Flood frequency analysis – Part 2: Development of a modified plotting position

dc.contributor.authorVan der Spuy Den_ZA
dc.contributor.authorDu Plessis JAen_ZA
dc.date.accessioned2024-01-30T09:13:09Z
dc.date.available2024-01-30T09:13:09Z
dc.date.issued2022-04-27en_ZA
dc.descriptionThe original publication is available at: https://watersa.net/article/view/13826en_ZA
dc.description.abstractThe original plotting position concept was suggested more than a century ago. Since then, many alternative plotting position approaches have been developed. Despite a general lack of agreement around which plotting position is theoretically ‘correct’ and the ‘best’ to use, all plotting positions fail to adequately address outliers and data of similar magnitude. Hydrologists generally fail to acknowledge that the plotting position primarily offers an informative display of data, against which distributions can be compared, rather than an absolute measure of probability. This paper does not intend to challenge any of the many lengthy theoretical mathematical arguments, utilised to ‘prove’ why one plotting position is superior to the others. These theoretical arguments may very well be valid for a ‘population’ of flood peaks – the reality, however, is that hydrologists are confronted with the challenge of analysing very limited ‘samples’ of the population. Consequently, the plotting position issue demands a more pragmatic approach, rather than a purely theoretical approach. This paper illustrates various problems with existing plotting position techniques in use and offers an alternative approach and a more sensible plotting position technique, using Z-scores and referred to as the Z-set PP, against which distributions can be checked. The study further illustrates how effectively the Z‑set PP deals with outliers and its robustness with various record lengths. Although derived from a study of flood peak data obtained from South African flow-gauging sites, it is deemed that it will be universally applicable.en_ZA
dc.description.sponsorshipSouth African Water Research Commissionen_ZA
dc.description.urihttps://watersa.net/article/view/13826en_ZA
dc.description.versionPublisher’s versionen_ZA
dc.format.extent14 pagesen_ZA
dc.identifier.citationvan der Spuy D and du Plessis JA .2022. “Flood frequency analysis – Part 2: Development of a modified plotting position”, Water SA, 48(2):14 pages. doi.10.17159/wsa/2022.v48.i2.3848.2.en_ZA
dc.identifier.doi10.17159/wsa/2022.v48.i2.3848.2.en_ZA
dc.identifier.issn0378-4738 (print)en_ZA
dc.identifier.issn1816-7950 (online)en_ZA
dc.identifier.urihttps://scholar.sun.ac.za/handle/10019.1/129206
dc.language.isoen
dc.publisherSouth African Water Research Commission.en_ZA
dc.rights.holderAuthors retain copyrighten_ZA
dc.titleFlood frequency analysis – Part 2: Development of a modified plotting positionen_ZA
dc.typeArticleen_ZA
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