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County gets going on Weber River floodplain mapping study

Dec 04, 2023 12:18PM ● By Linda Petersen

Morgan County is planning to hire an engineering firm to complete a floodplain mapping study for the portions of the Weber River within the county, from the downstream Morgan City corporate limits to the upstream limit of the Morgan County fairground property.

County officials are concerned that current FEMA maps do not accurately reflect actual floodplain impacts to properties along the river, so they are planning to contract with CRS Engineers for the study. CRS was the only firm that responded to the county’s request for proposals for the study. On Nov. 7 the county commission voted to accept CRS’ proposal.

“This has been a long time in coming,” Commissioner Jared Anderson said, “but we were able to obtain funding.”

The funding Anderson referred to is a $50,000 grant from the Community Impact Board which requires a 50 percent match. County officials are currently investigating options to come up with the matching funds.

“We've talked about it, but we can double-check on where that $50,000 is going to come from [but it appears it will be] mainly through tourism funds,” he said.

The two-phase study is expected to cost somewhere in the neighborhood of $84,000 (nearly $40,000 for the first phase and $44,500 for the second.) On top of that Morgan County will pay applicable FEMA fees, estimated at around $15,750 to submit a floodplain map revision application.

The area that will be mapped will be from the county fairgrounds to just west of the city dump and just east of the sewer plant, Anderson said. CRS will subcontract with Ben Rood of WSP to work on the flood mapping. In 2012 Rood actually performed the hydraulic analysis that was used to create the current floodplain maps.

“We’ve got the previous FEMA modeler who worked with another firm at the time and actually modeled this in a 1D method so fast forward to now they can do a 2D method which means what you see right now has a very good ability to be reduced,” Anderson said.

“You can never say it'll disappear obviously, but they'll reduce it,” he added.” They'll have meetings with us, discuss with us: ‘Hey how does this look?’ Have we seen previous flooding in this area? ‘We've reduced it this for this and this reason’ and they meet multiple times with the county [staff] and I think we'll get a much better more accurate representation of the flooding in that area.

In the first phase of the project CRS and Rood will evaluate potential floodplain changes that could be implemented to hopefully reduce the floodplain. 

“The advancements in hydraulic analysis over the past 10 years sets the stage for improving the accuracy and detail of hydraulic modeling,” the CRS materials say. “The analysis will be taken far enough upstream and

downstream so that the boundary conditions of the model will tie to the effective floodplain. If the results show a significant change, the CRS/WSP team will recommend that the model be advanced to a level that meets all FEMA criteria in preparation for a map revision application.

The team has already completed a hydrologic analysis of the river and has found that “a reduction in the 100-year peak flow would be acceptable under the new … FEMA guidelines,” according to the materials CRS submitted in response to the county’s request for proposals. That analysis could be incorporated into the first phase of the Morgan County study.

In the second phase of the study CRS/WSP will prepare a physical map revision to submit to FEMA to update the floodplain map

The commissioners then voted unanimously that evening to approve the CRS/WP proposal. They are expected to approve an actual contract with the engineering firms in the coming weeks.

“Thank you for the work on that,” Commission Chair Mike Newman said. “I know it's it has been a long time coming so I’m excited to see the results now.” λ

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