Free Access for Riverine Fish along the Dutch Rhine, Hydraulics and Construction of a Fishway

摘要

Till 1985 migration of riverine fish for instance salmon and sea trout through the river Rhine system has dramatically declined due to the tremendous decrease of water quality and the construction of river regulation works such as weirs and dams and hydropower stations. During the last decades the water quality in the Rhine and therefore the environmental circumstances for migratory fish has improved significantly. At the same time on international level a discussion was started on the feasibility of restoring fish migration. In 1987 all countries along the river Rhine adopted the Rhine Action Programme. One of the aims of this plan is to restore the main stream as the backbone of the complex Rhine ecosystem and its main tributaries as habitats for migratory fish. The construction of fishways at the three weirs in the river Neder -Rhine is the major Dutch activity in restoring the migration route in the Rhine. Accurate investigations of the behaviour of different fish species and the required migration circumstances, resulted in a design of spacious pool — and weir fishways as bypass channels in the floodplain. To enable migration of different migratory fish species during the various discharge situations of the river the channels have V — shaped weirs with vertical slots. The design and construction of a fishway is not easy. Knowledge of the behaviour of migratory fish, the required hydraulic circumstances, water management, engineering and construction are very necessary and important. Only a multidisciplinary team can succeed. All these aspects will be discussed in the paper.