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.