Editor’s Note: This is the second of three posts celebrating the work of local and State partners to restore and protect the waters of Plymouth and Ludlow.
Prior to Tropical Storm Irene, Vermont’s Watershed Management Division (WSMD) knew about a steep v-shaped ravine with exposed dirt ledges, bare rocks, and tumbled trees about one-third of a mile upstream from Route 100. When Tropical Storm Irene dropped more than eight inches of rain over the 1.2 square miles of drainage basin, the raging water carried excessive sediment down the ravine before meeting the relatively flat valley of the Black River at Route 100 and then flowing into the Black River downstream.
The floodwaters carried an enormous load of debris, sediment, and rocks of various sizes, closing large sections of Route 100, damaging homes, and inundating large areas of floodplain. The largest debris dropped out of the flood waters, while the finer sediments were carried further downstream, into Lake Amherst, Round Pond and Lake Rescue.
In addition to needing to address the heavy sediment load in the Lakes, there was an immediate need to reopen Route 100. Following the storm, cleanup required removing the tonnage of silt, sand, rock and gigantic boulders that were barricading Route 100. The material was removed, and the brook was dug deep, with high banks. The result was a channel that carried water straight as an arrow across the flat plane before entering the Black River. The dredging meant that without any meanders (curves) to slow the flow, even a small summer storm of one-half inch rainfall could generate significant turbidity (muddy water carrying sediment) in Money Brook.
The severity of the landslide erosion, and the very steep 20 percent grade of terrain made stabilization of the ravine difficult to rehabilitate. In the spring of 2012 WSMD staff hiked up to the site where most of the erosion was originating. The elevation was 1200 feet, and the ravine was 800 – 1000 feet long and 75 – 100 feet high. The slope of the failing bank was nearly vertical in places, and the soil was comprised of material left behind when glaciers retreated, abundant with boulders, cobbles, and pebbles in a silty-sand matrix. It was determined that this ravine would continue to erode, even with remediation (planting trees and grass) and the solution for stopping sediment transfer would need to be found downstream.
During the winter of 2014, 800 dormant live willow stakes about one-half to two inches in diameter and one-to-two feet long were cut, bundled together and hauled up to the steep ravine for planting to help stabilize the ravine walls. 40 pounds of conservation mix seed was broadcasted, with the expectation that native grasses would spread in following years, filling in between willow stakes. By November 2015 the planting was complete, and winter arrived. In the summer of 2016, WSMD staff confirmed that the willow stakes had sprouted new shoots and the conservation seed mix was a soft green carpet of growth in the barren ravine.