Modeling of storm water runoff for Kitwe CBD drainage system using SWMM software

Abstract

The 2007/08 rain season caused urban flash floods in urban districts of Lusaka, Central and Copperbelt Provinces. In the Copperbelt, Kitwe City town the flash flood was assumed to be caused by rapid urbanisation, faulty city drainage network and poor storm-water management. This meant that Local Authority of Kitwe City Council are required to mitigate and prevent the reoccurrence of urban flash flood, but this need assessment to determine the true cause of urban flash floods. In some countries the Storm Water Management Model (SWMM) is widely used for planning, analysing and designing storm water runoff and other drainage system in urban areas. SWM is a dynamic rainfall-runoff simulation model which is used for single event or longterm (continuous) simulation of runoff quantity and quality from urban areas.

This research was to model storm-water runoff for Kitwe Central Business District with the size of 0.146km², containing 115 storm-water inlets and 5 storm water outlets with SWMM software. The hydrological assessment for rainfall data and rainfall characteristics, land cover for drainage characteristics and usage of land as well as the hydraulic assessment for conveyance network elements were used.

Modelling and simulation was conducted using various situations as obtained on project site and these included completely blocked, partially and open drainage system situations, whereas, perfect condition was used to assess the operation of the software. After simulation, status report indicated that urban flash flood experienced in Kitwe CBD during the 2007/08 rainfall was due to lack of drainage maintenance.

Keywords: Urban flash floods, Storm Water Management Model, hydrological assessment, Hydraulic assessment, drainage maintenance and modeling/simulation