European Geosciences Union

General Assembly 2011

Vienna | Austria | 03 – 08 April 2011

The European Water Framework Directive (2007/60), The River Júcar Water Board (Spain)

commissioned a study in order to analyse the effect of flooding on different urban centres and

hydraulic structures of two counties, Marina Alta and Marina Baja (Alicante, Spain), aiming to redact

a basin management plan against risk and following the European Water Framework Directive

(2007/60).

The first stage, identification of potential flood risk zones, was carried out by coupling a stochastic

extreme rainfall generation model, a conceptual distributed hydrological model, and a hydraulic

model. The rainfall-runoff model provided the boundary conditions for the hydraulic modelling. 22

hydraulic models were set up with a total of 70 km2 of detailed bidimensional modelling based on

digital elevation models 1x1m obtained by Lidar. The results are five maximum water level maps,

associated with the 10, 25, 50, 100 and 500 years of return period, for each one of the flood zones.

In order to analyse the vulnerability and the economic impact of flooding, the European Water

Framework directive was followed: the flood hazard was evaluated considering hydraulic variables

(such as the maximum water level) and other variables such as the sediment production and the

vulnerability was computed taking into account economical, social and environmental variables

(number of affected inhabitants, possible sources of pollution, etc)

In order to evaluate the vulnerability as previously explained, it was necessary to elaborate water

level – economical damage curves, which were calibrated following the economical damages

subsequent to historical floods. Integrating these curves with the results of the hydraulics studies, the

risks maps are obtained. Once determined the risk of the studied zones the next step is the

elaboration of a management plan in order to reduce the flood risk.

ABSTRACT

CASE-STUDY

2D HYDRAULIC MODELING

CONCLUSIONS REFERENCES

Flash flood risk assessment following the European Water Framework

Directive. The case of Marina Alta and Marina Baja (Alicante, Spain).

Enrique Ortiz (1)(3), Félix Francés (2), Gianbattista Bussi (1)(2)

METHODOLOGY

Stochastic extreme rainfall

generator:

RAINGEN(Salsón and García-Bartual,

2003)

Rainfall –runoff model:

TETIS(Francés et al., 2007)

Hydraulic model:

INFOWORKS(Wallingford)

VULNERABILIT

Y ASSESSMENT

(1) Hidrogaia s.l., Avda. Juan de la Cierva, 27, Parque Tecnológico 46980 - Paterna – Valencia, Spain

(2) Research Institute of Water and Environmental Engineering, Universidad Politécnica de Valencia, Spain

(3) Idrologia e Ambiente s.r.l., Riviera di Chiaia 72, 80122, Napoli, Italy

VULNERABILITY ASSESSMENT

SPAINCOMUNITAT

VALENCIANA

MARINA ALTA and MARINA

BAJA (in grey the 22 2D

hydraulic models)

22 study areas

- 368 synthetic rainfall extreme events covering the whole study area

- Hydrological simulation of the 368 events x 3 initial moisture states (10%,

40% and 80%) in more than 250 subcatchments

- Probability estimation of maximum discharges in every subcatchment

- 2D hydraulic modelling of 22 areas of special interest (5 events simulated,

with 10, 25, 50, 100 and 500 years return period)

-Vulnerability assessment by means of calibrated damage curves (damages

vs water depth)

1 – MODEL TOPOLOGY 2 – SEA LEVEL INITIAL CONDITIOS

-NUMBER OF 2D HYDRAULIC MODELS: 22

-NUMBER OF SIMULATED FLOOD EVENTS: 6 for each model

-RETURN PERIOD OF MAXIMUM DISCHARGE = 10, 25, 50, 500 years and 2x100 years (in order to

check the effect of different flood volumes)

-SOFTWARE USED: InfoWorks (Wallingford)

-DIGITAL ELEVATION MODEL: Lidar 1x1 m

-ROUGHNESS: CORINE Land Use

3 – VOIDS (Buildings)

The study area is located in the Spanish Mediterranean coast. The zone is affected by

severe flash floods due to the “cold drop” effect, especially during the fall season.

