Using WaTEM/SEDEM and HEC-HMS models for the simulation of episodic hydrological and erosion events in a small agricultural catchment

A careful analysis of rainfall-runoff events and patterns of sediment and pollution load to water bodies is crucial for the proper management of agricultural land. This study simultaneously employed the WaTEM/SEDEM long-term erosion model and the HEC-HMS episodic hydrological and erosion model to describe the runoff and sediment load evoked by extreme rainfall events in a small agricultural catchment in Czechia, using the long-term monitoring discharge and water quality episodic data. WaTEM/SEDEM helped to delineate the runoff and sediment critical source areas, subsequently incorporated into HEC-HMS. The acquired results showed that the spatial distribution of land use is a fundamental factor in the protection of watercourses from diffuse pollution sources and the transport and delivery of sediment profoundly depends on the status of crop cover on arable land near a watercourse. Integrating both models, it was shown that the tabulated Curve Number (CN) values as well as the average C-factor values had to be lowered for the majority of the modelled events to match the monitored data. A noticeable role of catchment runoff response most probably played tile drainage, which appeared to profoundly modify the episodic runoff pattern. This study showed a promising approach for the simulation of different rainfall-runoff responses of small agricultural catchments and could be applied for the delineation of areas where soil conservation measures or protective management is of high priority. The results further revealed the obvious need to revise the CN values for tile-drained catchments.