Roadway Flooding Coming to Marin

MARIN COUNTY, CA -- High-tide flooding is expected in Marin County starting Sunday, Dec. 11, and the County’s flood control experts are urging residents and visitors to stay informed of changing weather conditions and research how high tides might affect travel plans.

Travelers can expect flooded roadways in parts of Marin County from Dec. 10 to Dec. 16, based on tide predictions published by the National Oceanic and Atmospheric Administration, as well as Jan. 8 to Jan. 14. Drivers are encouraged to consider using alternative routes, avoid driving through ponded water, and allow extra time for trips, especially during peak commute times.

The California Department of Transportation says it plans to close the lower half of the Manzanita Park and Ride Lot, located at the junction of Highways 101 and 1 near Mill Valley, from Dec. 8 through Dec. 16. The closure, consistent with previous years, is done because the area is notoriously susceptible to tidal flooding when tide levels exceed 6.2 feet.

The Marin County Department of Public Works and Marin County Flood Control and Water Conservation District have worked with Caltrans staff over the past several months on various potential short and long-term options to alleviate the flooding situation along Highway 1 in the Manzanita area.

District staff provided a temporary solution for this winter by building a 175-foot-long sandbag wall along Highway 1, adjacent to the Caltrans maintenance yard, where flooding from the bay historically inundates the road. This created a barrier for the west side culvert and ditch system. While the sandbag wall will help with flooding from this one location, the risk of flooding is still high at other locations in the area given the predicted tides levels.

The accompanying chart includes predicted high tides at or above 6.3 feet during December and January at the San Francisco tide gauge, as provided by NOAA.

• Saturday, Dec. 10, 7:52 a.m. -- 6.36 ft.
• Sunday, Dec. 11, 8:36 a.m. -- 6.70 ft.
• Monday, Dec. 12, 9:20 a.m. -- 6.96 ft.
• Tuesday, Dec. 13, 10:06 a.m. (king tide) -- 7.09 ft.
• Wednesday, Dec. 14, 10:53 a.m. (king tide) -- 7.06 ft.
• Thursday, Dec. 15, 11:41 a.m. -- 6.86 ft.
• Friday, Dec. 16, 12:30 p.m. -- 6.49 ft.
• Sunday, Jan. 8, 7:22 a.m. -- 6.45 ft.
• Monday, Jan. 9, 8:12 a.m. -- 6.74 ft.
• Tuesday, Jan. 10, 9:02 a.m. -- 6.93 ft.
• Wednesday, Jan. 11, 9:51 a.m. (king tide) -- 7.01 ft.
• Thursday, Jan. 12, 10:40 a.m. -- 6.93 ft.
• Friday, Jan. 13, 11:28 a.m. -- 6.71 ft.
• Saturday, Jan. 14, 12:06 p.m. -- 6.34 ft.

December 13 and 14 and January 11 are predicted to be extreme high tides, also known as king tides. These occur when the Earth is closest to the sun and when the moon’s orbit is closest to the Earth, thereby causing a strong gravitational pull on surface water.

Future projections by the California King Tides Project indicate that these annual king tides are a preview of what could become the normal, daily tides as sea level rises in the coming years. The project predicts that there are potential impacts on future tidal flooding.

“Steps are being taken to help with flooding in the Manzanita area, as with all the flood control zones throughout Marin,” DPW Principal Civil Engineer Tony Williams said. “But there is still much to be done to protect our coastal regions in future years.”

The latest traffic and transit information is available at 511.org. DPW’s Twitter feed, the California Highway Patrol (CHP) traffic website and CHP Marin’s Twitter feed are also available resources for travelers.

Image courtesy County of Marin