Simulation model for subsurface drainage design to replace surface intakes in depressional areas

Abstract

Studies conducted by Baker et al. (1985) cite the presence of nitrate in the study attributable to agricultural drainage wells rather than infiltration of nitrates from the land surface. Studies have also shown surface water to contain higher concentrations of agricultural chemicals (herbicides), bacteria and sediments than is found in subsurface drainage water. This evidence suggests that either alternatives to the use of agricultural drainage wells should be sought or the quality of water entering agricultural drainage wells should be better controlled. The elimination of surface water inlets to agricultural drainage wells prevent direct entry of surface water runoff and can be expected to reduce the impact of agricultural drainage wells on ground water quality significantly. Surface runoff generally carries the bulk of contamination in the form of suspended solids, bacteria and pesticides and is therefore of greatest concern. The elimination of surface water inlets may give rise to surface ponding problems and thereby significantly retard land drainage if adequate alternate drainage is not provided. The objectives of this study are to determine the saturated hydraulic conductivity of some common types of soils in the depressional areas in north central Iowa, to develop a method (simulation model) to aid in the selection of the spacing of subsurface system layout in depressional areas, and to demonstrate a procedure to obtain an economical optimum spacings for subsurface drains in the soil types for which the hydraulic conductivities were determined.