RIGHTING PAST WRONGS – A GEOLOGIC JUMP-START FOR COLD BROOK

As it flows from the flank of Haystack Mountain to its confluence with the North Branch Deerfield River, the otherwise steep Cold Brook passes through a wide, flat valley in Wilmington, Vermont. The tendency for its gravel and cobble bedload to accumulate there made the site a prime target for gravel extraction operation during the 1980s and 1990s. Previous owners took advantage of this depositional environment and excavated two large ponds on the valley floor, artificially altering the course of Cold Brook to facilitate mining operations. When mining ceased, the ponds eventually captured the brook, creating large open-water reaches that resulted in increased water temperatures and negative impacts to the downstream aquatic biota.

Mount Snow Resort acquired the property that included the ponds to construct an off-line reservoir for snowmaking water supply at an adjacent, upland location. While working with state and federal regulators to obtain permits for the reservoir, Mount Snow became aware that these former gravel ponds were negatively impacting water quality in Cold Brook. In partnership with these regulators, Mount Snow made plans to use the equipment and spoil materials available from the reservoir construction and engaged in a unique landscape-scale restoration effort that included filling the larger of the two ponds and shaping a pilot channel for Cold Brook. This effort would effectively provide the valley with a geologic jump-start to improve water quality and restore downstream sediment transport.

The work was substantially completed in 2016 and an upstream diversion berm was left in place to give the filled pond time to revegetate. After high flows in 2017, the Brook naturally breached this berm, activating the pilot channel and the adjacent floodplain, and restarting the process of bedload transport through the reach. Although a single-thread system is present upstream and downstream from the project site, the wide and gradual slope of the reach will likely result in the return to an active braided-channel system and wetland complex. In addition, water quality and temperature and floodplain wetland habitat are expected to substantially improve. Annual monitoring will be performed to evaluate channel stability and document the resilience of the system to future flooding events.