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<br />Mancos Formation shale underlies most of the Uncompahgre Valley. The <br />Xancos is a calcareous marine shale and is fractured and jointed near the <br />surface. During the weathering process, salts in the shale were dissolved <br />and redeposited in the joints and bedding planes of the weathered shale. <br />Residual soils formed during the weathering process and prior to leaching <br />contained the same minerals. Adobe soils contribute about 5.8 tons of <br />salt per acre. <br /> <br />Ground water movement takes place within two distinct aquifers; <br />however, evidence suggests the two aquifers interact freely, with the <br />overall water table being dependent upon both systems. <br /> <br />The build-up of ground water is accompanied by an increase in salts <br />within the soil profile. Many of these areas are clearly evidenced in <br />parts of the study area by a white encrustation of salts on the soil <br />surface. (During the irrigation season, enough water is added to the soil <br />to keep these salts flushed.) <br /> <br />Reduction of canal and lateral seepage by implementation of any of <br />the lining alternatives would lower the water table and capillary action <br />would be reduced. Rain and properly applied irrigation water could then <br />leach salt from the topsoil resulting in better vegetation growth. <br /> <br />For Lower Gunnison Basin Unit studies, samples of water and salt <br />flows were collected in the lower Uncompahgre Valley from 1976 through <br />1979. The 4 year average for these measurements and the associated <br />salinity concentrations are shown on the following table. <br /> <br />Lower Gunnison Basin Unit study area <br />water and salt inflow-outflow <br /> <br />Description <br />Inflow <br />Uncompahgre River <br />upstream of <br />study area <br />Gunnison River at <br />west portal <br />Tributaries on east <br />side of valley <br />Tributaries on west <br />side of valley <br />Total <br />Flow-weighted average <br />Out flow <br />Uncompahgre River <br />at Delta <br />East side of valley <br />to Gunnison River <br />West side of valley <br />to Gunnison River <br />Total <br />Flow-weighted average <br />Difference of outflow <br />and inflow <br /> <br />Water <br />{ acre-feet> <br /> <br />Salt <br />(tons) <br /> <br />Total <br />dissolved <br />solids <br />(mg/L) <br /> <br />146,400 79,900 <br />345,700 63,500 <br />6,800 15,100 <br />15,100 7,500 <br />514,000 166,000 <br /> <br />400 <br /> <br />135 <br /> <br />1,630 <br /> <br />365 <br /> <br />240 <br /> <br />171,100 298,200 <br />57,000 145,500 <br />53,000 86,700 <br />281,100 530,400 <br />-232,900 364,400 <br />12 <br /> <br />1,280 <br /> <br />1,875 <br /> <br />1,200 <br /> <br />1,390 <br />001730 <br />