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Last modified
7/14/2009 5:02:31 PM
Creation date
5/20/2009 10:10:47 AM
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UCREFRP
UCREFRP Catalog Number
7848
Author
Burdick, B. D.
Title
Minimum Flow Recommendation For Passage Of Colorado Squawfish And Razorback Sucker In The 2.3-Mile Reach Of The Lower Gunnison River
USFW Year
1997.
USFW - Doc Type
Redlands Diversion Dam To The Colorado River Confluence.
Copyright Material
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Modde and Wick (1996) hypothesize that the shape of a natural hydrograph <br />(both magnitude and duration of high flows) benefits the spawning success, <br />growth, survival, and recruitment of razorback sucker. Furthermore, they add <br />that spawning migrations of razorback sucker seem to be influenced both by rising <br />discharge and temperature. Timing of spring flows seems to be an important cue <br />to spawning, and the magnitude of flows may influence post-spawning razorback <br />sucker movement. Additionally, the habitats provided by high flows provide <br />important post-spawning habitat for larval and adult razorback sucker. High <br />flows and the duration of flows which maintain connectivity of the river and <br />floodplain are, thus, important attributes in defining quality and quantity of <br />spring habitat for adult razorback sucker. <br />Osmundson et al. (1995) believed that a flow regime that eliminates the <br />transition period placed native fish at risk because of the negative effects it <br />may have on aquatic organisms long adapted to a naturally shaped hydrograph with <br />daily and diurnal fluctuations. Abrupt decreases in flow might negatively effect <br />Colorado squawfish spawning, which typically occurs in July, and strand benthic <br />invertebrates and disrupt riverine food webs (Stanford 1994). For the Gunnison <br />River, flows during June should gradually decline to provide a transition period <br />between the spring high in late-May and base flow beginning in late-June to mid- <br />July. <br />The general shape of the hydrograph for years with similar precipitation <br />was determined. Total annual discharge recorded at the USGS gaging station at <br />Whitewater was used as the criterion for establishing low- and moderate-water <br />years (Appendix; Table H.2.). Usually by 1 April, snowpack and moisture content <br />data are available for water managers to determine whether it will be a high, <br />medium, or low-water year. For high and most moderate years, streamflows in the <br />2.3-mile reach should not be of concern. On the other hand, in low-water years, <br />the hydrograph could be used as a guide to water managers for apportioning flows <br />during summer low-flow periods. <br />The hydrographs for five low- (1972, 1977, 1981, 1989, and 1990) and five <br />moderate water years (1969, 1973, 1975, 1982, 1992) in the Gunnison River <br />drainage are given in Figures 8 and 9, respectively. The lowest water year from <br />the low- (1990) and moderate- (1992) groups was graphed and compared to the <br />Aspinall water development time period, 1967-1994. Four of the lowest water <br />years (1931, 1934, 1935, and 1937) from the pre-water development period were <br />also analyzed to compare the shape of the hydrograph with low-water years during <br />the post-Aspinall water period. Because this study was concerned with low flows <br />during the summer months following runoff, six months were used in the analyses, <br />May through October. <br />For flows to be biologically beneficial, flow recommendations should be <br />made for the shortest time step possible. Technical and institutional <br />constraints make it impractical to administer flows on a daily or even weekly <br />basis. BR hydrology personnel indicated that flows recommended by 10-day steps <br />could be reasonably administered and practically implemented from Federal dams <br />in the Gunnison River drainage during low-flow periods (Personal communication, <br />Coll Stanton). Therefore, daily flows from each of the five years from the post- <br />Aspinall and four from the pre-water development period were averaged by 10- and <br />11-day time steps. <br />30
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