Water study addresses flooding issues near State Street bridge

Morgan City has completed a water study of the Weber River at the State Street bridge. The main purpose of the study is to determine how “to get more water to bypass the bridge and lower the flood plain” in that area, Morgan City Manager Ty Bailey told the city council Feb. 13.

The bridge is located in a developed neighborhood, with several homes and commercial buildings within what is considered a 100-year floodplain and floodway.

Although the bridge was originally constructed with the expectation it would not lead to any flooding issues, it was built prior to the mapping programs that are available today that give much better information on how to accomplish that, Bailey said.

The river has had flooding issues at that location. “The bridge and the elevated banks on either side of the channel upstream of the bridge provide a pinch point that causes water levels to rise and spread out into town,” the study said. 

To mitigate this problem the consultants with WSP USA Environment & Infrastructure considered four options to improve the hydraulic efficiency and capacity of the bridge. They looked at reconstruction to enlarge the opening of the bridge, vegetation management (removing vegetation along the banks and in the channel), excavating the river floor, or increasing the bridge’s capacity by installing a box culvert adjacent to the bridge.

The study determined that it would be the most effective and cost-efficient solution to install a 6'xl0' concrete box culvert which would be placed in an already available depression in the terrain along the left bank, downstream of the bridge. This option had the second-lowest projected cost of the four options at $1,600,000 (the lowest projected cost was $60,000 for vegetation management).

“The culvert greatly reduces flooding downstream of the bridge and State Street is no longer being overtopped to the north during the 100-year event,” the study said. “The floodway can be confined to the channel for much of the section around the bridge.”

A secondary goal of the study was to determine the feasibility of developing an inlet on city-owned property next to Tractor Supply where a two-acre community fishpond could be built, Bailey said.

“The concept is to allow fish to migrate in and out of the Weaver River into habitat,” he said. “We're working with DNR on that; it’s several years out but, of course, it has to start somewhere.”

With the study completed, Bailey hopes to be able to apply for grants that would fund the installation of the box culvert along with the future pond and a surrounding park with a natural trail, green space, and a restroom.

“Now that we have a study done it really helps our chances of qualifying for a grant,” he said.

Addressing this problem will have a side benefit for some residents in the area.

“By reducing the floodway there's quite a few homes that wouldn't be obligated to pay flood insurance anymore,” Bailey said.

The study was funded by a Utah Division of Emergency Management grant. λ