The Dec 26/05 tsunami meets the Water Table, Banda Aceh, Sumatra Island, Indonesia

Wednesday, March 1, 2006

The magnitude 9.0 earthquake that struck the area off the western coast of northern Sumatra on Sunday morning, 26 December 2004, at 7:59 am local time (00:59 GMT) triggered massive tsunamis that inundated coastal areas in countries all around the Indian Ocean rim, including India, Indonesia, Sri Lanka and Thailand. The region is historically prone to seismic upheaval due to its location on the margins of tectonic plates. However, tsunami waves of this magnitude are rare and the level of preparedness was very low. This area of the earth has also become one of the most tectonically active zones on the face of the earth since the Dec 26/04 earthquake.

An estimated 5 million people were directly affected, and the death toll is one of the highest in recorded history some 280,000 individuals. The economic and environmental impact of this disaster has also been devastating and will affect livelihoods, economies and natural systems for years to come.

While this article focuses on the impacts of the tsunami in Indonesia, the effects I witnessed in Sri Lanka were equally compelling, and devastating. However, since much of the footage and video we observed on the TV were taken from tourists on vacation in Sri Lanka, I will take you to a place where no tourists or ex-Patriots were allowed prior to the tsunami Banda Aceh, Indonesia.

On Friday May 13, 2005 I found myself standing on the very shores where the tsunami waves broke ground, while working on a contract with World Vision Canada / CIDA to conduct community based environmental assessments (EA's) on projects being implemented in the tsunami effected countries of Indonesia, Sri Lanka, India and Thailand. Although only five months had passed since the tsunami, the effects of it were obvious, and will haunt my memory for my lifetime.

The results of our EA work have been published under separate cover to World Vision Canada and their partner countries, so the intention of this article is to pose some questions and present some antidotal evidence that I'm sure you will find interesting, if not awesome in scale. There are so many directions that this article could go; however I am going to focus on the effects of the tsunami on the shallow water table.

One of the first things I picked up from reading the rapid environmental assessment reports, or other reports that I read in preparation for our overseas trips was that more than 30,000 shallow wells in the immediate vicinity of Banda Aceh had become salinized as a result of the tsunami. While not reading of the mechanism of how this actually happened, I have to admit that I was skeptical that this was actually the case, both in terms of the number of wells impacted and the degree to which they were salinized. I had so much to learn.

When I first looked around the landscape I was struck by the sheer degree of destruction that the tsunami left behind, as shown on the figures attached. I will note also that all of the stories and anecdotes were collected first hand by meetings with the survivors of the tsunami. And while we all speak of the tsunami, there were actually several tsunami waves Ð reportedly up to four waves that broke ground at Banda Aceh, but most particularly two primary waves that caused all of the destruction.

As we all know, the source of the tsunami waves was a magnitude 9.0 earthquake located off the western shore of Sumatra. As I learned while in Banda Aceh, most earthquakes last 30 seconds or less (I was actually rocked out of bed one night by a magnitude 5.6 earthquake with the epicenter only 30 km away Ð which did not create a tsunami -fortunately), while the December 26/04 earthquake lasted reportedly up to 10 minutes. This must have seemed like hell on Earth for the people there.

The first mentionable wave was reportably 10 m high, of which most people apparently survived, and this wave arrived some time after the earthquake had subsided Ð possibly 10 - 20 minutes later. This caused panic, severe flooding and chaos. The water then withdrew and collected again up to two kilometers off shore Ð leaving fish flapping on the sea bed while some fisherman and villagers ran out to collect what they could Ð others turned and ran. The time between this 10 m wave and the next killer wave was in the order of minutes. As one survivor put it "I looked back and thought that there was a storm on the horizon, only to be swept up seconds or minutes later and become separated from my wife and daughter who were never to be seen again" as the killer 30 m high tsunami broke ground. There is real evidence to support a 30 high tsunami, waste in the tops of trees, boats on the top of buildings, and more telling the removal of the light beacon from the top of the tower on the very shore where the waves broke.

When I surveyed the land, I noticed that basically every house had its own well and latrine (open ended pit). Surveying base maps and talking with survivors I could now understand why the reported number of 30,000 wells had been affected in this area alone. This was a very densely populated area Ð and I had no idea that every house had its own shallow (dug) well. Attached are numerous pictures of the remains of these wells. The concrete casings were destroyed, their caps were destroyed and the wells were filled with whatever rubble the tsunami left behind.

Between the first and second wave survivors reported a "sucking" sound from the wells and noticed that they had dried up. We have learned that the shallow unconsolidated aquifer, with a high water table level of approximately 1-2 metres below grade, is significant in depth (10's of metres), and comprised basically of medium sand. However, the freshwater / saline water interface (or bottom of the aquifer) is located at a depth of approximately 6 metres, resulting in an available drawdown of 4-5 metres. Under typical conditions the wells pump saline water from beneath the six metres depth, so the bottom of the wells were terminated at a depth of six metres below grade.

When the second wave broke ground, these shallow wells then reportedly geysered in front of the advancing wave. The result after the floodwater subsided Ð and many months later, was a salinized shallow water table aquifer and thousands of rubble / waste filled shallow dug wells. Reportedly one of the NGO's on the scene decided to undertake a well cleanout program whereby the waste was removed from some wells and the wells were pumped dry many times, although these efforts proved unsuccessful, as the wells continued to pump salinized water many months later.

Flooded wellLeft: Flooded well in foreground

So questions I will leave for you to ponder include what happened to the shallow water table aquifer? Did it become dewatered Ð or drained when the second wave collected two km off shore? How did all the wells become salinized? What was the result of the force from the tsunami on the shallow water table? Was all the fresh water forced out of the ground by the advancing waves? Is the groundwater between the wells salinized or just in the immediate vicinity of the wells themselves? How long will it take (or how many monsoon seasons) for the shallow water table aquifer to re-establish itself? How do the survivors in the coastal areas that have been affected in a similar manner as Banda Aceh secure a safe and potable water supply? Can the shallow water table aquifer be protected from another tsunami?

Children in building

Above: Hope

The other aspect of the tsunami that I did not describe is the emotional and psychological trauma that has affected people all over the world. Talking with the survivors and seeing the looks of absolute fear on peoples faces when earthquakes struck the region while I was in country only gives me a glimpse of what really happened, and what they have survived. The human ability, desire, instinct Ð call it what you want - to simply survive is indescribable. People coming together from around the world, and from different communities or villages to help each other out speaks to this. I feel truly blessed to have been able to participate in some small way with the tsunami assessment / clean-up related efforts and have a much greater appreciation for just how small the world is and how dynamic the forces are that shape the earth and its inhabitants on a daily basis.

Peter A. Gray, P.Geo. 
Managing Partner, Senior Hydrogeologist
Frontline Environmental Management Inc. Kitchener, Ontario, Canada

Below: Peter Gray beside rubble filled dug well

Peter Gray beside rubble filled dug well

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