3.2. Studies on pool-and-weir fishways with a V-shaped crest
Experiments on fishways with a V-shaped sharp crested weir were carried out by the author at the T. Blench Hydraulic Laboratory, University of Alberta, Canada in 1996. Studies were performed in a straight channel with several discharges and slopes, using three pool lengths and two weir heights.
A flume with transparent plexiglass walls and a bottom of aluminum was used in these experiments (Fig. 9 and 10). The flume could be set to any desired slope. The width of the flume was 560 mm and the length was about 6 000 mm. The wall height was 600 mm. Weirs were made of aluminum. The weirs had a V-shaped crest with the opening angle of 120°. The weirs were installed to be vertical at a 10 % slope to the bed. Although this causes deviation when using other slopes, its effect is considered to be negligible in the slopes studied.
Weir spacings of 1.83B. 1.22B, and 0.61B, where B is the pool width, and two weir heights P of 305 mm and 150 mm were studied. The slopes of 5%, 7%, 10%, and 12% (1:20, 1:14, 1:10, and 1:8, respectively) were applied. The studies were carried out with several discharges for each slope and structure. This arrangement can be considered an approximately 1:5 scale model of a pool-and-weir fishway with 5 feet from the bottom to the lowest point of the V-notch in the highest weir. The pool dimensions are for the ‘basic design’ (higher weir, mean pool length) were B:L:P = 1 : 1.22 : 0.68.
Discharges were measured using a magnetic flow meter, which was placed before the model. In these studies, heads and water depths at the weir were measured by a gauge. Velocities were measured by a four-hole probe that was developed at the T. Blench Hydraulic Laboratory, University of Alberta, Canada (Wu et al. 1999). Pressure heads were measured using a manometer (Fig. 11).
Flow patterns for every structure were visualized mostly with dye, and photographed. Water surface profiles were determined along the centerline for one pool for several discharges and for all slopes. Water surface profiles at one weir were also determined for each situation. Velocities were measured at one weir at several depths in the middle of the opening and vertical sections in the side area. Velocity measurements at the weir were carried out for each structure, but only for weir heights of 300 mm and for the slope of 7 %. Experiments were carried out for all the three structures with four discharges. The reason for the small number of experiments was that the procedure is so time-consuming.
