EFFECTS OF DRAINAGE AND WATER-MANAGEMENT PRACTICES ON HYDROLOGY

The hydrology of two North Carolina muck soils was simulated using four water-management methods, conventional drainage, improved subsurface drainage, and two types of controlled drainage. One soil was much more responsive to water management than the other. For the more responsive soil, improved subsurface drainage reduced surface runoff by 192 mm/year (66%) but raised out-flow by 40 mm/year (10%). Large daily flows (>25 mm/day) accounted for only 11 mm/year of flow from an improved subsurface drainage system versus 31 mm/year from a conventional drainage system. Controlled drainage moderated the effects of improved subsurface drainage. Water management did not alter the likelihood of very large (>10-year return period) runoff events on either soil. A three-year return period event was similated for the Wasda soil on different-size watersheds. Compared to conventional drainage, improved subsurface drainage reduced peak runoff from 101 to 28 mm/day on a 8.1-ha field, from 68 to 20 mm/day on a 130-ha watershed, from 30 to 15 mm/day on a 1,030-ha watershed, and from 20 to 13 mm/day on a 6,216-ha watershed.