Abstract
Abstract. Suspended sediment load in rivers is highly uncertain because sediment production and transport at catchment scale are strongly variable in space and time, and they are affected by catchment hydrology, topography, and land cover. Among the main sources of this variability are the spatially distributed nature of overland flow as an erosion driver and of surface erodibility given by soil type and vegetation cover distribution. Temporal variability mainly results from the time sequence of rainfall intensity during storms and snowmelt leading to soil saturation and overland flow. We present a new spatially distributed soil erosion and suspended sediment transport module integrated into the computationally efficient physically based hydrological model TOPKAPI-ETH, with which we investigate the effects of the two erosion drivers – precipitation and surface erodibility – on catchment sediment fluxes in a typical pre-Alpine mesoscale catchment. By conducting a series of numerical experiments, we quantify the impact of spatial variability in the two key erosion drivers on erosion–deposition patterns, sediment delivery ratio, and catchment sediment yields. Main findings are that the spatial variability in erosion drivers affects sediment yield by (i) increasing sediment production due to a spatially variable precipitation, while decreasing it due to a spatially variable surface erodibility, (ii) favouring the clustering of sediment source areas in space by surface runoff generation, and (iii) decreasing their connectivity to the river network by magnifying sediment buffers. The results highlight the importance of resolving spatial gradients controlling hydrology and sediment processes when modelling sediment dynamics at the mesoscale, in order to capture the key effects of sediment sources, buffers, and hillslope hydrological pathways in determining the sediment signal.
Highlights
Fine sediment produced in catchments by upland erosion and transported by rivers as suspended load is an important part of the global sediment budget (e.g. Peucker-Ehrenbrink, 2009) and an important driver of water quality and aquatic biota in rivers (e.g. Bilotta and Brazier, 2008)
For a comparison between the suspended sediment concentrations (SSCs)–Q scatter generated by the different scenarios of erosion drivers, the reader is referred to Figs
We presented a new spatially distributed soil erosion and suspended sediment transport module integrated into the computationally efficient physically based hydrological model
Summary
Fine sediment produced in catchments by upland erosion and transported by rivers as suspended load is an important part of the global sediment budget (e.g. Peucker-Ehrenbrink, 2009) and an important driver of water quality and aquatic biota in rivers (e.g. Bilotta and Brazier, 2008). Fine sediment produced in catchments by upland erosion and transported by rivers as suspended load is an important part of the global sediment budget (e.g. Peucker-Ehrenbrink, 2009) and an important driver of water quality and aquatic biota in rivers Human activity strongly interacts with the natural processes of suspended sediment production and transport, on the one hand by practices that enhance soil erosion, like agriculture, mining, and deforestation, and on the other hand with the construction of sediment retention structures such as dams The combined effect of enhanced soil erosion and sediment retention by dams modifies the river sediment equilibrium and can result in river incision in the case of sediment starvation, contributing to the undermining of the stability of bridges and other infrastructures and leading to coastal erosion (Kondolf, 1997; Chen and Zong, 1998; Schmidt and Wilcock, 2008). Battista et al.: Modelling impacts of spatially variable erosion drivers on suspended sediment dynamics
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