Healing the Thousand Cuts: Understanding and Responding to the Impacts of Dams and Roads in the Gulf of Maine

March 30, 2012


by Slade Moore
Biological Conservation


The issue

As our understanding of aquatic systems matures, we’re finding that the connections between our ponds, streams and upland areas are much more than incidental. In fact, the chemical, physical, and biological linkages between these systems are often very important to their character, including their ability to support healthy fish and wildlife populations.

River herring congregate at the outlet of a perched culert on the lower Kennebec River.
Photo by Slade Moore.

When the linkages in these networks are severed or impaired, so too is the “connectivity” on which so much, including species of economic, ecological, and cultural importance, depends.

Since the region’s first major modifications of rivers and streams in the 1600s, impaired aquatic connectivity in the Gulf of Maine has a long history and also a wide range of consequences, not all of which are well understood.

One of the most obvious outcomes happens when physical barriers like dams restrict the flow of water. Regardless of the barrier type, restricting or altogether stopping that flow likewise restricts fish and wildlife access to habitats that support spawning and nursery functions, as well as seasonal refuges from extremely cold or hot weather.

The distance between key habitats necessary for the survival of individual species can range from a few miles to thousands. Impaired connectivity can also limit the mixing of populations, which for some species, raises concerns of lost genetic diversity. Affected species can include not only iconic fish species like Eastern brook trout, but also lesser-known stream dependent organisms, like salamanders and turtles. It’s unlikely we can know the full suite of Maine’s native aquatic organisms that were and continue to be impacted by impaired connectivity, because adequate population trend information is available for only a relatively few species that were historically subject to commercial and resource management interest.

Among these species are Atlantic salmon and river herring (alewife and blueback herring), both of which require open access to marine and freshwater habitats alike, and all of which experienced devastating population declines when barriers blocked their traditional movements to upstream spawning habitat in the Gulf of Maine watershed.

Head Tide dam in Alna, Maine, is representative of dams that block fish passage and impair stream processes.
Photo by Slade Moore.

In addition to blocking the movements of stream organisms, physical barriers that restrict flow also prevent or hinder the physical processes that are essential to creating and sustaining habitat for a range of species. These processes include sediment transport and deposition, movement of woody debris, and tidal flow. Notable changes from native habitat conditions are caused when barriers:

• create impounded, lake-like environments upstream of dams. Among other consequences, these environments can promote shifts in fish community assemblages, hinderingmanagement and/or recovery of native species, such as Eastern brook trout and Atlantic salmon.

• block downstream sediment transport and reconfigure stream morphology downstream of the barrier, limiting  habitat available for spawning, nursery, and other critical life stages of stream-dependent species.

• interrupt tidal flow into coastal marshes, limiting the amount of area that is flooded by the tides. Among other consequences, these changes facilitate the replacement of native tidal marsh plants by plant species to which salt marsh wildlife are poorly adapted.


Until very recently, proposed solutions for correcting impaired aquatic connectivity focused almost exclusively on installation of fish passage structures on dams or dam removal. State databases report about 4,500 dams in the United States portion of the Gulf of Maine watershed. However, more dams exist than the official numbers reflect. For instance, official State of Maine records show 831 dams from the Association of Dam Safety Officials in 2005, which do not include dams that were never registered with the state, such as log drive structures that are long forgotten but continue to act as barriers to connectivity. Most of these dams do not serve their original purposes and relatively few (179) are used to generate hydroelectric power (Whippelhauser 2008).

Dams can block access to all habitats upstream of a given point on the mainstem of rivers and streams. Consequently, for some species requiring access to the marine environment and also freshwater areas far inland (i.e. “diadromous” species), dams have an especially dramatic impact on productivity. A recent study in Maine reported that by the mid-1800s, dams in Maine reduced available alewife spawning habitat (mostly ponds and lakes) to less than 5 percent of the pre-colonial amount (Hall et al. 2010).

These changes precipitated devastating population declines for a host of diadromous species, a fact that was well articulated by fisheries managers of the age, but did not seem to limit the harnessing of Maine’s rivers for a variety of industries. While construction of fish passage structures has featured prominently in actions intended to mediate the effects of this legacy, it is well known among restoration practitioners and fishery managers that no single passage structure can meet the needs of all species and to some degree, most passage structures limit the movements of even the species for which they were designed.

Moreover, fish passage structures require dedicated and well-provisioned operational, maintenance, and funding support to ensure optimal efficiency.  Despite these shortcomings, fish passage structures are often more feasible to construct than dams are to remove. Aesthetics and historical preservation concerns are among constraints that can hinder dam removals, as are perceptions that land values and future opportunities for hydropower diminish when dams are removed.

