2.1 Study area
The forested Shale Hills catchment has an area of 7.9-ha, and is located in Huntingdon County, PA, on the eastern coast of the USA. The catchment is V-shaped overall, with a first-order stream in the valley and moderately steep slopes (up to 25%–48%) on both sides of the stream (Fig. 1). Swales are inter-dispersed within the catchment, with five on the south-facing slope and two on the north-facing slope. Elevation ranges from 256 m at the outlet of the catchment to 310 m at the highest ridge. The catchment is underlain by approximately 300-m thick, steeply bedded, highly fractured Rose Hill Shale. The soils were formed from shale colluvium or residuum, with many channery shale fragments throughout most of the soil profiles. Five soil series were identified in the catchment according to the USDA classification (Takagi et al., 2011; Fig. 2). The Shale Hills catchment has a typical humid continental climate, with mean monthly temperatures minimum of −3°C in January and maximum of 22°C in July, and an annual precipitation of about 980 mm (National Weather Service, State College, PA). The precipitation is roughly evenly distributed throughout the year, during the summer months typically occurs in convective weather fronts that can produce high intensity, short duration storm events.