Flood regimes of mid sized and mixed land use catchments can we assess the urban contribution
Download
1 / 39

FLOOD REGIMES OF MID-SIZED AND MIXED LAND-USE CATCHMENTS: CAN WE ASSESS THE URBAN CONTRIBUTION ? - PowerPoint PPT Presentation


  • 79 Views
  • Uploaded on

FLOOD REGIMES OF MID-SIZED AND MIXED LAND-USE CATCHMENTS: CAN WE ASSESS THE URBAN CONTRIBUTION ?. B. Radojevic (1), P. Breil (2), B. Chocat (3) (1) UNESCO [email protected] (2) CEMAGREF Lyon [email protected] (3) URGC – INSA Lyon [email protected]

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about ' FLOOD REGIMES OF MID-SIZED AND MIXED LAND-USE CATCHMENTS: CAN WE ASSESS THE URBAN CONTRIBUTION ?' - marcel


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Flood regimes of mid sized and mixed land use catchments can we assess the urban contribution

FLOOD REGIMES OF MID-SIZED AND MIXED LAND-USE CATCHMENTS: CAN WE ASSESS THE URBAN CONTRIBUTION ?

B. Radojevic (1), P. Breil (2), B. Chocat (3)

(1) [email protected]

(2) CEMAGREF [email protected]

(3) URGC – INSA [email protected]

International Symposium on Flood Defense, Toronto, Canada, May 6-8, 2008


Urban sprawling a world wide trend unep 2003
Urban sprawling: a world wide trend CAN WE ASSESS THE URBAN CONTRIBUTION ?(UNEP, 2003 )

Urban growth of Lyon city

(with courtesy from Lyon city council, 2005)


Population growth in Lyon CAN WE ASSESS THE URBAN CONTRIBUTION ?

Periurban area

Urban area

Urban unit

Data from French National Institute

for Statistics and Economic Studies


What could be the impact of land use change on flood discharge

2.5 CAN WE ASSESS THE URBAN CONTRIBUTION ?

2

1.5

1

0.5

0

What could be the impact of land-use change on flood discharge?

Adapted from GALEA et al., 1993

Rural change

  • The ten years flood is doubled both for :

  • a change of 70% from forest to vineyard land use

  • an impervious rate of 20%

Peak flood ratio of Post to Pre land use change

100

0.1

1

10

Recurrence interval (years)

Adapted from HOLLIS, 1975

20

20

20

20 % imperviousness

15

15

15

50 %

10

10

10

Urban change

x 4

x 4

5

5

5

4

4

4

x 2

x 2

2

2

2

1

1

1

0.1

0.1

0.1

1

1

1

10

10

10

100

100

100

200

200

200

2

2

2

25

25

25

50

50

50

Recurrence interval (years)


Flood event in Yzeron basin CAN WE ASSESS THE URBAN CONTRIBUTION ?


Outline of the presentation
Outline of the presentation CAN WE ASSESS THE URBAN CONTRIBUTION ?

  • Objective of the study

  • Study area

  • Method

  • Results

  • Conclusion


Objective of the study

< CAN WE ASSESS THE URBAN CONTRIBUTION ?

Vulnerability

in terms of flood frequency

Hazard

In terms of flood frequency

>

Objective of the study

Flood risk concept

The flood risk meets the local objective when the hazard frequency

is smaller than the vulnerability frequency

and vice versa

Each aspect of the flood risk

can be expressed as a recurrence interval in year units


Study CAN WE ASSESS THE URBAN CONTRIBUTION ?Area


Land use in the l yzeron basin
Land-use in the l’Yzeron basin CAN WE ASSESS THE URBAN CONTRIBUTION ?


Instrumentation within the basin
Instrumentation within the basin CAN WE ASSESS THE URBAN CONTRIBUTION ?

Taffignon

Craponne


Increase in flood frequency
Increase in flood frequency CAN WE ASSESS THE URBAN CONTRIBUTION ?

m3/s

Years ’70’

Years ’90’


Stationary test number of floods according to lang 1995
Stationary Test – number of floods CAN WE ASSESS THE URBAN CONTRIBUTION ? (according to Lang, 1995)


Stationary test on number of floods rural part according to lang 1995
Stationary test on number of floods - rural part CAN WE ASSESS THE URBAN CONTRIBUTION ?(according to Lang, 1995)



Daily max rainfall regime for the rain gauge bron
Daily max. rainfall regime for the rain gauge Bron station

  • Daily intensity:

  • The most intense in the ’90’

  • The lowest in the ’70’


Method
Method station

  • Built a semi-distributed hydrological model with the land use on the 90’

  • Use the rainfall and stream-flow data to calibrate the 90’ model

  • Validate the 90’ model

  • Built a semi-distributed hydrological model with the land use on the 70’

  • Use the 90’ fitted parameters and the 90’ rainfall series to simulate the 70’ stream flows

  • Make projection of the land use evolution and simulate the stream flow evolution- virtual series


Method1

débits station

débits

simu.

corresp.

corresp.

corresp.

