Ecological transformation of the detention basin Grimmelshausen (river Werra) The aim of the project is to restore the ecological continuity of the basin. Therefore the permanent storage should be abolished and the outlet construction will be made passable. The flood control function is intended to be maintained without restriction. In the model experiments on the detailed model, possible variations of the outlet construction are verified, including bypass and spillway. Furthermore, investigations are necessary on excavating sediments and the avoidance of log jams and deposits.