Numerical models in context of coastal climate change, adaptation and protection schemes. Nils Drønen Head of Innovation, CED, DHI

Transcription

1 Numerical models in context of coastal climate change, adaptation and protection schemes Nils Drønen Head of Innovation, CED, DHI

2 Agenda Introduction How can we quantify coastal response to climate change and adaptation/protection schemes? Dunes and dikes Coastal defence against flooding Coastal flooding Modelling hinterland flooding Long term effects - Protection and sand availability Outlook Consolidation of findings in future applications

3 01. Introduction How can we quantify coastal response to climate change and adaptation/protection schemes?

4 Climate change and coastal change We do not know exactly how the climate will change We anticipate global sea level rise but do not know the exact levels We anticipate higher frequency of storms but we do not know the details and the regional effects To plan for these changes means dealing with a large degree of uncertainty All regions have their specific problems Coastal planning can only be done in the above sketched context COADAPT has developed different numerical modelling tools that can be used in the planning for a broad spectrum of regional problems and strategies for protection and adaptation

5 Numerical models for coastal processes Example downdrift erosion

6 Numerical models for coastal processes Example downdrift erosion Eroding coastline - exposed dunes

7 Numerical models for coastal processes Example downdrift erosion Eroding coastline - exposed dunes Coupling between long term processes and extreme erosion events

8 Breaching and flooding Wave induced erosion of dunes Breaching is initiated and develops Flooding behind dunes

9 COADAPT WP1 model development 1. Short term erosion and breaching models 2. Long term shoreline models 3. Coastal flooding models

10 COADAPT WP1 model development 1. Short term erosion and breaching models 2. Long term shoreline models 3. Coastal flooding models

11 02. Dunes and dikes Coastal defence against flooding

12 Breaching and flooding Three processes: 1. Wave impact erosion 2. Overwash erosion 3. Breaching

13 Dune erosion MIKE21 BW further development Wave impact erosion Slumping of dune front Sediment transport

14 Overwash erosion Breaching developed as erosion on backside Phase 1: Overtopping erosion Phase 2: Overwash erosion

15 Overtopping behind bar with lower part in middle

16 Dike breaching

17 Dike breaching Random distribution of weak spots how can we quantify this? What is the probalility distribution for critical shear stress?

18 Initial bathymetry

19 Dike breaching development of weak spot in dike Left: Water surface Mid: Critical shear stress Right: Dike/bed topography

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21 Perspectives Principles for modelling erosion and breaching of dunes and dikes have been developed and tested with succes! Field and laboratory studies of strength parameters for real dikes (and dunes) has still not been developed the physical experiments lags the numerical model development, but is expected to come in the near future Models show great potential for evaluating wave impact, pulsating overtopping rates and shear stress related erosional characteristics How can dike weaknesses be parameterised? Empirical data is still missing

22 COADAPT WP1 model development 1. Short term erosion and breaching models 2. Long term shoreline models 3. Coastal flooding models

23 03. Coastal flooding Modelling hinterland flooding

24 Modelling coastal flooding Exposed coasts Sheltered coasts Static flooding modelling: Fixed level analysis Dynamic flooding modelling: MIKE 21 FM

25 Breaching of dunes/dikes (exposed coasts) Opening in sea defense line Temporal development of breach prescribed Hydraulic friction formula overflow Dynamic flood model

26 Ribe (KDI project) Dynamic flooding aspect is essential

27 Sheltered coasts Max surface elevation Water level at Hornbæk during Bodil Dynamic aspect of local flooding not as important as the dynamic aspect of local water level

28 Perspectives Coastal flooding modelling techniques are quit mature and can be applied in many different contexts Erosion and breaching of dikes and dunes still rely on scarse data sets for model calibration and semi-empirical relationships Dynamic approach is needed A number of initiatives have been the spin off of the COADAPT flooding work, e.g. a DHI-DMI project for flood forecasting Coupling with rural and urban rain run-off will come Coupling with environmental aspects is a possibility Coupling the continous improvements in climate projections and downscaling will come

29 COADAPT WP1 model development 1. Short term erosion and breaching models 2. Long term shoreline models 3. Coastal flooding models

30 04. Long term effect Protection and sand availability

31 Modelling long term protection schemes Hard structures Soft solutions

32 Shoreline model A. A number of transects are defined B. ST flux through each transect is calculated from a 2D wave, hd, st model run C. The shoreline is adjusted according to the differences between the fluxes through each segment

33 Shoreline model 2D area 1 Line model A. A number of transects are defined B. ST flux through each transect is calculated from a 2D wave, hd, st model run C. The shoreline is adjusted according to the differences between the fluxes through each segment

34 Hard structures Shore normal breakwaters - groynes Shore parallel breakwaters

35 Shore parallel breakwaters Modelled 2D area 1-line model Salient after 4 years Survey

36 Shore parallel breakwaters Groyne fields Different groyne lengths Different alongshore spacings

37 Soft solutions: Nourishment Beach nourishment Shoreface nourishment Dune nourishment Mega nourishment

38 Mega nourishment The sand engine (The Netherlands)

39 Temporal evolution as modelled Profiles extracted from initial 2D bathymetry contour lines Aug 2011 Feb 2012 Waves from one of DHI s Northsea models Feb 2013 Dec 2013

40 Perspectives Different shoreline protection schemes can be analysed with the new model concept The model fills a gap between fully developed morphological models - difficult to apply - and simplistic shoreline models with a number of limits in the context of shoreline protection The problem of how to meet the specific regional problem can be solved with a process oriented model like this Future application: Geomorphological phenomena Skagen, long term spit formation

41 COADAPT model development 1. Short term erosion and breaching models 2. Long term shoreline models 3. Coastal flooding models

42 05. Outlook Consolidation of findings in future applications

43 Outcome of COADAPT Significant boost in modelling capacity to study coastal protection Kick starting coastal flooding modelling for the future Establish new short and long term erosion/morphological modelling techniques Modelling methodologies already applied in projects Increasing awareness of model s relevance for preparing for extreme events and long term planning Identification of most critical needs for further development Increased communication between research (KU), applied research (DHI) and application/end-user (KDI)

44 Increasing model capabilities and understanding