Analysis of a detention basin impact on dike failure probabilities and flood risk for a channel-dike-floodplain system along the river Elbe, Germany

Highly concentrated asset values are often protected by dikes stretching along the river course. During extreme floods, dikes may fail due to various breach mechanisms and cause considerable damage. Therefore detention basins are often additionally installed to reduce the flood risk for downstream communities. In such situations, however, the systemic performance of dikes and spatial redistribution of inundation patterns are often unknown. Intuitively expected effects such as more probable breaches downstream due to fewer breaches upstream and consequently higher conveyance of upstream reaches lack evidential proof. With a coupled probabilistic-deterministic 1D-channel - dike breach - 2D-inundation - flood damage model chain the impact of a detention basin on losses to residential buildings and agricultural crops is investigated. We demonstrate the changes in dike performance due to systemic load and relief along the river course on the Middle Elbe, Germany considering three breach mechanisms: overtopping, piping and slope micro-instability. The reduction of overtopping failures due to the detention basin resulted in the slightly increased breach probabilities due to piping and micro-instability farther downstream. Finally, the uncertainty in hazard and damage estimations are analysed using the Monte Carlo simulation and applying several damage models. Despite high uncertainties in flood hazard and damage estimations, we conclude that the risk reduction to residential buildings downstream of the detention basin exceeds the higher losses to agricultural crops within the filled detention area. (C) 2012 Elsevier B.V. All rights reserved.