Dear Editor,
I read the report on the ‘Georgetown-Lethem Road, Guyana Pre-Feasibility Study Final Report November 2008’ that is available on the GINA website. Evidently great effort was put into this work. The report states, “In developing the improvement alternatives for analysis the Consultants were guided by Chapter 8 of the National Development Strategy (NDS) which calls for ‘The road between Linden and Lethem to be improved to the same standard as the highway between Georgetown and Linden.’” I cannot help but ask, isn’t there a design standard/manual for highways in Guyana, and if not when will the Government of Guyana pursue such an objective? It is hard to comprehend that Guyana’s planning document, the NDS, would make reference to a portion of roadway as its guideline rather than to a perceived design manual. I feel the terms of reference should have been specific. This is another excellent example of a poor approach to spending millions of US dollars. There are other questions: What design standard (geometric, structural, etc) was used for the Georgetown to Linden Highway? To the best of my knowledge it was done by a US firm and hence a US design model (AASHTO). Could someone familiar with this highway design shed some light on this information because the final report was not specific about this guideline.
The consultants, Mott MacDonald in conjunction with the local firm CEMCO, used the UK, Transport and Road Research Laboratory (TRL) Overseas Road Note 6 model as the basis for their geometric design. Does this mean that this will be the approach for similar roadway designs in Guyana for the future?
Circumventing the subject of geometric design and focusing on the area of drainage, I would rate the effort of the drainage technical write-up as poor, the work of inexperienced roadway drainage design engineers. The drainage effort seems to have been lost in producing numerous sketches of existing roadway structures rather than providing beneficial technical information to enable a realistic cost of each road improvement alternative to be derived. I think the drainage team, amongst other tasks, should have been in a position to lend support to the roadway team to identify lengths of roadway that have drainage suspect areas, as well as anything drainage related that will influence the profile and cost, etc. It takes experienced roadway drainage engineers to perform and review drainage tasks during the conceptual stage of a project. An example of poor engineering is seen by examining the shoulder conditions in the visual condition survey in Appendix A; it is a drainage concern if the shoulder shows signs of erosion. Runoff velocity, runoff volume, roadway spread, vertical road profile, etc, should be looked at. I feel the GoG is again showing weakness in the drainage department by acceptance of this report, and lending institutions should insist that it employ qualified technical experts to review the project documents and not leave it entirely to the consultants and the technical review team. I have abstracted the descriptions of the drainage technical write-up for the four sections comprising the Linden–Lethem highway, to substantiate my view. For persons who are not familiar, this write-up is for 451 km of roadway.
The drainage description for the Linden to Mabura Hill section is as follows: “There is no real incidence of flooding since the alignment follows the watershed between the Demerara and Essequibo Rivers. Drainage structures along this section are fully functional and are made up predominately of culverts with one log-type bridge.” The drainage description of the Mabura Hill to Kurupukari section reads: “drainage of this section is good with numerous log-type bridges and the alignment follows the watershed between the Demerara and Essequibo Rivers.” The drainage description of the Kurupukari to Annai section says: “Most of the drainage structures are timber bridges in fair condition with few culverts and the elevation of the roadway is above the flood plain. The drainage description of the Annai to Lethem section states: “In the past, however, it has been subject to seasonal flooding as it was below the flood plain. However since 2005 the Ministry of Public Works and Communication has progressively raised the grade and it is reported that this section no longer floods,” and “Most of the drainage structures are functional and mainly comprise corrugated metal pipe culverts and timber bridges.”
I wonder which manual was used to determine the hydraulic capability of roadway structures and what the experience of the inspecting personnel for ditches, cross drains/culverts and bridges was? It can be deduced from the drainage technical write-up that the impact due to drainage for this project is not an area of concern, but I would dispute this assertion. Are we going to adopt the Ministry of Public Works and Communica-tion’s approach to roadway drainage whereby the road is “progressively” raised until there is no more flooding (the ‘guesstimation’ approach), or should we adopt a scientific approach whereby the drainage contributing area for each roadside ditch, cross drain/culvert and bridge is developed for design rainfalls so that the roadway structures are adequately sized hydraulically rather than make generalized statements, like “the drainage structures are functional.” Drainage has always been and will always remain a subject that is not taken seriously until a catastrophic event proves otherwise. Finally, the treatment of flood plain impacts, that is, roadways constructed in flood plain areas, takes away flood storage areas and should lead to flood plain compensation. This is a high cost item, so was this done? For the drainage engineer, flood plain compensation is synonymous to LCD compensation, but without the monetary rewards from rich nations.
Yours faithfully,
Ralph V. Seegobin
