material may endanger human infrastructures, such as bridge piles, canals, or weirs, notably increasing flood hazards and potential damages. Therefore, sediment and large-wood dynamics should be considered in the flood hazard evaluation, particularly in mountain areas. However, traditional flood hazard assessment often relies solely on hydraulic models assuming non-movable riverbed and no sediment or wood supply. These assumptions neglect the important role that sediment-transport and geomorphic changes have on the evolution of water levels during floods, potentially leading to strong under- or over-estimations of related hazards.   

In this work, we developed a methodological framework that incorporates sediment- and wood-transport to assess flood hazards in the Darro River (Andalusia, Southern Iberian Peninsula); a mountainous torrent turned into an urban river characterized by a flash-flood regime, and high sediment and wood supplies. We selected a river reach, 3 km in length, where the river Darro crosses the city of Granada. The monumental city of Granada is highly populated and welcomes >5 million visitors every year; so, the reliability of previous flood-hazard assessments, without considering sediment and wood transport, was questioned by river managers. The selected study reach includes an area of high urban pressure where the river flows under a vault. Thus, it is crucial to consider the sediment and wood transport, as they could potentially trigger a catastrophe (as already happened in 1951, when the vault partially collapsed).

We conducted a field survey to identify mobile-sediment patches and large-wood jams along the selected reach. Sediment patches were sampled following the Wolman method to characterize the grain-size distribution. Wood pieces were measured, and characterized in terms of size, position and susceptibility to be incorporated into flood flows. This information is being used to build a 2D hydraulic and morpho-sedimentary (assuming a mobile bed) numerical model (IBER software), coupled to a specific module (IBERwood) that simulates wood transport and deposition. A scenario-based approach is used to explore the effect of sediment and wood supplies on the flooded area, the flow depth and the velocities.  This contribution will show preliminary results.

This work has been developed in the framework of the RISKCOAST project: “Development of tools to prevent and manage geological risks on the coast linked to climate change” (Ref: SOE3/P4/E0868) funded by the Interreg SUDOE programme.

How to cite: Vazquez-Tarrio, D., Mateos-Ruiz, R. M., Ruiz-Villanueva, V., Iglesias-Asenjo, S., and Diez-Herrero, A.: Exploring the role of sediment and wood transport during flash floods in the Darro River crossing the city of Granada (Spain) , 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-191, https://doi.org/10.5194/icg2022-191, 2022.

P51
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ICG2022-212
Davinia Moreno and Alfonso Benito-Calvo

Intraplate basins potentially preserve the most complete record of tectonic, geomorphic, and climatic evolution within the interior of continents. In the Iberian Peninsula, most of the largest Cenozoic sedimentary basins show a change from aggradation to degradation. Determining the cause of the transition from aggradation to degradation and how this was linked to tectonic, climatic, and geomorphic events hinges on the chronology of the fluvial network incision and excavation of the basins fill. Fluvial terrace staircases provide a direct record of exorheic river incisions and are known to be controlled by base-level changes, climatic changes, and tectonic uplift.

 The incision of most of the Iberian Peninsula basins appears to have initiated in the Quaternary but the precise timing of its initiation is actually poorly known and constrained. In order to overcome the lack of chronologies for these basins, in the following study, we studied the Duero basin and its terrace system. It is a major intracratonic basin bounded by Cenozoic structures and characterized by a maximum of 16 terrace levels from +141-144 m to +8-10 m, with the present alluvial plain at +4-5 m (Pérez-González et al., 1994). During the last decade, some tributaries (e.g. Arlanzón, Arlanza, or Esla) and the Duero itself have provided a few ages obtained by Electron Spin Resonance (ESR) (Moreno et al, 2012; 2016), Luminescence (Cunha et al., 2019) and Cosmogenic Nuclides dating (Rodríguez et al., 2020; Schaller et al., 2016; Antón et al., 2012), shedding some light on the chronological framework of the Duero basin.

In this work, ESR was systematically applied to the main river, the Duero River, dating 4 different fluvial levels spanning from the high to the medium levels: T2 (+135m), T3 (+114m), T5 (+90m), and T10 (+41m). ESR dates are coherent with the analyzed terrace system and allow defining the onset and development of the Duero valley in the center of the basin. Additionally, these results also allow the reconstruction of the incision response of the tributary system, comparing these ESR results with those previously published.

