Flood

Belvedere suffered its worst coastal storm damage in December 1983 when an extreme tide of over 8 feet NAVD88* coupled with 4 ft waves overwhelmed San Rafael Avenue. The City lost its wastewater supply and 35 lagoon-area homes flooded.

Considerable work has been done since 1983 to reinforce our flood defenses. The Belvedere Lagoon Property Owners’ Association has invested vigilantly in its floodplain management program, including the purchase of two high-capacity water pumps, and the riprap on San Rafael Avenue was raised in the immediate aftermath of the 1983 storm.

Even with these reinforcements, our community is at risk of coastal flooding. Our levees have settled by 3-4 ft since they were built in the 1940s – 1 ft since the 1980s – and now undulate between 8 and 11 ft NAVD88 through core sections. The Bay has also risen by more than half a foot over the past century. Every year, there is a 2% chance that a coastal storm will result in a still-water elevation of over 9 ft, which would overwhelm our levees and lagoon defenses. Wastewater pump stations would flood and sewage would rise into the streets through manhole covers. The electricity and telecommunication assets buried under our access roads could corrode and fail. Emergency services might be unable to access island or lagoon-area properties for an extended period.

Of course, storms do pass, and the damage might be manageable from a one-time event. But with sea levels conservatively predicted to rise by 1.1 ft by 2050, by then the highest tides of each year will over-top our levees. This is not a sustainable situation, with cascading implications for property prices, city-wide revenues, public safety and insurance coverage.

The good news is that we have engineering solutions that can protect our access roads and utilities through to 2050 and beyond.


*NAVD88 refers to the North American Vertical Datum 1988, which is the official vertical datum for surveying and mapping activities in the United States. It serves as a reference for calculating other elevations.

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