Improving urban drainage in Abidjan, Côte d’Ivoire

Abstract

Tropical humid climates of sub-Saharan Africa with a high level of variability build a challenge for hygienic models used in urban drainage. Global models of urban drainage used in this region – for example the Caquot’s rate-of-flow model – are based on the parameters of Montana’s rain model. This model indicates the evolution of the maximum rainfall intensity according to the duration and the return period. In Côte d’Ivoire, several studies highlighted that adapting Montana’s rain model is not satisfactory for particular time slots, which in turn affects urban drainage calculations. This work aims at optimising and designing models which best simulate tropical downpours and improving calculations related to urban drainage in Abidjan and in other urban settings with similar climatic conditions. Various statistical processing undertaken showed that the rainfall distribution in the area of Abidjan is in line with the laws of Gumbel (10 – 30 mn rainfall) and Galton (45 – 240 mn rainfall). Including the data in mathematical conversion formulas made it possible to optimise Montana’s parameters and to design a new model that best simulates downpours in Abidjan. In addition, analysis of the Nicholson index revealed a drop in rainfall in Abidjan with a cyclical evolution ( about 17 year period), alternating dry, normal and wet periods. The new model is relevant since it overlaps two very satisfactory models and could be used to improve urban drainage calculations in Abidjan and similar climatic conditions.

Keywords Abidjan; climatic variability; Montana’s model; sub-Saharan African tropical wet region; urban drainage