Ventura Harbor Commission recommends 17-foot guide piles
VENTURA – The Ventura Port District Board of Port Commissioners unanimously recommended all new dock pilings within Ventura Harbor have set height limits. Accordingly, all new or replacement docks will be set at 17 feet above Mean Lower Low Water (MLLW), or about 2 feet higher than what was recommended by consultants.
Commissioners approved the new height Oct. 22 to help Ventura Harbor combat elevated water levels and to adequately protect vessels within the marina from events like tsunamis.
The cost of new guide piles would increase by 6 percent, or $200 per pile, as a result of the board’s decision.
“The Port District concluded after a professional engineering review of the extreme high water levels experienced in Ventura Harbor as a result of the tsunamis generated by the 2010 Chile and 2011 Japan earthquakes that in order to protect the public health and safety it was necessary to require that all future dock guide piles placed in the waters of the harbor shall have a minimum top elevation of +15 feet (MLLW),” said Greg Carlson, chair of the Ventura Harbor Commission.
At its September 10 meeting, the Board of Port Commissioners were presented with a report by Noble Consultants advising the body of how high the guide pile height should be in order to accommodate the possibility of tsunami events in the future.
Jon Moore of Noble Consultants recommended Ventura Harbor establish new guide pile heights at 15 feet above MLLW.
In his report to Ventura Harbor General Manager Oscar Pena, Moore said “it is imperative that the floating dock systems be structurally resilient, well maintained, and adequately held in place during a tsunami occurrence to the maximum extent practical.”
A tsunami triggered from an earthquake in Japan in March 2011 sparked a discussion in Ventura about whether its harbor was adequately protecting its docks and vessels.
According to a report from Moore to Pena written in April, the 2011 tsunami on the other side of the Pacific Ocean “impacted Ventura Harbor” by elevating “water levels with the mooring basins such that docks were reportedly close to floating off their guide pile restraints.”
“The incident raised questions about the adequacy of the existing guide pile system throughout the harbor,” Moore wrote in his report, adding the maximum amplitude inside Ventura Harbor reached 4.3 feet as a result of the Japanese tsunami.
“One observer indicated that early in the morning of March 12, the end of F Dock at Ventura West’s Phase II Marina rose to within inches of the bottom of the existing guide pile’s cap,” Moore continued.
Docks and boats in Ventura were reportedly damaged as a result of the tsunami.
Another tsunami triggered by an 8.8 earthquake in Chile one year earlier also reached the harbor. Moore stated amplitudes within the harbor were less than 3 feet, but oscillating currents in the marina were believed to reach speeds of 15 knots.
According to Moore’s report, the potential for severe damage to dock facilities and guide pile restraints increases when tsunami currents inside the marina basin reaches at least 6 knots.
Existing guide piles within Ventura Harbor have top elevations ranging from 11 to 12.5 feet above MLLW, according to Moore.
In suggesting new guide piles be 15 feet above MLLW, Moore added “there is no standard currently available that dictates what measures should be employed to increase marina resiliency during tsunami occurrence.”
Interestingly enough, Moore said Ventura Harbor would likely set a precedent and “play a leading role” in the development of guidelines of how to address tsunami exposure to California’s harbors.
The earliest record of a tsunami occurrence in Ventura County was in 1812, when a magnitude 7.0 earthquake reportedly triggered a submarine landslide and caused a 7-foot high wave.
An 8.8 earthquake off the Aleutian Islands in Alaska on April 1, 1946, reportedly caused minor berthing problems for ships in Port Hueneme.
When a 9.2 earthquake struck in Alaska in 1964, the tide reportedly dropped eight feet in Ventura while large swells were reported in Oxnard.
The tsunami triggered from the 2010 earthquake in Chile resulted in more than 20 docks being damaged in Ventura.
No timeline was given as to when new guide piles would be installed or current ones would be replaced.
According to Moore, the California Geological Survey and University of Southern California are working with state and federal agencies to study areas where tsunamis are likely sourced in order to “better quantify damage potential and the frequency of occurrence for the known local and distant source that could impact Ventura Harbor.”