Humboldt Bay King Tides Initiative, and Sea Level Rise Inundation Mapping Project

December, 2015


Humboldt Bay King Tides Photo Initiative 2015-16

Humboldt Baykeeper continues to spearhead the annual King Tides Photo Initiative, in which volunteers photo-document the highest tides of the year around Humboldt Bay. King Tides are extreme high tide events that occur when the sun and moon’s gravitational forces magnify one another. King Tides tend to be more dramatic in the winter, especially when storms cause increased wind and waves along the coast. These high water events allow us to envision how flooding from rising sea level will increasingly impact our beaches, shoreline, neighborhoods, and low-lying infrastructure such as roads, water and sewer pipelines, electric and gas transmission lines, and sewage treatment plants.

On December 24, one of the highest tides of 2015-16 is predicted at the North Spit tide gage at 11:03 a.m. (times vary depending on location by as much as one hour). The tide is predicted to reach 8.1 feet, although actual high tide could be higher depending on rainfall, atmospheric pressure, and wind. On October 28, the actual high tide was 8.85 feet—nearly one foot higher than predicted due to overnight precipitation and low atmospheric pressure.

These images will help document flooding, erosion, and dike breaches that we are likely to face with increasing frequency as sea level continues to rise. The photos also help scientists and planners gain insight into how rising sea levels will impact coastal areas in the future. The King Tides Photo Initiative is a great opportunity for Citizen Scientists to contribute to a long-term dataset, while helping inform residents and decision makers about the need to plan for the impending changes to our natural and built environments. To volunteer to help us document this year’s King Tide, or to submit your photos, email us at

For photo tips and to view the Humboldt Bay King Tides Photo Initiative album of past events, visit For more information about King Tides and sea level rise, visit our website at (go to the Sea Level Rise page on the upper left). For more info on shoreline vulnerability, inundation maps, and related issues, visit the Humboldt Bay Sea Level Rise Adaptation Planning Project website at


Sea Level Rise Inundation Mapping Project – Humboldt Bay

Northeastern Eureka and Highway 101 with a half-meter of sea level rise, which is currently predicted for the year 2050. Map courtesy of Jeff Anderson, Northern Hydrology & Engineering.Jeff Anderson of Northern Hydrology & Engineering recently developed a series of inundation maps for the Humboldt Bay Sea Level Rise Vulnerability Assessment Project. The maps show areas vulnerable to existing and future sea levels that are currently protected from inundation due to the natural shoreline, dikes or berms, and railroad or road grades.

Five scenarios were assessed: existing conditions and increments of 0.5, 1.0, 1.5, and 2 meters of sea level rise above Year 2000. Inundation maps were produced for each scenario for mean higher high water (MHHW), mean monthly maximum water (MMMW), mean annual maximum water (MAMW), and 10-year and 100-year flood events.

The maps are available online as downloadable kmz files which can be opened in Google Earth, and as shapefiles which can be imported into GIS software. For more info or to download
the maps, visit



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