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Restoration Methods

Seagrass - Salt Marsh - Anadromous Fish Habitat

Anadromous Fish Habitat

Dam on the Saugatucket River, Wakefield, R.I.
Dam on the Saugatucket River, Wakefield, R.I.
Courtesy: D. Yozzo, Barry Vittor & Associates

Dam removal is the best solution to restoring streams and anadromous fish runs, as it permanently restores the waterway and does not require ongoing operation and maintenance of fishways (Connecticut River Watershed Council, Inc. 2000). However, dam removal is not always feasible due to existing land uses, industrial and residential infrastructure in the vicinity of a dam or immediately downstream, and concerns regarding increased stream flows and erosion and sedimentation patterns. Fish ladders, or fishways can be used to bypass blockages; this is the most commonly applied solution to restoring fish passage over impediments in Rhode Island. Dams which no longer provide a function but which cannot be completely removed can often be notched or partially breached to allow fish access upstream.

Fish Ladders | Fish Lifts (Elevators) | Stocking

Fish Ladders

Pallisades fish ladder in Peacedale, R.I.
Pallisades fish ladder in Peacedale, R.I.
Courtesy: D. Yozzo, Barry Vittor & Associates

Fish ladders consist of a series of gradually inclining steps with resting pools located at regular intervals. These provide the fish with a means for active migration that simulates natural river conditions. Most ladders are designed with a 10 percent grade. If a fish ladder does not provide sufficient water, fish will not be attracted to the fishway. If too much flow is generated, fish will be deterred from using the fishway.

A steeppass fishway is a prefabricated aluminum chute with vanes along the sides and bottom that create turbulence, which lowers water velocity. Steeppass fishways are particularly well-suited for small dams, and they are relatively easy to install and maintain.

A denil fishway is a type of fish ladder designed with a series of sloped channels. The fishway can be constructed with an overall slope of 10 to 25 percent. Wooden baffles are placed at regular intervals, and are usually constructed with a 45 percent slope. A narrow entrance creates high water velocity to attract fish. Resting pools may be located between long segments of the fishway. A denil fishway is larger than a steeppass fishway, and is best for medium to large dams.

A pool-and-weir fishway is a series of individual pools separated by walls or weirs. These structures may be constructed of stone, wood, or concrete. This type of fishway is suitable for both small and large dams (Connecticut River Watershed Council, Inc).

Fish ladders can be built of concrete, wood or aluminum. Selection of the appropriate ladder type and construction material depends on the target species, dam size, and anticipated project cost (Connecticut River Watershed Council, Inc. 2000). If a fish run restoration project is aimed at several target species, ladders should be designed for the weakest swimmer. Among the target species considered for restoration in Rhode Island, salmon are the strongest swimmers, followed by river herring, and American shad. Shad can be blocked by an obstruction only one foot high. Herring are unable to jump over obstructions and require a moderately sloped fishway (e.g., steeppass or denil). Salmon and trout can jump, and will ascend small waterfalls.

The following considerations will help determine the selection of the type of fish ladder to be used at a particular site.

  1. Which species are likely to be found in a particular tributary or at that particular blockage?
  2. Is the design of fishway appropriate for the swimming capabilities of the species?
  3. What water velocity will attract a fish to a fishway without inducing it to spawn halfway up the fishway?
  4. In which part of the river are the target species likely to be found?
  5. How many fish will need to pass the blockage and use the fishway?
  6. Is the method cost effective? Is it durable?

Fish Lifts (Elevators)
A mechanized lift provides passive migration of fish over dams to spawning areas. Fish swim into chambers at the base of the dam, guided by currents, and the chambers are mechanically lifted up and over the dam, depositing fish on the other side. Lifts have been used to overcome large dams in other states, such as the Susquehanna River and its tributaries in Pennsylvania. Another well-known example is in operation on the Connecticut River at Holyoke, Massachusetts, but none have yet been constructed in Rhode Island.

For information on fish run restoration on the Susquehanna River and drawings of how fishlifts work, visit the Safe Harbor Water Power Corporation Web site.

Often, stocking of adults and juveniles is employed in fish run restoration projects to supplement dwindling local stocks, to reintroduce fish in systems in which they have been completely extirpated, or to simply accelerate the rate of recovery in fisheries undergoing restoration. Live adult herring or shad are trapped in East Coast rivers that support healthy, sustainable runs and are released into the waterway to be restored. In some cases, where the system still supports a remnant run, adults can simply be trapped in lower reaches of a river below the impediments, and transported to locations above the impediments to be breached or overcome.

In some cases, particularly when a stock has been completely eradicated within a stream or river, hatchery production of young fish (larvae and juveniles) is used for reestablishment. Eggs are collected from adults spawning in other river systems. These eggs are fertilized in a laboratory and reared to the juvenile stage. The juveniles are then introduced into the river system undergoing restoration (within which water quality and impediments to migration have been addressed) to restore the historic run.

Stocking was used in the restoration of the historic herring run in the Narrow River to Carr Pond (upstream of Gilbert Stuart's Birthplace). Breeding adult herring from the Connecticut River and tributary streams in Massachusetts were stocked in Carr Pond in the mid-1990s. The original brood stock returned to their native streams after spawning, however their offspring returned to the Narrow River and Carr Pond in successive years. The current annual herring run at Gilbert Stuart's Birthplace exceeds 300,000 individuals (Gilbert Stuart Museum 2002).

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Connecticut River Watershed Council, Inc. 2000. A fishway for your stream: providing fish passage around dams in the Northeast. The Connecticut River Watershed Council, Inc., Easthampton, Massachusetts. Visit http://www.ctriver.org/ to order copies of this publication.

Gilbert Stuart Museum. 2002. "River Herring Restoration" Web page (http://www.gilbertstuartmuseum.com/riverherringpage.htm). Saunderstown, Rhode Island.

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