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ATTACHMENT A ".0 t'~~ ~t o~ \VI..4tJ ~ iJ'J(~ I," I} ~~:;''' (~~ OJI73't November 23, 2001 NAVAJO RESER VOIR OPERATION EIS San Juan River Navajo Dam to Animas River Low Flow Analysis - Hydrology This analysis. was done to evaluate proposed flow recommendations of the San Juan River Recovery Implementation Program. Operating criteria for Navajo Dam were developed to demonstrate how the dam might be operated to meet the flow recommendations. These suggested criteria determine the timing and size of release flows to maximize the ability of the river to meet the flow recommendations, These proposed criteria could reduce releases from Navajo Reservoir to 250 cfs for a portion of time during the non-spring runoff period when fish releases or flood control releases are not being made. This analysis will address hydrologic impacts that may affect water diverters in the San Juan River from Navajo Dam to the Animas River confluence under these low flow conditions. Impacts to the trout fishery and the riparian environment will be addressed in other sections. In a 6-day test, July 9,2001 through July 15,2001, average releases from Navajo Dam were reduce from a previous rate of approximately 500 cfs to a target minimum of approximately 250 cfs. All releases during the test were made through the Navajo Hydroelectric Plant via the Navajo Dam Main Outlet Works penstock. Release criteria for the test included flows as low as 250 cfs at Navajo Dam, provided that a minimum flow of 500 cfs was maintained in the San Juan River in the critical habitat area, During the test, nine river gaging stations were monitored, The minimum flow recorded in the recovery area was 609 cfs at Shiprock on July 15th, Daily flow data from the six gaging stations are shown in Table 1. Flow rates shown are mean daily values and are provisional data only, Figure 1 is a graph of the data in Table 1. To evaluate impacts between San Juan River USGS gage at Archuleta to the Animas River confluence, streamflow measurements were collected over a three-day period, July 10-12, The San Juan River, and canal diversions from the river, canal flow at various points along the canal and canal wasteways were measured. When necessary, flow data was collected through interviews with water users, All flow measurements, reported flow and observed or estimated flows are summarized in Table 2, Data types are Station Number, Station Name, Description, River Mile, Flow Measurements and Average of the Measured Flow, and Field P~rsonnel (who preformed measurements) and are arrayed by River, Canals, Personal Contacts and Observations, and Hammond Data Sheets, Map 1 and Map 2 show the location of measurement points, calculation points and irrigated areas. A complication of the hydrology evaluation was the occurrence of thunderstorm events during the initial two days of the test. Figure 2 compares the flows at the USGS Archuleta station. The chart for Archuleta compares the USGS IS-minute reported values vs the USGS mean daily streamflow vs two field measurements taken during the Test period, Figure 3 compares the flow