In Bennington, Vermont,
Milone & MacBroom, Inc. has been working with the Town and State to design
and construct a floodplain restoration project to reduce flood and erosion
hazards along the Roaring Branch. The channel is located on an alluvial
fan and consists of large coarse sediment deposits and a braided channel that
is highly dynamic. The river has a history of flooding and has been repeatedly
confined with beams in an attempt to control the river and reduce the extent of
flood damage. This strategy has energized the channel during floods that
mobilize the coarse bedload and cause excessive sedimentation at bridges.
Hydrology, hydraulics, and
sediment transport analysis were performed using LIDAR, survey, and HEC-GeoRAS.
A combined approach was selected as the preferred alternative where floodplain
creation established sediment deposition areas upstream and away from a bridge,
and removal of existing sediments at the bridge helped the channel towards a
more natural sediment regime.Fifteen hundred feet of the floodplain has currently been
restored and additional phases of the project are planned for the next
construction season in 2011.