Suffolk shouldn't rush to rebuild two failed dams

The dam failures that occurred in Blydenburgh County Park and Stony Brook last month were a sobering reminder of the mounting impacts of our changing climate. In the wake of the storm’s devastation, calls to quickly repair the dams are understandable; the lost ponds were valued community resources that have been part of the landscape for hundreds of years.

However, we urge public officials to carefully weigh all factors before deciding on a path forward. While there may sometimes be unique justifications to rebuild dams, there are generally strong reasons — fiscal, resilience and ecological — to instead allow the streams to return to their natural free-flowing state.

In most cases, the broadest public interest is served by letting streams run free.

Regarding fiscal impacts, the cost of rebuilding and maintaining a dam greatly exceeds the cost of letting the stream flow. Dams — originally built to power gristmills, harvest ice, grow cranberries, etc. — create silt in which grows submerged aquatic vegetation, requiring ongoing costs to maintain open water, pond views, and opportunities for boating and fishing. Such efforts, which usually involve dredging or herbicides, are expensive and rarely more than temporary "solutions."

In terms of resiliency, healthy waterways are more able to adapt and support resilient landscapes and communities. This includes withstanding storms that a changing climate will increasingly bring to Long Island. Put simply, naturally flowing streams are more resilient than those that are dammed and constrained. These streams and their associated wetlands and floodplains are "natural infrastructure" that provide cost-effective resiliency by capturing, retaining, and filtering stormwater and modulating floods.

Dams, by their very nature, create resiliency risks by impounding millions of gallons of water upstream from homes, businesses and public infrastructure. The risk of dam failure and the high cost of guarding against it is a major reason dams have been coming down across the country. Long Island’s relatively small dams generally don’t rise to the level of being considered "high-hazard," but our recent experience might change the way we think about the risk.

From an ecological perspective, there are rarely good reasons for repairing failed dams. Before Long Island’s waterways were dammed to form mill ponds, they flowed freely for thousands of years. These streams were an integral part of our coastal ecosystem, providing a critical avenue for the movement of sediments, nutrients and wildlife between fresh and saltwater. Significantly, dams block the movement of migratory fish, including alewife and American eel, that provide important forage for a wide range of species, from whales to osprey to striped bass. Dams create warm-water habitat that favors nonnative species, and degrade the overall ecological health of rivers and streams.

While a failed dam initially leaves a muddy mess, it doesn’t last long. Within months, as the pond basin dries, the natural restoration process commences. Native plants grow and form a riparian meadow that buzzes with the activity of insects and birds. Invasive species sometimes have to be managed, but if left alone such sites eventually become native riparian forests. These woodlands provide important wildlife habitat, fight climate change by sequestering carbon, and increase resiliency by buffering winds and holding on to soils.

Rebuilding failed dams may occasionally make sense, but in most cases allowing rivers and streams to revert to their natural state will help make the region and its coastal ecosystem more healthy, resilient and sustainable.

This guest essay reflects the views of Enrico Nardone and John Turner, executive director and senior conservation policy advocate, respectively at the Seatuck Environmental Association, a nonprofit dedicated to conserving Long Island wildlife and the environment.