Author(s): G. K. Jacoub; W. Hu; B. Westrich
Linked Author(s): Bernhard Westrich, Wentong Hu
Keywords: Contaminated sediments; Numerical modelling; River reservoir; Depth profile
Abstract: Deposited contaminated sediments in river reservoirs very often show highly non-uniform depth concentration profiles due to temporal variation of sediments, contaminants and flow regimes. The contaminated sediments have long term negative environmental and ecological influence on the river system especially when they are remobilized by high flow regimes such as floods. The governing processes of multi-layer sediment deposition are sedimentation, erosion and mixing. Mixing occurs if sedimentation and erosion take place simultaneously. If sedimentation and erosion rates are almost balanced, mixing becomes more important and dominates the river bed contaminant concentration and the depth profiles. Mixing of fine contaminated sediments takes places in a very thin layer on the top of the deposited sediment layer. The thickness of this layer is a key parameter which is difficult to determine due to lack of data. However, this paper focuses on the mixing layer thickness and presents an application of 1D and 2D numerical modelling to estimate a range of the mixing layer thickness and its influence on the deposited contaminant concentration for a reach of 11 km of the River Neckar, Germany, where the deposited sediments were contaminated with Cadmium. The 1D and 2D modelling show a very good agreement in terms of flow, sedimentation/erosion rate and consequently the total volume of eroded and deposited sediments for an applied hydrograph in the whole domain. Based on this agreement, contaminant transport simulations are performed and a suitable range of this thickness of 0. 001-0. 01 m is found reasonable for the area of investigation.
Year: 2007