Role of Soils in Landscape Hydrology of a Forested Catchment

The value of detailed soil mapping includes an understanding of water flow paths and soil depth variation over the landscape. Mapping the fabric of soils over a catchment and characterizing soil layering helps the interpretations of the spatio-temporal organization of soil moisture, landscape-scale preferential flow pathways, and their relationships with catchment hydrology. We used this hydropedological approach to investigate soil moisture patterns at multiple depths in a 7.9-ha forested catchment in central Pennsylvania. A total of 73 sites were monitored from July to December 2004 using Time Domain Reflectometries, tensiometers, pizometers, thermocouples, observation wells, rain gauges, and a stream gauge. Soil distribution and topographic metrics were correlated with the observed soil moisture patterns to reveal the relationships with soil type, depth to bedrock, topographic wetness index, slope, precipitation, and stream discharge. Four main flow pathways downslope were identified in this V-shaped forested catchment, i.e., subsurface macropore flow, subsurface lateral flow at A-B horizon interface, return flow at footslope and toeslope, and flow at the soil-bedrock interface. There were complex interplays between soils and topography in this steep terrain. Time series data showed quick stream flow responses to precipitation forcing in the catchment, indicating the rapid movement of water within the catchment into the stream channel. We developed a conceptual model of the hillslope hydrology that elaborated the patterns of soil moisture distribution along the hillslope and within different soil profiles in the catchment. This conceptualization enhances the understanding and modeling of preferential flow dynamics at the catchment scale, particularly with regard to the role of detailed soil mapping and lateral flow in hillslope hydrology.