 

 

How to cite: Moreno, D. and Benito-Calvo, A.: First ESR chronology of the Duero River terrace system in Northern Spain, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-212, https://doi.org/10.5194/icg2022-212, 2022.

P52
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ICG2022-343
Camille Imbert, Quintia Vaessen, Mila Tripon, and Geoffrey Houbrechts

Well-oxygenated riverbed is essential for the proper ecological functioning of watercourses and the clogging of interstitial spaces by fine sediments considerably reduces the ecological quality of aquatic habitats. This phenomenon is linked to several parameters: the availability of fine sediments in catchments, soil erosion and land use, and the dynamics of the bed load. Within the framework of two European LIFE projects (LIFE19 NAT/BE/000093 and LIFE 19 NAT BE000054), which aim, among other things, to reintroduce endangered freshwater mussels (Margaritifera margaritifera and Unio crassus) into gravel-bed rivers of the Ardennes region, the clogging/unclogging extent of substrates and the sediment dynamics are monitored. Several monitoring devices were set up.Fine sediment traps were installed in the counter-slope of pools which is known to be a favourable habitat for mussels. This method makes it possible to quantify the amount of fine particles that can infiltrate the subsurface layer. Scour chains were placed on riffles to quantify the thickness of the active layer, which corresponds to the thickness of the bed that can be unclogged during floods. Grainsize surveys were also carried out on riffles to characterise the flow competence of rivers. Finally, the dynamics of the bed load was monitoredthanks to pebbles marked with PIT-tags. At the end, these results alongside biomonitoring and physico-chemical data will enable the identification ofthe most appropriate sites for the reintroduction of freshwater mussels.

 

How to cite: Imbert, C., Vaessen, Q., Tripon, M., and Houbrechts, G.: Geomorphological monitoring of the clogging and unclogging of gravel-bed rivers substrate for the reintroduction of freshwater mussels (Margaritifera margaritifera and Unio crassus) in the Ardennes massif (Belgium), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-343, https://doi.org/10.5194/icg2022-343, 2022.

P53
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ICG2022-352
Anastasiia Derii

Changes in river valleys due to human activity can be seen at many sites throughout the world. Nowadays, this notorious issue becomes extremely relevant due to the intensification of floods in developed regions.  Therefore, investigating changes in the valley after the flood can help the local government develop rules related to the use of the valley. The work is an attempt of valley typological classification and analyze of human influence on intensification of flood in 2020.  Chorna Tisha is an example of a site where signs of strong antropopresion reach 200 years. The Chorna Tisha river was mapped from the mouth of the Apshynets river to the mouth of the Biala Tisha river (about 45 kilometers).  The mapping method contributes to the analysis of the distribution of valley forms. The effects of the hydro-engineering structures (splash dams), road building, and gravel extraction can be seen after the typological classification of the valley. The erosion curve of selected valley is non-classical, due to local geological conditions, but due to human activity, most of the parts where we can predict the accumulation of gravel material are now transportation sites. This result led to the conclusion that the river valleys in mountainous areas of Ukraine are highly altered.

How to cite: Derii, A.: Change in mountainous river system due to human influence (on the example of Chorna Tisha, Ukrainian Carpathians), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-352, https://doi.org/10.5194/icg2022-352, 2022.

P54
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ICG2022-400
Quintia Vaessen and Geoffrey Houbrechts

Physical microhabitat descriptors are important to predict species habitat and therefore, are critical to river management as a mean to identify and manage habitats of aquatic fauna. Flow velocity, water depth and substrate constitute the fundamental microhabitat of benthic macroinvertebrates. The thick shelled river mussel (Unio crassus) is an endangered European freshwater mussel. The species and its habitat are protected in Europe by Council Directive 92/43/EEC (Annexes II and IV) on the conservation of natural habitats and of wild fauna and flora. Therefore, Member States must establish conservation strategies for this species. In this context, microhabitats of the thick shelled river mussel are mapped in several Belgian rivers, along with the use of the microhabitat by the species. For each microhabitat descriptor i.e., bathymetry, flow velocity, and substrate grain size, a habitat suitability index is computed. Habitat suitability index is defined as the ratio of the species’ use of a microhabitat to its availability. Optimal microhabitat is defined as the microhabitat having to highest frequency of use by mussels. Each shell is measured to detect size-related differences in microhabitat use. The hydromorphological preferences of the threatened mussel are thus identified which will allow the development of habitat suitability criteria for the adult life stage of the species.

