City to begin flood control improvements in spring
WORTHINGTON -- Bill Douglas, from the engineering firm Bolton and Menk Inc., presented a flood mitigation study and made recommendations to Worthington City Council members during a special meeting Friday.
Over the years, the city, through the help of engineering firms, has conducted several flood control studies to address the condition of County Ditch 12, which runs through the city. The goal is to reduce flooding risk in the identified flood plain area and accommodate future development in the U.S. 59 Commercial/Industrial Park.
"The flood plain (northwest of the city), under a large enough event, will potentially flood with water trying to get out of this ditch system," City Engineer Dwayne Haffield said.
As recommended by Douglas, the city would need to begin the work of building storm retention ponds and widening a portion of County Ditch 12 at the bottom of the stream as preconditions to counter other flooding-related issues.
The downstream of the ditch lies north of Interstate 90. Based on the recommendation, two primary retention ponds -- at three and four acres respectively -- will be constructed at U.S. 59 Commercial/Industrial Park.
"The ponds will intercept water coming to the ditch to take the load off, and the ditch will be (widened) for it to start looking like retention itself," Haffield said.
The project is part of the city's U.S. 59 North infrastructure project, which will be funded primarily by a $3.4 million grant from the Minnesota Department of Employment and Economic Development and Minnesota Department of Transportation. Work is scheduled to begin next spring.
Other improvements that will follow include constructing additional retention ponds south of I-90 and upstream of the ditch, replacing undersized culverts -- especially ones that are in the flood plain -- and redefining the ditch structure.
Haffield explained if the city resorted to expanding the culverts prior to having necessary storm water management in place, the problem will be diverted downstream and not be solved.
"You can't just pull the plug on the upper part of the stream and just let it go down the stream," City Administrator Craig Clark said in reference to what Douglas presented Friday.
"We can't increase the flooding upstream or downstream," Haffield added about legal implications of replacing culverts without other accommodations.
Apart from the U.S. 59 North infrastructure project, he said that the city does not have a timeline yet for the other improvements because of the uncertainty in funding.
In the long run, when all flood control improvements are completed and the city's new mapping information is approved by the Federal Emergency Management Agency (FEMA), most of the residents in the flood plain area will be relieved of their flood insurance.