The Gavins Point Dam is located just west of Yankton, South Dakota.
It is the first of the six major Missouri River dams when heading
upstream, or the last of the six when heading downstream. It was
authorized in 1944 as part of the Pick-Sloan Act, which sought to
control the floods on the Missouri River and provide electrical
power as a side benefit.
While being the smallest of the 6 major dams, the Gavins Point dam is
still very impressive at 8,700 feet long and 74 feet high, with a typical
waterfall of 45 feet. The spillway is 664 feet long and features 14
tainter gates, each 40 feet wide by 30 feet tall. The power plant has
three generators each with a capacity of 44 megawatts, for a total maximum
output of 132.32 megawatts. However, the powerplant typically runs at about
120-megawatts of power output, enough to supply the needs of 65,000
people. From this point and north to eastern Montana, the river is
very much like a stairway with each dam being a tall step. Water flows
down these steps, generating electricity on each step. As a result,
water that flows through the powerhouse at Gavins Point dam may have
generated power 6 different times so far.
The Gavins Point Dam is a major center for recreation for the upper
plains area. There are fishing and boating opportunities, a visitor
center that offers power house tours, and a well developed campground.
History remembers news anchor Tom Brokaw who was a tour guide at the Gavins
Point Dam in 1958. Downstream, the Missouri River channel is untamed
most of the way down to Sioux City, one of the only non-channelized
portions of the Mighty Mo downstream of central Montana.
The Gavins Point Dam garnered a lot of attention during the historic flood
of 2011. The flood was caused by record snowfalls and then record spring
rains. The large storage dams could not hold all of this water, so it
was released downstream. The US Army Corps of Engineers had no choice
but to let the water through Gavins Point. The flow reached an all time
high volume of 150,000 cubic feet per second on June 14, 2011, six times
the typical flow rate. All this water caused massive flooding downtream.
The flooding lingered through the summer of 2011, and the resulting silt
covered large swathes of farmland, causing the 2012 crops to be lost as well.
As the water flow returned to more normal levels, the US Army Corps of
Engineers noted an anomoly with the dam structure. Water flow was
completely turned off between 8 AM and 4 PM on Wednesday, May 9, 2012,
to give access to the spillway apron to be check with ground penetrating
radar. A small amount of concrete damage was found, some errosion of
a gravel frost blanket, and a few small voids in the gravel under the
spillway. This damage is not considered to be serious. The Corps
plans to fix the structure during the summer of 2012.
The photo above is a close-up view of the dam power house. The power house
was finished in 1957, two years after the dam was completed. It features
3 generating units, each of which can produce 44-megawatts.
The photo below is a view of the main dam control structure. The
spillway is 664 feet across, and features 14 Tainter gates that are
40 feet by 30 feet. When this photo was taken, the gates were all
closed, which meant that any water flowing out of the dam was going
through the powerplant.
The photo above is a view of the dam embankment, the fishing deck, and
the Lewis & Clark Lake. The lake is 25 miles long, runs as deep as
45 feet, and has 90 miles of shoreline.
The photo below is a close-up view of the electrical substation that
handles the power being generated in the power house.
The photo above is the start of a crossing of the dam from the Nebraska
side to the South Dakota side. We start by driving up a hill around the
back side of the power substation. There is a one-lane section behind
the power house, so a set of stop lights handles the task of alternating
the direction of traffic flow. What is odd about this light is that it
goes green before all the cars are clear from the road behind the power
plant. The reason is that the road is still 2-way, and they accounted
for that in the light timing. The photo below shows the one-lane
section of road behind the power plant.
In the photo above, we continue traveling past the power plant. The
large metal structure is a traveling crane that is used to adjust the
opening of the gates that allow water into the power house inlet.
The photo below is a view traveling across the spillway. The spillway
is very narrow, so it is also part of the one-way travel section.
The photo above is a view of the spillway from downstream. Notice that
the gates are all closed, and no water is flowing through the spillway.
Every so often, an especially large wave would hit one of the gates,
causing it to vibrate, and a small trickle of water would seep out of
the bottom of the gate. That manages to keep the concrete wet below
The photo below is the main Missouri River channel looking downriver.
This is a very popular fishing spot. The parking lot for the fishing
deck was full, and there are a number of boats in the river.
The photo above is a view down the length of the dam embankment from
below the dam. The photo below is a view looking towards the dam as
we approach the ramp that leads to the top of the dam. The embankment
is 74 feet tall. It is mowed on a regular basis so workers can more
easily identify seepage before it threatens the integrity of the
These two photos are views from the road that crosses the crest of
the dam embankment. The photo above shows the dam just after the
spillway, while the photo below shows the dam as we near the end
of the crossing. The dam is a total of 8,700 feet across.