Sediment-trapping by Beaver Ponds in Streams of the Mid-Atlantic Piedmont and Coastal Plain, USA

The effect of beaver ponds on sediment deposition is undocumented in the Piedmont and Coastal Plain of Virginia and North Carolina. We used 3 methods to examine sedimentation: 1) depth-integrated base-flow sampling, 2) repeat channel-surveys, and 3) sediment-accumulation pads. During base flow, Piedmont ponds exported sediment and Coastal Plain ponds had little or no effect on downstream suspended-sediment concentration. Most ponds accumulated sediment within the channel until dam breaching. Ponds inundating the floodplain trapped more sediment. Ponds of varying configuration trapped sediment differently. Mean floodplain accretion rates in these beaver ponds (2002-2003: 20 mm/yr 2003-2005: 15 mm/yr) greatly exceeded the mean deposition rate of similar unimpounded streams in these areas. Intact Piedmont ponds trapped 11 m(3)/yr on the floodplain and 77 m(3)/yr in the channel. Intact Coastal Plain ponds trapped 107 m(3)/yr on the floodplain and 8 m(3)/yr in the channel.