EUROPEAN COMMISSION

WG F Thematic Workshop on Implementation of the Floods Directive 2007/60/EC

“FLASH FLOODS AND PLUVIAL FLOODING”

26th – 28th May 2010, Cagliari, Italy

PLUVIAL FLOODS

FLOOD RISK ASSESSMEN

C. Leeb(1), M. Moser(2) *

(1) Bavarian State Ministry of the Environment and Public Health

Rivers and Lakes

(2) Regierungspräsidium Stuttgart

Abstract

The methodology described in the following is the result of a workshop

held in Karlsruhe on the 12th April 2010. The workshop was participated

by representatives of German

and other institutions involved in the implementation of the European

Floods Directive (EG - FD).

In the south of Germany

local intense rainfall of convective cells

The following part describes

considering those having occurred in the past and an estimation

impacts have to be expected for

conclusion is arrived, that floodings of

precipitation are not significant in the sense of EG

* Corresponding authors:

Christian Leeb – Bavarian State Ministry of the Environment and Public Health

and Lakes

Rosenkavalierplatz 2, 81925 München

E-mail: christian.leeb@stmug.bayern.de

Markus Moser – Regierungspräsidium Stuttgart

Ruppmannstr. 21, 70565 Stuttgart

E-mail: markus.moser@rps.bwl.de

EUROPEAN COMMISSION – WFD COMMON IMPLEMENTATION STRATEGY

WG F Thematic Workshop on Implementation of the Floods Directive 2007/60/EC

“FLASH FLOODS AND PLUVIAL FLOODING”

May 2010, Cagliari, Italy

PLUVIAL FLOODS – CRITERIA FOR THE PRE

FLOOD RISK ASSESSMENT IN THE SOUTH OF GE

Bavarian State Ministry of the Environment and Public Health - Unit 55

Regierungspräsidium Stuttgart

The methodology described in the following is the result of a workshop

held in Karlsruhe on the 12th April 2010. The workshop was participated

German and Swiss authorities, science, engineering

institutions involved in the implementation of the European

FD).

In the south of Germany pluvial flood incidents are caused

of convective cells.

part describes criteria for the assessment of

having occurred in the past and an estimation

impacts have to be expected for similar events in the future. The

conclusion is arrived, that floodings of surface runoff, due to intense

precipitation are not significant in the sense of EG-FD.

Bavarian State Ministry of the Environment and Public Health - Unit 55

Rosenkavalierplatz 2, 81925 München, Germany

christian.leeb@stmug.bayern.de

Regierungspräsidium Stuttgart

Ruppmannstr. 21, 70565 Stuttgart, Germany

markus.moser@rps.bwl.de

1 WG F Thematic Workshop on Implementation of the Floods Directive 2007/60/EC

CRITERIA FOR THE PRELIMINARY

T IN THE SOUTH OF GERMANY

Unit 55 - State owned

The methodology described in the following is the result of a workshop

held in Karlsruhe on the 12th April 2010. The workshop was participated

and Swiss authorities, science, engineering

institutions involved in the implementation of the European

caused typically by

of pluvial floods,

having occurred in the past and an estimation if such

similar events in the future. The

surface runoff, due to intense

Unit 55 - State owned Rivers

EUROPEAN COMMISSION

WG F Thematic Workshop on Implementation of the Floods Directive 2007/60/EC

“FLASH FLOODS AND PLUVIAL FLOODING”

26th – 28th May 2010, Cagliari, Italy

1 Introduction

The aim of the EG-FD

human health, the environment, cultural heritage and economic activity

associated with floods. Therefore, all types of floods should be taken into

consideration. Besides floodings along surface water bodies

appearing those caused by surface runoff due to

In the context of the preliminary flood risk assessment, according to

articles 4 and 5 of the EFD, available information on pluvial floods is

analysed for mapping the areas

run-off where appropriate.

2 Surrounding conditions in the south of Germany

Flood incidents are natural appearances having different causes and

characteristics, especially hydro

The south of Germany is located in temperate climate zone, having a

moderate-warm rain climate.

and moderate hot summers.

which provide intense

precipitation cells are at small scale

square-kilometres. They can occur anywhere in the south of Germany

which makes it not possible to map areas with a significant flood risk

For those torrential precipitation incidents in the south of Germany, which

have caused appreciable impacts, where gauged precipitation heights of

240 mm within three hours

mentioned in the statistical convective precipitation analysi

the German state weather service (DWD).

considered as an extreme incident with a very low occurrence probability.

The relief of the south of Germany is highly structured and shaped by the

low mountain ranges, covered of woodlands in a high percentage.

8 % of the territories are sealed.

