386 fish hatchery management 



Table D-1. relation between head and discharge for cippoletti and rec- 

 tangular WEIRS, discharge VALUES ASSUME A 1-FOOT-LONG WEIR CREST; FOR 

 SHORTER OR LONGER CRESTS, MULTIPLY THESE VALUES BY THE ACTUAL LENGTH 

 IN FEET. 



(3) The weir crest, formed with a metal plate, must be leak- proof, sharp 

 or square-edged, and no thicker than ^-inch. The distance of the weir 

 crest above the bottom of the channel should be at least 2- times the water 

 head on the weir to minimize approach water velocities. 



(4) Air must have access to the underside of falling water as it flows over 

 the weir crest. Otherwise, air pressure may force water against the down- 

 stream face of the weir, increasing the rate of discharge above the flow 

 rates indicated in Table D-1. 



(5) The channel above the weir must be straight, level, and clean to 

 ensure smooth water flow. Sediment and debris should not be allowed to 

 collect on or behind the weir. 



