Columbia Ecosystem

Environmental Affects

Mitagation

Columbia Basin

Hydro News

Links

Glossary

Common Protection, Mitigation and Enhancement Strategies
Structural Features
Operational Changes
Transportation
Predator Control
Stream Enhancements
Land Use
Hatcheries
Conclusion
Bibliography

Overview

Hydropower is considered an attractive means of producing electricity because it is a renewable and clean energy resource. Like any energy resource, however, there are environmental affects associated with its use.

As described fully in the article How A Hydroelectric Project Can Affect A River, impacts can vary greatly from one hydroelectric facility to the next.

At any given project, government agencies, utilities, non-profit groups or others monitor these variables and resultant environmental affects. In some cases, the environmental affects are considered positive. For instance, reservoirs can provide important resting and feeding areas for birds and quality habitat for bass and other fish species.

On the other hand, habitat conditions for some fish, wildlife and plants can be adversely affected. Determining the best means to avoid, minimize or mitigate such affects can be a difficult task. Not only is more than one approach often possible, but each approach can affect environmental and human interests differently. Implementing measures to help one species of fish, for example, may harm another species of fish and change recreational opportunities.

In addition, there may be more than one reason for declining habitat conditions. For instance, water quality (e.g.-- temperature or oxygen and nitrogen levels) in a reservoir can be affected by a hydroelectric project's operation. Other conditions, however, may also affect the water quality, including runoff from agricultural uses, logging or land development.

To the extent a hydroelectric project does affect habitat conditions, a number of protection, mitigation and enhancement strategies can be employed to minimize these affects. This article reviews the strategies most common to hydroelectric projects in the Northwest.

Protection, mitigation and enhancement strategies are defined in Figure A. Collectively, these strategies are often referred to as PM&E's.

What this section describes are PM&E strategies commonly used and discussed by Northwest hydropower operators. As shown by the Figure B matrix, each strategy is designed to address one or more social and environmental issues.

For instance, surface collectors represent a strategy to positively affect fish migration and fish population issues. To reinforce this connection, subheadings in this article refer to both the strategy being employed and the issue(s) it addresses.

Further, when considering the description of issues and the strategies used to minimize them, it is important to remember that circumstances vary from project to project. Some projects, for instance, have only a couple of issues present. At other projects, the degree to which an issue is present can differ greatly.

For more detailed information about the environmental issues identified, read the article How A Hydroelectric Project Can Affect A River.

When a hydroelectric project is built, its physical structure can address specific needs that arise. For instance, fish passage facilities may require improvements or water temperature further regulated. Sometimes, modifications to a project's physical structure can effectively address such issues.

A fish passage is a waterway which allows fish to pass a dam or other obstruction. At hydroelectric projects, examples include lifts or elevators, barging, fish pumps, locks, screens and other bypass devices.

For juvenile fish migrating downstream, there are essentially three "in-river" ways for fish to pass from one side of a hydroelectric project to the other. These are for fish to follow the path of water:

1. through the turbines and exit at the tailrace of the project,
2. to fish screens or surface collectors, which then route fish to a bypass system that channels them around a dam, or
3. over a project's spillway.

These are called "in-river" paths because they do not rely on barging or trucks to "taxi" fish downriver before being released. For the Columbia and its tributaries, these paths primarily affect juvenile salmon (also called smolts) migrating downstream. These paths may also affect fluvial fish (those who migrate up and downstream but not to and from the ocean). Examples of fluvial fish receiving close attention because of declining populations include bull trout and cutthroat trout.

The success of traveling each path also varies from project to project. The reason is that the design of each project, the flow rate of the river, and the particular geologic and topographic circumstances of projects widely differ. Some variables that affect successful migration via each path include:

1. When fish flow through turbines, they can die as a result of being bruised, stressed, and/or disoriented. The U.S. Department of Energy and a consortium of hydropower industry participants are addressing this issue by designing "fish friendly turbines" for both large and small projects. Currently, the large turbine design has been lab tested and is now ready to be field tested. The small turbine design is expected to be ready for lab testing in 1998. Such turbine modifications maximize both fish passage and the amount of electricity a project can generate.

