Posted on Sunday 23 January 2005

by Robin T

May I offer my suggestion for a Tsunami shelter suitable for single family dwelling? It uses economical, appropriate technology and is available to all neighboring countries - namely a Coconut Palm tree trunk.

As will be well known already, coconut palms are built to withstand typhoon winds by flexing with the wind force. However, you probably cannot just shin up a palm tree when a Tsunami threatens. These trees they have a relatively shallow ball root system (around half a metre deep) spreading up to 2 metres in radius. Whilst this may withstand the average wind onslaught it is unlikely to withstand torrential flooding because the ground is washed away and turned into a waterlogged mire of sand and mud with no significant strength. Similarly, when the palm gets too old and tall and is likely to be uprooted naturally by the wind and replaced by younger fry. Most trees suffer a similar fate. However, these old palm trunks can reach 10 straight metres or more and in the vertical position are surprisingly strong yet flexible (also very heavy). If not already freely available as fallen debris, they can be purchased for a modest sum as old trees become increasingly uneconomical for coconut production. Coconut wood is often derided as a building material because of its habit of delaminating and weakening as it ages. This doesn’t seem to happen with tree trunks.

Excavator machines are probably already on site under government clearance operations. A simple swipe from a bucket will dig a 2.5 metre deep hole in which to place this palm trunk (or you can dig it manually). The excavator can also help lift and position the trunk, which could weigh as much as 2 tonnes. Note that the base of the trunk must be encase fully in stout polythene (non bio-degradable) and duck tape to prevent termite destruction. Better still, it can be painted with hot tar. Depending on funds available, a reinforced concrete base and collar may be used for additional strength (but IMHO is probably icing on the cake). Also if funds permit, the trunk should be treated with wood preservative (old diesel engine oil can help if expensive preservative is not available). The ground must then be filled in, watered and tamped down. I would also created a raised circular ground area around the base of say half a metre high and 2 metres diameter supported by a ring of used beer bottles, crushed concrete of similar device. Cap this area with cement and plant soil retaining grass around the edge. The idea is to keep the ground around the trunk from softening as long as possible. A Tsunami flood generally subsides within half a day. Even a heavy monsoon does not penetrate a compacted laterite soil more than half a metre except after prolonged soaking of many weeks so the ground supporting the trunk should remain solid. Compacted laterite is almost like concrete.

The trunk should be equipped with simple steel spikes made from 8mm rebar drilled and hammered into holes either side into the trunk (like an electricity pylon). The top of the trunk should be equipped with a simple platform for the refuge of a family of 4 – 6 adults. As a wonderful bonus, this platform may be equipped with a small water storage tank with an inverted conical roof. This can serve as a sun-shelter and fresh water container. The tank should be made of polythene or cement/clay “ong” not PVC which becomes brittle. The family may have to stay up there for 24 hours. A major problem for post flooding is an adequate supply of drinking water so the tank should be circular of about 200 litres in size for 10 days supply. The height of the trunk should be at least 6 metres or more. The total cost should be around 2000Baht in materials assuming some government guidance.

I don’t claim my suggestion is 100% perfect but it may offer an improved survival rate for those living in coastal flat areas where there is no high ground to run to. Remember that a Tsunami travels at 80 – 100 km/h – highway speeds - so if you can see it coming you are too late to run. The trunk should have a life span of at least 10 years in my own experience and if properly built and preserved against insects, may last 50 years – who knows? I would apply old engine oil to the structure once a year and clean the tank, make it a family ritual. Termites hate engine oil.

As with any design that concerns human safety I would insist that my suggestions are reviewed by the competent local authority and a licensed Thai structural engineer. It would make a great research project for a technical university.

I, for one, would bet my family’s life on this option in the absence of an alternative. This method works successfully for offshore oil platforms by the way. I would not recommend more that a single leg for this platform (called a monopod) simply because of the danger of large floating debris becoming entangled in the additional legs and adding to the stress. I might also suggest some simple vortex breaking device connected between the spikes to prevent the pole oscillating during freak winds – very easy to do. Do not put the pole near any building that is likely to collapse, or it might topple the pole.

I have many friends and relations how have lost love ones so I hope my contribution may be of help. No one can be blamed for this disaster as events in the Indian Ocean are rare. This event was by far the largest human catastrophe of this type since records began (17 century) yet such events on a small scale are common in the pacific and the western coast of Sumatra. There is an average of 2 Tsunamis spreading across the pacific every year. Because of this, the USA has had a chain of highly sophisticated sensors protecting the whole of its western coast installed for many years. It will take a long time and a billion dollar budget to protect the Indian Ocean to the same degree (how can that be funded?). In the meantime people need some peace of mind.

My sympathies to all those affected