ICG2022-23

ICG2022
Connectivity in Geomorphology 

In the past two decades, connectivity has emerged as a relevant conceptual framework for understanding the transfer of water and sediment through landscapes. The concept has had particular success in the fields of fluvial and hillslope geomorphology to better explain rates and patterns of geomorphic change. This session is organized by the IAG Working Group on “Connectivity in Geomorphology”. The specific objectives of this WG are to foster international scientific exchange related to the advancement of the theory of connectivity in geomorphology, method development, and concept implementation (incl. sustainable land and water management applications). We invite a broad range of contributions to the session that will aim to showcase the role of (dis-)connectivity in geomorphology.

Conveners: Ronald Pöppl, Anthony Parsons, Archimedes Perez Filho, Isabel Paiva
Orals
| Mon, 12 Sep, 17:00–19:00|Room Sala Inês de Castro-C1E
Poster
| Attendance Mon, 12 Sep, 16:45–17:00 | Display Mon, 12 Sep, 09:00–Tue, 13 Sep, 19:00|Poster area

Orals: Mon, 12 Sep | Room Sala Inês de Castro-C1E

Chairpersons: Ronald Pöppl, Isabel Paiva
17:00–17:15
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ICG2022-16
Michael Slattery, Sharra Blair-Kucera, and Peter McKone

Groundwater seeps are characteristic hydrological and ecological features of many landscapes, yet their hydrology remains poorly understood. Within the North Central Texas Grand Prairie Ecoregion, seep systems developed in soils over interbedded limestone and marl are prevalent. However, previous attempts to gather data on runoff generation from these systems, and to assess their connectivity and contribution to headwater stream hydrology, have been unsuccessful due to widespread drought across the state, principally between 2010 and 2015. A priori reasoning suggests that seeps must contribute flow to headwater streams, but no work to date has been able to document or quantify those contributions.

In this paper, we document a hitherto undiscovered hillslope seep system in Somervell County, Texas. The overall aim of our research is to gain a deeper understanding of the hydrology of these seep systems and to determine whether they function (and can therefore be classified) as wetlands. To achieve this, we (1) quantify the spatial and temporal variability of soil moisture and matric potential across the hillslope seep system; (2) assess the relationship between changes in soil moisture and vegetation; and (3) quantify the magnitude and timing of runoff generation from the seep system to channel flow. We hypothesized that these systems might qualify as isolated wetlands during non-drought conditions, and our field measurements and wetland delineations demonstrate this to be true. The findings of this study indicate that, while these wetlands are separated by a glade and barrens, they are hydrologically connected to the associated headwater stream via overland flow occurring during storm events. Moreover, they remain hydrologically connected to the main channel for prolonged periods via seeping after a precipitation event. Our research provides a more complete understanding of how these seep systems behave as intermittent wetlands which could serve to improve habitat management and conservation of riparian areas within Texas.

How to cite: Slattery, M., Blair-Kucera, S., and McKone, P.: Hydrologic connectivity in a prairie hillslope seep system, Texas, USA, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-16, https://doi.org/10.5194/icg2022-16, 2022.

17:15–17:30
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ICG2022-92
Janet Hooke

Connectivity within fluvial systems can change over time at a variety of spatial and temporal scales, and can be due to differing agencies and drivers.  Here, the range and scale of alterations in dryland systems, where flow is ephemeral, are analysed, using evidence of field sites and catchments documented over several decades.

Three main types of agency or drivers are examined:  anthropogenic alterations, which may be deliberate or inadvertent; alteration from vegetation changes; effects of extreme flows.  The modifications of connectivity vary from gradual and progressive to very sudden. The persistence of the alteration also varies. Examples of each type of change are provided and the spatial scale of modification assessed. The morphodynamics and feedbacks into the operation of the systems are discussed.  Changes that are exemplified include effects of structures such as check dams on differing timescales, and the modifications produced by growth and destruction of vegetation. The connectivity of varying flows in these ephemeral changes is related to event characteristics and channel state.  The extent of human impact and their repercussions in these systems are discussed.  The various modifications of connectivity present challenges to modelling and prediction of impacts at varying spatial and temporal scales. The implications for sustainable management and functioning of the systems are considered.

How to cite: Hooke, J.: Types and scales of changes in connectivity in dryland fluvial systems , 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-92, https://doi.org/10.5194/icg2022-92, 2022.