2. Bypass systems use surface collectors, fish screens, and other devices to guide fish through or around a hydroelectric project. Limitations to these systems sometimes occur because the natural instincts of fish draw them toward areas where the water flow is strongest. Often, this is the path that will lead fish into a project's penstock and turbine area.

At some projects, "behavioral" guidance devices are used to guide fish to a bypass system. Examples include lights, sound repulsion, and air bubble curtains. By avoiding lights, sound, and other unattractive disturbances, the behavior of fish is affected to encourage them to swim away from hazards and/or toward a bypass system.

As with any path, issues of stress and disorientation are also present with bypass systems. Finally, such systems tend to release fish into a relatively small area. Here, they can become easy prey for predators such as squawfish.

3. When fish pass over a spillway, they fall into the pool of water below. Changes in pressure can cause gas-bubble disease (which is the equivalent of "the bends" for divers). Stress and disorientation represent additional challenges to their mortality. Spill deflectors are sometimes used to help minimize these issues.

Other major structural features to assist fish passage relates to the upstream journey of fish. Along the Columbia and its tributaries, this journey often relates to adult salmon migrating upstream to spawn. Examples of fluvial fish that may also need such assistance include bull trout and cutthroat trout.

Fish ladders are the most common structural modification designed to assist this journey. Different designs are used to maximize a ladder's effectiveness at each project. For instance, design modifications can help fish find the small attraction flows at the entrance of a ladder, or reduce the possibility of fish falling back over a spillway when they exit a ladder.

Beyond fish migration, structural features at a project can be used to assist with addressing water quality issues that affect aquatic life and plants. As mentioned above, spill deflectors (also called flip lips) can help reduce nitrogen supersaturation caused by water plunging into a pool several to a few hundred feet below a spillway.

In addition, some projects have gates built at different depths of water. By allowing water to pass through these gates, adjustments (often called selective withdrawl) can be made to regulate changes in water temperature and oxygen levels.

The building of boat ramps, camp grounds, picnic areas and similar improvements are done to support the social interests of a community. These modifications do not directly affect the project itself. Rather, they are made up and downstream of a project to help ensure a river reach is as accessible and friendly to people as possible. Such improvements can also be aesthetic in nature and help the local economy by supporting tourism.

Operational changes refer to how projects can regulate either 1) the rate of water flow in a river, or b) how water passes through a project.

Run-of-river projects and those with fairly small reservoirs have limited or no ability to regulate the rate of water flow in a river. The reason is that the water is already flowing at or near the river's natural flow rate.

At projects with reservoirs, the most common operational changes involve "flow augmentation" or "permanent drawdowns." These changes commonly result in lost capacity to generate power when it is in highest demand and most valuable.

One of the factors in juvenile salmon mortality is the length of time it takes to migrate to the ocean. To reduce the in-river time of this journey, a "water budget" has been used to release water from the largest upstream storage reservoirs in the Snake (Dworshak) and Columbia (Lake Roosevelt). When this occurs, water not passing through a turbine area is released over a dam's spillway.

Water is stored and then released in concert with juveniles migrating downstream in the Spring. By increasing water flows and "flushing" juveniles downstream, another advantage may be that more natural freshet conditions during migration are duplicated. Freshet refers to the turbidity and other water conditions that occur when water is flowing rapidly downstream as a result of conditions such as rainfall, snowmelt, or sudden release of water from a reservoir.

From a recreational perspective, the timing and length of spills can dramatically affect conditions for white water rafting, kayaking, and similar activities.

Permanent drawdowns speed up the rate (velocity) of water flowing down the river by lowering the water level at a project's reservoir. In effect, it largely or completely restores a river to its "natural" state. By doing so, a project loses all or most of its ability to store water and thus regulate the generation of electricity to times when it is most needed and valuable. Rather than being or remaining a storage project, it becomes a run-of-river project.

How much to draw down reservoirs has been the subject of much debate. One issue is that while new rearing and spawning habitats for some species will emerge, habitat for other fish and wildlife will be lost. Other issues include erosion and possibly needing to reconstruct fish passage and recreation facilities due to reduced water levels.