How to cite: Vaessen, Q. and Houbrechts, G.: Microhabitats of a threatened freshwater mussel in gravel-bed rivers (Belgium)., 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-400, https://doi.org/10.5194/icg2022-400, 2022.

Poster: Tue, 13 Sep, 16:30–16:45 | Poster area

Chairpersons: Frédéric Liébault, Vittoria Scorpio
P55
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ICG2022-426
Adriana Holušová and Tomáš Galia

Since river regulations extensively changed the natural course and regime of many European gravel-bed rivers, most gravel bars tend to lose some of their natural dynamics. Gravel bars are often overgrown by vegetation when there is a lack of high flows for a long time. In many areas, they are objects of protection, as they are in some cases related to preserved parts of naturally braided rivers, and they represent a unique habitat for rare species of vegetation and fauna.

In our research, we analysed spatio-temporal gravel bar dynamics, with a focus on vegetation succession progress, in two rivers of the Outer Western Carpathians for twenty years (2000–2020): the Czech part of the Olše River (73 km) and the part of the Ostravice river downstream the valley dam (46 km). We used nine archive orthophotos (2000–2020) and hydrological data to analyse the effects of flood events, vegetation succession and river regulations on the gravel bar dynamics. The orthophotos were processed in ArcGIS Pro to analyse the coverage of vegetation and unvegetated area on gravel bars where the reference banks lines from the first two studied orthophotos (2000, 2003) were used to determine the edges of bars.

Two major floods in 1997 and 2010 greatly affected the vegetation cover of gravel bars in both rivers. After the 1997 and 1999 moderate floods, the total vegetated area on gravel bars in 2000 was the lowest in all studied years in the Olše (42 %) and the second lowest in the Ostravice (54 %). Following years, trends showed slow but progressive succession until the next major flood in 2010 and moderate floods in 2014. The total area of bar vegetation in the Olše decreased by 19,2 % in 2012 compared to the last studied year of 2009 (81,8 %), and by another 9 % in 2014 probably due to the time proximity of the flood event. Similarly, the total vegetated bar area in the Ostravice decreased by 24 % in 2012 (from 92 % in 2009) and by another 13,7 % in 2014. However, only two years later, the vegetated bar area significantly increased in both rivers: compared to the year 2014, it increased by 39,8 % in the Olše and by 42,1 % in the Ostravice. The remaining studied years showed a similarly high percentage of vegetation cover (2018=87,1–93,6 %, 2020=84,5–91 %). Although the Ostravice is regulated by a valley dam, the floods had a very similar effect on both rivers. The main difference is in the rate of vegetation coverage in the years not affected by floods. In the Ostravice almost all the bars were vegetated completely or for the most part, while in the Olše, there was more variability in vegetation coverage on gravel bars including only partially vegetated or unvegetated bars. Our results suggest an ongoing succession of vegetation on most gravel bars in the last twenty years and show a significant effect of major flood events and river regulations on their morphodynamics.

How to cite: Holušová, A. and Galia, T.: Contradictory effect of flood events and vegetation succession on the dynamics of gravel bars, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-426, https://doi.org/10.5194/icg2022-426, 2022.

P56
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ICG2022-435
Albert Scrieciu, Sabin Rotaru, Raffaele Giordano, and Alessandro Pagano

The Lower Danube wetlands, one of the most important European wetland ecosystem, lost nearly 80% of its surface over the last century due to river dredging, land reclamation and flood control. Anthropic interventions along the Danube river water course, such as construction of the hydropower plants Iron Gates I and Iron Gates II and alterations along its banks, have generated high bank erosion processes as well as riverbed changes with negative impact on navigation. The negative effects induced by anthropic interventions coupled with climate change impact have intensified the flooding and drought events.

