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Section 7 Availability of Existing Water Supplies 7.3.1 Arkansas Basin 7.3.1.1 Arkansas Basin Surface Water Supplies StateMod datasets are not available for the Arkansas Basin. There are, however, a number of USGS flow gages, with extensive periods of record, located throughout the basin. Three of these gages, shown in Figure 7-7, were used to characterize historical physically available flow in the basin. These flows are measured and reflect actual historical diversions and demands, which may or may not reflect current conditions. The period of record varies by gage, spanning the time period 1890 to 2002 (full calendar years). The selected gage locations are: ^ Arkansas River at Canon City (1890 to 2002) ^ Arkansas River at Las Animas (1940 to 2002) ^ Arkansas River at Lamar (1914 to 2002) Minimum, median, and maximum annual measured flows are summarized for each location in Figure 7-8. To better represent the effects of seasonal and year to year hydrologic variation, monthly summaries and annual time series of historical physical flows are shown in Figures 7-9 through 7-14. Median annual flows and 3-year running averages are also included on the annual time series plots. The monthly analyses highlight the fact that physical flows vary greatly with season, with the greatest amounts of water present in the spring and summer runoff months and a sharp decline in flows in the autumn and winter. The annual time series plots also show large variation with notable extended drought periods in the late 1950s, throughout the 1970s, and in the mid-1990s. Extended wet periods appear to have occurred in the 1920s and 1940s. The interpretation above is in general agreement with the CWCB Drought Study (HDR 2003), which summarized the history of drought in Colorado and identified significant drought periods in the last 100 years. The Drought Study notes that the most recent drought analyzed for years 2000 to 2003 exceeds many of the drought records established during the 20th century. A recent hydrologic analysis (SECWCD 2000) showed very little legally available flow in the basin (Figure 7-15). The analysis used hydrologic data from 1966 to 1995. Native Arkansas River flows were available for a junior water right in only 3 of the 30 years evaluated. This interpretation was confirmed during the Arkansas Basin Roundtable Technical Meetings where there was consensus that there are no reliable available water supplies for development, but that there are infrequent very wet periods where water would be available. These flows could be developed for use in a conjunctive use project where non-tributary groundwater could be used as a drought backup. The 1948 Arkansas River Compact plays a major role in the limited supply availability in the basin. The Compact apportions the waters of the Arkansas River between Colorado (60 percent) and Kansas (40 percent), as administered by the Arkansas River Compact Administration. Another factor that may affect supply availability in the basin, now or in the future, is the need and/or desire to maintain or enhance recreational and environmental flows. Environmental and recreational considerations are further developed in Sections 6 and 10 of this report. For example, a number of renowned whitewater rafting reaches are located in the basin, particularly along the Arkansas River upstream of Pueblo Reservoir. Additionally, as shown in Figure 3-8, the federally-listed Arkansas Darter is present in the Arkansas River and tributaries, and requires special attention with respect to habitat conditions. The City of Pueblo has filed for a RICD for a kayak course in the Arkansas River at the City of Pueblo, which, if approved, may impact water supply management alternatives for M&I and agricultural users. ~ $~ole'ri~ice Wo~e' $upplY Initia~ive ~~ S:\REPORT\WORD PROCESSING\REPORT\S7 11-10.04.DOC 7-13