Drainage design coefficients for eastern United States

The development of drainage simulation models has made it possible to quantitatively describe the performance of drainage systems, including the effects of design parameters on yields. While this was a primary goal of drainage researchers 40 years ago, it is no longer sufficient. Currently, the effect of drainage on nutrient loads and surface water quality is of equal or greater importance to production goals. Limited field data and modeling results indicate that nitrogen (N) loss in drainage water is proportional to subsurface drainage intensity (DI). This implies that the drainage system should be tailored to soil and site conditions, such that the DI is as small as possible. While simulation models can be used to determine drain depth and spacing required to maximize yields or profits for a specific site, the modeling expertise and/or the extensive data required are often not available. Simple approaches are still needed for estimating drain spacing and depth. The Hooghoudt equation has been used for many years for this purpose. Its application requires knowledge of the design drainage rate, which has not been defined for many locations in the US.