HYDROLOGY OF A DRAINED FORESTED POCOSIN WATERSHED

In order to assess the effects of silvicultural and drainage practices on water quality it is necessary to understand their impacts on hydro logy. The hydrology of a 340 ha artificially drained forested watershe d in eastern North Carolina was studied for a five-year period (1988-9 2). Effects of soils, beds and changes in vegetation on water table de pth, evapotranspiration (ET) and drainage outflows were analyzed. Tota l annual outflows from the watershed varied from 29 percent of the rai nfall during the driest year (1990) when mostly mature trees were pres ent to as much as 53 percent during a year of normal rainfall (1992) a fter about a third of the trees were harvested. Annual ET from the wat ershed, calculated as the difference between annual rainfall and outfl ow, varied from 76 percent of the calculated potential ET for a dry ye ar to as much as 99 percent for a wet year. Average estimated ET was 5 8 percent of rainfall for the five-year period. Flow rates per unit ar ea were consistently higher from a smaller harvested block (Block B - 82 ha) of the watershed than from the watershed as a whole. This is li kely due to time lags, as drainage water flows through the ditch-canal network in the watershed, and to timber harvesting of the smaller gag ed block.