Hydrologic modeling of drained forested lands

Hydrologic data collected for a four-year (1988-91) period from three experimental watersheds in Carteret county, North Carolina were used to determine water balance components of a drained loblolly pine forest. The effects of weir treatment for controlled drainage on Watersheds 2 and 3 were to reduce drainage volumes as compared to Watershed 1 under free drainage. Sensitivity of evapotranspiration (ET) and interception losses to Leaf Area Index (LAI) and stomatal conductance parameters were demonstrated.; Testing of modified DRAINMOD (McCarthy, 1990), the field scale model for drained forested lands, with four years (1988-91) of data for these three watersheds yielded good results. The predicted mean annual drainage outflow was in excellent agreement with observed data. The results showed that the two years of measured data for controlled drainage did not adequately represent the wide variation in weather and thus the range in hydrologic impacts that would occur at this location.; The field scale model for drained forested watershed was coupled with the channel and stream routing component of the medium scale agricultural water management model (Konyha, 1989) to develop a watershed scale model for drained forested lands. The model was tested on a large and a small watershed with five years (1988-92) of data collected at the Cozier Tract in Carteret county, North Carolina. Three methods were used to predict ET: the Penman-Monteith ET method with two different stomatal conductance submodels and the Thornthwaite method. All three methods resulted in better predictions for the larger watershed than for the smaller one. Effects of ET on monthly outflows due to errors in estimating LAI of a 5-year old loblolly pine stand during the growing season were presented and discussed.; The model performance in predicting hourly event hydrographs was excellent for some events and only satisfactory for others. Most of the discrepancies between the observed and predicted data were attributed to errors in rainfall input data and weir submergence during the larger events. Errors as affected by the complex interaction of the diurnal pattern of stomatal conductance, vapor pressure deficit, net radiation and root zone water were recognized as a possible major source of concern in modeling the transpiration process and the field hydrology. (Abstract shortened by UMI.)...