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<br />rights appropriators realized that remaining natural streamflow was generally too variable to supply <br />irrigation requirements during many years, they constructed reservoirs to capture flood flows. The <br />estimated 25-year average annual native streamflow is estimated at 524,343' acre feet (at), measured <br />at the Arkansas River gage below Pueblo Reservoir. An additional net 172,000 af is imported from <br />other basins by transmountain diversion projects for use in the Arkansas River Valley. Total <br />diversions for Colorado ditches between Pueblo and the Kansas state line are estimated to be <br />838,000 af (1950-1987 data). Thus, due to diversion and use of return flows, water is used more than <br />once in the Lower Arkansas Valley before leaving the state. <br /> <br />Ground water levels in the valley rose after irrigation began as a result of canal seepage and deep <br />percolation. Irrigation wells have been drilled in suitable areas and supply about 25 percent of the <br />irrigated acres. These wells have been subject of litigation for decades. <br /> <br />The Arkansas River of southeastern Colorado is one of the most saline rivers in the United States, <br />with total dissolved solids (tds) levels exceeding 4,000 ppm between Lamar and the state line. Water <br />containing more than 2,000 ppm tds is generally considered unsuitable for irrigation, but such water <br />has been used successfully in the lower Arkansas Valley for many years. The salinity problem is <br />discussed by Miles (1977). Most of the salt comes from natural sources in the soil. More <br />information on water quality of the lower Arkansas River and the study area is presented in Chapter <br />3. <br /> <br />1.3 Descriotion of Study Area <br /> <br /> <br />The Ft. 4'on Canal is the largest irrigation company on the Arkansas River, stretching 120 miles and <br />providing irrigation water to approximately 92,600 acres. The study area covered by this report <br />includes Kiowa, Crowley, Otero, Bent, and Prowers counties of southeastern Colorado, and is noted <br />on Figure 1.1. The immediate vicinity of the Ft. 4'on system is roughly bounded by Lamar on the <br />east, La Junta on the south, Eads on the north, and Manzanola on the west, an area of <br />approximately 2,500 square miles, or 2.4 percent of the state of Colorado. The five counties <br />represent the economic region which is under direct influence of production and associated spending <br />distribution of the Ft. Lyon Canal Company system. Most relevant data is available by county. The <br />five county population was 43,183 in 1990. The area includes about 100 river miles of the Arkansas <br />River and the principal towns are Lamar, Las Animas, La Junta and Rocky Ford. It is described in <br />more detail in Chapter 4. <br /> <br />1.4 Concurrent Studies <br /> <br />Three other studies of this area are known to be pending or underway. The U. S. Geological Survey, <br />Pueblo Subdistrict (USGS) has conducted extensive research on the Arkansas River of Colorado for <br /> <br />'Calculated by the u.s. Bureau of Reclamation as mean native flow (1966-1990) in connection with modeling <br />studies of the FryingPan-Arkansas Project. <br /> <br />1-3 <br />