Dear Editor,
In an article which appeared in Stabroek News of March 13, Residents of New Hope, EBD have expressed grave concerns about design flaws and failure of the Contractor to complete on schedule the revetment works on the New Hope river defence.
The success and/or failure of this project will ultimately depend on whether the project was designed by competent professional engineers within the limits of their personal expertise and not using data that is not known by their first hand knowledge to be true, built by a knowledgeable and experienced contractor and supervised for quality control and assurance by a qualified inspector.
The revetment when completed is expected to prevent further erosion of the river embankment which threatens the stability of the EBD road. However, it will not prevent scouring of the river bed which is influenced by complex flow patterns at this location due to a bend in the river.
The design of this revetment would have required the skills of many engineers. Firstly, a hydraulic engineer would have had to estimate the extent and scouring depth of the river at the New Hope location for the next ten years or so.
Based on this depth bore hole samples would have had to be taken by a geotechnical engineer to ascertain the soil profile and physical characteristics such as shear strengths, moisture content, permeability, etc. of the subsoil. In collaboration with the structural engineer lateral earth and hydrostatic pressures for the in situ and back fill materials have had to be determined and an economic design developed to give a factor of safety with respect to failure of at least 1.5 during or immediately after construction. In this case it seems that interlocking steel sheet piling was chosen for the revetment and it can only be hoped that it is of the correct length/strength/ corrosion resistant and anchored well below the slip circle into suitable material for stability and to resist sliding of the toe and/or failure by overturning.
Some residents have expressed serious reservations over the use of sand as a backfill material. It should be noted that clean sand and gravels are considered among the best materials for backfilling because they are free draining and do not become less stable with the passing of time. Further, clay as a backfill is unsuitable because it could hardly be drained and it could lose much of its shearing strength if moisture accumulates.
Finally, it was reported that the Hon. Robeson Benn, Minister of Transport and Hydraulics when asked could not give a date when this project will be completed and shunted the questioner for an answer from his chief river and sea defence officer which in any case would have been an exercise in futility since stonewalling by public officials is common practice for projects which are behind schedule and cost overruns are high and still to be determined.
It is evident that Minister Benn is not up to the task entrusted to him. Under his watch are the Amaila Falls access road fiasco, the Supenaam Stelling debacle, the Parika/Good Hope ferry service is still inoperable, the steamer Northcote caught afire endangering the lives of passengers due to lack of regular maintenance of the vessel, the sea and river defence contracts to protect the coastline are behind schedule with the possibility of Guyana losing funding from the EU and so forth and so on. I sincerely believe it is time for a reality check on the performance of Minister Benn.
Yours faithfully,
Charles Sohan
