Colorado Springs crews will start building a detention pond and culvert this fall, extending Tutt Boulevard north over Cottonwood Creek to mitigate floodwater that otherwise would flow downstream.

The City Council approved a $346,506 appropriation Tuesday to kick-start the project. Property owners northeast of Powers Boulevard and East Woodmen Road generated that money with fees they paid since 2003. Design work will begin immediately, said city Stormwater Manager Rich Mulledy.

The project will cost about $1.75 million, said Brian Kelley, the city’s engineering programs manager. The city’s stormwater fund will pay the balance.

A detention pond will be built northeast of Tutt Boulevard’s dead-end near Cowpoke Road, Mulledy said. Then a box culvert, to control the flow in and out of the detention pond, will span the creek, and the roadway will be extended on top of that culvert to serve as a bridge with two lanes in each direction, he said.

“It’s all to protect the infrastructure and the buildings downstream and to lower the flows on Cottonwood Creek and subsequently lower the flows on Monument Creek,” Mulledy said. “Cottonwood Creek has some significant flows, and in a large event, we’re trying to knock those down.”

The culvert will be built to handle a 100-year flood, Kelley said.

While residents will get a bridge across Cottonwood Creek, the project also counts toward the city’s agreement with Pueblo County. That 20-year, $460 million pact began in April 2016 and requires the city to invest in stormwater projects each year.

Construction is expected to start in late September or early October, when the creek’s water levels are low, and should be finished by next spring.