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 Westernregion.  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.

Key words: Sewer choke, hot spot, GIS spatial analysis, Nairobi City Water and Sewerage Company