GM4.4 | (Dis)connectivity in landscape systems: emerging concepts and their applications
EDI

Connectivity has emerged as a significant conceptual framework for understanding the transfer of water and materials (e.g. sediment, nutrients, POC, large wood, plant propagules) through landscapes. The concept of connectivity has had particular success in the fields of hydrology, fluvial geomorphology and soil erosion, but has also been employed in, for example, studies of hydrochory. Connectivity as applied in various disciplines can be a transformative concept in understanding complex systems, allowing analyses of how such systems behave in terms of scaling, catastrophic/phase transitions, critical nodes, emergence and self-organization, e.g. by applying network-based analyses and modelling. Recent research also highlights the widespread nature of dis-connectivity landscape systems, caused by natural and anthropogenic structures including dams, log jams, or agricultural terraces. These and other forms of dis-connectivity can have large spatial and temporal implications on ecological, geomorphic, hydrological and biogeochemical processes, e.g. through buffering water and material fluxes. We aim to create a diverse interdisciplinary session that reflects a broad range of research seeking to illustrate the role of (dis-)connectivity in landscape systems. We hope to use the session to develop a discussion on the importance of (dis-)connectivity to generate a basis for an integrated framework to be applied across different fields of geosciences (incl. management applications).

Co-sponsored by IAG
Convener: Ronald Pöppl | Co-conveners: Lina Polvi Sjöberg, Laura Turnbull-Lloyd, Anthony Parsons
Orals
| Tue, 25 Apr, 16:15–18:00 (CEST)
 
Room G1
Posters on site
| Attendance Tue, 25 Apr, 14:00–15:45 (CEST)
 
Hall X3
Posters virtual
| Attendance Tue, 25 Apr, 14:00–15:45 (CEST)
 
vHall SSP/GM
Orals |
Tue, 16:15
Tue, 14:00
Tue, 14:00

Orals: Tue, 25 Apr | Room G1

Chairpersons: Ronald Pöppl, Laura Turnbull-Lloyd
16:15–16:20
16:20–16:30
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EGU23-10825
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GM4.4
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ECS
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Highlight
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Virtual presentation
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Sana Khan, Pascal Castellazzi, Rebecca Bartley, Anne Kinsey-Henderson, Aaron Hawdon, Simon Walker, and Scott Wilkinson

In the Great Barrier Reef (GBR) catchments of northeast Australia, high source to sink sediment connectivity, particularly from gullies and streambanks are adversely impacting the coral ecosystems and millions of dollars are being spent on landscape rehabilitation to help reduce excess sediment delivery. Understanding sediment dynamics and mapping erosion hotspots provides improved data and information to support erosion management practices. There is an urgent need to develop methodologies to help (i) prioritise active gullies for rehabilitation; and (ii) to inform which treatments are most effective at reducing fine sediment yields. Previous research in the highly erosive landscapes of northeast Australia has demonstrated that multiple lines of evidence are needed to support informed management efforts and investment decision making.  

Here we discuss the applicability of multi-temporal spatial datasets- differential LiDAR DEMs (Laser Light Detection and Ranging Digital Elevation Models) and Interferometric SAR (InSAR) from Sentinel-1 imagery archives as two lines of evidence for detecting erosion hotspots and assessing gully sediment dynamics within the highly erosive Burdekin catchment. At several case study sites, multi-temporal LiDAR DEMs are used to derive DEMs of Difference (DoDs) to (i) assess the spatial pattern of erosion and deposition within contrasting gully types and (ii) measure sediment yield from control and treatment gullies to analyse rehabilitation efforts. Coherence Change Detection (CCD) from Sentinel-1 archives is used to assess the spatial pattern of geomorphic change (erosion and deposition). Here we will discuss the strengths and limitations of both approaches and how these multiple lines of evidence can be combined to identify erosion hotspots and gully sediment dynamics for better prioritisation of rehabilitation efforts in the GBR catchments.

How to cite: Khan, S., Castellazzi, P., Bartley, R., Kinsey-Henderson, A., Hawdon, A., Walker, S., and Wilkinson, S.: Integrating multiple lines of evidence to identify erosion hotspots for reducing sediment connectivity and delivery to the Great Barrier Reef, Australia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10825, https://doi.org/10.5194/egusphere-egu23-10825, 2023.

16:30–16:40
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EGU23-7225
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GM4.4
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Highlight
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On-site presentation
Mathias Collins, Matthew Baker, Matthew Cashman, Andrew Miller, and Stephen Van Ryswick

Sediment management is an important aspect of river reconnection projects, often driving costs and influencing community acceptance. At sites with uncontaminated sediments, downstream release is an attractive option because it is often the cheapest and most practical approach and the sediment can be ecologically beneficial to downstream areas deprived of it for years by the dam. To employ this option, project proponents must estimate the sediment quantity to be released and, if substantial, estimate how long it will take to erode, where it will go, and how long it will stay there. We investigated these issues for sediments released by the 2018 removal of Bloede Dam on the Patapsco River in Maryland, USA. The dam was about 10 m high and its impoundment filled with sand and mud. Taking the surface elevations of these sediments surveyed immediately before removal and subtracting estimates of the pre-dam valley elevations derived from 21 cores and post-removal surveys of exhumed pre-dam surfaces, we estimate there was approximately 186,600 m3 of stored sediment composed of 70% sand and 30% mud. These proportions match estimates made during pre-removal engineering studies, but our total stored sediment estimate is about 20% less. The difference between estimates reflects a real change in stored sediment quantity between 2018 and 2012 when the engineering studies were completed, additional data available to us after removal, and different estimation methods. After removal, using elevation surveys generated by traditional methods as well as UAS-based aerial imagery and structure-from-motion (SfM) at high temporal resolution, we documented rapid erosion of the stored sediments in the first six months (~60%) followed by greatly reduced erosion rates for the next couple of years. A stable channel was developed in the impoundment during the rapid erosion phase. These results are similar to a two-phased erosion response reported for sediment releases at dam removals around the world across a range of dam and watershed scales, indicating what practitioners and communities should expect when reconnecting rivers in similar settings. Downstream, repeat surveys combined with discharge and sediment gaging show rapid transport of eroded sediments through a 5 km reach, especially during the first year when discharges were above normal, and little overbank storage.

