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is releases from off-stream storage for municipal or irrigation purposes. Data for diversions to <br />storage are usually available because they are administered as part of the river. Measurements of <br />off-channel reservoir releases are typically an owner's decision that are not administered and <br />therefore often go unrecorded. Therefore, the total water supply for a given structure may not be <br />known because the diversion records do not reflect the water supplied by an off-channel <br />reservoir. In addition, coding of the types of water diverted by a given structure, such as <br />reservoir water or water taken by exchange, has not been consistent over the years. Finally, there <br />also exist situations that are so complex that they cannot be described adequately with existing <br />diversion coding. <br />3.3.3 Additional Data Required <br />For water resources planning, a complete record of diversions for the study period of record is <br />needed for major structures in Division 1 and Water District 47. The explicit modeling of the <br />major structures comprising 75 to 85 percent of the total diversion in the basin and aggregating <br />minor diversions spatially has been adequate for modeling 100 percent of a basin's consumptive <br />use in the Colorado and Rio Grande River basin DSS models. Because of the relatively greater <br />competition for water from some of the tributaries to the South Platte River (e.g., Clear Creek <br />and South Boulder Creek), it may be necessary to explicitly model more than 75 to 85 percent of <br />total diversions in these tributaries. However, explicitly modeling 75 to 85 percent overall in the <br />South Platte basin will be adequate for SPDSS purposes. <br />Major diversion structures with average diversions greater than 2,000 acre-feet/year representing <br />approximately 85 percent of the diversions in the basin as calculated from the data shown in <br />Table B-2, will be explicitly modeled. It is anticipated that the remaining diversion structures <br />with average annual diversions between 0 and 2,000 acre-feet per year, including structures <br />reporting infrequent diversion data, will not be explicitly incorporated into the surface water <br />planning tool. Rather, these structures will be combined into "aggregate" structures for <br />modeling purposes. Therefore, it is not necessary to estimate the missing diversions at these <br />smaller diversion structures. <br />The data collection effort for the diversion data should concentrate on identifying the major <br />diversion structures in the basin with missing data and developing estimates for the missing <br />records at these key structures. Table B-2 shows 319 diversion with average annual diversions <br />greater than 2,000 acre-feet/year. Approximately 25 percent of these diversion structures have <br />some missing diversion records based on the information in Table B-2, spot inspection of the <br />diversion records, experience from working in the South Platte River basin and past experience <br />from the CRDSS and RGDSS. Diversion records will therefore need to be filled for <br />approximately 80 major diversion structures with average annual diversions greater than 2,000 <br />acre-feet/year (see Table 3-1). <br />p:data\gen\spdss~final report\chapter 3.doc 3-9 <br />October 31, 2001 <br />