HYDROLOGY OF COASTAL SANDY SOILS THAT DIFFER BY DRAINAGE CLASS

Abstract

Determination of the hydroperiod of a particular site requires a long period of water table record. On the lower coastal plain hydrology of sites is determined by subtle differences in topography and landscape position. Without vegetational clues, as after plantation establishment, estimation of site hydroperiod becomes even more problematic. Soil classification includes an estimation of drainage class. These classifications are done primarily by noting physical aspects of iron oxide and organic matter. The underlying assumption is that iron oxidation and hydration and organic matter accumulation are a direct indication of long-term average water table depth. A long-term study of water table position on Hobcaw Forest allows examination of the correlation of long- term water table depth to soil drainage class. Hobcaw Forest is located in eastern Georgetown County South Carolina on a Late Pleistocene aged beach ridge with primarily sandy spodosols. Drainage classes of these sandy soils range from excessively well to very poorly. From July 1975 through September 1989 water tables were measured weekly on a grid of 45 shallow wells, distributed across this forest. While all soils displayed a range of water table depths over 150 cm, high temporal correlation allows determination of significant differences in water table depth of wells with averages that differed as little as 5 cm. For the 14 years of measurements, soil drainage class was found to reflect average water table depth. Soil drainage class, combined with taxonomic description, revealed differences of average water table depth that were not significant with less than 4 -5 years of water table measurement.