How to cite: Collins, M., Baker, M., Cashman, M., Miller, A., and Van Ryswick, S.: Releasing sediments while reconnecting rivers: how do channels respond and how long does it take?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7225, https://doi.org/10.5194/egusphere-egu23-7225, 2023.

16:40–16:50
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EGU23-12365
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GM4.4
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Highlight
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On-site presentation
Florian Betz, Rafael Schmitt, Magdalena Lauermann, Akylbek Chymyrov, and Tobias Heckmann

Connectivity is crucial for the functioning of river corridors as it determines the natural flow and sediment regime as well as the ability of species to migrate. Thus, it is a property highly relevant for the development of riverine landscapes and their potential of ecosystem service provision. Today, the connectivity of most (large) rivers is affected by anthropogenic infrastructure such as hydropower dams. This is also true for the Aral Sea Basin in Central Asia. The importance of rivers as freshwater resource led to an intensive exploitation of water resources and to the construction of a large number of dams and thus to a fragmentation of the river network. Despite its relevance for the functioning of the river corridors, connectivity remains unexplored for this  basin. This is partly due to the fact that the large scale assessment of connectivity for such data-scarce regions is challenging. For instance, there is the need to delineate a robust and accurate river network from globally available digital elevation models (DEM) as readily available datasets like the Hydrosheds river network suffer from significant errors in this region. In this study, we present a first assessment of the connectivity of the river network in the Aral Sea Basin. In addition, we discuss the challenges associated with large scale modeling of structural connectivity of river networks in data-scarce regions and how to overcome them.

We take as a basis a channel network delineated from the 30 m Copernicus DEM along with geomorphon-based major geomorphological units to derive landscape-specific channel initiation thresholds. We use a least-cost path approach for flow routing to avoid artifacts resulting from sink filling. Multispectral satellite time series from the Landsat mission are used to remove abandoned channels and to correct the river network. Additional input are the barriers in the Aral Sea Basin. We use the dam data from Global Dam Watch and complement it by mapping from high resolution Google Earth imagery. The river network and the barrier locations are used to create a graph representation of the river network where river reaches are represented by edges and confluences as well as dam locations by nodes. This river graph is used to compute connectivity metrics such as the dendritic connectivity index, for both the whole network and at the subcatchment scale.

The results of our study deliver the first analysis of connectivity of the river network in the Aral Sea Basin. Along with the insights in this particular river basin, we present an approach which is optimized for the application in large, data-scarce study areas. Such static analysis of structural connectivity is of course a first indicator only, and further analysis is required to understand the impact of hydrological and sediment connectivity on the riverine landscapes of the river corridors of the region. Thus, rather than a final result, we see our study on river network connectivity as an important basis for assessing sediment dynamics across the network, natural flow regime and its impairment as well as river and floodplain habitat integrity.

How to cite: Betz, F., Schmitt, R., Lauermann, M., Chymyrov, A., and Heckmann, T.: First Assessment of the Connectivity of the River Network in the Aral Sea Basin in Central Asia: Challenges of Large Scale Connectivity Modeling in Data-Scarce Regions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12365, https://doi.org/10.5194/egusphere-egu23-12365, 2023.

16:50–17:00
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EGU23-470
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GM4.4
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ECS
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On-site presentation
Stephania Rodriguez, Marcel Hürlimann, Vicente Medina, Ona Torra, Raül Oorthuis, and Càrol Puig Polo

In the scope of soil erosion modeling few attempts have been made to assess the coarse-grained sediments at steep slopes. The current approach results in a lack of correspondence in mountain watersheds because most models perform validation for different scales, topography, and land use, especially in the agricultural field. Available models normally prioritize the estimation of fine sediment in the field while the contribution of course-grained sediment is simplified or even neglected, especially in areas that require an analysis of hillslope failure events. 

Herein, we selected the Upper Llobregat River Basin (Pre-Pyrenees, Spain) as a study area and focus on the 1982 rainstorm, which triggered more than 1000 mass movements. The present investigation aims to allow an assessment of sediment production that focuses on the characterization of coarse sediment source areas from a mountain range.

The methodology includes analysis through geomatic methods, field surveys, and historic landslide inventories, followed by an index connectivity calculation to main rivers, morphometric parameters, and triggering factors. Preliminary results of this ongoing study confirm the importance of hillslope processes for the assessment of the sediment budget in mountainous areas. The outcomes will be incorporated into a modular sediment-budget model, which will be calibrated in our study area and tested in other watersheds in the Pyrenees. In addition, the impact of future changes (climate and land use) will be analyzed since extreme weather scenarios strongly affect both the production and transport of sediment in mountainous areas.

