High tides often cause flooding along shoreline communities and low-lying roadways of Marin County, which can be exacerbated during winter storms. But tide-related flooding can happen whether it’s raining or not. Such inconveniences are likely to occur over the next few months and may begin as soon as November 13.
“High tides can bring localized flooding to coastal areas, such as Tam Junction, even on sunny days,” says Roger Leventhal, senior civil engineer for the Marin County Department of Public Works (DPW). “However, when coupled with a significant storm, these predicted high tides could increase impact to various areas of Marin where signs of sea-level rise are already causing year-round tidal flooding issues.”
Department of Public Works (DPW). “However, when coupled with a significant storm, these predicted high tides could increase impact to various areas of Marin where signs of sea level rise are already causing year-round tidal flooding issues.”
DPW and the Marin County Flood Control and Water Conservation District are urging residents and visitors to stay informed of changing weather conditions this winter and be aware of the seasonal high tides that have been predicted.
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, primarily coastal areas, are expected November 13-18, December 11-17, and January 8-14. Drivers should allow extra time for trips and should be prepared to use alternative routes if they encounter localized flooded roadways. Travelers should always avoid driving through ponded water, as even six inches of standing water can stall a low-clearance car and 12 inches can strand a standard vehicle.
The following chart shows predicted high tides at or above 6.3 feet through January 2021 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 eastern San Rafael, Greenwood Cove Drive in Tiburon, and Manzanita Park & Ride near Tam Junction.
Future projections by the California King Tides Project indicate that annual king tides, which are extreme high tides, could become the new normal tides as sea level rise continues. King tides occur when the earth, moon and sun are aligned to exert the maximum upward gravitational pull on the tides, thereby increasing overall water elevations. Members of the public are encouraged to participate in the statewide project by taking and sharing photos of shoreline changes during king tide events. The project also predicts that there will be an increase in daily tidal flooding as sea levels rise. 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.
An example of impacted infrastructure is the multiple closures of Highway 37 in the past few years. The route along the San Pablo Bay marshlands, which is under the California Department of Transportation’s (Caltrans) jurisdiction, is a crucial part of the North Bay’s road infrastructure. Studies have been done, including one by DPW, to assess the resiliency and potential solutions in the face of future sea-level rise expectations.
As storms exacerbate high tides, DPW prepares year-round for the rainy season, conducting various maintenance tasks intended to help reduce the risk of flooding. This maintenance includes work such as the recent sediment removal from three Novato creeks and other critical creek clearing efforts and storm drain cleaning activities across the county. Additionally, the Flood District has recently improved several infrastructure sites including a pump station in Tiburon, installation of new tide and creek level monitoring gauges, and the beginning phase of the San Anselmo Flood Risk Reduction Project.
Travelers can check 511.org for latest traffic and transit information. DPW’s Twitter, Marin County Sheriff’s Office’s Twitter, the California Highway Patrol (CHP) traffic website and CHP Marin’s Twitter are excellent resources for travelers and residents looking for updates during storm events. Additionally, weather gauges showing rainfall and tide elevations can be viewed in real-time at Marin County’s OneRain webpage.