Modeling hydromorphological processes in a mountainous basin using a composite mathematical model and ArcSWAT

Abstract

Hydromorphology is a matter of water and sediment. This constitutes the study of hydrological processes, as well as of the soil and streambed erosion processes imperative. This study presents two different models aiming at continuous simulations of hydromorphological processes at the basin scale. The first model is a Composite Mathematical Model (CMM), consisting of three submodels: a rainfall-runoff submodel, a soil erosion submodel and a stream sediment transport submodel. The second model is the GIS version of the Soil and Water Assessment Tool, SWAT. The application of both models results to continuous hydrographs and sediment graphs at the basin outlet. The computed stream discharge and sediment discharge values are compared with field measurements and both models are evaluated, as to their competence of simulating the hydromorphological processes in a basin. The novelty of this research primarily lies in the fact that different ways for producing continuous sediment graphs, are presented. This can be achieved at any stream segment and provides a continuous assessment of the sediment discharge. Additionally, the application of all models is performed at an hourly time step, for long periods of time. This imparts high precision and detail to the hydromorphological study of a basin at the temporal scale. Sediment discharge is a highly nonlinear physical procedure and high levels of disaggregation (subdaily to hourly time steps) incorporate a very high degree of nonlinearity, especially in flooding periods. In this respect, this research highlights the importance of calculating sediment discharge at fine time scales and offers different methodologies to achieve it. Several statistic efficiency criteria were used to evaluate the models' efficiency to simulate the aforementioned processes. As far as the evaluation of CMM is concerned, values for Nash-Sutcliffe Efficiency (NSE), determination coefficient (r2) and Percent BIAS (PBIAS) amount to 0.974, 0.985 and −10.344, respectively, for water discharge, and 0.647, 0.660 and 12.371, for sediment discharge, whilst regarding the evaluation of SWAT the corresponding values for NSE, r2 and PBIAS are 0.978, 0.981 and −5.104, for water discharge, and 0.593, 0.664 and −37.155, for sediment discharge. It is considered that the efficiency criteria provide satisfying results.