Columbia River Basin Fish Screen Programs
Funding for Construction and Maintenance through the Council’s Fish and Wildlife Program
Entrainment and Unscreened Diversions: Potential Effects on Fish
When addressing factors contributing to the decline of fish populations in the Columbia River Basin, the focus is usually on hydropower development and degraded habitat. A common factor associated with these issues is water withdrawals.
Irrigating field in eastern Washington. Photo: Zach Mazur, Washington State University
Water withdrawals can entrain fish into irrigation and hydropower diversions. The fate of these fish migrating past water diversions depends on whether the diversions are screened. A properly screened diversion should keep fish in their natural environment or return them to the stream through a bypass system.
In an unscreened diversion, fish can enter the artificial channel and become stranded and potentially die since a bypass system, that would facilitate a safe return to the main waterway, typically does not exist.
If a diversion is screened, a bypass feature exists that allows fish to return to the main waterway.
As fish are entrained into a diversion channel and encounter the fish screen, an underground bypass pipe allows the fish to swim back to the main waterway. Illustration: Idaho Department of Fish and Game
Fish screen structure prior to the attachment of the bypass pipe. Photo: Washington Department of Fish and Wildlife
Bypass pipe attached to the fish screen structure. Photo: Washington Department of Fish and Wildlife
Bypass pipe extending to the main waterway. Photo: Washington Department of Fish and Wildlife
Juvenile fish returning to a main waterway via a fish screen bypass pipe. Photo: Idaho Department of Fish and Game
Inset Photo: QW Consulting, LLC
Diversions and Screening in the Columbia River Basin: The Early Days
The presence of irrigation ditches in the Columbia River Basin dates back to the 1800s. By the late-1800s and early 1900s, the effects of these diversions had been realized and fish screening laws were being enacted in Oregon and Washington that required water diverters to screen their diversions.
Photo: Oregon Encyclopedia
Mitchell Act – Funding for Columbia River Basin Fish Screening Programs
Starting in the early-1930s, state agencies began to implement fish screening programs and by the 1950s the programs were being funded through the Mitchell Act which provides mitigation funding for losses resulting from hydroelectric projects, logging, mining, and agricultural developments.
As Mitchell Act funding started to plateau in the late-1980s and early-1990s, it became apparent this funding could not solely support the construction of new projects while supporting the annual operation and maintenance costs of existing screens in the Columbia River Basin.
Installation of a paddle wheel-driven drum screen constructed by the Washington Department of Fish and Wildlife. Photo: Washington Department of Fish and Wildlife
A fish screen structure filled with debris following a high-flow event. This scenario occurs annually throughout the Columbia River Basin, requiring significant maintenance. Photo: Oregon Department of Fish and Wildlife
Following high flow events, maintenance is required to ensure fish screens are operational. Photo: Oregon Department of Fish and Wildlife
Northwest Power and Conservation Council’s Fish and Wildlife Program: Cooperative Funding for Columbia River Basin Fish Screening Programs
In an effort to support the existing Columbia River Basin's fish screen programs funded by the Mitchell Act, in 1991 the Northwest Power and Conservation Council (Council) directed the Columbia Basin Fish and Wildlife Authority to coordinate the basin’s fish screen programs through the establishment of the Fish Screen Oversight Committee (FSOC).
This effort was led by the Council’s commitment to fund fish screen and passage programs through its fish and wildlife program. Today the states, tribes, and others in the Columbia River Basin manage and maintain more than 1,900 screens that are cooperatively funded through the Mitchell Act and the Bonneville Power Administration. Displayed on the map to the left are the 1,900 screens, associated with the Council’s fish and wildlife program, that can be viewed on the Council’s Fish Screen Tracker.
Studies Reveal the Importance of Screening Diversions
The continued support of the basin’s fish screening programs is essential to ensure fish and agriculture can coexist. Recent studies highlight the potential impacts that unscreened diversions can have on fish populations. For example, a study conducted in the Lemhi River, Idaho demonstrated that under median-streamflow conditions with unscreened diversions, the estimated cumulative effect of the diversions was a loss of 71.1% of the juvenile anadromous fish that were migrating downstream.
However, the researchers found that estimated mortality could be reduced to 1.9% when all diversions were screened.
Dead anadromous fish in an unscreened irrigation diversion in Idaho. Photo: Idaho Department of Fish and Game
Results from the entrainment study conducted in the Lemhi River.
Other irrigation diversion studies that focused on resident fish also found that entrainment can result in significant mortality. Such an example occurred in Wyoming where researchers found that 77% of the entrained Bonneville Cutthroat Trout and Brown Trout died when water levels were reduced during late summer.
