Evaluation of a Weir Designed to Reduce Entrainment of Endangered Colorado River Fish in Canals

The Hogback Diversion Canal near Shiprock, NM diverts approximately 7.08 cms^-1 of the San Juan River from May through October; this diversion can take > 50% of the river’s flow at low-flow periods and entrains a significant number of native fish. A 2.43-meter tall, 167-meter long weir was constructed in the canal with the goal of diverting fish and debris back to the river in a bypass channel.  We used PIT tag antennas to determine the effectiveness of the weir wall by evaluating movements of a total of 803 Colorado Pikeminnow (Ptychocheilus lucius) and Razorback Sucker (Xyrauchen texanus) that were stocked in the canal upstream of the weir.  We detected a total of 18 fish that were entrained in the canal, for an overall entrainment rate of 2.3%, and 143 (17.8%) that were bypassed back to the river. Over 400 (50%) fish exited the canal upstream back to the river, and 234 (29%) fish remained in the upper canal after the test was completed (i.e., were not bypassed or entrained)—we did not anticipate the high rate of either these movements.  Future plans are to test the facility under more natural conditions and to evaluate entrainment of larval fish.