San Rafael, CA – During late fall and winter months, high tides in Marin County can cause flooding along shoreline communities and low-lying roadways, particularly when coupled with winter storms. The Marin County Department of Public Works (DPW) and the Marin County Flood Control and Water Conservation District are urging residents and visitors to stay informed of changing weather conditions and be aware of expected high tides that might affect holiday travel plans.
Based on tide predictions published by the National Oceanic and Atmospheric Administration (NOAA), tides levels that could be high enough to cause roadway flooding in parts of Marin are expected December 6 and 7, and December 20 to 25, as well as January 1 to 4, and January 18 to 23. Drivers are encouraged to consider using alternative routes and should allow extra time for trips, especially during peak commute times. Travelers should avoid driving through ponded water, as even six inches of standing water can stall a low-clearance car.
The following chart shows predicted high tides at or above 6.3 feet during December and January at the San Francisco tide gauge, as provided by NOAA. If significant rainfall occurs during a high tide of 6.3 feet or more, the likelihood of localized flooding increases for coastal communities and other historically susceptible areas, such as North San Pedro Road through China Camp in outer San Rafael, Greenwood Cove Drive in Tiburon, and Manzanita Park & Ride in Tamalpais Valley Junction.
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Thursday, December 6, 10:12 a.m.
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6.43 feet
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Friday, December 7, 10:46 a.m.
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6.31 feet
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Thursday, December 20, 8:57 a.m.
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6.46 feet
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Friday, December 21, 9:37 a.m.
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6.71 feet
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Saturday, December 22, 10:20 a.m. (king tide)
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6.87 feet
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Sunday, December 23, 11:05 a.m. (king tide)
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6.91 feet
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Monday, December 24, 11:54 a.m.
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6.79 feet
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Tuesday, December 25, 12:45 p.m.
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6.49 feet
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Tuesday, January 1, 7:48 a.m.
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6.33 feet
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Wednesday, January 2, 8:30 a.m.
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6.41 feet
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Thursday, January 3, 9:09 a.m.
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6.42 feet
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Friday, January 4, 9:46 a.m.
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6.37 feet
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Friday, January 18, 8:25 a.m.
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6.56 feet
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Saturday, January 19, 9:14 a.m.
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6.84 feet
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Sunday, January 20, 10:03 a.m. (king tide)
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7.02 feet
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Monday, January 21, 10:53 a.m. (king tide)
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7.05 feet
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Tuesday, January 22, 11:44 a.m. (king tide)
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6.89 feet
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Wednesday, January 23, 12:37 p.m.
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6.52 feet
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December 22 and 23, and January 20, 21 and 22 are predicted to be extreme high tides, also known as king tides. They occur when the earth, moon and sun are aligned to exert the maximum upward gravitational pull on the tides, thereby increasing water elevations. But even normal high tides can still have a significant impact due to non-astronomical factors, such as wave surges during storms.
Future projections by the California King Tides Project indicate that the annual king tides are a preview of what could become the normal, daily tides as sea level rise continues in the coming years. The project also predicts that there will be an increase in daily tidal flooding. In the same vein, the County of Marin released the Marin Shoreline Sea Level Rise Vulnerability Assessment in 2017, a comprehensive study that showed the expected impacts that sea level rise will have on flooding in the region.
The Manzanita Park & Ride Lot, which is located at the junction of Highways 101 and 1 and is overseen by the California Department of Transportation (Caltrans), has a history of flooding when tide levels pass into the mid-six feet range. As in previous years, this sometimes requires Caltrans to close the lower half of the parking lot.
To help lessen the severity of flooding in the Manzanita area, Caltrans has installed two new tide gates in the area. In conjunction with the new Caltrans infrastructure, DPW and Flood District teams have installed a 175-foot-long sandbag wall along Highway 1, adjacent to the Caltrans maintenance yard, where flooding from the bay historically inundates the road.
The public can check 511.org for latest traffic and transit information; DPW’s Twitter feed, the California Highway Patrol (CHP) traffic website and CHP Marin’s Twitter feed are also excellent resources for travelers. Additionally, weather gauges showing rainfall and tide elevations can be viewed in real-time at the County’s OneRain webpage.