Hydraulic Modelling, Sectorisation, Interventions for Assessment and Improvement of Equity in Intermittent Water Supply Systems

Abstract

Intermittency in water supply is experienced by almost a billion people worldwide. Water scarcity, ageing infrastructure, population growth and lack of water resources management are contributing to the perpetuation of the intermittency issue. Other than the poor quality of supplied water and overall service, intermittent water supply often results in inequitable distribution of water among people. Thus, it is important to improve our understanding of such water supply systems, gaining knowledge and developing appropriate tools to mitigate the issue and its consequences. The present work addresses the current shortcomings in hydraulic modelling and management of intermittent water supply systems, as well as the lack of appropriate measures of water distribution equity among consumers. Existing hydraulic models for intermittent water supply are reviewed with regards to their suitability for modelling different intermittent systems. Apart from the filling/emptying process of the distribution network, attention is given to the lack of sufficient residual pressure in the system to satisfy demand. Another core element investigated are the peculiarities in consumer behavior observed during supply shortage and how these are incorporated in hydraulic models. A critical discussion and summary of these is provided, which could help engineers and modelers adjust their modelling approach to the specific system’s needs. Sectorisation and creation of district metered areas across the distribution network is a necessary step for improved operational management and overall resources management. A lack of such sectorisation techniques is observed in the literature for the specific type of water supply. A novel highly automated sectorisation methodology is presented here. It is based on graph theory’s Breadth-First-Search algorithm as well as an iterative optimization process. The optimal position of sector boundary gate valves is defined based on the objective of water distribution equity improvement. Further, the optimal status of these valves (closed or open) during extended period simulation is determined. The methodology is applied successfully in two case studies and eventually improved equity substantially, proving that there is space for equity improvement in IWS systems via sectorisation. In the first example, UC and SRs are improved in the isolated sector mode and these further improved when different valve operation schedules were considered increasing the UC across all nodes from 0.34 in the initial situation to 0.94 after sectorisation. In the second example, residual pressure at demand nodes was the critical factor for supply of demand. The WDN was examined in steady state simulations and the resulting solutions successfully redistributed pressures and increased the UC from 0.64 to 0.67. Finally, during the investigation of equity improvement, the lack of a reliable and representative water distribution equity measure was identified. For this reason, a sensitivity analysis of the previously used equity measures is performed. The sensitivity of each measure to the statistical properties of the distribution of water at demand nodes is determined. Observations on the behavior of the existing equity measures to changes in the distribution of water across the network lead to the definition of a new equity measure. Demand satisfaction ratio, the supply duration ratio, and population weights at demand nodes are the main parameters included in the proposed new equity measure. The demand satisfaction ratio and supply duration ratio components are represented by a generic sigmoid function. The sensitivity analysis of the new equity measure demonstrates its behavior to changes in statistical properties of demand satisfaction ratio samples, and the level of adjustability via its parameters. The above contributions in hydraulic modelling approaches, operational management via sectorisation for equity improvement, and measuring equity can be utilized by engineers and policy makers to improve the water supply service during intermittencies in supply from source or substantial pressure deficiencies in the distribution network.