ABSTRACT veloped to evaluate the effect of drainage on machinery size and cost. The DREMS (Drainage Effect on Machinery Size) model was developed and consists of a machinery management model, a drainage cost estimation model, and a yield loss estimation model which uses the DRAINMOD water management model. Seventy combinations of machinery and drainage systems were simulated with the DREMS model. Simulation results indicate that machinery size and cost are significantly affected by drain spacings in a poorly drained soil. The effect of drainage on timeliness cost was found to be more significant than that of machinery size. An optimum combination of machinery and drainage system was selected for a farm in central Ohio.