Hydrologic modeling of a drained pine plantation on poorly drained soils

Three experimental watersheds in eastern North Carolina have been continuou sly monitored since 1988 to study long-term hydrology of loblolly pine (Pin us taeda L.) forests on poorly drained soils. This study was conducted to t est the forestry version of an agricultural hydrology model DRAINMOD with 1 0 yr (1988-1997) of data collected at one of these watersheds under convent ional (open ditch) drainage. The model, wh ich is based on hourly water bal ance for the land between parallel drainage ditches, simulates interception , evapotranspiration (ET) as the sum of canopy transpiration and soil evapo ration, drainage, and surface runoff. Results showed that model predictions of daily water table elevations and flow rates on an average annual basis were within 0.15 m and 0.61 mm, respectively, compared to the measured data . Relative errors on drainage outflow varied from -18% to 23%, with an aver age of 0.4%, Errors in measured flow rates during weir submergence, missing rainfall and weather data, and uncertainty in estimates of stomatal conduc tance contributed to the differences between model predictions and field ob servations. It was concluded that the model is a reliable tool for assessin g hydrologic impacts of silvicultural and water management treatments, as w ell as climate changes, on these pine stands.