How to cite: Rodriguez, S., Hürlimann, M., Medina, V., Torra, O., Oorthuis, R., and Puig Polo, C.: Characterization of coarse-grained sediment supply for the assessment of soil erosion in mountainous areas. Application to the Upper Llobregat River Basin (Pyrenees, Spain), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-470, https://doi.org/10.5194/egusphere-egu23-470, 2023.

17:00–17:10
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EGU23-498
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GM4.4
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ECS
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Virtual presentation
Ying-Tong Lin, Laura Turnbull, and John Wainwright

Small mountainous rivers (SMRs) produce about 40% of the world’s sediment discharge from land to ocean. The dominant sources of this sediment are earthquake and typhoon-driven landslides. It is widely accepted that earthquake-induced landslides tend to locate at hillslopes, while typhoon-induced landslides tend to cluster at hillslope toe areas. These differences in landslide drivers and landslide location together determine the connectivity of resulting sediment transfers from the source (landslides) to the river network. Therefore, understanding when and where earthquake and typhoon-driven landslides occur, and the pathways and timescales over which these sediment sources are connected to river channels can help us determine the relative controls of earthquakes and typhoons on sediment discharge in SMRs. Here, we illustrate how detailed spatial and temporal mapping of landslides, using Landsat imagery within Google Earth Engine, enables us to better understand sediment connectivity in SMRs, and improve our understanding of the controls on sediment discharge in SMRs. We focus our analysis on the period between 1999 and 2020, which includes the 1999 Chi-Chi earthquake (Mw=7.7) and typhoon Morakot, which generated over 3000 mm of rainfall between 5th and 10th August 2009. The results show that we can identify event-induced landslide areas at a higher temporal resolution than the open-source landslide dataset from the Forest Bureau, Taiwan, which enables us to refine our understanding of the relative controls of discrete events (i.e. earthquakes and typhoons) on landslides and connected sediment transport pathways, and determine the timescales over which they lead to elevated sediment discharge in SMRs. Refining our understanding of earthquake and typhoon-driven controls on landslides in SMR catchments and cascading impacts on sediment export from SMRs is particularly important given the recent intensification of rainfall intensities that are anticipated to continue in the future.

How to cite: Lin, Y.-T., Turnbull, L., and Wainwright, J.: Landslide impacts on sediment dynamics in mountainous rivers after large earthquake and typhoon events: A sediment connectivity approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-498, https://doi.org/10.5194/egusphere-egu23-498, 2023.

17:10–17:20
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EGU23-7271
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GM4.4
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On-site presentation
Gianluca Botter and Nicola Durighetto

The flowing portion of river networks experiences never-ending event-based and seasonal expansion/retraction cycles, which mirror the unsteady nature of the climatic forcing.  These "temporary" rivers constitute a major fraction of the global river network, and are found across a variety of settings, especially in the headwaters. A dominant feature of these channel network dynamics is represented by the fact that the active streams are dynamically fragmented, i.e. they do not simply expand upstream when the catchment wets up, to dry down in the downstream direction during the recessions. Instead, the wetting/drying processes frequently happen in complicated spatio-temporal patterns, either activating disconnected reaches first, that will only eventually get connected to the main channel, or generating disconnections by drying out segments in the middle of the river network before the flow heads start retracting. This contribution analyzes the spatial patterns of local persistency along river networks (i.e. the fraction of time for which flowing water can be observed at each location, which is related to the wetting/drying order of the different reaches) combining field data on the spatiotemporal evolution of flowing channels and theoretical analyses, with the aim of elucidating the physical drivers of stream connectivity and disconnectivity in temporary streams. The analysis reveals that river fragmentation is related to the spatial heterogeneity of subsurface properties other than the contributing area (e.g. slope, local width, permeability). The proposed framework provides a clue for analyzing the impact of the spatial and temporal heterogeneity of streamflow presence for a variety of morphologic and biogeochemical processes (sediment transport, ecological dispersion and stream metabolism).

How to cite: Botter, G. and Durighetto, N.: Dynamically fragmented stream networks: field observations and physical drivers, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7271, https://doi.org/10.5194/egusphere-egu23-7271, 2023.

17:20–17:30
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EGU23-12616
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GM4.4
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ECS
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On-site presentation
John Edward Perez, Ronald Poeppl, Laura Turnbull, Shubham Tiwari, and John Wainwright

Fine-sediment input into river networks presents one of the biggest environmental pressures in agricultural catchment systems due to accelerating soil erosion rates associated with agricultural practices. To understand and effectively manage this problem, it is essential to identify sediment source areas and the pattern of linkages between different landscape compartments along the sediment pathways that ultimately end up in the river channel. Sediment connectivity is an increasingly used concept to help assess both on-site and off-site impacts of soil erosion by describing the efficiency of fine-sediment transfer through these different zones. Natural Water Retention Measures (NWRM) that emulate natural processes to enhance or restore the water retention capacity of ecosystems, available to be applied at agricultural fields, can be understood within this framework as they modify connectivity and provide benefits that include erosion and sediment control. The aim of this study is to assess the differences in sediment connectivity associated with scenarios of different NWRM (e.g. buffer strips, strip cropping, terracing, mulching) in a selected hillslope of the Fugnitz Catchment (Austria). Using a process-based sediment-transport model (MAHLERAN; Wainwright et al., 2008), runoff and sediment transport were dynamically simulated. Simulation results of water and sediment fluxes were then translated into a graph representing the flow network, consisting of nodes and edges, where connectivity and network properties can be quantified using graph-theoretical metrics (e.g. betweenness centrality). The same workflow was used for other NWRM scenarios, modifying parameters of the sediment transport model to capture the NWRM conditions. The results show notable changes in connectivity between scenarios as well as varying patterns of hot spots where sediment delivery is high and where interventions may be targeted, thus providing options of agricultural practices that can be implemented to improve sustainability in agricultural catchments.

