ICG2022-23

Fine sediment input into river systems is an environmental challenge of increasing significance due to accelerating soil-erosion rates in agricultural catchment systems. Along with erosion, sediment transport within cultivated hillslopes determines the amount of material that can be delivered into river channels in such systems. To effectively manage this problem, it is necessary to identify sediment sources, sinks, and the pattern of linkages within and between different landscape compartments along sediment pathways. Sediment connectivity is an emerging concept that can help to address on- and off-site effects of soil erosion by describing the efficiency of fine sediment transfer through these different zones. Field assessments and process-based modeling has been typically used in quantitative soil erosion and connectivity investigations. However, a major advance in recent years has been the adoption of network analysis as an approach to quantify sediment connectivity. The aim of this study is to assess sediment connectivity in selected agricultural hillslopes of the Fugnitz Catchment (Austria) by combining sediment transport modeling and network analysis. Sediment transport was dynamically simulated using the process-based MAHLERAN model (Wainwright et al., 2008). Simulated results were then translated into an adjacency matrix and its corresponding network graph – composed of nodes and links that represent individual geomorphic units and the fluxes between them as connected through runoff and sediment pathways. Structural properties of the generated network were finally quantified using network-analysis tools in MATLAB. The results show different patterns of sediment pathways which exhibit greater propensity to deliver sediments. These insights can be used to designate connectivity hotspots where interventions may be targeted to mitigate on- and off-site impacts of soil erosion.

How to cite: Perez, J. E., Poeppl, R., Turnbull, L., and Wainwright, J.: Assessing sediment connectivity on agricultural hillslopes using sediment transport modeling and network analysis, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-415, https://doi.org/10.5194/icg2022-415, 2022.

The Pou Roig-Quisi and Mascarat catchments in eastern Spain (Calpe) are located as neighbouring catchment systems in a Mediterranean, mostly mountainous and anthropogenically modified environment. The catchments drain directly into the Mediterranean sea. The selected study areas are characterized by a mild Mediterranean climate with a mean annual air temperature of ca. 18°C and a mean annual precipitation sum around 400 mm (measured slightly above sea level). During the coldest months (January, February) frost and snow can occur in the highest elevations although the mountain ranges are situated close to the coast. In contrast, maximum summer temperatures (July, August) can easily exceed 30°C and south-facing hillslopes and rockwalls are exposed to high solar radiation. The lithology in the area is clearly dominated by marine limestones. Elevation ranges from sea level up to 1126 m a.s.l. Geomorphological processes include chemical and mechanical weathering, rock falls, debris flows, splash and slope wash, fluvial erosion, and fluvial solute, suspended sediment and bedload transport.

This ongoing GFL research is focussed on sediment sources, sediment (dis-)connectivity, spatiotemporal variability and rates of contemporary denudational processes and land-to-sea solute and sedimentary fluxes. Our work includes detailed field and remotely sensed geomorphological mapping and computing of morphometric catchment parameters combined with the extended statistical analysis of high-resolution meteorological and rock temperature data and the observation and monitoring of sediment-transfer, runoff and fluvial transport events. In the field, we are using a combination of different observation, monitoring and sampling techniques, including different tracer techniques and sediment traps in stream channels, remote time-laps cameras, and event-based high-resolution field monitoring combined with frequent water and sediment samplings. Sediment connectivity is significantly reduced by extended terraced areas within the catchment systems. Sediment transfers, the intermittent runoff, and fluvial transport and land-to-ocean fluxes are almost entirely controlled by pluvial events. High runoff during extreme rainfall events forms a relevant hazard particularly in the lowest parts of the catchment systems. Mechanical fluvial denudation shows a higher spatiotemporal variability than chemical denudation. Altogether, drainage-basin wide chemical denudation dominates over drainage-basin wide mechanical fluvial denudation which is explained by partly limited sediment availability, long-term sediment storage at defined locations, and by the predominant marine limestones found in the catchment areas.

