The Hinesburg Town Garage site contained impervious surface, buildings, heavy equipment activity, berms and material storage, fuels, and open gravel pits that are adjacent to Beecher Hill Brook, a tributary of the LaPlatte River. The riparian area at the project site was almost entirely impervious, compacted, or barren, and contributed stormwater runoff and sediment to the river channel. The Vermont Ecosystem Restoration Program (ERP) funded studies in 2007 and 2008 that showed Beecher Hill Brook as incised and disconnected from its historic floodplain due to berming, encroachment of buildings and fill, channel straightening, and subsequent down-cutting. Beecher Hill Brook has undergone a range of historic human impacts such as straightening to make space for agriculture and roads, berming to reduce floodplain access to protect nearby fields and infrastructure, and constriction to allow for road crossings. Mass failures are occurring upstream of the Garage site and river bank erosion is occurring locally at the site that has added sediment to the river. Erosion is expected to continue until the channel stabilizes. Berm removal and floodplain reconnection at this site were recommended in numerous past studies.
Floodplain restoration is proposed at the Town Garage site for 2019 to restore a naturally functioning floodplain that will help to reduce sediment inputs and improve water quality. Thanks to a 2018 grant award from the Vermont Agency of Natural Resources to Lewis Creek Association, a final floodplain restoration design was prepared by Milone and McBroom, Inc. in cooperation with the Town of Hinesburg.
The Town of Hinesburg passed a bond vote for redevelopment of the site to move facilities out of the river corridor, the adopted fluvial erosion hazard zone, and the 75-foot buffer area. This grant-funded design to restore the river corridor floodplain relied on the removal of Town Garage buildings, which were removed last month. The hopeful implementation of this project will complement the facility improvement design. Milone & MacBroom, Inc., engineers have worked with LCA on a range of stormwater mitigation and water quality projects throughout the LaPlatte River watershed. The Beecher Hill Brook floodplain restoration project is part of LCA’s Ahead of the Storm (AOTS) program, which aims to showcase a range of landscapes and land uses and a variety of optimal conservation practices that mitigate stormwater flows and be more flood resilient in an effort to improve water quality in an ever-changing climate.
The floodplain restoration will restore the functions and values of a healthy, vegetated riparian corridor, reduce risk to nearby culverts, reduce local bank erosion, and provide a floodplain deposition zone. An active restoration element will include the removal of fill to reduce future incision in the reach and avoid compromising the stability of the North Road culvert.
The improved connection between the channel and floodplain will provide an area for water to slow, sediment to be deposited, and nutrients to be taken up by vegetation. A previous assessment of reconnected floodplains in northern Vermont showed 1,400 cubic yards of deposited sediment and 1.3 tons of total phosphorus over four floods. The sediment deposition rate was 18 cubic yards per acre.
For more information on the Ahead of the Storm Program, visit www.lewiscreek.org/ahead-of-the-storm.