One wet spring was enough to convince Joseph Robidoux to move his trading post from the mouth of Roy’s Branch to higher ground one mile south near Blacksnake Creek.

More than 180 years later, the city plans to regain control of the Roy’s Branch watershed.

The city will accept bids until May 21 on the second phase of a project to build a separate stormwater system to capture runoff before it enters the sanitary sewer system. The job is part of the city’s Combined Sewer Overflow Long Term Control Plan, which aims to reduce the annual volume of raw sewage that flows into the Missouri River.

City Public Works Director Bruce Woody explained how the Roy’s Branch work will address the problem.

Government agencies measure the city’s sewer issue by the number of days when the city experiences an overflow. Roy’s Branch experiences some of the fewest overflows of the local streams that flow into the Missouri River, which means the number of days likely will not drop.

“It still makes a dent in the overall volume, and that is what we’re really trying to do,” Mr. Woody said.

The North Side stream is one of the city’s smallest combined sewer systems — better measured in blocks than miles.

The area’s hilly terrain made it difficult to extend sewer lines into the area when it was developed in the 1940s and ’50s, Mr. Woody said. As a result, many homes use septic tanks, which cuts down on sewer volume.

Work is expected to begin this summer on the second and final phase of the Roy’s Branch project. Upon completion, the city will capture an estimated 95 percent of all stormwater runoff from the watershed.

The city completed the first phase of the project in 2008 near the intersection of Highland and Dewey avenues. This summer’s work will take place along Chestnut Street, east of Prospect Avenue, and on Elwood and Bellevue streets, east of Chestnut.

On the surface, it will appear that workers are doing street and curb upgrades.

“The fringe benefit is that you’re going to have a much-improved roadway,” Mr. Woody said. “It’s just icing on the cake.”

Clinton Thomas can be reached at clintonthomas@npgco.com.