Experimental investigation of flow through different arrangements of synthetic grasses in Canoe-fishway channel

Background and objectives: Dams and diversion dams are structures that prevent of fish migration to upstream. Fishways provide access of fishes to their favorite habitat. Canoe_fishway channel is considered friendly environment because of having maximum compliance with it in many countries. In this fishway, synthetic vegetation grasses are used for energy dissipation, opposite of other usual fishways. In fact synthetic grasses are organized of vertical elements that play role of vegetation stems. In addition to creating a safe environment for fish passage, small boats can pass on it easily, because of having proper stems bend radius. Brushes are placed with different arrangements in the Canoe_fishway channel. Each of the arrangements has different effects on amount of dissipation. The main object of the research is experimental investigation of arrangements effect on water depth in the basins and velocity in the slot fish inlet. Also in terms of hydraulic condition is introduced the best arrangement.
Materials and methods: Tests were done in a channel with length of 12 meters and width of 0.5 meters, with four arrangements of brushes that were designed with the number of fixed elements. For making of brushes, polyethylene pipes are used with the diameter of 6mm and 20cm length that placed on PVC plates with the thickness of 16 mm. by considering each arrangement, brushes were placed on the bed of the channel. Depth of Flow in the center of basins was measured by depth gauge and velocity in the slot fish inlet was measured by flowmeter in 1cm distances from the bed upto water surface. Also by dimensional analysis be determined effective dimensionless parameters on roughness coefficient (n).
Results: Results show that submergence depth (y/h) has the most effect on roughness coefficient (n) in comparison with other parameters. By increasing the submergence depth (y/h), the Manning coefficient (n) increases and it decreases when submerged completely. The maximum coefficient (n) occurs at the base of submerging. In non-submerged condition in comparison with submerged condition, increase rate of roughness coefficient (n) is for, first arrangement 18%, second arrangement 5%, third arrangement 6% and forth arrangement 20%. This research shows process of velocity diagram (V) is increasing from the bed upto water surface. The velocity range is between 0.6_0.7 m/s. The velocity profile shows increasing process upto height of grasses is very slow. But in higher depth is so fast. Also the process of discharge_depth curve is always increasing that it increases with more slope in non-submerged conditions than submerged condition. According to dimensionless discharge (Q*) are found that roughness coefficient (n) range has difference in constant experimental condition for different arrangements. Roughness coefficient (n) increases 90% for forth arrangement.
Conclusions: According to the obtained results of this study, brushes are effective in roughness coefficient. In this research forth arrangement creates more roughness coefficient, because of having the most overlapping against water flow. So this arrangement in the canoe_fishway provide safe place for fishes, as well as canoes.