Review and improvement of sedimentation development in the Krückau and its impact on the sewerage system of the city Elmshorn
The Krückau River is the central waters of the city of Elmshorn. It is of great importance for secure storm water drainage of the city, as it almost completely conveys the amount of rain water. Thus the functionality of the storm water system depends critically on the capacity of the Krückau.
The water level and the runoff of the river Krückau is influenced by the tide of the Elbe till far above Elmshorn. In the case of a storm surge of the Elbe the Krückau is shut off through a flood barrier. For extreme floods in the Krückau it is uncertain as to what extent the backwater effect will impact the urban drainage network. Due to the tidal influence, sediment is moved during flood tide from the Elbe River in the upstream direction of Elmshorn. It is unclear how much material is transported downstream during ebb tide and how much is deposited in the urban section of Elmshorn. Similarly, the exact flow conditions, which cause the movement of sediments from the source to the mouth as well in the opposite direction, are unknown.
Especially in the urban section of the Krückau a deposition trend was observed over the last years. It needs to be clarified how the rising river bed influences the drainage capacity of the Krückau and from which height an impact to the drainage of the city arises. For secure management of the sewerage network of the city of Elmshorn the questions raised should be clarified. Furthermore, the study should clarify what measures will cause a lasting improvement.
Against this background in the framework of a research and development operation, the flow conditions and sedimentation processes were analysed in detail, critical conditions for the drainage network of the town of Elmshorn and their effectiveness were detected. For this purpose, a comprehensive field monitoring program was performed to record the morphological evolution of Krückau. On the basis of the acquired system knowledge, a numerical 2-D model was built to simulate future morphodynamic developments. With the help of a newly developed long-term method for imaging morphodynamics, the effectiveness of measures and future actions can be estimated.