EUROPEAN COMMISSION – WFD COMMON IMPLEMENTATION STRATEGY

WG F Thematic Workshop on Implementation of the Floods Directive 2007/60/EC

“FLASH FLOODS AND PLUVIAL FLOODING”

May 2010, Cagliari, Italy

is the reduction of the adverse consequences for

human health, the environment, cultural heritage and economic activity

associated with floods. Therefore, all types of floods should be taken into

consideration. Besides floodings along surface water bodies

appearing those caused by surface runoff due to intense rainfall.

In the context of the preliminary flood risk assessment, according to

articles 4 and 5 of the EFD, available information on pluvial floods is

analysed for mapping the areas with a significant flood risk by surface

off where appropriate.

urrounding conditions in the south of Germany

Flood incidents are natural appearances having different causes and

, especially hydro-meteorological and geomorphologic ones

The south of Germany is located in temperate climate zone, having a

warm rain climate. The oceanic influence provides mild winters

and moderate hot summers. In the warm season, convective cells occur,

intense precipitation of large height. These convective

precipitation cells are at small scale – in most cases less than a few

kilometres. They can occur anywhere in the south of Germany

not possible to map areas with a significant flood risk

ial precipitation incidents in the south of Germany, which

have caused appreciable impacts, where gauged precipitation heights of

240 mm within three hours or less. These values exceed far those

statistical convective precipitation analysi

the German state weather service (DWD). For this reason, they have to be

extreme incident with a very low occurrence probability.

The relief of the south of Germany is highly structured and shaped by the

covered of woodlands in a high percentage.

8 % of the territories are sealed. Water storage capacity in the area can

2 WG F Thematic Workshop on Implementation of the Floods Directive 2007/60/EC

is the reduction of the adverse consequences for

human health, the environment, cultural heritage and economic activity

associated with floods. Therefore, all types of floods should be taken into

consideration. Besides floodings along surface water bodies, there are also

rainfall.

In the context of the preliminary flood risk assessment, according to

articles 4 and 5 of the EFD, available information on pluvial floods is

with a significant flood risk by surface

Flood incidents are natural appearances having different causes and

meteorological and geomorphologic ones.

The south of Germany is located in temperate climate zone, having a

provides mild winters

In the warm season, convective cells occur,

These convective

in most cases less than a few

kilometres. They can occur anywhere in the south of Germany,

not possible to map areas with a significant flood risk.

ial precipitation incidents in the south of Germany, which

have caused appreciable impacts, where gauged precipitation heights of

These values exceed far those

statistical convective precipitation analysis (KOSTRA) of

they have to be

extreme incident with a very low occurrence probability.

The relief of the south of Germany is highly structured and shaped by the

covered of woodlands in a high percentage. Only 5-

Water storage capacity in the area can

EUROPEAN COMMISSION

WG F Thematic Workshop on Implementation of the Floods Directive 2007/60/EC

“FLASH FLOODS AND PLUVIAL FLOODING”

26th – 28th May 2010, Cagliari, Italy

be considered as high, according to the rank vegetation and the

abundantly covered soil. Due to the highly structured relief and the

ramified water distribution network the drainage capability can be

regarded as convenient. During torrential rainfall, the surface runoff can

easily reach the next water body within a short range. Therewith the sub

basins to survey in the context o

This also means, that accumulations of surface runoff have only little

adverse impact.

3 Summary of previous incidents

Within the research project “Forecasting and management of pluvial floods

in urban areas (URBAS)” previous pluvial flood incidents in Germany have

been analysed. The database of URBAS contains 422 incidents within a

period of rather 30 years. The given sum

uncertain estimations, mixing different kinds of damages. Mainly, there

are documented singular incidents with relatively high damage sums, with

an average of 160 million

such torrential rainfalls are located in very small areas. Often only a

district of a municipality is affected.

reactions of areas due to convective precipitation with short durations and

large precipitation heights respectively i

ramified water distribution network and the relatively small sub basins,

precipitation incidents of middle (return period 100 years) or high (return

period 10 years) occurrence probability do not cause noteworthy

damages. Only extreme incidents cause higher damages.

4 Assessment of future flood incidents in Baden

In addition to Bavaria and Rhineland

incidents of pluvial were surveyed, Baden

analysis for the assessment of future incidents. The model is based

EUROPEAN COMMISSION – WFD COMMON IMPLEMENTATION STRATEGY

WG F Thematic Workshop on Implementation of the Floods Directive 2007/60/EC

“FLASH FLOODS AND PLUVIAL FLOODING”

May 2010, Cagliari, Italy

be considered as high, according to the rank vegetation and the

abundantly covered soil. Due to the highly structured relief and the

ramified water distribution network the drainage capability can be

regarded as convenient. During torrential rainfall, the surface runoff can

easily reach the next water body within a short range. Therewith the sub

basins to survey in the context of surface runoff are comparatively small.

