Performance Assessment of Sewer Network in Addis Ababa: The Case of Kality Catchment
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Date
2023-12
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Addis Ababa University
Abstract
Urban development usually exerts enormous pressure on the existing sewer network systems. The deficiency in the performance of the sewer network becomes one of the most critical issues in the sewer system sector that requires immediate action. Kality Catchment sewer system has problems related to sewer system coverage, manholes overflow, and capacity deficiency. The main objective of this study is to assess the performance of existing sewer network in Kality’s Catchment with respect to pipe capacity (depth/rise), and surcharge using Bentley SewerGEMS CONNECT. Both primary and secondary data were collected and TOOLS such as Arc GIS, AutoCAD, Microsoft Office Excel, and Geographic positioning system (GPS) were used. Model analyses were conducted under three possible scenarios. The wastewater generations for the first and second scenarios were estimated based on water consumption bill data by considering active and potential sewer customers for both scenarios, respectively. Additionally, a projected wastewater generation was derived from land use data for the third scenario. The sewer system coverage in the Kality Catchment was estimated to be 17.63%, showing only the proportion of active sewer customers relative to water customers in the study area. The steady-state analysis of the sewer network, considering peak flow conditions, revealed that approximately 1.01%, 1.49%, and 4.16% of pipes exceeded their capacity (d/D) (>90%) values. This accounts for lengths of 5,415.10m, 7,956.20m, and 22,249.10m for the first, second, and third scenarios respectively. Additionally, approximately 2.88%, 3.74%, and 8.35% of pipes experienced surcharge, accounting for lengths of 15,372.40m, 20,019.10m, and 44,654.50m for the respective scenarios. The pipe capacity (d/D) exceeded when the d/D ratio reached 0.9(90%), and surcharge occurred when the water level rose above 15cm of the manhole rim elevation during peak flow conditions. These locations with deficiencies in both pipe capacity (d/D) and surcharge covered lengths of 1,691.90m, 5,334.80m, and 17,577.50m for the first, second, and third scenarios respectively. It is recommended that the utility upgrade the existing sewer network, as well as expand a new sewer system and connect to the system unserved areas and customers.
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Keywords
Addis Ababa, Kality Catchment, Hydraulic Model, Sewer Network, and SewerGEMS