Impact of flow regulation on near-channel floodplain sedimentation

Rates and the spatial extent of near-channel floodplain sedimentation on regulated and unregulated reaches in two upland rivers in central Vermont, U.S.A. are measured using the short-lived fallout radionuclide 210Pb. We find consistent profiles of 210Pb inventories across all sites; inventories are low immediately next to the channel, increase to a peak value as the inundation frequency decreases and then asymptotically diminish with distance from the channel to the equilibrium inventory associated with atmospheric deposition alone. We infer from our data that flow regulation has impacted sediment deposition to floodplains below the dam; total sediment deposition is less and it is constrained to a narrower band immediately along the active channel. Flow regulation does not appear, however, to impact the general form of the 210Pb inventory profile, suggesting a uniformity of process across regulated and unregulated floodplains.