Comparison of models for computing drainage discharge

The WAVE model describes the transport and transformations of matter and en ergy in the soil, crop, and vadose environment. A lateral field drainage su bprogram was added to the WAVE model to simulate lateral subsurface drainag e flow. The subsurface drainage is considered as the drainage provided by e venly spaced parallel drains with a free outlet: drain tubing or ditch. The rate of subsurface water movement into drain tubes or ditches depends on t he hydraulic conductivity of the soil, drain or ditch spacing, hydraulic he ad in the drains, profile depth, and water table elevation. Hooghoudt's ste ady-state equation was selected for incorporation in the WAVE model. The su bsurface drainage subprogram was calibrated and validated by comparison wit h the SWAP model (The Netherlands) and DRAINMOD (the United States) and par tially by using 7 years of drain outflow data from an experimental field un der fallow and cropped conditions. The comparative study revealed that the three models performed equally well and that the models were reliable and a ccurate tools for predicting the drainage flux as a function of rainfall-ev apotranspiration and local conditions. The WAVE model, in comparison to the SWAP and DRAINMOD model, provided as good a prediction of the lateral subs urface drainage flow to drains. The statistical analysis between each model and observed data revealed that the three models were able to predict with sufficient accuracy the observed drainage discharge. The DRAINMOD model, h owever, has the advantage of giving a more accurate estimate of the dischar ge, resulting in a more precise modeling. The models were consistent in pre dicting water table levels, but they could not be verified against field da ta because of a lack of suitable measurements.