Soil Morphology and Water Table Relations: I. Annual Water Table Fluctuations

Abstract

AbstractWater table positions with respect to the soil surface and precipitation were measured daily over a 2‐year period at representative sites of five soil series comprising the Willamette association of nearly level soils with good to poor natural drainage. All soils had water tables present for some period during the winter. Perched water tables were present near the surface of the two most poorly‐drained series most of the winter.A mathematical model was developed for predicting water table positions on the basis of rainfall input and soil physical characteristics. The model was calibrated with measurements made during the 2 years and then used with rainfall data from the previous 29 years, to reconstruct water table positions as they had occurred in the past. The computer procedure did not apply to the two poorly‐drained series because of the presence of an impermeable soil horizon (clay B) near the surface. However, water table positions of these series were estimated satisfactorily by correlation with water table positions on the better‐drained series. The average percent of time the water table was above a given level during each month, calculated for the period of 1929 to 1957 showed that for a specific depth and month, the percent of time the water table was above a given level increased as the natural drainage conditions became poorer. The percentages for the 30.4‐cm depth during April for example were 1.8, 15.4, 66.7, 81.5, and 92.0, respectively, for the five series. Thus, particular water table regimes are associated with drainage conditions of specific soil series.