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<br />Attachement A <br />Hydrologic Data - Typical San Juan River Basin Hydrographs <br /> <br />The Bureau of Reclamation has prepared a Draft Environmental Impact Statement (DEIS) for the <br />purpose of operating Navajo Dam to implement Endangered Species Act (ESA) related flow <br />recommendations on the San Juan River. This attachment describes hydrologic data associated <br />with the project. <br /> <br />The following graphs depict typical wet, average and dry year conditions for the San Juan River <br />at Archuleta, Farmington and Four Comers, and the Animas River at Farmington comparing the <br />flows resulting from implementation of the Preferred Alternative (250/5000) to the No Action . <br />Alternative. The graphs were developed from model simulations of the system for the two <br />conditions. In each case, two years were chosen to represent each of the conditions. The two <br />dry years were selected from the lowest 10 percent of the years, the average years were selected <br />from the middle 10 percent of the years, and the wet years from the wettest 10 percent. The <br />model simulations represent hydrologic conditions from the 1929-1993 water year period. <br /> <br />The San Juan River at Archuleta graphs demonstrate how operating Navajo Dam to implement <br />flow recommendations will alter releases patterns. In dry conditions. spring peak releases would <br />probably not be required, and the minimum release of250 cfs might not be adequate to support <br />target base flows in the recovery reach of the river. Under average conditions, lower release can <br />be expected during the non-spring release period. During spring release times, releases would be <br />substantially larger than under the No Action alternative. In wet years, releases needed to <br />evacuate flood storage space will be attempted to be made during the spring release period. <br /> <br />Graphs of the Animas River at Farmington show the impacts of the modified Animas-La Plata <br />Project. <br /> <br />. <br /> <br />Graphs of the San Juan River at Farmington and Four Comers generally show that flows will be <br />higher during the spring peak release and lower the remainder of the time. <br /> <br />Three graphs show a frequency distribution of monthly Navajo Reservoir releases for each <br />alternative. Releases are sorted by month and ranked in ascending order. <br /> <br />Also shown are the end-of-month contents and water surface elevations of Navajo Reservoir for <br />each alternative. A frequency distribution of end-of-month contents is shown in one graph and <br />the three remaining time series graphs depict end-of-month water surface elevations with each <br />alternative compared against the historical elevations. <br />