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? l 10 y , . limbs; 28 sets of sediment data were collected on the rising limb and 15 sets on the falling limb. The sediment samples were supplemented with measurements of water surface slope, river width, cross section profiles and velocity. Suspended sediment samples were collected at ten foot verticls with a U.S. Geological Survey (USGS) D-74 depth integrating, suspended - sediment sampler using the ETR (Equal Transit Rate) method. The Helley- Smith sampler was employed to collect unmeasured sediment zone samples near the bed. It was operated at each vertical in conjunction with the D-74 sampler. The Helley-Smith is not a sanctioned sampler by the USGS but represents the best available technology for bedload and unmeasured suspended zone sampling. Of the forty-three sets of sediment samples, forty-two Helley-Smith samples and thirty-nine sets of suspended sediment were collected. Discharge measurements were facilitated in 1983 by erecting a staff gage. A stage-discharge relationship was calibrated with 24 measure- ments over the two field seasons. The Mathers Hole cross section becomes a more effective conveyor of discharge at higher stages which results in the nonlinear stage-discharge relationship shown in Figure 5. Discharge was measured from 600 cfs to 19,000 cfs to define the relationship. Substrate analysis was accomplished with a probe. The composition was verified at low flow by observation of the exposed channel and by walking the cross section at shallow depths. Numerous photographic analyses were made with calibrated square. These photographs were evaluated with collected surface and subsurface substrate samples at several cross sections on the spawning bar (Photo 1). The velocity, depth, slope and substrate data was reduced and presented to the USFWS for input to PHABSIM computer model. All the data was prepared in standard forms and the cross section profiles were all referenced to a single point assigned the arbitrary elevation value of 100 feet, This data constitutes the subreach data base for eight of the eleven cross sections used in the water and sediment routing model. RESULTS AND DISCUSSION Yampa River Canyon Morphology The Yampa River canyon incised meanders are the dominant physical feature in the plateau topography. This unique physical environment creates a diverse biological habitat. Complex relationships exist between the aquatic species and the habitat created by the river. Response of the physical system to changes in flow regime would disturb the stable, equilibrium conditions which support the river ecosystem. The channel morphology and aquatic environment is a function of several interrelated physical features of the system including geology, climate, basin size, topography, sediment transport, and others. The following .discussion will focus on the important aspects which define the range of natural conditions and processes that exist in critical or sensitive habitat reaches of the Yampa River.