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accumulation of interstitial fine sediments in gravels, and (3) maintaining gravel looseness. There are several ecological reasons why riffle habitat should be maintained. reduce oS urvlvcd Fine sediment on and within spawning gravels ciegras@ thg 8urvivor3hip of eggs.~ ~c.ha~e to pi ke<11iollOl-,) thNJ.:!jhcc.,c thpc~ R'il.?;t"'t'j' Although there are no known Colorado sqU(f';.i'isR spawning areas in the White River, some aquatic invertebrates use open interstices in cobbles and gravel, and accumulated fine sediment can eliminate this habitat characteristic. Another purpose of high flows is to restore or enhance pool habitat by preventing the accumulation of fine sediment in pools. Deep pools provide cover and adequately cool watelj which permit survival of some species during warm)low-flow months. Another objective of including high flows as part of an in-stream flow recommendation is to maintain active channel width and topographic diversity of the channel. Ecological diversity and productivity of river channels and flood plains are directly related to the areal extent, complexity, and variety of available physical habitats. Hesse and Sheets (1993) pointed out that "we must be careful not to assume that the minimum flow necessary to move sediment is the correct flow to achieve a dynamic channel morphology." To accomplish this purpose of maintaining channel width and chmmel diversity, it is often necessary to prevent vegetation from encroaching on the active channel. This necessitates that seedlings of riparian plants be scoured at least .b ~en n ict~. yeo..r .. I:Jl M;l:Illwl . Kondolf and Wilcock (1996) suggested that the 2-1.'" flood accomplIshes thIS objective. Pa3~ .break Background -- Channel and habitat maintenance in Relation to the Geomorphic Concepts of Effective and Bankfull Discharge 2