Appendix 6. Pool -type fishway with V-shaped overfalls– studies at the Delft Hydraulics and Agricultural University, Netherlands
Pool-type fishways with V-shaped overfalls have been applied throughout the Netherlands, especially in small steep rivers. Design discharges have ranged from 0.35 to 5.50 m3/s. In order to optimize the hydraulic design of the pool-type fishway with V-shaped overfalls, in the late 1980’s the Dutch Ministry of Agriculture and Fisheries requested Delft Hydraulics to undertake model studies, which were carried out in close co-operation with the Agricultural University Wageningen.
The design studied consisted of a series of pools, separated by overfalls at equal distances, L. Each of the overfalls consists of sheetpiling covered by a pattern which forms a crest. From a frontview the overfall is V-shaped with tan(α/2)=7 (Fig. A6.1). The bottom of the pools are at a depth of P below the deepest point of the overfallcrest at the end of the pool with Pmin being 0.40 m. The drop, Δt, between adjacent pools is 0.2 to 0.3 meters in most cases. The overfalls extend from bank to bank, or at least have a width of half the river width.
The aim of the studies was to define the optimal dimensions for the pools (mainly the pool length L) when the design discharge for the prototype in a river is 2 m3/s, with a river width of 10 meters. In optimization, the number of pools was to be minimized in order to reduce construction costs. The studies were carried out in a hydraulic model with a scale of 1:5. The following dimensions were used:
Pool length L 4.50 m ≤ L ≤9.00 m
Pool drop Δt 0.15 m ≤ Δ t 0.35 m
Pool depth P 0.40 m and 0.80 m
V-shape tan(α/2) 5 and 7
The following measurements were performed:
Discharges by electromagnetic flowmeter,
Water levels by pointgauges,
Flow velocities by electromagnetic sensors,
Stream patterns visually and by photographs, and
Length of energy dissipation visually and by velocity profiles.
The results of the studies are presented in Boiten 1989, 1990a, and 1990b
Reports and papers
Boiten W (1989) De V-vormige vistrap. Optimalisatie van het hydraulisch ontwerp (The V-shaped pool fishway, optimization of the hydraulic design), Report Q930 Delft Hydraulics, December. 24 p. + app. In Dutch.
Boiten W (1990a). Afvoerrelatie V-vormige vistrap (Discharge relation V-shaped pool fishways, optimization of the hydraulic design), Agricultural University Wageningen, July. 36 p. in Dutch.
Boiten W (1990b) Hydraulic design of the pool-type fishway with v-shaped overfalls. Proc. Int. Symposium on Fishways "90 in Gifu, Japan, October 8-10. p. 483-490.