This also means, that accumulations of surface runoff have only little

Summary of previous incidents

Within the research project “Forecasting and management of pluvial floods

in urban areas (URBAS)” previous pluvial flood incidents in Germany have

The database of URBAS contains 422 incidents within a

period of rather 30 years. The given sums for the adverse impacts base on

uncertain estimations, mixing different kinds of damages. Mainly, there

are documented singular incidents with relatively high damage sums, with

an average of 160 million € per year in Germany. Almost all damages of

orrential rainfalls are located in very small areas. Often only a

district of a municipality is affected. Pluvial floods are hydrological

reactions of areas due to convective precipitation with short durations and

large precipitation heights respectively intensities. According to the widely

ramified water distribution network and the relatively small sub basins,

precipitation incidents of middle (return period 100 years) or high (return

period 10 years) occurrence probability do not cause noteworthy

. Only extreme incidents cause higher damages.

Assessment of future flood incidents in Baden-Württemberg

In addition to Bavaria and Rhineland-Palatinate, where only previous

incidents of pluvial were surveyed, Baden-Württemberg has done a further

for the assessment of future incidents. The model is based

3 WG F Thematic Workshop on Implementation of the Floods Directive 2007/60/EC

be considered as high, according to the rank vegetation and the

abundantly covered soil. Due to the highly structured relief and the widely

ramified water distribution network the drainage capability can be

regarded as convenient. During torrential rainfall, the surface runoff can

easily reach the next water body within a short range. Therewith the sub-

f surface runoff are comparatively small.

This also means, that accumulations of surface runoff have only little

Within the research project “Forecasting and management of pluvial floods

in urban areas (URBAS)” previous pluvial flood incidents in Germany have

The database of URBAS contains 422 incidents within a

s for the adverse impacts base on

uncertain estimations, mixing different kinds of damages. Mainly, there

are documented singular incidents with relatively high damage sums, with

Almost all damages of

orrential rainfalls are located in very small areas. Often only a

Pluvial floods are hydrological

reactions of areas due to convective precipitation with short durations and

ntensities. According to the widely

ramified water distribution network and the relatively small sub basins,

precipitation incidents of middle (return period 100 years) or high (return

period 10 years) occurrence probability do not cause noteworthy

Württemberg

Palatinate, where only previous

Württemberg has done a further

for the assessment of future incidents. The model is based

EUROPEAN COMMISSION

WG F Thematic Workshop on Implementation of the Floods Directive 2007/60/EC

“FLASH FLOODS AND PLUVIAL FLOODING”

26th – 28th May 2010, Cagliari, Italy

available data for soil, geologie, topography and soil

surface runoff and infiltration by using physical equations.

The essential results of this analysis are:

- In slope areas the water depths of surface runoff are less then 5 cm.

- The duration of surface runoff is very short.

- Floodings with depths more than 50 cm appear only in the flood plains

in the bottom of the valley; due to fluvial floods.

- Asserted damages in slope areas

alluvial sedimentation.

5 Assessment of the potential significant flood risk

As described above, intense rainfall appears at small scale and does only

activate appreciable surface runoff at incidents with a return perio

considerable over 100 years. Such events can occur anywhere in the

south of Germany, so that areas with a significant higher risk can not be

identified. Previous incidents have shown, that adverse impacts to the EG

FD subjects of protection occur only in

In Germany, the assessment of the significance of flood risks, is also

linked to the public interest in flood protection infrastructure. Measures of

public interest are required, where human lives or health are affected in a

larger number or economic activities are impacted in a regional scale.

Flood protection against pluvial floods can easiliy be realised by indiviuals.

For this reasons, in our point of view, for floodings of surface runoff a

potential significant flood risk does not exist

likely to occur.

Acknowledgements

The authors thank Mrs. Merz (

Hennegriff (LUBW, Baden

EUROPEAN COMMISSION – WFD COMMON IMPLEMENTATION STRATEGY

WG F Thematic Workshop on Implementation of the Floods Directive 2007/60/EC

“FLASH FLOODS AND PLUVIAL FLOODING”

May 2010, Cagliari, Italy

available data for soil, geologie, topography and soil-sealing. It displays

surface runoff and infiltration by using physical equations.

The essential results of this analysis are:

the water depths of surface runoff are less then 5 cm.

The duration of surface runoff is very short.

Floodings with depths more than 50 cm appear only in the flood plains

in the bottom of the valley; due to fluvial floods.

Asserted damages in slope areas are mostly related to soil erosion or

alluvial sedimentation.

