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water rights administration are realistic. For this feasibility study, potential alternatives to <br />improve measurement accuracy and lower maintenance have been considered, including: <br />• Grouted rock grade control structure <br />• Sheet-pile structure <br />• Dual sheet-pile design <br />• Flow measuring structure in the primary low flow channel with improvements upstream <br />to direct low flows towards that channel <br />• Low flow diversion channel to redirect and accurately measure compact deliveries <br />• Chemical tracer methods <br />• Radar or sonar measurement methods <br />Wyoming has had some success with sheet-pile weirs in similar channels on the North Platte <br />River. Also, the DWR is currently working with the Urban Drainage and Flood Control District <br />(UDFCD) to install a rock control on the South Platte River below Henderson. Other methods, <br />including the last two listed above, are currently being investigated by the USGS as possible <br />solutions for difficult gaging locations. <br />An appropriate solution for establishing a stable rating control is dependent on local site <br />conditions and the application of available technologies to the site. A Conceptual Design <br />Investigation (CDI) could be performed to fully evaluate alternative solutions. Given the <br />importance of the Julesburg gage in administering the Compact, the CDI would focus on that <br />site, though recommendations will be developed for solutions at all three gaging locations. The <br />CDI would include the following tasks: <br />• Identify and evaluate historic channel and floodplain migration to characterize channel <br />stability using available satellite or topographic mapping, aerial photo analysis, and field <br />reconnaissance surveys of the Julesburg location <br />• Define extent of current and historic channel morphology <br />• Identify gaging technologies that are currently available or are under development <br />• Investigate opportunities for utilizing (and modifying as necessary) existing diversion <br />structures to continuously monitor streamflow <br />• Evaluate potential effect of gaging technologies on hydraulic characteristics of the <br />existing flow regime (e.g., forcing alluvial flow to the surface by impeding groundwater <br />flow) <br />• Develop cost estimates for implementing existing candidate technologies <br />• Evaluate institutional issues (location of site potentially in NE, water rights implications, <br />etc.) <br />• Develop a technically feasible and legally and financially implementable solution <br />CDI recommendations could range from building a grouted rock control structure across the <br />entire channel at one, two, or all three gage locations, to modifications of existing diversion <br />p:data\gen\spdss~final report\chapter 3.doc 3-S <br />October 31, 2001 <br />