Stream restoration, also called river restoration or river reclamation, is work done to improve the health of a river or stream. This helps support plant and animal life, provide areas for people to enjoy, manage flooding, and develop the surrounding land.

There are two main types of stream restoration: form-based restoration and process-based restoration. Form-based restoration uses physical changes, such as building structures like deflectors, cross-vanes, weirs, step-pools, engineered log jams, and methods to stabilize riverbanks. These changes can quickly improve a stream's condition, but they may not always fix larger problems that affect the entire area.

Process-based restoration focuses on restoring natural water and sediment movement, such as connecting the river channel to floodplains, and limiting changes within areas defined by the stream's water flow and land shape. The benefits of this type of restoration may take longer to appear because changes happen slowly based on how the stream naturally behaves.

Although many stream-restoration projects have been done worldwide, it is still difficult to measure how well they work. This is partly because not enough monitoring has been done. However, as people become more aware of environmental issues, more countries are including stream-restoration requirements in their laws.

Definition, objectives and popularity

Stream restoration, also known as river restoration or river reclamation in the United Kingdom, is a process that helps improve the health of rivers and streams. These efforts aim to return rivers and streams to their natural conditions or to a state similar to their original condition. This work supports the variety of plants and animals living in these areas, helps with activities like swimming and fishing, manages flooding, and improves the appearance of the land. Stream restoration is closely connected to environmental and ecological restoration. It is different from:

• River engineering, which involves changes to a water body, such as building structures to help boats move, control flooding, or direct water flow. These changes are not always focused on helping nature;
• Waterway restoration, a term used in the United Kingdom to describe changes to canals or rivers to make them easier to travel on and improve recreational areas.

Better stream health can be seen through more homes for fish, insects, and other wildlife, and less erosion of the stream banks. While erosion was once thought to harm streams, it is now understood to play a role in their health. Other improvements may include cleaner water with fewer pollutants and more oxygen, and creating a stream system that can survive on its own without needing regular human help, such as digging or building flood barriers. Stream restoration can also increase the value of homes near restored areas.

In recent years, stream restoration has become an important part of managing water resources because many rivers and streams have suffered damage from human activities. In the United States alone, it was estimated in the early 2000s that over one billion dollars were spent each year on river restoration projects, and nearly 40,000 such projects had been completed across the country.

Restoration approaches and techniques

Stream restoration projects can include improving or removing structures that block natural stream functions, such as fixing or replacing culverts or removing barriers that stop fish from swimming, like weirs. Other actions may involve stabilizing stream banks, restoring areas near streams (riparian zones), or building stormwater-management systems like wetlands. Using recycled water to increase stream flow that has been reduced by human activities is also a type of stream restoration. Navigation locks can sometimes be used as fishways to help fish move through streams, even those that swim slowly.

Before starting a stream-restoration project, experts study the stream system. This includes looking at climate data, geology, how water flows in the watershed, how water moves in the stream, how sediment moves, the shape of the stream channel, how the stream has changed over time, and past flood records. Scientists use different systems to classify streams based on their physical features. This initial study helps understand why the stream is damaged and what the goals of the restoration should be, especially since the original, undisturbed state of a stream may no longer be possible due to human or natural factors.

There are two main types of stream restoration: form-based and process-based. Form-based restoration focuses on rebuilding the physical structure of the stream, such as its shape or pattern, to match what is considered ideal for the stream. Process-based restoration aims to restore natural processes, like how water and sediment move, to help the stream stay healthy and resilient.

Form-based restoration changes the stream channel to improve conditions. Goals may include better water quality, more fish habitat, and stronger banks and channels. This method is widely used and supported by groups like the U.S. Environmental Protection Agency. It can be done at different scales, such as working on a small section of the stream. Projects may include adding structures in the stream, stabilizing banks, or reshaping the stream channel. These changes affect how water moves, which can influence flow speed, water depth, and how sediment moves.

