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Ken Nelson <br />December 20, 2011 <br />Page 2 <br />scales that are exaggerated, where elevation (vertical) dirnensiom are 10 times greater than the <br />horizontal dimensions, i.e., vertical scale is 1 "=40', horizontal scale is 1 "=400'. The canal system <br />profile, flowline presented in black represents preliminary field measurements collected by WWE's <br />engineering technicians for preliminary report basis in September 2011. Canal flowline presented in <br />red represents subsequent field data collected by MVS during December 2011 for final hydraulic <br />assessment and design confirmation, I I fie MVS data tilay be more representative of actual <br />conditions, since the measure-down at the tunnel vertical shaft was taken with personnel inside the <br />tunnel (as compared to preliminary measurement using as weighted survey tape), and since the field <br />crew included a professional land surveyor (PLS). I"lie basis of vertical datum control is apparently <br />different between WWE and MVS surveys, however, the difference in relative elevations is not <br />great enough to substantially impact tile hydraulic assessment herein. <br />The irrigation tunnel shut-down affected several other NDIC irrigation facilities including an <br />inverted siphon to the west that crosses 'Fongue Creek and Highway 65, and reaches of open ditch <br />each side of the tunnel. To provide irrigation water set-vice in the canal system west of Highway 65, <br />the NDIC purchased and diverted water from Tongue Creek. With one (1) exception, the alternative <br />Tongue Creek diversion provided a ton-timal level of service to the approximate 171 headgates <br />downstream from the tunnel. Normal flow of irrigation water from Marshall Road located upstream <br />from the tunnel's east entrance portal to the main intake off the Gunnison River above Austin <br />remained in service, and was diverted back to the Gunnison River at an existing overflow upstream <br />from the Marshall Road canal bridge. This maintained normal service to all headgates upstmarn <br />from the tunnel. Diverting Gunnison River at the intake also fully utilized decreed water rights for <br />the 2011 irrigation season. <br />Upcoming emergency repairs of the tunnel has raised other issues related to a) annual maintenance, <br />b) the remaining useful service life of the subject stretch of the irrigation system, c) potential <br />impacts of open channel flow on water quality, and d) efficiency of open chartnel flow. The canal <br />system was constructed during the early 1900'5 using construction materials and technology <br />available at that time. The composite system has since required seasonal maintenance and repairs at <br />increasing .frequency and urgency, but has been sul jeci to very few major upgrades to improve <br />management and maintenance. <br />Evaluation Metliodology <br />Hydraulic analysis begins at the doiwnstrcain limit of an approximate 2-mile stretch of the canal <br />system and proceeds upgradient, Although this is opposite of the direction of flow, it is consistent <br />with system hydraulics that are downstream controlled; ix., existing flow conditions and any <br />modifications or improvements made downstream will impact the flow regime upstream, This <br />sequence of discussion is not intended to iniplyart order of` priority for needed iniprovenients, nora <br />sequence for construction while the system is not in service between agricultural seasons. <br />The sul�ject segment of the canal system flows in a westerly direction north of die Gunnison River. <br />The downstream limit is approximately 1/3 mile west of Highway 65, and the upstream limit is about <br />13/4 miles east ol' the highway. Since only three (3) headgates are serviced along this section of the <br />