SummaryTo establish a design rainfall and flow estimation methodology compatible with the Ethiopian environment and to facilitate standard design practices in all works road design in Ethiopia, the Ethiopian Road Authority (ERA) commissioned Louis Berger Group to prepare a road drainage design manual in 2002 with credit from the International Development Agency (IDA). This technical note was prepared for the Ethiopian Roads Authority (ERA) following a brief review of the above manual published in 2002. The brief received from ERA requested me to review the design manual of the drainage mentioned above and to make comments and recommendations where appropriate. 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. Obviously, in the time I had, I was not able to do a full technical review of the manual. However, I have used my local knowledge and past experience to review the manual with a critical eye, with the aim of identifying information and technology gaps, uncertainties, misconceptions or missed opportunities. During the technical review, it was revealed that the ERA Drainage Design Manual contains most of the relevant technical information required for the design of road drainage structures in Ethiopia. The design methodologies were adopted by the American Association of State Highway and Transportation Officials (ASSHTO) and the design schemes were adopted by the Federal Highway Administration's Bureau of Reclamation Hydraulic Laboratory. Road development in Ethiopia has accelerated significantly in recent years. ... middle of article ...... of tools available for forecasting rainfall runoff volume and peak flow from rural and urban watersheds. However, it should be noted that no method is considered "right", while the others are "wrong". However, to avoid confusion, a preferred method is recommended as good practice. It is important to emphasize that using multiple methods can provide additional information on the decisions to be made. This can be particularly useful in situations where the consequences of a "failure" of a drainage structure would be particularly severe (e.g. culverts and bridges). The comments and recommendations made in this technical review note are the result of a careful review of numerous hydraulic and hydrological modeling. methodologies, hydrological and hydraulic modeling software and design procedures available today for the drainage engineer.