In some jurisdictions of the Gulf of Maine, the public safety liability associated with aging and inadequately maintained dams is also under-represented in the public discourse and left wanting in terms of funding necessary for more confidently assessing risk. For instance, the Association of Dam Safety Officials ranked Maine’s dam safety program as 41st in the country in terms of staffing.

Road Crossings

Despite a traditional emphasis in stream restoration circles that focuses on dams, there is also growing awareness throughout the region that road crossings act as barriers to aquatic connectivity. In addition to investigations in other jurisdictions, a string of projects by numerous partnering organizations in Maine since 2007 is responsible for illustrating the magnitude and scale of this issue (Moore 2011).

As a result of surveys at over 4,000 road-perennial stream crossings (mostly culverts), researchers found that 43 percent of culverts are physical barriers to the movements of at least the weakest-swimming fish (which may includes early juvenile trout and salmon) and other stream-dependent organisms (USFWS unpublished data) (Figure 1). At most (84 percent) of these crossings, the culvert bottom was elevated above the stream surface or “perched,” which necessitates some level of leaping ability in fish and other stream species if upstream movement is to be accomplished.

River herring return to spawn in the lower Kennebec estuary.
Photo by Slade Moore.

A smaller number of culverts were designated as barriers because they were blocked and some were both perched and blocked. During the same surveys, another 47 percent of crossings were designated as “potential barriers.” These structures were not perched or blocked, but showed signs of excessive current velocities within the culvert, which likely resulted from undersized culvert diameters that “pinch” the stream channel, concentrate flow, increase velocities and ultimately can represent a barrier to upstream fish passage.

Thus, even if a fish can leap up into a moderately perched culvert, it may not have the swimming ability to pass through the structure. Data collected during Sheepscot River and Kennebec Estuary surveys indicate that most culverts were sized smaller than required to avoid “pinching” of the channel (Sheepscot River Watershed Council, unpublished data). Restoration practitioners in the state think the proportion of undersized culverts in the Sheepscot and Kennebec Watersheds may reflect conditions in other regions of Maine.

Although these data suggest that the number of culverts warranting attention is in the thousands, knowing their impact on the recovery of key stream species is important to understanding the urgency of the issue and magnitude of the challenge. In terms of landscape-wide impacts, this research demonstrates that perched/blocked road culverts in the lower Kennebec and Penobscot Watersheds may block fish passage and stream processes on 25-40 percent of stream miles (Figure 2). Even without adding the effects of potential barriers (another 40  percent of crossings), it’s clear that the solutions for restoring aquatic connectivity must do more than only focus on dams.

Uneven and uncertain capacity for response

Restoring connectivity to a meaningful degree brings with it some technical challenges, but the low levels of funding remain the greatest obstacle to meaningful progress. Within the US side of the Gulf, each state provides different approaches and levels of capacity to address statewide restoration needs. Massachusetts Fish and Game’s Division of Ecological Restoration is a model of marshaling resources dedicated to restoring diverse systems in a state subject to intense land and water-use pressure for centuries.

The New Hampshire Department of Environmental Services (DES) funds a “River Restoration Coordinator” through annual fees paid by owners of dams falling within specific hazard categories. The coordinator is imbedded in the DES Dam Bureau, so dam safety and restoration interests work to mutual benefit. In addition to the Dam Bureau’s work, the New Hampshire Coastal Program staffs a Habitat Restoration Coordinator who works on a range of project types. In both New Hampshire and Massachusetts, other agency staff complement the work of programs dedicated primarily to habitat restoration.

In Maine, no single, dedicated or comprehensive habitat restoration program exists, with most work being implemented by a handful of people working across  several state and federal agencies and non-governmental organizations (NGOs). Maine Coastal Program’s Habitat Restoration Coordinator is a position funded through a competitive National Oceanic and Atmospheric Administration (NOAA) Restoration Partnership Grant and matching supports from a wide variety of sources, so its sustainability and ability to maintain a consistent presence is uncertain.

The NOAA Restoration Center, US Department of Agriculture (USDA) Natural Resources Conservation Service, and US Fish and Wildlife Service (USFWS) provide most of the federal funding available for individual habitat restoration projects. A recent assessment in Maine found that these programs contributed about $1 million per year for barrier removal projects, not including staff time or one-time investments such as the American Recovery and Reinvestment Act (i.e. “stimulus” funding).

With thousands of potential dam and road crossing projects warranting restorative action at a cost typically exceeding $50,000 – $100,000 each, it’s unlikely that current federal funding levels can adequately address the degree of need or the level of urgency that comes with the designation of multiple stream-dependent species as at-risk or endangered, largely due to barriers.  Absent a major infusion of new annual funding, each jurisdiction in the Gulf of Maine must find ways to cope with the problem within their budget constraints.