How to cite: Perez, J. E., Poeppl, R., Turnbull, L., Tiwari, S., and Wainwright, J.: How do Natural Water Retention Measures modify connectivity on agricultural hillslopes?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12616, https://doi.org/10.5194/egusphere-egu23-12616, 2023.

17:30–17:40
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EGU23-12681
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GM4.4
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ECS
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On-site presentation
Niguse Abebe, Jantiene Baartman, Joris Eekhout, Bart Vermeulen, Carolina Boix-Fayos, Joris de Vente, Berhane Grum, and Ton Hoitink

Soil erosion is a process accelerated by natural and anthropogenic disturbances over time and space, leading to land degradation and causing geomorphological change. It is difficult to investigate the spatial and temporal distribution of soil erosion and sedimentation in data-scare areas, in that case, the use of simplified methods to analyze soil erosion and sediment connectivity variations over time and space can help. Sediment connectivity denotes the transfer of sediment from source to sink areas through channel systems of landscape compartments within a watershed. In this study, we aimed to investigate sediment yield (SY) variation over time and space and understand the link between hillslope soil erosion and sediment connectivity to identify hotspot areas in the Rogativa catchment (∼53 km2) in Southeast Spain. The (specific) sediment yield (S)SY was estimated by combining the Revised Universal Soil Loss Equation (RUSLE) model with the sediment delivery ratio (SDR). The SDR was calculated based on the Index of Connectivity (IC). In the channels, 100% delivery was assumed. In the Rogativa catchment, 58 check dams were constructed in 1976/77. Their trapping efficiency, obtained from field observations of sediment retained behind the checkdams in 2003, was included in the SDR estimation of the checkdams. SY was estimated from accumulated hillslope soil erosion in the local stream network while accounting for sedimentation through the SDR. Soil erosion, IC, SDR, and (S)SY were quantified and compared for the years 1956, 1977, 2001, and 2016, for which different land use maps were available. SY model results for the year 2001 were compared with observed SY (in 2003) behind the check dams. Only for about half of the checkdams, model results were comparable. This is investigated further and could be explained by complex sediment dynamics within the channels and between checkdams (i.e. one check dam retaining part of the sediment, the next downstream checkdam as well, etc) – these dynamics are not included in the RUSLE-SDR model. The RUSLE-generated soil erosion and sediment connectivity signatures (IC, SDR, and (S) SY) showed higher values in the channels and croplands than in hillslopes and decreased over time due to significant changes in land use and construction of check dams in the catchment. Moreover, the combined proportion of erosion-connectivity patterns showed about 7% of the area adjacent to some of the streams was found both highly erodible and highly connected, which indicates an adverse erosion-prone part. It is possible to apply this method to understand SY amount and distribution and identify hotspot locations in drainage systems with limited field data in data-scarce semi-arid areas like the Rogativa catchment. However, more field observations to validate the models to identify hotspot locations and investigate river network systems rather than focusing only on hillslopes, which could help to know where to intervene in the catchment.

Keywords: Soil erosion-RUSLE, Sediment connectivity, Sediment delivery ratio, Sediment yield, hotspot location

How to cite: Abebe, N., Baartman, J., Eekhout, J., Vermeulen, B., Boix-Fayos, C., de Vente, J., Grum, B., and Hoitink, T.: Quantifying hillslope erosion and sediment connectivity in the Rogativa catchment, Southeast Spain, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12681, https://doi.org/10.5194/egusphere-egu23-12681, 2023.

17:40–17:50
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EGU23-12999
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GM4.4
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ECS
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On-site presentation
Leonardo Rodolfo Paul, Vittoria Scorpio, Gean Paulo Michel, Francesco Comiti, Franciele Zanandrea, and Heron Schwarz

Debris flows are major geophysical processes which are able to modify the landscape. Structural sediment connectivity describes the physical coupling of landscape units, and it may be affected by the occurrence of single large-magnitude debris flows and/or by the cumulative changes determined by frequent, small-magnitude events. Understanding the coupling of hillslopes to the main channel during and after debris flows is essential for comprehending catchments sediment transfer at different timescales. Debris flows might provoke sudden changes in the landscape through processes such as bed and bank erosion, overbank deposition and natural dam formation. While debris flows may modify the landscape, their characteristics (e.g., path, runout) are strongly affected by the geomorphological settings. Indeed, there is an interplay between landscape morphology and debris flows, one conditioning the other and vice versa. In this regard, determining how much structural connectivity influences the coupling of debris flow with the channel network remains a challenge. An evaluation of the structural connectivity before and after storm events that triggered debris flow has been carried out on multi-temporal DTMs available for the Stolla basin (Autonomous Province of Bozen-Bolzano, Italian Alps) utilizing the Index of Connectivity (IC) and on a pre-event DTM for the Revolver basin (Santa Catarina state, Southern Brazil). To understand whether the morphological changes caused by the debris flows had an impact on flow routing during the event, some of the debris flow events were simulated by a physically based model. The topographic changes caused by the simulated scenarios have been used to compare pre- vs post-event sediment connectivity.

