Rising Ocean Will Flood New Trancas Bridge Under Best Global Warming Scenario

Written by on September 20, 2019

Caltrans has issued a new assessment of what global warming will mean for the state highway system.

And it predicts that major sections of Pacific Coast Highway in Malibu will go underwater in 80 years … under a worst case scenario.

And even under the best-case scenario … we are going to see big problems.

The report says that the worst-case scenario … an ocean level rise of about 16 feet … would put Highway 1 under water from Malibu Pier to Las Flores Creek.

Also at several places east of there …. and all along the coast from Topanga Creek to the McClure Tunnel.

The lengthy Caltrans report inventories vulnerabilities for the entire state.

And it highlights one specific location as an example event.

That would be the Trancas Creek bridge.

Even before the Woolsey Fire … that 90 year old bridge is in trouble.

In 2017 … the bridge was scoured by heavy rain runoff … and the bridge footings were exposed. Caltrans installed an extensive system of tilt sensors, water level sensors, sonar, and a wireless camera on the bridge piers.

A new bridge will be built soon … but even it might be affected by high ocean levels if the local sea level rise hits almost six fee.

That is not expected for 80 years,

But if a major rain flood is added into the predictions … high waters could reach the bridge with only one foot of sea level rise.

Caltrans has included considerations of the tides and sea level rise on the new Trancas Creek structure … but it is still working on a wave run-up study to see how big waves … a big flood and high tides will affect Trancas.

Longtimers may remember that waves broke underneath that bridge during a big flood in 1999.

The report notes that PCH already has had to be saved in two places from rising ocean levels … at Tuna Beach on the city’s east side … and at the big sand dune near Point Mugu.

In both those places … rocks were placed where sandy beaches used to sit.

But … those repairs are only designed to withstand a maximum sea level rise of

5-1/2 feet.


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