Models and modellers for coastal flooding Presented by Dr. Ole Svenstrup Petersen, osp@dhigroup.com Head of Research Coastal and Estuarine Engineering, DHI And colleagues at DHI

Agenda

22 May, 2013 © DHI #2

• Introduction to DHI and DHI’s models

• Examples of model applications and validation relevant for coastal flooding

• Examples of model coupling

• Discussion of points of interest

About DHI

• Founded 1963 as Coastal Lab from Danish Technical University

• Independent, not-for-profit foundation

• All about water – Marine, coastal, inland, urban and industrial

• 30 % Research - 20 % Software – 50 % international consulting

22 May, 2013 © DHI #3

© DHI 2013

Offices

Head office

RD Centre

DHI OFFICES 1100 Staff, 700 outside DK in 36 offices

RD centers in Denmark and Singapore

A modeling timeline – the history of DHI’s models

• 1958-59 Thyborøn Inlet, Lundgren and Sørensen (DHI’s first director) develop a 14-box diffusive-

wave storm surge model of the Limfjord on DASK

22 May, 2013 © DHI #5

A modeling timeline – the history of DHI’s models

• 1959 Limfjord model on DASK

• 1962 Mike Abbott, IHE, initiates DHI’s modeling team

• 1983 MIKE 21 commercial software products

• 1986 MIKE 3

• 1998 Start of FM development

• 2000 Generalized Wave equation, 2D and 3D

• 2004 Finite Volume 2D and 3D with flooding and drying

• 2004 First Spectral Wave model based on Flexible Mesh

• 2012 MIKE 3/21 on 1000 cores

• 201X GPU, non-hydrostatic, BW ……

22 May, 2013 © DHI #6 MIKE 11 Limfjord model

DHI Modeling systems

DHI’s modeling platforms - MIKE by DHI

• A platform for customised software building on

top of the modeling engines in order to make

results more accessible and useful for the

public

• http://www.dhigroup.com/MIKECUSTOMISEDbyDHI.aspx

MIKE by DHI Marine models

22 May, 2013 © DHI #9

http://mikebydhi.com/Products/CoastAndSea.aspx

MIKE 3/21 basics • Shallow water equations (hydrostatic) in cartesian or radial projections

• Fractional step with Partial mode split

• Explicit time integration – strict conditions for Courant numbers

• Adaptive time stepping – global (for HD) or local (for SW)

• 3 step flooding and drying

• Finite volume method

• Unstructured horizontally

• Sigma or combined sigma-z vertically

Know more ?

http://mikebydhi.com/~/media/Microsite_MIKEbyDHI/Publications/PDF/Short%20descriptions/MIKE213_FM_HD_Short_Description.ashx

Z-level

-level

Vertical Discretization in MIKE 3 FM

MIKE 3/21 Spatial

Combined sigma and z-layers

Improved description along steep slopes

Better description of stratified layers

Accurate description of heat exchange

MIKE 21 Spectral Wave

• Fully spectral (FS) and directionally decoupled parametric (DS) formulations

• Instationary and quasi-stationary formulations with adaptive and local timestepping

• Source functions based on state-of-the-art formulations (WAM cycle 4)

• Unstructured mesh

• Dynamic coupling with hydrodynamic flow model for modeling of wave-current interaction and time-varying water

depth

22 May, 2013 © DHI #12

Know more ?

http://mikebydhi.com/~/media/Microsite_MIKEbyDHI/Publications/PDF/Short%20descriptions/MIKE21_SW_FM_Short_Description.ashx

MIKE 21 BW (BOUSSINESQ WAVE)

• Time domain,deterministic free surface model

• Calculation and analysis of short- and long-

period waves in ports, harbours and coastal

areas.

• Solves a set of enhanced Boussinesq type

equations

• Includes diffraction, refraction, breaking, runup,

overtopping, non-linear, random directional

seas

• Wave agitation in harbours and wave

assessments in the coastal zone

© DHI 2013

MIKE 21 BW (BOUSSINESQ WAVE)

© DHI 2013

Know more ?

http://mikebydhi.com/~/media/Microsite_MIKEbyDHI/Publications/PDF/Short%20descriptions/MIKE21_BW_short_description.ashx

Sand Transport Processes – MIKE 21 STP

• Building mainly on Fredsøe and Dejgaard’s work

• Uses a profile ”intra-wave parameterisation” to calculate stress, turbulence and transport in wave-

currents

• Can use the wave and flow models to calculate forces

• Feed back on bathymetry

22 May, 2013 © DHI #15

Know more ?

http://www.mikebydhi.com/upload/dhisoftwarearchive/shortdescriptions/marine/SandTransportModuleST.pdf

