Dear Editor,
I refer to an article in SN dated 25/02/08 wherein Dr Singh Executive Director Conservation International is calling for upgrading the sea defence design by building the concrete sea walls higher to cater for overtopping caused by rising sea levels due to global warming.
There are indeed some concrete walls built a little low in the 1950’s but in the 1960’s the design was changed when the coping wall height was revised to 63.50GD and the earthen embankment to 59.00 GD. Any increase in the wall height or weight will decrease the factor of safety of rotational slips in the sea wall in the event the foreshore erodes.
As the Designer and Engineer responsible for the construction, these 1960’s walls were structurally and geotechnically adequate for the sea levels at that time. Evidence of their longevity and quality of construction is that they are still in good condition some 42 years later. Some of these concrete walls can be seen from Kitty going towards East. The Georgetown Sea Wall is different in that the old Baron Sicama Wall was re-capped and a new sea defence built in 1972. I was also involved with this design and construction.
Light overtopping of the walls in some areas is to be expected and the normal remedy is to carry out regular maintenance. Unfortunately, there has been no maintenance of the sea defences since 1975. If however, heavy overtopping continues Engineers in the Hydraulics Division at that time developed a procedure to minimize the overtopping and break the celerity of the waves by placing ackmons at strategic locations on the foreshore. This procedure also builds up the foreshore levels reducing the force of the waves that break at the grouted concrete boulder slope.
In my opinion this procedure can still be utilized in the event sea levels rise. Recently, it was reported by a UN official that sea levels have risen 1.7 feet and if this is correct the Govt. should take the appropriate action. Frankly, I do not know how this official arrived at this increase which appears exorbitant to me.
I notice Dr Singh did not mention anything about the riprap sea defence walls built since 1992 and now standard, which have no coping walls, and have a low design shelf life.
I strongly objected to this type of wall especially for the coastal areas since the riprap was recommended only for the riverain areas. The coastal areas sea defences were re-aligned in the 1960’s. When this Government came to power in 1992 I met with the PS Min. of Agriculture and after explaining the problems the new Government faces he assured me that everything was under control and that the Govt. had a plan to rectify the sea defences as well as all the potential drainage problems.
Since that time hardly any sea defence concrete walls were ever built in the coastal areas except for a section of riprap at Mon Repos which ended up in a disastrous breach.
We all know the state of the drainage system today.
To date there are a lot of vulnerable areas where some sea defence walls are well over 80 years old and are in a dilapidated condition especially in the areas between Mon Repos/Buxton/Bladen Hall and up to Enmore. During the early and late sixties several breaches occurred in these areas. I was able to hold the line on account of the excellent workers and machines that I had under my control. You do not have that today. The Govt. has to rely on locals who do not have the requisite experience.
The 40/45-year cycle of erosion and heavy wave action are also due any time and it would be difficult to control the enormous flooding that would emanate from the breaches if and when they recur.
In my opinion Dr Singh should be more concerned about these potential sea defence problems rather than considering raising the height of the concrete walls.
I would also suggest that he site visit the critical areas mentioned above during high and low tides and observe conditions himself.
Yours faithfully,
Malcolm Alli
