How to cope with floods - the Bavarian experience

Prof. Dr. Peter Rutschmann S. Giehl, D. Skublics, M.-D. Bui, M. Reisenbüchler

Technical University Munich (TUM) Department of Civil, Geo and Environmental Engineering Chair of Hydraulic and Water Resources Management

Athens, 31 October 2018 Contents

1. Flood mitigation at large rivers in 2. Are floods pure water events 3. Flash floods in Bavaria/Greece 4. Flash flood risk management concept in Bavaria 5. The steps to flash flood risk minimization 6. Conclusions

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 2 Flood retention at and river

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 3 Flood retention at Danube and Inn river

VFlutpolder Qmax,Ist [m³/s] dQoptimal

Qmax,Plan [m³/s] Abfluss Zeit Schematic sketch of polder operation

Floodpolder: components and functioning

Separation dike Inlet Outlet

Floodpolder (retention space)

Flood Dialogue Bavaria: https://www.hochwasserdialog.bayern.de/technischer_schutz/flutpolder/index.htm One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 4 Flood retention at Danube and Inn river

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 5 Flood retention at Danube river

Effect of flood polders on relative wave peak reduction and inhabitants along the river

3000 120000 betroffene Einwohner pro Flusskilometer Summe der betroffenen Einwohner 2500 mögliche Flutpolderstandorte 100000

Regensburg 2000 80000 Hochwasserschutzkonzept Straubing-Vilshofen 1500

60000 ] - Neu-Ulm Deggendorf Neuburg 1000 40000 Straubing Vohburg/Neustadt Donauwörth 20000 500 Ingolstadt Kelheim Passau Number of inhabitants affected 0 0

betroffene Einwohner [ Einwohnerbetroffene by floods along the 2588 2538 2488 2438 2388 2338 2288 2238 [1/km]Flusskilometerpro Einwohnerbetroffene Danube river 0 50 100 150 200 250 300 350 (annuality of flood Flusskilometer [km] event > 100) One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 6 Floods in the historical/present virtual Danube

until 1900 1950 today

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 7 Flooding in the historical/present Danube

Flooded areas from a 100 year flood with a medium hydrograph. Nowadays dams and dikes are overflown during the peak discharge and very efficiently attenuate the event.

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 8 Floods as pure water events?

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 9 2013 Flood (River Saalach)

Since one century Freilassing has never been flooded until 2013.

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 10 Flooding for differing bed topography

Equivalent flow discharges for river bed topographies of 2005 and 2013

Richard Heinz, WWA-TS river bed 2005 Richard Heinz, WWA-TS. river bed 2013

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 11 HPC and hydromorphological modelling

Increasing the complexity and the computational effort

SYSIPHE

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 12 HPC and hydromorphological modelling

Increasing the complexity and the computational effort

Leibnitz-Computational-Center LRZ Garching SuperMUC and SuperMUC2: • 2012: #4 of world TOP 500 • 2016: #36 of world TOP 500 • In total 241000 Cores at SuperMUC

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 13 Flash Flood Simbach

Before and after Source: BayernAtlas and googlemaps

http://www.br.de/nachrichten/dokthema- toedliches-wasser-hochwasser-gruende-100.html

Picture (left): Courtesy of the Bavarian State Ministry of the Envorronment and Consumer Protection,

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 14 Flash Flood Simbach

Urban development

Simbach Bayernatlas 1817-1841

Simbach Bayernatlas 1925

Simbach Bayernatlas 1965

Simbach Bayernatlas 2005

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 15 Flash Flood Simbach

Before and after

Hübl, J. et al. 2017: IAN REPORT 180, Ereignisdokumentation und Ereignisanalyse Rottal-Inn 2016, Band 1: Ereignisdokumentation. University of Natural Resources and Life Sciences, Vienna, 2017, page 75 ff. https://www.baunat.boku.ac.at/fileadmin/data/H03000/H87000/ H87100/DAN_IAN_Reports/Rep180_Band_1_mit_Anhang.pdf

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 16 Flash Flood Attica (Mandra)

Damage and bottle necks

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 17 Flash Flood Attica (Mandra)

Damage and bottle necks

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 18 Bavarian Flashflood Strategy

1. Screening / status analysis “What might happen and where?”

2. Hazard analysis

“What should not happen where and 3. Hazard and risk assessment what could be allowed where?”

