Contra Costa County is undertaking the largest public works project in its history after the Board of Supervisors voted recently to spend more than $11 million on the sweeping Lower Walnut Creek Restoration Project that aims to improve both flood control and conditions for wildlife and recreation.

The board at its March 23 meeting followed county staff recommendation in approving a deal with Four M Contracting, which came in with the lowest bid on the project, at $11.285 million.

The Winters-based civil engineering firm specializes in wetland enhancement projects and the creation of wildlife habitat. The company has done more than 100 projects in California and Oregon, and recently finished the Lower Yolo Restoration Project in the northern section of the Delta, transforming cattle land into wetland habitat for endangered Delta smelt and other wildlife.

Lower Walnut Creek covers the northernmost area of where Walnut Creek meets Suisun Bay. The watershed is the largest in Contra Costa County, draining more than 150 square miles in eight cities containing more than 300,000 residents, according to the project’s website.

The channel is heavily impacted by sediment from the surrounding valley, effecting its flood-control capacity. The goal is to remove sediment without harming the local ecology. The project — decades in the making — would open the area and increase tidal wetlands, improving access for wildlife, including Chinook salmon and steelhead.

Another goal of the plan to is increase human recreational opportunities in the channel. The Contra Costa County Flood District and East Bay Regional Park District have discussed extending the Iron Horse Trail from its current ends near state Highway 4 at Marsh Drive another three miles along Lower Walnut Creek to the park district’s Waterbird Regional Preserve, east of Interstate Highway 680 near Martinez.

The project would add levees to establish the trail extension. The plan would also add public access to Pacheco Marsh, including 2.4 miles of new trails, staging area, elevated vistas, bird-watching blinds, and restrooms. There could also be at least one bridge over the channel and a launch area for small watercraft.