LITTLE ROCK — The Arkansas Highway and Transportation Department has figured out how to stop the flooding that has interrupted traffic three times along a section of Interstate 30 in Little Rock, but it doesn’t yet have the more than $800,000 estimated to take care of the problem.
The department is proposing to widen the channel of Crooked Creek in the vicinity of a flood-prone section of I-30 and possibly add a small levee on the south side of the interstate. A study of the area concluded these steps should offset the placement of fill in the creek’s flood plain, a result of development at the creek’s headwaters near Bryant and the residential development between Bryant and Alexander since the mid-1990s.
The Arkansas Highway Commission authorized the department Wednesday to begin surveys, plans and construction “as funds become available.”
The section, about a mile west of the Otter Creek exit, flooded most recently on Nov. 21, 2011, closing all six lanes for about three hours. It also was closed for more than 10 hours on Christmas Eve 2009 because of high water. The study noted the section has flooded at least one other time since the section was rebuilt in 2005.
I-30 is a major corridor between North Little Rock and Dallas.
Before rebuilding that section of the road, the department relied on existing hydraulic models developed for the Little Rock Flood Insurance Study by a Federal Emergency Management Agency contractor in the mid-1980s, according to Michael Fugett, the department’s chief engineer for design. The department verified the models in January. The water elevation estimates the models produce don’t explain why that section of the roadway has flooded so often, he said.
Fugett came up with two factors that have contributed to the flooding.
One is development within the Crooked Creek drainage basin, which Fugett said has contributed to an increase in surface-water runoff. That runoff produces an increase in “peak flood flows approaching I-30 at Crooked Creek,” he said in a memorandum to Frank Vozel, the department’s deputy director and chief engineer. The other is the “placement of fill material within the [stream’s] floodplain near the I-30 crossing,” he said.
Fugett said extensive development has taken place at the Crooked Creek headwaters, which are near the I-30 overpass at Exit 123 in Bryant, and “numerous residential developments” have been built within the stream’s basin between Bryant and Alexander. “The placement of fill in the stream’s floodplain has constricted the stream and caused an increase in the depth of flooding along the creek in the vicinity of the highway crossing,” he wrote.
All interstates in the United States are supposed to be designed to withstand what is sometimes termed a 50-year flood elevation, which means a flood that, in any given year, has a 2 percent chance of occurring. Widening the creek channel, now about 20 feet across, to 100 feet would allow that section of I-30 to withstand a 25-year flood elevation. The widened part of the creek would extend from about 100 feet downstream of the north frontage road bridge to 3,000 feet upstream of the south frontage road bridge.
To withstand a 50-year flood elevation, Fugett said, a floodgate would have to be constructed at the confluence of Crooked Creek and a channel that drains the south frontage road ditch. To prevent floodwater from entering the south frontage road ditch, a levee should be constructed between Crooked Creek and the south frontage road, he said. The levee would be less than 4 feet tall.
Total construction and right-of-way costs are estimated at $824,107.
Randy Ort, a spokesman for the department, said the agency will work with the city to obtain the necessary permits to do the work.
Arkansas, Pages 9 on 11/29/2012