Reservoirsʹ siltation measurments and sediment transport assessment in the Czech Republic, the Vrchlice catchment study

Sediment transport from agricultural land into rivers and reservoirs is a problem within the Czech Republic. This problem was highly accelerated almost 50 years ago during the communist period. At that time strong collectivization was undertaken leading to destruction of traditional landscape patterns, surface outflow, erosion processes intensification and surface water quality deterioration. Thirteen years after political changes erosion problems remain. Department of Irrigation, Drainage and Landscape Engineering at the CTU Prague there has been continuous research undertaken in the field of erosion and sediment transport assessment. There are several modelling tools available for this purpose. One of them—USLE (Universal Soil Loss Equation) is commonly used in the Czech Republic for many years at a plot-scale but modern GIS (geographical information systems) tools in computer science allow using it at larger scales. Very important is the validation of this model for two-dimensional topography and GIS routines. Moreover USLE produces only local erosion amount values and has to be completed by another tool to get sediment amounts. For this purpose SDR (sediment delivery ratio) is usually used, applying a lumped approach—total erosion of every watershed is reduced by SDR and by pond’s trapping efficiency. Another available approach is using the Watem/SEDEM model that puts together RUSLE (Revised USLE) and a distributive approach to sediment transport modelling. This has already been used for estimating sediment amount in several catchments of the Czech Republic, but has to be validated as well. Dept. of Drainage, Irrigation and Landscape Engineering there are datasets of sediment amount from different reservoirs available and other reservoirs are to be measured soon. As the dataset of various watersheds is expanded, a methodology for sediment amount measurements is needed. The main objective of this paper is to propose a simple methodology to measure the sediment amount within reservoirs as well as to present a review of available methods. The application of the methodology at Vrchlice Catchments (97 km2) case study is presented. Total sediment amounts between 125 000∼140 000 m3 were measured in Vrchlice reservoir and values of 110 976 m3 (using USLE), resp. 105833 m3 (using Watem/SEDEM) were predicted by the erosion models. For catchments of this scale it is a sufficient validation.