Passe migratoire favorisant la montée continue du poisson

Abstract

The conception of this fishway was made from observations of fish movements behind stones in rapids. Figure 5 shows a channel into which we have introduced two alternate obstacles (A) representing the downstream part of two boulders. If, in the (B) zones at ground level, we succeed in maintaining a well regulated flow of suitable speed (2 to 8 ft/sec for salmons) the fish will find natural conditions of progression. It will exercise only sufficient effort to penetrate into the jet (C) flowing around the obstacles. The efficiency of the design will be greatly increased if the tips of obstacles (A) are Borda mouthpieces. The fish will then penetrate the jet through the zone of separation at point (D) where the velocity is greatly reduced for a given head differential at the partition wall. This design was materialized as shown in Figure 8 and adjusted in a hydraulic laboratory to obtain a suitable velocity field at ground level as shown in Figures 9 and 10. This design was finally built on an experimental basis at the biological station of the Nabisipi river as shown in Figure 12. Although the construction was completed late in the season, 16 salmons and 40 sea trouts took the fish ladder. It was found that the fishes, starting from 10 to 12 inches trout, went up the ladder without stopping at an average rate of progress of 1.5 ft/sec. A 6 inches trout could also climb the ladder but had to stop at every partition. A computation then shows that this type of fishway allows a level differential three times as great for the same fish as those having standard orifices. The final characteristics of the fishway for salmon and trout are shown on the table given in the text. An analysis of the relative economy of this fishway was made and the results are also shown in a table in the text. For small numbers of migratory fishes the economy world be at least 38 % compare to a fishway with overflow weirs and it would be up to 48 % for bigger capacities. This fishway is particularly advantageous when there is a variable upstream and downstream level.