Study On Hydraulic Characteristics Of Double Vertical Slot Fishways

The Double vertical slot fishway is a basic type of vertical slot fishways. It could provide double migration routes and effectively increase the magnitude of fish to pass through. However, relative researches are rarely reported.In this paper, three-dimensional numerical model and physical model were both adopted, and the studies focused on the hydraulic characteristics in double vertical slot fishways were conducted. The main research results are as follows:1. In the double vertical slot fishway with a bottom slope of 2%, the vertical velocity is small enough to be neglected. The flow field structure of general pools shows a typical plane feature and the velocity plane distribution at different depth sections are almost the same.2. The ratios of mainstream zones to the total area were approximately equivalent for the double vertical slot fishway with length-to-width ratio of 5:8 and a traditional single vertical slot fishway with length-to-width ratio of 10:8, the ratios are about 29%. The ratios of recirculation zones are same for the both type fishway as well, and the ratios are about 61%. However, the mainstream of the former is closer to the middle of the general pools.3. The flow field structures of general pools with different length-to-width ratios were studied. The results showed that there are three typical flow structures in the general pools. For different flow structures, the mainstream curve, the velocity attenuation curve and recirculation region size were different. The three typical flow structures correspond with three typical length to width ratio ranges (4:8-5.5:8,5.75:8-6.5:8,7:8-9:8), respectively. The flow structure with a length-to-width ratio range of 5.75:8-6.5:8 showed more reasonable.4. The position and size of central baffles affected the flow structures of general pools obviously. Both a shorter forward central baffle and a longer backward central baffle could increase the length and the defection degree of the mainstream. For the forward central baffles with a length of 0-0.075B, the flow structures are allsimilar. It’s resonable to recommend to cancel the central baffle for avoid deposit of debris or sediments.5. While the oriented angle of the rest pool has little influence effect on the area ratio of the mainstream zones and recirculation zones, but shows a significant influence on their flow structures. Decreasing the oriented angle can reduce the ratio of the recirculation zones located outside of the mainstream, and enlarge the ratio of the recirculation region between the two mainstreams. It also can enlarge the width of the mainstreams in the center of the pools. As the oriented angle varied in the range of 20°～25°, the mainstream curves in the rest pools are similar with the general pools, but the velocities along the mainstream curve are much smaller, so it can provide good conditions for the migration fish to have a break.6. The large-scale recirculation regions appeared in both 90°and 180°urning parts. The proportions of the recirculation regions to the total area are 38.8% and 50.6% respectively, and the migration fish may be trapped in these regions. By adding baffles, the flow direction can be adjusted, so that the ratio of the mainstream area will be enlarged, the ratio of the recirculation zones may be reduced, and the single large-scale of recirculation zones will be avoided, it seems to optimize the flow structer of the turning part.7. Experiment research of fish pass through the fishway has been carried out.The traces of fish motion were recorded and analyzed by using Zootracer software. Several useful conclusions have been made and provided reference resources for further research.