Rather than using a bypass system to channel fish back into the river downstream of a project, transportation uses the bypass system to move fish into barges. These barges then release the juvenile salmon back into the water several miles downstream. By doing this, the salmon do not need to risk different types of mortality as they travel downstream and pass through several projects during their migration to the ocean.

This process has been used extensively to assist salmon migration that begins in the Snake River. Issues with this method include the unnatural conditions introduced to the migratory path, disease that can occur while barging and the stress caused to juveniles by this process.

In some cases where migration paths are blocked going upstream, fish collection facilities and trucks are used to pass returning adults from one area of the river to another. Such a process is also referred to as "trap and haul."

As smolts exit the turbine area or bypass system they are particularly vulnerable to predators, particularly squawfish. These predatory fish essentially "camp out" below the dam. One means of reducing the abundance of squawfish below a project is to provide fishermen bounties to catch them. Another is to select a release point where predators find it more difficult to thrive.

Seagulls and arctic terns also prey on smolts. One method of reducing their effect is to place piano string across the river, causing a hazing that makes seeing and therefore preying on smolts more difficult.

Changing water levels can be a significant source of erosion and sedimentation. Use of vegetation is one method of stabilizing banks and thus minimizing this issue. Another method is to add vegetation to stream banks. In addition, stabilizing banks can improve wildlife access to these areas.

Careful management of vegetation, including plant removal within a river, can also be employed to address issues related to nutrient loading and reduced oxygen levels.

Further, the stream and tributary conditions that flow into a reservoir or project are of great importance. By restoring spawning areas and using materials such as logs and vegetation to restore instream habitat structures, the health of these areas can be enhanced. Working with property owners and government agencies to do this may be part of a project owner's commitment to assist with maintaining the overall health of a watershed area.

When hydroelectric projects are constructed, some wildlife habitats are inundated. Inundation refers to areas behind a dam that become "flooded" when the water level rises to a new height. How much habitat is gained or lost relates to the topography and the size of the project's reservoir (if one exists).

As a new equilibrium takes hold, new habitat conditions emerge. For some species, these new conditions are an advantage in their quest for survival. For other species, these new conditions can cause their population to decline or be eliminated in these areas.

One method of minimizing the effects of inundation is to protect and/or enhance other lands for wildlife. This may include purchase of lands that can be protected, changes in land use, or creation of refuges.

Hydropower operators also participate in programs to protect or reintroduce species. For instance, a significant benefit of reservoirs is that they provide important nesting, resting, and feeding grounds for migratory birds and waterfowl. Other examples of activity include efforts to reintroduce peregrine falcons to the Northwest and rehabilitating streambanks to benefit wildlife who live and feed along the banks.

One of the oldest ways to mitigate the effects of dams and other practices (such as logging and commercial fishing) is to build hatcheries. Here, millions of fish are born and fed until they can be released into the river.

Since the mid 1980s, for instance, two to three hundred million juvenile salmon have been released into the Columbia River basin each year. As a result, hatcheries currently account for over 70% of salmon stock in the Snake and Columbia rivers.

The use and operation of hatcheries, however, has become controversial. Possible consequences of relying on hatcheries to keep the abundance of salmon high include 1) reducing the genetic diversity between salmon stocks, 2) hatchery salmon "mixing" with wild salmon and thus further diluting the natural population, 3) changes in behavior that occur from being raised in a hatchery environment, 4) ecological problems because nutrients from wild salmon carcasses no longer fill stream beds, 5) wild salmon smolts being at a competitive disadvantage when looking for food because hatchery salmon are larger when released, and 6) the introduction of diseases that began at hatchery facilities.

Because of these effects, hatchery planning, management, and operations have become far more rigorous.

Developing and implementing protection, mitigation, and enhancement strategies at hydroelectric projects is a complex task. The reasons for this include: 1) the river and geologic conditions can vary widely from project to project, 2) different strategies can affect human and other species' interests very differently, and 3) technologies and knowledge are continually changing and improving.

Determining the best mix of strategies is something in which generators of hydropower, government agencies, Native American tribes, elected officials, recreators, affected industries, environmental groups, and the general public can and should participate.