This document describes a method for modeling wave attenuation over foreshores using Earth observation data and the XBeach model. There are three levels of assessment: 1) a quick scan using global data, 2) a moderate validation plan using local Earth observation data and global data, and 3) a fully tuned assessment of the actual local situation. For the second level, Earth observation data on vegetation cover, type and geometry is combined with global data sets on water levels and wave conditions in XBeach to model wave attenuation over the foreshore. XBeach is a process-based model that can simulate wave transformation and account for the effects of vegetation on short and long waves through drag formulations. The method is demonstrated for sites in the

1. 7FP – SPACE
no. 607131
FAST-Wave attenuation modelling
using EO data and XBeach

2. DelftSoftwareDays,28-10-2015
7FP – SPACE
Goal: assessment of wave reduction
over foreshore
Three assessment levels:
• 1-Quick scan, transect. Fully based on global data and vegetation
presence/absence. How relevant is wave attenuation by
vegetation on ‘my’ (or any other) foreshore?
• 2-MVP, transect. Based on local EarthObservation data
(vegetation, geometry) and global data (waves, water level). How
much can the actual vegetation do, and how sensitive is its
function?
• 3-Actual assessment, 2D horizontal. Fully tuned to local situation.
What is the wave reduction under design conditions?

3. DelftSoftwareDays,28-10-2015
7FP – SPACE
Step 2: Assessment of actual transect
Foreshore
parameters
relevant for
flood safety
Earth observation
data
(vegetation cover and
properties)
Global data sets
(hydraulic boundary
conditions)
Wave model
XBeach
Wave
attenuation
over foreshore

4. DelftSoftwareDays,28-10-2015
7FP – SPACE
Step 2: Assessment of actual transect
EO data:
Vegetation cover and type
Geometry
Global data:
Water level
Wave conditions

5. DelftSoftwareDays,28-10-2015
7FP – SPACE
Global data: water levels
• Global Tide Surge Model (Martin Verlaan et al.)

6. DelftSoftwareDays,28-10-2015
7FP – SPACE
Global data: wave conditions
• ERA-interim (1979-2014)

7. DelftSoftwareDays,28-10-2015
7FP – SPACE
Global/EO data: geometry
• fast.openearth.eu, site Donna Nook (East UK)
LiDAR: resolution 50 x 50 cm

8. DelftSoftwareDays,28-10-2015
7FP – SPACE
Global/EO data: vegetation
• e.g. Giri et al. (2011)

9. DelftSoftwareDays,28-10-2015
7FP – SPACE
Global/EO data: vegetation
• NDVI from Sentinel satellite: vegetation presence + biomass
• in-situ data: translation to meaningful vegetation properties
resolution 5 x 5 m

10. DelftSoftwareDays,28-10-2015
7FP – SPACE
Dataflows
Foreshore
parameters
relevant for
flood safety
Earth observation
data
(vegetation cover and
properties)
Global data sets
(hydraulic boundary
conditions)
Wave model
XBeach
Wave
attenuation
over foreshore

11. DelftSoftwareDays,28-10-2015
7FP – SPACE
What is XBeach?
• 2DH process-based model to simulate nearshore wave transformation,
long wave motion, sediment transport and morphological change
• 2 modes:
• Surfbeat hydrostatic:
• Nonlinear shallow water equations with radiation stress forcing
from wave action equation.
• Resolves long waves and the amplitude variation of short waves
• Non-hydrostatic:
• Solves NLSW with pressure correction
• Resolves phase of long and short waves.
short wave envelope
gC
leaky wave
gh
bound long wave
short waves
Van Rooijen et al.,
submitted to JGR
www.xbeach.org

12. DelftSoftwareDays,28-10-2015
7FP – SPACE
Vegetation in XBeach
•Physical aspects
• Effect of vegetation on short waves
• Effect of vegetation on long (infragravity) waves
• Effect of vegetation on wave setup
•Schematization
• Vertically non-uniform vegetation (e.g. mangroves)
• Horizontally non-uniform vegetation (different types per location)
24 november 2015

13. DelftSoftwareDays,28-10-2015
7FP – SPACE
Vegetation: short and long wave
attenuation
• Short wave attenuation
• Method of Mendez & Losada (2004)
• The work done due to the wave orbital motion acting on vegetation
stem is related to wave energy dissipation induced by the vegetation
• This can be approximated by the drag force times the velocity
• Use linear wave theory to get wave energy dissipation
• Adjustments by Suzuki et al. (2011), implementation in SWAN
• Take into account vertical variability of vegetation (e.g.
mangroves)
•Long wave attenuation
• Calculate drag force, and apply in the momentum equations
24 november 2015

 

 
h s
V D
h
F udz
1
2
D DF C Au u
-> This formulation is also used to take into account wave dissipation by
vegetation in XBeach Nonhydrostatic

14. DelftSoftwareDays,28-10-2015
7FP – SPACE
Implementation in XBeach
• XBeach surfbeat • XBeach non-hydrostatic

15. DelftSoftwareDays,28-10-2015
7FP – SPACE
Model validation
• Sea-swell (-) and infragravity (--) waves: Lovas (2000)
24 november 2015
No vegetation
With vegetation

16. DelftSoftwareDays,28-10-2015
7FP – SPACE
Demonstration: Wadden Sea

17. DelftSoftwareDays,28-10-2015
7FP – SPACE
Wadden Sea: geometry and
vegetation
• Vegetation properties: Möller et al. 2014 Nature Geoscience:
– h = 0.3 m
– b = 0.00125 m
– N = 1225 /m2
– Cd = 0.19

18. DelftSoftwareDays,28-10-2015
7FP – SPACE
Xbeach Salt marsh Wadden Sea

19. DelftSoftwareDays,28-10-2015
7FP – SPACE
Xbeach Mangroves Louisiana

20. DelftSoftwareDays,28-10-2015
7FP – SPACE
Xbeach on FAST field sites

21. DelftSoftwareDays,28-10-2015
7FP – SPACE
DIY: Session 3 12:10