How to cite: Beylich, A. A. and Laute, K.: Sediment sources, sediment dis-connectivity and rates of denudation and land-to-sea solute and sedimentary fluxes in selected Mediterranean catchment systems in eastern Spain, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-49, https://doi.org/10.5194/icg2022-49, 2022.

Debris flows are among the most widespread natural hazards in mountain areas. They play an important role in sediment transfer from low order channel networks to downstream areas and, thus, they can pose a serious threat to infrastructure. For debris flows to be released, in addition to a considerable amount of rainfall, sediment availability and a peculiar morphological setting (e.g. inclined terrain) are required. However, areas prone to trigger debris flows are not always structurally connected to the main channel, and thus do not necessarily provide sediments to the draining channel network. Despite the relatively high number of published research in the fields of debris flow susceptibility mapping and sediment connectivity analyses, to our knowledge, no attempts have yet been made to combine these two aspects, explicitly by means of data-driven procedures.

This work builds upon a novel data-driven approach developed by Steger et al. (under review), which allows to categorize areas based on both aspects, debris flow release susceptibility and structural connectivity. The original method was tested within three mountain catchments in the South Tyrolean Alps (max area 140 km²). This study aims at upscaling this approach at the regional scale and to this end, the whole South Tyrolean Dolomites (1,120 km²) has been selected as study area. In summary, the methodical framework comprised (i) modelling of debris flow release susceptibility using an interpretable machine learning algorithm (generalized additive model) and derivation of a quantitative threshold (susceptible vs. not-susceptible areas), (ii) training a logistic regression model to calculate the probability of an area being structurally connected in terms of debris flow release and subsequent thresholding (connected vs. disconnected areas), and (iii) combination of both previously generated and validated binary maps to create a joint susceptibility-connectivity map.

The results are represented via a variety of maps and associated statistics. It is shown that only 1.7% of the Dolomites were determined to be both susceptible to debris flow initiation and structurally connected to a target channel system, whereas areas that are susceptible but disconnected cover 8.2% of the whole study area. 16.5% of the area represents hillslopes that are potentially connected to the river network but result not susceptible in terms of debris flow release.

The straightforward implementation of this approach allows it to be an effective tool to assist hazard mapping and management. This study shows that the presented method provides spatial information useful to preliminary identify areas of interest for connected debris flows at the regional scale, but at the same time, it also highlights the need for further ground truth data to validate the results quantitatively beyond single catchment analyses.

Stefan Steger, Vittoria Scorpio, Francesco Comiti, Marco Cavalli. Data-driven modelling of joint debris flow release susceptibility and connectivity. Earth Surface Processes and Landforms. Under review.

How to cite: Pitscheider, F., Steger, S., Cavalli, M., Comiti, F., and Scorpio, V.: Regional-scale application of a novel data-driven approach to assess susceptibility and (dis-)connectivity of debris flow: a case study in the Dolomites in South Tyrol (Italy), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-306, https://doi.org/10.5194/icg2022-306, 2022.

Landscape evolution is driven by the patterns and rates of sediment transfer between the hillslope and the fluvial domains, and along the river network. The efficiency of sediment transport through the sediment cascade is controlled by the spatial configuration of landforms and the sediment connectivity between the geomorphic domains. In mountainous environments, large volumes of sediment are mobilized on hillslopes by e.g. mass-wasting and glacial processes. However, the mobilized sediment will be efficiently transported downstream only if sediment connectivity within river catchments is high. The latter therefore has potential impacts on denudation rates quantified at the catchment scale.

In this contribution, we explore the potential link between sediment connectivity and catchment-wide denudation rates in the Upper Rhone valley. To achieve this goal, we implemented an automatic workflow to compute the topography-based sediment connectivity index from Cavalli et al. (2013) using digital terrain models with a spatial resolution of 2 m, and to process spatial information on connectivity at the regional scale. We quantified sediment connectivity for 32 tributary catchments of the Upper Rhone, for which catchment-wide denudation rates are reported in the literature. We then contrasted sediment connectivity with denudation rates and discuss the spatial pattern of our results with data on mass-wasting processes.

