September 26, 2019
Did you know that one of the reasons Hinesburg’s current water quality is only in fair condition is historic activities, such as the straightening of channels, creating berms next to streams, and building or filling in next to streams? This caused water in streams to move faster, which in turn caused down-cutting (the stream’s channel getting deeper by removing material from the stream’s bed). Erosion then occurs along stream banks, which adds sediment to the stream (and eventually, downstream sites like Lake Champlain). Erosion often continues working its way upstream. When the stream channel is deepened like this (and berms are created to keep the water in), water from flood events can’t spread out onto the natural floodplain, which would naturally allow the water to drop the sediment before carrying it downstream.
So, what does all this have to do with water quality? Our area was once part of the old Lake Vermont and Champlain Sea, which had clay soils deposited post-glaciation. Clay soils limit infiltration and increase runoff. Past agricultural practices added phosphorus to the soil (fertilizers to help plants grow). Phosphorus never “disappears” out of the water or ground. It can be taken up by plants, but eventually returns to the soil or water. It can bind to soil and sediment particles. When flooding takes these sediments (with phosphorus attached) downstream, they may end up in Lake Champlain, which can contribute to toxic blue-green algae blooms and fish die-offs. If the LaPlatte River becomes deemed “impaired,” it will put town taxpayers on the hook for costly mitigation efforts.
The Hinesburg Town Garage site, adjacent to Beecher Hill Brook, contained impervious surfaces, buildings, heavy equipment activity, berms, fuels and open gravel pits. Beecher Hill Brook drains into the LaPlatte River, which flows through Hinesburg under Silver Street near the Hinesburg Community School, then on under Charlotte Road behind Hinesburg Town Hall, and from there through Charlotte and Shelburne to Lake Champlain. The Vermont Ecosystem Restoration Program funded studies in 2007 and 2008 that showed Beecher Hill Brook as incised and disconnected from its historic floodplain due to berming, nearby buildings and fill, channel straightening, and subsequent down-cutting and river bank erosion. Berm removal and floodplain reconnection at this site were recommended in numerous past studies. 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 & MacBroom in cooperation with the town of Hinesburg. A 2019 ERP grant will allow this floodplain restoration to be constructed! This will help reduce sediment inputs to Beecher Hill Brook, the LaPlatte River and eventually Lake Champlain, thereby improving water quality.
In 2018, the town of Hinesburg passed a bond vote for redevelopment of the site, and Town Garage buildings were removed from near the brook area last fall. LCA, in conjunction with the town of Hinesburg and engineers at Milone & MacBroom, have selected a construction contractor, and work is slated to begin in September 2019 to continue until July 2020. Construction will involve installation and maintenance of erosion and sediment controls, excavation of earth fill and hauling to an upland location onsite, installation of heavy stone fill, installation of channel bed raising features (rocks and logs), planting of trees and site restoration.
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. The removal of fill will reduce future down-cutting and erosion and avoid de-stabilizing the North Road culvert (just upstream).
The Beecher Hill Brook floodplain restoration project is part of LCA’s Ahead of the Storm program, which aims to showcase a range of landscapes and land uses and a variety of optimal conservation practices that mitigate stormwater flows, and to be more flood resilient in an effort to improve water quality in an ever-changing climate. For more information on the AOTS program, visit www.lewiscreek.org/ahead-of-the-storm.