Abstract
Hydrologic designs require accurate estimation of quartiles of extreme floods. But in many developing regions, records of flood data are seldom available. A model framework using the dimensionless index flood for the transfer of Flood Frequency Curve (FFC) among stream gauging sites in a hydrologically homogeneous region is proposed. Key elements of the model framework include: (1) confirmation of the homogeneity of the region; (2) estimation of index flood-basin area relation; (3) derivation of the regional flood frequency curve (RFFC) and deduction of FFC of an ungauged catchment as a product of index flood and dimensionless RFFC. As an application, 1983 to 2004 annual extreme flood from six selected gauging sites located in Anambra-Imo River basin of southeast Nigeria, were used to demonstrate that the developed index flood model: , overestimated flood quartiles in an ungauged site of the basin. It is recommended that, for wider application, the model results can be improved by the availability and use of over 100 years length of flood data spatially distributed at critical locations of the watershed. Doi: 10.28991/cej-2020-03091627 Full Text: PDF
Highlights
The estimation of extreme flood probabilities has been a long-standing problem in hydrology because of insufficiently long flood records needed to estimate the annual exceedence probabilities (AEPs) at the site of interest [1]
The spatial extent of stream gauging network is rarely sufficient for accurate estimates of extreme floods needed for design purposes
The dimensionless index flood model was regionalized in terms of watershed area
Summary
The estimation of extreme flood probabilities has been a long-standing problem in hydrology because of insufficiently long flood records needed to estimate the annual exceedence probabilities (AEPs) at the site of interest [1]. According to Robson and Reed [2], the fitting of a defined probability distribution to historical annual maximum or partial discharge time series in order to determine the magnitude of a flood event at set AEP or return period is called flood frequency analysis (FFA). The estimated flood quartiles of these sites are based on large degree of extrapolation by simulation with associated high level of uncertainties [5]. In such cases, the widely used at-site flood frequency analysis is most preferred as historical flood records are drawn from a single site of interest. Using HEC-RAS and Gumbel’s distributions, Parhi [9] estimated peak floods with up to 100years return period in the same Mahanadi River at Hirakud and Naraj dams
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