 

 

How to cite: Paul, L. R., Scorpio, V., Michel, G. P., Comiti, F., Zanandrea, F., and Schwarz, H.: The effects of debris flow on structural sediment connectivity: case studies in the Italian Alps and in Southern Brazil, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12999, https://doi.org/10.5194/egusphere-egu23-12999, 2023.

17:50–18:00
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EGU23-16272
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GM4.4
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ECS
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On-site presentation
Heron Schwarz, Francesco Comiti, Gean Paulo Michel, and Leonardo Rodolfo Paul

Rainfall-induced landslides are natural processes inherent to the sediment dynamics, fundamentally acting in landscape evolution, while favoring the occurrence of hazardous conditions. Given their potential to mobilize large volumes of sediments from the release zones, they play a major role in sediment production in mountain basins, while affecting sediment connectivity through the deformations produced on the landscape.

These landslides are triggered out by the imbalance of shear strength and shear stress acting on a soil layer, promoted by the presence of water. The soil wetting through infiltration, namely, the vertical transfer of water from the surface layer of the soil to its interior, during intense precipitation events, has thus historically been associated with landslide triggering.

Whereas precipitation intensity and/or volume are recurrently related, the failure of a slope can occasionally be caused by precipitation events with magnitudes that are lower than those that have previously occurred. The triggering is dependent on the overlay of hydrological processes with different spatial and timescales, including the antecedent moisture conditions of the soil and the water storage in the watershed. Thus, different processes that act in the filling, storing, and draining of water in the soil, from seconds to weeks prior to the triggering, as preferential flow or bedrock infiltration and exfiltration are all equally relevant to understand and quantify landslide behavior and sediment connectivity. Furthermore, the soil moisture conditions not only govern landslide triggering but also their potential to fluidize and travel across longer distances, influencing their connectivity.

In this way, we analyzed how soil-water processes affect the filling, storing and draining dynamics during landslide triggering and their effects on sediment connectivity. Two study areas with distinct climatic and geomorphological characteristics located in southern Brazil (Mascarada River Catchment, Rio Grande do Sul) and northern Italy (Gadria River Catchment, Autonomous Province of Bozen-Bolzano) were analyzed. Field collected data was used, together with physical-based models to simulate slope stability as well as saturated and unsaturated flow and water retention in the soil layer. Scenarios including infiltration, preferential flow and bedrock exfiltration were simulated to assess whether this increase in uncertainty and complexity brings better results to the representation of the processes.

How to cite: Schwarz, H., Comiti, F., Michel, G. P., and Paul, L. R.: SOIL-WATER PROCESSES AND SEDIMENT CONNECTIVITY IN RAINFALL-TRIGGERED LANDSLIDES: A comparative analysis between small catchments in Italy and Brazil, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16272, https://doi.org/10.5194/egusphere-egu23-16272, 2023.

Posters on site: Tue, 25 Apr, 14:00–15:45 | Hall X3

Chairperson: Anthony Parsons
X3.41
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EGU23-2788
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GM4.4
Soil erosion dynamics in the White Nile-Congo ridge region – two years of high frequency UAV monitoring
(withdrawn)
Florian Wilken, Sebastian Doetterl, Matthew Cooper, Jasmin Haist, Daniel Muhindo, Kristof van Oost, Martin Rueegg, and Peter Fiener
X3.42
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EGU23-3455
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GM4.4
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ECS
Francesco Barbadori, Samuel Pelacani, Federico Raspini, and Samuele Segoni

The problem of soil erosion is a current issue, especially in hilly and mountainous areas where the driving force is surface runoff, able to mobilize large amounts of sediment that may be delivered to rivers. This process must be considered in a context of climate change, where the number of extreme rainfall events is observed to increase, and their temporal distribution is bound to concentrate in very short periods between long dry intervals of time. The potential soil erosion and degradation can be assessed through the study of the linkages between sources and sinks in a watershed, typically called sediment connectivity assessment. The evaluation of sediment connectivity allows to identify areas prone to the delivery of sediments through the catchment and local depressions that may disconnect land units. The quantitative assessment of sediment connectivity can be evaluated by the using of indexes (e.g. Index of connectivity – IC) with a pixel by pixel procedure in a GIS environment. It is also possible to differentiate structural connectivity, which is evaluated with a geomorphological view, and functional connectivity, which consider the forcing processes and antecedent conditions (e.g. soil moisture). In this study we applied two well established approaches for calculating ICs that use geomorphological and driving force approaches in a small catchment area located in Tuscany. The area was mapped using LiDAR technology to have a high resolution digital terrain model and was affected by recent extreme rainfall events. The application of these two approaches to a small catchment area permitted to concentrate in a nearly homogenous site in terms of land use and focus on geomorphological features that contribute to a connection or a disconnection of catchment’s land units with high spatial resolution. Furthermore, the use of two different indexes allows to study the topic of sediment connectivity and associated soil erosion potential from two points of view with, considering both land management and future warning systems development. Further activities are focusing on the validation of the connectivity indexes, at the rainfall event scale, by monitoring the river suspended sediment transport at the outlet of the watershed in order to relate GIS calculated indexes with the amount of sediments delivered in the riverbed during each rainfall event.

