48 Landscape and Hydrologic Response and Recovery from Watershed Disturbance (Posters)

Tuesday, 22 March 2016
1:30 PM - 5:30 PM
Convention Hall

FIVE YEARS AFTER THE FLOOD: ANALYSIS OF A RIVER TWICE-RESTORED IN THE DEERFIELD WATERSHED

Paper number: 48-5
Program: Theme Sessions
Time: 1:30 PM – 5:30 PM

Authors

Abstract

River restoration is a growing industry that uses expertise in hydrology, geomorphology, and ecology. However, its practices vary in objectives and projects do not necessarily follow uniform guidelines. River restoration is often performed in response to floods, as was case in New England following Hurricane Irene. The Chickley River in the MA Deerfield River Watershed underwent 5.1 miles of channelization in 2011 and subsequent restoration in 2012. The channelization, somewhat of a return to conditions when the USACE channelized the river 50 years ago, was found by the MassDEP to have caused extensive habitat destruction. In 2012, the Chickley River underwent restoration with a focus on natural river design, including planting trees, filling channelized locations, and placing large woody debris (LWD). This study examines the Chickley River’s geomorphic and habitat at post-Irene (2011), post-channelization (2011), post-restoration (2012), three years post-restoration (2015) conditions. Channel stability was computed at three cross sections. After channelization, the Shields parameter exceeded 0.05, indicating channel instability. After restoration, the Shields parameter was approximately 0.05 at all cross sections, suggesting channel stability. Changes (<15 cm of erosion/deposition) were observed in channel dimensions. GIS analysis of vegetation indicated the average width of canopy opening above the channel was 5.8 m in 2009 (pre-Irene), 12.3 m in 2011 (post-Irene/pre-channelization), and 17.5 m 2014 (post-channelization). This demonstrates notable reductions in riparian cover due to Irene and channelization, and that restoration planting has so far had little effect on riparian cover. Aerial photo analysis shows that LWD increased due to Irene in the form of large log jams of >50 logs spaced at ~1 per km. Channelization removed nearly all LWD and restoration replaced LWD with log jams of 3-5 logs. These observations show that channelization reduced channel stability, riparian cover, and LWD. Restoration improved channel stability relative to the channelized conditions, but did not restore LWD or riparian vegetation to pre-channelization conditions. This study can be applied to better understand a recent shift in river management to consider ecological and geomorphic conditions.

Geological Society of America Abstracts with Programs. Vol. 48, No. 1

doi: 10.1130/abs/2016NE-271668

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