Model calibration and validation

• A key activity in modeling

• The amount of time/data used is directly reflected in model quality

• Software quality assurance

• Making the right decisions

• ISO certification

• Daily build and basic tests, update procedures

• New feature tests in real environment

• Application/projects

• Use of relevant data is important

• Typically 50 % for model calibration/validation

22 May, 2013 © DHI #16

Tide and surge modeling, Sakhalin

• Metocean study of waves and currents

Tidal calibration

• MIKE 21 FM hydrodynamic model

• DTU10 tidal data on boundary and inside

• Customized wind fields (OWI)

The (modern) Limfjord models

22 May, 2013 © DHI #19

• Study of impact on storm surge from

morphological changes in Thyborøn Inlet

The Limfjord

Model calibration and model verification

22 May, 2013 © DHI #20

Six storms were selected to calibrate and verify the model

Performance criteria was defined

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Hvalpsund

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Alle stationer

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Ålborg Øst

Model calibration and model verification

22 May, 2013 © DHI #21

Example: Comparison of modelled and observed water level at Lemvig

Femern Belt Link

• 20 km combined hi-speed rail and car bridge or tunnel between Denmark and Germany

• Planned completion 2021

• Very large EIA partly due to concern for Baltic ecosystem

22 May, 2013 © DHI #22

MIKE 3 Model set up for Femern Belt

Regional model

• 3-5 km, 1 m vertical

• 30+ years

Local model

• 500 m, 1 m vertical

• 1 year

Regional MIKE 3 Oceanographic Model 30 years simulation

Example of Calibration of 3D model

The model does reproduce

the major inflows of saline

water that are crucial for

the ecosystem of the Baltic

Sea

25

0.5° spatial resolution requires app. 2.7 GB RAM

0.25° spatial resolution requires app. 6 GB RAM

MIKE 21 SW Global wave prediction

26

January storm 2005

in the North Atlantic

Global wave prediction

27

Horns Rev

Offshore wind farm with 80 turbines (168 MW)

(m)

Objective (waves)

Establishment of 4 day wave forecast for planning of marine

operations (maintenance etc.)

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Horns Rev

Atlantic model Number of elements: 8334

Maximum edge length: 1.0 degree Minimum edge length: 0.5 degree

North Sea-Baltic Sea model Number of elements: 8985 Maximum edge length:

40 km Minimum edge length: 1.5 km

(m)

(m)

29

Horns Rev

Measurements stations

Horns Rev S

Harald W

Fjaltring

Station Longitude

(Degree E)

Latitude

(Degree N)

Depth, MSL

(m)

Harald W 4.219722 56.338056 65.0

Fjaltring 8 058221 56.475075 17.5

Horns Rev S 7.836733 55.483617 10.0

(m)

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Horns Rev

Fjaltring

Wave period, T02 Significant wave height, Hm0

Horns Rev S Significant wave height, Hm0 Wave period, T02

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Horns Rev

Horns Rev S - frequency spectrum

Fjaltring - frequency spectrum

*) Kirkwall Marine is used in the MIKE 21 BW step-by-step-guide

Kirkwall Marina, UK

• MIKE 21 Spectral Waves

• MIKE 21 Boussinesq Wave

• Physical model

Results from MIKE 21 BW Results from MIKE 21 SW*)

*) Using the DS (directionally decoupled parametric formulation) with diffraction and reflection

Kirkwall Marina

• Comparison between SW and BW

MIKE 21 Spectral Waves FM - Kirkwall Marina, UK

Comparison with measurements

Kirkwall Marina

• Comparison between BW and Lab inside harbour

Coastal flooding - two perspectives

1. Extreme events and their consequences - short term

• Wave impact on sea defense => Breaching => Hinterland inundation.

2. Long term changes in the coast’s resillience to potential extreme events

• Dune and dike stability.

• Importance of foreshore.

• Natural evolution versus anthropological activity (including climate adaptation).

Dune breaching

22 May, 2013 © DHI #36

Dune breach at Danish Westcoast 1991

Cross shore sediment transport in the surf zone

Dune erosion

Validation of dune erosion model

against results from DELTA flume (DELTARES)

Hs=1,5m Tp=4,9s

Measured dune erosion

Modelled dune erosion

during 6 hr

The dune erosion model illustrates that these narrow dunes are best

strengthened by adding sand behind the crest

Which is being done…

Comparison: dynamic simulation >< stationary analysis based on

topographic info only:

Extreme 40 hour storm event with max water level in the sea of 2.2 m ( i.e. present day extreme

event). Max flooded area to the left. Estimate based on topography to the right (2 m contour

line).