Deflectors are wooden or rock structures placed at the edge of a stream to direct water away from the banks. They help prevent erosion and create varied water conditions that benefit fish. Cross-vanes are U-shaped structures made of rocks or logs placed across the stream to direct water toward the center, reducing erosion. Similar structures like W-weirs and J-Hook vanes also help manage water energy.

Engineered log jams are a newer technique used to restore streams. Many streams lack natural features like large logs or woody debris because of human activities, such as removing beaver dams. Adding logs to streams, like in Lagunitas Creek and Thornton Creek, creates varied water flow patterns, such as riffles and pools. However, logs in these jams can move downstream over time and may cause issues for people.

Bank stabilization is a common goal in stream-restoration projects, even though some erosion is natural and helps support habitats. This is often done when a stream is tightly confined or when nearby structures are at risk. Methods include using rocks, wire baskets, or planting vegetation to hold soil in place. Vegetation helps stabilize banks naturally and adapts to changing conditions.

Channel reconfiguration involves changing the stream’s physical shape. This can include reshaping the stream’s cross-section or creating meanders through earthwork. In the U.S., this is often done using the Natural Channel Design (NCD) method, which classifies streams based on features like slope and bed material. The method includes detailed steps to design and build the desired stream shape using natural materials like rocks and plants.

Form-based restoration has been criticized for being too small in scale compared to the large natural processes that affect streams. It is also criticized for focusing on how a stream looks rather than its natural conditions. The NCD method has been criticized for being overly simplified and not always suitable for certain types of streams, like small, forested streams in wetlands.

Effectiveness of stream restoration projects

In the 2000s, a study of stream restoration projects in the United States led to the creation of the National River Restoration Science Synthesis (NRRSS) database. This database contains information about more than 35,000 stream restoration projects completed in the U.S. Similar efforts to combine information about restoration projects are also happening in other parts of the world, such as Europe. However, even though many stream restoration projects are carried out each year worldwide, it is still difficult to measure how well these projects work. This is partly because there is not enough information about the physical and chemical conditions of the streams before and after restoration. It is also due to limited follow-up monitoring and the use of different methods to measure project success. The time needed to achieve a project’s goals, such as restoring fish populations or natural river processes, depends on the specific goals of the project. Therefore, monitoring efforts should match the size of the problem being addressed, and long-term monitoring is often needed to fully understand a project’s success.

In general, the success of a restoration project depends on choosing the right method based on the type, cause, and size of the damage to the stream. For example, projects that focus on small sections of a river often fail to fix problems that affect the entire watershed, such as poor water quality. Some project failures have been linked to designs that are not based on solid scientific research. In some cases, restoration methods were chosen more for how they look than for how well they work. Other factors that can affect project success include the choice of restoration sites (for example, sites near undisturbed areas may recover more easily) and the amount of tree cutting or other harmful activities needed to complete the work (which can harm the habitat for a long time). While public involvement in projects can be challenging, it is usually seen as a helpful factor for the long-term success of stream restoration efforts.

Introduction in legislation

Stream restoration is slowly becoming part of the laws in many states. Examples include the European water framework's goal to restore surface water bodies, France's use of the freedom space concept, Switzerland's laws that set aside areas for rivers and require streams to be restored to a natural state, and the inclusion of river corridors in land use planning in Vermont and Washington. While scientists generally see this as a good development, some are worried that it might reduce flexibility and limit new ideas in an area that is still growing.

Informational resources

The River Restoration Centre, located at Cranfield University, manages the National River Restoration Inventory. This inventory records successful methods for restoring, improving, and managing rivers and their floodplains in the United Kingdom. Other reliable sources of information about stream restoration include the NRRSS in the United States and the European Centre for River Restoration (ECRR), which collects details about river projects across Europe. The ECRR and the LIFE+ RESTORE project have created a website that gathers examples of river restoration projects from around the world.