Dear Editor,
I refer to an Article in KN dated 25th. Jan 07 on the subject of the above floating bridge to be located at Crab Island as well as the Study for this bridge carried out by the Main Consultant ND Lea of Canada.
I have not seen the Sedimentation Study carried out by the Louis Berger Group.
In Section 2 of the Lea Study the catchment areas of the Berbice and Canje Rivers were given and it should be noted the study was limited to 20 kms from the mouth of the Berbice River. The length of this river was given as 644 kms.
The study noted that the bridge near the estuary was the preferred location in terms of cost according to the Louis Berger Group but also noted that this location would be far more interfering than any other location being considered and would cause scouring under the physical structure and deposition elsewhere.
Despite the positive benefits of the bridge, concerns were expressed in the study about the hydraulics and sedimentation regime of the river resulting in scouring around the supporting pontoons and the in filling of the D’Edward Sluice.
Under section 4 of the study Lea postulated several mitigation alternatives as follows – carry out regular dredging under the pontoons and the sluice outfall, re-locate the floating bridge further upstream where the channel is deeper, construct piled causeways on both banks of the river and re-locate the D’Edward Sluice further upstream.
I do not know what the design of the proposed bridge entails.
The study indicated that 180,000 metre cube annually will have to be excavated under the pontoons and around the sluice, but did not indicate where this large volume of earth will be deposited. The cost of maintenance work will also skyrocket.
Siltation in the river will build up causing a backup of the water resulting in a change in morphology of the river and inducing flooding similar to what the Demerara Floating Bridge caused at Craig on the East Bank Demerara. The Berbice is a longer river and transports a tremendous amount of silt downstream. It should also be noted that the MMA Project drains its excess water via the spill weir at Dageraad directly into the Berbice River
The main concern, however, is whether any investigation was carried out to see what impact the siltation at the mouth of the Canje will have on the Canje Basin as a whole noting any change in the hydraulic conveyance on pumped irrigation.
The Torani Canal takes in water from the Berbice River further upstream which is then pumped for irrigation purposes.
This could very well be a repeat of the siltation of the Abary River Basin on account of the 7 Door sluice not releasing compensation flows to keep the Abary River alive resulting in its premature death.
Yours faithfully,
Malcolm Alli
