Soil Water Concepts

The Agricultural Drainage series covers topics including basic concepts; planning and design; surface intakes; economics,· environmental impacts; wetlands; and legal issues. The growing use of artificial subsurface or "tile" drainage in Minnesota has sparked much debate about its impact on local hydrology and water quantity and quality. Discussions are typically focused on the following questions that have important policy implications for local and state decision makers. • Does subsurface drainage lessen or worsen localized flooding? • Are catastrophic floods more frequent because of subsurface drainage? • Does subsurface drainage alter th.e quantity of flow in a river basin? • Do subsurface-drained soils respond more like a "sponge" to excess rainfall, as compared to poorly drained soils? • How do surface inlets (intakes) affect the quantity and quality of drainage flow? • How do artificially drained lands impact water quality? This publication presents concepts that are fundamental to understanding how subsurface drainage affects soil water and the water balance. It provides information about components of the water balance in the crop/soil system and their relationship to drainage. In addition, several commonly asked questions about drainage, soil water, and hydrology are addressed. Understanding these concepts is helpful in addressing broad issues and policy questions related to drainage and water management.