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fl:-~"l"'7 'J' ~ ~ CHAPTER III - ALTERNATIVES AND IMPACTS The major water and rel ated land resource issues, opportunities, and needs in the Upper Platte River Basin were presented in the previous chapter. An effort was made to describe these items from a state perspective, to set a scene for "what if" questions which will provide information on possible impacts of carrying out various actions. These questions were appl ied through a hydrologic model of the Upper Pl atte drainage developed by combining several component parts. This chapter presents a brief description of the model, a more detailed description of the alternatives depicted, and a summary of the impacts which could occur if actions were implemented on these alternatives. An important part of the description process is an indication of 1 ikely flow conditions at certain points on the hydrologic system under the influence of these alternatives. It must be noted that there is no intent to assume these alternatives as all inclusive. The primary Objective was to illustrate some possible future conditions representing various levels of development. No specific future projects--be they private, state, or Federal--are being touted through this effort. In addition to depicting various levels of future development, two alternat ives were formul ated to address the issue of attempting to maintain the present riverine habitat conditions along the Pl atte River in central Nebraska through the use of surface flows. Since site specific future projects have not been included in each of the future conditions presented, water qual ity impacts from these levels of .development have not been addressed. THE UPPER PLATTE RIVER MODEL A combination of several individual modeling efforts was used to obtain an operable model of the Upper Platte drainage. Present condition flows (1977) were used in this modeling effort. Historic gains and losses have been adjusted for those reaches impacted by present levels of ground-water development. One important target of this overall effort has been to develop capability to simulate monthly streamflow conditions at specified major stream gage points identified in figure 2. A pOint flow study was made to account for waters from Guernsey, Wyoming, to Duncan, Nebraska. The Bureau of Reclamation had previously completed a point flow study for the South Platte system from Denver to Julesburg, Colorado. This was extended to North Platte, Nebraska. Published records of the Geological Survey and the State of Nebraska's Department of Water Resources were used together wi th av ail ab 1 e power generation and irrigation diversion records. All measured river flows, divers ions, and infl ()ws were identified. The results were hi storical flow records at all of the major points of diversion. Modifications to the operation study of the Narrows Unit, Colorado, were made to simulate future condi t ions for the South Pl atte River at Jul esburg, Colorado. 41