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Institut für Wasser- und Umweltsystemmodellierung - IWS



"Automating River Rehabilitation Measure Design Considering Ecological and Economic Constraints "

An automated design method has been developed in order to assess the cost effectiveness of various small-scale instream (< 1000m) river remediation measures. The methodology consists of coupling a steady-state, two-dimensional flow model with a fuzzy logic based fish habitat model to construction cost estimates of computer generated remediation measures. The goal is to create a process whereby the user can define improvements to the fish habitat of a given life stage (i.e. juvenile or adult) against estimated construction costs. The method allows engineers to focus on exploring the tradeoffs between remediation costs and their benefits, while the program is left to the tedious task of augmenting the mesh to simulate different design options. In order to assess the effects of possible mitigation measures, the program automatically modifies the bed morphology of the two-dimensional hydraulic model to include evenly-spaced macroroughness elements with identical dimensions onto the mesh, and the hydraulics and fish habitat model are rerun.

In this paper, a single type of rehabilitation measure is considered. Macroroughness elements (small groynes) are constructed at specific locations along the river bank, and are used to improve habitat heterogeneity, especially in rivers subject to rapidly fluctuating flow regimes downstream of hydropower operations. An investigation reach is investigated in order to determine the base habitat suitability for the juvenile brown trout (Salmo trutta) considering the minimum flow. Based on the size and number of elements, an estimate of the mitigation measure cost is calculated. The mitigation costs of various configurations are then compared to the predicted improvement in the base habitat suitability. Finally, a cost-impact curve relating the change in habitat suitability to the construction cost is constructed.

Keywords: Hydraulic Structures, Rapid Prototyping, River Restoration, Fish Habitat Model