Although the water is mostly gone, questions still remain concerning how the U.S. Army Corps of Engineers handled the rising water at the Coralville Dam.
But, for better or for worse, the water pouring out of the Reservoir was controlled through a system that gave little discretion to those manning the outflow.
Despite widespread flooding and a combined $263 million in damages to the University of Iowa and Iowa City, UI and Corps officials say that the Corps did the best it could to limit the amount of flooding, given the regulations imposed on it by regional and federal agencies.
Intense weather circumstances, including two weeks of almost daily rain in the river's watershed, as well as a rigid lake-regulation schedule caused the water to rise over the Reservoir's spillway.
In an analysis of Iowa River data, the Corps didn't deviate from its regulation schedule, which dictated the outflow according to a variety of factors. River levels downstream were the most apparent criteria used.
The Corps of Engineers will begin reviewing its response to the flood this week in order to report its findings in a congressional hearing at the end of July.
"Hydrologically, there was a lot going on," said Larry Weber, the director of IIHR - Hydroscience and Engineering at the UI. "Events like this happen because of extreme situations."
In addition to a winter with heavy snowfall, Iowa received large amounts of rain. In June, Iowa City saw rainfall amounts at 200 percent of the month's usual average, according to the National Weather Service. Rainfall upstream was also considerably above average, especially during the first half of June.
This jump in precipitation placed strain on a strict protocol that determines how much water is let out of the Reservoir. The primary components in the formula are lake level and time of year. Reservoir levels are to be kept at their lowest during spring.
During the spring months, outflow is not supposed to exceed 10,000 cubic feet per second. Once the water levels reach a certain point at the Reservoir, however, maximum outflow can be increased accordingly.
On a day-to-day level, water levels on the Cedar and Mississippi Rivers also influenced outflow. There is no dam on the Cedar, which merges with the Iowa River at Columbus Junction.
Because the Coralville Reservoir is the last control point for any of the water flowing toward the Mississippi from Columbus Junction, managing water levels quickly became a balancing act.
The story downstream determined the decisions at the dam for much of the past few months.
The Daily Iowan analyzed outflow levels, Reservoir levels, and river gage readings for the past four months. There were three instances in which outflow was noticeably reduced and Reservoir levels were allowed to climb.
From March 14 to 22, outflows decreased to as low as 1,218 cubic feet per second before quickly jumping to 9,798 - nearly the maximum permitted at the time - on March 24.
This drop was mainly due to worrying water levels at Wapello, which were at 23.42 feet at the time. According to the Corps' operational plan, outflows must be reduced when river levels are at or forecasted to exceed 22 feet at Wapello.
In late April, another notable drop in outflow occurred. This time, the Corps was operating for gages at Wapello and on the Mississippi River in Burlington. Flood stage at the Mississippi gage is 18 feet, which the Mississippi surpassed on April 24 did not drop below until May 9.
At this point, Reservoir waters were nearing 707 feet above sea level, five feet below the top of the spillway. That situation i considered to be so extreme the Reservoir's tight regulations demand drastically higher outflows to avoid cresting the spillway.
By May 1, 707 feet was reached, and outflow stayed at around 10,000 cubic feet per second for most of the month.
Officials at the dam usually slow down outflow rates to protect fields after May 1. This was not the case this year, because fields were already saturated to a point where extra water would not make much of a difference, said John Castle, the Corps of Engineers operational manager for the Coralville Dam. "Once we hit the 707 mark at the Reservoir, downstream gages don't matter," said Jim Stiman, the water management chief with the Corps.
At the end of May, outflows were decreased dramatically to around 5,995 cubic feet per second after the Reservoir had dropped below the "magic" number of 707 feet. Once below this level, the Corps must reduce outflows to a maximum of 6,000 cubic feet per second for the growing season downstream.
But this year, downpours buffeted the areas upstream, starting with a storm on May 30 that more than doubled water levels on the south branch of the Iowa River at New Providence. After that point, dam outflows increased well above 10,000 cubic feet per second until June 15, when they peaked at 39,100.
"I won't lie - as a manager, I wish we could have let more out," said Randy Haas, chief ranger at the Reservoir. "But the Corps believed it was interpreting the plan as aggressively as possible."
Entities downstream from the lake, such as the UI or Iowa City, can affect the regulated plan by requesting reduced outflows, although it is ultimately the Corps' decision.
The UI requested that the outflow be reduced for half a day on May 11 during finals week in order to keep Dubuque Street clear for Cambuses, said Ken Lloyd, associate director for utilities and energy management for UI Facilities Management, in an e-mail.
Iowa City requested that outflows be reduced by a few thousand cubic feet per second for a few hours during the major flooding in order to give residents more time to sandbag.
Haas and Castle both said neither of those reductions had an effect on flooding.
One facet that many thought was impeding the outflow was the Corps' concern for recreation.
"Recreation is not even a concern," said Ron Fournier, spokesman for the Corps of Engineers in Rock Island, which oversees operations at Coralville. "Our main objective is to prevent flooding downstream."
Clearly, this goal was not met in recent months, but without the dam, flooding would be much more frequent, Castle said. Corps officials maintain that they did not deviate from their regulation schedule.
Any such deviations from the schedule must go through the local Rock Island, Ill., office and the main headquarters in Washington, D.C. Such a decision would take only hours at the most to approve and wouldn't hinder the effectiveness of such a deviation, Fournier said.
The plan is really a political situation," Castle said. "Someone has to decide which areas should benefit more than others."
Many parts of Johnson County, including Normandy Drive in Iowa City and the Coralville Strip, were not developed until after the Dam was completed in 1958, which affected the regulation schedule's development. Input from such contingencies as the UI, the city, and farmers downstream from the Dam were taken into account with the formation of the operations plan.
After the flood of 1993, the Corps came under fire for poor flood prevention. Following every major event, procedures are reviewed and appropriate changes are made, Corps officials said.
Flash flooding on Clear and Rapid Creeks was a major issue in1993, and officials say they have taken steps to better handle those situations. One of the key changes was the addition of water gages in Clear Creek, which runs through Coralville, Castle said.
Public hearings were held in 1999 before the gages were put into place, Stiman said.
Technological advances have allowed for easier and quick access to gage readings and forecasts, allowing for faster reaction by the Corps.
As the city begins recovery, new high-tech developments are always in the works, Weber said.
At the UI, a river hydraulics and hydrology research team is working to design models that will shed light on many aspects of flood prevention.
"There's still a lot to be done to better understand watershed," Weber said. "Also, river gages upstream [from the Reservoir] need to be better understood." But even with new technology, floods are a part of life in eastern Iowa.
"People need to learn how to live with floods," Weber said. "It's going to be a pretty constant theme over the next several years."
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