Saturday, November 9, 2013

Coastal Configuration Played a Key Role in Tacloban's Massive Storm Surge

Tropical Cyclone Haiyan generated a massive and destructive storm surge in portions of the Philippines. One of the worst hit areas was Tacloban, where the water levels reached the second story on some buildings, according to CNN. (link: http://www.cnn.com/2013/11/09/world/asia/philippines-typhoon-haiyan/index.html?hpt=hp_t1)

Images and videos now depict classic storm surge destruction, like upended cars and vans that were floated by the massive wall of water. Paula Hancocks, a CNN correspondent, indicated that she saw evidence of much water damage and the destruction was similar to what she has seen in massive tsunamis. (see video link above).

Upended cars are a classic sign of a massive storm surge or tsunami inundation. As water floats vehicles, the front part containing the engine is heavier and will sink, causing the back end of the car to rise. As a result cars appear upended. Such sights were common during Hurricane Katrina, and are seen again today in Tacloban, Philippines. Image: CNN (http://www.cnn.com/2013/11/09/world/asia/philippines-typhoon-haiyan/index.html?hpt=hp_t1)

Tacloban was located at a very vulnerable location for storm surge during Haiyan. The center of Haiyan's circulation passed to the south of this coastal city, enabling strong onshore winds to funnel water into San Pedro and San Pablo Bay. The shape of the bay magnified the surge levels, as the bay narrows near the north end. Displaced water doesn't just disappear, and when water gets funneled into narrow bays and inlets it has nowhere to go but "up", spilling out onto the land and causing much devastation.

Tropical Cyclone Haiyan (Yolanda) tracked just south of Tacloban City. After the eye of the storm passed to the southwest of the city, very intense winds from the southeast pushed a massive storm surge into the area. Image: Matthew Pace (https://twitter.com/DrMatt12News/status/399018637391953921/photo/1)

Coastal configuration, or the shape of coastal bays and inlets, often enhances surge levels in the Philippines. Maps of the island nation show numerous bays and inlets. While such coastal shapes often enhance surge levels, they also create very localized surge levels. For example, at the narrow portion of a bay, water levels may reach 5 meters (16.5 feet), while water levels may just be 2 meters (6.56 feet) a few miles away.

Coastal configuration enhanced storm surge levels near Tacloban City, Philippines. Strong southeasterly winds funneled a large storm surge into the north portion of San Pedro and San Pablo Bay, which created a wall of water two stories high in Tacloban City. Image: Hal Needham


Coastal shape and configuration is one reason why Pass Christian, Mississippi, has observed the highest two storm surges in U.S. history. This location observed an 8.47-meter (27.8 foot) surge from Hurricane Katrina in 2005, and a 7.5-meter (24.6 foot) surge from Hurricane Camille in 1969. Water tends to funnel into Bay St. Louis and get trapped, causing it spill out on the land. Unlike the Philippines, water levels in coastal Mississippi are also enhanced by very shallow offshore water depth, or bathymetry.

Tropical Cyclone Haiyan is now a category-3 cyclone headed towards Vietnam. It should impact Vietnam and portions of extreme southern China with strong winds and elevated water levels.

SURGEDAT is currently under expansion, as we are adding many new events from East Asia to our database. Our historical research is now finding many surge events in China, Japan, the Philippines and Vietnam. The database should be updated next spring, as we submit a paper on historical global storm surge observations and impacts.

2 comments:

  1. What data on surge levels are available at the moment?

    Do you know whether the marks left on trees in these photos are left by the surge? http://i.huffpost.com/gen/1454009/thumbs/o-HAIYAN-facebook.jpg
    (From tacloban airport at +3m above sea level -according to wikipedia)


    A quantitative media quote with a good source:
    On Samar (island facing Tacloban). L. Dacaynos said "the storm surge caused sea waters to rise 6 meters (20 feet)."
    source: http://wamc.org/post/thousands-feared-dead-after-typhoon-haiyan

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  2. I have been trying to look for stripped bark like in this photo from Katrina.

    But I am not good at reading the damage in photos like the one linked here. In this photo there is green grass and not much mud. which makes me doubt that this particular parking lot was flooded at all. (yet media reports say that the airport was covered in mud due to the flood). I'd be happy if you know how to interpret these kinds of images.

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