Dear Editor,
In the Sunday Stabroek article of June 13 captioned ‘Drainage sluices working properly, Persaud says,’ Agriculture Minister Robert Persaud stated that all the East Demerara Water Conservancy (EDWC) flood relief structures discharging into the Demerara River are working properly, but nevertheless concluded they were not functioning at their maximum capacity because of existing cross conservancy difference in the hydraulic head.
The Minister claimed that works in progress to open up additional waterways such as the Lama would increase the upstream hydraulic head in the conservancy, thereby allowing for greater flows through the flood relief structures and thus enabling them to function at design capacity.
The opening of additional water flows within the EDWC that conducts water towards the west will facilitate greater discharges into the Demerara River through the existing outlet structures, but it will not increase the hydraulic head as postulated by the Minister.
Currently, vegetation and overgrowth of the internal flow network of EDWC impedes water flow towards the west causing water to be impounded along the eastern and most vulnerable side of the system. The hydraulic head difference across the conservancy (east to west) because of these impediments could be as much as 3ft.
A number of complex parameters have to be satisfied before a hydraulic structure such as a sluice could function at its rated capacity. Firstly, the hydraulic head (available energy) across the structure (difference between the upstream and downstream water levels) has to be achieved as per design for optimum discharge and not just a change in the upstream water level as the Minister alluded to, since if upstream and downstream water levels are the same, flow through the structure is going nowhere. However, the greater this differential, the greater will be the flow, generally. The geometry (shape) of the structure also influences its discharge characteristics as well as the weeds and other obstructions upstream/downstream of it.
Yours faithfully,
Charles Sohan
