Sediment Movement and Knickpoint Behavior in a Small Piedmont Drainage Basin

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Abstract
Movement of all sizes of sediment in the channel of a 4.03 km2 drainage basin, Baisman Run, in the Piedmont of Maryland, USA, is episodic. Sediment yield to a forested basin from a headwater agriculture source area of 0.96 km2 averaged 473 tonnes/km2/yr, with silt and clay predominant. This was transported in 20 to 30 events per year constituting 1 percent of the actual 4 year time span. Transient storage in 3.2 km of the second to fourth order channel represented 4–5 years of sediment inflow from the source area during years of relatively low runoff. Sand in patches and gravel (50 mm) moved roughly 5 to 7 times per year, and boulders (300- 600 mm) moved perhaps once every year or two. The proximity of large boulders (gneissic-schist containing much quartz) to bedrock outcrops suggests breakup rather than long distance transport. Headcut retreat at one site (18.2 m in 3 years) and translation of cobble bars en masse over a downstream distance of 4 to 6 channel widths indicates that channel processes are episodic in time and stepwise in space.

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