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<br />t.. <br />~ <br />,,,,", <br />~ <br /> <br />.....1 <br /> <br />This aquifer is recharged by deep percolation losses from irrigation and <br />canal and lateral seepage. In some places the aquifer is under artesian <br />pressure. Sal inity of the water in the aquifer varies from 5,000 to <br />36,000 parts per million of total dissolved salts. Salinity concen- <br />trations normally increase with depth. <br /> <br />C~~, <br /> <br />Topography in the irrigated area is gently sloping to rolling. The <br />major overall slope is to the river. Most of the irrigated lands are <br />in the 0 to 2 percent and 2 to 5 percent slope groups. Some breaks and <br />hummocky soils are also irrigated. <br /> <br />The upland watershed or diffuse salt source area is the drainage above <br />the Grand Valley irrigated area. The study area encompasses 839,000 <br />acres. Annual precipitation varies from about 8 inches in the lower <br />valley to 20 inches on a small portion in the northwest corner of the <br />basin. <br /> <br />Grand Junction, the largest city in Colorado west of the Continental <br />Divide, is located in the valley. The mean annual temperature at Grand <br />Junction is 52oF. and ranges from a July mean of 780F. to a January mean <br />of 260F. Annual precipltatlon averages only 8.29 inches and is rather <br />uniformly distributed throughout the year. The elevation at Grand <br />Junction is around 4,850 feet above sea level. The average growing <br />season is 190 days. <br /> <br />Four irrigation entities divert water from the Colorado River for use <br />in the valley. These include the Grand Valley Water Users Association <br />(~ureau of Reclamation Project), Grand Valley Irrigation Company, <br />Palisade Irrigation District, and Mesa County Irrigation District. A <br />fifth irrigation company, the Redlands Power and Water Company, diverts <br />water from the Gunnison River. A number of other small companies have <br />carriage agreements with the major canal companies for del ivery of <br />water. <br /> <br /> <br />lined ditches and siphon tubes are popular <br />irrigation improvements in the Grand Valley. <br /> <br />11 <br />