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<br />Memorandum <br /> <br />To: <br /> <br />Todd Doherty, CWCB <br /> <br />Prom: <br /> <br />Subject: <br /> <br />Erin Wilson, Leonard Rice Engineers, Inc. <br /> <br />Available Plow to Instream Plow Reaches in the North Pork of the <br />Gunnison Drainage <br /> <br />June 30, 2005 <br /> <br />Date: <br /> <br />Introduction <br /> <br />Instream flow reaches have been recommended for several tributaries to the North Pork <br />and Smith Pork of the Gunnison. Historical stream flow measurements on these <br />tributaries, or nearby tributaries, provide an estimate of physical flow through the <br />recommended instream flow reaches. However, water users in the basin have voiced <br />concerns regarding limitations to future development as a result of the instream flow <br />rights. As a first step to address these concerns, the CWCB requested that Leonard Rice <br />Engineers develop an estimate of current legally available flow for future development. <br /> <br />Approach <br /> <br />The Colorado Decision Support System (CDSS) Surface Water Planning Model of the <br />Gunnison Basin was used to estimate both physically and legally available flow in the <br />instream flow reaches. The model represents current levels of agricultural, municipal, <br />industrial, and in-channel demands and water rights. Legally available flow determined <br />by the model represents flow that could be developed based on a 2005 water right filing. <br />The differences between physically and legally available flows represent water that must <br />be bypassed to meet downstream senior demands. <br /> <br />In some cases, the requested instream flow is on a tributary not explicitly modeled in the <br />CDSS model. In these cases, the available flow was estimated by prorating downstream <br />available flows based on drainage areas. <br /> <br />Results <br /> <br />Pigures 1 through 8 show physically and legally available flow estimated by the CDSS <br />model from 1990 through 2002. Also shown on each figure is the instream flow <br />requested rate. Por all reaches, available flow during the winter months is zero, reflecting <br />the downstream senior call at the Redlands Power Canal on the main stem of the <br />Gunnison River. During the late irrigation season, end of July through September, <br />downstream senior irrigation rights on the North Pork and Smith Pork of the Gunnison <br />generally call all available flow through the instream flow reaches. <br />