We propose a wetland restoration project in the Lower Danube by designing a Nature Based Solution (NBS) for dealing with flood risk. Our research is focused on the Dabuleni-Potelu-Corabia (DPC) enclosure, a land reclamation area dammed in 1965 against catastrophic floods, having a safety reserve height of 1 meter. This area along with other Lower Danube stretches have been heavily impacted by the catastrophic flood of 2006 and their resilience to such events is even more weaken by less destructive but more frequent floods. We propose different scenarios for the restoration of the DPC enclosure based on a hydraulic model of the catastrophic flood from 2006. Furthermore, we explore the potential of implementing this NBS discussing the generated benefits and co-benefits and describe the different steps to develop a Natural Assurance Scheme for the Lower Danube.



How to cite: Scrieciu, A., Rotaru, S., Giordano, R., and Pagano, A.: Reducing water related risks in the Lower Danube through Nature Based Solution implementation, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-435, https://doi.org/10.5194/icg2022-435, 2022.

P57
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ICG2022-465
Alfredo Ollero, Askoa Ibisate, Daniel Ballarín, Jesús Horacio García, Marcos Gimeno, Álvaro Gómez-Gutiérrez, Marcos Martínez-Segura, Rubén Moral, Josu Ortiz, Yilena Hermoso, Sergio Sanmartín, and Marco David Vásconez

Ephemeral streams are an important reality in the Mediterranean area, constituting more than 50% of the channel network in the eastern region of the Iberian Peninsula. The northernmost cases are located in the semi-arid areas of the Ebro basin. Among the 592 cases registered (under the CCAMICEM project) in the Ebro basin, the Rambla de Cariñena stands out for its representativeness and dimensions.

With a basin area of 330 km2, it drains the northern piedmont of Sierra de Algairén (Iberian Mountain Range). It is a temporary river in its headwaters and upper course (Frasno River), which becomes ephemeral (Rambla) in its middle and lower courses, where it forms a large gravel bed river morphology, until it disappears without flowing into any river. In the past, there are references, as well as geomorphological evidence, that it had surface flow, but intensive vineyard agriculture and the global change recorded in the last 50 years have transformed it in ephemeral.

Recent years have showed relevant flash-floods, such as in the springs of 2008, 2015 and 2018. Its geomorphological dynamics is very interesting, with a highly sinuous meander, formation and destruction of gravel bars in each flood, and some incipient signs of incision. The Rambla de Cariñena constitutes a remarkable case for analyzing climate and global change in this type of fluvial course, as it has been worked on in the CCAMICEM project.

In this project, different characterization, assessment and monitoring works have been carried out in recent years, applying river survey techniques such as field reconnaissance, analysis and geomorphological mapping using drone flights, and radioelectric tomography to observe the depth of the alluvium. The evolutionary dynamics of the Rambla de Cariñena has also been explained through a multi-temporal analysis using aerial images and LiDAR PNOA data with a density of 0.5-4 points/m² to model the current channel. And the IHG hydrogeomorphological index has been applied to observe its impacts and assess its ecological status.

All this work has result in a database which is a base to follow the evolution of these streams in the future, as well as a pilot research for these river typologies in the Ebro basin and the identification of symptoms linked to climate change.

Key words: river survey techniques, flash flood, channel dynamics, IHG index, Rambla de Cariñena

How to cite: Ollero, A., Ibisate, A., Ballarín, D., García, J. H., Gimeno, M., Gómez-Gutiérrez, Á., Martínez-Segura, M., Moral, R., Ortiz, J., Hermoso, Y., Sanmartín, S., and Vásconez, M. D.: Hydromorphological characterization, assessment and monitoring in ephemeral streams: a case study in NE Iberian Peninsula., 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-465, https://doi.org/10.5194/icg2022-465, 2022.

