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A model-based sediment connectivity assessment for patchy agricultural catchments

Authors:
Pedro Batista at University of Augsburg
Pedro Batista
Peter Fiener at University of Augsburg
Peter Fiener
Simon Scheper at Dr. Simon Scheper - Research | Consulting | Teaching
Simon Scheper
  • Dr. Simon Scheper - Research | Consulting | Teaching
Christine Alewell at University of Basel
Christine Alewell
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Abstract

Sediment connectivity is highly influenced by landscape patchiness. In particular, linear features such as roads, ditches, and terraces, modify landscape patterns and affect sediment transport from hillslopes to surface waters. Connectivity patterns are commonly assessed by spatially-distributed models, which rely on semi-qualitative indices or numerical simulations of soil erosion and sediment transport. However, model-based connectivity assessments are hindered by the uncertainty in model structure and parameter estimation. Moreover, representing linear landscape features is often limited by the spatial resolution of the model input data. Here we demonstrate how a global sensitivity analysis of the WaTEM/SEDEM model can be used to improve our understanding of sediment connectivity in patchy agricultural catchments of the Swiss Plateau. Specifically, we explored model structural connectivity assumptions regarding road drainage and the presence of edge-of-field buffer strips, as well as the uncertainty in the input data, by means of a Monte Carlo simulation and a high resolution 2 m x 2 m DEM. Our results showed that roads are the main regulators of sediment connectivity in ameliorated Swiss landscapes. That is, our sensitivity analysis revealed that assumptions about how the road network (dis)connects sediment transport from cropland to water courses had a much higher impact on modelled sediment loads than the uncertainty in model parameters. These results illustrate how a high-density road network combined with an effective drainage system increases sediment connectivity from arable land to surface waters in Switzerland. Additionally, our approach underlines the usefulness of sensitivity and uncertainty analysis for identifying relevant processes in model-based sediment connectivity assessments.
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EGU21-562
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.
A model-based sediment connectivity assessment for patchy
agricultural catchments
Pedro Velloso Gomes Batista1, Peter Fiener2, Simon Scheper1, and Christine Alewell1
1Department of Environmental Geosciences, Universität Basel, Basel, Switzerland
2Institute for Geography, Universität Augsburg, Augsburg, Germany
Sediment connectivity is highly influenced by landscape patchiness. In particular, linear features
such as roads, ditches, and terraces, modify landscape patterns and affect sediment transport
from hillslopes to surface waters. Connectivity patterns are commonly assessed by spatially-
distributed models, which rely on semi-qualitative indices or numerical simulations of soil erosion
and sediment transport. However, model-based connectivity assessments are hindered by the
uncertainty in model structure and parameter estimation. Moreover, representing linear
landscape features is often limited by the spatial resolution of the model input data. Here we
demonstrate how a global sensitivity analysis of the WaTEM/SEDEM model can be used to improve
our understanding of sediment connectivity in patchy agricultural catchments of the Swiss Plateau.
Specifically, we explored model structural connectivity assumptions regarding road drainage and
the presence of edge-of-field buffer strips, as well as the uncertainty in the input data, by means of
a Monte Carlo simulation and a high resolution 2 m x 2 m DEM. Our results showed that roads are
the main regulators of sediment connectivity in ameliorated Swiss landscapes. That is, our
sensitivity analysis revealed that assumptions about how the road network (dis)connects sediment
transport from cropland to water courses had a much higher impact on modelled sediment loads
than the uncertainty in model parameters. These results illustrate how a high-density road
network combined with an effective drainage system increases sediment connectivity from arable
land to surface waters in Switzerland. Additionally, our approach underlines the usefulness of
sensitivity and uncertainty analysis for identifying relevant processes in model-based sediment
connectivity assessments.
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Effect of historical land use change on soil erosion in a Mediterranean catchment by integrating 137Cs measurements and WaTEM/SEDEM model
Article
Full-text available
  • Apr 2022
Soil erosion is especially severe in areas affected by intermittent heavy rainfalls after dry periods, and human practices such as deforestation. Mediterranean mountain environments underwent conversion of rangelands into croplands during the previous centuries to increase agricultural production but this process was reversed after land abandonment in the middle of the 20th century allowing the natural revegetation. To understand the effect of the past practices and the current agricultural management, we have combined the strength of empirical data and spatially distributed modelling in a medium‐sized catchment representative of agroforestry landscapes of NE Spain. We developed an ensemble technique composed of 137Cs‐derived soil redistribution rates as specific point values and as grid‐based setup calibration for the WaTEM/SEDEM. Thus, we overcame the point specific limitation of the 137Cs measurement and the need for calibration of spatially distributed models that allow a spatial interpretation of soil redistribution in the catchment. We implemented an automated routine model tool to increase the calculation speed and calibrate the model thus, allowing estimates of the main model parameters for simulating a variety of temporal scenarios. With this method a good fit between modelled and measured soil redistribution rates (R2=0.82) was obtained (Nash–Sutcliffe efficiency: 0.79). Estimates were also consistent with previous apportions of sediment provenance obtained by the fingerprinting technique. An increase of 300% in sediment export was predicted for the past scenario when most of the catchment was cultivated, while a reduction of 40% occurred in the future scenario of land abandonment. A high influence of input resolution was found, wherein model efficiency was reduced when pixel‐size was increased. Our study demonstrates that spatially‐distributed models combined with 137Cs‐derived rates provide a powerful tool to understand the driving factors of erosion and delineate the hotspot areas that could suffer high erosion if submitted to certain management practices. This article is protected by copyright. All rights reserved.
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