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ti .? r f 9 4) Determine the range of discharges required to preserve the morphological conditions that have been observed or projected to have existed during the 1981-1983 squawfish spawning periods. Additionally, a physical model study was conducted to define the phenomena of sand transport over cobble substrate. This flume investigation. was also designed to calibrate the Helley-Smith sampler. This entire investigation was conducted concurrently with the NPS hydraulic and sediment transport study whose overall objective was to quantify a minimum streamflow hydrograph, based on an understanding of hydraulic and sediment transport phenomena, that will preserve and maintain, on an annual basis, a range of natural conditions and processes vital to the biological system of the Yampa River in Dinosaur National Monument. METHODS Field Data Collection Program At river mile 16.5, eight cross sections were established for hydraulic data collection. Similarly, five cross sections were selected at a second site, RM 18.5. Water surface slope, velocity, depth and substrate data were collected at both sites. One set of data at each cross section was obtained in April, three additional sets were taken in July and August at RM 16.5. At RM 18.5, the cross sections were monitored three times during the recessional limb, just one or two days prior to the measurements at RM 16.5. This data was reduced and prepared for input to the PHABSIM habitat simulated computer model. Cross section profiles were plotted with a sonar depth chart recorder. These profiles were monitored at ten foot stations across the channel width and were calibrated by surveying the end points. Water surface slopes and cross section reference points were surveyed. The slope was determined by surveying the distance between the cross sections on each bank and recording the water surface elevation. The slopes were also measured, at other incidental sites, several river widths upstream and downstream. Velocity was measured with the Price current meter or the Price pygmy meter in all facets of the project. The average velocity for each ten foot cell was taken at the 0.6 depth below the water surface. Several vertical velocity distributions were plotted to check the reliability of 0.6 depth measurement. In several instances velocity measurements were taken at 0.2 and 0.8 depth interval to improve the accuracy of the measurements. Sediment discharge measurements were collected at the Mathers Hole site. These measurements constitute the sediment supply to the cobble bar reach of river mile 16.5. Data collection for 1983 was greatly expanded over the previous year's program. Forty-three daily sets of sediment data were collected, with the highest sampling discharge being 19,300 cfs. Measurements were made on both the rising and recessional