4 – BREAK LINES

5 – ROUGHNESS

6 – HYDROGRAPHS

(BOUNDARY CONDITIONS)

0

200

400

600

800

1000

1200

1400

1600

1 - 00:00 1 - 06:00 1 - 12:00 1 - 18:00 2 - 00:00

Dis

cha

rge

(m

3/s

)

Return Period T=500 years

1.- Bco. de Portelles

2.- Río Girona

3.- Barranc de l'Alberca

4.- Barranc de la Losa

5.- Barranc de la Fusta

EXAMPLE: Girona river (25 km2)

RESULT: Water depth map of the study zone

It is necessary to assess

VULNERABILITY in order

to evaluate the risk

Examples of flash floods damages

affecting the study zone

Methodology:

1 – ELEMENTAL DAMAGE CURVES

2 – OBSERVED DATA 3 – VULNERABILITY CURVES 4 – RISK ASSESSMENT

∫∫∞=

=

=

=

==h

h

H

F

F

H dhhfhVdFhVD0

1

0

)()()(

In this stage of the work,

elemental damage curves are

elaborated. This curves

represent the percentage of total

damage versus the water depth.

Every land use (taken from

CORINE) has a different

elemental curve, since the

damage is proportional to the

value of the affected goods.

0%

20%

40%

60%

80%

100%

120%

0 1 2 3

% o

f d

am

ag

e

Water depth (m)

First floor rooms Garages

Garden Roadway cleaning

Roadway damage Veichles in garages

Observed data of damages

caused by a real flash flood

(October 2007) are collected

(insurance remboursments, police

reports, city hall official reports,

…), which will be use to estimate

the damages in € depending on

the water depth.

The same flood is also modelled

by means of the hydraulic model,

in order to obtain observed water

depths.

In this stage, elemental curves are transformed into

vulnerability curves (water depth versus damage in

€), taking into accout the different land uses and

the different residential densities. These curves

are calibrated taking into account the damages in €

caused by the observed flood used for calibration

(October 2007).

The result is a curve which relates water depths

with the damages quantified in euros that it will

generate.

The total damage sin € are calculated for each

return period, using vulnerability curves and

hydraulic modeling results. The hydraulic model

provides water depths, which are turned into

monetary damage by means of the vulnerability

curves, depending on the land use and the density

of population. This damages are computed for every

town.

Later, the total risk in euros is calculated, taking

into account the probability of the flood event and

the damages generated by the same flood event.

The following formula is used (D is the damage in €,

V(h) is the vulnerability curve, F is the cumulative

frequency of the flood):

-Following theWater Framework Directive, a multidisciplinary study of flood risk has been carried out;

- The study has integrated different models (rainfall generation, rainfall-runoff, bidimensional hydraulic) to obtain flood mapping associated

with a probability value;

-Damages vs water depth curves have been calibrated using real floods damage data, in order to calculate the cost of flood depending on

water depth and land use;

-The damages in € caused by different floods has been calculated and associated with its cumulative probability, in order to provide a value

which may used for cost-benefit analysis in remediation and mitigation structures design

0

100

200

300

400

500

600

700

800

1 - 00:00 1 - 06:00 1 - 12:00 1 - 18:00 2 - 00:00

Dis

cha

rge

(m

3/s

)

Return period T = 50 years

1.- Bco. de Portelles (Ev. 3-1-596)

2.- Río Girona (Ev. 3-1-596)

3.- Barranc de l'Alberca (Ev. 2-2-164)

4.- Barranc de l'Alberca 2 (Ev. 3-2-014)

0

100

200

300

400

500

600

700

800

900

1000

1 - 00:00 1 - 06:00 1 - 12:00 1 - 18:00 2 - 00:00

Dis

cha

rge

(m

3/s

)

Return period T = 100 years

1.- Bco. de Portelles

2.- Río Girona

3.- Barranc de l'Alberca

4.- Barranc de la Losa

5.- Barranc de la Fusta

Salsón, S. and Garcia-Bartual, R.: A space-time rainfall generator for highly

convective Mediterranean rainstorms, Nat. Hazards Earth Syst. Sci., 3, 103–

114, 2003

Frances, F., Velez, J.I., and Velez, J.J. Split-parameter structure for the

automatic calibration of distributed hydrological models, Journal of

Hydrology, 332 (1-2), 226-240, 2007.

FREQUENCY

MAGNITUDE

PELIGROSITY VULNERABILITY

RISK

Società

Idrologica

ItalianaLe Giornate dell’Idrologia 2011, Bologna 1- 2 Dicembre 2011