FLOOD FREQUENCY ANALYSIS

Abstract

Flood has since long been one of the worst natural calamity causing hazards to the mankind in terms of loss of life, property including damages of strategic and costly hydraulic structures. To combat floods, government is spending a large sum of money every year on flood control and flood forecasting (based on flood frequency analysis). Several researchers have given flood frequency analysis models for estimation of design flood. Availability of only limited flood records or even their absence at a particular site has given rise to the development of empirical formulae based on various catchment characteristics (e.g. are?, slope, Vegotel cover etc.) of different stations spread over whole country. The empirical modeis are plagued by several weaknessess like dimensional non-homogeneity, poor prediction ability and non-compliance of boundary conditions. To make the situation even worse, the researchers have considered rainfall of only one reccurrence interval. Though rainfall data available at various stations is for different reccurrence intervals, not even a single researcher has so far attempted the flood ireqwenoy estimation employing the data of all reccurrence intervals. In the present work, to rectify the inherent weaknessess of available approaches, an empirical dimensionally homogeneous model satisfying the boundary conditions and employing the data of rainfall for all durations and reccurence intervals has been presented. Any combination of rainfall duration and reccurrence interval can be used in predicting flood using the present model. (iv) The cumbersome exercise of preparing Indian Meteorological Department IIMDI rainfall frequency maps can even be avoided by making use of rainfall intensity-duration relationship available at certain stations of the country. The interpolation/extrapolation procedure, presented employs shape function technique.