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Empty Chamber Inside an Idaho Dam Filled with Water to Test for Another Turbine by Daniel Garcia Energies Media, August 11, 2026

The dam's constructors built a chamber next to three generators
anticipating the possibility that a fourth generator would be required

Water flooded a concrete chamber in Idaho's Dworshak Dam that has been dry for about 50 years.

A powerhouse with an empty bay inside can appear incomplete or neglected. This one had been stored for a future generator.

Engineers flooded it for the first time in July 2025 to test the components under the powerhouse floor. It was an early sign of increased hydro capacity in the Pacific Northwest.

What might one learn from a controlled flood of that space about converting it into an active unit?

The construction of Dworshak with growth potential

Dworshak Dam is located on the North Fork Clearwater River near Ahsahka, Idaho.

The dam was authorized by Congress in 1962 and finished by the U.S. Army Corps of Engineers in 1973.

It has a power house designed to accommodate six generating units. Only three were installed, leaving additional bays as concrete shells.

The combined capacity of the operating units is now 450 megawatts. The Corps' biggest single unit is one generator that produces 250 megawatts.

Another turbine was revived in the 2010s as the region looked for more dependable renewable energy.

The idea was reauthorized by Congress in 2014. The feasibility study was completed in 2019, and formal design work started in January 2025.

The July flooding was centered on the bay that was meant for Unit 4.

The engineers filled the chamber to test the draft-tube bulkheads and to study the behaviour of the structure under water pressure.

No machinery was installed during the exercise. It determined if decades old infrastructure could accommodate the next design phase.

A new machine could transform more than output The proposed generator would bring in 250 to 300 megawatts of capacity.

Depending on operating conditions and electricity demand, output can provide over 200,000 homes, the Corps says.

Its value would extend beyond producing additional power.

Hydropower units can ramp up and down within minutes, allowing the grid to adjust when demand increases or other generation decreases unexpectedly.

A fourth machine would also be available to serve as a backup if Dworshak's largest generator went out of service or needed repair.

Another important consequence is water management.

Excessive amounts of atmospheric gases can be absorbed by water when it flows over a spillway. Fish downstream can be affected by high levels of dissolved gas.

Increasing the amount of water passed through turbines may decrease the amount of spill during certain operations.

The existing release of cold water from Dworshak Reservoir provides habitat for migrating salmon and steelhead further downstream in the Snake River system.

Another unit might provide additional options for operators to balance electricity generation, reservoir levels, and fish requirements.

But those benefits are still subject to engineering studies and environmental review. That unfinished process was provided by the flooded chamber, according to America's Engineers.

The infrastructure behind the concrete walls

This was not a chamber into which a turbine width was to be inserted.

It was designed with future expansion in mind, and much of the supporting infrastructure is already in place.

Original construction consisted of penstock, intake gate, bulkheads, cranes, drainage equipment and powerhouse systems.

That preparation is the gap between Unit 4 and a proposed turbine at a new site.

For the first time in decades, water was placed against the draft-tube bulkheads in the July test.

Those barriers separate the downstream water passage when crews require a dry workspace.

When the flooding occurred, engineers were able to evaluate their condition and move forward with detailed design.

It transformed preserved blueprints and concrete into up-to-the-minute information about a structure built in another time.

What needs to occur before the turbine can spin

The test was not used to approve construction or to determine if Unit 4 will be in service.

In August 2025, the Corps reported the flooding while in the early design phase.

It was thought that design would take 3-4 years. Then another 5 to 7 years of construction would be required.

Fiscal year 2036 was a targeted, but not guaranteed, operating year identified by the agency.

A comprehensive environmental impact statement and biological assessment were planned to commence in 2026.

Those reviews should consider impacts under environmental legislation, such as protection for endangered species and water quality.

Engineers also have to determine how the existing systems will expand around a new 250- to 300-megawatt machine.

The chamber is therefore a benefit and not a completed work

It has concrete walls that shorten the journey as earlier builders left room, water passages and lifting equipment.

The flood proved that a possibility that had been a dream for fifty years could come into reality in modern engineering. In 2026, the Corps continued to report Unit 4 as one of its active modernization projects.

The water within Skeleton Bay altered the look of a space waiting since Dworshak's first construction.

It failed to establish that a fourth turbine will be received. It demonstrated to the engineers where to start serious design work.

That's a more interesting announcement than an expansion announcement.

The dam's constructors built a chamber next to three generators that were in operation, anticipating the possibility that a fourth generator would be required.

After 50 years, water finally came in, pushing against old barriers while engineers measured a possible new role.

Related Pages:
Corps Looks to Add Another Turbine to Dworshak Dam by Eric Barker, Moscow-Pullman Daily News, 8/22/25
Dworshak's "Skeleton Bay" Flooded in Key Step Toward Regional Energy Growth by Marcy Sanchez, Daily Fly, 8/21/25