Influences on flood frequency distributions in Irish river catchments

DC FieldValueLanguage
dc.contributor.authorAhilan, Sangaralingam
dc.contributor.authorBruen, Michael
dc.contributor.authorO'Sullivan, J. J.
dc.date.accessioned2012-09-27T13:58:14Z
dc.date.available2012-09-27T13:58:14Z
dc.date.copyright2012 Copernicus Publications on behalf of the European Geosciences Unionen
dc.date.issued2012
dc.identifier.citationHydrology and Earth System Sciences (HESS)en
dc.identifier.urihttp://hdl.handle.net/10197/3824
dc.description.abstractThis study explores influences on flood frequency distributions in Irish rivers. Generalised Extreme Value (GEV) type I distributions are recommended in Ireland for estimating flood quantiles. This paper presents the findings of an investigation that identified the GEV statistical distributions that best fit the annual maximum (AM) data series extracted from 172 gauging stations of 126 rivers in Ireland. Analysis of these data was undertaken to explore hydraulic and hydro-geological factors that influence flood frequency distributions. A hierarchical approach of increasing statistical power that used probability plots, moment and L-moment diagrams, the Hosking goodness of fit algorithm and a modified Anderson-Darling (A-D) statistical test was followed to determine whether a type I, type II or type III distribution was valid. Results of the Hosking et al. method indicated that of the 143 stations with flow records exceeding 25 years, data for 95 (67%) was best represented by GEV type I distributions and a further 9 (6%) and 39 (27%) stations followed type II and type III distributions respectively. Type I, type II and type III distributions were determined for 83 (58%), 16 (11%) and 34 (24%) stations respectively using the modified A-D method (data from 10 stations was not represented by GEV family distributions). The influence of karst terrain on these flood frequency distributions was assessed by incorporating results on an Arc-GIS platform showing karst features and using Monte Carlo simulations to assess the significance of the number and clustering of the observed distributions. Floodplain effects were identified by using two-sample t-tests to identify statistical correlations between the distributions and catchment properties that are indicative of strong floodplain activity. The data reveals that type I distributions are spatially well represented throughout the country. While also well represented throughout the country, the majority of type III distributions appear in areas where attenuation influences from floodplains are likely. The majority of type II distributions appear in a single cluster in a region in the west of the country that is underlain by karst but importantly, is characterised by shallow of glacial drift with frequent exposures of rock outcrops. The presence of karst in river catchments would be expected to provide additional subsurface storage and in this regard, type III distributions might be expected. The prevalence of type II distributions in this area reflects the finite nature of this storage. For prolonged periods of rainfall, rising groundwater levels will fill karst voids, remove subsurface storage and contribute to recharge related sinkhole flooding. Situations where rainfall intensities exceed karst percolation rates also produce high levels of surface runoff (discharge related flooding) that can promote type II distributions in nearby river catchments. Results therefore indicate that in some instances, assuming type I distributions is incorrect and may result in erroneous estimates of flood quantiles at these locations. Where actual data follows a type II distribution, flood quantiles may be underestimated by in excess of 35% and for type III distributions, overestimates by over 25% can occur.en
dc.description.sponsorshipNot applicableen
dc.language.isoenen
dc.publisherCopernicus Publications on behalf of the European Geosciences Unionen
dc.relation.requiresCentre for Water Resources Research Collectionen
dc.subjectRiver hydraulicsen
dc.subjectGeneralised extreme value distributionen
dc.subjectFlood frequency analysesen
dc.subjectHydrologyen
dc.subjectHydrogeologyen
dc.subjectFloodplainsen
dc.subject.lcshRivers--Irelanden
dc.subject.lcshFloods--Irelanden
dc.subject.lcshExtreme value theoryen
dc.subject.lcshHydrologyen
dc.subject.lcshFloodplains--Irelanden
dc.titleInfluences on flood frequency distributions in Irish river catchmentsen
dc.typeJournal Articleen
dc.internal.availabilityFull text availableen
dc.internal.webversionswww.hydrol-earth-syst-sci.net/16/1137/2012/-
dc.statusPeer revieweden
dc.identifier.volume16en
dc.identifier.issue4en
dc.identifier.startpage1137en
dc.identifier.endpage1150en
dc.identifier.doi10.5194/hess-16-1137-2012-
dc.neeo.contributorAhilan|Sangaralingam|aut|-
dc.neeo.contributorBruen|Michael|aut|-
dc.neeo.contributorO'Sullivan|J. J.|aut|-
dc.description.othersponsorshipOffice of Public Worksen
dc.description.othersponsorshipCentre for Water Resources Research, School of Civil, Structural and Environmental Engineering, University College Dublin.en
item.grantfulltextopen-
item.fulltextWith Fulltext-
Appears in Collections:Centre for Water Resources Research Collection
Civil Engineering Research Collection
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