Hydraulic impacts and management of intermittent water supply

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Stellenbosch : Stellenbosch University
ENGLISH ABSTRACT: Various challenges, such as limited freshwater resources, climate change impacts, rapid population growth, urbanisation and underinvestment in water supply infrastructure, have led to intermittent water supply (IWS) in potable water distribution systems. Earlier research has confirmed that IWS negatively impacts the consumers, the infrastructure and the water supply authorities. In potable water distribution systems, water quality is of the utmost importance. In systems subjected to IWS, water quality is often compromised. However, there is a large body of literature addressing issues related to water quality in IWS systems. In contrast, a number of more elementary and hydraulic aspects related to IWS systems have not been researched in depth. This research sets out to answer the following questions that are unrelated to water quality, but instead focusses on the hydraulics and infrastructure elements of the IWS systems. Is IWS prevalent in South African water supply systems? Can IWS be avoided in urban areas faced with water scarcity and which mechanisms are available to water services providers to avoid having to implement IWS? Can a model be developed to crudely assess the pipe infrastructure in order to evaluate whether IWS is a threat based on the potential maximum capacity of the network? How can systems subjected to IWS be compared in a quantifiable manner? And, how can the reliability of supply be assessed in systems subjected to IWS and what are the potential consequences of unreliable supply schedules? Earlier research on the global prevalence of IWS indicated that South Africa practises continuous water supply. Data on IWS in South Africa was collated by considering four different source types. The data were spatially and temporally analysed to determine the prevalence of IWS in South Africa. The population affected by IWS increased by ~26% between 2008 and 2017, which exceeds the population increase of ~12% over the same period. Moreover, 22 million people in South Africa were affected by IWS in 2017. Results from this research confirm an increased prevalence of IWS over time and show that 65 of the 231 municipalities in South Africa supplied water intermittently; 32 had continuous water supply and no data was available for the remainder. The outcomes highlight the widespread occurrence of IWS in South Africa. Between the years 2015 and 2018, the City of Cape Town, South Africa, experienced the worst drought on record, which placed tremendous pressure on the city’s bulk water resources. Despite many of the major dams nearly running dry in the summer of 2017/2018, and the available water diminishing to only a few months of supply, the City of Cape Town managed to avoid implementing IWS. This research presents the various strategies adopted and implemented by the City of Cape Town in order to avoid IWS. The successes achieved led to the City of Cape Town reputedly becoming the number one water saving city in the world in October 2018, saving as much as 500 ML per day, which equates to about half the normal demand before the drought. Given the well-known and widely published negative impacts associated with IWS, it would be useful for water services providers in water scarce regions to take cognisance of how the City of Cape Town managed to avoid implementing IWS. Planners are often faced with the challenge to provide crude estimates of water distribution system infrastructure capacity and associated cost in the early phases of greenfield developments. This research investigated the relationship between physical and hydraulic characteristics of a water distribution system and the corresponding serviced area. A model was compiled linking the total pipeline length of a water distribution system to the peak flow rate. The model enables prediction of the total length of water distribution system pipes required to service a future development area as a function of the peak flow rate. Alternatively, the model can estimate the potential maximum peak flow rate that can be supplied if the total pipeline length is known. IWS can result from several potential causes, including inadequate overall pipeline length or a lack of network reinforcements when new developments are added on the fringes of developed areas. Systems subjected to IWS due to these causes could be expected to have insufficient overall pipe length or different diameter distributions when compared to the model results. Thus, the model would allow a user to ascertain whether an existing water distribution system has potentially been stretched beyond its design capacity. Water supply authorities need tools to help understand IWS and the associated implications. A new indexing framework involving the causes and impacts associated with IWS has been developed. In addition, a novel approach allows for quantification of the severity of IWS based on knowledge of a few readily available inputs. The indexing framework and quantification tool could lead to improved understanding of IWS and could assist water supply authorities faced with IWS to make informed decisions. Two towns located in the Mpumalanga Province of South Africa, had IWS implemented for a number of years prior to this study. While the general causes and impacts of IWS are fairly well researched and documented, the causal-consequential pathways of IWS as experienced in one of the study areas, offer a new perspective on consumer acceptance and conduct related to various forms of IWS. Logging of flow rates recorded by meters supplying water intermittently, also offers new information on supply availability, supply durations and reliability of supply when supply schedules are managed by manually opening and closing of zone valves. Unreliable and unavailable supply led to an increased number of illegal connections. Once water theft and leakage rates exceeded certain levels, the water services provider struggled to maintain control over the water supply infrastructure and a spiral of decline was observed.
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.
Thesis (PhD)--Stellenbosch University, 2023.