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Wapato diversion project

Project Overview

The U.S. Bureau of Indian Affairs (BIA), in coordination with the Yakama Nation, is designing and constructing improvements to the Wapato Diversion Dam (Diversion) on the Yakima River, about two miles south of Union Gap, Washington. The Diversion project is being developed over several years and consists of two main stages: (1) A series of short-term repairs constructed in March of 2024 and (2) The design and construction of features to achieve long-term, multidisciplinary objectives.

Definitions

1. Main Canal Headworks

The Main Canal Headworks is the point where water enters the WIP Main Canal through a series of headgates.

2. West Diversion

Because an island separates the two channels of the river, there are two diversions. The West Diversion is the smaller of the two and features one fish ladder.

3. East Diversion

Because an island separates the two channels, there are two diversions. The East Diversion is the larger of the two and features two fish ladders.

4. Earthen Embankment

A mound of soil extends from the East Diversion to Interstate 82 forcing floodwaters over the spillways.

5. Overflow Spillway

The overflow spillway is a low point between the two diversions that provides additional flood capacity.

6. Rock Weirs

Rocks are arranged downstream from both diversions to increase the water level to improve fish passage and reduce erosion.

7. Fish Ladders

The Wapato Diversion has three fish ladders that provide a path for upstream fish migration through the structures.

project background

The Diversion was originally constructed in 1917 by the BIA and includes diversion dam structures across the east and west channels of the Yakima River. This facility is the primary point of diversion for the Wapato-Satus Unit of the Wapato Irrigation Project (WIP), diverting up to approximately 2,200 cubic feet per second (cfs) of water into the WIP Main Canal.

Modifications at the Diversion within the last 40 years include:

Construction of improved fish ladders and dam crest raises in 1985.
Construction of an improved fish screen in 1986.
Installation of rock weirs and an island overflow spillway in 2007.
Removal of accumulated bedload in the west channel dam forebay in 2015.
Repairs to the undermined west channel spillway and adjacent fish ladder in 2023
Headworks reconditioning in 2024.

Why this project is needed

Operator Safety

Existing headworks safety features such as the walkways and trash rake mechanism do not meet current industry standards. The trash rake is particularly problematic, as wood and large debris in the Yakima River are often trapped in the headworks forebay and can become lodged in the headgates. In addition, WIP crews cannot safely dewater the Main Canal headworks forebay to perform maintenance on the headworks facility.

Operational Issues

Due to bedload accumulation in the west channel upstream from the headworks, the BIA is often challenged to maintain adequate water diversions during peak irrigation demand. The only existing method available to manage sediment accumulation is mechanical dredging, requiring heavy equipment in the river channel and significant associated environmental considerations.

Fish Passage and Entrainment

The current fish passage facilities are operated and maintained according to federal criteria for salmon and steelhead. Fish ladders at diversion dams in the Yakima Basin were not originally designed to pass Pacific lamprey, but some, including ladders at the Wapato Diversion, have been retrofitted to accommodate adult lamprey. Bypass systems at the Diversion and the numerous other diversions in the Yakima River were designed to screen juvenile salmon and steelhead out of irrigation canals and safely return them to the river, but recent studies have shown that their cumulative effect on juvenile migration timing and survival is significant. This project provides an opportunity to modify the Diversion to improve adult and juvenile fish passage and survival.

Sediment Transport

Sediment continuity is recognized as a healthy river system characteristic. The current structure restricts sediment transport resulting in the accumulation of sediment upstream of the Diversion.

Flooding Concerns

The 1996 flood event reportedly came close to overtopping the railroad tracks on the west bank of the Yakima River. In addition to localized infrastructure risk, an overtopping event could result in an uncontrolled release of water into the WIP Main Canal, with catastrophic results.

Fish Harvest

Existing Diversion features were not designed to accommodate traditional fishers. Opportunity and access for traditional fishers will be considered in developing long-term design modifications to the Diversion.

What's Next?

Long-term rehabilitation is in the planning and design phase with construction potentially beginning as early as 2027. Below are four key milestones of the long-term rehabilitation:

Concept Development and Feasibility-level Design (current milestone): This milestone involves investigating the feasibility of proposed improvements and identifying a preferred design concept for the long-term rehabilitation. The feasibility-level investigations are on pace for completion by the end of 2024 .
Stakeholder Engagement: The preferred design concept(s) will be reviewed by the Bureau of Reclamation and other key stakeholders. This stakeholder engagement process will help determine the preferred design concept to advance for physical modeling.
Physical Modeling: This milestone involves building scale models of the Diversion facilities and adjacent river reach to evaluate and inform further development of the preferred design concept for the long-term rehabilitation. The models will evaluate hydraulics, fish mortality, sediment and debris transport, and the preferred design concept’s ability to achieve project objectives. Physical modeling is expected to be conducted throughout 2025. The physical modeling will culminate in the selection (with stakeholder input) of a proposed action for implementation.
Final Design and Implementation: When the physical modeling milestone is complete, the project team will begin working on final design and identifying construction methods and sequencing for the long-term rehabilitation improvements. Once the design and permitting are complete, and funding is secured, the project will advance into the construction phase. We anticipate multiple construction phases implemented over a period of roughly five years.

