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Ken Nelson <br />December 20, 2011 <br />Page 3 <br />canal system, and because there are only a few water users between this segment and the intake <br />above Austin, now conveyance through this segment closely matches decreed water rights of almost <br />50 efs. <br />Evaluation of the canal system is based on providing long -term management, reliable operation and <br />routine maintenance needed for efficient. uninterrupted, and the reliable conveyance and delivery of <br />irrigation water to agricultural and residential users. <br />Condition otExisting System <br />General, Operating Parameters. The NDIC provides irrigation water to approximately 183 hcadgates <br />during the growing season from April through October. Peak irrigation usage, generally occurs in <br />August and September, Irrigation flow is diverted from the Gunnison River above Austin, and is <br />conveyed through open ditches, several tunnels and buried conduit(s), <br />According to tile local Water Commissioner, Steve Tuck, the 2011 alternative diversion from <br />Tongue Creek was able to provide approxiixiately 25 to 30 cfs during the height of the irrigation <br />season. Although the full 50 cfs was not available to divert into the canal system for the use by a <br />majority of headgates, loss of crops was not an issue. Mr. Tuck also noted that 2011 was an <br />atypically high water year; with flow in Tongue Creek well above its more typical 2 to 3 cfs in <br />August and September, <br />Inverted Siphon. The inverted siphon was constructed as as part of the original irrigation systern <br />during the early 1900's. It is buried 48" diameter pipe at each end, and is approximately 1,700 feet <br />in length between concrete inlet and outlet structures. The majority of its length is reportedly <br />constructed of aged timber and concrete, and is aligned across private property in the shortest <br />distance between inlet and Outlet, locations. Details of construction beneath Highway 65 are <br />unknown. The inverted siphon is subject to at least 22 psi pressure at the lowest elevation beneath <br />Tongue Creek. It is estimated that the 50 cfs decreed water right flows at a velocity of about 4 fps, <br />which is adequate to maintain solid material (i.e., sediment or mud) in suspension. A headgate is <br />installed at Tongue Creek for seasonal draining. <br />The outlet structure is 18.5-feet deep at the pipe connection, and includes two (2) raised steps prior <br />to discharging to the open ditch. The inlet structure has a concrete Rowline and wing wall <br />approaches adjacent to the canal, and a drop strUCUR-C at the pipe connection that is 8.25-feet below <br />timber plank-s across the top. Inlet and outlet pipes are SUNnerged when water flows. Elevation <br />differential between tile upstream and downstream canal nowiines is 2.2- feet. The depth of flow in <br />the upstream canal provides the hydrau tic pressure gradient necessary to overcome headlosses <br />through the inverted siphon. <br />The NDIC has experienced as few ruptures of the inverted siphon across agricultural field(s) west of <br />Highway 65, These failures are reportedly easy to locate because of water rising from the ground <br />surface at the failed section. Thernethod of repair has generally been concrete, patches at isolated <br />