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I I I I I I I I I I I I I I I I I I I 53 Table 11. Summary of Flow Modeling Site Characteristics and Conditions for Transport of D50 ---------------------------------------------------------------------------------------------------------------------- location D50 shear stress (N / m2) discharge (cms) (river mile) (mm) initial signif. ini tial signif . ---------------------------------------------------------------------------------------------------------------------- Palisade (184.2)* 75 37 73 350 725 * 48 525 Corn (177.3) 24 47 250 Redlands (166.0) 57 28 55 420 1100 Site (162.4) 55 27 53 575 1300 Old gauge (139.5) 50 24 49 525 1050 New gauge (134.0) 50 24 49 275 875 * indicates sites above the confluence of the Gunnison River Flows in the above range are important to fish habitat since they are responsible for both creating new channel forms and "flushing" fine sediments from the gravel bed. Gravel bars and islands increase habitat quality by providing an array of habitats for several life stages, and it is generally believed by biologists that the endangered fish prefer "clean" substrates (Osmundson and Kaeding, 1991; Tyus and Karp, 1989; Hamman, 1981). Flows greater than the threshold for motion should be important for winnowing fines from the bed because fine particles "hide" in the interstices of the framework gravels and are not removed until that framework is disrupted (Stalnaker et aI., 1989). It is likely that some winnowing of surface fines occurs at lower flows but the deeper interstices which are important for . invertebrate production and egg incubation would not be flushed. The flows which create new channel features are likely to be close to the upper end of the flow range since this is when there is significant transport of bed material.