Coralville Dam on Iowa River near Coralville, IA

(Satellite)

Street View, Oct 2015

USACE, Rock Island District posted two photos with the comment:

Today's edition of 'Then & Now' takes us over to Coralville Lake! The first photo, taken in 1957, shows construction of the dam and spillway. The area looks much different today as the reservoir has filled in to help with flood control in the area.

Coralville is one of three lakes/reservoirs in the District that help with flood control, in addition to two "dry" reservoirs we have as well!

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USACE, Rock Island District posted

This week's #FlashbackFriday takes us to Coralville Lake just outside of Iowa City, Iowa. Dating back to 1957, this photo shows concrete work being done on the bridge leading to the control tower.

The dam at Coralville was completed in 1958 and regulates runoff from 3,084 square miles of land upstream providing flood protection to 1,703 square miles of Iowa River Valley below the dam.

The emergency spillway is a parking lot for the boat ramp and beach when the lake is at its normal level.

Street View, Oct 2015

The spillway waters flow over some very old rocks.

Street View, Oct 2015

They are from the Devonian Period.

uiowa, p2
This bedrock was exposed by the floods in 1993 and 2008.
"The limestone rocks exposed at the Devonian Fossil Gorge are of middle Devonian age (about 375 million years old) and include the Rapid and Solon members of the Little Cedar Formation. During this time, Iowa and much of North America lay at tropical latitudes just south of the equator, and the Devonian sea covered most of what is now the United States."

USACE, Rock Island District posted

Just a short drive from Iowa City lies one of the Midwest’s most unique geological treasures. Managed by the U.S. Army Corps of Engineers, Rock Island District, the Devonian Fossil Gorge at Coralville Lake preserves a 375-million-year-old ocean floor.

During the Devonian Period, the region that is now a landlocked Midwestern state was positioned south of the equator and covered by a warm, shallow tropical sea. Today, managing this site is a unique part of the USACE environmental stewardship mission, offering visitors a rare opportunity to step back in time.

Read more about the Devonian Fossil Gorge from the latest edition of the Tower Times: https://www.dvidshub.net/.../hidden-earth-revealed-water...

The record 2008 flood:

By United States Army Corps of Engineers - Photo, Public Domain, Link
"View of Coralville Dam at floodstage, Sunday June 15, 2008. The spillway fully open with water about 5 feet deep -- the record for the dam"