Project Planning: Anadromous Fish Habitat (Rivers)
Within a geographic area or river system, a large number of dams or impediments may exist to be considered for removal. Project proponents or stakeholders should conduct a comprehensive inventory of potential restoration sites. Evaluation of site-specific factors (e.g., ecological, land-use, ownership, construction costs) can allow ranking of potential projects to be considered for funding.
After a dam or other impediment has been selected to be removed or modified, several initial planning tasks should be conducted (Connecticut River Watershed Council, Inc. 2000):
- Document the presence of anadromous fish.
- Document the presence of suitable habitat upstream of the barrier. Dredging, channelization, or siltation may have altered upstream habitats.
- Determine whether dam removal is possible as an alternative to fishways. Often, recreation or infrastructure prohibits dam removal or partial breaching.
- Determine dam ownership (private vs. municipal or state).
Defining project goals and objectives
Baseline data collection
- Size and age class distribution of the target species to be restored upstream (if present) and downstream of the impediment.
- Current flow in upstream and downstream portions of the study area.
- Water quality conditions in upstream and downstream portions of the study area (e.g., temperature, salinity, pH, turbidity, dissolved oxygen).
- An assessment of stream channel morphology, depth, and sediment/stream bed characteristics (including the presence of contaminated sediments) upstream and downstream of the impediment.
- A survey of spawning habitats upstream of the impediment.
- A survey to identify other species that may be affected by the proposed restoration activities, both upstream and downstream of the impediment.
Fisheries biologists can monitor downstream migration of juveniles using nets and hydroacoustics technology, and they are able to provide information on fish movement, population size, and size-class distribution. Additional survey techniques include radio tagging of adult herring to track movements and residence time in a particular habitat, and mark-and-recapture studies to track fish movements over extended (multi-year) time periods.
Permitting and regulatory consideration
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. Dams that no longer serve a useful function but that cannot be completely removed can often be notched or partially breached to allow fish access upstream.
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 it. 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 the Gulf of Maine, salmon are the strongest swimmers, followed by river herring and American shad. Shad can be blocked by an obstruction only one foot high. Herring cannot jump over obstructions and require a moderately sloped fishway (e.g., steeppass or denil). Salmon and trout can jump and are able to ascend small waterfalls. The following considerations will help determine the selection of the type of fish ladder to be used at a particular site.
- Which species are likely to be found in a particular tributary or at that particular blockage?
- Is the fishway design appropriate for the swimming capabilities of the species?
- What water velocity will attract the fish to a fishway and not induce them to spawn partway up the fishway?
- In which part of the river are the target species likely to be found?
- How many fish will need to pass the blockage and use the fishway?
- 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. A well-known example is in operation on the Connecticut River at Holyoke, Massachusetts. Lifts have been used to overcome large dams in other states, such as the Susquehanna River and its tributaries in Pennsylvania. For information on fish-run restoration and drawings of how fish lifts 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 simply to accelerate the rate of recovery in fisheries undergoing restoration. Live adult herring or shad may be trapped in East Coast rivers that support healthy, sustainable runs and then 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.
Industrialization and urbanization present special problems for dam removal. Contaminated sediments that have accumulated over decades upstream of dams located in densely populated or industrialized watersheds may be subject to release and downstream transport if certain dams are removed or breached. For example, removal or breaching was proposed for an obsolete dam located on the Woonasquatucket River in Providence, Rhode Island. However, the discovery of dioxin-contaminated sediments upstream has prompted reconstruction of the dam to prevent the release of contaminants downstream (US EPA 2002).
In non-contaminated waters, dam removal or breaching may result in undesired changes in sedimentation rates and in channel scour, which may induce erosion of stream banks. These conditions may be temporary, or they may result in permanent alteration of downstream habitats (Connecticut River Watershed Council, Inc. 2000). The effect of dam removal or breaching on rare species must be considered in fish-run restoration projects. Threatened or endangered fish or invertebrate species, if present downstream of an impediment to be modified or eliminated, may be unable to persist in the presence of changing water levels or downstream flow rates. Threatened or endangered species present upstream of the impediment may be unable to adapt to lower water levels and/or increased channel velocity resulting from removal or breaching of an impediment (Connecticut River Watershed Council, Inc. 2000). As with other restoration projects in the coastal zone, dam removal or breaching must consider the effect on cultural resources. Many of the dams in the Gulf of Maine region date back to early colonial times, and may represent significant cultural resources. Native American sites are particularly abundant in the vicinity of rivers and streams, and they could be subject to disturbance during a dam removal or fishway construction project. A professional archaeologist or agency cultural resources specialist should be a participant on any technical advisory team tasked with planning and designing a fish run restoration project. Fishway construction projects must consider and allow for the downstream passage of juvenile fish as well as spawning adults. In some cases, multiple fishways must be incorporated into the design to accommodate both juvenile and adult life stages.
Equipment sources and contacts
Anadromous fish habitat (riverine)