Frequently Asked Questions

Why is this project needed?

Some project features were constructed more than 100 years ago and require large-scale rehabilitation to maintain reliable irrigation diversions and improve operator safety, flood control, and flow capacity into the future.

Where is the funding for this project coming from?

Current funding sources include BIA funds and grant funding acquired by the Yakama Nation.

Why can't the long-term rehabilitation project be implemented now?

The design, permitting, and construction processes for the long-term rehabilitation of the Wapato Diversion require years of planning. Furthermore, the cost of long-term rehabilitation is estimated to approach or exceed $100,000,000; final funding sources for the comprehensive solution have not yet been secured.

Who is working on this project?

The major participants of this project include the BIA, the Yakama Nation, Bureau of Reclamation, and BNSF Railway Company. Emails to the project team can be sent to wapatodiversion@dowl.com.

Will this project impact fishing access?

The project will maintain conditions for traditional fish harvest below the Diversion. Making improvements for public fishing access is not part of this project.

Will this project impact irrigation?

The project will improve irrigation delivery reliability; adverse irrigation impacts are not anticipated during construction.

Is irrigation modernization being incorporated into the planning and rehabilitation efforts?

Yes, modernization features are under consideration and will be implemented.

Is the cultural use of the site and facility being taken into consideration?

Yes, the project team is working in coordination with the BIA and Yakama Nation to identify and respectfully address cultural and historic resources.

Are safety considerations being made?

Yes, the project will include modernized safety features and rectify deficiencies to provide a safe environment for operations and maintenance personnel.

How will construction impact recreation on the Yakima River?

Boating and fishing on the Yakima River may be restricted in designated areas while construction is underway. The immediate Diversion vicinity should be avoided by recreationalists before and after construction due to the potential presence of swift currents and hydraulic rollers.

When will construction occur?

Construction of long-term rehabilitation improvements is expected to be completed over 3 to 4 construction seasons and may begin as early as 2027. Construction timing depends on several factors such as funding and permitting.

Will the project require environmental permitting?

Yes. The project is subject to the Yakama Nation Water Code, the Clean Water Act and National Environmental Policy Act (NEPA) of the United States, and potentially other permitting requirements. The BIA will prepare the necessary documents to comply with environmental requirements, including protecting threatened and endangered species and water quality in the Yakima River.

Will the public be notified regarding the status of the project?

Yes. The BIA anticipates a formal public engagement process will be completed as part of NEPA compliance for the project. Regular updates will also be posted to the project website and sent to interested parties via email. You can sign up for email updates here .

Definitions

Diversion

A diversion, in the context of this project, is a type of irrigation facility that is used to divert a portion of the flow of a river from its natural course. Diversions do not impound significant water in a reservoir; rather, they are used to divert river water into an artificial water course or canal. For the Wapato Diversion, the diverted water is used for irrigation of the surrounding agricultural lands of the WIP.

Fish Ladder

A fish ladder, or fishway, is a structure designed to facilitate generally upstream movement of fish past a natural or artificial barrier.

Forebay

A forebay is a small reservoir that separates the water from the river immediately upstream of the irrigation diversion gates and is intended to prevent debris and sediment from entering the irrigation canal system.

Tailwater

Tailwater refers to water located immediately downstream of a hydraulic structure, such as a dam, diversion, spillway, bridge, or culvert.

Trash Rake

A trash rake is a mechanism designed to remove things like branches, trash, and other water-borne debris from an intake structure.

Wapato Diversion

Wapato Diversion Improvement Project

Wapato Diversion Improvement Project

Wapato diversion project

Project Overview

1. Main Canal Headworks

2. West Diversion

3. East Diversion

4. Earthen Embankment

5. Overflow Spillway

6. Rock Weirs

7. Fish Ladders

project background

Why this project is needed

What's Next?

Project Updates

Frequently Asked Questions

Definitions

Diversion

Fish Ladder

Forebay

Tailwater

Trash Rake

Documents

related links

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