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<br />001162 <br /> <br />,.;-.,.... <br />'/)~';1 <br /> <br />25 <br /> <br />Multi-step solutions <br /> <br />It is often convenient to develop a solution to a defined network by solving the out-of-kilter <br />algorithm multiple times. . In between 'the intermediate steps arcs can be forced to be held constant or <br />"frozen" and/or ranks of arcs can be changed prior to the next step. When the network is resolved in <br />the second step, a new solution is found but the conditions specified after the first solution are <br />maintained. A common use of this technique is the accounting of reservoir deliveries to contract users. <br />Multi.step models arc also used to more easily implement complex ranking schemes of basin water rights <br />such as subordinations and exchanges. <br /> <br />Representation of Inflows in the Model <br /> <br />Inflow arcs represent the net monthly accretions (or, in some cases, depletions) in various <br />reaches of the Yampa River system. In the headwaters areas, inflows generally represent virgin flows. <br />Lower down in the basin they represent net reach gains or losses computed by mass balance techniques <br />from gage flow records. In both the headwaters and mainstem areas some flow records were <br />reconstructed using statistical methods in order to support these mass balance calculations. In reaches <br />having diversions, the calculated reach gain or (ass reflects the net effect, as evidenced in the gage <br />records at the upper and lower ends of the reac~, of diversions and return flows in that reach. <br /> <br />Included in the model are 15 inflows which represent return flows from municipal, industrial or <br />irrigation diversions. Monthly values of these inflows are not set in the input data file but instead are <br />internally calculated in an iterative process based on the amount of water delivered toa given demand. <br />For municipal and industrial demands, return inflows generally occur in the same time period as the <br />diversion. For agricultural demands, a portion of the returns occur in the same period while additional <br />returns occur in a lagged fashion several time periods later. Return flows from snowmaking in the <br />Steamboat area are lagged to reflect the spring melt and runoff. <br /> <br />Table 4-3 describes the inflows shown on the model diagram (Figurc 4.2). Actual inflow files <br />comprise monthly values for the entire 19:;0-82 study period. Some inflows have been lumped together; <br />this was done because of the difficulty associated with disaggrcgating gains in certain river reaches <br />where there are insufficient gage records. <br /> <br />Representation of Demands in the Model <br /> <br />Existing and future demands in the Yampa River Basin were defined in Task 2 of this study and a <br />detailed discussion of demand location and derivation can be found in the Task 2 Technical <br />Memorandum. This section describes the correspondence between demands projected in Task 2 and <br />demands represented in the Yahtpa Basin model. This section will be limited to a description of which <br />demands have been modeled, how demands have been disaggregated into monthly values and where <br />. each demand is spatially located in the model. <br /> <br />Modeled demands fall into three categories corresponding to one of three possible demand <br />levels: 1) year 1989 maximum conditions, 2) year 2015 near.term conditions, and j) year 2040 long term <br />conditions. <br /> <br /> <br />Demand level 1 represents demands imposed to deplete historical hydrology to a level reflecting <br />maximum potential Welter use ,in the basin under 1989 conditions of development. . These demands have <br />a water right priority within the existing subordination agreement. <br /> <br />..j <br />