Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The design of a water supply system relies on the knowledge of the water demands of its specific end-users.
It is also important to understand the end-users’ temporal variation in water demand. Failure of the system to
provide the required volume of water at the required flow-rate is deemed a system failure. The system
therefore needs to be designed with sufficient capacity to ensure that it is able to supply the required volume
of water during the highest demand periods. In practice, bulk water supply systems do not have to cater for
the high frequency, short duration high peak demand scenarios of the end-user, such as the peak hour or peak
day events, as the impact of events is reduced by the provision of water storage capacity at the off-take from
the bulk supply system. However, for peak demand scenarios with durations longer than an hour or a day,
depending on the situation, the provision of sufficient storage capacity to reduce the impact on the bulk water
system, becomes impractical and could lead to potential water quality issues during low demand periods. It
is, therefore, a requirement that bulk water systems be designed to be able to meet the peak weekly or peak
month end-user demands. These peak demand scenarios usually occur only during a certain portion of the
year, generally concentrated in a two to three month period during the drier months. Existing design
guidelines usually follow a deterministic design approach, whereby a suitable DPF is applied to the average
annual daily system demand in order to determine the expected peak demand on the system. This DPF does
not account for the potential variability in end-user demand profiles, or the impact that end-storage has on
the required peak design factor of the bulk system.
This study investigated the temporal variations of end-user demand on two bulk water supply systems. These
systems are located in the winter rainfall region of the Western Cape province of South Africa. The data
analysed was the monthly measured consumption figures of different end-users supplied from the two
systems. The data-sets extended over 14 years of data. Actual monthly peak factors were extracted from this
data and used in deterministic and probabilistic methods to determine the expected monthly peak factor for
both the end-user and the system design. The probabilistic method made use of a Monte Carlo analysis,
whereby the actual recorded monthly peak factor for each end-user per bulk system was used as an input into
discrete probability functions. The Monte Carlo analysis executed 1 500 000 iterations in order to produce
probability distributions of the monthly peak factors for each system. The deterministic and probabilistic
results were compared to the actual monthly peak factors as calculated from the existing water use data, as
well as against current DPFs as published in guidelines used in the industry. The study demonstrated that the
deterministic method would overstate the expected peak system demand and result in an oversized system.
The probabilistic method yielded good results and compared well with the actual monthly peak factors. It is
thus deemed an appropriate tool to use to determine the required DPF of a bulk water system for a chosen
reliability of supply. The study also indicated the DPFs proposed by current guidelines to be too low. The
study identified a potential relationship between the average demand of an end-user and the expected
maximum monthly peak factor, whereas in current guidelines peak factors are not indicated as being
influenced by the end-user average demand. / AFRIKAANSE OPSOMMING: Die ontwerp van ‘n watervoorsiening stelsel berus op die kennis van die water aanvraag van sy spesifieke
eindverbruikers. Dit is ook belangrik om ‘n begrip te hê van die tydelike variasie van die eindverbruiker se
water-aanvraag. Indien die voorsieningstelsel nie in staat is om die benodigde volume water teen die
verlangde vloeitempo te kan lewer nie, word dit beskou as ‘n faling. Die stelsel word dus ontwerp met
voldoende kapasiteit wat dit sal in staat stel om die benodigde volume gedurende die hoogste aanvraag
periodes te kan voorsien. In die praktyk hoef grootmaat water-voorsiening stelsels nie te voldoen aan spits
watergebeurtenisse met hoë frekwensie en kort duurtes, soos piek-dag of piek-uur aanvraag nie, aangesien
hierdie gebeurtenisse se impak op die grootmaat stelsel verminder word deur die voorsiening van wateropgaring
fasiliteite by die aftap-punte vanaf die grootmaatstelsels. Nieteenstaande, vir piek-aanvraag
gebeurtenisse met langer duurtes as ‘n uur of dag, raak die voorsiening van voldoende wateropgaring
kapasiteit by die aftap-punt onprakties en kan dit selfs lei tot waterkwaliteits probleme. Dit is dus ‘n vereiste
dat grootmaat watervoorsienings stelsels ontwerp moet word om die piek-week of piek-maand eindverbruiker
aanvrae te kan voorsien. Hierdie piek-aanvraag gebeurtenisse vind algemeen in gekonsentreerde
twee- of drie maand periodes tydens die droeër maande plaas. Bestaande ontwerpsriglyne volg gewoonlik ‘n
deterministiese ontwerp benadering, deurdat ‘n voldoende ontwerp spits faktor toegepas word op die
gemiddelde jaarlikse daaglikse stelsel aanvraag om sodoende te bepaal wat die verwagte spits aanvraag van
die stelsel sal wees. Hierdie ontwerp spits faktor maak nie voorsiening vir die potensiële variasie in die
eindverbruiker se aanvraag karakter of die impak van die beskikbare water-opgaring fasiliteit op die
benodigde ontwerp spits faktor van die grootmaat-stelsel nie.
Hierdie studie ondersoek die tydelike variasie van die eindverbruiker se aanvraag op twee grootmaat watervoorsiening
stelsels. Die twee stelsels is geleë in die winter reënval streek van die Wes-Kaap provinsie van
Suid-Afrika. Die data wat geanaliseer is was die maandelikse gemeterde verbruiksyfers van verskillende
eindverbruikers voorsien deur die twee stelsels. Die datastelle het oor 14 jaar gestrek. Die ware maand piekfaktore
is bereken vanaf die data en is in deterministiese en probabilistiese metodes gebruik om die verwagte
eindverbruiker en stelsel ontwerp se maand spits-faktore te bereken. Die probabilistiese metode het gebruik
gemaak van ‘n Monte Carlo analise metode, waardeur die ware gemeette maand spits-faktor vir elke
eindverbruiker vir elke grootmaatstelsel gebruik is as invoer tot diskrete waarskynlikheids funksies. Die
Monte Carlo analise het 1 500 000 iterasies voltooi om waarskynlikheids-verdelings van elke maand spitsfaktor
vir elke stelsel te bereken. Die deterministiese en probabilistiese resultate is vergelyk met die ware
maand spits faktore soos bereken vanuit die bestaande waterverbruik data, asook teen huidige gepubliseerde
ontwerp spits-faktore, wat in die bedryf gebruik word.
Die studie het aangetoon dat die deterministiese metode te konserwatief is en dat dit die verwagte piekaanvraag
van die stelsel sal oorskat en dus sal lei tot ‘n oorgrootte stelsel. Die probabilistiese metode het
goeie resultate opgelewer wat goed vergelyk met die ware maand piek-faktore. Dit word gereken as ‘n
toepaslike metode om die benodigde ontwerp spits-faktor van ‘n grootmaat-watervoorsiening stelsel te bepaal vir ‘n gekose voorsieningsbetroubaarheid. Die studie het ook aangedui dat die ontwerps piek-faktore
voorgestel deur die huidige riglyne te laag is en dat dit tot die falings van ‘n stelsel sal lei. Die studie het ‘n
moontlike verwantskap tussen die gemiddelde daaglikse wateraanvraag van die eindverbruiker en die
verwagte maksimum maand spits faktor geïdentifiseer, nademaal die piek-faktore soos voorgestel deur die
huidige riglyne nie beïnvloed word deur die eindverbruiker se gemiddelde verbruik nie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/85738 |
| Date | 12 1900 |
| Creators | Kriegler, Benjamin Jacobus |
| Contributors | Jacobs, H. E., Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xiv, 102 p. : ill. |
| Rights | Stellenbosch University |
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