City discusses levee study, next step

The El Dorado City Commission is faced with a decision of if to spend up to $200,000 to certify a levee north of town or not to certify it and possibly have FEMA increase the flood area in the city, raising flood insurance rates on those areas.

This came about due to FEMA remapping the entire United States' flood plains following Hurricane Katrina.

"When FEMA started remapping we had to certify the levee could withstand a hundred year flood," explained Scott Rickard, assistant city engineer during a workshop held Wednesday.

They hired Wilson & Company, Inc., Engineers and Architects to evaluate the levee and certify it.
Wilson & Company has competed phase one of that study and brought the results to the El Dorado City Commission.

The levee controls flooding along the west branch of the Walnut River and modifies the flood plain.
This system was built when Highway 54 was constructed. Rather than building two bridges over the river, a diversion channel was put in to change the path of the river.

In looking at the levee, the company reviewed several high-water events in El Dorado over the years.
The first was in 1953, followed by another high-water event in 1965.

Then from 1976 to 2006, 11 watershed dams were constructed north of the city, which reduced the peak flow of water through the levee.

In 1979, there was another flood and the levee was breached.

Following that, the reservoir was constructed, having a big impact.

The last high-water event was in 2005, which was close to a hundred year flood.

"With the watershed dams and lake, the levee almost is not needed," said Doug Danaher, operations manager. "What it handles on peak today is almost half of what it did when it was built."

The certification of the levee will have the most impact on the city because it has the most land in the area that would be changed to a flood plain, including City Hall, McDonald Stadium, the water treatment plant and the Community (4-H) Building.

Butler County would be affected second most.

There also are about three houses that would be affected by the change.

"We talked about letting it be set as flood plain but decided to see if the levees could be certified," said Herb Llewellyn, city manager.

After a standard levee safety inspection, Danaher said there were only minor maintenance items that would need to be addressed because the city has done a good job of maintaining it.

If the city decided to move forward with certifying the levee, the next step would be to do a hydrology study, said Danaher.

While FEMA will be doing new maps of the area in question, they are not going to do a new hydrology study, rather using the information that is 30 years old. That information includes eight of the 11 watershed dams and an estimate of the lake's impact.

FEMA will create flood plain maps with and without the levee.

Danaher said with the new hydrology numbers they may find they don't need to re-certify the levee. The cost of that study would be $30,000.

Among the items looked at for certification are embankment stability and settlement analysis.

The city also would need an operational plan and a formal maintenance plan.

There is a time constraint as well. If the city doesn't have the hydrology study done by the time FEMA is through mapping the area, they will use the old data. That will be about two months.

Rickard recommended they move forward with the study, adding it could be beneficial when looking at development in the future.

The area that could be added to the flood plain is from Griffith Street east, totaling about 160 acres.

"The whole purpose (of FEMA's remapping) is if someone builds in a flood plain, they need to have their own insurance and not rely on FEMA," Danaher explained.

The decision on hydrology will be brought back to the commission at their meeting Monday, along with information on insurance costs so they can decide how to move forward.