17:30–17:45
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ICG2022-250
Miloš Rusnák, Milan Lehotský, Anna Kidová, Ján Kaňuk, Ján Šašak, Peter Labaš, Lukáš Michaleje, and Ján Sládek

The sediment transport is crucial for maintaining a good ecological condition of the aquatic ecosystem. Moreover, the study of sediment transport requires multitemporal and multiscale approaches using more sophisticated tools, such as precise imaging and generation of novel 3D technology, calculation elevation model, tracer particles analyses, ground-penetrating radar recording, grain size analyses etc. Consequently, transitioning from local to catchment scale, using high-resolution topography datasets, is the main challenge for system linkage identification using numerical methods and an exhaustive inventory of processes involved in the sediment cascade. The sediment bedload transport monitoring and analyses of spatio-temporal variability of this process were studied in the natural, braided-wandering river system of the Belá River with a multi-channel planform. High-resolution data collection from UAV (Unmanned Aerial Vehicle) and TLS (Terrestrial Laser Scanning) will be used for detailed topographic model and point cloud generation. Channel bathymetry was calculated from drone imagery and field inventory depth data. Historical aerial photographs were used for long-term channel adjustment and represent the horizontal extent of sedimentation with the impact of vegetation cover. Historical analyses have shown that pattern dynamics activate channel-floodplain movement and initiate a sediment cascade. Sediment supply to the channels correlates with the magnitude of flood events (maximum discharge, cumulative discharge, cumulative discharge higher than RI1.5, and duration of discharges higher than RI1.5) and lateral migration is the main factor controlling system. During the one specific reach survey from March 2016 to November 2018, were transported 10,103 m3 (25,964 tonnes) of fine-grained sediment into the river channel and intensive bed incisions accelerated into the channel bedrock.   

How to cite: Rusnák, M., Lehotský, M., Kidová, A., Kaňuk, J., Šašak, J., Labaš, P., Michaleje, L., and Sládek, J.: Sediment transport connectivity and its response in the fluvial ecosystem detected with high-resolution data, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-250, https://doi.org/10.5194/icg2022-250, 2022.

17:45–18:00
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ICG2022-320
Ian Fuller, Gary Brierley, Brenda Rosser, Jon Tunnicliffe, and Mike Marden

The 2208 km2 Waipaoa River catchment, the onshore portion of the Waipaoa source-to-sink (S2S) sedimentary system in the East Coast of New Zealand’s North Island, is a tremendously data-rich study area for obtaining insights into catchment function and connectivity (Kuehl et al. 2016). There have been longstanding concerns about erosion severity and mitigation dating back to 1895 (Hill, 1895). High rates of erosion in the Waipaoa have been the defining catchment management issue since the mid-twentieth century, triggered by forest clearance for pastoral agriculture in the late nineteenth and early twentieth century and primed by a combination of highly erodible lithologies, steepland terrain, regular intense storm events, and slopes undercut by postglacial river incision. The magnitude of erosion in the East Coast Region since European forest clearance has exceeded that in any other part of New Zealand.  Connectivity relationships in the Waipaoa catchment have been profoundly altered. Simultaneous sediment inputs from deforested slopes deliver sediment directly into tributary and trunk stream channels, causing significant bed aggradation and channel infilling. Gullies overwhelm receiving streams, forming alluvial fans and represent the single largest source of sediment to the system. Sediment derived from shallow landslides is significant during storm events, but gully, sheet and riverbank erosion have the potential to generate sediment whenever it rains. In the upper catchment, channel widening contributes further sediment, particularly through bank and cliff erosion. The fine-grained nature of sediment supplied by lithologies in the upper catchment accentuates downstream delivery of materials, resulting in channel contraction and floodplain accretion in the lower Waipaoa.  Efforts to mitigate erosion by afforestation using plantation forestry have been successful in some headwater tributaries, with channel degradation beginning, but this process generates additional sediment, which is conveyed downstream. We use a combination of LiDAR and river channel cross-sections to demonstrate contemporary longitudinal patterns of connectivity in the Waipaoa River and assess the prospective river futures of this anthropogenically altered system.

 

References

Hill, H. (1895) Denudation as a factor of Geological Time. Transactions and Proceedings of the New Zealand Institute, 1895, Volume XXVIII.

