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Cover The type of cover present at each vertical was visually determined. The following <br />cover types were used: <br />No cover -- depth <0.5 ft, velocity >0.5 ft /sec in riffle; pools <1.5 ft deep, no <br />security cover <br />Instream cover — water level 1 ft deep behind objects 1 ft in width, reducing <br />velocities to <0.5 cfs, LOD (tree trunks, root wads), boulders <br />Overhead cover — within 2 ft of water surface, vegetation like shrubs above glide <br />or pool, undercutbanks, protruding banks providing a minimum of 1 ft2 of <br />cover, water min. depth 0.5 ft, velocity <0.5 cfs, and offers no velocity <br />shelter <br />Combination cover — water depth >0.5 ft, passing over fallen trees, debris dams <br />w/branches and /or root masses, overhanging banks with roots, rubble or <br />boulder piles within the stream channel; provides reduced water velocities <br />and overhead cover <br />Pool depth cover — plunge pools over debris jam, lateral scour pools in undercut <br />banks, any area of pooling >1.5 ft. deep after codes #2, 3, & 4 have been <br />measured; the remainder is then measured as pool depth cover. <br />Minimum Flows <br />Minimum flows were quantified following the R2Cross methodology. R2CROSS, which is the <br />hydraulic model used by the Colorado Water Conservation Board, is a standard setting technique <br />that uses specific hydraulic criteria for average depth, average velocity and wetted perimeter <br />based on stream size to determine the minimum flow needed to protect aquatic life. General <br />criteria for minimum flow determinations as discussed in Nehring (1979) for R2CROSS are <br />listed in Table 1. <br />Cross sections were placed in critical riffles and hydraulic parameters measured. Streambed <br />profiles were surveyed using standard differential leveling techniques. Data analysis consisted <br />of hydraulic modeling using the instream flow program RHABSIM (Thomas Payne & <br />Associates, 1998) to determine change in water depth, velocity and width as a function of change <br />in flow. Computer simulations were conducted for a range of flows from 2 to 100 cfs. <br />Minimum Flow Study, South Fork of the South Platte River — Final Report Page 6 <br />February 19, 2001 <br />