The influence of both process descriptions and runoff patterns on predictions from a spatially distributed soil erosion model

Abstract

Spatially distributed, process-based erosion models have been built to predict both erosion and deposition rates and patterns. However, predictions by these models often do not meet our expectations. There are several possible reasons for this, which can be subdivided into three groups: (i) process descriptions within the models may be incomplete or incorrect, leading to structural errors (model error); (ii) parameterization is difficult leading to a high degree of uncertainty regarding model inputs (input error); and (iii) the spatial implementation of the model (the spatial discretization and the routing methods used) may be inadequate. Hitherto, most studies of erosion model performance have focused on input parameter uncertainty: the effects of process description and spatial implementation of the model have often been neglected. In this study an attempt is made to compare some aspects of the effects of process description, parameter uncertainty and model implementation on model performance. A series of model runs was carried out to evaluate to what extent the predictions of the spatially distributed erosion model LISEM are affected by the description of the hydraulic resistance, the parameter values used to characterize hydraulic resistance as well as the routing algorithm used to generate the runoff pattern.The process description used for overland flow resistance and velocity has a clear effect on the erosion and deposition rates predicted by the model. However, relatively minor variations in a single parameter value (hydraulic roughness) appear to affect model output more strongly than variations in the process description itself. The use of different routing algorithms leads to notably different erosion and deposition patterns, but total erosion and deposition rates are much less affected.

Regional scale modeling of hillslope sediment delivery: A case study in the Barasona Reservoir watershed (Spain) using WATEM/SEDEM

“…It seems clear that, for getting reliable estimation of spatial erosion and sediment transport patterns a spatially distributed validation is required, as it has been suggested by some authors (Takken et al 1999(Takken et al , 2005Vigiak 2006). …”

“…These and other applications suggest that WATEM/SEDEM is a valid tool for assessing spatial patterns of erosion and sediment flux on the landscape. However, some questions of the model's appliction still arise, such as the need for a spatially distributed calibration (Takken et al, 1999(Takken et al, , 2005Vigiak, 2006) or the importance of processes not included in the model (de Vente et al, 2008).…”

Modelización espacialmente distribuida de la erosión y el transporte de sedimento en cuencas de montaña del Pirineo aragonés: retos para la calibración y validación

“…La calibración de los parámetros de capacidad de transporte es un aspecto fundamental de WATEM/SEDEM que todavía no ha sido resuelto. Los resultados aquí obtenidos confirman que para obtener una estimación más fiable de la distribución espacial de los procesos de erosión y sedimentación se requiere una calibración y una validación con datos espacialmente distribuidos, tal y como ya ha sido sugerido por otros autores (Takken et al 1999(Takken et al , 2005Vigiak et al, 2006). En el caso de la cuenca experimental de Arnás, el proceso de calibración consistió en realizar un gran número de simulaciones (n=100) para el periodo 1963-2003, modificando discretamente los valores de ktc min y ktc max .…”

Implementation of a distributed sediment model in different data availability scenarios.

“…Moreover, the measurement scale is often very different from the model scale. Some relevant examples are WEPP [Laflen et al, 1991a], EUROSEM [Morgan et al, 1998] and LISEM The conceptual or parametric approach is probably the methodology with the best perspective, although its calibrated parameters lack of physical meaning [Dickinson et al, 1986;Ferro and Minacapilli, 1995;Takken et al, 2005]. In the last 15 years, many conceptual models were developed, such as LASCAM [Viney and Sivapalan, 1999] and CASC2D-SED [Johnson et al, 2000].…”

“…The authors demonstrated that the uncertainty was higher in the UK catchments rather than the USA catchments, where the model was developed, in spite of the physical bases of WEPP, which should be valid all over the world. In literature, many other papers show the sensibility of sediment models to their parameters [Folly et al, 1999;Brazier et al, 2000;Takken et al, 2005].…”