ASSESSING THE APPROPRIATE STORMWATER MANAGEMENT SYSTEM FOR KISII MUNICIPALITY, KISII COUNTY, KENYA
Authors:
James Okinyi Manyara Meja* Getabu Albert, Onchieku James, Ogendi George, Okwadha George
Abstract:
Urban storm drains are crucial in draining water from the city to major water bodies and finally to retention Bonds, lakes and dams. The storm drains Stormwater is a direct result of rainfall, where water flows before it joins the main drainage systems. In urban areas, stormwater is a major contributor of non-point source pollution emanating from urban liquid wastes that are washed down to the main water channels. This study aimed at developing an efficient and effective stormwater management system within the Municipality. The need to study an appropriate design for the Kisii stormwater system was informed by researches that indicated urban flooding was majorly caused by poor drainage systems and unsynchronized water channels with culverts. The study aggregated all data collected from the Kenya Metrological department on rainfall intensity for Kisii Municipality and Field research Data on storm channels alignment, depth, width and formation. The SWMM model used two scenarios Low Impact Development (LID) model and Manning’s formula storm channels adjustment. The LID model introduced retention bonds, storage tanks and infiltration within Kisii town while manning formulae was used to adjust culverts levels to adjoining culverts. The study was analyzed using PCSWMM software and it was established that infiltration accounted for 50.4% while storage barrels comprised of 24.3%. The introduction of LID in Kisii town reduced flood water by 28.8%, though this wasn’t enough to reduce flooding downstream the introduction of channels realignment and LID simultaneously reduced flooding at Daraja Mbili by upto 66.7%.