Abstract:
Food chain and life cycle of natural fish and other aquatic species have become vulnerable due to interruption in the natural sequence of flooding and floodplain in Bangladesh. As a technical solution to this problem, fish friendly structures and fish passes have been built in different locations of Bangladesh mainly on the important fish migrations routes. Some field investigations and research works have been performed several agencies and researchers to analyze the performance of the existing fish friendly structures and fish passes. But no laboratory study with a physical model structures have been done with some selected fish species in Bangladesh.
In this research work an experimental study has been performed with a distorted physical model in the laboratory flume of DWRE, BUET by down scaling the existing prototype at Sarikandi, Bogra. The experimental arrangement consists of an adverse slope of 6% followed by a 3.4% mild slope. The model structure consists of four pools. Each of the pool was approximately 1 m long, 0.762 m wide and 0.60 m high. The width of the opening of each pool was 0.127 m. The experiments were conducted by maintaining upstream water level of 40 cm, 50 cm and 60 cm for different ranges of velocities. Velocities were in the range of 0.3 m/s to 0.8 m/s and discharges were in the range of 37 m3/hr to 145 m3/hr. Total 18 sets of experiments have been conducted for this study. For each set of experiments, three dimensional velocity data were collected at 0.4, 0.6 and 0.8 hydraulic depth by using an ADV (Acoustic Doppler Velocimeter).
The X and Y components of velocity data have been analyzed to plot the velocity vector fields and velocity contour maps to understand the flow pattern. The response of the selected fish species (Rui, Katla and Mrigel) of different sizes with respect to different hydrodynamic conditions provided has been analyzed. It has been found that though the developed hydrodynamic conditions were favourable for the juvenile size of the selected species but were quite unfavourable for the fry and fingerling size of the selected species in most of the cases. The results that have been found from this study will be very much helpful to carry out further field and laboratory studies in future.
