Oct 29 2009
Initial Observations – Sunday/Monday
On Sunday, October 25, 2009 a technical assessment team comprised of Coasts, Oceans, Ports, and Rivers Institute members traveled to the Samoan islands to study the impact of the September 29 earthquake and tsunami on the region’s infrastructure. The team will remain in the region until November 1, examining the performance of systems such as drinking water and sewage, roads and power supplies; looking at the effectiveness of shore protection and coastal management efforts; and gathering information on forces and loading that could aid resilient development efforts.
The team’s efforts are a part of the American Society of Civil Engineers’ disaster response procedure, which supports the formation of technical teams to study infrastructure damage caused by natural or man-made disasters. Such studies are conducted so that engineers may learn from the disaster, and perhaps more importantly, so that those lessons learned may be documented to inform future actions. ASCE has participated in more than a dozen assessments in the last decade, including studies of the World Trade Center and Pentagon in 2001; earthquake assessments in Italy, China, Peru, Japan, Sumatra-Andaman, Algeria, Alaska and California; and assessments following hurricanes Katrina and Ike.
Initial Observations – Sunday/Monday
American Samoa is a South Seas paradise that experiences its share of coastal hazards. We are staying in Alega, one of the many areas around American Samoa damaged by the tsunami. Our accommodations at the small beach hotel, Tisa’s, are basic – a raised mattress surrounded by mosquito netting in a fale (a covered beach hut with open walls) – but functional.
Coastal area; structure washed off of its foundation.
The residents here first thought the ground shaking could be a landslide and rushed down to the beach to look for slumps in vegetation or rockfalls. Then they realized it was an earthquake, so Tisa’s partner got on the internet to look up information about the earthquake. That’s when the tsunami arrived. He did not notice the first small wave, but the ocean recession of the next wave was dramatic, causing them to run for high ground. Waves washed over the open air deck and through the fales, where we are now sleeping. A neighbor down the road, on the inland side, had waves crash into his house and shatter the front door. The water level inside his house was about waist deep, but, while there was some water damage, no serious structural damage occurred.
Monday was our first full day on American Samoa, and most of the day was spent getting familiar with the area and tsunami damage patterns (our drive from the airport on Sunday was in the dark, so we only had a very general impression of the coast). We drove west from Alega, through Pago Pago, where the wave wrapped around the eastern shore of the harbor and caused significant damage along the coastal road. Most of the roadway is revetted and the tsunami waves washed over without doing much damage to the road itself. However, many buildings around the harbor were damaged or destroyed, and often the only evidence of a structure is the remaining slab on grade. The Red Cross is giving people who have lost their homes, or whose houses are unusable, white dome tents, cots, an ice cooler and a cook stove. These tents dot the landscape.
Pago Pago Harbor is a natural deep draft harbor with reported entrance water depths of 400 feet; 300 feet further in. the Fuel Loading Dock on the western bank was not damaged. When ships offload fuel it is pumped under the road to a nearby tank farm. Fortunately, no ships were offloading at the time of the tsunami. While there is a preparedness plan for the fuel dock, there was no time to put any response into action.
We stopped at a store in Afao on the west side of the island (on the sea-side of the road) where the earthquake shook goods off the shelves. The woman in the store didn’t know that a tsunami had been created until the first wave shut down the electric power. That first wave washed across the road; the second wave came into the store. After the first wave, she went out of the building and ran through ankle deep water to get to higher ground.
The inland area experienced a lot of wave damage, with very localized impacts. Buildings affected water flows and damage was concentrated in areas between the remaining buildings. The villagers evacuated up a hillside trail to safety. After the tsunami, a fissure developed on the evacuation route and the community has been forced to establish a new route for use in the next evacuation.
Church in Amanave
We also visited the village of Amanave, most of which had been destroyed. People were living in tents. A church and temple of worship were damaged, but repair work was being done. Both buildings had some cracking at connecting points that are indicative of earthquake damage; both were also leaning strongly to the west, indicating that the wave came on land sweeping east to west, pushing some buildings to the west and washing others away entirely. We approximated the elevation of a water mark in the back wall of the church at +27 feet MSL, but we did not find the run-up elevation.
Chris Jones measuring a high water mark on the church wall.
Our final stops for the day were in Pago Pago Harbor, where there were a number boats that were sunk near the wharfs, and several hundred feet of bulkhead damage – all seeming to be damaged, in part, by the wave as it was rushing back to the ocean. There were no signs of drainage channels or concentrations of flow, suggesting that the floodwater returned to the harbor more as sheet flow. One aged sheetpile bulkhead separated from the wharf with very little rotation or tilting. Backfill behind another wall seemed to have been carried out of the gaps at the bottom of the wall where it was no longer embedded into the substrate. A section of revetment was washed away, exposing the water line and causing the sidewalk to collapse.
Throughout our travels, people tell us of the impact from the recent disaster, though they also recall earlier events—1991’s tropical cyclone Val, which stalled over American Samoa for a full day, the more recent Hurricane Heta, the 1917 tsunami, and the recent landslides from the heavy rains just months before the tsunami.
These observations of damage and possible failure mechanisms are only preliminary. On Tuesday we plan to see more areas of the island, make more observations and use these to put together a better picture of the damaging forces and the types of structures that survived, as well as to develop lessons from this event that can make community development more resilient to future coastal hazards.
– ASCE/COPRI tsunami assessment team
Lesley Ewing, P.E., Team Leader, Coastal Engineer, California Coastal Commission
Jennifer L. Irish, Ph.D., P.E.; Assistant Professor, Texas A&M University
Christopher P. Jones, P.E.; Senior Engineer, Christopher P. Jones & Associates
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