RAINFALL, FLOOD MAGNITUDE, AND GEOMORPHIC IMPACTS OF TROPICAL STORM IRENE ON THE WHITE RIVER WATERSHED, EAST-CENTRAL VERMONT
The headwater tributary reaches are transport-dominated, cascade or step/pool channels. During TSI, woody debris and sediments were mobilized from these tributaries and gullying, streambank erosion, landslides, headcutting of channels, and debris jams were widespread. Roads, bridges, culverts, and homes in the narrow tributary valleys were heavily damaged and in many cases, destroyed.
Along the mainstem above Bethel the valley bottom is relatively broad, but historic channel incision and channel and floodplain alterations had reduced floodplain access. In unconfined reaches, extensive areas of the floodplain surface and low stream terraces were overtopped. Vast sheets of sand and gravel were left behind on these surfaces. Woody debris was deposited as individual pieces stranded in the channel and on the floodplains and terraces, as debris jams at obstructions, and as woody debris ramparts up against the trees at the edges of floodplains and low stream terraces. Scour was severe at valley pinch points, but even in reaches with floodplain access the channel was scoured and widened. Large landslides occurred along the mainstem, many of which appear to have been reactivated.
The Lower WR from Bethel to Hartford has a relatively confined channel, which resulted in very high flood stages. Channel widening there was limited due to extensive bedrock exposures.