A GIS-BASED ANALYSIS OF SEWER CHOKES IN NAIROBI

Abstract

Cities and towns in Kenya have been facing sanitation problems related to sewage outflows and sewage pipe bursts. In some cases, this has resulted in deaths attributed to cholera. Operation and Maintenance Information System (OMIS) is used to assist Nairobi City Water and Sewerage Company (NCWSC), a state owned water utility, in sewer choke analysis. The analysis helps in decision-making process to reduce the number of chokes occurring within their jurisdiction. This study focused on spatial sewer choke analysis in Nairobi using Geographic Information Systems (GIS) which would enable easier visual interpretation of otherwise complicated and detailed raw data. GIS was found to be useful as it spatially reflected the relationship and strength of each factor to choke formation. Also helpful information such as pipe diameter and their spatial distribution was symbolized. Furthermore, queries could be run to select data according to the user’s preferences; for example, querying data on chokes occurring due to a specific cause, such as blockage by rags or debris, or pipe fats. GIS was used to compute the extent of extent of the area affected by concentrating on chokes occurring in the Nairobi Western region. This facilitated identification of areas with high or low concentrations of sewer choke problems easily. Areas like Kawangware and Kabiria had high sewer choke problems whereas Spring Valley and Loresho had low choke problems. In addition, factors causing high concentrations were spatially revealed; population and poverty. Further Geographic Weighted Regression (GWR) was used to spatially reveal the trends of factors that influence choke frequencies.