1 XXVII CONVEGNO DI IDRAULICA E COSTRUZIONI IDRAULICHE - IDRA2000 Genova, 12-15 settembre 2000...

1XXVII CONVEGNO DI IDRAULICA E COSTRUZIONI XXVII CONVEGNO DI IDRAULICA E COSTRUZIONI IDRAULICHE - IDRA2000IDRAULICHE - IDRA2000

Genova, 12-15 settembre 2000Genova, 12-15 settembre 2000

Università della Basilicata Italy

Dipartimento di Ingegneria e Fisica

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DifaDifaCentro Interuniversitario per il Monitoraggio AmbientaleCimaCima

Mauro Fiorentino - [email protected] 1

Lectures Lectures

onon

Hydrologic Modelling of Hydrologic Modelling of Extreme FloodsExtreme 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





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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

•





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Parameter estimation technique

at site or regional

Hydrometric information Pluviometric Information Phisical Information (base processes) Geology Climate

Vegetation

StochasticModel

Estimation schemes





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at site or regional

Hydrometric information Pluviometric Information Phisical Information (base processes) Geology Climate

Vegetation

StochasticModel

How to improve it?

Estimation schemes





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Base processes information

Hydrometric information Pluviometric Information Geology Climate Vegetation

StochasticModel


at site or regional

Estimation schemes





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One possible solution:

Theoretical models for derivationof flood frequency distribution





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a = variable contributing

area

Two random variables::

The variable contributing area the peak runoff per unit

contributing area

p(ua )p(a )

uaa

(a)

time

ia,

f

fa

i

(a) = the lag time of the area a

f = hydrologic loss rate

fa =loss rate significant to peak

i = rainfall intensity

Q = ua a

ua = ( ia, - fa )

= routing coefficient

= (a)= 1 a= critical duration

The routing model:

Summarizing





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CDF of flood annual maxima

PDF of contributing area

0 500 1000 150010

0

101

102

Q

T

0 500 1000 1500 20000

0.2

0.4

0.6

0.8

1

1.2x 10

-3

a

f(a)

0 200 400 600 80010

0

101

102

Q

T

0 100 200 300 400 5000

1

2

3

4

5x 10

-3

a

f(a)

Bradano-San Giuliano

Bradano-P.te ColonnaCDF of flood annual maxima


Sample application

of the theoretical

model





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Basento - Menzena

Sinni - Valsinni

0 200 400 600 800 1000 120010

0

101

102

Q

T

0 500 1000 150010

0

101

102

Q

T

0 500 1000 15000

1

2

3

4x 10

-3

a

f(a)

0 500 1000 15000

1

2

3

4x 10

-3

a

f(a)





Sample application of the theoretical

model





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Non linearity causes

0 500 1000 15000

1

2

3

4x 10

-3

a

f(a)

0 500 1000 1500 20000

0.2

0.4

0.6

0.8

1

1.2x 10

-3

a

f(a)

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





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Log T

Q/E[Q]arido

umido

Cv

(grande impatto tecnico)

1 XXVII CONVEGNO DI IDRAULICA E COSTRUZIONI IDRAULICHE - IDRA2000 Genova, 12-15 settembre 2000...

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