Upstream of Iowa City on the Iowa River lies the Coralville Reservoir. Started in 1949 and completed in 1958 by the U.S. Army Corp of Engineers, the dam across the Iowa River provides recreation, flood control, and guaranteed water flow for the city’s water supply. A marina provides boat docks, while sand heaped on the shore of the reservoir provides a popular sunning and relaxation spot. The spillway (a raceway on the side of the dam designed to allow overflow water to bypass the dam when water levels exceed the dam’s safe storage limits) doubles as a parking lot with a ramp for putting in small boats.
But in June 2008, the spillway filled its original purpose. Heavy rains triggered unprecedented flooding on rivers throughout Iowa. Water levels on the Iowa River rose, flooding parts of Iowa City, and the Coralville Reservoir also filled and poured over its spillway. This trilogy of false-color images, obtained from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite, shows Coralville Reservoir in a typical (bottom), high water (center), and severely flooded state (top).
In the typical state, the sandy beach is visible, tan against a background of red plant-covered land, and the water outlet from the dam provides a steady flow of water downstream into the Iowa River. In a high-water state, such as was present in late June 2004, the beach is completely underwater, and the dam outlet is opened more fully to allow a higher flow rate into the river downstream. The turbid, fast-moving water is a large stream of white in the center image. In the top image, taken during the June 2008 floods, water levels have reached such a high state that the parking lot is completely underwater, and substantial amounts of water are flowing through the spillway. In the extreme flood, the reservoir is only able to slow the heavy flow of excess water in the river and is not able to provide its usual protection from flooding.
The flooding may have one positive outcome. The last time water flowed over the spillway from the Coralville Reservoir was during the memorable floods in 1993, reported The Gazette, a local newspaper. The overflowing water gouged the land down to the bedrock, revealing a bed of fossils. The fossilized sea lilies, corals, and other sea creatures lived 375 million years ago when Iowa was covered by a warm sea, said The Gazette. Called the Devonian Fossil Gorge, the fossil bed may be expanded as fresh flood waters burst through the spillway.
Upstream of Iowa City on the Iowa River lies the Coralville Reservoir. Started in 1949 and completed in 1958 by the U.S. Army Corp of Engineers, the dam across the Iowa River provides recreation, flood control, and guaranteed water flow for the city’s water supply. A marina provides boat docks, while sand heaped on the shore of the reservoir provides a popular sunning and relaxation spot. The spillway (a raceway on the side of the dam designed to allow overflow water to bypass the dam when water levels exceed the dam’s safe storage limits) doubles as a parking lot with a ramp for putting in small boats.
But in June 2008, the spillway filled its original purpose. Heavy rains triggered unprecedented flooding on rivers throughout Iowa. Water levels on the Iowa River rose, flooding parts of Iowa City, and the Coralville Reservoir also filled and poured over its spillway. This trilogy of false-color images, obtained from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite, shows Coralville Reservoir in a typical (bottom), high water (center), and severely flooded state (top).
In the typical state, the sandy beach is visible, tan against a background of red plant-covered land, and the water outlet from the dam provides a steady flow of water downstream into the Iowa River. In a high-water state, such as was present in late June 2004, the beach is completely underwater, and the dam outlet is opened more fully to allow a higher flow rate into the river downstream. The turbid, fast-moving water is a large stream of white in the center image. In the top image, taken during the June 2008 floods, water levels have reached such a high state that the parking lot is completely underwater, and substantial amounts of water are flowing through the spillway. In the extreme flood, the reservoir is only able to slow the heavy flow of excess water in the river and is not able to provide its usual protection from flooding.
The flooding may have one positive outcome. The last time water flowed over the spillway from the Coralville Reservoir was during the memorable floods in 1993, reported The Gazette, a local newspaper. The overflowing water gouged the land down to the bedrock, revealing a bed of fossils. The fossilized sea lilies, corals, and other sea creatures lived 375 million years ago when Iowa was covered by a warm sea, said The Gazette. Called the Devonian Fossil Gorge, the fossil bed may be expanded as fresh flood waters burst through the spillway.
NASA image created by Jesse Allen, using data provided courtesy of NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team. Caption by Holli Riebeek.