4. Conceptual development of (protection) measures “What measures could be taken?”

5. Integral strategy for flash flood risk management on municipal level

Implementation of measures

Source: „Integrale Konzepte zum kommunalen Sturzflut-Risikomanagement“, Infoblatt zum Sonderprogramm nach Nr. 2.4 RZWas 2016, Bavarian Statesministry for the Environment, 2016, 24 pages.

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 19 Flashflood properties

• Flashfloods are local phenomena and very difficult to spatially predict, • they are short but very intense events, • they are everything else than pure water events, • their physical processes are very complicated, cascading and therefore: • The unbelievable can happen! Thus one has to verify: • Where are flashfloods likely to happen • What consequences can they have • What can immediately be done on a very local and municipal level (identification of bottlenecks) • What protection measures could and should be tacken in a next step • How can information and early warning of the public be organized

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 20 Where can flashfloods happen?

Possible method: • Setup a large scale but coarse terrain model • Charge it with havy rain scenarios • Do a simplified rainfall-runoff hydraulic computation • Concentrate on high velocities, high water depths and high bottom shears • Check whether such regions interfere with civilization • Thus • Endangered regions/municipalities can better be identified • Possible risk must be communicated to the municipalities • A process has to be initiated at the municipal level to protect the population

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 21 Topography and vegetation is easily available

• Topographic date from remote sensing or airborne laser scanning • Vegetation data also available from remote sensing • Simpliefied flow computation is possible • Critical spots from flows can be identified

Gabriel, 2009

Gabriel, 2009

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 22 What can happen during a flashflood?

Possible processes: • Heavy floods can occur which river cross sections cannot contain. We can probably cope with this idea. • The rain and the flow will transport high sediment and debris loads. In parts heavy erosion but also heavy deposition of material can occur. We understand this, but we have difficulties to figure out the consequences. • During flash floods the infrastructure can completely be modified to other purpose than intended and fullfilling new functions which were out of their design. We have to be innovative to find worst case scenarios. Theoretically we can model such processes but the models will mostly show only the processes we anticipate. Anticipation is therefore important not only for an eventual modelling attempt but also for site visits and protection measures on a municipal level! One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 23 Radar rainfall observation

Hübl, J. et al. 2017: IAN REPORT 180, Ereignisdokumentation und Ereignisanalyse Rottal-Inn 2016, Band 1: Ereignisdokumentation. Universität für Bodenkultur Wien, 2017.

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 24 Radar observation and rain forecasts

Importance: • Radar observation is important to predict spatial distribution of rain. Meteo models are helpful to predict future developments. • From radar observation the local and heavy precipitation centers can be identified and their propagation can be estimated. This is valuable information for early warning systems. • If no radar is present, mobile phones can serve to determine the rain intensity. • In case no super computers are available fast predictions can be achieved with ANNs.

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 25 Fast computationVirtueller/prediction Wasser Raum Bayern

Fernerkundungs- Modelle und Simulation Daten- Daten Hydrologischen Analyse Landoberflächenprozesse Erosion, Stofftransport Visualisierung Aquatische Biodiversität Szenarien

Ressortdaten Modelle und Simulation Datenanalyse LfU-Messnetze CSC-2.0 Hydraulische Gerinneprozesse Ensembles Wasserwirt. Strukturen DWD LfL-Messnetze Management

Management- Daten

Verwaltung SuperMUC Wirtschaft High Performance Umweltsimulation

Szenarien-Raum (z.B. Katastrophen- Simulation) Trainings-Raum (Weiterbildung, Qualifikation)

Informations-Raum Verhandlungs-Raum (Verbreitung, Partizipation) (Konfliktlösung)

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 26 Fast computation/prediction

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 27 VieWBay TELEMAC goes HPC

Research Consortium

Hydro-BITS Fine Discretization of Bavaria (LRZ) TELEMAC - Bavary

HYDRODYNAMICS + HYDROLOGY MORPHOLOGY (LMU) (TUM)

Funded by

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece VieWBay - Vision Conclusions

• Unlike with river floods, flashfloods are short events, difficult to predict in space and therefore early warning has to take place prior of flooding. • Computations (for complex situations) or expert judge site seeings must be done before events. • Necessary protection measures must be initiated dependent on this analysis. • An early warning, dependent on meteorological information must, must happen and initiate a flood management plan. • Information and training of endangered municipalities has to be performed.

