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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 on the Yakima River was originally constructed in 1916 by the BIA and includes two diversion structures spanning the east and west channels of the Yakima River south of Union Gap, WA. This facility is the primary point of diversion for the Wapato-Satus Unit of the Wapato Irrigation Project (WIP), allowing diversion of approximately 2,040 cfs into the WIP Main Canal.

Previous work on the diversion structures include:

Fish passage structures and crest raises were constructed in 1985.
Tailwater modifications constructed in 2004.

Ongoing operational, structural, and environmental issues impact the short-term delivery of irrigation water and the long-term operation of the Diversion facilities. The BIA has partnered with the Yakama Nation to perform temporary repairs on the Main Canal Headworks structure adjacent the Diversion to help alleviate short-term operational concerns and extend the operable service life of the existing headworks. The BIA and Yakama Nation have hired the engineering firm DOWL to develop and design a more permanent solution addressing the operational, structural, and environmental issues of the facility.

Why this project is needed

Operator Safety

The existing safety features, specifically, walkways and the trash rake mechanism do not meet current industry standards. The trash rake is particularly problematic, as wood and large debris in the Yakima River is often trapped in the headworks forebay where it can become lodged in the headgates.

Operational Issues

The BIA is challenged, at times, to maintain adequate water diversions at peak irrigation demand during the summer. In addition, WIP crews cannot safely dewater the Main Canal headworks forebay to perform maintenance on the deteriorating headworks facility.

Fish Passage and Entrainment

The current fish passage facilities are operated and maintained according to Federal criteria for adult and juvenile salmon and steelhead. Fish ladders at diversion dams in the Yakima Basin were not originally designed to pass Pacific lamprey efficiently, and lamprey passage modifications recently tested at other diversion dams will need to be retrofitted at the Wapato Diversion. 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 serious. This project provides an opportunity to modify the headworks and bypass system at the Diversion to minimize its contribution to this problem.

Sediment Transport

The current structure provides very limited ability to pass transported river sediments downriver. Sediment accumulates upstream of the Diversion and contributes to the operational challenges of the facility. Dredging has historically been performed in the west channel upstream of the Diversion to clear sediment and debris; however, the environmental impact of this practice makes dredging undesirable.

Evaluation of Possible Stability Concerns

In 1996 a severe flood event on the Yakima River resulted in undermining (erosion caused by the water current) below the East Diversion. This was addressed in 2004; however, additional undermining may have occurred during subsequent flood events.

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 infrastructure risk, an overtopping event could result in an uncontrolled release of water into the WIP Main Canal, with catastrophic results.

Fish Harvest

Modifications to the Wapato Diversion will be designed to minimize impacts on traditional fish harvest and to improve access for traditional fishers as much as possible.

Frequently Asked Questions

Why is this project needed? What are the goals of this project?

The irrigation diversion structures were constructed in 1916. The structures are showing their age 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?

The project is being funded by the BIA.

Why are both short- and long-term construction projects proposed? Why can't the long-term repair be implemented now?

The design, permitting, and construction processes for the long-term rehabilitation of the Wapato Diversion require years of planning, preparation, and construction. However, issues with the irrigation headworks require repair on a faster timeline to continue reliable delivery of irrigation water to approximately 120,000 acres within the Wapato-Satus Unit of the WIP.

Who is working on this project?

The major participants of this project include the Bureau of Indian Affairs, the Wapato Irrigation Project, the Yakama Nation, and DOWL, the design engineer. Emails to the project team can be sent to wapatodiversion@dowl.com.

Will fishing access be impacted by this project?

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 irrigation be impacted by this project?

No adverse impacts to irrigation deliveries are anticipated. Major construction efforts will generally occur outside of the irrigation season.

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

Yes. we are considering potential opportunities and needs to modernize aspects of the facility.

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 potential cultural and historic resources and will seek to avoid, minimize, or mitigate project impacts to these resources.

Are safety considerations being made?

Yes. Safety of operations and maintenance personnel is a key focus of the project.

How will recreation be impacted by the construction on the Yakima River?

Boating and fishing on the Yakima River will likely be restricted in construction areas while improvements are underway. Swift currents and hydraulic rollers at the Diversion pose a hazard to recreationalists, and the Diversion structures should be avoided before and after construction as well.

When will construction occur?

Construction to address short-term operational issues is currently planned for the fall of 2022. The major construction rehabilitation effort of the Diversion may begin as early 2025. This construction effort depends on several factors such as funding and permitting. Adjustments to the schedule will be made as needed.

Will the project require environmental permitting?

Yes. Because the project is federally funded, it is subject to the National Environmental Policy Act (NEPA). The BIA will prepare the necessary documents to comply with environmental requirements, including protecting threatened and endangered fish, minimizing impacts to wetlands, and protection of water quality in the Yakima River.

Will public notice be given regarding the progress of the construction?

Yes. Public notice will be given approximately four weeks prior to the beginning of construction with regular updates provided throughout the duration of the project. 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

Schedule

Anticipated Project Schedule

Project Updates

Frequently Asked Questions

Definitions

Diversion

Fish Ladder

Forebay

Tailwater

Trash Rake

Documents

related links

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