Kuehl, S. A., Alexander, C. R., Blair, N. E., Harris, C. K., Marsaglia, K. M., Ogston, A. S., Orpin, A. R., Roering, J. J., Bever, A. J. & Bilderback, E. L. 2016. A source-to-sink perspective of the Waipaoa River margin. Earth-Science Reviews, 153, 301-334.

How to cite: Fuller, I., Brierley, G., Rosser, B., Tunnicliffe, J., and Marden, M.: The Waipaoa River Story: how changing connectivity modulates catchment-scale response times and prospective river futures, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-320, https://doi.org/10.5194/icg2022-320, 2022.

18:00–18:15
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ICG2022-491
Allan James

Forecasting fluvial sediment yields involves several assumptions about catchment dynamics that should be explicitly realized. For example, sediment delivery ratios (SDR), the ratio of sediment yield to sediment production (Y/P), are often assumed constant and used to translate upland sediment production to downstream deliveries or estimate yields from erosion models.  Constant SDR values may be lumped basin-wide or applied in distributed grids or sub-catchment response units. The assumption of constant SDRs, however, tacitly subsumes an assumption of approximately constant sediment production rates averaged over time. Yet, SDRs may vary substantially and systematically over time in response to changing land-use, climate, or other factors that govern sediment production. With human disturbances, it’s common to have a punctuated sediment production followed by a systematic peak and decline of yields as the legacy sediment is translated downstream through time. 

            Hydraulic mining in California is an extreme case of punctuated sediment production where massive amounts of hydraulic mining sediment (HMS) were produced between 1853 and 1884 and then abruptly stopped. This research used geomorphic change detection and DEM differencing in two small, mountain catchments in the mining districts to document sediment production, initial storage, and recent storage of HMS. Total sediment production from mining in the two catchments was 41.3 and 23.5 106m3, which was used to compute SDRs for the various periods. Average sediment yields were calculated from the changes in storage between periods. Changes in sediment yields show the dynamics of SDRs through time. Initial SDRs were high in the late 19th century but increased further as cumulative deliveries increased. On a catchment scale, the two basins had SDRs of 62 and 70% in 1884 when mining ceased, but this had increased to 88 and 84% by 2014 as the cumulative yields increased. Lateral connectivity played an important role in changing yields as easily eroded sediment became less accessible, but yields also decreased in response to channel gradient declines and bed armoring. Longitudinal connectivity was also important within the catchments through the emergence of bedrock gorges that trapped large pockets of sediment for some periods. The dynamics of delivery ratios calls for a knowledge of the history of geomorphic changes in catchments in order to recognize systematic changes in sediment production.

How to cite: James, A.: Sediment Connectivity: Punctuated Anthropogenic Sediment Production and Dynamic Sediment Delivery Ratios, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-491, https://doi.org/10.5194/icg2022-491, 2022.

18:15–18:30
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ICG2022-568
Marco Cavalli, Stefano Crema, Stefan Steger, Vittoria Scorpio, Francesco Comiti, Giorgia Macchi, and Lorenzo Marchi

The growing interest of the Earth sciences community in sediment connectivity has led this property to become a key concept for modern geomorphology. At the same time, a great effort has been made to develop new methods to measure it. The increasing availability of high-resolution Digital Elevation Models (DEMs) for different spatial and temporal scales from various sources, such as LiDAR and photogrammetry, has laid the foundations for the development of approaches exploiting DEM derivatives as slope, flow accumulation, and surface roughness through geomorphometry for a (semi)quantitative assessment of sediment connectivity. Among the different methods, the index of sediment connectivity, which aims at depicting spatial connectivity patterns to support the assessment of the contribution of a given part of the catchment as a sediment source and define sediment transfer paths, was particularly successful thanks also to its intrinsic simplicity and the relative ease of computation through the dedicated open-source software application. The index saw many applications in different geographical and environmental contexts and for different study objectives, reflecting the increasing need for an objective characterization of the linkages between landscape units. Traditional applications of the index are based on qualitative and semi-quantitative analyses to investigate hillslope-channel coupling, sediment transfer dynamics, the impact of extreme natural events, and prioritization of sediment source inventories. This work aims at presenting and discussing the main applications of the sediment connectivity index. If the intrinsic limitations of the index are considered, it is demonstrated that the index can provide a spatial characterization of sediment dynamics, thus improving the understanding of geomorphic systems' behavior. A specific focus will be made on the most recent applications that are moving towards a more quantitative approach to identify areas in a catchment that are both susceptible to slope instability/mass movements and connected to a specific target. Although other fields of application can be envisaged, the applications so far implemented deal especially with debris flows, one of the most active processes in supplying sediment to the main river channels. We believe that this kind of approach paves the way for a new generation of susceptibility maps that, encompassing the sediment connectivity concept, can be adopted for a better hazard and risk assessment and, consequently, for improved countermeasures planning.