How to cite: Clapuyt, F. and Vanacker, V.: Linking spatial patterns of catchment-averaged denudation rates with sediment connectivity in Alpine catchments, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-470, https://doi.org/10.5194/icg2022-470, 2022.

Mid-mountain catchments across the Mediterranean basin undergone a decrease in runoff and sediment yield during the second half of the 20^th century mainly due to forest cover increase following rural abandonment together with a transition to drier climatic conditions. In the same way, due to the revegetation and afforestation processes these zones experienced the homogenization of the ancient cultural landscapes, which have several consequences from ecological, geomorphological and hydrological points of view. During last decades, land use management of these areas have become a target of environmental policy makers and stakeholders to ensure the sustainability of ecosystem services. In some areas have been applied an active management through the reduction of vegetation density or by human afforestation, while others undergone a natural process of revegetation. In these setting, the conservation status of agricultural terraces plays a key role on the overall catchment response in terms of overland flow and sediment transport due to its potential effects on water and sediment connectivity between the hillslopes and the main channels. In this context, assessing the contribution of different land use management on runoff is fundamental for addressing water management and soil loss at the catchment and regional scales, especially in a context of climate change. Within this background, the aim of this work is to analyse the relative effects of terracing and land use management techniques to hydrological connectivity and water yield in a Mediterranean mid-mountain basin. To pursue this objective, we applied hydrological connectivity (IC index) and ecohydrological (RHESSys) models to different sub-catchments of the Leza Valley (Iberian System, Spain), representative of five different landscapes: (i) natural revegetation; (ii) natural revegetation with terracing reconstruction; (iii) human afforestation; (iv) human afforestation with terracing reconstruction; and (v) shrub clearing.

This research is part of the MANMOUNT project (PID2019-105983RB-100/AEI/ 10.13039/501100011033) funded by the MICINN.

How to cite: Llena, M., Nadal-Romero, E., Khorchani, M., Cortijos-López, M., Zabalza, J., and Lasanta, T.: Effects of terracing and land use management techniques on hydrological connectivity and water yield in a Mediterranean mid-mountain basin, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-409, https://doi.org/10.5194/icg2022-409, 2022.

Human activities in the most different environments produce gradual morphology and associated water changes. In different cultures, spread throughout history, the morphological and artificial channels are a valid example of how the superficial changes impact the hydrogeomorphological processes that take place in the hydrographic basins. Recognizing that these modifications make more complex the comprehension of how the systems/channels operate, considering that hydrological connectivity becomes subordinate to anthropic interventions, this investigation aims to verify if marginal dikes, originated from the opening and cleaning of artificial channels, generate changes in the hydro-sedimentation behavior between the slopes, artificial and natural mechanisms. This research’s effort generated analyses during rain events in a system of derivation, with focus in the production of flow data, transport data and turbidity which were associated with the presence of the marginal dikes along the channel troughs and of elements present in the interior of these troughs, such as vegetation. The study was carried on slopes located in the Central Brazil area, in a continental tropical environment. The morphology imposed by the cleaning activities has an impact on the capacity of artificial gain that follows the losses and not the volume of water (80% reductions in the flow in a 1000-meter stretch). This is meaningful data because the measurements took place in scenarios where the slopes had lines of concentrated surface runoff promoted by precipitation. Also, the presence of sediments in artificial channels is low and influenced by the vegetation that has a filtering role and by this disconnection between slope and channel. Thus, a reduction of 98.5% in the suspended sediment load was observed in the artificial channel along a stretch of 870 meters. In the natural channels, source of the water transposed in the artificial gutters, there was a gain in the sedimentary load of 29% along a stretch of 900 meters, suggesting a greater connectivity between slope and channel, especially in an area of traditional human occupation with suppression of riparian vegetation in several stretches. It is also important to point out that the flow in the natural channel continued to increase along with the contributions of the flows connected to them along the stretch in question (increase of 284%). Also, the turbidity in the artificial channel dropped from 90 to 3.5 Nephelometric Units (N.T.U’s), while in the natural channel there was an increase from 110 to 140 N.T.U’s. The disparity in the hydrogeomorphological behavior between the artificial channel, based on the interruption of connectivity made by the marginal dikes, and the natural one with the exposure of its banks, reinforce the human potential to transform the hydrogeomorphological dynamics of drainage systemsIt is also evident the need to consider how human topographic signatures, even if at first classified as small, actually have the potential to transform surface and subsurface dynamics, with changes in natural responses that reverberate and accumulate as they are repeated in the most different watersheds.

