Characterization of Rainwater Drainage Infrastructure in the City of Lomé (Togo, West Africa)

Abstract

Despite Togo government’s efforts to maintain and expand its storm drainage networks, urban flood disasters remain recurrent. Beyond Shallow zones occupation for construction and climatic causes, it is essential to circumscribe the determinants linked to infrastructure. Based on the inventory and characterization of rainwater drainage infrastructure, this study is a contribution to the reduction of flood risk in the city of Lome in Togo. Surveys were conducted on rainwater drainage works of the 172 paved roads in Lome. A sample of each network group is selected by considering the areas of recurring hazards and broadest catchment areas in the city for the evaluation of their structural and functional states according to the readapted VIZIR method. The relationship between these two states was computed using multiple correspondence analysis (MCA). This study reveals notable insufficiencies in rainwater drainage management in the city, expressed by the existence of roads built without drains, gutters without outlets, and open gutters and makeshift trenches built by the population. Functionally and structurally, almost all the structures are constructed of reinforced concrete. The most cracked are the mainly open pit (92.02%) works of the lagoon complex. The retention basin network includes 36 retention ponds 18 of which are interconnected, 11 drained by gravity and 4 by pumping. The latter are inherently hazardous insofar as pumping energy is not guaranteed. The MCA has shown that the network of piping related to the retention ponds are in similar conditions, and that generally, the closed gutters are not cracked while the open gutters are cracked.