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Walzbachtal, Germany

The vertical slot pass is the most common fishpass in Europe. Based on the experience of the author in designing and implementing of more than 20 vertical slot passes in Central Europe the planning process is explained. The ecological requirements, based on the fish species and the size offish, appoint the minimum pool dimensions and the maximum flow velocity. On the other hand the hydraulic conditions require certain relations between slot width, pool width and pool length. Three different flow patterns in the pools can be observed: A curved jet from slot to slot, a jet that hits strongly the opposite side wall and an oscillating jet in the centre of the pool, which is the common design aim. The hydraulic design criteria of a vertical slot pass are based primarily on investigations on fish passes for salmon with heads of 30 cm. With the new actual guidelines in Germany, Austria and Switzerland the head between two pools will be reduced in the most cases to 10 to 15 cm often accompanied by slot width of 35 to 50 cm. The common hydraulic design criteria lead to very large pools and thus huge constructions and high costs, so a review of these hydraulic design criteria is required. The main question is: Is it feasible to reduce the pool dimensions in case of reduced pool heads and reduced input of energy? Source

Gebier R.-J.,Ingenieurburo Dr. Gebier | Lehmann P.,Ingenieurburo Dr. Gebier

Since several years near-nature water courses are installed at large hydropower stations in Germany and Switzerland. They serve as fishways and as well as habitats, especially for rheophilic species. The bypassing water course at the hydropower plant Rheinfelden, on the High Rhine, is the largest fish pass facilitiy of this type. Three fishways are installed at the new run-of-river power plant, a vertical slot pass at the power house (left bank), the new bypassing river course installed in the old headrace channel (right bank) and a rock cascade pass which connect the tailwater of the weir with the river course. With a width of 50 m, a mean gradient of 0.8 % and a discharge between 10 and 35 m3/s the bypass channel has the character of a mountain river. The aim is to provide a high variety of bottom and flow structures induced by sequences of riffles, bars, pools and single gravel islands. A deeper flow path ensures fish passage. The bypass channel is connected to the weir impoundment with a gentle transition involving several braided channels. The intake structure itself is divided into two sections. The unregulated section will guarantee a constant discharge of 10 m3/s. Additional discharge up to 25 m3/s can be provided via the regulated gates in order to provide a dynamic flow regime. The downstream entrance is designed as a rock ramp with a steeper gradient (3 %), thus downstream water-level fluctuations are limited to this ramp. This prevents the impounding of potential spawning grounds in the bypass channel. A water race was integrated in the rock ramp to provide more efficient attraction flow into the tailrace. Source

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