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4.2 Diversions <br />Diversions are described in the Yampa Model by five files: <br />4.2.1 Direct Diversion Station File <br />4.2.2 Return Flow Delay File <br />4.2.3 Historical Diversion File <br />4.2.4 Direct Diversion Demand File <br />4.2.5 Direct Diversion Right File <br />4.2.1 Direct Diversion Station File - yampaT.dds <br />The file yampaT.dds describes the physical properties of each diversion simulated in the Yampa <br />Model. As described in Table 4.1.1a, 279 diversion structures were modeled. Table 4.2.1a presents <br />the structures that were modeled, their capacity, area served, average annual system efficiency, and <br />average annual demand. Structures with zero or -999 acres, zero efficiency, or 100 percent efficiency <br />represent municipal, industrial, and/or transbasin diversions. <br />Six-digit structure IDs are included in the direct diversion station file. The six-digit ID is a <br />combination of water district number and structure ID obtained from the Division of Water <br />Resources' (DWR's) structure and water rights tabulations. Aggregated irrigation structures were <br />given the identifiers "ADY xxx ", for Aggregated Diversion Yampa; the "xxx" ranged from 001 to <br />027. Similarly, aggregated municipal and industrial structures were named "AMY xxx" for <br />Aggregated Municipal Yampa. The Wyoming diversion nodes were given custom identifiers <br />990528, 990533, 990534, and 990535, having no particular significance except that they are clearly <br />different from identifiers drawn from the DWR database. <br />System efficiencies describe the percentage of diverted water that is consumed. The portion of the <br />diversion that is not consumed returns to the stream system and is available for subsequent diversion. <br />Efficiencies were estimated for different structure types as follows: <br />• For explicitly modeled irrigation structures, a constant efficiency was determined for each month <br />of the year based on the ratio of average historical monthly diversions and the estimated farm <br />irrigation requirement. <br />• For aggregated irrigation diversions, including the Wyoming irrigation structures, monthly <br />efficiencies were assigned to be the basinwide average acreage- weighted efficiency of explicitly <br />model structures. <br />• For explicitly modeled M &I diversions a constant efficiency was adopted based on use and <br />engineering judgment. <br />• For aggregated M &I diversions, efficiency was set to 100 percent because demands were <br />modeled as depletions. <br />• Transmountain diversions were given an efficiency of 100 percent because the water leaves the <br />basin. <br />Return flow locations specify where return flows will re -enter the stream system. Table 4.2.1b <br />presents the return flow locations and patterns for each modeled structure. The delay patterns are <br />described in more detail in Section 4.2.2. <br />Diversions 4 -7 <br />