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| Titel |
Examination of homogeneity of selected Irish pooling groups |
| VerfasserIn |
S. Das, C. Cunnane |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 15, no. 3 ; Nr. 15, no. 3 (2011-03-09), S.819-830 |
| Datensatznummer |
250012683
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| Publikation (Nr.) |
 copernicus.org/hess-15-819-2011.pdf |
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| Zusammenfassung |
| Flood frequency analysis is a necessary and important part of flood risk
assessment and management studies. Regional flood frequency methods, in which
flood data from groups of catchments are pooled together in order to enhance
the precision of flood estimates at project locations, is an accepted part of
such studies. This enhancement of precision is based on the assumption that
catchments so pooled together are homogeneous in their flood producing
properties. If homogeneity is assured then a homogeneous pooling group of
sites lead to a reduction in the error of quantile estimates, relative to
estimators based on single at-site data series alone. Homogeneous pooling
groups are selected by using a previously nominated rule and this paper
examines how effective one such rule is in selecting homogeneous groups. In
this paper a study, based on annual maximum series obtained from 85 Irish
gauging stations, examines how successful a common method of identifying
pooling group membership is in selecting groups that actually are
homogeneous. Each station has its own unique pooling group selected by use of
a Euclidean distance measure in catchment descriptor space, commonly denoted
dij and with a minimum of 500 station years of data in the pooling
group. It was found that dij could be effectively defined in terms of
catchment area, mean rainfall and baseflow index. The study then investigated
how effective this selected method is in selecting groups of catchments that
are actually homogenous as indicated by their L-Cv values. The sampling
distribution of L-CV (t2) in each pooling group and the 95% confidence
limits about the pooled estimate of t2 are obtained by simulation. The
t2 values of the selected group members are compared with these
confidence limits both graphically and numerically. Of the 85 stations, only
1 station's pooling group members have all their t2 values within the
confidence limits, while 7, 33 and 44 of them have 1, 2 or 3 or more, t2
values outside the confidence limits. The outcomes are also compared with the
heterogeneity measures H1 and H2. The H1 values show an upward trend with the
ranges of t2 values in the pooling group whereas the H2 values do not
show any such dependency. A selection of 27 pooling groups, found to be
heterogeneous, were further examined with the help of box-plots of catchment
descriptor values and one particular case is considered in detail. Overall
the results show that even with a carefully considered selection procedure,
it is not certain that perfectly homogeneous pooling groups are identified. |
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