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<br />0011.48 <br /> <br />11 <br /> <br />Data Needs for Basin Model <br /> <br />The Yampa River Basin Model requires a monthly inflow data set. In most instances, monthly <br />flows are reported in the USGS gage records. For cases when only records of Iota I annual flow were <br />available, monthly distributions were derived from the seasonal flow patterns at nearby gages, <br /> <br />The Yampa River Basin Model currently has 46 disaggregated inflows. The number and <br />locations of required inflows are dependent on user specified detail of the basin representation. <br />Inflows in the Yampa model are disaggregated by specific tributaries and include return flows from <br />several of the modeled diversions. . A more detailed discussion of modeled return flows is given in <br />Section later in this memorandum: <br /> <br />Inflows were generated for every location that has been identified as a potential reservoir site. <br />Table 4-3 lists each model inflow; and where applicable, shows average annual inflow amount in acre. <br />feet (at). <br /> <br />Twenty nine of the modeled inflows represent contributions from tributaries to the Yampa <br />River or gains (or losses) not associated with a specific tributary or diversion, On the Yampa River <br />mainstem, major tributaries are represented by individual inflows. Among these are the Elk River, <br />E1khead Creek, Fortification Creek, the Williams Fork River, and the Little Snake River. These inflows are <br />based on gage records, portions of which were synthetically generated. <br /> <br />Other modeled inflows were strictly based on mass balance calculations between two gages. In <br />the model, a typical reach of the Yampa River will have an inflow representing a major tributary and also <br />have an inflow representing all other gains (or losses) within the reach, There are several instances <br /> <br />when a reach of the Yampa has historically lost water. either from diversions or seepage losses, and the <br />resulting predicted inl10w is negative. At first glance this may appear peculiar in the modeled inflow, <br />however it is consistent with our approach of using the gage hydrology to rel1ect historical demand <br />conditions. . <br /> <br />Synthesis of Missing Data <br /> <br />Many of the stream gage records in the Yampa Basin are incomplete over the study period 1930 <br />to 1982. For this reason, data had to be synthesized to fill in missing years. Missing data were generated <br />using a variety of techniques including regression analysis and unit area techniques using data from <br />nearby drainage basins. All regressions were based on total annual flows. These totals were then <br />disaggregated into monthly flows based on the average monthly distribution oi nows for the existing <br />period of record. Methods of data synthesis used for various reaches or the river ,)'stem are described <br />below. <br /> <br />Vamps River <br /> <br />Of the eight gages on the mainstem of the Yampa River only two have complete records over the <br />1930 - 1982 period. the Steamboat Springs gage and the Maybell gage. The remaining gages have <br />several years of missing data over the stu'dy period. These missing years were synthesized with <br />regression against either the Steamboat or Maybell gages. In all cases, correlation coefficients of <br />regression equations were greater than 0.90 and many were as high as 0.98 and 0.99. <br /> <br />. <br /> <br />llij;:;;~ <br />