How to cite: Rodrigues, S., Rodrigues, G., and Silva, R.: Marginal dikes promote disconnection between slopes and artificial channels: Study case in Central Brazil., 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-637, https://doi.org/10.5194/icg2022-637, 2022.

Nalón River is one of the most important rivers draining the Northern watershed of Cantabrian Mountains (NW Iberian Peninsula). This drainage basin was subject to an intense coal mining activity during the 19th and 20th centuries. The resulting products of this mining activity (mainly those derived from coal washing) have been incorporated into the stratigraphic sequence of floodplains. This makes Nalón river a unique opportunity to study accretion rates in floodplains and to investigate the rate of sand sediment propagation and dispersion in gravel-bed rivers (two processes whose study is complex and elusive), as well as to study the spread of coal residues and other contaminants in the fluvial environment.
With these aims, we accomplished a stratigraphic survey of floodpain deposits in the lower alluvial plain of Nalón river. We identified a total number of 17 stratigraphic levels in a 3-m thick floodplain sequence. Some of these levels correspond to low-energy deposits (fine sand), while others correspond to high-stage flood deposits (very coarse sand and gravel), with abundant   sediment structures such as parallel lamination, cross-bedding and ripples. Samples taken from the floodplain sequence were prepared for grain-size analysis, organic petrography determinations (16 samples) and geochemical analysis (24 samples). Geochemical analysis measures the total concentrations for 63 elements by inductively coupled plasma-mass spectrometry (ICP-MS). ?). Additionally, we took 7 samples for luminescence (OSL) dating and one (small wood pieces) for 14C.
Coal is very abundant throughout the stratigraphic section, which suggests that sedimentation was simultaneous with the development of intensive mining that has developed in the last 150 years. On the other hand, there are several dams upstream the study section, the oldest one built in 1952. These dams have undoubtedly interrupted sediment continuity, so mining-derived sediments might not have represented a significant contribution to floodplain deposits after dam construction. However, the upper levels of the stratigraphic section contain abundant coal particles, which suggests that these levels pre-date dams (1952) or that the upper levels incorporated material derived from riverbed and bank erosion.
The objectives of this study are twofold: 1) to  analyse coal and  their associated  contaminants incorporated into fluvial sediments in the Nalón river; and 2) to reconstruct the sedimentary history of the alluvial plain, while exploring the use of coal and geochemical data as sediment markers.

How to cite: Menendez-Duarte, R., Vazquez-Tarrio, D., Fernandez-Iglesias, E., Tomillo, P., Suarez-Ruiz, I., Rodriguez-Valdes, E., and Medialdea, A.: Natural and mining legacies in Nalón river floodplain deposits (NW Iberian Peninsula), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-42, https://doi.org/10.5194/icg2022-42, 2022.

Over the last few decades, environmental changes have occurred in the Cantabrian Mountains (Northwest Spain) as a result of economic, social and climatic transformations. The depopulation in the rural environment with the transformation of traditional land uses, the closure of coal mining operations, and the increase in temperatures have modified the geometry of channels, water flow, and sediment connectivity of mountain rivers.

The runoff and the sediment load are modified, and the reservoirs located downstream collect all these changes thanks to the gauging stations for water flow, up and down the reservoir and the sediment sequences inside the reservoir. Studies have been carried out in natural cuts of several reservoirs during their dry season with the aim of knowing in detail the effects of each environmental change. The studied variables are accumulation rhythms, exceptional events, granulometry, and some chemical patterns. Data have already been published in the Pisuerga River basin (Palencia) from the analysis of the sediments retained in the La Requejada Reservoir (Pisabarro et al., 2019) but are not still published in Tuerto River basin in the Villameca Reservoir (León) and in Ibias River in the Grandas de Salime Reservoir (Lugo-Asturias).

