Evaluation of Hogback Diversion Canal Fish Weir on Adult and Larval Fish
The diversion of river water for irrigation or power-generating purposes is well known to have deleterious effects on fish populations. Fish either become entrained into water diversion intakes or become impinged on intake screens. Fishes with drifting early life history phases (i.e., young-of-year) are very likely to become entrained into water diversions as they are passively transported downstream with the current. Highly mobile fish species (juvenile and adults) are also quite likely to become entrained into water diversions, often as a result of their seasonal movements throughout the river channel.
The Hogback Diversion Canal on the San Juan River diverts up to 250 CFS of water from April to November for irrigation. This diversion is a major source of fish entrainment in the San Juan River (Renfro et al. 2006). In 2007 a Value Engineering (VE) Team was commissioned to develop and evaluate various proposals to modify Hogback Diversion Canal to continue to deliver water, yet eliminate or drastically reduce the entrainment of fish in the canal (Good et al. 2007). Several concepts were discussed by this team including traditional screening, electric barriers, and infiltration galleries. The team met several times and finally concluded that the most cost-effective and efficient means of reducing fish entrainment in the canal was to construct a 550 foot weir, approximately 8 feet tall, at an oblique angle in the canal, with the goal of passing a few inches of water over the top of the weir that would be diverted into the canal. Fish and debris would be moved past the wall/weir and through automated gates into a return channel back to the river. The weir was constructed in 2013 at a cost of $3.5 million, but to date no evaluation has taken place. We propose to evaluate the efficacy of this new innovative design and its ability to reduce entrainment of fish in the Hogback Canal.
Need and Benefit
Concerns for Colorado River endangered fishes (Colorado pikeminnow, razorback sucker, bonytail [Gila elegans], and humpback chub [Gila cypha]) have long been recognized by resource managers in the Colorado River Basin. Construction of fish screens are the recommended alternative for several Environment Assessments addressing this problem within the Basin (U.S. Bureau of Reclamation 2003), although there are many problems that arise with the use
of screens. Recent information suggests that the Green River Canal near Green River, UT on the Green River is a significant source of fish entrainment, and it is proposed that a similar weir be developed for that canal. Likewise, the concept is being discussed for other canals throughout the Colorado River Basin, although little is known about the
effectiveness of the weir. The scope and magnitude of this problem has also been recognized in California where policies have been
implemented to help minimize the mortality of fishes caused by water diversions. The California Department of Game and Fish has adopted a statewide fish screening policy for the purpose of excluding salmon, steelhead, and federally (ESA) listed species from irrigation diversions. The installation of fish screens is now mandated for any new or modified diversions and for all diversions within the critical habitat boundaries of federally listed species.
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