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<br /> <br />-6- <br /> <br /> <br />One form of "consumptive use" not yet 'practiced in the basin may <br />ultimately be an important factor in alleviating the problems of increasing <br />salt content of waters, particularly in the lo~er basin. Most of the saline <br />matter in streams is derived from ground-water; and in some places, it may <br />be possible to intercept this ground-water by wells before it picks up its <br />mineral load, and while it is still suitable for use. Such a program would <br />achieve an increase in usable water supply and'possibly a decrease in quantity <br />of unusable waters. An adequate knowledge of the ground-water hydrology and <br />geochemistry would be prerequisite. <br /> <br />Many uses of water are nonconsumptive, that is, the water returns' <br />to a stream or ground-water body after use. p;erhaps only half the water <br />used for irrigation is used consumptively, and nonconsumptive use accounts <br />f6r an even larger proportion of the water taken for municipal or industrial <br />purposes. Each nonconsumptive use can be expected to result in some further <br />deterioration in quality of the water. When water is reused several times <br />for irrigation, the net return water often contains so much soluble salt <br />that it is unfit for most purposes. If adeqUate drainage for irrigated land <br />were not provided, sooner or later the soil would become supercharged with <br />minerals and no longer suited for agricultura~ use. <br /> <br />The headwater areas in the Colorado River Basin have a natural <br />advantage in quality of water. After leaving: these high areas the river <br />and its principal tributaries traverse broad regions containing considerable <br />volumes of soluble materials, and arid enough to induce substantial water <br />losses by evaporation and transpiration. In lower reaches, therefore, there <br />is substantial increase in dissolved matter with no corresponding increase <br />in water volume. <br /> <br />Nonconsumptive use of water in the upper part of the basin must <br />necessarily aggravate the quality problem fot' the downstream user. Return <br />water from irrigated lands, sewage, and industrial return water are likely <br />to increase the concentration of soluble matt.er in the stream. The down- <br />stream user is entitled to assurance that th9se above him will take every <br />precaution to avoid "unnecessary" contamination of the water, but he would <br />have to prevent all upstream use of water in: order to be assured that there <br />will be no man-made deterioration in quality:. Laws, compacts, and public <br />opinion all agree that the people of headwater areas are entitled to some <br />use of the water in their areas. <br /> <br />; <br />In all the upper basin States t~e ~enters of population are outside <br />the Colorado River Basin, and in each of th~se States projects are proposed <br />or constructed to divert water from the Col~rado River Basin into the more <br />populous areas. The chief problem created qy these exports is that many of <br />them draw water from ,headwater areas, and therefore remove some of the best <br />waters from the drainage basin. These waters, if they were to continue <br />downstream, would act as dilutants to the m$re mineralized waters that enter <br />the river in its middle and lower reaches.fDiversion of these headwaters <br />thus may result in a greater concentration 9f mineral matter in the waters <br />that remain in the stream. i <br /> <br />If man dries up a river, the river; retaliates by dumping its entire <br />load of solid matter in his lap. The devel:opment of the Gila River Basin <br />has just about reached this point, and the problems of salt accumulation <br />