Evaluation of a Water Management Model for Irrigated Agriculture

Abstract

ABSTRACT DRAINMOD is a computer model simulating the movement and storage of water in soils with a shallow water table in the humid region. It was developed for the comprehensive analysis of soil water transformation on a field scale where most water management facilities are designed and installed as a single unit. The basis of DRAINMOD is a water balance at midpoint between two parallel drains. Using the approach of successive steady state equilibrium, the unsteady and transient water movement in a tile drained field is analyzed as steady state flow at sufficient small time increments. The reliability of the model for irrigated cropland in semiarid climate was tested with field data from California. Water table elevations predicted by DRAINMOD agreed reasonably well with measurements for five experimental locations differing in soil texture in the San Joaquin Valley and the Imperial Valley. Water loss by deep seepage ia a significant component in soil water balance from irrigated cropland. When the water table drawdown exceeds 150 cm, the model tends to over estimate the depth to the water table.