Assessing sediment connectivity on agricultural hillslopes using sediment transport modeling and network analysis

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.