Dune overtopping

• MIKE 21 BW

• Hydrodynamics as storm

surge events

• Parameterisation of

overtopping

• Combined with Dune

erosion and sand transport

© DHI 2013

Ribe Polder flooding

• Flood Risk analysis of Polder

• Dynamic breach and flood modelling with MIKE 21

• Carried out by Danish Coastal Authority as part of

Climate Change Adaptation study

Levee breaching, Ribe

• Breaching dynamics from detailled model

Hinterland indundation

MIKE21 FM, HD – Development of breach

Hinterland indundation

MIKE21 FM, HD – Development of breach

Hinterland indundation

MIKE21 FM, HD – Development of breach

Know more ?

http://www.dhigroup.com/Aboutus/DHIAnnualReport2011/MakingKnowledgeAccessible/GuidanceOnClimateChangeAdaptation.aspx

Longterm - Hybridmodel

© DHI

• Under development !

• Combines Flow, wave and STP models for long term

morphology

• Quasi-steady flow and waves

• Morphology described in profiles

Know more ?

Kaergaard, K. and Fredsoe, J. (2013). A numerical shoreline model for shorelines with

large curvature. Coastal Engineering, Vol. 74, p. 19-32.

Kaergaard, K., Fredsoe, J. and Knudsen, S. B. (2012). Coastline undulations on the

West Coast of Denmark: Offshore extent, relation to breaker bars and transported

sediment volume. Coastal Engineering, Vol. 60, p. 109-122

Hybrid model – spit development

© DHI

Model coupling

• Loads on wind turbine foundation, MIKE 21 BW + CFD

22 May, 2013 © DHI #48

Nielsen, A.W, Mortensen, S. B., Christensen, E.D (2008) “Numerical

Modeling of Wave Run-up on a Wind Turbine Foundation”, Proc.

OMAE 2007, Lisbon, Portugal.

Model coupling

• Levee overtopping using MIKE 21 BW + CFD

22 May, 2013 © DHI #49

Model coupling - Hvide Sande harbour

• Study of sand bypass using MIKE 21 HD + SW + ST

Dis

tan

ce a

lon

g s

ho

relin

e (

km

)

Shoreline evolution (m/year)

1957-2008 profile data

~400 m northern breakwater established in 1963:

• updrift accumulation up to ~3,5 km north of breakwater in total 3,600,000 m3 80.000

m3/yr

• shoreline advance ~3 m/yr 500 m to the north downdrift erosion counteracted by

nourishment of 300,000 m3/yr along 2-4 km to the south

Sedimentation in access channel

Navigation depth of 4,5 m is maintained

maintenance dredging ~170,000 m3/yr

hydraulically pumped to downdrift shore

With the present harbour layout, the natural depth of bypass bar is ~2.5 m

Yellow colour: depths between 3 and 4 m

Calibration results Bar crest elevation across the access channel during calibration period

Measured pre-storm

Measured post-storm

Modelled post-storm

Accurate reproduction of bypass bar evolution:

350 m southward migration of the bar

crest elevation along the bar from -2.5 to -3.5 m

The Limfjord model anno 2012

Key problems in Thyboron Harbour after 2004:

• Larger waves in the entry area

• Navigation

• Overtopping

• Wave disturbance in the harbour

• Sedimentation causing reduced depth

in the harbour entry area

Thyborøn

Harbour

Limfjord

Thyborøn

Channel

North Sea

http://www.youtube.com/watch?v=wPRQDpXHj6w

The Limfjord

• Since 2004 increasing overtopping at outer breakwater in Thyborøn Harbour

• Possible cause in morphological active entrance channel

• Approach

• Model sediment dynamics in entrance using HD + SW + ST

• Model wave activity using Boussinesque model (MIKE 21 BW)

22 May, 2013 © DHI #54

Thyborøn

Harbour

Limfjord

Thyborøn

Channel

North Sea

Niemann, S.L., Sloth, P., Buhl, J., Deigaard, R. and

Brøker, I. Thyborøn Harbour - Study of Wave

Agitation and Sedimentation. ICCE No 32 (2010):

Proceedings of the 32nd Conference on Coastal

Engineering, Shanghai, China, 2010.

Historical benchmark for Danish Coastal Engineers

Limfjord

Before 1862: The shoreline was located

more than 1500m further

offshore and there was no connection

between the North Sea

and the Limfjord

1862: Large breach occurred

1875-1930’ies: A large

groyne system were constructed

along the 22 km barrier

Today: Coastline is mitigated by

nourishment of about 750000 m3/year

North

Sea

Change in bathymetry have changed the wave conditions

2004 2008 Reduced

depth

Reduced

depth and

increased

bed slope

Erosion,

steeper beach

Impact on waves of 400.000 m3 excavation 2008 After excavation

Hs decreases

to 50-70%

Hs increases

by 10-50%

Summary

• Model have developed since 1960 and we have been

able to make use of this

• Model and data should be an integrated entity

osp@dhigroup.com www.dhigroup.com

22 May, 2013 © DHI #59