Laserfiche WebLink
<br />c') <br />00 <br />'.::..J <br />..-4 <br />C-' <br />.--) <br />~-I In past time, the Colorado River has eroded a deep wide channel <br /> <br />2 thOrough the Mancos Shale formation which has since been refi lIed with <br /> <br />3 alluvial materials to a depth of some 50 to 60 feet. The present <br /> <br />4 channel of the Colorado River is incised in the alluvial materials <br /> <br />5 which are much more permeable than the shale and serve as a general <br /> <br />6 aquifer for the f~oodplaln area. This aquifer is recharged by deep <br /> <br />7 percolation losses from irrigation and canal and lateral seepage. <br /> <br />8 In some places the aquifer Is under artesian pressure, and the sa! inity <br /> <br />9 of the water in the aquifer varies from 5,000 to 36,000 parts per mill ion <br /> <br />10 of total dissolved salts. Salinity concentrations normally increase with <br /> <br />11 depth. <br /> <br />12 The topography in the Irrigated area is gently sloping to roll ing. The <br /> <br />13 major overall slope is to the river. Most of the irrigated lands are in <br /> <br />14 the 0 to 2 percent and 2 to 5 percent slope groups. Some breaks and <br /> <br />15 <br /> <br />hummocky soils are also irrigated. <br /> <br />16 <br /> <br />The upland watershed or diffuse salt source area is the drainage above <br /> <br />17 the Grand Valley irrigated area. The study area encompasses some 839,000 <br /> <br /> <br />18 acres. Annual precipitation varies from about 8 inches in the lower <br /> <br />19 valley to 20 inches on a small portion in the northwest corner of the <br />20 basin. <br /> <br />15 <br />