état urba.

pluies 70

pluies 90

pluies 90

années 70

oui (1)

non

oui (3)

(amont)

années 90

non

oui (2)

oui (4)

influence

influence

urbanisation

variabilité

pluies

entre (1) et (2)

oui

oui

ent

re (1) et (3)

non

oui

entre (1) et (4)

oui

oui

entre (2) et (3)

oui

non

entre (2) et (4)

non

non

entre (3) et (4)

oui

non

Method

Influence of rainfall

Model quality

Impact of urbanisation


Model development
Model development station

  • Dividing the l’Yzeron basin in hydrological units

  • Calibration of the rainfall – runoff model CANOE

  • Validation of CANOE



forest station

mainly forest

Farming-grass land

periurban

urban

The land use change over 17 years


Land use change in 70 and 90 grid based estimation
Land use change in ‘70 and ‘90 station(grid based estimation)

Upstream (Craponne)

Total basin (Taffignon)



Definition of hydrological units
Definition of stationhydrological units

  • if the % of urban grid of sub-basin is:

    • higher 50% option ‘strictely urban’ of CANOE was applied

  • if the % of périurban grid of sub-basin is:

    • higher 50% option ‘urbain-rural’ of CANOE was applied

  • if the % of rurale grid of sub-basin is:

    • higher 50% option ‘strictely rural’ of CANOE was applied


Rural station

Peri-urban

Urban

Distribution of hydrological units

70’ land use model

90’ land use model


Semi distributed rainfall runoff model canoe

Impervious areas station

Impervious areas

Direct runoff to water courses

Un-Direct runoff to water courses

Semi-distributed Rainfall-Runoff Model CANOE

Permeable areas

( Forest, grassland,..)

Production function

Runoff coef.

Production function

Horton’s infilt. law

Production function

Runoff coef.

Transfer function

Nash cascade

Transfer function

Nash cascade

Transfer function

Linear reservoir

3 hydrographs summation



Description of comparison
Description of comparison station

Influence of urbanisation

Comparison between simulated runoff (land use 1970) with observed rainfall series of 1990 (Taffignon) and simulated runoff (land use 1990) with observed rainfall series of 1990 (Taffignon)

Model Quality

Comparison between simulated and observed runoff series (Taffignon, Craponne)


Characteristic of selected runoff for description of flood regime qcx d

m3/s station

1h

QCX1h

3h

6h

1h

QCX1h

12h

QCX1h

24h

1h

time t

Characteristic of selected runoff for description of flood regime: QCX(d)

QCX (d) are discharge values continuously overpassed for selected durations. Shorter is the duration, higher is the discharge and vice versa.

QCX(d) allow to describe the pattern of floods.

QCX(d)

Threshold level for duration d

Selected durations

1h, 3h, 6h, 12h and 24h


Model validation rural part
Model validation – rural part station

Null hypothesis H0 tested :

The simulated population is equivalent to the observed population?

“H0 accepted”

“H0 rejected”

“H0 accepted”

Only large durations (24hours) are rejected from the statistical test. Model is validated for the flood regimes simulation


Model validation urban rural parts
Model validation – urban + rural parts station

Null hypothesis H0 tested :

Is the simulated population equivalent to the observed population?

ok

“H0 acceptable”

“H0 accepted”

“H0 rejected”


Flood regimes change between 70 and 90 urban units on 1970 6 and 1990 19
Flood regimes change between ’70’ and ’90’ station(urban units on 1970: 6% and 1990: 19%)

Only the small floods are affected T=1

Null hypothesis H0 tested :

The 90’population is equivalent with the 70’ population?

“H0 rejected”

“H0 rejected”

“H0 accepted”


Flood regimes change for future development of 24 and 33 urban area
Flood regimes change for future development of 24% and 33% urban area

Null hypothesis H0 tested :

Is the future population equivalent with the present population?

Imperviousness rate of 24 %

Imperviousness rate of 33 %

“H0 accepted”

“H0 rejected”


Full bank flow urban area

24 % urbanized

(simulated)

+6%

1996 - 19% urbanized

(observed)

+14%

  • - 6% urbanized

  • (simulated)

Flood hazard evolution

From 6 to 19% of urbanization only small floods are affected, only T=1year.

Over 20% of urbanization, also large floods are affected. It means that both transfer and production were affected


Conclusion on flood hazard evolution
Conclusion on flood hazard evolution urban area

  • Model results are sensitive to an increase of urbanisation by 13% only (Taffignon station).It is detected over 6%

  • For rural part of the basin (2/3 of the total basin): No urban influence (even small floods are not effected). For urban part mainly floods with a small return period are affected.

  • Simulation results indicate the increase in flood frequency does not result only from the land use change. It means the rainfall regime is a major factor but …

  • Expected urban development on 2025 should have a very sensitive effect on flood peak increase. The effect on large floods would be very sensitive for 33% urbanisation.

  • Unexpected compensation effects of the periurban growth exists and should be considered as a mitigating potential if managed.


Flood vulnerability assessment urban area (I)

Flooded area boundaries are determined from a DEM analysis considering at least all grid cells

connected to a water course with no more than a given height (e.g.1 meter) above the full bank altitude

DEM- Digital Elevation Model


Flood vulnerability assessment (II) urban area

Flooded areas can be split into vulnerability categories from

forest, grassland and farming , periurban and urban types


Flood vulnerability Evolution urban area

As a consequence of the land use change in the vicinity of the stream corridor the average acceptable flooding return period has doubled from years 79 to 96; meaning the need for protection.


Conclusion perspectives
Conclusion & Perspectives urban area

  • The urban development increases upstream flood frequencies.

  • The periurban development has sensitive effect on large flood frequencies since a 33% urbanized area.

  • The flood risk is not proportional to imperviousness rate but rather to spatial distribution in mixed land use catchments

  • Mainly the vulnerability of flooded areas can explain theincrease in flood risk. Vulnerability is however manageable under 20 % and should allow to reduce flood risk.

  • Over 20% urban it seems necessary to have a better characterization of the hydrological functioning of periurban areas, which is not trivial!


Thank you
Thank you ! urban area


ad