In order to a establish a design rainfall and flow estimation methodology compatible to the Ethiopian environment and facilitate standard design practices in all road design works in Ethiopia, the Ethiopian Road Authority (ERA) had commissioned Louis Berger Group to prepare a road drainage design manual in 2002 under a credit from the International Development Agency (IDA).
This technical note has been prepared for Ethiopian Roads Authority (ERA) as a result of a brief review of the above manual published in 2002.
The brief received from ERA required me to review the drainage design manual referred above and make comments and recommendations if any.
In preparing this technical note, I have read the ERA drainage design manual-and various road drainage design manuals produced by other countries including USA, UK, Australia, Gahanna, South Africa, Uganda and Kenya.
Clearly, in the time available, I have not been able to carry out a full technical review of the manual. However, I have used my local knowledge and past experience to review the manual with critical eye, with the aim of identifying information and technology gaps, any uncertainties, misconceptions or missed opportunities.
During the technical review it was revealed that the ERA drainage design manual contains most of the necessary relevant technical information which is required for design of road drainage structures in Ethiopia. The design methodologies had been adopted from the American Association of State Highway and Transportation Officials (ASSHTO) and the design charts were adopted from the Federal Highway Administration of the Bureau of Reclamation Hydraulic Laboratory.
Road Development in Ethiopia has vastly accelerated in recent years. Road construction has progressed from foot tracks to modern highways and the application of road drainage design procedures developed for other countries has brought problems, such as in the field of drainage and hydrology where tropical conditions are very different from those in more temperate zones for which many design procedures were initially developed.
Most of the design criteria and equations available come from empherical studies applicable only to limited geographical regions where the study had originally been undertaken. Therefore it is important that procedures used for design rainfall and flow estimation should be in accordance with the specific hydrological analysis that is applicable to the Ethiopian environment.
It is also understood that , the regional drainage engineers in Ethiopia have few opportunities to consult with technical specialists related to road drainage design technology due to lack of skilled human resources and advanced technology in the country. Hence, another reason for ERA to prepare road drainage design manual to provide practical guidance for regional drainage engineers.
In striving to reach these key objectives, ERA has also been, pro-active in compiling relevant...