Presentation by Stijn Dijsselbloem (CDR International B.V., Netherlands) at the Delft3D User Days, during the Delft Software Days - Edition 2023 (DSD-INT 2023). Wednesday, 15 November 2023, Delft.

1. Baseline studies for
Strategic Coastal protection
Long Island, Bahamas

2. Content
1. Introduction
2. Background
3. Motivation and Objectives of the assignment
4. Project sites and boundaries
5. Methodology
6. SFINCS Modelling & Implementation
7. Co-Creation
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3. Team
CDR International
Subconsultants:
• Island by Design
• IHE Delft
• Rebel Group
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+ DELTARES
SUPPORT

4. Hurricane Joaquin
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5. Hurricane Joaquin
• Total damage by Hurricane Joaquin for Bahamas is
estimated to be $104,788,224
• Long Island suffered the greatest percentage of
damage across all Family Islands from Hurricane
Joaquin, with an estimated $35,693,528 of damage
and $ 3,542,833 of losses
• The hurricane affected over 60% of the population of
Long Island, equivalent to 3,094 people. It is estimated
that 60% of dwellings were destroyed or damaged on
Long Island, with a total damage associated with
dwellings to be $18,908,500.
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6. Objectives of this assignment
Development of sustainable coastal protection and flood mitigation
for Central Long Island
• Sustainable coastal protection
• Reduce flood risk
• Hurricanes and Climate Change
• Nature Based Solutions and bio diversity
• Critical infrastructure
• Environmental and Socio-economic context
• Stakeholder participation, awareness and commitment
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11. Phase II - Baseline Data Collection
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12. Phase II - Baseline Data Collection
• Purchased data sets:
• FABDEM: Forrest And Buildings removed DTM
• IEEE: Satellite Derived Bathymetry (SDB)
• Local SDB developed by IHE
• Field survey data
• Ground truthing
• Special attention to composition of DEM
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13. Phase III – Disaster Risk Assessment
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SFINCS

14. Hazard assessment
• Sources of flooding
• Tide
• Storm surge
• Sea level rise
• Run-off
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SFINCS!

15. Hurricane and flood modelling
• Modelling of surge levels and wave action by
Hurricanes
• Modelling and tools
• TCWiSE (synthetic tracks)
• SFINCS (surge and inundation modelling)
• Objective to determine return periods of
hurricane events and their impact
TC’s generated by Deltares for three projection
years:
2020, 2050, 2100
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17. Flood modelling
Global Model
• Tidal boundary condition
• Sea Level Rise
• TC’s (wind & rainfall) as forcing
Land Model
• Water level time series from Global Model
• TC’s (wind & rainfall) as forcing
Multiple filtering steps to keep reducing number of conditions with
increasing complexity and computational effort
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18. SFINCS Modelling
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Cuba
*grid not to scale
500m depth contour

19. SFINCS Modelling
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x 175
x 1000
(random)

20. SFINCS Modelling
Implementation
• Coastal road as weir
structure
• Culverts
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21. SFINCS Modelling - Calibration
• Flood duration focus
• Infiltration coefficient
• Emergency response
• Accessibility
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22. SFINCS Modelling - Validation
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23. SFINCS Modelling - Results
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24. Proposed Interventions
• Rehabilitate and increase culvert capacity
• Trenches
• Levees with Mangrove restoration
• Bypass road
• Saline resistant vegetation
Additional measures and non-physical:
Flood zoning policies, updating building codes, relocation of shelters, landfill cleaning and
relocation, Flood Early Warning System, Emergency Response Plan, psychological support,
additional levee structures
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25. Implementation interventions
• Trenches not yet possible in SFINCS, therefore separate
analysis with DFLOW 1D2D for drainage channels and
culverts
→ Workaround in SFINCS by implementing multiple
elongated “culverts” that ensure connection of depressions
in DEM and provided proper resistance to flow.
• Levee resolution; Special attention to the exact grid cells
that are covered by the thin dam.
→ Plot grid cells and draw levee on top
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DFLOW 1D2D

26. SFINCS Modelling – Co-Creation
• Support from Deltares
• Initial model setup by Deltares
• Short lines, regular check-ins
• Feedback loops, updating SFINCS
executable
• CDR testing features for application
within project
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Focus in this project on duration of
flooding (thus infiltration important)
and drainage structures. → different
aspects from previous SFINCS models
by Deltares

27. Improvements
• For translating hazards to expected damages, another output parameter was requested:
Depth x Velocity. This translates to the impact of the surge wave on buildings
• Due to our focus on flood duration, the importance of the (bulk) infiltration parameter
became eminent
• Tested and improved the functioning of both the culvert and the valve structure in the
SFINCS model.
• Debugging in general. By deploying the model to a new case study, new errors popped up
and some malfunctions came to surface.
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28. SFINCS Modelling – Co-Creation
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Friday night 22:34!

29. Thank you for your attention
Any questions?

30. SFINCS Modelling
• Hazard Assessment
• Derivation of return
period maps
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