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Section E.6 <br />TO: File <br />FROM: David M. Frick and Dana Moore <br />SUBJECT: Subtask 11.5 Characterize Streamflow Data <br />Introduction <br />This memorandum describes the results of Subtask 11.5 Characterize Streamflow Data. The <br />objective of this task was as follows: <br />Identify the wetness condition of each month of strean~ow record ft•om 1909- <br />1996 fo~° up to three indicator gages in each of the CRDSS Wafer Resources <br />Planning l~lodels. Establish standard cutoff criterion to define average, wet, and <br />dry conditions, based on distributions of the data and engineering judgment. <br />Approach and Results <br />Gage Selection <br />Indicator gages were identified for each of the five CRDSS Water Resources Planning Models <br />(basins) according to three basic criteria: (1) length and level of completeness of the period of <br />record, (2) good spatial representation of differing hydrologic conditions from the tops to the <br />bottoms of the basins, and (3) degree of influence of upstream water resource development such <br />as reservoir operation, transbasin diversions, and consumptive use. <br />The final selection of indicator gages for each basin is shown in Exhibit 1. Gage locations are <br />shown in Exhibit 2. Three gages were selected for the Yampa Basin, representing the upper, <br />middle, and lower portions of the basin. Only one gage in the White Basin contained a <br />significant period of record. It is located near the mid to upper portion of the basin. Four gages <br />were selected for the Colorado River Basin, one each for the lower and middle portions of the <br />basin, and two for the upper portions of the basin. Three indicator gages were chosen to <br />represent the lower, middle, and upper portions of the Guruiison Basin. Finally, six gages were <br />chosen to represent the San Juan and Dolores Basins. Two of these gages will represent the <br />Dolores Basin, and four will represent the San Juan Basin. <br />Cutoff Criteria Used by Other Agencies <br />Once indicator gages were selected, cutoff criteria for establishing wet, dry, and average <br />characterizations were evaluated. Criteria used by other agencies were investigated. Nolan <br />Doeskin, Assistant Mate Climatologist, and Randy Peterson, from the U.S. Bureau of <br />Appendix E E-68 <br />