Drainage design for water quality management: Overview

Drainage design for water quality management in irrigated areas requires use of hydrodynamic models that delineate flow paths of subsurface water moving to drains. Use of only traditional drainage design equations for protection against water logging and salinization are inadequate for water quality management; these equations should be coupled with mechanistic models that account for transport and chemical changes in the vadose and saturated zones that replace those associated with a leaching fraction, or requirement concepts. Drainage designs should now make use of hydrodynamic and chemical models that simulate flow and transport of water and chemical constituents from infiltration to drainage discharge. Management should be able to manipulate the models prior to implementing steps aimed at controlling the quantity and quality of drainage discharge.