Hydrologic modeling of a drained pine plantation on poorly drained soils
Three experimental watersheds in eastern North Carolina have been continuously monitored since 1988 to study long-term hydrology of loblolly pine (Pinus taeda L.) forests on poorly drained soils. This study was conducted to test the forestry version of an agricultural hydrology model DRAINMOD with 10 yr (1988-1997) of data collected at one of these watersheds under conventional (open ditch) drainage. The model, which is based on hourly water balance for the land between parallel drainage ditches, simulates interception, evapotranspiration (ET) as the sum of canopy transpiration and soil evaporation, 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 average of 0.4%. Errors in measured flow rates during weir submergence, missing rainfall and weather data, and uncertainty in estimates of stomatal conductance contributed to the differences between model predictions and field observations. It was concluded that the model is a reliable tool for assessing hydrologic impacts of silvicultural and water management treatments, as well as climate changes, on these pine stands.