by Kristen Leahy
HARDWICK – Over the past few weeks I’ve written about Jackson Dam, the sediment that has accumulated behind it, and the reality that rivers and infrastructure do not remain frozen in time. One of the questions that naturally follows is simple: what happens when a dam is removed or significantly altered?
Many people picture an empty basin or a sudden transformation. In reality, river systems tend to adjust more gradually.
Behind most older dams, decades of sediment have accumulated. Sand, gravel and finer material carried downstream during storms settle out where the water slows. Over time, that material builds up and reshapes the impoundment.
If a dam is eventually removed or lowered, the river does not suddenly disappear into a void. Instead, it begins to reestablish a channel through those accumulated sediments. The process is influenced by flow, slope and the shape of the valley, but the river generally finds a path like the one it occupied before the structure was built.
As that channel forms, the surrounding sediments begin to stabilize. Vegetation quickly takes root in exposed areas. Grasses, willows, and alders often establish themselves first, helping hold soil in place. Over time, the landscape can begin to resemble a natural river corridor rather than an open impoundment.
Floodplains also begin to function differently. Instead of water backing up behind a structure, flood flows can spread across low areas of the valley during larger events. That ability to spread out reduces pressure and energy within the channel while allowing sediment to move through the system more naturally.
The timeline for these adjustments varies from place to place. In many projects, the transition happens over several seasons or years as vegetation grows and the river settles into a new equilibrium. Engineers and river scientists often phase changes carefully so sediments stabilize and downstream areas are protected during the adjustment.
Wildlife often responds quickly to these new conditions. Flowing water, wetlands and vegetated floodplains support a wide range of birds, fish, amphibians and insects. In many restored river corridors, biodiversity increases as habitats diversify.
All of this is why projects involving dams tend to involve careful planning and sequencing. The goal is not to force the river into a new shape, but to allow natural processes to reestablish a more stable channel and floodplain.
In Hardwick, the Jackson Dam study is helping the community understand what those processes might look like in this particular reach of the Lamoille River.
The work so far has focused on gathering information: how much sediment has accumulated, how flood flows move through the reach today and what options might exist for the future.
Those questions will take time to answer fully. They also involve more than engineering. They involve how a community thinks about the landscape around it and how that landscape may continue to evolve.
Rivers have always reshaped their valleys. The question communities face is how thoughtfully they guide that change when aging infrastructure and changing river conditions meet.
Kristen Leahy serves as the zoning and floodplain administrator and the resilience and adaptation coordinator for the Town of Hardwick.
