engleski

Pool fishway hydraulic analysis

Artificial barriers such as dams, weirs, drops, gates, etc. interrupt fish migration on natural watercourses. Pool fishways are one of the most commonly used structures for enabling fish to pass such an obstacle. The main principle of pool fishway consists in dividing up a channel from the headwater to the tailwater by building cross-walls to form a succession of stepped pools and riffles. The flow passes through small openings in the cross-walls, causing tailwater to raise and form pools. Pools with their low flow velocities offer fish shelter and opportunities to rest and fish encounter high flow velocities only during their passage through the walls. Pool fishway built on the small hydropower plant (SHPP) Ilovac on Kupa river is a concrete channel with constant slope from headwater to tailwater, divided in 14 pools. The difference in water level between individual pools is 0.2 m and each pool has dimension 2x2.5 m. Conditions in the fishway have been determined by field measurements using ADV instrument to measure water depth and flow velocity. Furthermore, in order to establish a tool that enables accurate determination of the hydraulic characteristics of the flow in pool fishways, a 3D numerical model has been established and calibrated using field data. In order to convert the existing fishway into a hydraulically more appropriate channel for fish migration several openings geometries have been evaluated. Using simple empirical approach each geometry was calculated in order to convey flow through adequate openings for fish migration. The geometry of the opening is rectangular and located on the bottom of the channel arranged alternately on the left or the right side of the pool and in the middle. The desired geometry of the pools was initially evaluated using 3D numerical model. Once the resulting hydraulic conditions in the fishway formed designed pools, the numerical model was verified using field conditions as a physical model in scale 1:1. Measurements confirmed the appropriateness of the proposed model which can be used for dimensioning of new pool fishways.

pool fishway, numerical model, physical model, small hydropower plant Ilovac

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