At 2-1/2 miles wide and 210 feet tall, the Garrison Dam is the fifth largest
earthen dam on the planet. The reservoir behind the dam, named Lake
Sakakawea, stretches across 178 miles and contains enough water to cover
the entire state of North Dakota six inches deep. The dam was built for
flood control, hydroelectric power, and irrigation. While the first two
goals were met, the irrigation project was never finished. Canals
running long distances across the state remain empty due to a 22 mile
section of canal that was never completed. The million new acres of
irrigated farmland never materialized, and the best farmland in the state
was flooded out when the dam was closed off, including nearly all tillable
land allotted to Indian tribes. As a result, local tribes refer to the
Garrison Dam as the unfinished dream.
The photo above is looking east towards the dam from the west end of
the structure. The powerplant is located on the near right side of the
photo, while the intakes are on the near left side. The spillway is
located on the east end of the dam, some 3 miles in the distance.
The photo above is the power plant intake. Water flows into this structure,
though pipes under the dam, and into the powerhouse. There are 8 intakes in
total. Five are for the five power power turbines, and three are for flood
control. The flood control intakes bypass the powerplant and flow directly
into the river downstream. The intake pipes are 24-feet in diameter, while
the flood control pipes vary between 22-feet and 26-feet in diameter. The
water is approximately 180 feet deep at this location.
The photo below is looking downstream at the power plant and the tail
channel flowing away form the dam. There are ten large tanks on top
of the power plan building. These are surge tanks. They act like
buffers to briefly hold the water flowing into the power turbines. This
tends to smooth out the flow, which keeps the pressure on the turbine
blades more even, resulting in much longer life.
The photo above is another view of the power plant and electrical power
substation. The power plant has five turbine generating units capable of
generating 515 megawatts of power, though typical operation is about half
The photo below is looking east along the highway that runs across the
dam. The lake is to the left, and the downstream face of the dam is to
the right. The base of the dam is 2,050 feet thick, and it tapers to a
width of only 60 feet wide at the top.
The photo above is taken from the lower service road looking up towards the
top of the face of the dam. The main highway is on top of the dam, some
200 feet higher in elevation. The dam is planted with grass and mowed at
least twice a year. Mowing the grass is essential to keeping weeds and
brush down, and to be able to see any wet spots due to leakage long before
it becomes a problem.
Below is another view looking east across the dam. The highway across
the top of the dam has several curves connected by long stretches of
The photo above is another view looking east along the highway at the
top of the dam. We are getting very close to the spillway. The red and
white rock riprap on the left side of the photo is the edge of the lake
and part of the wall between the lake and the spillway. The red layer
is normally above lake level, while the white section is normally below
water. The height of the white rock shows how far down the lake is in
late 2007 when this photo was taken.
The photo below shows the downstream side of the emergency spillway.
The spillway is used in the event of a major flood where the lake is
low, and the power plant cannot pass enough water to prevent the dam
from over-topping. An over-top situation could lead to dam failure,
so the spillway is needed to divert flood waters though the dam. There
are a total of 28 gates, each of which are 40 feet wide and 29 feet
tall. Under normal operation, the spillway is dry.
Here are two views of the highway bridge over the spillway. Both photos
are looking east. The upper photo is entering the bridge from the west
end. The lower photo is exiting the bridge on the far east end of the