Estimating historic water table fluctuations in coastal plain soils using a hydrologic model and hydric soil indicators

To determine whether a soil is in a wetland or whether it is suitable for a septic system, we need to know the frequency and duration that a water table comes within a certain distance of the soil surface. The objectives of this study were (1) to use DRAINMOD to predict water table fluctuations at two sites on the NC Coastal Plain, (2) to correlate the redoximorphic features and saturation index at two sites, and (3) to compare the relationships obtained at two sites. The study was conducted along a soil catena at each site. There were 21 plots established at two sites. Water table levels, redox potentials, redoximorphic features, and other soil data were determined at each plot.; The drainage parameter inputs in DRAINMOD were adjusted to account for soils with different landscape positions. Forty years (1959--1998) of historic weather data were used to simulate the historic water table fluctuations in each plot. Simulations were made during four periods for six depths. Saturation index was correlated with redoximorphic features by simple linear regressions.; Percentages of redox depletions were highly correlated with saturation index with most R2 values were above 0.90. Most R2 values were >0.93 when redox depletions and concentrations were correlated with saturation index. The relationships obtained at two sites are slightly different. When data for both sites were combined, however, the R2 values were above 0.93 for correlations between saturation index and redoximorphic features. All these relationships are expected to be useful in estimating the hydrology using soil colors in soils in other areas on NC Coastal Plain.