How to cite: Barbadori, F., Pelacani, S., Raspini, F., and Segoni, S.: Preliminary assessment and comparison of sediment connectivity indexes in a small catchment area: A case study in Tuscany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3455, https://doi.org/10.5194/egusphere-egu23-3455, 2023.

X3.43
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EGU23-4433
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GM4.4
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ECS
Bruno Henrique Abatti, Gean Paulo Michel, Ronald Pöppl, Franciele Zanandrea, and Marina Refatti Fagundes

Investigating sediment dynamics and delivery in low-order streams still a topic with numerous challenges to be overcome. The processes underlying these dynamics are complex and often not linear, especially due to river emerging feedback processes varying significantly across space and through time as being governed by the connectivity relationships in these systems. Sediment connectivity in fluvial systems is controlled by different environmental factors such as hydrology (e.g. precipitation, overland flow) and structural elements (e.g. hillslope runoff pathways, pools, sinks, or natural barriers such as log jams). Most studies use discharge derived variables to estimate transport of sediment but there is a need to understand how structural elements can control the dynamics. Therefore, the main goal of this work is to study the effects of natural barriers (especially large wood accumulations) and their removal on longitudinal water and sediment (dis-)connectivity and sediment delivery via continuous monitoring/estimating of precipitation, discharge, critical shear stress (CSS), and sediment transport. The monitoring will be carried out in different scenarios, which will be determined according to the structural changes in the river corridor, due to the removal of the currently existing barriers with evident retention of sediments. The study will be conducted in the Baio stream catchment (0.89 km²), located in the Campos Gerais plateau, northeast of the state of Rio Grande do Sul, southern Brazil. In this catchment, there is an intense agricultural activity without any conservation practices, being the main sources of sediments coming from rill, sheet and channel stream erosion. At the same time, there are many sources of recruitment of woody debris, especially due to nearby reforestation activities. By investigating the effect of wood barriers in the stream, we look to understand the sensitivity of the sediment transport to the structural elements.

How to cite: Abatti, B. H., Michel, G. P., Pöppl, R., Zanandrea, F., and Refatti Fagundes, M.: Evaluation of sediment (dis-)connectivity due structural changes in a low-order stream, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4433, https://doi.org/10.5194/egusphere-egu23-4433, 2023.

X3.44
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EGU23-4937
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GM4.4
Eun-sub Kim, Young-suk Lee, Dong-kun Lee, Hui-cheul Jung, Jung-hee Hyun, and Seong-cheol Kim

A recent issue highlights the need for Ecological mitigation measures to mitigate habitat and biodiversity loss caused by increasing human disturbance and urban development. Ecological mitigation measures have become quite effective and efficient in habitat preservation and reducing the extinction rate of the population. In this study, a decision support tool was developed to mitigate environmental impacts on urban development using optimization algorithms. This study seeks to identify a spatial planning model that determines the optimal location and type of mitigation measures based on increasing biodiversity and mitigating the impact of species on urban development and calculates the implementation cost using meta-heuristic optimization algorithms.

We used the evaluation fitness value as landscape structural and functional and threat factors. It is possible to analyze the biodiversity and connectivity using the landscape pattern index and landscape connectivity. As a result of this study, the optimal location of ecological mitigation measures (ecological corridor, guide fences, and alternative habitats) was different for each species, and the Pareto plan showed that a trade-off effect was presented between cost and environmental impact minimization. Then we validated through comparison between the results of the optimization model and planning mitigation in the previous report. It is also expected to increase the effectiveness of the mitigation measures with a flexible model that can be planned within a limited cost.

This work was supported by Korea Environment Industry &Technology Institute(KEITI) through "Climate Change R&D Project for New Climate Regime." , funded by Korea Ministry of Environment(MOE) (RE202201509)

 

How to cite: Kim, E., Lee, Y., Lee, D., Jung, H., Hyun, J., and Kim, S.: A decision support tool for evaluating the Ecological mitigation measures based on optimization algorithms, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4937, https://doi.org/10.5194/egusphere-egu23-4937, 2023.

X3.45
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EGU23-10698
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GM4.4
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ECS
Evaluation of the land use change influence on the hydrosedimentological connectivity in a small catchment of southern Brazilian plateau
(withdrawn)
Franciele Zanandrea, Rodrigo Biz Willig, Bruno Henrique Abatti, and Gean Paulo Michel
X3.46
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EGU23-12297
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GM4.4
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ECS
Francesco Caponi, Daniel A. S. Conde, and David F. Vetsch

Fluvial seed dispersal is a key mechanism controlling riparian vegetation dynamics along rivers. Riparian plant species produce a large number of lightweight seeds that are well adapted to be transported by wind and water over long distances both along channels and across floodplains. Water-mediated dispersal (hydrochory) is particularly sensitive on how water flows into secondary channels, low-flow velocity areas where seeds can land and eventually germinate. River-floodplain connectivity is thus a key factor to understand the spatial and temporal distribution of riparian vegetation and its modifications due to morphological changes.

Despite our general understanding of hydrochory, the specific relationship between water discharge, river morphology and seed dispersal at the reach scale remains largely unexplored. To quantify this relationship, we investigated the transport and deposition mechanisms of plant seeds in a 1 km long reach of the Moesa river, Switzerland. The reach is characterized by a relative wide gravel bed floodplain that has been activated by multiple flood events in the past years. Vegetation patches and wood debris are sparsely located across the floodplain, creating a mosaic of morphological structures. We combine field experiments with mimics and numerical modelling to understand the influence of such structures and discharge variability on plant seed dispersal.

