COMPARISON OF EPIC-WT AND DRAINMOD SIMULATED PERFORMANCE OF LAND DRAINAGE SYSTEMS

Data from the Louisiana Agricultural Experiment Station Ben Hur Resear ch Farm were used to compare the performance of EPIC- WT and DRAINMOD models in simulating the effect of subsurface drainage systems on surf ace and subsurface drained volumes and the fluctuations of field water table depth. Both models overestimated the total cumulative drainage f lows for the simulation period (1981-1987). The long-term cumulative v alues simulated by DRAINMOD and EPIC-WT were 7% and 32% greater than t hose observed for surface drainage volumes, and 34% and 20% greater th an the observed volumes for subsurface drainage. The slope and correla tion coefficients of the regression lines associated with EPIC-WT mont hly flows were 0.86 and 0.85 for the surface volumes, and 0.98 and 0.9 2 for the subsurface volumes. The regression equation describing the l inear relationships between the monthly observed flows and the flows p redicted by DRAINMOD had slope and correlation coefficients of 0.95 an d 0.90 for surface volumes, and 1.02 and 0.77 for subsurface volumes. The watertable fluctuations were predicted better by DRAINMOD than EPI C- WT during relatively dry periods when the watertable depth was belo w the root zone; however, the overall performances of the two models i n simulating the watertable fluctuations over the seven-year period we re about the same.