The relatively young, low-relief landscape of northern Indiana is characterized by poorly drained, glacially derived soils and hydrologically isolated surface depressions. In the last century, installation of subsurface drainage networks has lowered the naturally high seasonal water table and made arable some of the most fertile land in the world. The purpose of this research was to quantify the interaction of soil hydrologic properties, subsurface drainage, and surface depressions on the generation of peak streamflow as well as the temporal distribution of stream discharge following rain events in a small, agricultural watershed. Several geographic information system (GIS) techniques were used to digitally represent the soil-landscape relationship, estimate the extent of subsurface drainage, and determine the volume of surface depressional storage in the watershed for input to the semi-distributed Soil Water Assessment Tool (SWAT) model. Results of the study indicate that the influence of natural soil hydrologic properties on modeled streamflow is greatly reduced in a managed (i.e. subsurface drained) landscape. Antecedent moisture condition, or soil water content, increased with depressional storage included in the model and was the dominant factor in streamflow generation. However, the addition of subsurface drainage to the model reduced soil moisture, allowing water previously held in surface depressions to seep into the soil profile. The liberated depressional storage was found to intercept surface runoff and act as a buffer to reduce both peak streamflow events and flashiness. The overall conclusion from this study indicates that highly managed, subsurface drained landscapes overcome the inherited differences in soil hydrologic properties within the Tipton Till Plain of northern Indiana.
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