Assessment of the potential significant flood risk

As described above, intense rainfall appears at small scale and does only

activate appreciable surface runoff at incidents with a return perio

considerable over 100 years. Such events can occur anywhere in the

south of Germany, so that areas with a significant higher risk can not be

identified. Previous incidents have shown, that adverse impacts to the EG

FD subjects of protection occur only in a local scale.

In Germany, the assessment of the significance of flood risks, is also

linked to the public interest in flood protection infrastructure. Measures of

public interest are required, where human lives or health are affected in a

r economic activities are impacted in a regional scale.

Flood protection against pluvial floods can easiliy be realised by indiviuals.

For this reasons, in our point of view, for floodings of surface runoff a

potential significant flood risk does not exist nor could it be considered

Mrs. Merz (Bavarian Environment Agency

Hennegriff (LUBW, Baden-Württemberg) and Mr. Schernikau (Ministry for

4 WG F Thematic Workshop on Implementation of the Floods Directive 2007/60/EC

sealing. It displays

the water depths of surface runoff are less then 5 cm.

Floodings with depths more than 50 cm appear only in the flood plains

are mostly related to soil erosion or

As described above, intense rainfall appears at small scale and does only

activate appreciable surface runoff at incidents with a return period

considerable over 100 years. Such events can occur anywhere in the

south of Germany, so that areas with a significant higher risk can not be

identified. Previous incidents have shown, that adverse impacts to the EG-

In Germany, the assessment of the significance of flood risks, is also

linked to the public interest in flood protection infrastructure. Measures of

public interest are required, where human lives or health are affected in a

r economic activities are impacted in a regional scale.

Flood protection against pluvial floods can easiliy be realised by indiviuals.

For this reasons, in our point of view, for floodings of surface runoff a

nor could it be considered

Bavarian Environment Agency), Mr.

Württemberg) and Mr. Schernikau (Ministry for

EUROPEAN COMMISSION

WG F Thematic Workshop on Implementation of the Floods Directive 2007/60/EC

“FLASH FLOODS AND PLUVIAL FLOODING”

26th – 28th May 2010, Cagliari, Italy

the environment, forestry and consumer protection Rhineland

for their support.

References

- Deutscher Wetterdienst [Hrsg.].:

Starkniederschlagshöhen für Deutschland (1951

2005

- Bundesministerium für Bildung und Forschung

und Management von

Aachen; 2008

- University of Padova

Resources and Technologies for Effective Flash Flood Forecasting

(HYDRATE Project).: Post Flood Event Analysis : Report on the Starzel

River Flash Flood; 2008

- Weiler, M., Steinbrich, A.: „Integrative Ausweisung von

Abflussbildungsprozessen zur räumlichen und zeitlichen

Bewirtschaftung von Wassermenge und Wassergüte“ Institut für

Hydrologie, Universität Freiburg, Vortrag zum „Tag der Hydrologie

2010“ am 25./26. März 2010 in Braunschweig

EUROPEAN COMMISSION – WFD COMMON IMPLEMENTATION STRATEGY

WG F Thematic Workshop on Implementation of the Floods Directive 2007/60/EC

“FLASH FLOODS AND PLUVIAL FLOODING”

May 2010, Cagliari, Italy

the environment, forestry and consumer protection Rhineland

Deutscher Wetterdienst [Hrsg.].: KOSTRA

Starkniederschlagshöhen für Deutschland (1951-2000)

Bundesministerium für Bildung und Forschung [Hrsg.].:

und Management von Sturzfluten in urbanen Gebieten (URBAS)

University of Padova et. al. [Hrsg.] Hydrometeorological Data

Resources and Technologies for Effective Flash Flood Forecasting

: Post Flood Event Analysis : Report on the Starzel

2008

Weiler, M., Steinbrich, A.: „Integrative Ausweisung von

Abflussbildungsprozessen zur räumlichen und zeitlichen

Bewirtschaftung von Wassermenge und Wassergüte“ Institut für

Hydrologie, Universität Freiburg, Vortrag zum „Tag der Hydrologie

5./26. März 2010 in Braunschweig

5 WG F Thematic Workshop on Implementation of the Floods Directive 2007/60/EC

the environment, forestry and consumer protection Rhineland-Palatinate)

KOSTRA-DWD-2000

2000); Offenbach;

[Hrsg.].: Vorhersage

in urbanen Gebieten (URBAS);

Hydrometeorological Data

Resources and Technologies for Effective Flash Flood Forecasting

: Post Flood Event Analysis : Report on the Starzel

Weiler, M., Steinbrich, A.: „Integrative Ausweisung von

Abflussbildungsprozessen zur räumlichen und zeitlichen

Bewirtschaftung von Wassermenge und Wassergüte“ Institut für

Hydrologie, Universität Freiburg, Vortrag zum „Tag der Hydrologie