A portable 6-inch diesel-powered trash pump was used to pump water from Little Topashaw Creek for gully erosion tests February 4 and 5, 2002.

Flow rates were controlled by adjusting the throttle on the diesel engine. The pump discharged into a fire hose. During the final test, a second pump was used to pump water from a small slough on the floodplain to achieve the desired discharge (~170 L/s).

The fire hose discharged into an 18-inch diameter poly pipe that carried the water into an open channel lined with plastic.

The open channel discharged into a small the retention basin at the top of the gully.

The water flowed from the retention basin into the gully, which was planted with hedges of switchgrass two growing seasons prior to the test.

An acoustic Doppler flow meter recorded flow depth and velocity in the open channel.

Readings from the acoustic Doppler logger were used to control the pump speed and thus the inflow rate.

Continuous records were obtained for turbidity at the upstream and downstream ends of the grassed gully, and four additional Doppler loggers recorded flow depth and velocity. The black cylinder on the left is the turbidity probe, and the gray box on the right is the Doppler logger.

Hydraulic conditions in the bottom of the vegetated gully during one of the flow tests. The black geotextile is a “silt fence” placed shortly after switchgrass hedges were planted to support the plants during the period of establishment.

Flow from right to left. Switchgrass hedge on left. Typical data from Doppler logger shown on inset plot.

Although the grass hedges provided good control of erosion within the gully proper, they were not adequate to control erosion at the ~1.5 m headcut that was located at the mouth of the gully where it emptied into Little Topashaw Creek channel.

The erosion of this headcut was to have been limited by deposition within a large woody debris structure placed on the outside of the bend in Little Topashaw Creek where the mouth of the gully was located. However, the deposition in the woody debris structure was not high enough to provide control.

Hedges performed better in the steep upper slope of the gully near its head. Wire survey flags were used to establish water marks during peak flow which were later surveyed.

Failure of hedge at gully mouth during final test. Maximum discharge was about 0.2 m 3 /s.