Improving Efficiency of Desalinization with Subsurface Drainage

Desalinization of soils, by flooding the surface completely and leaching salts through subsurface drains, removes salts rapidly above the drains but only slowly midway between the drains. More uniform leaching using less water can be obtained by constraining the seepage area with the use of bunds, initially flooding only the region midway between the drains and then progressively increasing the flooded area toward the drains until the whole area is flooded. The improvement in the efficiency of desalinization using this procedure was shown by obtaining an analytical solution of the flow regime for the seepage from a ponded surface strip to a 2D pipe-drain system using conformal transformations and then estimating the leaching of salts from the soil below the surface by assuming that salts were transported only by convection. The analysis shows that the progressive leaching procedure requires <16% of the water needed using the conventional method, in which the soil surface is completely flooded the entire time, and that it can be attained in <24% of the time.