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<br />001257 <br /> <br />. <br /> <br />. <br /> <br />Draft Task 7 Technical Memorandum <br /> <br />The primary factors considered in development of the long-term alternatives included the <br />following: <br /> <br />. Ability to meet long-term water demands <br />. Water rights considerationS in transfer of Juniper decrees <br />. Environmental impact (on and off site) <br />. Cost of project development (capital and unit) <br /> <br />Use of the Basin Model <br /> <br />Evaluation of alternative water development projects relied heavily on the basin <br />hydrologic and water rights model. The Yampa River Basin Model was developed in Task 4 <br />of the Feasibility Study and was documented in detail in the Task 4 Technical Memorandum. <br />The basin model was an application of a general network modeling tool known as the Central <br />Resource Allocation Model (CRAM). The network structure of the model consists of <br />numerous demand and inflow points and represents various inflows, river reaches and existing <br />major storage projects. Several potential storage projects identified in Task 5 were also <br />represented in the model but were operated only in selected model scenarios. Existing minor <br />storage projects were ~ot considered explicitly in the model with the understanding that they <br />will continue to operate as they have in the past and that their historical operations were <br />adequately reflected in the gage hydrology of the basin. <br /> <br />The basin model was based on historical gage hydrology, as opposed to natural or <br />"virgin" hydrology. The use of gage hydrology in the model implies that historical water uses <br />(which are embedded in the gage record) are effectively senior to any water uses represented <br />explicitly in the model. Because historical depletions are embedded in the gage hydrology, <br />demands explicitly represented in the model were actually increments to bring these historical <br />depletions up to current or future conditions. <br /> <br />Figure 1 is a diagram illustrating the Yampa River Basin showing the larger existing and <br />potential storage projects. A network diagram of the Yampa River Basin, Figure 2, and tables <br />of demands and inflows, Tables 1 and 2, are provided for reference purposes to help the reader <br />understand the results of the model scenarios described in later sections of this memorandum. <br />There are a total of 44 demands and 54 inflows represented in the Yampa River basin model. <br /> <br />Computations in the model were driven by the priorities assigned to the various demands <br />and reservoirs in the basin. The model algorithm allocates water to arcs in order of their <br />priorities in an effort to maximize the total value of flol'{ in the basin network (computed as the <br />sum of flow times the priority over all arcs in the network). At a higher level, more <br />sophisticated kinds of operations were simulated by the manipulation of priorities on specific <br />arcs based on annual or seasonal targets or descriptors of system state; certain common types <br />of operations, e.g. reservoir evaporation and storage carryover, were automated in the CRAM <br />modeling system. The two most fundamental types of operations occurring in the model were <br />the allocation of water according to water rights priorities and the storage and release of water <br />from reservoirs. <br /> <br />Five model scenarios were defined to represent a variety of alternative future water <br />development projects in the basin. Included was a No Action (baseline) alternative designed to <br />reflect water rights administration, reservoir operations and institutional controls as they <br />currently exist. Alternatives reflected the results of the reservoir site identification and , <br />screening process of Task 3 and Task 5. <br /> <br />3 <br /> <br />,t,.. ~ <br />