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Lectures on Hydrologic Modelling of Extreme Floods

Lectures on Hydrologic Modelling of Extreme Floods. Mauro Fiorentino. Grand Combin Summer School on Physics and Predictability of Rainfall and Floods". Saint-Oyen (Valle d’Asta, Italy) June 26 – July 5 2002. Problems related to the use of pure statistical methods.

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Lectures on Hydrologic Modelling of Extreme Floods

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  1. Lectures on Hydrologic Modelling of Extreme Floods Mauro Fiorentino Grand Combin Summer School on Physics and Predictability of Rainfall and Floods" Saint-Oyen (Valle d’Asta, Italy) June 26 – July 5 2002

  2. Problems related to the use of pure statistical methods • Lack of observations of extreme events (crucial for the estimation of high return periods) • flood risk evaluation in ungauged basins • uncertainty in the individuation of homogeneous regions

  3. Estimation schemes Parameter estimation technique at site or regional Stochastic Model • Hydrometricinformation • Pluviometric Information • Phisical Information (base processes) • Geology • Climate • Vegetation

  4. Estimation schemes Parameter estimation technique at site or regional Stochastic Model • Hydrometricinformation • Pluviometric Information • Phisical Information (base processes) • Geology • Climate • Vegetation How to improve it?

  5. Estimation schemes Parameter estimation technique at site or regional Stochastic Model • Hydrometricinformation • Pluviometric Information • Geology • Climate • Vegetation • Base processes information

  6. One possible solution: Theoretical models for derivation of flood frequency distribution

  7. Two random variables:: a = variable contributing area Q = ua a • The variable contributing area • the peak runoff per unit contributing area t (a) = the lag time of the area a f = hydrologic loss rate fa =loss rate significant to peak i = rainfall intensity f i p(a) p(ua ) ia,t a ua The routing model: fa ua = x( ia,t - fa ) time x = routing coefficient t = t (a)= t1 ag= critical duration t (a) Summarizing

  8. Sample application of the theoretical model Bradano-San Giuliano CDF of flood annual maxima PDF of contributing area Bradano-P.te Colonna CDF of flood annual maxima PDF of contributing area

  9. Sample application of the theoretical model Basento - Menzena CDF of flood annual maxima PDF of contributing area Sinni - Valsinni CDF of flood annual maxima PDF of contributing area

  10. Non linearity causes For rainfall intensity below a certain threshold the prevailing runoff generation mechanism is of Dunne’s type For rainfall intensity above that threshold the prevailing runoff generation mechanism is of Horton’s type

  11. (grande impatto tecnico) arido Q/E[Q] Cv umido Log T

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