Dear Editor,
In a release by the European Union expressing grave concern with respect to recent overtopping of the sea defence along the Rupert Craig Highway (RCH) in the vicinity of Conversation Tree and reported in SN on April 9, it appears that Minister of Public Works (MPW), Mr Robeson Benn, has suddenly decided to do something tangible to contain and prevent the flooding of residential areas south of RCH and elsewhere due to overtopping.
Since this segment of seawall was constructed in the ’60s, there has been a significant rise in sea level and its clay embankment has consolidated and deformed. Therefore the top elevation of its coping is no more at its design 62.50 GD but considerably less, and at high tide unusual wave heights generated with swells cause sea water to easily overtop the seawall and flood adjoining low-lying lands.
In a 1972 Report on the sea defence by NEDECO, Dutch consultants, it was recommended that the public should not be allowed access to the sea defences in order to protect them from damage of all sorts. Unfortunately, Minister Benn with tacit support from the Georgetown Chamber of Commerce and Industry (GCCI) has allowed ‘liming’ on the seawall along RCH for many years now, and the traffic has destroyed the turf and eroded the clay embankment, thereby reducing its effectiveness to arrest erosion from the elements which if not addressed could eventually threaten the stability of the clay embankment. He has further allowed building on the sea defence reserve in contravention of the Sea Defence Ordinance.
During his tenure Minister Benn has shown scant interest in a planned and executed programme to maintain the sea defences, such as having MPW carry-out regular and detailed surveys of the foreshore, soundings of the coastal waters, settlement of structures/embankments, inspection of constructed works and so forth and so on, since the changes observed over time with respect to these constituents would have alerted MPW of the situation it now faces and with some advance time for appropriate action to be taken, the disaster which has occurred no doubt could have been mitigated. After all, doing nothing and waiting for the overtopping phenomenon with the resulting flooding of valuable coastal areas to move from one location to another should not be the philosophical view Minister Benn should be taking, and certainly not under the pretext of cost, as many people have suffered and lost much and they fear that a repeat of the same could occur any time soon.
It is inconceivable that Minister Benn should state that the placement of sandbags along RCH as is currently being done is the best solution to deal with overtopping. At high tide, sea water flows over the top of the coping down the sloping clay embankment into a drain and then overflows onto RCH. Sandbags placed on the south side of this drain (which is inadequate since it was intended to drain the road and not accommodate overtopping) and on top of the divide of the east-west carriageways of RCH would probably help to channel some floodwater towards the Liliendaal pumps, but most of it will still find its way through the many gaps in the intricate sandbagging and into the residential areas south of RCH and flood them, as has been happening and will continue to happen.
The sandbags placed on the south side of the drain will trap overtopping sea water and excess rainfall, the build-up of which could induce slippage of the sloping clay embankment due to saturation, and eventually compromise its stability, evidence of which could be seen at the head of Sheriff Street. A cost effective engineering solution to prevent overtopping of the seawall is still possible.
In hindsight and having regard to hydraulic and stability considerations, if this segment of seawall was built at a top elevation of 65.00 GD and with a curved inner coping (as at the Georgetown seawall) to return the breaking waves back to the ocean rather than over it, there is no doubt that the present overtopping would have been substantially reduced, if not contained. However, the placement of sandbags by MPW in a seemingly unplanned way to contain overtopping from the sea appears to be more of a rearguard action than a serious attempt to solve the problem.
Finally, Minister Benn stated that MPW was looking to build groynes as he noticed that these were assisting to break the waves as was evident at the Carifesta Avenue groyne (CAG) just north of Kitty Pump Station. Construction of groynes on oceanic coasts were not intended to break wave action, but to trap/prevent the drift or movement of material (sand and shell) along the coast due to the action of littoral current. The breaking/dampening of waves as was observed at CAG was due primarily to the presence of sand/shell banks trapped around the groyne because of the accretion taking place at this location, as well as the movement of sling-mud westwards. There is no supporting data per se to corroborate Minister Benn’s claim that groynes are the proper means to prevent large scale erosion or the dampening/ breaking of wave action along the coast and he should stay his assertion and make an informed judgement when the present erosion cycle reaches the CAG location some time soon.
Yours faithfully,
Charles Sohan
