Physical and Numerical Modelling of Pool-weir Fishway: A Case Study for Dalyan Fish Pass in Bafa Lake, Turkey

One of the main requirement in the river ecosystem is the continuity of migration of aquatic biota. But, this continuity eventually has been disrupted by the construction of too many hydraulic structures in rivers, which have different operational conditions and functions. As a result, there happened persistent negative impact on biological diversity. The similar case is valid also in Turkey. There are 382 different fresh water species in Turkey, about 1/3 of which are endemic. There are also 5 cm long adult endemic ones among these species. The upstream (spawning) migration of these endemic species may be impossible in case of pool-weir fish passes due to high bed slopes and discharges. In Turkey, the most common fish pass type is pool-weir which is similar to Portugal. In order to provide and to optimize passage of these local fish species in pool weir type fish passes, physical and numerical modelling of those structures under different hydraulic conditions are important. In this study, the hydraulic characteristic of Dalyan pool-weir fish pass, which has been in operation at the outlet of Bafa Lake in Turkey, was evaluated. The measured data in the 1:3 physical model are compared with the computed data of governing equations and of numerical model which was established by using Flow 3D. The results are evaluated under different real-time operational conditions considering the target fish species in the project area. In the physical model, the flow characteristics were tested under low and high discharge conditions. Also, the structure inlet and outlet boundary conditions effects on the flow conditions in the pools were investigated. The variations of water surface profiles through the structure and velocity distributions in the pools are presented. Moreover, vertical velocity profile in the orifice-weir region was obtained by using an acoustic correlation principle in a device of type Nivus PCM Pro, which was installed on the channel bed behind the weir. The inferences from the project will play a key role in structural modifications, which will be done to improve the continuity of migration way in existing fish passes in Turkey.