We will show how specific river planform structures, such as confluences, riffles, pools, and log jams affect particles travel times, long-distance dispersal, and deposition patterns. We will be able to show how daily and seasonal fluctuations in the water discharge may influence these processes, considering some key seed morphological traits. Our results will be analyzed with connectivity metrics applied at the reach scale but at different temporal scales to disentangle the role of each underlying process. Overall, this study is expected to aid river managers to mitigate impacts of flow discontinuities such as dams and physical barriers on riparian vegetation dynamics and design better e-flows regulations favoring plant biodiversity and ecosystem resilience in the face of climate change.

How to cite: Caponi, F., Conde, D. A. S., and Vetsch, D. F.: Investigating transport and deposition of plant seeds in an alpine braided floodplain, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12297, https://doi.org/10.5194/egusphere-egu23-12297, 2023.

X3.47
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EGU23-13468
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GM4.4
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ECS
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Toni Himmelstoss, Sarah Betz-Nutz, Jakob Rom, Moritz Altmann, Fabian Fleischer, Florian Haas, Michael Becht, and Tobias Heckmann

Sediment connectivity is defined as the potential of a catchment to route material through itself. It is a system property that regulates the propagation of geomorphic changes through a catchment and is therefore a factor of its sensitivity to climatic change. In well-connected catchments, changes are effectively propagated; where the coupling of hillslopes to channels, or between channel reaches is poor, changes may remain localised. Structural connectivity itself is not a static property; it can be affected by process-response feedbacks, gradual or rapid changes, for example as a consequence of extreme events. In this study, we use a multi-method approach to investigate changes in structural sediment connectivity over time periods of up to 70 years in three alpine catchments.

First, we calculate the Index of Connectivity (IC) and corresponding change maps to identify areas and time periods with major changes in structural connectivity.  The required multitemporal digital elevation models (DEMs) are computed with historical aerial images and Structure-from-Motion Photogrammetry, more recent DEMs are obtained from ALS surveys. The channel networks as targets are manually mapped using the DEMs and orthomosaics.

The second approach for selected areas makes use of multitemporal geomorphological maps, digital elevation models and graph theory. The geomorphological maps were produced based on historical orthomosaics, DEM derivatives and DEMs of Difference. The landforms in the geomorphological maps form the nodes of a graph, and edges connecting the nodes along the direction of flow represent potential or actual sediment transfer between them. The graphs reflect the system structure for a certain point in time; graph metrics can be used to assess the structural connectivity including spatial differences and temporal changes.  

How to cite: Himmelstoss, T., Betz-Nutz, S., Rom, J., Altmann, M., Fleischer, F., Haas, F., Becht, M., and Heckmann, T.: Multidecadal changes of structural sediment connectivity in alpine catchments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13468, https://doi.org/10.5194/egusphere-egu23-13468, 2023.

X3.48
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EGU23-15046
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GM4.4
Joris de Vente, Carolina Boix-Fayos, Pedro Pérez-Cutillas, Antonio Jodar-Abellan, and Joris Eekhout

Previous research suggests that channels have a significant contribution to the total sediment balance in large catchments. Channels are also very sensitive to changes in land use and management, with implications for channel morphodynamics and the quantity of sediments and nutrients flowing through the system. Here we present a new channel module for the coupled hydrology-soil erosion model SPHY, with the aim to quantify the contribution of hillslope and channel erosional processes to the total sediment balance in large catchments. SPHY simulates all relevant hydrological and soil erosion processes, including infiltration excess surface runoff and soil detachment by raindrop impact and runoff. We developed a novel channel module that simulates river hydraulics and morphodynamics in the channel network, while accounting for sedimentation in reservoirs and check dams. The channel module requires channel characteristics as input, including channel width, channel depth and bed material. The model was applied to a Mediterranean catchment (316 km2) in Southeast Spain, where channel characteristics were obtained from a combination of field measurements and GIS analyses. The model was calibrated using observed discharge, hillslope erosion and check dam sedimentation. Model validation focused on how channel morphodynamics changed in response to reforestation and check dam construction in the period 1956-2001. The model successfully simulates the observed changes in channel morphology, including an overall increase of channel morphodynamics and channel incision downstream of the check dams. Subsequently, the model was applied in a climate change impact assessment, to show how the sediment balance is projected to change under future climate conditions, characterized by an increase of extreme precipitation. The climate change simulations show that rill erosion is projected to increase, while channel erosion decreases. However, channel erosion still remains the main contribution to the total sediment yield in the catchment, which highlights the importance of accounting for channel morphological processes in large-scale erosion assessments.

 

We acknowledge funding from the Spanish Ministry of Science and Innovation (AEI) (PID2019-109381RB-I00/AEI/10.13039/501100011033).

How to cite: de Vente, J., Boix-Fayos, C., Pérez-Cutillas, P., Jodar-Abellan, A., and Eekhout, J.: Assessing the hillslope-channel contributions to the catchment sediment balance under climate change, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15046, https://doi.org/10.5194/egusphere-egu23-15046, 2023.

