EVALUATION OF THE WATER MANAGEMENT MODEL PREFLO

ABSTRACT PREFLO uses a one-dimensional finite difference solution of the Richards equation to model vertical soil water movement with the added capability of simulating preferential flow on a macroscopic scale. Results presented in this article are a comparison of PREFLO simulations to observed field data excluding preferential flow, a comparison between PREFLO and DRAINMOD, and a sensitivity analysis. Field data, collected in eastern North Carolina during the five-year period 1973-1977, were used to evaluate the model. The field site consisted of three drainage treatments with provisions for subirrigation and controlled drainage. The values of midpoint water table depth as simulated with the PREFLO model agreed well with the field measured values. The average deviation was 13.9 cm. The average deviation between the simulated and measured water table depths for the DRAINMOD model was 14.4 cm. Agreement between the simulated water table depths of the DRAINMOD and PREFLO models was excellent. The sensitivity of the PREFLO model to errors in ten of the input parameters was determined by simulating the performance of a drainage system over three years of climatological record and three drain spacings. Extremes in parameters related to soil water movement and storage [K(h) and 9(h)] caused the greatest errors in the simulations.