Rather than a silver bullet, the emerging approach is more one that relies on silver “buckshot,” which can at least partly address distinct elements of the problem, with little expectation of funding increases. For instance, in Maine, where there is no dedicated state aquatic restoration program, members of the Stream Connectivity Work Group (a collaborative of over 25 agencies and NGOs) have developed a diverse list of priority actions intended to achieve progress in restoring connectivity.

These actions include drawing attention to the need for updated road crossing regulations, lower-cost methods for replacing substandard road crossings, cost share programs for dam and road owners, training for dam removal and “stream smart” road crossings, integration of dam safety restoration objectives, and prioritization of restoration action.


Despite these efforts to squeeze the most value from every restoration action taken and dollar spent, the unlikelihood of new restoration funding is a major concern for all jurisdictions. Yet opportunities for support from other sectors may not be so remote.

Click for larger view
Most road crossings are barriers or potential barriers to the movements of fish and wildlife and also the materials they need for quality habitat. Data compiled by the U.S. Dept. of Fish and Wildlife.
Chart prepared by Slade Moore.

For instance, recognition is growing that the issues of fish and wildlife population declines, impaired connectivity, and stewardship of aging infrastructure (dams, roads, etc.) are deeply entwined. At each dam or road crossing that constitutes a barrier, there can be considerable overlap between the interests of those who own that infrastructure and those charged with the recovery of at-risk fish and wildlife species.

In some cases, opportunities for cost-sharing exist, especially where non-federal support in the form of cash, materials, or staff time can be used to satisfy the match requirements of habitat restoration funding, such as that provided by the Gulf of Maine Council on the Marine Environment (GOMC)-NOAA Habitat Restoration Program. Even so, the amounts of restoration funding provided by NOAA and other federal restoration programs is not sufficient to provide support for more than a few projects annually in each jurisdiction of the Gulf of Maine.

For road crossings, another approach that might have more sustainable and far-reaching results would be to seek increases in funding for transportation infrastructure. Despite current economic conditions, polls appear to consistently demonstrate public support for improved transportation funding that would come directly out of their pockets. By which mechanism that takes place seems to be the only real subject of controversy. Since 2008, increases in sales and gas taxes, user fees, and bond caps provided Oregon, Kansas and Los Angeles with $240 million to $1 billion dollars more in transportation funding.

More locally, Rhode Island and Vermont increased gas taxes in 2009 and Massachusetts raised the state sales tax in 2009 to address transportation needs. In addition to addressing traditional concerns like transportation safety and uninterrupted commerce and emergency services, transportation funding focused on barrier removals requires materials and services of the construction industry, much of it locally derived. The confluence of restoration and job benefits associated with these projects has the unassailable hallmarks of a true “green jobs” initiative.

For every aging road-stream crossing that is replaced without upgrades to support fish and wildlife passage and stream processes, we lose the opportunity to efficiently address the problems at that site for anywhere from 30-100 years or more, depending on the design life of the structure. And with each non-conforming replacement to a substandard road crossing, we incrementally undermine ongoing restoration efforts.

Click for larger view
Points on the map represent barriers to fish passage and stream processes that were identified during surveys of the lower Penobscot River Watershed. Alex Abbott, U.S. Fish and Wildlife Service.

Each day this routine is repeated, we extend what subsequent generations may remember as the era when thousands of barriers choked the Gulf of Maine’s flowing waters. But with increased awareness, there’s hope that funding and other essential support will be available and scaled to sufficiently meet the challenge.

Slade Moore is director of the organization Biological Conservation and works under contract to the Maine Coastal Program. 

Additional resources:

Association of Dam Safety Officials. No date. Maine Dam Safety Fact Sheet.


Hall, C. J., A. Jordaan and M. G. Frisk. 2010. The historic influence of dams on diadromous fish habitat with a focus on river herring and hydrologic longitudinal connectivity. Landscape Ecology 26:95-107.

Moore, S.  2011. Maine Stream Connectivity Work Group 2011-2012 Objectives, Progress, and Priority Actions. A joint report of the Maine Coastal Program, Maine State Planning Office and Bureau of Sea Run Fisheries and Habitat, Maine Department of Marine Resources, Augusta, Maine.

Whippelhauser, G.  2008.  A report on fish passage plans and standards, by Maine DMR and DEP, Jan. 30, 2008, to the Joint Standing Committee on Marine Resources and the Joint Standing Committee on Natural Resources, in response to Resolve Chapter 109 (LD 1528, LR 1911).  Maine Department of Marine Resources, Hallowell, Maine.


“Maine high-hazard dam article” from August 2011 http://www.sunjournal.com/state/story/1076955




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