P58
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ICG2022-486
Caio Breda, Fabiano Nascimento Pupim, Sebastian Gomez M., and Maurício Parra

Mountain regions and their foreland basins sustain a set of landforms (e.g., floodplains, fluvial terraces, and alluvial fans) that are sensitive to climatic and tectonic changes. The variation of these factors can change the rates of incision and aggradation in river valleys and trigger the propagation of the imbalance signal along with the river profile, transforming the local relief. Geomorphic indices (e.g., the normalized channel steepness index, ksn) highlight river profile and slope gradient changes. In order to advance the knowledge about the dynamics of the foreland regions, a central question emerged: Are larger fans more related to basins with high stream power (ksn) or to drainage area? To answer this question, we mapped alluvial fans and used Ksn indices to identify significant variations in stream power along the basins that constitute the headwaters of the Guaviare River, in the Eastern Cordillera of Andes, Colombia. The alluvial fans were mapped using visual interpretation of Landsat imagens and digital elevation models from Coopernicus DEM (30 m resolution). The ksn index and drainage area of basins upstream of the alluvial fan apex were quantified using TopoToolBox package. Results will be present in the conference. FAPESP Grant (#2020/11047-1)

How to cite: Breda, C., Nascimento Pupim, F., Gomez M., S., and Parra, M.: Relationships between alluvial fans, channel steepness and drainage area in the Andean piedmont, Colombia., 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-486, https://doi.org/10.5194/icg2022-486, 2022.

P59
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ICG2022-617
Sabin Rotaru, Albert Scrieciu, and Adrian Popa

Danube River is one of the largest fluvial systems in Europe in terms of length, drainage area, discharge and sediment load. Multiple anthropogenic pressures in the Danube River Basin have led to evident hydromorphological alterations, amongst which the most heavily disturbed component is the sediment regime. Like many temperate zone rivers, the sediment load of the Danube River has been substantially reduced due to the combined impact of flood protection, navigation and hydropower measures applied over a long period of time.

In this study, we analyse sand bar morphology for a period of five years (2018-2022) using various data recorded from single-beam bathymetry, river discharge and sediment load measurements. The investigated sandbar is located in the Bechet reach of the Lower Danube, downstream of the Iron Gates I and II Dams; it has a 2 km length and emerges during the low discharge season. The analyses revealed an accelerated riverbed incision around the islet and moderate accumulation on top of the bar. Furthermore, the results are discussed in relation to anthropogenic interventions such as dredging for ensuring optimal navigable conditions in the area, floodplain embankment and hydropower generation in the upstream.

How to cite: Rotaru, S., Scrieciu, A., and Popa, A.: Annual dynamics of a river sandbar in the Lower Danube: geomorphic adjustments under anthropogenic pressures, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-617, https://doi.org/10.5194/icg2022-617, 2022.

P60
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ICG2022-638
Kharchoufi Mohamed Houcine

The watershed of the upstream course of Oued el Khil is part of south-east Tunisia, of the Matmata-Dahar plateau also called Jbel Demmer. It covers parts of the governorates of Medenine and Tataouine between the delegations of Beni Khadeche, Ghomrassen and Bir Lahmar. This watershed is encased in a relief of a plateau of modest altitude divided into three tiered plateaus. The study area is characterized by a variety of geological rocks. Its monoclinic cuesta type structure presents a double to triple cuesta and forms of witness buttes and outliers.

The quaternary landforms and deposits are well linked to climate change which has manifested by dynamics of water and wind action. They present deposits of coarse elements (blocks, pebbles, gravel ...) and other fine (silts and sands) and sometimes mixed (blocks, silts, pebbles and sands ...). At the level of the Jurassic cornices and on the slopes, develop various deposits and quaternary landforms such as taffonis, friable colluvium and consolidated one by limestone crust and landslides. Mini-glacis with or without crust and mini-glacis-terraces extend over the foothills, and terraces at the bottom of the valleys. These landforms were established during the different periods from the Lower Pleistocene to the Holocene.

Currently, the most remarkable morphodynamic evolution is manifested by water erosion which is characterized by stripping, badlands, receding heads from ravines and the destruction of the Jessour. The manifestation of wind erosion corresponds to the development of Nebkas, regs, dunes and veneers.

How to cite: Mohamed Houcine, K.: The watershed of the upstream course of Oued el Khil (South-East Tunisia) Geomorphological study, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-638, https://doi.org/10.5194/icg2022-638, 2022.