X3.49
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EGU23-1733
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GM4.4
Unraveling the effects of geomorphic restrictions on sediment connectivity in a debris flow small watershed
(withdrawn)
Peng Zhao, Daojie Wang, Songtang He, and Zengli Pei

Posters virtual: Tue, 25 Apr, 14:00–15:45 | vHall SSP/GM

Chairpersons: Laura Turnbull-Lloyd, Anthony Parsons, Ronald Pöppl
vSG.4
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EGU23-1205
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GM4.4
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ECS
Joanna Piasecka-Rodak and Jolanta Święchowicz

The construction of reservoirs and associated river regulation, on the one hand, positively affects human quality of life and related economic considerations (i.e. construction of drinking water reservoirs, storage of water for farmland irrigation purposes, flood prevention measures), but on the other hand constitutes a major form of interference in the environment by generating irreversible changes in its functioning. One key impact of reservoir construction is the severance of natural connectivity in the river channel upstream of the dam. This leads to a disruption in the dynamic equilibrium of the river due to the accumulation of sediment upstream of the reservoir’s dam, limited sediment outflow from the reservoir, and increased downcutting downstream of the dam. The main aim of the present study is to examine the impact of a midsize reservoir and dam located along an upstream part of a mountain river and associated river engineering structures on the Wapienica River on (dis)connectivity in terms of sediment transfer.

The Wapienica river catchment area has an area of 51.36 km2 and is located in southern Poland (Śląskie Province). It has a longitudinal shape and runs from south to north across three geographic mesoregions – Beskid Śląski Mountains, Śląskie Foothills, Upper Vistula Valley. Each mesoregion is characterized by different relief, land use, and climate, all of which help determine a different rate of change of erosional processes in each of the studied regions.  The construction plan for the Wapienica Reservoir was created in 1911 in response to growing drought conditions in the region and increasing water usage by textile plants operating in the region. The reservoir was to  perform three distinct functions – water storage, flood control, and creation of a key source of drinking water for area residents. Construction work on the reservoir was completed in 1932.

Archived materials and maps, orthophotomaps  as well as a digital elevation model (DEM) with a resolution of one meter were examined in the study along with survey data on suspended sediment accumulation sites along the river. In addition, the Connectivity Index tool in ArcMap software was used, as well as the Soil and Water Assessment Tool (SWAT).

The internal structure of the studied catchment has changed due to strong human impact in the form of reservoir construction in the upstream part of the catchment and regulation in the river channel of the Wapienica along its entire length. This has made it possible to identify six zones characterized by different degrees of structural and functional connectivity.

How to cite: Piasecka-Rodak, J. and Święchowicz, J.: Wapienica dam as a contributing factor in (dis)connectivity associated with sediment transfer in mountain river catchment (Poland), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1205, https://doi.org/10.5194/egusphere-egu23-1205, 2023.

vSG.5
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EGU23-9885
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GM4.4
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ECS
Emanuel Martínez-Urgilés, Andrea Urgilez-Clavijo, and David Rivas-Tabares

Multifunctional margins are strips of land naturally growed or planted vegetation, usually found on the margins of agricultural or natural plots such as the banks of rivers and streams. The study of priority areas where this agro-environmental practice can improve agricultural processes and biological connectivity. In the Andean region, constant urban expansion is affecting the peri-urban landscape, causing its fragmentation and degradation. Andean peri-urban expansion areas face frequent dilemmas between territorial management of urban land use and environmental measures for landscape conservation. Current measures should motivate the updating of existing legislation to include biophysical aspects of interaction at the landscape scale. However, this remains a pending task for local authorities to avoid landscape degradation and its functionality with various environmental factors (i.e. hydrology, soils, climate, etc.). This study aims to develop a methodological framework to assess the multifunctionality of the margins in a peri-urban Andean watershed, its connectivity and priority areas to guide the implementation of sustainable agro-environmental measures. The study site is the sub-basin of the Tarqui River, which is located southwest of the city of Cuenca, Ecuador in South America is of great strategic importance for the environmental services it provides, especially in the provision and regulation of water for the city. As a result, the theoretical framework for the indexed cartographic products was developed for the establishment of conservation programs of three agri-environmental measures, i) forest islands, ii) riparian corridors and iii) living fences. This includes a biotic study of vegetation, its functionality and fauna relationships. Besides, the suitability and success in the midterm for their maintenance are because of the soil properties and water availability. These were considered to support the decision to prioritise linear elements programmes.

Acknowledgements

The authors acknowledge the support of Master in Climate Change, Agriculture and Sustainable Rural Development (MACCARD), co-funded by the Erasmus + Programme of the European Union.

References

  • Urgilez-Clavijo, A., Rivas-Tabares, D. A., Martín-Sotoca, J. J., & Tarquis Alfonso, A. M. (2021). Local Fractal Connections to Characterize the Spatial Processes of Deforestation in the Ecuadorian Amazon. Entropy, 23(6), 748.
  • Rivas-Tabares, D. A., Saa-Requejo, A., Martín-Sotoca, J. J., & Tarquis, A. M. (2021). Multiscaling NDVI Series Analysis of Rainfed Cereal in Central Spain. Remote Sensing, 13(4), 568.

How to cite: Martínez-Urgilés, E., Urgilez-Clavijo, A., and Rivas-Tabares, D.: Spatial indicators of multifunctional margins in the Andean peri-urban landscape. A case study of Tarqui basin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9885, https://doi.org/10.5194/egusphere-egu23-9885, 2023.