8211 - Laserfiche WebLink

Home Browse Search

CHAPTER II - PROPOSED ACTION AND ALTERNATIVES Alternatives Two basic alternatives were examined in detail and several alternatives were discarded from detailed analysis. Under the No Action alternative, the barrier caused by the GVIC Diversion Dam would continue to have a negative impact on the endangered Colorado squawfish and razorback sucker under low flow conditions. The preferred alternative would be to place large rocks (riprap) on the downstream face of the GVIC Diversion Dam. The riprap and the river channel would be arranged in a manner that simulates natural pools and riffles. This pool and riffle pathway would permit upstream fish movement. This natural passage design at GVIC, as well as the passageway structure recently completed on the Gunnison River, will be monitored and evaluated to help determine the best designs for additional passageways on the river at the Price-Stubb and the. Government Highline Diversion Dams. GVIC Fish Passage Design FLO Engineering, Inc. (1997) provided a brief history and description of the existing GVIC Diversion: "The GVIC is the oldest major irrigation project in the Grand Valley. It initially went into operation in 1883. The original headgates were destroyed by a flood in 1898 and replaced in 1901 by the current structure. The original wooden cribbing diversion structure was modified over a three year period around 1980 to incorporate a concrete cutoff wall and an additional concrete cap across its crest." "The system provides water to approximately 38,000 acres through 100 miles of canals." "To supply the system, GVIC owns 640 cubic feet per second (cfs) of irrigation water rights which are comprised of 520 cfs with a 1882 priority date and 120 cfs with a 1914 priority date." At high streamflows of approximately 12,000 cfs, the diversion dam becomes submerged and is not a barrier to fish passage. However, at lower streamflows, the diversion darn effectively blocks fish passage to upstream reaches. The preferred alternative was selected based on the behavior of the endangered fish, their swimming abilities, GVIC operation and maintenance needs, and the need to not interfere with irrigation diversions. To simulate a "natural-like" stream feature, the plan includes a 30-foot wide notch in the existing GVIC dam to allow the fish to swim upstream through the notch at flows of less than 5,000 cfs. Rocks (2-foot diameter) would be placed downstream from the diversion dam in a series of pools and riffles and on a slope designed to reduce velocities significantly to accommodate the swimming abilities of the endangered fishes. The series of 20- foot long pools with intervening riffles about 50 feet long would extend over 400 feet. The 7