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~r k Green River Razorback Sucker Spawning Reach Hydrologic Study Near Jensen, Utah I. Introduction This study presents the results of a hydrographic data collection project on the Green River near the Dinosaur National Monument Quarry. The primary focus of the study was to investigate the hydraulic flow conditions and channel geometry changes at a large cobble bar which splits the river several miles downstream of the Jensen bridge. This vegetated cobble bar (or island since the bar has perennial vegetation) is referred to as the razorback sucker spawning bar. The upstream extent of the bar is slightly inundated during the spring runoff, but the main portion of the bar has not been covered with water in recent years based on the established upland semi-arid vegetation. Razorback suckers (an endangered fish species in the Colorado River system) has been observed to spawn over the cobble substrate in the channels around the bar. River cross sections were surveyed in this bar reach before, during and after the 1993 spring high flows in the Green River. Peak discharge exceeded 20,000 cfs in early June based on preliminary estimates of the Jensen USGS gaging station just a few miles upstream of the spawning bar. -Three cross sections were located upstream of the bar, two cross sections were surveyed across the bar and three cross sections were established just downstream of the bar. Monitoring these cross sections during the course of the spring runoff enabled an analysis of the river response to the spring runoff sediment load. In addition to the cross section surveys, river discharge, suspended sediment load and bed material size were investigated and are discussed in this report. As compliment to the spawning bar investigation, additional hydrographic data was collected in a reach of the Green River near a series of abandoned meander bends just downstream of the Monument entrance. On the east side of the Green River, about one-half mile downstream of the Monument boundary, the abandoned meander bends store ponded water throughout the spring and summer to create the Escalante wetlands. River cross sections were surveyed to predict overbank flows into the Escalante Wetlands. The wetlands serve as migratory waterfowl habitat and are projected to be a lar~-al fish recruitment site for the razorback sucker.