The private landowner and the FWS Partners for Fish & Wildlife Program propose to enhance approximately 72.3 acres of wetland through the construction and repair of dikes and water control structures on flood-irrigated land. Projects in the currently irrigated meadows comprise 14.3 acres of the 72.3 acres, which will be completed in the first phase of the project. Irrigation infrastructure will be enhanced to aid in spreading and backing flood-irrigation water on 14.3 acres of land within the approximately 575 acre complex of irrigated wet meadows. More specifically, 7 dikes and 8 water control structures will enhance the landowner’s ability to irrigate the land, while increasing open water in the wetlands. Incremental water control structures that allow top-down water level manipulation will provide wetland wildlife habitat benefits that are otherwise unrealized with traiditional headgates. Maximum proposed dike heights range from 2 to 5.5 feet and maxiumum water depths will range from 0 to 4.5 feet. (The 5.5 foot dike height is a low-lying section where irrigation waste water enters Millburne Canal. The intention of the project is not to create deep, permanent ponds.) While water control structures will be installed with the intention of providing flexibility in manipulating water levels in the meadows in a manner consistent with agricultural production, the landowner has agreed to maintain a some late-season waterfowl brood-rearing water when water is available.
The second phase of the project involves repairs to Cottonwood Reservoir and accounts for 58 acres of the wetland enhanced. This reservoir was constructed in 1902 and while not "natural", provides important wetland habitat that local and migratory wildlife depend on. In spring 2011, the water overtopped the reservoir dam, but the dam fortunately did not breach. Under past ownership, the original emergency spillway for the dam had been blocked and an unstable ditch is serving as the emergency spillway, although it has an insufficient hydraulic capacity to serve as such. This more recent ditch has lowered the maximum water level. In addition, the dam top has been lowered through many years of livestock trampling and wave action. These factors combine to threaten complete dam failure. Reservoir dam repairs will restore historic water storage, providing on-site habitat benefits and protecting a major water source for the irrigated meadows/wetlands to be enhanced in first phase of the project. Currently, 27 acres of the reservoir's surface acreage is < 3 feet deep when the reservoir is full, providing the preferred habitat for most waterbirds, shorebirds, and waterfowl. Because of the seasonal draw-down of the reservoir, deeper water in the spring becomes preferred shallow water in the summer and fall. If this project application is successful, the landowner has agreed to maintain a minimum reservoir pool of 20% of total reservoir capacity. At existing levels, this is 16 surface acres. The site potential exists for an increase in reservoir storage beyond what is existing, pending final engineering. If the reservoir is expanded from an existing 46 acres to approximately 58 surface acres, then approximately 23 acres would be maintained as a minimum pool. (The approximately 12 acres on land potentially inundated by raising the reservoir's water level is a primarily a mix of greasewood and salt-tolerant grasses.) Also, the infrastructure improvements planned for the meadows are expected to increase efficiency, which will further increase the water available in the reservoir for wildlife.
