Coverage of Downtown Laguna Beach from Different Flood Heights

We show maps of downtown Laguna Beach from flood heights beyond 6 feet above mean highest high tide.  There are of course two high tides and two low tides a day.  The average of the highest high tide is used to measure flood heights.  Presumably, sea coast regions will will be adapted to the highest or King tides, which are about three feet above the mean highest high tides.

We use the climate central website http://ss2.climatecentral.org/ which has the Surging Seas Risk Zone Map, to focus on Laguna Beach.  Another link is to http://riskfinder.climatecentral.org/

In the downtown Laguna Beach area, we first see an incursion when the water level is at 7 feet on the vertical scale.  The incursion covers the Coast Highway between Broadway and Ocean Avenue.  It is colored green since it actually is protected by a levee, namely the boardwalk.

Then we add water level maps for 8, 9, and 10 feet above mean highest high tide, just because the app we used goes up that high.  At 10 feet, the water level is up Broadway and Ocean about half the way up to Beach Street.

Why might these be relevant?  When examining projections for sea level rise due to climate change, even in the Intermediate Scenario projection (for RCP 4.5), the Global Mean Sea Level (GMSL) rise for 2100 is 3.3 feet.  If there is rapid Antarctic melting, we might add to this the Relative Sea Level (RSL) rise, which depends on location.   For the West Coast of North America, this is projected to be 2-3 feet.  So, we are up to 5-6 feet already, as  a mean highest high tide level.  Over that daily level, we add the possibility of a broad storm surge, of 2-3 feet, and wind raised waves of 2 feet.  We are now up to 9 or 10 feet.  The Relative Sea Level rise does have an additional speculation that there are instabilities in Antarctica that lead to more melting of the ice sheets.  In any case, rise in sea level is very, very slow.  As the years go by, we can find out how fast Antarctica and Greenland melt, and adapt to that on a much faster time scale.

This combined height doesn’t have to happen every day or storm, but the key thing to remember, is that this only has to happen ONCE in the 50 year lifetime of a house or business to be a disaster.  Expensive to insure against, expensive and years of work to repair or replace.  Expensive in loss of business for the months to repair or rebuild.  Flooded highways often need repairs also, which can severely mess up traffic, especially on Coast Highway and Broadway.

 

About Dennis SILVERMAN

I am a retired Professor of Physics and Astronomy at U C Irvine. For a decade I have been active in learning about energy and the environment, and in lecturing and attending classes at the Osher Lifelong Learning Institute (OLLI) at UC Irvine.
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