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The movement and fate of nutrients such as nitrogen (N) and phosphorus (P) from agricultural fields and land treatment sites are dependent on the route and rate of water movement. The relative proportions of water removed from poorly drained, high water table soils, as surface runoff, and through the profile as subsurface drainage, depend on precipitation, drain spacing and depth, soil hydraulic properties, and crop parameters. DRAINMOD simulations were conducted to determine long-term average annual surface runoff and subsurface drainage for a range of drain spacing and depths for five coastal plain soils. Drainage intensity was defined in terms of profile hydraulic transmissivity, drain spacing, and depth. Regression analyses were used to define simple algebraic equations for predicting average annual runoff and subsurface drainage in terms of drainage intensity, annual precipitation and crop for conditions in North Carolina. The equations explain most of the variability of surface runoff and subsurface drainage with R2 values greater than 0.90 for all cases. These methods are used in PLAT to assess impacts of long term applications for animal wastes on the movement and fate of P on poorly or artificially drained lands.