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Arkansas River Water Needs Assessment - Section 1. Executive Summary ranging from 300 cfs to 500 cfs. The riparian community is dormant during this time, and very little boating occurs. Since 1990, BOR has typically transferred water from the upper reser- voirs to Pueblo Reservoir during this time period. These releases have seldom created a situation in which reservoir releases caused total flows to exceed 500 cfs. Winter releases have also made it possible to meet flow targets for supporting fishery values after April 15 because a significant volume of water has already been transported to Pueblo Reservoir. Snowmelt Runoff Period (typically April 15- July 15) - Higher flows experienced during this period are not optimal for the fish population or for angling, but spring runoff is an uncontrolled, natural function of rivers. Resource managers recognize that there must be a window to pass significant quantities of water. Conversely, the annual runoff periods usually provide flows that satisfY needs for recreational boating. The vari- ability of the annual high flow events also provides river channel maintenance, habitat maintenance, and habirat creation functions that are critical for riparian and wildlife values. BOR attempts to avoid Project water releases during this time because the channel below Twin Lakes Dam has a limited capacity that is usually already filled with runoff water. End of Snowmelt Runoff (typically July 15) to Labor Day - During this period, there is a signifi- cant difference in flow needs to support fish popu- lations and recreational values. The fish popula- tion prefers flows from 300 to 500 cfs. Rafters prefer flows of 1,500 to 2,000 cfs, while kayakers prefer flows of 1,300 to 1,500 cfs. Float fishermen prefer flows of 900 to 1,200 cfs, spin fishermen prefer flows of 700 ro 1,200 cfs, and fly fishermen prefer flows of 400 to 500 cfs. If the annual flow management program were not in place, BOR would not release water during this period to avoid unnecessarily storing water in Pueblo Reservoir. Water unnecessarily stored in Pueblo Reservoir increases the risk of spilling winter water, slighdy increases the evaporation loss of Project water, and may advetsely impact flatwater recreation at the upper reservoirs. Labor Day-October 31 - Resource needs are similar during this period. Fish population and angling needs are well-supported by flows from 300 to 500 cfs, as is the riparian zone at the end of its growing season. While boating use would be betrer supported by flows of at least 1,000 cfs, the demand for such use declines sharply after Labor Day weekend. If the annual flow manage- ment program were not in place, BOR would not make water releases during this period for the same reasons cited in the discussion for the July 15 to Labor Day period. Comparison of Natural Resource Flow Preferences to Baseline Arkansas River Flows When evaluating the effect of various flows on natural resource values, it is important to under- stand how well baseline Arkansas River flows have supported natural resource values. During some periods of the year, baseline Arkansas River flows are substantially different than the preferred flows for many resource values. To facilitate a compar- ison between baseline Arkansas River flows and resource needs, the following hydro graphs were developed to illustrate flows during the 1982 to 1994 period, when the Ftyingpan-Arkansas Project was in full operation. Please note that flows released to fulfill the objectives of the annual flow management program have been subtracted from these hydrographs whenever a separate accounting of these releases was recorded. This means that summer flow augmentation releases have been subtracted out of the hydrographs,rwhile releases during fall, winter, and spring under the annual flow management program have not been subtracted out of the hydrographs. 1-12 - Water Needed to Protect or Promote Critical Resource Values