Mitigation measures towards morphological alterations of rivers: The receiving water as part of the integrated wastewater system

Measures in the rivers, their potential to mitigate morphological alterations caused by overflow events of urban drainage structures and their cost-effectiveness have been investigated. The receiving water is seen as part of the urban wastewater system since integrated management of the system has to consider measures in the receiving water as an option for improvement of the system. In this study the measures were evaluated using the software tool REBEKA. It has been found that increase of combined sewer overflow storage volume is less cost-effective than the investigated in-stream measures. Bed paving with coarse material is an effective and cheap method to reduce erosion problems. Reduction of slope required the smallest relative changes but has to be transferred into applicable methods like ‘increase of meandering’. The effectiveness of the methods for reduction of slope as well as of the measure ‘channel widening’ strongly depends on the dimension of the erosion problem- their applicability is limited for huge impacts. Evaluation of measures in different sub systems of the wastewater system with simulation tools can reveal interesting alternatives. Measures in the receiving water can be cost-effective and enhance the ecological quality which is an important aspect in the implementation of the European Water Framework Directive