Evaluation of minimum pressure head during peak flow as design criterion for water distribution systems
Thesis (MEng)--Stellenbosch University, 2016.
ENGLISH ABSTRACT: One of the factors that drives infrastructure cost for water distribution systems (WDS), whether it being the cost of newly designed systems or the cost for maintaining and upgrading existing systems, is the hydraulic design criterion. The South African civil engineering fraternity has generally grown to accept the design criterion for water distribution systems as providing a minimum residual pressure head (MPH) of 24m at the most critical node in the system under theoretical peak demand conditions. Previous studies have indicated that the above criterion is relatively stringent, especially due to the fact that theoretical peak factors used in design to simulate the peak demand condition are often too conservative. The aim of this study was to evaluate the criterion with the focus on the MPH value of 24m employed as a guideline in South Africa. As part of the study, current hydraulic models of existing South African WDSs were evaluated. In total, 71 towns located within 17 municipalities were included in this study. A total of 52 hydraulic models comprising a total of 539 388 modelled nodes were analysed. The number of nodes experiencing pressures below 24m was determined and the time spent at pressures under 24m was assessed. Furthermore, the consequences of nodal pressures decreasing to below the minimum local standards were investigated. The results of the study confirmed previous findings that the current design criterion of 24m is too stringent and recommendations were made for water-providing authorities to relax the current design criterion. Three alternatives for a relaxed criterion were proposed.
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