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Daily river losses were developed on a seasonal basis for each of the four river <br />reaches included in the routing tool. The seasonal variation was limited to winter <br />(October - April) and summer (May - September) periods. Loss factors were <br />evaluated for both winter and summer values for each of the water year <br />classifications. The analysis resulted in a single loss factor for winter months for each <br />classification and three loss factors for the summer months corresponding to the year <br />classification. <br />Loss factors were developed based on an empirical analysis of historic daily flows at <br />the upstream and downstream gages of each reach. Major diversions occurring in the <br />reach were added back at the downstream gage and major returns were subtracted <br />from the downstream gage to remove these influences from the hydrologic record. <br />For reaches and periods that appeared to be gaining, the baseflow portion of flow was <br />estimated using a straight line method and subtracted from the downstream gage. This <br />estimation of a naturalized flow was constructed for each reach for the period of 1947 <br />through 2006 if data were available. <br />Using these naturalized flows, a downstream flow was estimated based on the <br />upstream flow and compared graphically with the naturalized flow. This technique <br />was applied to several isolated events in the hydrologic record. Isolated events were <br />utilized for two reasons: 1) by evaluating a single event, the influence of other <br />unknown events or operations is minimized; 2) a single large event provides an <br />estimate similar to that resulting from a pulse flow such as the intent of this study. <br />Because no two events will result in the same loss estimate, the empirical values were <br />derived by inspection of the hydrograph and combined into a single representative <br />value for each year classification and season. For the summer months the estimated <br />loss factors vary based on year classification. In the case of winter months, little <br />variability was seen across year classification, and therefore a single winter loss <br />factor is used. Table 3-6 entitled, "Daily Loss Factor Estimates" summarizes the loss <br />terms by season and water year classification. <br />BOViLE Page 19 of 58 January 29, 2008 <br />PRRIP - Draft Water Management Study, Phase I