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<br />):~. 000626 <br />.h'" <br /> <br />\l\l2c'd\ <br /> <br />[- ;$0-'1' \" <br /> <br />CROSS <br />TASK MEMORANDUM 1.15-29 <br />PHASE /I <br /> <br />Scsnario Simulation - Instream Flow Rights <br /> <br />1.0 ISSUE <br /> <br />Fish and Wildlife biologists have asked the State of Colorado to consider granting instream flow <br />appropriations for several river reaches to promote recovery of threatened and endangered fish <br />species under the Endangered Species Recovery Program, The additional flow would help provide <br />a more natural annual hydrograph for these endangered species. On the average, more water <br />originates in the Colorado River basin within Colorado than the State is entitled to use under the <br />apportionments made in the 1922 Colorado River Compact and the 1 948 Upper Colorado River <br />Basin Compact. Moreover, Colorado has not developed the use of all of the water it is entitled to <br />under the compacts. A number of questions arise, including: (a) What magnitude of instream flow <br />can be accommodated without impacting the rights of existing water users? (b) When and how <br />much water is available at a point in a basin for instream flow appropriation? (c) What are the <br />impacts of instream flow rights on the development of new projects in the basin? and others, <br />Similar considerations apply for establishment of reserved water rights either by federal interests <br />or by Indian tribes, <br /> <br />The purpose of this Task Memorandum is to describe and document the use of the Gunnison River <br />prototype Water Rights Planning Model (WRPM) to simulate a scenario involving a key water right <br />planning issue in the basin, For this task, an example is developed to demonstrate how a <br />hypothetical instream flow requirement for endangered species can be added to an existing <br />MODSIM network and how the impacts of this appropriation on existing water rights can be <br />evaluated, <br /> <br />2,0 DISCUSSION <br /> <br />The instream flow demand is added to an existing MODSIM network by creating a new demand <br />node and connecting it to the network at the desired location, The attributes of the instream flow <br />demand, including the monthly hydrograph of flow demand (cfs or acre-feet/month), the priority <br />date and the associated "flow through node" and "bypass credit link" are defined in the MODSIM <br />spreadsheets. The bypass credit link is that link which is monitored by the instream flow demand <br />to determine how much water is already flowing through the stream reach and how much <br />additional water must be called for by the demand to the satisfy the requirement. The procedures <br />for creating the new demand node and specifying the attributes of the instream flow requirement <br />are described in the on-line documentation. <br /> <br />Two scenarios involving instream flow rights in the Gunnison River basin have been considered, <br />as described below, <br /> <br />2.1 Instream Flow at Redlands Power Canal <br /> <br />The first scenario is for imposition of a new instream flow right for the Gunnison River for the river <br />reach just downstream of the diversion dam for the Redlands Power Canal. For purposes of this <br />demonstration, the demand is assumed to be at a year round flow rate of 300 cfs (approximately <br /> <br />A276 01-27-96 <br /> <br />1 <br /> <br />1. 16-29 Fosh., Ritsch <br />