Performance optimization of unplanned water distribution networks in fast growing towns: a case study of Mwanza city, Tanzania

Abstract

High Non-Revenue Water (NRW) and unreliable water supply services are major challenges in operations of the water networks in most of the fast-growing cities in developing countries. The present study aims at investigating the extent that the existing distribution network contributes to the prevailing high percentage of the NRW; and explore optimization scenarios focusing on water loss reduction and system improvement in the unplanned network. The measured system flow and pressure were used for water balance assessment, calibration and modelling to simulate different scenarios in order to improve system performance. The results showed 52% of the junctions in the system had high pressure above recommended which contributed to 87% of real loss and 83% of pipes had low velocities below the set thresholds. These indicate that uneven distribution of pressures and velocities are driven by improper topology of both pipe sizing and supply directions in the unplanned network. About 50% of NRW was detected in the study area while the entire network had 37%, thus small areas assessment and pressure management are required. The pressure reduction by optimizing installation of pressure reducing valves and change network topology reduced NRW by 46%. In addition, regular nodal hydraulic analysis and flow modifications performed well when integrated with stochastic town growth for system capacity torelance. The study provides ways for sustainably improving the poorly performing water networks in fast-growing towns. It also recommends methods of integrating pressure management, network topology change and resilient to future demand for attaining a better system performance.