Why they exist
A postwar river project reshaped the canyon.
Congress authorized the North Santiam project for flood control, hydropower, navigation, irrigation, and other public benefits. Construction began in 1949; the two dams were completed in 1953.
Detroit Reservoir inundated the original townsite of Detroit, and the community relocated to higher ground. Remnants of the old city can still be seen today when the water level is low. The project became part of the Corps' larger Willamette Valley system.
Read the Oregon Encyclopedia historyThe layout
How water moves through the pair
Upstream
Detroit Dam
The tall concrete dam holds Detroit Lake, stores seasonal runoff, controls floods, and sends water through turbines to generate electricity.
About 3 miles downstream
Big Cliff Dam
The smaller dam captures uneven releases from Detroit and releases them more steadily, reducing rapid downstream fluctuations while also producing power.
Follow the water
Detroit and Big Cliff on the North Santiam
The river flows west from Detroit Dam through Big Cliff's reregulating reservoir, then toward Gates and Mill City.
Why two dams?
Detroit does the heavy lifting. Big Cliff steadies the handoff.
Detroit's large reservoir can store winter storms, release water in dry months, and send extra water through its powerhouse when electricity demand rises. Those changing releases would otherwise create rapid rises and falls in the North Santiam.
Big Cliff sits 2.8 miles downstream as a smaller re-regulating reservoir. It temporarily catches Detroit's uneven outflow, then meters that water into a more consistent downstream flow. That lets Detroit respond to power and reservoir needs without passing every operational swing directly to communities and habitat below.
Why that partnership matters to the drawdown debate
The proposed deep drawdown changes how water leaves Detroit Dam: lower outlets may help juvenile fish pass, but reservoir depth also affects sediment movement, water temperature, power operations, and water quality. Big Cliff can smooth the timing of releases, but it cannot put sediment back in Detroit Lake or erase changes in the water arriving from upstream. That is why the debate involves the whole two-dam system—not Detroit Lake alone.
One system, several jobs
What the dams manage
Flood storage
Detroit Lake holds winter runoff and helps reduce flood peaks downstream.
Hydropower
Both projects generate electricity as water passes through their powerhouses.
Flow timing
Big Cliff evens out Detroit's power-driven release changes before water travels downstream.
Temperature
Outlet depth and operations affect downstream water temperature and fish habitat.
Why this matters now
The drawdown uses the same plumbing in a new way.
The current debate centers on how low Detroit Reservoir should go to help young fish pass through lower outlets—and what that operation could mean for sediment, temperature, drinking water, recreation, and downstream communities.
Cited resources