Yampa River Basin Water Resources Planning Model Final Report

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2.0 INTRODUCTION 2.1 Basin Description The Yampa River basin is approximately 7,660 square miles in size, ranging in elevation from 12,200 feet in the headwater areas near the town of Yampa to 5,600 feet in the vicinity of Dinosaur National Monument at the lower end of the basin. The Yampa River is the primary stream in the basin, with major tributaries including the Bear River, Walton Creek, Fish Creek, Trout Creek, Elk River, Elkhead Creek, Fortification Creek, the Williams Fork River, and the Little Snake River. Average annual streamflow in the upper portions of the drainage (United States Geological Survey [USGS] gage near. Stagecoach Reservoir) is approximately 62,000 acre -feet, which increases to an annual average of 1,623,000 acre -feet at the Dinosaur Monument (USGS gage near Deerlodge Park). The principal water use in the basin is irrigation, with hundreds of small irrigation ditches diverting from the mainstem and the numerous tributary streams throughout the basin. This irrigation has remained relatively constant since the late 1800s, with only small increases in the irrigated acreage as new ditches and storage systems were constructed. The total irrigated acreage in the basin, according to the State's 1993 geographic information system (GIS) data, is estimated to be approximately 80,600 acres. Other major water uses in the Yampa River basin include diversions for power generation at the Hayden Station and Craig Station plants (historical diversions of approximately 16,500 acre -feet per year) and diversions for municipal use in the larger towns of Steamboat Springs and Craig, and in a number of smaller towns. Three transbasin diversions, the Sarvis Ditch, Stillwater Ditch, and Dome Creek Ditch export water from the Yampa River basin to the Colorado River drainage. There are also a number of smaller transbasin diversions from one tributary drainage to another. See Figure 2.1a for a general layout of the basin. In addition to the direct ditch diversions, there are nine major reservoirs (greater than 4,000 acre -feet in capacity) in the Yampa River basin that are represented explicitly in the Yampa Model. Three of the reservoirs are used for irrigation (Stillwater Reservoir No. 1, Allen Basin Reservoir, and Yamcolo Reservoir); three are predominantly used for recreational and fishery purposes (Lake Catamount, Pearl Lake, and Steamboat Lake); and the remaining reservoirs are used for multiple uses, including municipal, industrial, irrigation, and recreation (Fish Creek Reservoir, Stagecoach Reservoir, and Elkhead Reservoir). For purposes of the Yampa Model, it is noted that these reservoirs were constructed prior to the 1975 -1991 water year study period, with the exceptions of Lake Catamount (1977), Yamcolo Reservoir (1981), and Stagecoach Reservoir (1988). 2.2 Water Resources Developments The Yampa River basin has seen substantial water resources developments in the form of private irrigation systems and municipal and industrial diversions. Table 2.2a presents a timeline of key developments within the basin. Introduction 2 -1