P61
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ICG2022-649
Rafał Kroczak and Tomasz Bryndal

In our presentation we analyze human impact on development of active drainage system (ADS) operating during heavy rainfall in mountain catchments. Few flysch catchments located in the Carpathian foothills and Beskidy - medium-high mountain areas were selected for this poster sesion.
The ADS is reconstructed with use of ALS-LiDAR data. The results revealed that the density of the ADS may be even 5 times higher compared to the river system. Moreover, in the studied catchments c.a. 25% of the ADS constitute man-origin elements (roads, ditches and plough furrows) incorporated to the drainage system. 
The Hortonian type of analysis revealed that man-origin elements significantly change the structure of the natural, river drainage system. Those man-origin elements are predominantly attributed to 1st and 2nd order stream, which drain the upper part of the hillslopes. 
The results will be discussed in the context of geomorphological transformation of the hillslopes and catchments hydrological response. 

How to cite: Kroczak, R. and Bryndal, T.: How human activity changes the drainage system in the small mountain catchments? (Carpathian Mountains, Poland), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-649, https://doi.org/10.5194/icg2022-649, 2022.

P62
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ICG2022-656
Pâmela Assis, Maximiliano Bayer, and Ana Amaral

The Araguaia river basin covers an area of 386,000 km2, with an average flow of 6,420 m3/s, being one of the main priority areas for the conservation of the Cerrado (Brazilian savannah) and water resources in Brazil. However, in the last five decades (since 1970), large extensions of this hydrographic region have been the object of an intense process of transformation associated with the advance of the agricultural frontier, particularly by monocultures of pastures, soybeans, corn, sugarcane and livestock. As a consequence of these processes of land use and occupation, the Araguaia river basin presents high levels of anthropization, mainly the emergence and acceleration of erosion and silting processes present in various sectors of the basin. There is also an intensification of channel silting, changes in water quality and negative impacts on aquatic ecosystems, as well as on the geomorphological and ecological processes of the alluvial plain, which represents a rapid response of the Araguaia river system to the changes that occurred in this historical period, shaping the middle section of this river system, in one of the areas with the greatest storage and transport of sediments in the Cerrado and in Brazil. In this article, using aerophotogrammetry techniques and three-dimensional models of the landscape, combined with the use of an RPAS, the objective was to quantify the volume of sediments deposited and/or stored at the confluence of the Araguaia River with the Vermelho River, in Aruanã, State of Goiás. The methodology was based on a set of aerial photos obtained with multi-rotor, DJI/Phantom4, low-cost and easy-to-operate RPAS, processed in PIX4D Mapper, allowing the elaboration of Digital Surface Models (DSM), and high-quality mosaics. spatial resolution, as well as the granulometric and sedimentological characteristics in the study area (sandy bars in the middle channel of the Araguaia River). In addition to geoprocessing tools and the use of satellite images (SENTINEL 2) to assist in the interpretation of sedimentary dynamics. With aerial records, modeling and sedimentological characteristics, the technique proved to be quite efficient in the quantification of sediments deposited/stored in the channel, allowing the identification of an area of 1.15 km2 and a volume of ~1318312.63 tons, in an extension 2 km from the middle section of the Araguaia River, with a hydrological quota of 163 cm. It was also identified that the Araguaia river in this stretch has a width of 300 to 500 meters, covering a large number of fluvial geoforms, with emphasis on the accumulation of sedimentary deposits, lateral and central bars, with the intercalation of coarse and medium sands, with fine sediments that mark changes in the hydrological cycles, different levels of connectivity with the river channel and the process of vegetation consolidation between the annual hydrological cycles.

How to cite: Assis, P., Bayer, M., and Amaral, A.: Estimated volume of sedimentary deposits in river Araguaia, State of Goiás – Brazil, through Remotely Piloted Aircraft System (RPAS), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-656, https://doi.org/10.5194/icg2022-656, 2022.

