Loss of live storage capacity in the conservancy would result in higher flood levels in the rainy season
Stabroek News
November 30, 2001

Dear Editor,

We refer to the letter of Mr. David Dewar captioned "The East Demerara Water Conservancy Board has been underfunded for decades" [ please note: links provided by LOSP web site ] (l7.ll.200l) which dealt with the past operation and maintenance of the conservancy as well as Dr. Dyalgee's letter of the 14 Nov. 01 which mentioned the geotechnical aspects of the conservancy breach and their relation to construction hazard. Having worked on the conservancy and irrigation and drainage works in the area, we would like to comment as follows:

Mr. Dewar raised some valid and pertinent points in his letter relating to the deterioration of the conservancy and if true, these would im-pact on the integrity of the conservancy dam and any dam - heightening works. Loss of conservancy live storage over the years due to the proliferation and accumulation of weeds in the reservoir and water paths should have been evaluated prior to implementing the dam heightening works, if it was structurally safe to do so. Surveys and field inspections would have provided a good estimate as to whether this was significant or not. Also, reservoir routing for the new conditions should have been carried out to determine any changes in the hydraulic operating conditions of the conservancy. From our experience with the conservancy, a loss of live storage would directly result in higher flood levels during the rainy seasons due to reduced flood absorption capacity. The question of water charges and their recovery from the estates and water users for conservancy operations and maintenance are at the core of sustainable conservancy operations.

We hope that these aspects will be examined by the expert team investigating the underlying causes of the breach. In view of the risks involved, we feel this team should also examine the need to have a comprehensive dam safety assessment of the conservancy carried out.

As regards Dr. Dyalgee, his letter contained general geotechnical information relating to dam failures. His experience in dealing with the construction of earth dams through pegasse soils is not evident although he gives the impression that this is a trivial matter. We are of a different opinion. The majority of this type of failure is usually through piping and not slip failure. He implies that it may be possible to raise the level of the conservancy dam since its pegasse foundation ( commonly known as peat throughout the world) would have consolidated over the years. It may be worthwhile for the Govt. to consider giving this learned gentleman a contract to do so. A part of this task should also be to prepare a manual on how the construction works should be implemented. To assist in this endeavour, we wish to correct one point in his letter. First of all, the conservancy dam was constructed over 100 years ago and not 32 years as mentioned in his letter. The 32 years he referred to (probably meant 33 years) was when the previous Cane Grove Breach occurred and the portion of the dam was re- constructed in 1968.

Yours faithfully,

Malcolm Alli

Michael Ragwen