Dear Editor,
In an article which appeared in SN on October 11 captioned ‘Revetment won’t end Craig river woes – engineers,’ it is stated that the Ministry of Works (MoW) has awarded yet another contract to construct a replacement revetment on the right bank of the Demerara River in the vicinity of Craig. Photos which appeared in SN show that the existing revetment which was constructed not so long ago has failed, as the structure is rapidly creeping westwards into the river’s channel, taking the embankment with it.
Before pouring scarce resources into another sinkhole, Minister Benn should have held an inquiry as to why the existing revetment failed and the lessons to be learned so that the mistakes made are not repeated. The evidence suggests that poor design and construction lapses have led to the costly failure of the existing revetment and unless Minister Benn is satisfied that the new design has been prepared by competent consulting engineers and not ‘fly by night’ designers, and that the contractor has the experience and capability to undertake the work on hand, the Guyanese people will be back to square one having regard to the recent failures of the Good Hope stelling and the revetment on the right bank of the Pomeroom River at Charity.
Erosion of the right bank of the Demerara River in the vicinity of Craig has been a perennial problem, particularly so since the construction of the Demerara Harbour Bridge which has caused the river channel to change its course, with accretion occurring at locations such as the Vreed-en-Hoop Stelling foreshore, and erosion of the embankment at the bend in the river at Craig.
Half-hearted efforts have been made to tackle the erosion at Craig, but the underlying technical issues have not been addressed. For example, hydrographic surveys should have been carried out at regular intervals to determine changes in the channel’s geometry. It is only with this data and an understanding of the soil/geology of the stratified formation under the embankment that a properly designed revetment could be undertaken.
Finally, Engineer Willis, the government’s chief technical advisor should know that clay is not the best of materials for building embankments, because of the build-up of pore pressures and the development of cracks on the surface which allow for the easy channel of water to the dam core, and the slow consolidation of the material to gain strength. He should be advising on the use of a selected fill instead. After all, a well designed and constructed project doesn’t come cheaply, and as President Jagdeo succinctly stated a few days ago at the start of excavation for the Hope Canal, “no venture is too expensive to protect citizens.”
Yours faithfully,
Charles Sohan