P63
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ICG2022-675
Paul R. Hanson, Clayton Reinier, Robert Joeckel, Jacob Bruihler, and Aaron Young

Despite the prominence of the Platte River in the literature on fluvial sedimentology, its alluvial history has not been well documented. We have studied the Platte’s alluvial fill to understand how the river system responded to climate changes over the last glacial-interglacial cycle. Geoprobe cores from multiple locations along the river’s valley in Nebraska demonstrate that the fill is dominated by sand and gravelly sand, and that deposits of silty clay through silty sand are minor components. We also generated an alluvial chronology using luminescence dating methods on sand samples collected from depths of up to 15 m below the present floodplain. Our results demonstrate that sediments dating to Oxygen Isotope Stages 2 and 3 lie at depths of 2–15 m below the present floodplain, and that portions of the upper 5–8 m of the alluvial fill dates to the Holocene. We hypothesize that: (1) the Platte River aggraded during the late Pleistocene, and (2) the upper portions of these Pleistocene sediments were reworked as the river locally entrenched into those older sediments during the Holocene. Late Pleistocene valley aggradation was likely related to increases in sediment availability in the Rocky Mountain headwaters, as well as sediment influx from local landscapes in Nebraska. 

How to cite: Hanson, P. R., Reinier, C., Joeckel, R., Bruihler, J., and Young, A.: Late Quaternary Evolution of an Iconic Braided Stream: Dating the Alluvial Fill of the Platte River, Nebraska, USA, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-675, https://doi.org/10.5194/icg2022-675, 2022.

P64
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ICG2022-734
Meiqin Han, Gary Brierley, Baotian Pan, Haopeng Geng, and Yan Shi

The Fluvial Biogeomorphic Succession phase model (FBS model) differentiates Geomorphic (G), Pioneer (P), Biogeomorphic (B) and Ecological (E) phases of hydro-geophysical-biological interactions in river systems. To date, quantitative applications of this model have been restricted to field surveys of vegetation composition analysis at the patch-scale. Here we develop a biogeomorphic landform mapping approach to determine the dominant biogeomorphic succession phase at the reach scale. We categorize river morphology into four biogeomorphic landform types (G-, P-, B- and E-landforms) that have particular geomorphic, substrate and vegetation cover characteristics. Ratios of these landforms are used to calculate the dominant succession phase in a given reach. A test of this method conducted for two contrasting anabranching reaches of the Upper Yellow River indicates that landform ratios provide an efficient and reliable approach to assess river biogeomorphic succession phase. The approach can be adapted to support systematic cross-scalar analyses across the range of river environments.

Key words: FBS model, Biogeomorphology, river processes, riparian vegetation, geomorphic mapping, interdisciplinary method

How to cite: Han, M., Brierley, G., Pan, B., Geng, H., and Shi, Y.: An approach to evaluate the dominant river biogeomorphic succession phase at the reach-scale , 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-734, https://doi.org/10.5194/icg2022-734, 2022.

P65
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ICG2022-735
Ana Maria Costaa, Maria da Conceição Freitas, Rogério Mota, Manel Leira, and Pablo Arias

The infilling of coastal incised river valleys is an important sedimentary record that holds imprinting’s of depositional environments and sea-level variations. Notwithstanding, the stratigraphic record is difficult to interpret once: i) incised valley coastal areas preserve information both from marine and fluvial processes; ii) the morphology of the valley can derive from a simple incision cycle (e.g. LGM) or be the result of multiple incisions during pre-LGM Quaternary low-stands; iii) the stratigraphic sequence depends on the type of estuary, wave-, tide-or mixed-dominated estuary; iv) palaeomorphology; v) fluvial discharge; and vi) sediment availability. To bypass these issues, several proposals have been published to help in the interpretation of incised valley stratigraphic successions and the identification of estuarine deposits preserved in depth.

The Sado estuary is the second large estuary in Portugal (after the Tagus estuary) occupying an area of ca. 200 km2 combining both the external and internal domains. It is one of the most important wetlands in Europe concerning biodiversity being protected by law since 1980. At present it hosts important industries and serves as a stage for the development of other traditional economic activities. As a coastal wetland, the Sado estuary is highly sensitive to climatic and sea level changes. Notwithstanding the Sado valley morphology, its morphological and environmental evolution and the fluvial and estuarine responses to sea level changes are still poorly understood.