Results from these studies supports the premise that unscreened diversions are a significant source of mortality for all fish species and that screens are an essential investment for the fish and wildlife program. The fate of entrained fish depends on whether diversions are screened. In an unscreened diversion, there is a high likelihood that fish entering the diversion will likely die; however, screened diversions allow the fish to be bypassed and returned to the main river channel.
Results from the entrainment study conducted in Wyoming.
Photo: Idaho Department of Fish and Game
Property Owner Cooperation: The Key to Success
The fish screening programs funded through the Council’s fish and wildlife program are a principle foundation for the recovery of ESA-listed fish, especially in locations where extensive irrigation exists. Since a significant amount of fish habitat is on private land, the success of these programs would not be possible without the support, cooperation, and commitment from private landowners and irrigators.
Photo: Idaho Department of Fish and Game
Fish Screens: Types Used in the Columbia River Basin
All fish screens that are operated in the Columbia River Basin must meet NOAA’s design criteria . These criteria are designed to provide adequate protection of salmonids during all life stages and have been adopted by U.S. Fish and Wildlife Service for resident fish species. Through the years, these criteria have been updated with the assistance of the FSOC.
Screening and passage structures that meet NOAA criteria have been shown to be 90-99% effective at passing fish at all life stages.
Screen types commonly used in the Columbia River Basin include:
Pump Screens
Self-Cleaning
Screens of this type are attached to the intake of the pump. Debris is removed when: 1) the pump screen rotates around a fixed water nozzle installed inside the screen that sprays debris off the screen and 2) the screen material is fixed and debris is removed from the screen as the water nozzles spray water at the screen during rotation.
Pump Screens
Passive
This type of screens relies on the sweeping flow of the water for the removal of debris and is not recommended unless conditions prevent a self-cleaning pump screen from operating properly. Shallow water depths at the pump site are a common justification for using a passive pump screen; however, this type of screen is only allowed when diverting less than 3 cubic feet per second.
Rotary Drum Screens
Paddle Wheel-Driven
A common screen type that uses water current to rotate the drum to clear debris and maintain effective screen operation. The site must have sufficient water current to turn the paddle wheel and a consistent water depth to appropriately size and place the drum screen. Shallow water levels at the screen will prevent it from cleaning properly and if water depth increases above the screen design, fish may get over the screen and lost down the ditch. Because this screen type passes debris over the screen and down the diversion ditch, it is not preferred for municipal water diversions or sites that feed sprinklers due to the presence of debris in the source water.
Solar Powered
For this screen type, solar power rotates the drum to clear debris and maintain effective operation. Appropriate screen submergence is necessary for the drum to clear debris without allowing fish over the drum. Since this screen type will pass debris over the screen and down the diversion ditch, it is not ideal for municipal water diversions or sites that supply sprinklers. This screen type is generally utilized in areas that are appropriate for a rotary drum screen but do not have enough current to drive a paddle wheel cleaning mechanism.
Photo: Washington Department of Fish and Wildlife
Vertical Traveling Belt
Traveling belt screens are effective for sites with a wide range of water depths during the period of use. This screen is not as sensitive to water depths as the rotary drum screen. Although traveling belt screens usually pass debris down a diversion canal, they can be modified to collect debris on the back side of the screen and reduce the amount of material in the water delivered to the place of use.
Vertical Panel
Vertical panel screens direct debris and fish towards the bypass and back into the source stream. Water is diverted to the user without the debris load present in systems that use a rotary drum or traveling belt screen. Municipal and sprinkler irrigation operations benefit from the reduced debris load that is provided by a vertical panel screen. These screens usually have one or more wiper brushes that travel along the screen to remove debris which maintains maximum fish protection and water delivery to the user.
Horizontal
The horizontal screen operates with no moving parts and is substantially self-cleaning, typically resulting in less maintenance. Water flows over the screen surface allowing fish and debris to pass quickly over the screen and back to the river or stream, while a portion of the water moves slowly through the screen. This screen works well in high sediment and high gradient systems, but does require at least one foot of elevation differential and adequate by-pass flow. This patented screen technology is available through the Farmers Conservation Alliance .
Brushed Cone
Cone screens are ideal for shallow water intake scenarios where they are permanently submerged below the surface with external brushes that facilitate a self-cleaning function. The external brush-cleaning action prevents the build-up of materials that could foul the equipment.
Water passes through the wire screen, then through the base structure, and into the intake system. The cone-shaped design delivers minimal head loss through the screen to ensure efficient water delivery.