How to cite: Cavalli, M., Crema, S., Steger, S., Scorpio, V., Comiti, F., Macchi, G., and Marchi, L.: Overview on Index of Connectivity applications: towards a quantitative approach., 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-568, https://doi.org/10.5194/icg2022-568, 2022.

18:30–18:45
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ICG2022-581
Bryce Finch and Virginia Ruiz-Villanueva

Instream large wood (LW), downed trees, trunks, root wads, branches, and fragments of wood at least one meter in length and ten centimeters in diameter, contribute to maintaining rivers´ physical and ecological integrity. Additionally, LW can be hazardous to infrastructure, which makes management of LW a priority for local services. Post-analysis of flood events has demonstrated recruitment of LW through several mechanisms such as bank erosion, landslides, and debris flows. Such recruitment and transfer of LW to fluvial networks vary spatially and temporally, which makes predictions of these processes challenging.

The current studies lack a method to express the structure of supply and transfer of LW throughout a catchment. An improvement would be to provide a means to interpret the structural connectivity of LW or the potential impact one recruitment area may have on another. Therefore, we propose to apply the graph theory to construct the network of LW recruitment from its source location to the fluvial network and to a designated outlet. In so doing, we aim to identify critical spatial connections that have previously not been realized, provide a means to view LW recruitment and transfer for an entire catchment wholistically, and explore the application of the graph theory in the realm of LW, which has not previously been done.

The graph theory requires a simple sequence for input data. The sequence is constructed based on physical connections that exist in nature. For instance, a forested region which has been determined to be intersected by a landslide prone area would represent a source of LW and the process which would supply the LW to the channel would be the landslide. Graph theory interprets the source area of LW as well as the location along the river to which the landslide connects as two unique nodes. The mechanism supplying the LW, in this case landslides, would represent an edge that would connect the two nodes. This same principal is then applied to the entire network for all pertinent recruitment mechanisms. The network can then be analyzed for a variety of different purposes including the identification of critical hot spots where multiple processes may be coinciding or locations along the channel where LW recruitment is relatively absent. Each node can additionally be given attributes which can later be extracted, such as the amount of LW available.

Determination of recruitment process prone areas has been based on previously developed methods for landslides, bank erosion, and debris flows. Swiss inventories of the forested area have been applied to delineate the forested area.

This contribution will show preliminary results done in the Vallon de Nant, Canton of Vaud, Switzerland. The catchment is relatively small (approx. 13km2) with active landslide, debris flow, bank erosion, and avalanche processes which supply LW. Current findings indicate landslide and bank erosion processes to be more widespread throughout the catchment with debris flows occurring more intermittently. The constructed LW network will provide a means to relate different recruitment mechanisms to one another and to LW found in rivers.

How to cite: Finch, B. and Ruiz-Villanueva, V.: Understanding the transfer of instream large wood through river networks with graph theory, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-581, https://doi.org/10.5194/icg2022-581, 2022.

18:45–19:00
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ICG2022-733
Raphael Spiekermann, Hugh Smith, Sam McColl, Lucy Burkitt, and Ian Fuller

We present a morphometric landslide connectivity model using lasso logistic regression that aims to predict the likelihood of sediment delivery to streams following landslide initiation. The model is used to investigate determinants of sediment connectivity for a landslide-triggering storm event in 1977 in the Wairarapa, New Zealand. A range of connectivity scenarios are explored by defining a set of sinks and simulating varying rates of sediment generation during flood events of increasing magnitude. Sediment delivery ratios ranged between 0.21 and 0.29, depending on the definition of sink. When accounting only for direct deposition into streams, the event sediment yield was estimated at 3548 t/km2. However, when assuming continued sediment recruitment at reduced rate by overland flow across saturated soils as well as post-event reworking of deposited material, the maximum sediment yield was estimated at 9033 t/km2. This estimate of event sediment yield is approximately 2.5 times greater than estimates only considering landslide deposits connecting to streams directly and challenges previous assumptions related to sediment delivery ratios and the importance of shallow landsliding for sediment budgets.

