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<br />~j <br />~.: , <br />~T') <br />....-4 <br /> <br />o <br /> <br />INTRODUCTION <br /> <br />This report has been prepared as an annual status report to present <br />the results of the 1990 monitoring and evaluation activities in <br />various discipl ines. Annual reports have been prepared and presented <br />since 1985; this is the sixth annual report. <br /> <br />The monitoring program was designed to evaluate the impacts of <br />sal inity practices due to the USDA Sal inity Control Programs in the <br />Grand Va II ey area (F i gure 1>. The effects of i rr i gat ion pract ices on <br />salt load reduction, economics, wi Idl ife habitat and soi I sal inity <br />I eve I s have been eva I uated annua II y on se I ected fie I ds as out lined In <br />the 1983 USDA Monitoring and Evaluation Plan. Monitoring wi II be <br />continued for several years to determine the long-term impacts of <br />improved sal inity practices. <br /> <br />PROJECT LOCATION <br /> <br />The Grand Valley Project Area is located along the Colorado River in <br />West Mesa County in West Central Colorado (Figure 1> near the <br />Colorado-Utah State I ine. The Grand Valley is underlain by Mancos <br />shale formation and covers about 126,000 acres, of which 66,000 acres <br />is irrigated cropland. About 6,000 acres of cropland are not <br />cultivated in anyone year. Irrigation water is obtained mostly from <br />the Colorado River and is del ivered to the fields through Federal and <br />pr i vate cana I systems. Commun i ties located in the Grand Va II ey area <br />are Grand Junction, Pal isade and CI if ton to the east; Fruita, Loma and <br />Mack on the west end. <br /> <br />PROBLEMS IN THE GRAND VALLEV <br /> <br />The Grand Val ley contributes about 600,000 to 700,000 tons of salt <br />annually to the Colorado River. It is assumed that most of these <br />salts (gypsum, calcite and sodium sulphate> are leached from the soi I <br />and underlying Mancos shale and carried to the river by deep <br />percolation through over-irrigation and by seepage from water delivery <br />and tai Iwater collection ditches. Seepage losses from unl ined farm <br />del ivery ditches, tai Iwater collection ditches and deep percolation <br />from field irrigation are considered to be major sources of water that <br />carries salt to the river. Salt loading is the major cause of <br />sal inity increase in the Colorado River and has caused water qual ity <br />problems for downstream water users. <br /> <br />2 <br />