Dear Editor,
I refer to a letter captioned “Torrid times may lie ahead for people living along the coastal areas”, (08.03.28) that was followed by another, captioned “The start of the cycle of erosion”. The first was alarmist and the second misleading. Both indicated misunderstanding of the behavioural pattern of erosion on the Guyana coast. The public deserves to be enlightened but not frightened. I do not believe that impending doom lurks on the coast of Guyana if the problem of coastal management is tackled intelligently and continuously.
The writer of the letters joined the staff of the Drainage and Irrigation Department as a Structural Engineer in the 1960s. That Department had little to do with sea defences which were entirely within the purview of the Public Works Department in the Ministry of Works and Communications. Later both were combined within the Ministry of Works and Hydraulics when I was Deputy Chief and later Chief Works and Hydraulics Officer with overall responsibility for sea defences and other works. Mr Alli did not have the privilege of involvement in the studies relating to design and construction of sea defences conducted by the Delft Hydraulic Laboratory and Netherlands Engineering Consultants (NEDECO) in collaboration with our staff, and his technical understanding of the problem may have been incomplete. The claims he made of involvement in sea defences in the 1960s cannot be substantiated. His criticism of the ‘rip-rap’ placement on the seaward slopes which formed part of the NEDECO design, was very strong, but he was given the opportunity by the Guyana Association of Professional Engineers to explain his technical viewpoint and failed to convince them.
Let me briefly explain. There is a cycle of erosion and accretion along the Guyana coast whereby there are zones of erosion alternating with zones of accretion (i.e sling mud) and the whole pattern moving from east to west at a speed of approximately three quarters of a mile per year. In short there are protective mud bands (sling mud) alternating with troughs of erosion (lowered foreshores) and moving steadily westwards. The studies indicate that every section of the sea defences is exposed to erosion about three times a century. It is wrong to state that the cycle of erosion is now starting – it has been going on as long as the Amazon discharged mud into the Atlantic, and it is wrong to state that the cycle is 40 years – it is closer to 38 years. This pattern was first observed by a Director of Public Works (then called the Colonial Engineer) around 1920 and confirmed and quantified by the Delft Hydraulics team in 1960-61. I have records to prove this. If this pattern is identified and studied then it is possible to predict where and when erosion will occur and plan your maintenance accordingly. This was done in the 1960s very effectively.
At that time the ministry had a hydrographic survey launch and two excellent hydrographic surveyors in the persons of ‘Sammy’ Luck and Paul Kranenburg who surveyed the coast continuously and reported their foreshore measurements to the Sea Defence Board and to Barry Manson Hing, the Executive Engineer on a monthly basis. This practice ceased some years ago; there is no survey launch and it has not been possible to monitor the areas of erosion to permit of forward planning by the Sea Defence Board. In the present age of satellite scanning this should be achievable.
Overtopping of the walls is not an unusual occurrence, but it would happen only in the zones of erosion such as Montrose, during the high tides which were aggravated by an unusual swell in the Atlantic coupled with high winds. A similar case was that of Canvey Island in the Thames estuary which I observed as a research student in 1953. It was made inhabitable. It should not be difficult to repair the washed out portions of the embankment on the back slopes of the walls, but this must be done immediately or the unsupported walls would collapse. The important point here is that this condition could have been anticipated if proper hydrographic surveys had been in effect. At least one hydrographic survey launch is necessary for effective coastal management.
The writer of the two letters under reference seems to have composed a history of his own times in a manner which omits the achievements of his contemporaries and disregards their tutelage in a speciality which was not wholly familiar to him.
Yours faithfully,
Philip Allsopp
