Contra Costa Flood Control Completes Miranda Creek Box Culvert and Bank Restoration in Alamo

Hydraulic engineers with the Contra Costa County Flood Control and Water Conservation District and County Public Works reopened both shoulders of Danville Boulevard near Miranda Avenue in Alamo on Friday afternoon after completing the $1.28 million Miranda Creek Box Culvert and Channel Stabilization Project. During heavy atmospheric river storms in recent winters, woody debris descending from the Las Trampas foothills periodically snagged on a narrow, twin-pipe corrugated metal culvert built in 1962, causing storm runoff to back up toward adjacent Alamo properties and roadside walkways. Over an eight-week dry-season construction window, crews replaced the constricted pipes with a single sixteen-foot-wide by seven-foot-high precast concrete box culvert capable of passing a 100-year peak storm flow with two feet of freeboard clearance.

Inside the culvert floor, engineers recessed a sunken low-flow gravel and cobble channel bordered by natural sandstone boulders so aquatic amphibians and seasonal creek flows can pass unimpeded without encountering flat concrete sheets. Upstream and downstream of the Danville Boulevard crossing, watershed restoration contractors reshaped 140 linear feet of vertical dirt banks into terraced stone revetments planted with native creeping wildrye, sedges, and bigleaf maple saplings.

Above ground at street level, masons constructed a hand-laid fieldstone headwall topped with bronze-finished steel pedestrian guardrails and widened the eastern Danville Boulevard sidewalk to eight feet, creating a smoother connection for residents walking to the Alamo Plaza shopping district and the Iron Horse Trail. An automated ultrasonic water-level gauge mounted beneath the headwall now transmits five-minute creek stage readings directly to the county's winter flood-watch network.

Funding for the $1.28 million drainage improvement was provided through Flood Control Zone 3B capital reserves and Contra Costa County Road Fund allocations reviewed by the Alamo Municipal Advisory Council. Residents can monitor live winter creek stage gauges and download sandbag station maps on the Contra Costa County Flood Control Portal.