A New Approach to Improving Sediment Transport Modeling in River Reservoirs wth Non-cohesive Fine Sediment

A general obstacle to the implementation of both physical and numerical investigations with sediment transport are incomplete to poor data. Important information for calibration and validation of the models used is lacking, especially when modelling single flood events. Most of the time, these are data that reflect changes in selected parameters over time such as flow depths at several points in the investigated area, velocity distributions and especially the development of the river bed elevation. However, only presence of these data allows for a precise comparison with the calculations carried out and the underlying assumptions.

The authors present a comparative study for the improved mapping of dynamic sediment transport processes in river reservoirs with mainly non-cohesive fine sediments using morphodynamic software. The measurement data used are generated in large-scale physical laboratory tests with lightweight bed material and then numerically calculated 1:1, which means that the results of the physical and numerical investigations can be directly compared with each other and no uncertainty arises from similarity assumptions.

In order to generate the measurement data, idealized river reservoirs are built in a physical laboratory canal with a width of up to 8 and a length of up to 60 meters and operated dynamically with various flood waves with a maximum discharge of 750 l/s. By means of a contactless method for measuring the bed elevation using laser scanning, accurate and reliable measurements of the bed level changes can be carried out during ongoing test operation and provide information of the reservoir bed during a flood. At the same time, an optical measurement method ensures continuous monitoring of sediment transport in the reservoir and velocity profiles are recorded multiple times during a flood wave. In addition to insights into sediment transport processes and their effects on flood discharge, adapted strategies for the operation of reservoirs are also investigated.

The results of the physical investigations serve as input and control parameters for calculations with morphodynamic software, which are normally used for similar questions either alone or with mostly incomplete data. The TELEMAC SISYPHE and Hydrotec HYDRO_FT-2D software are used mainly. Due to the precise data from the laboratory tests, the quality of the numerical calculations can be evaluated systematically and the sensitivity of individual transport-relevant parameters can be checked for the simulation results. Here, there is great development potential for the transport modeling of non-cohesive bed material.