2023 Top Projects: Dry-weather diversion captures low-flow runoff

To help Ballona Creek with it s Total Maximum Daily Load (TMDL), the city of Culver embarked on this project. While the primary goal is to improve water quality in Ballona Creek, the project includes a dry-weather diversion that will capture low flow runoff from Centinela Creek Channel, a tributary to Ballona Creek and Santa Monica Bay, that will be discharged into the City of Los Angeles’ sewer system. An inlet with a steel grate will be placed in the channel to allow for the runoff to flow.

The runoff will then be conveyed to a pump station within the channel and pumped to the Mesmer Pump Station with a 6-inch force main. When wet weather occurs, the diversion pump station will shut off, leaving sufficient capacity for sewer flows.

Securing the proper environmental permits proved challenging. Because the project includes improvements within an open channel subject to environmental permit regulation, the team had to secure permits for Sections 401, 404, 408, and 1602 before construction.

Permit restrictions also crunched the channel construc- tion timeline. Work was not allowed in the open channel between April and October without extensive and expensive bypass controls. Nevertheless, the team secured the correct permitting with proper, and early, planning and the project began. The contractor implemented two mobilizations to avoid work in the channel during the storm season. This project is the first of three identified for Ballona Creek.

"This project is important because it improves water quality and increases local water supply reliability, both of which enhance the environment now and in the future,” said Katie Harrel, special projects manager for CWE.