HYDROLOGY OF A DRAINED FORESTED POCOSIN WATERSHED1

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Abstract
In order to assess the effects. of silvicultural and drainage practices on water quality it is necessary to understand their impacts on hydrology. The hydrology of a 340 ha artificially drained forested watershed in eastern North Carolina was studied for a five‐year period (1988–92). Effects of soils, beds and changes in vegetation on water table depth, evapotranspiration (ET) and drainage outflows were analyzed. Total annual outflows from the watershed varied from 29 percent of the rainfall during the driest year (1990) when mostly mature trees were present to as much as 53 percent during a year of normal rainfall (1992) after about a third of the trees were harvested. Annual ET from the watershed, calculated as the difference between annual rainfall and outflow, varied from 76 percent of the calculated potential ET for a dry year to as much as 99 percent for a wet year. Average estimated ET was 58 percent of rainfall for the five‐year period. Flow rates per unit area were consistently higher from a smaller harvested block (Block B ‐ 82 ha) of the watershed than from the watershed as a whole. This is likely due to time lags, as drainage water flows through the ditch‐canal network in the watershed, and to timber harvesting of the smaller gaged block.