Hydraulics of Bottom Rack Intake

Bottom racks are a standard hydraulic structure used as intakes in mountainous regions, to divert water to turbines, and to retain sediment and other solid matter larger than rack spacing. These racks are also used for fish ways, and to retain floating matter. The present project was directed to explore the hydraulics of bottom rack intakes, without considering any solids in the fluid. Based on extended laboratory observations, the effect of various parameters were explored, such as the bottom slope, the rack geometry, and the rack porosity. In addition, a novel approach to determine the discharge coefficient of a rack structure was developed. Finally, the intake channel below the bottom rack was investigated and several interesting features were found, including a significant flow instability that may have a strongly adverse effect on the rack performance. Guidelines for successful rack designs are given, and the results of the present study may be readily applied. ©2003 American Society of Civil Engineers