This is a cutout view of a river.
The dark blue water is water that flows
into the drainage system behind the dams.
The light blue water is water that flows
into the system from uncontrolled
rivers and streams.
When the rains come and the uncontrolled
streams fill the Willamette's system,
the Corps holds water behind the dams.
As the river level drops,
the Corps releases the water into the system.
Every dam has at least two ways to release water.
Some, like this dam at Lookout Point, have three.
For dams that generate electricity,
water passes through the powerhouse
and into the river below the dam.
The second option at Lookout Point
– and the primary route
for dams without powerhouses-
is the regulating outlet.
This is a gated route through the dam itself.
The spillway gates, near the top of the dam,
are used to move water through the dams
when other routes are unavailable
or when the reservoir gets too full.
These gates are always a back-up system
and are not used very often-or even every year.