One day conference on Climate Change and Natural Desaster, 31 October 2018, Athens, Greece 30 Thanks for your attention! Fishfriendly-hydropower (EU-H2020 project coordinated by TUM): http://www.FIThydro.eu

Markus Reisenbüchler, M.Sc. (TUM) | Symposium | Potsdam, 06-08.March.2017 31

Telemac for morpho-dynamic computations

2005/06 a ramp has been constructed at River Saalach at river-km 4,6. Morpho-dynamic processes at the ramp have been investigated to study their effect on the 2013 flooding

• Transport capacity at the ramp • Sedimentation and erosion of bed-load on and around the ramp • Effects on the discharge capacity of the river Saalach

Prof. Dr. P. Rutschmann (TUM), Symposium on Global Change Effects, Potsdam, 06-08 March.2017 33 Methodology

Steps of performing numerical computations with morpho-dynamic models. Details of the Freilassing case are presented by M. Reisenbüchler (TUM), session 4

Prof. Dr. P. Rutschmann (TUM), Symposium on Global Change Effects, Potsdam, 06-08 March.2017 34 Sediment transport for various scenarios (2013)

Detailed results presented by M. Reisenbüchler (TUM), S4

100

90 S0 S1 S2 Χιλιάδες

80 S3 S4 P1997

70

60

50

40

Geschiebemenge [m³] Geschiebemenge 30

20

10

0 5,4 4,8 4,2 3,6 3 2,8 2,6 Querprofil [Fkm]

Prof. Dr. P. Rutschmann (TUM), Symposium on Global Change Effects, Potsdam, 06-08 March.2017 35 ANN methods for sediment transport in rivers

An artificial neural network is a computational model based on the structure and functions of biological neural networks (e.g. the human brain). It can be used: • to derive meaning from complicated or imprecise data, • to extract patterns and detect trends, • to provide projections given new situations.

Prof. Dr. P. Rutschmann (TUM), Symposium on Global Change Effects, Potsdam, 06-08 March.2017 36 New hydro-morphological modeling system

numerical approach ANN flow/sediment

ANN for sediment

Prof. Dr. P. Rutschmann (TUM), Symposium on Global Change Effects, Potsdam, 06-08 March.2017 37 Future computational resources

Modell purpose: - Simulation of long term developments - Reservoir management - Evalation of river construction measures Modell scales and concept: 1. Spatial • Nowadays we compute river reaches with a few kilometers, in the future we want to compute reservoirs and complete river systems with many kilometers 2. Temporal • Nowasays we compute flood scenarios of several days in the future we want to compute developments over years Future developments – years 3. Conceptual • Nowadays wie simplify as much as possible, in the future we want an accuracy as high as possible → Long term simulation with a high spatial resolution and highest accuracy!

Prof. Dr. P. Rutschmann (TUM), Symposium on Global Change Effects, Potsdam, 06-08 March.2017 38 Conclusions

• We should consider sediments for all flood considerations • For mountainous floods and flash floods sediments are a key issue • In order to do this we must go new ways. We should stick as close as possible to the physics while saving CPU time with new algorithms • Climate change will have an effect on floods but possibly even more on sediment transport. This may have dramatic effects on spawning of aquatic populations. • In the future we should therefore put more weight on managing our environment to compensate for effects of climate change • …and we should consider such effects when we plan our today mitigation measures, e.g. the present river restauration projects.

Prof. Dr. P. Rutschmann (TUM), Symposium on Global Change Effects, Potsdam, 06-08 March.2017 39 Flash Flood Simbach

Before and after Source: BayernAtlas and googlemaps

Stefan Giehl | floods 40 Retention in the historical/present Danube

Flood damping for a medium hydrograph is more efficient in the present then in the past Danube

Prof. Dr. P. Rutschmann (TUM), Symposium on Global Change Effects, Potsdam, 06-08 March.2017 41