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<br />2 <br /> <br />o <br />~ <br />w <br />w <br /> <br />an acceptable salt balance in the root zone which will productively <br /> <br />support the crops grown. In many cases this not only requires leach- <br /> <br />ing the salts in the soil profile which are deposited by evapotranspira- <br /> <br />tion, but also necessitates leaching excessive salts which are <br /> <br />naturally occurring in the soil. Problems of increased salt loading <br /> <br />arise when additional quantities of water are lost to deep percolation <br /> <br />from excessive irrigation and conveyance seepage. Maximum bene- <br /> <br />fits can be derived from the water supply if at this stage of develop- <br /> <br />ment salinity is considered on a basin wide scale. All interested <br /> <br />parties should participate in arriving at salinity controls if mutual <br /> <br />benefits are to be gained. Although nearly two-thirds of the salt load <br /> <br />in the river is from natU1:al sources, recent increases have at times <br /> <br />pushed the salt content to critical levels. Irrigation must be investi- <br /> <br />gated as a source of mineral pollution because most irrigation prac- <br /> <br />tices are to some degree wasteful. Thus, there is a real need to truly <br /> <br />delineate the effect of various management practices upon salt loading <br /> <br />in the river system in order to make improvements in water and <br /> <br />salinity management practices. <br /> <br />The Colorado River enters the Grand Valley from the east, <br /> <br />joins with the Gunnison River at the City of Grand Junction, Colorado, <br /> <br />and exits in the west as illustrated in Fig. 1. The contribution to the <br /> <br />salt load in the Color"do River as it flows through the valley repre- <br /> <br />sents one of the largest single increases in the upper basin. A <br />