In the first one, it was found a clear tendency to reduce the grain size since 80’s, when the land use change from crops and grasslands towards rewilding were increased. This process was aid with a decrease of runoff close to 20% between 60’s to 2010’s. In the other two reservoirs, the Villameca and the Grandas de Salime, there are interesting sediment outcrops too, in the last one affected by mining activity. Samples of sediment have been taken which also show the tendency to a smaller grain-size particle in the sediments’ upper levels. In the Villameca Reservoir at consequence of a clear reduction of the extreme events in the last decades.

Significant differences in sediment thickness have been observed between northern and southern slopes of the Cantabrian Mountains partly due to the marked asymmetry slopes, proper of this mountain range. In the first (the Grandas de Salime) up to 5.5 m has been found form since 1953 (2021), but in the La Requejada and Villameca reservoirs (in the Southern slope) only 1-2 m since 1940 (2016) and 1947 (2021). During the next dry season of the reservoirs, the research will be extended to other reservoirs with the main goal of extending this analysis and understanding the Global Change implications in the connectivity and the fluvial dynamics.

Pisabarro, A., Pellitero, R., Serrano, E., Lopez-Moreno, J.I. (2019) Impacts of land abandonment and climate variability on runoff generation and sediment transport in the Pisuerga headwaters (Cantabrian Mountains, Spain), Geografiska Annaler: Series A, Physical Geography, 101:3, 211-224, DOI: 10.1080/04353676.2019.1591042

How to cite: Pisabarro, A., Santos-González, J., Serrano, E., Rodríguez-Muñoz, I., Cebrián del Moral, M., Melón-Nava, A., Pérez-Muñoz, S., and González-Gutiérrez, R. B.: Global Change and sediment yield from the study of headwater reservoir sedimentation in the Cantabrian Mountains (Northwest Spain)., 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-242, https://doi.org/10.5194/icg2022-242, 2022.

Valleys associated with convergent topography are common features on the earth’s surface. Valley bottoms along which most rivers flow have been considered geomorphologically important since stream channels adjust their forms within them and, consequently, the width of the valley bottom determines the planform and type of channel reach. The headwater streams comprise transitional and colluvial channels and account for nearly 70 to 80 percent of the river network. They play a role in the movement or retention of sediments and nutrients transferred from surrounding hillslopes, and the provision of habitats for the various aquatic and riparian organisms in mountainous regions. Thus, accurate delineation of the valley bottoms, including colluvial valley portions, is fundamental for managing mountain rivers. In this study, we applied widely used methods for extracting valley bottoms into an intermontane catchment where colluvial valleys dominate (i.e., the Huengjeong basin in South Korea), verified and compared their results to suggest a practical procedure for applying these methods to the uppermost basins in a mountainous region. We compared two methods: the Valley Confinement Algorithm (VCA) which extracts valley bottoms based on flood-prone areas estimation, and the Geomorphon-based method using geomorphic units matching with the topography of valley bottoms. Our results show that the valley bottoms delineated from the VCA with flooding factor 1, smaller than the value (i.e., 3) used for extracting downstream unconfined valley bottoms, characterize well the valley bottoms in the study area. However, the valley bottom width becomes wider where low order tributary flows over flat areas such as river terraces. For the Geomorphon-based method, it turned out that the geomorphic units based on a Geomorphon calculated using a single set of parameter values (i.e., analysis radius and flatness threshold) did not properly capture both headwater colluvial valley and downstream fluvial valleys. Therefore, we extracted valley bottoms for colluvial and fluvial valley bottoms, respectively: Colluvial valley bottoms could be delineated by a set of geomorphic units (valley, hollow, slope, and spur) based on a Geomorphon calculated using a 50 m analysis radius and 0.5-degree flatness threshold; The fluvial valley bottoms could be delineated by a set of geomorphic units (valleys, depressions, foot slopes, and flats) based on 125 m analysis radius and 5-degree flatness threshold. While choosing the geomorphic units corresponding to valley bottoms for the Geomorphon-based method is highly subjective and time-consuming, the VCA could easily detect flood-prone areas below river terraces by only adjusting flooding depth. Thus, the VCA is thought to be suitable for extracting valley bottoms from colluvial valley-dominated areas.  

