Town of Carbondale Gateway Boating Park Hydrology Study June 2006

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replacement water for out -of- priority depletions to the Colorado River by the Frying Pan — Arkansas Project as well as water for West Slope irrigation, municipal, and industrial uses on a contractual basis. The reservoir is also operated to provide for recreation, wildlife habitat, and flood control'. Since the early 1970's streamflow in the RICD reach has be re- regulated by the winter release / spring storage pattern of Ruedi Reservoir operations. To determine the impact on RICD reach flows, two separate analyses were conducted. First, flow - exceedence curves for RICD reach were developed for a time period that predates Ruedi operations (1907 — 1966) and compared to the flow - exceedence curves that were used to determine the RICD claim. The latter include Ruedi operations (1907 — 2004). Second, Ruedi Reservoir storage content records were obtained from the U.S. Bureau of Reclamation (BOR) and analyzed. Table 6 summarizes the flow — exceedence analysis on a bi- monthly time step for the pre -Ruedi era (1907 — 1966). This table is identical to Table 3 except Table 3 covers the entire study period of 1907 — 2004, a period which incorporates Ruedi operations. To provide a better comparison between the two, Table 7 was prepared. The Table 7 values are the result of subtracting the Table 6 values from the Table 3 values. A positive value indicates that the flow in the RICD reach has increased with Ruedi operations. A negative value indicates that the flow has decreased with Ruedi operations. The table depicts a pattern of storage from approximately mid -April through mid- August and storage releases from approximately mid - August through April 15. It should be noted that values in Table 7 do not equate to the exact amounts that the flow in the RICD reach has changed due to Ruedi operations. This is because the 1907 — 2004 study period incorporates both pre -Ruedi and Ruedi operations. To gain a better understanding of the specific flow impact of Ruedi operations a review of daily reservoir operations was conducted. Daily reservoir operating data from January 1, 1974 — May 31, 2006 was obtained from the BOR. Graphs of storage and releases from storage are included in Appendix E. A pattern of fall and winter releases ranging from 50 — 200 cfs, and occasionally more, is shown. During runoff the space that was vacated in the previous fall and winter is filled, attenuating downstream flow. Fill rates are variable depending on hydrology and have exceeded 1,000 cfs in years like 1984 when peak flows were extremely high to less than 200 cfs in 2002 when it was critically dry. The flow regime of the Roaring Fork River will continue to be regulated by Ruedi Reservoir. The net effect to the RICD reach is that re- regulation increases fall, winter and spring flows while decreasing runoff period flows. The precise release and storage pattern will depend on hydrology and reservoir U.S. Bureau of Reclamation Annual Operating Plan Fryingpan- Arkansas Project Water Year 2004 Operations 16