Dilution of brackish waters in irrigation networks —An analytic approach

Summary

Rational method of improving poor water by the admixture of good-quality water for irrigation purposes is proposed and demonstrated. The principles of the dilution process, carried out in dilution junctions, are explained. Continuity equations for water and for the mass of relevant substances present in the water are derived for a dilution junction. These equations characterize the suitability of the mixture for irrigation. The optimal operation of a dilution network for irrigation with brackish, sewage and fresh water is formulated and analyzed based on graph theory. A system of non-linear constraints which satisfactorily describes requirements for water quality and flow rates in terms of field demands and water sources is presented. Optimal operation is defined as the minimum water delivery cost. In dilution networks having no more than one outflow conduit of unknown concentration per junction, the non-linear optimization problem can be reduced into a linear one, making the use of Linear Programming (LP) possible.

Adapting the proposed dilution network concept to irrigation can provide a practical means for controlling the quality of water applied in the field.