How to cite: Lee, W. Y., Chen, H., and Byun, J.: Comparison of the methods for valley bottom extraction: A case for the mountain drainage basin where colluvial and bedrock valleys dominate, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-363, https://doi.org/10.5194/icg2022-363, 2022.

Mediterranean catchments are within the most complex environments due to the seasonality of their climate, the catchment geology and the long history of landscape modification by human activity, which strongly influenced their hydrological response. These characteristics make this region sensitive to the global change (i.e. land uses and climate changes) and therefore subject to changes that will affect the sustainability, quantity, quality and management of water resources. In addition, mountainous areas play a key role for water supply as they provide between one and two thirds of the global freshwater discharge, which can reach more than a 90% of the runoff on the catchment scale. Furthermore, Mediterranean mountains constitute the wettest areas of catchments ranging from mild to arid climates, being natural reservoirs for water uses downstream. Thus, assessing the hydrological response at different timescales is fundamental for a better comprehension of process interactions and feedbacks between different runoff drivers across timescales.

This study investigates the runoff response at multiple temporal scales in two representative small Mediterranean catchments (< 2 km²) located in the Srou River basin (Middle Atlas - Morocco) to achieve a better understanding of their hydrological response. The first catchment (Talhiant, 1.14 km²) is agricultural (98%), while in the second one (Mougeryberdan, 1.15 km²) predominates forest (73%), especially in the upstream part. Continuous monitoring of water fluxes during two natural years (2018-2019) was used to establish rainfall-runoff relationships in order to recognize the role of land uses and lithology variables during two natural years in the runoff response at annual, seasonal and event scales. At the annual and seasonal scale, rainfall amount and runoff yields were computed. At the event scale, a rainfall-runoff relationship assessment was carried out with 84 events, being analysed through a Pearson correlation matrix using different variables extracted from the hyetograph and hydrograph.

At the annual scale, the annual rainfall ranged from 807 to 328 mm yr⁻¹ at Talhiant, and from 925 to 604 mm yr⁻¹ at Mougeryberdan for the natural years 2018 and 2019, respectively. According to the rainfall values, the annual runoff coefficient was 23% and 26% at Talhiant, and 14% and 39% at Mougeryberdan during the studied years respectively. At the seasonal scale, winter was the rainiest season (486-584 mm) at both studied catchments, followed by autumn, spring and summer. Monthly evapotranspiration increased from winter (< 17 mm) to summer (19-91 mm) and spring (39-142 mm). At both catchment, monthly runoff coefficient decreased from autumn (9%-45%) and winter (33%-49%) to summer (< 8%). At the event scale, rainfall amount had positive correlation with runoff and discharge peak at both catchments (R² > 0.55). At Talhiant, antecedent rainfall positively correlated with runoff, runoff coefficient and discharge peak, whereas rainfall intensity correlated with discharge peak. At Mougeryberdan, antecedent rainfall positively correlated with discharge peak, whereas no correlation was observed between rainfall intensity and other variables.

The results of this research will improve the comprehension of hydrological processes in regions characterized by a low water resources availability and scarcity of hydrological data.

How to cite: Ouakhir, H., Fortesa, J., Reddad, H., García-Comendador, J., El Khalki, Y., El Ghachi, M., and Estrany, J.: Hydrological response of two contrasting small Mediterranean Mountainous catchments in the Middle Atlas - Morocco, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-624, https://doi.org/10.5194/icg2022-624, 2022.