Restoring Great Bay Marshes

Why are we considering restoration options for these marshes?

Squeezed between rising seas and landward development, many of Great Bay’s tidal wetlands, including salt marshes, are in danger of disappearing. As sea level rise accelerates, we are increasingly noticing signs that our marshes can’t keep up. The seaward edge of many marshes are eroding and the natural pools of water on a marsh platform are growing, drowning out plants and leaving bare patches of mud. As marsh grasses become more sparse they can no longer hold marsh soils in place which can lead to additional subsidence and erosion.

In addition to the impacts of sea level rise and coastal storms, we also see the legacy effects of early farming in our marshes. Colonial settlers to the seacoast farmed nearly all of our salt marshes, creating berms to limit flooding and digging ditches to better drain the marshlands and make it easier to harvest the grasses and other crops. Unfortunately, these berms and ditches continue to affect the natural movement of water onto and off the marsh, making the marsh more vulnerable to the impacts of rising seas.

The restoration project team is carefully studying each of our focal marshes to identify impairments and priority locations for interventions.

What type of restoration work is being considered?

Fortunately, there are several techniques that can be implemented to gradually restore a more natural marsh hydrology, help a marsh rebuild its elevation and allow plants to revegetate bare patches. For example, at marshes in Hampton and Hampton Falls, a team is restoring a natural drainage pattern as explained in this story map – Building Coastal Resiliency at Two NH Audubon Salt Marshes.

We are too early in the planning stages for Great Bay marshes to know which techniques will be most appropriate for each site, but here are some of the strategies being considered:

• Single channel hydrology: Establishing a primary creek channel with small tributaries in order to promote natural drainage patterns, reduce inundation, and promote revegetation of salt marsh grasses. This overarching approach often involves techniques such as runnelling and ditch remediation.
• Runnels: Shallow channels constructed to help drain standing water off the marsh surface and allow for vegetation regrowth.
• Ditch remediation: Adding natural substrate to a clogged or collapsed ditch to reduce standing water that promotes water logging and marsh subsidence. The facilitated sedimentation allows for revegetation and peat development.
• Thin layer placement: Addition of a thin layer of sediment onto a subsided portion of marsh platform in order to increase elevation in relation to sea level and promote revegetation.
• Remove barriers to marsh migration: This could include re-grading the slope in the marsh transitional area, selectively thinning trees, or removing tidal restrictions such as undersized culverts, legacy berms, and managing phragmites stands.
• Living shorelines: Creation of a shoreline with natural materials such as vegetation, sand, oyster shells, rocks, or even tree stumps, in order to dampen wave energy and stabilize marsh eroding edges.
• Other actions: Depending on a site’s needs, this could include sediment mounds for sparrow nests, seeding or planting of select native marsh species, altered freshwater drainages, managing invasive species, etc.

Which factors go into planning a restoration project?

The restoration team is committed to a comprehensive planning process that includes site specific monitoring and conversations with the people that use and value each site. Our goal is to protect and sustain the attributes of the marsh that are important to people, wildlife and the Great Bay ecosystem. By talking with neighbors, bird watchers, anglers, boaters and hunters we can better understand the unique values and history of the site and minimize potential impacts on recreational use or an important plant or animal. 

We are lucky that there is a whole community of scientists that are eager to learn about how to best restore marshes in this part of New England. Our team is currently studying each site so that we can plan tailored habitat improvements and then track changes at the site. We hope to use some of the sites as demonstration projects that other practitioners can learn from over time. Learn more about Great Bay Reserve’s habitat science, monitoring and land management work.

Learn more about each location

The restoration team is currently studying eight marshes around Great Bay, developing summaries of local impairments and creating potential restoration plans. As information about each site becomes available, we’ll add links here.

Share your ideas for these marshes and receive updates from the team by completing this short survey.