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<br />,~7\ <br /> <br />Il.Q~ <br /> <br />-'." . <br />..... <br /> <br />N <br />--J <br />--J <br />W <br /> <br />Blending saline and Non-Saline Waters <br />Reduces Water Usable for Crop Production <br /> <br />J . D. Rhoades.~./ <br /> <br />Introduction <br /> <br />It is sometimes claimed that the return of agri- <br />cultural drainage to our water supplies is beneficial <br />from the point of view of conserving water and <br />increasing water use efficiency (Davenport and Hagan, <br />1982). Water quality agencies commonly deal with <br />agricultural drainage return problems by setting <br />allowable concentrations of total salts and specific <br />solutes in the waters that are returned to the water <br />supply system and to implement regulatory practices for <br />blending or diluting the drainage waters with a <br />good-quality water such that the concentration of total <br />salt (or of a specific solute) in the blend will not <br />exceed a value (the so-called safe limit) that is deemed <br />allowable in the water supply. Such claims and <br />regulatory practices are short sighted; they do not <br />recognize the potential deleterious effect that the <br />discharge of agricultural drainage water to our surface <br />and groundwater supplies and such blending - whether it <br />is natural or intentional - can have upon the usability <br />of the total - and the receiving-water supplies. The <br />blending process limits the benefit that can be derived <br />from the total water supply for some uses. The return <br />of saline waters to the water supply, even when <br />sufficient dilution occurs to keep the salinity of the <br />mixture within apparently safe limits, reduces the <br />quantity of that supply that can be used in consumptive <br />processes which are limited by salt concentration, such <br />as the growth of salt-sensitive crops. The ultimate <br />objective of water quality protection should be to <br />permit the maximum practical benefit (use) to be derived <br />from the available water supply. <br />The purpose of this paper is to provide theoretical <br />and conceptual evidence to show that water quality <br />protection programs which dispose of agricultural <br /> <br />" D~rector, u.s. Salinity Laboratory, 4500 Glenwood <br />Drive, Riverside, CA 92501. <br /> <br />1. <br /> <br />Rhoades <br />