Laserfiche WebLink
The Yampa baseflows at Craig and Maybell consistently exhibit a spike in October. These are <br />related to the operation of an aggregated reservoir above the Craig gage, which in Phase IIIa <br />released its contents over July, August, and September, and refilled in October. Standard <br />operations for aggregated reservoirs were changed after the Yampa Phase IIIa model was <br />developed, in order to avoid these spikes. The important characteristic of these hydrographs for <br />this task is that the "Task 11.7" baseflows mimic the "Phase IIIa" baseflows. That is, use of <br />diversion estimates instead of recorded diversions did not significantly affect baseflow <br />calculations. <br />Statistical summaries of the monthly and annual baseflow values are presented in Exhibit 2. <br />Monthly and annual means, standard deviations, and ranges of values (min and max) were <br />compared. Comparisons of the sample statistics between Phase IIIa baseflows and Subtask 11.7 <br />baseflows exhibit the following general patterns: <br />• Sample means between Subtask 11.7 and Phase IIIa baseflows were maintained. Good <br />agreement during winter months is to be expected because there are virtually no diversions <br />to be estimated. Agreement during the irrigation season is within 1 percent for most gages <br />and months. <br />• No clear trends exist with regard to standard deviations of the two samples. It was expected <br />that the sample standard deviations of baseflows generated in Subtask 11.7 would be <br />consistently smaller than for the baseflows generated in Phase IIIa. The sample size maybe <br />too small to exhibit a trend. <br />• Monthly maximum values between the two samples are similar. <br />• Monthly minimum values generated in Subtask 11.7 are generally higher than those <br />generated in Phase IIIa. In the San Juan basin, this is especially true for May and June, and <br />less true later in the season. In the Yampa basin, the reverse is the case: May and June <br />minimums agree well, but late summer minimums are higher for Subtask 11.7 than for <br />Phase IIIa. <br />Negative Baseflows <br />The number of occurrences of negative baseflows, on a basinwide basis, and the magnitude of <br />the negative baseflow estimates was next investigated. Tables 7 and 8 summarize this analysis <br />for the San Juan and Yampa models, respectively. <br />Table 7 -Comparison of Negative Baseflow Occurrences in San Juan Model. <br /> Occurrences Average Value(a~ <br /> Ph IIIa Task 11.7 Ph IIIa Task 11.7 <br />9379500 San Juan River Near Bluff, Utah 1 1 -5445 -2567 <br />9372000 Mcelmo Creek Near State Line 35 44 -2909 -2683 <br />9371500 Mcelmo Creek Near Cortez, Co. 39 47 -2673 -2420 <br />9371420 Mcelmo Creek Abv Alkali Canyon 10 21 -739 -504 <br />9371400 Hartman Draw At Cortez, Co. 22 30 -525 -266 <br />9371000 Mancos River Near Towaoc, Co. 3 3 -271 -124 <br />9368500 West Mancos River Nr Mancos, Co. 24 23 -794 -786 <br />Appendix E E-84 <br />