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INTRODUCTION This report is the culmination of two years of sediment trans ort and river morphology investigation of the Yampa River in Dino our National Monument. The purpose of this study was to define a min mum streamflow which will preserve the processes and natural Condit. oils vital to the channel morphology and aquatic life system of the ri er. The proposed minimum streamflow was prepared in the form of a seas nat. hydrograph which includes the constraints imposed by sediment deposi ion in the canyon, fishery habitat, riparian vegetation, and o her ecological considerations. The Yampa River is the last remaining major free flowing tribu ary of the Colorado River system. In 1938 the Monument was enlarge to preserve the unique land and water resources associated with the incised meanders and desert plateau country of the Green and Yampa Rivers. Now the river flows forty-five miles through Dinosaur National Monu ent before joining the Green River near the Colorado-Utah border. To further protect and maintain the water and related resources of the Yampa River the National Park Service, Department of the Inter - or, initiated this minimum streamflow study. Hydraulic and sediment transport data were collected during the spring and summer high flow periods of 1982 and 1983. Athough stream channel data was collected throughout the Yampa Canyon, all of the sediment data was collected at a site in a cobble substrate reach of the river. This four mile cobble bed reach is a unique substrate reach in the Yampa River system and is an observed spawning area for the endangered Colorado squawfish. The report describes the field sampling program, data colle tion methods and results. A computer program was developed to mod 1 a portion of the cobble substrate reach. The computer model simulate the sediment transport, deposition and scour in response to diff rent discharge hydrographs. In this manner a minimum streamflow hydro raph was designed to insure minimal sand deposition on the cobble subst ate. SPECIFIC RESEARCH OBJECTIVES The comprehensive objective of this study is to quantify, th ough the understanding of hydraulic and sediment transport phenomen , a minimum streamflow hydrograph that will preserve and maintain, on an annual basis, the natural conditions and processes vital to biolo ical. system of the Yampa River in Dinosaur National Monument. This hydrograph would be sufficient to minimize any adverse impacts ar sing from a reduced or otherwise altered seasonal stream discharge. The specific requirements to accomplish this overall study objective are: 1) Define the natural conditions of the cobble bed reach i the canyon including the hydraulic, sediment transport, subs rate and channel morphological conditions. 2) Establish a sediment transport rating curve in the c?bble substrate river reach.