EXPERIMENTAL DETERMINATION OF THE HYDROLOGIC COMPONENTS OF A DRAINED FOREST WATERSHED

Abstract

ABSTRACT This study was conducted to develop a better understanding of the hydrology in a drained forest. Data collected from a field study on an intensively monitored forest watershed are presented to describe the system's hydrologic components. The watershed is a 15-year-old loblolly pine (Pinus taeda) plantation located in the coastal plain region of North Carolina. The site is characterized by shallow water table soils (thermic typic umbraquults) which are drained with open ditches about 100 m apart. Water balances based on field measurements were conducted for various time frames during the two-year study period. Closure errors for the water balances were typically within 10% for longer time periods. Hydrologic components with characteristics unique to forest watersheds, including canopy interception loss, soil drainage, and forest evapotranspiration, were analyzed by examining different interactions among vegetation, soil, and meteorology. Canopy interception loss was measured to be up to 35% of the gross precipitation for unthinned stand conditions. Soil drainage was measured to be 42% of the gross rainfall in the winter and early spring months. For the water balances calculated, average evapotranspiration rates ranged from 1.4 mm/day for winter months to 4.1 mm/day for summer months. The field data and analysis procedures adequately described the hydrologic components of the forest system.