WATERSHED AND REACH SCALE RESPONSE OF VERMONT STREAMS TO TROPICAL STORM IRENE

In 2011, Tropical Storm Irene inundated New England watersheds with up to 28 cm of precipitation over two days, generating unprecedented regional flooding with many USGS gages documenting the largest flood of record. Previous research indicates that geomorphic impacts of extreme flood events may vary by reach due to differences in slope, reach geometry, extent and type of vegetation, and the presence of pre-existing bank failures, among other variables. However, ascertaining which geologic and geomorphic variables exert the most control on channel response to extreme floods remains poorly constrained. Taking advantage of this extreme event and the subsequent post-Irene period, we attempt to quantify and interpret the immediate geomorphic response and longer-term recovery of stream channels in southwestern Vermont using a combination of remote sensing and field measurements to capture the magnitude, rate, and location of change. We compare pre- and post-Irene lidar to identify the geomorphic change- erosional and depositional- at high resolution (1m to 3m) and on regional scales. Initial assessment of impacts shows extensive erosion along both straight reaches and channel bends, channel widening up to 36%, formation of new bars, and widespread activation of channel-adjacent landslides. This research contributes theoretically to the role of extreme floods on landscape form and the overall geomorphic effectiveness of rare floods. Moreover, these findings will ultimately help guide efforts to predict the location and type of channel responses to catastrophic events.