Developing a new model to predict the diurnal water demand pattern for residential areas subjected to formal intermittent supply in South Africa

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Stellenbosch : Stellenbosch University
ENGLISH ABSTRACT: Intermittent water supply (IWS) is one of the most common methods of water demand control under water scarcity conditions, however the implementation of IWS has many negative impacts and is not recommended for planned implementation (Vairavamoorthy et al., 2001; Mckenzie et al., 2014). However, in many water scarce countries, IWS is still being implemented out of necessity rather than choice (Totsuka & Trifunovic, 2004). An important step in the planning, design and analysis of water distribution systems (WDSs) to ensure adequate system performance and levels of service (LOS) is determining the peak water demand of the supply area. The peak water demand, along with the demand patterns, are used to validate the WDS capacity (CSIR, 2003; Van Zyl et al., 2008). Extensive research on the estimation of water demand and the derivation of diurnal water demand patterns for continuous water supply (CWS) WDSs has been conducted. However, there has been little similar research conducted for WDSs subjected to IWS. The purpose of this study was to develop a new theoretical model to predict the diurnal water demand patterns for residential areas subjected to formal IWS, by taking into account the WDS filling process, as well as the crucial parameters that impact the WDS during IWS. An attempt was made to define the typical form and characteristics of the diurnal water demand patterns associated with IWS conditions, and how these patterns can be estimated when logged field data is not available. This research consisted of a non-empirical study and an empirical study. The non-empirical study consisted of a literature review of key topics, an investigation of crucial influence parameters, and the development of the model. The empirical study consisted of the collection, processing and analysis of actual water consumption data from an area subjected to IWS, which in turn, was used for the model validation and calibration. The developed model was based on the results of the parameters investigation and the assumption of a three phase WDS filling process, using the theory from the literature review. From the parameters investigation, ten parameters were found to be the most influential parameters to water demand and WDS performance during IWS. These ten parameters are supply duration, network hydraulic capacity, the available pressure head at the outlet, pressure within the water distribution network (WDN), topography, flow rate within the WDN, climate, supply area population, network filling time, and supply area size. Out of these parameters, supply duration was found to be the most influential parameter. The most influential parameters for IWS systems were found to be different from those associated with CWS systems. IWS systems are driven by the operational and structural parameters, compared to the CWS systems which are mainly driven by the socio-economic parameters. The outcomes of the parameters investigation were combined with a three phase calculation process, where each phase represented a section of the pattern shape. Phase 1 represents the initial flow spike related to the filling of the bulk supply pipe from the reservoir to the reticulation network. Phase 2 is related to the reticulation network filling, and phase 3 is related to the water demand characteristics after the filling process is complete. As a result of the research, a hypothetical 15 minute peak factors diurnal water demand pattern model was derived. This pattern yielded a high similarity to the shape of the water demand patterns derived from the actual data collected, based on the Kolmogorov-Smirnov goodness of fit test. Furthermore, the peak factors determined from the model, were also similar to the peak factors derived from the actual logged data. The results of the study show that in order to estimate water demand and derive water demand patterns related to IWS, the parameters that impact water demand and WDS performance have to be identified, and the nature of the impact of these parameters has to be understood. By combining the crucial parameters with the governing hydraulic principles related to the WDS filling process, an estimate of the diurnal water demand pattern for residential areas subjected to IWS can be derived. This diurnal demand pattern model can be used as input for the reliability analysis of existing WDSs in a water scarce area. It can assist design engineers in identifying and planning the most effective ways of implementing IWS, in the process improving the resilience of the water supply during periods of water scarcity.
Thesis (MEng)--Stellenbosch University, 2020.
Intermittent water supply, Diurnal water demand patterns, Water-supply -- South Africa, Residential water consumption -- South Africa, Water demand management, UCTD