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166Q CHAPTER 1 '. . INTRODUCTION Scope and Purpose of the Study As established by the Colorado State Constitution, water is appropriated for beneficial use. In the development of the state, water supplies have been appropriated for domestic, agricultural and industrial purposes. As Colorado has continued to grow, the demands for domestic (municipal) water supplies have created economic incentives to sell! and transfer agricultural water supplies. This report, authorized by the Colorado General Assembl}' as a part of Senate Bill 92-87, documents a IT\ulti-disciplinary study of issues arising out of a possible large-scale transfer of water out of the Ft. Lyon Canal to alternative uses. It examines changes to be anticipated in such a water transfer and proposes alternative actions to such a water tran$fer. This chapter presents introductory information on the Arkansas River Basin and the area of study. In Chapter 2, issues associated with water transfers in and around the study area are presented along with information on historic water transfers. , Chapters 3 and 4 present descriptive information of the Ft. Lyon Canal Company system and t~e regional socio-economic characteristics. They include a physical description of the system, operational analysis, historical background, and characterization of the social, economic and environmehtal aspects of the study area. Chapter 5 identifies current and future demands for Ft. Lyon water, inside and outside the study area. Chapter 6 describes the methods employed in alternative analysis and identifies alternatives to potential water transfers out of the Ft. Lyon system. In Phase 2 of this report the most promising alternative{s) and proposed plans for implementation will be developed. Basin Characteristics The Arkansas River originates upstream from Leadville ~t an elevation of over 14,000 feet and exits the state near Holly at 3,400 feet. The basin is illustrated in Figure 1.1. In passing through the plains east of Pueblo to the state line, the river gradient is less than 9 feet per mile. About 25,600 square miles is tributary to the Arkansas River in Colorado. Geologically, in the plains the valley aquifer rests in a V-shaped trough, cut into cretaceous, shale and limestone bedrock. Climate in the Arkansas River Basin varies widely in b<ith temperature and precipitation. On the plains, annual precipitation levels increase moving east;ward from Pueblo, reaching an average of about 16 inches per year at the state line. Over the stu~y area, average rainfall is 11 to 15 inches, with a high degree of areal, daily, seasonal and annual variability. ! The basin's water resources consist of snowmelt, rainfall runoff and ground water development. Most of the surface irrigation systems were constructed between 1874 and 1890. As junior water rights appropriators realized that remaining natural streamflow was generally too variable to supply irrigation requirements during many years, they constructed reservoirs to capture flood flows. The estimated 30-year average annual native streamflow is 283,000 acre feet (aG measured at the Arkansas River gage below Pueblo Reservoir. An additional net 172,000 af is imported from other basins by transmountain diversion projects for use in ithe Arkansas River Valley (USGS and SCS 1992). Total diversions for Colorado ditches betw.:en Pueblo and the Kansas state line are 1-1