Integrated Urban Pluvial Flooding Analysis and Modelling for Nairobi West and South C in Nairobi City

Urban pluvial flooding cases have increased due to urban densification, fast changing urban hydrology as well as inadequate urban drainage design especially the combine storm-sewer systems. In Nairobi city, residents are at greater urban pluvial flooding risk as has been witnessed with a number of flood damages having already been experienced. However, there are a number of tools that have been developed to help in analysing urban pluvial flooding risks and support sound planning to avert such catastrophes. This purpose of the study was to analyse and model urban pluvial flooding in Nairobis South C and Nairobi West areas using Storm Water Management Model version 5.1 (SWMM5.1) and demonstrate to city planners among other key stakeholders the applicability of SWMM 5.1 in analysing urban pluvial flooding to support urban planning. Three main datasets were used in the study including Geographic Information Systems (GIS) data, rainfall data disaggregated into 15-minutes events and the sewer network data. Other key parameters were drawn from existing literature. The response of two delineated sub-catchments to the rainfall event of 26th December 2012 was then modelled and sensitivity analysis conducted to identify the relative influence of some model input parameters on the peak runoff. The results from the model showed significant flooding of 20.134 ha-m surface runoff and 81 % of sewer system surcharging. The peak runoff was found to be significantly responsive to variations in Impervious N and % imperviousness parameters. The study demonstrated that SWMM5.1 model is a useful tool for simulating urban pluvial flooding and improving urban stormwater management.