MODELING SUBSURFACE DRAINAGE FLOW OF A TILE-DRAINED SMALL WATERSHED USING DRAINMOD

Abstract

The watershed-scale simulation model DRAINMOD was used to model the hydrology of a tile-drained Indianaagricultural watershed. The goal of the research is to study whether local measured soil data can be replaced by publishedSSURGO soil survey data, and the Indiana Drainage Guideline can replace actual system design data in simulating thehydrology of the watershed. Field-scale DRAINMOD model output was compared to gauged field data, and then applied tothe watershed-scale using a GIS-integrated DRAINMOD for simulating the hydrology of tile drained watersheds. A sensitivityanalysis was performed to determine the parameters that would most affect drainage flow at the watershed scale. Theparameters that were determined to be the most effective in changing the model output were drain depth, drain spacing, andsaturated hydraulic conductivity. Simulations show that DRAINMOD was able to simulate the hydrology of the gaugedwatershed with reasonable accuracy when tile drainage system design was based on the Indiana Drainage Guidelines (IDG).The use of published soil hydraulic properties, guidelines for drainage system design and the understanding of parametersthat are most effective in changing drainage flow enables the user to predict drainage flow at the watershed scale with alimited set of available input data.