In this thesis work, general watershed modeling concepts with relevance to road drainage,rnsuch as the rational method (IDF curve approach as well as rainfall frequency analysisrnapproach), SCS Unit hydrograph, East African Flood Model etc. are reviewed. Theirrntheoretical backgrounds as well as their limitations in contemporary highway engineeringrnpractice are discussed in adequate detail with special emphasis to practical application in thernEthiopian context. The most common methods of road drainage design in current practice arernevaluated for their applicability in the Ethiopian context, the most practical ones are selected,rnand finally an algorithm is developed to be translated into a computer program which shallrnserve as an automated system for the selected procedures.rnAccordingly, the advantages and pitfalls associated with each method are evaluated in light ofrncontemporary Ethiopian road design practice. Improvements and new approaches arernsuggested where deemed necessary. Only after selection of the methods to be automated shallrnalgorithms be established that will serve as a basis for the development of the computer codernto be written in the Visual Basic programming language.rnAlthough disproportionate importance has been attached to the hydrologic analysis part in thernthesis, hydraulic design methods for nominal dimensioning of structures are also establishedrnthrough mathematical techniques in a view to prepare a simplified automation procedure.rnAs a result of this study, a user-friendly computer software has been developed in accordancernwith the procedures and methodology outlined in the previous paragraphs. The software isrntested with a real project and the output compared with that from a manual design. Bothrnhydrographs are included in this volume for comparison. Outcomes rely appreciably on arnnumber of decisions that are at the exclusive discretion of the drainage designer, and it mustrnbe noted that the software will be primarily a vehicle of these decisions.rnKey words: hydrologic analysis; watershed modeling; road drainage design; minor drainagernstructures; culvert; hydraulic design; software development; object-oriented programming