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27 Habitat Formation The formation of a variety of channel habitats, including gravel/cobble bars and substrates used by Colorado squawfish for spawning, is essential to ensure the availability of the range of habitats required by all endangered fish life stages to fulfill daily requirements (foraging, resting, spawning, avoiding predation. etc.) under various flow conditions. The number and distribution of these channel habitats can be described as channel habitat complexity, diversity, or heterogeneity, Qsmundson and Kaeding (1991) found that adult Colorado squawfish in the Grand Valley prefer river segments with a complex morphometry over those that are simple. Some important habitats. such as inundated floodplain depressions used by razorback suckers, are located outside the channel. Floodplain depressions are principally derived from abandoned main channels, side-channels. backwaters, and meander cutoffs. The creation of.complex channel habitat and the formation and eventual abandonment of channel features from which floodplain depressions are formed occur primarily during spring runoff when flows are of sufficient size and duration to cause major changes in channel morphology through significant erosion and deposition of bed and bank materials, The reduction in the magnitude, duration. and frequency of high spring flows has slowed the rate at which channel morphology changes. Consequently, the creation of complex channel habitat and floodplain depressions has slowed. The placement of riprap and other bank stabilization measures and the construction of dikes and levees impede changes in channel morphology and contribute to the slowed creation of complex channel habitat. In addition. the construction of dikes and levees reduces existing channel habitat complexity by causing channelization of the river. Dikes and levees also isolate existing floodplain depressions from the channel during high flows. The slowed creation of complex channel habitats and new floodplain depressions. the reduction of existing channel habitat complexity. and the isolation of existing floodplain depressions have acted to reduce the quantity and quality of important habitat for endangered fishes. Habitat Maintenance Backwaters. used by various life stages of endangered fish, are damaged by the deposition of fine sediments which reduces their depth and consequently their duration and frequency of inundation. Gravel and cobble substrates. used by squawfish for spawning, are affected by the infiltration of fine sediments. The establishment of vegetation on backwater sediments and on bars further