Effects of controlled drainage on storm event hydrology in a loblolly pineplantation

A paired watershed approach was utilized to study the effects of three wate r management regimes on storm event hydrology in three experimental watersh eds in a drained loblolly pine (Pinus taeda L.) plantation in eastern North Carolina. The regimes were: (1) conventional drainage, (2) controlled drai nage (GD) to reduce outflows during spring fish recruitment, and (3) contro lled drainage to reduce outflows and conserve water during the growing seas on. Data from two pre-treatment years and three years of CD treatment with raised weirs at the watershed outlet are presented. CD treatment resulted i n rises in water table elevations during the summer. But the rises were sma ll and short-lived due to increased evapotranspiration (ET) rates as compar ed to the spring treatment with lower ET demands. CD treatment had no effec t on water tables deeper than 1.3 m. CD treatments, however, significantly (alpha = 0.05) reduced the storm outflows for all events, and peak out flow rates for most of the events depending upon the outlet weir level. In some events, flows did not occur at all in watersheds with CD. When event outfl ows occurred, duration of the event was sharply reduced because of reduced effective ditch depth. Water table depth at the start of an event influence d the effect of CD treatment on storm event hydrology.