Surface Soil Moisture within a Watershed—Variations, Factors Influencing, and Relationship to Surface Runoff

Abstract

Surface soil moisture was measured within the upper 15 cm using neutron‐scattering equipment on six soil series within a 57.8‐ha Pennsylvania watershed during the 19 May to 11 Nov. 1971 period. Surface soil moisture was responsive to individual storm events, showed discernible seasonal trends, and displayed larger fluctuations at higher moisture levels than at lower moisture levels. An analysis of variance showed that well‐drained soils had significantly different surface soil moisture levels than the more poorly drained soils and could be grouped into a hydrologic unit distinct from the more poorly drained soils. Surface soil moisture measurements along parallel transects approximately perpendicular to the slope contours showed high surface soil moisture contents proximal to the stream indicating that these areas contribute more to surface runoff in a shorter period of time than areas distant from the stream channel. Multiple regression equations using pan evaporation and surface soil moisture for each soil series were used to show the relative importance of the internal soil drainage class in predicting surface runoff.