For anyone who has ever white-knuckled it through southern Marin during a king tide, this will sound familiar: that low stretch of U.S. Highway 101 by Marin City and the Manzanita Park & Ride floods, traffic grinds to a halt, and the detours pile up. Now, engineers and planners are weighing two very different and very expensive ways to keep that key link out of the water, warning that constant closures and emergency work are costly too.
As reported by KTVU, officials have narrowed the conversation to two big ideas to protect the highway and nearby neighborhoods: regional tidal barriers at the mouth of Richardson Bay, or a local rebuild that relies on raising the road, improving drainage, and adding pumps and floodwalls.
Two Very Different Paths To Dry Pavement
One concept, outlined in county shoreline planning, would put large high-tide barriers at the entrance to Richardson Bay, essentially tide gates or similar structures that would limit how much bay water can surge into the estuary. Marin County’s Richardson Bay Shoreline Study maps two potential alignments for those barriers and includes conceptual cost and alignment tables that planners still use to evaluate the option. The same Richardson Bay study shows how different barrier scenarios would change flooding patterns in areas that include the Manzanita lot and the Donahue Street interchange.
The other approach on the table is more surgical and staged. Instead of blocking tides farther out, it would focus on the immediate problem area by raising roadway grades where possible, rebuilding or reconfiguring interchanges, and upgrading onsite drainage with a permanent pump station and shorter floodwalls to protect both the highway and the Marin City neighborhood. Caltrans has identified possibilities such as elevating specific segments or shifting portions of Shoreline Highway, while county staff have been crafting a Marin City stormwater plan that directly budgets work on pumps, floodwalls, and dredging to cut down on repeat flooding…