Furthermore, the influence of coalescing landslide deposits in determining sediment delivery is assessed. An important outcome of the lasso regression is the potential consequence of over-reliance on individual landslide scar size as a predictor of connectivity. Without considering contributions of landslide-derived material from multiple sources to the transport of delivery downslope, the run-out distance is likely to be underestimated for shallow landslides.

Finally, sediment mobility from shallow landslides is quantified by coupling statistical landslide susceptibility and sediment connectivity models in a modular form.  We present results from scenario modelling for fifty silvopastoral farms and quantify the cost-effectiveness of targeted versus non-targeted approaches to shallow landslide mitigation at the scale of individual trees. The cost-effectiveness of targeted mitigation of landslide-derived sediment is found to be approximately 10-fold greater than a non-targeted approach. An important finding of the landslide susceptibility and connectivity modelling is that, in total, only 6.5% of farmland is the potential source of approximately two-thirds of landslide-derived sediment across the 50 farms. Due to existing vegetation, this area has already been reduced to 4.7%. Further reductions in future sediment delivery can be achieved by increasing slope stability on these highly susceptible and connected slopes through additional biological mitigation.

How to cite: Spiekermann, R., Smith, H., McColl, S., Burkitt, L., and Fuller, I.: Coupling landslide susceptibility and connectivity models for cost-effective mitigation of landslide-derived sediment delivered to streams, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-733, https://doi.org/10.5194/icg2022-733, 2022.

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

Poster: Mon, 12 Sep, 16:45–17:00 | Poster area

Chairpersons: Ronald Pöppl, Isabel Paiva
P138
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ICG2022-415
John Edward Perez, Ronald Poeppl, Laura Turnbull, and John Wainwright

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.

P139
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ICG2022-49
Achim A. Beylich and Katja Laute

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.

P140
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ICG2022-306
Felix Pitscheider, Stefan Steger, Marco Cavalli, Francesco Comiti, and Vittoria Scorpio

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.

P141
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ICG2022-470
François Clapuyt and Veerle Vanacker

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.

P142
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ICG2022-559
Spatial patterns of erosion susceptibility and sediment connectivity in an agricultural catchment : the case of Mercurey (Burgundy, France) over the Holocene
(withdrawn)
Brian Chaize, Mathieu Fressard, and Étienne Cossart
P143
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ICG2022-564
Graph theory structure to describe sediment connectivity: application in the Beaujolais vineyard landscapes
(withdrawn)
Jessaica Pic, Mathieu Fressard, and Etienne Cossart
P144
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ICG2022-409
Manel Llena, Estela Nadal-Romero, Makki Khorchani, Melani Cortijos-López, Javier Zabalza, and Teodoro Lasanta

Mid-mountain catchments across the Mediterranean basin undergone a decrease in runoff and sediment yield during the second half of the 20th 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.

P145
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ICG2022-637
Sílvio Rodrigues, Gelze Rodrigues, and Renato Silva

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.

P146
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ICG2022-42
Rosana Menendez-Duarte, Daniel Vazquez-Tarrio, Elena Fernandez-Iglesias, Pelayo Tomillo, Isabel Suarez-Ruiz, Eduardo Rodriguez-Valdes, and Alicia Medialdea

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.

P147
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ICG2022-242
Alfonso Pisabarro, Javier Santos-González, Enrique Serrano, Ignacio Rodríguez-Muñoz, Mariano Cebrián del Moral, Adrián Melón-Nava, Sergio Pérez-Muñoz, and Rosa Blanca González-Gutiérrez

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.

P148
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ICG2022-276
Identification and assessment of sediment sources and sediment transfer processes in a Mediterranean Agroecosystem in the Northern Apennines, Italy 
(withdrawn)
Manuel La Licata, Manuele Bettoni, Alberto Bosino, and Michael Maerker
P149
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ICG2022-363
Won Young Lee, Hui Chen, and Jongmin Byun

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.

P150
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ICG2022-624
Hassan Ouakhir, Josep Fortesa, Hanane Reddad, Julián García-Comendador, Yahia El Khalki, Mohamed El Ghachi, and Joan Estrany

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.