WSP11081

• File Number: 8273.600.30
• Description: Colorado River Basin Salinity Control - Federal Agencies - USDA
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/1989
• Title: Intercepting Isolating and Reusing Drainage waters for Irrigation to Conserve Water and Protect Water Quality
• Water Supply Pro - Doc Type: Report/Study

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Agricultural Water Management, 16 (1989) 37-52
Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlsnds

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Intercepting, Isolating and Reusing Drainage
Waters for Irrigation to Conserve Water and
Protect Water Quality

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J.D. RHOADES

USDA-ARS, u.s. Salinity Laboratory, Riverside, CA (U.S.A.)
(Accepted 6 July 1988)

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ABSTRACT

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Rhoades, J.R., 1989. Intercepting, isolating and reusing drainage waters for irrigation to conserve
water and protect water quality. Agric, Water Manage., 16: 37-52.

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Theoretical and conceptual evidence is given along with four ca8e examples to show that a loss
of usable water occurs in the total water supply when agricultural drainage waters are returned to
the water supply, even when blending is carried out such that apparently safe limits of salt con-
centration are not exceeded in the final mixture. An alternative means of managing agricultural
drainage waters is offered that provides a greater practical benefit to be derived from the total
water supply than does blending.

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INTRODUCTION

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It is sometimes claimed that the return of agricultural drainage to our water
supplies is beneficial from the point of view of conserving water and increasing
water use efficiency (Davenport and Hagan, 1982). Water quality agencies
commonly deal with agricultural drainage return problems by setting allowable
concentrations of total salts and specific solutes in the waters that are returned
to the water supply system and to implement regulatory practices for blending
or diluting the drainage waters with a go~d-quality water such that the con-
centration of total salt (or of a specific solute) in the blend will not exceed a
value (the so-called safe limit) that is deemed allowable in the water supply.
Such claims and regulatory practices are short sighted; they do not recognize
the potential deleterious effect that the discharge of agricultural drainage water
to our surface and groundwater supplies and such blending - whether it is
natural or intentional - can have upon the usability of the total- and the re-
ceiving-water supplies. The ultimate objective of water quality protection should
be to permit the maximum practical benefit (use) to be derived from the avail-
able water supply. Water quality protection programs which dispose of agri-
cultural drainage waters through blending practices do not protect the quality

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@ 1989 Elsevier Science Publishers B.V.

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0378-3774/89/$03.50

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