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24 APPENDIX A: PHYSICAL HABITAT STRATIFICATION PROCEDURES The following habitat stratification approach is designed to reflect the geomorphic/hydrologic variability of the Upper Colorado River drainage. These habitat evaluation methods are designed to quantify physical variables in such a manner as to provide high resolution relative to fish habitat electivity. The habitat evaluation and data recording procedures are used by both the NW Region survey personnel who concentrate largely on adult fishes collected by electrofishing and research personnel who concentrate on larval forms collected largely by seining. With minor modifications, the system will interface with procedures used by FWS (Colorado River Fisheries Project) and is computer compatible with the MANAGE database system. Figure A-1 depicts most habitat descriptors in a generalized river reach. For each sample collected at an intensive, intervening, or special site, a "primary habitat" designation is assigned. Primary habitats are designed to reflect largely riverine geomorphic variation. Within each primary habitat, a variety of "specific habitat" types exist, which reflect the variability of discharge and flow. For each primary-specific habitat pair, substrate, cover, current velocity, water temperature, depth, and area sampled are determined. Strata Definitions: I. Primarv habitat MC (Main Channel). That section of a river which carries the greatest part of the flow during all seasons. CC (Chute Channel). High gradient secondary channel with high velocity and large substrate size in the upper section typically followed by a deep pool. Lower section is usually characterized by decreased velocity and small substrate size. SC (Side Channel). A secondary channel which may carry appreciable flow and provide either low velocity or near stagnant habitat, particularly in the lower section. Gradient and velocity are low and similar to main channel. Side channels are usually depositional with substrates of small particle size. Emmergent and/or submerged macrophytes frequently abundant. TS (Tributary Stream). An inflowing permanent or ephemeral stream. ID (Irrigation Ditch). Man-made diversion from river, used chiefly for irrigation. IK (Lake). A natural lake or manmade impoundment on a permanently flowing stream. GP (Gravel Pit). Excavation for gravel mining. May be periodically or permanently connected to river. _