The present study aims to characterise the palaeomorphology, morphological and estuarine evolution and sedimentary infilling in the upper areas of the estuarine zone located in the Sado (Alcácer do Sal) channel by combining information retrieved from sedimentary cores, geotechnical descriptions and Electric Resistivity Tomography (ERT) profiles. Geotechnical and ERT information reveal a deep incised palaeovalley reaching depths of 38 m and 24 m below MSL between Alcácer do Sal and Laxique (ca. 45 and 65 km upstream the estuarine inlet, respectively). The ERT data points to the occurrence of coarse sedimentary deposits in depth between Vale do Guizo (ca. 52 km upstream the estuarine inlet) and Laxique. Environmental and ecological proxies analised in the sediments retrieved from the Sado channel and tributaries reflect marine influence in the area (ca. 52 km upstream the estuarine inlet) since at least 8850 cal BP. The maximum extension of marine influence was detected in Laxique during the Middle to Late Holocene transition. Brackish conditions at this upstream location may have occurred earlier, but the coarseness of the sediment infilling prevented its recovery using coring devices and, consequently, its palaeoenvironmental characterization. Marine influence prevailed until 4000 cal BP at Laxique, from when the aggradation and progradation of the alluvial plain started. The aggradation of the alluvial plain began later (3250 cal BP) at Arapouco (ca. 50 km upstream the estuarine inlet).

This research was funded by the Portuguese Foundation for Science and Technology, I.P./MCTES through national funding (PIDDAC) – UIDB/50019/2020 – Instituto Dom Luiz and by the Spanish Ministry of Science and Innovation through the project SimTIC (HAR2017-82557-P).

How to cite: Costaa, A. M., da Conceição Freitas, M., Mota, R., Leira, M., and Arias, P.: Palaeomorphology and environmental evolution of the Sado incised valley, SW Portugal, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-735, https://doi.org/10.5194/icg2022-735, 2022.

P66
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ICG2022-50
Ekaterina Matlakhova and Andrei Panin

Large meandering palaeochannels (macromeanders) are found in the river valleys of the East European Plain. Channel parameters of such macromeanders are few times larger than the recent ones of the same rivers. Such macromeanders are widespread in the temperate climate zone of the Northern Hemisphere. Formation of these macromeanders is usually associated with Late Glacial (the end of MIS 2). The main aim of our study was the reconstruction of the river valleys’ development of the Central part of the East European Plain and establishing of the absolute chronology of the large paleochannels formation in this region. Few key sites were studied in the river valleys of the Central part of the East European Plain. Hand and mechanical coring, examination of natural and human-made exposures, sampling for different types of analysis, geomorphological discriptions and topographic profiling were done during the fieldworks on the key sites. Radiocarbon and OSL dating, grain-size and spore-pollen analysis were done in the laboratories.

Data analysis shows the following results and conclusions. The alternation of high and low river runoff was typical for the valleys of the study region in the end of the Late Pleistocene. This led to the alternation of river incision and aggradation in the valleys. About 30-35(40) ka ago there was epoch of rivers incision. High runoff is proposed as the reason of this incision. Before LGM rivers had already been incised down deeper than the modern levels. LGM time (20-23 ka ago) was characterized by cryoaridic conditions, low runoff and accumulation in the river valleys. Not only alluvial, but also aeolian accumulation in the river valleys was characteristic for this period. In that time aeolian covers and aprons few meters thick were formed in river valleys (mostly on the terraces’ surfaces). After LGM the high runoff epoch started, which was dated 12-19 ka ago. In that time large meandering palaeochannels (macromeanders) and modern wide high floodplains were formed in the river valleys. These macromeanders were formed under conditions of extremely high spring discharges in severe climate conditions. Our data shows that this epoch of high runoff was interrupted by a short low runoff period (~15-16 ka ago). So, the Late Pleistocene epoch of high floods and large paleochannels formation had two periods – about 17-19 ka and 12-15 ka ago. Runoff in the Holocene became lower than in the Late Pleistocene, channel parameters decreased.

How to cite: Matlakhova, E. and Panin, A.: Late Pleistocene History of the River Valleys of the East European Plain's center, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-50, https://doi.org/10.5194/icg2022-50, 2022.