This document summarizes research using the numerical model XBeach to simulate beach morphodynamic changes under storm conditions. It discusses modelling of storm-induced erosion at beaches in Australia, the UK, and reef environments. XBeach successfully reproduced beach erosion from storms and storm clusters, though recovery simulations require improvement. The model captured the complex response of the Sefton Coast in the UK to a 2013/2014 winter storm cluster, where beach recovery between closely spaced storms was minimal. Accounting for tidal effects and sediment transport processes was important for accurate modelling.

1. College of Engineering College of Engineering
Modelling Morphodynamic
Impacts of Storm Clusters
Harshinie Karunarathna
XBeachX Conference
Delft
03 November 2017

2. College of Engineering College of Engineering
Are beaches worse off when a cluster of storms
occur at close succession?
After 2013/2014 winter storms
Before 2013/2014 winter storms
Sefton Coast, Liverpool, UK

3. College of Engineering College of Engineering
Hallsands, Devon, UK
Before 2013/2014 winter storms
After 2013/2014 winter storms

4. College of Engineering College of Engineering
Can we computationally reproduce
morphodynamic impacts of storm clusters?

5. College of Engineering College of Engineering
Modelling beach change from storm clusters
Narrabeen Beach, Australia

6. College of Engineering College of Engineering
Modelling beach change from storm clusters
Narrabeen Beach, Australia
- Wave dominated embayment
- Spring tidal range 1.6m
- Sandy beach
- Frequent storms

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0
2
4
6
8
6/6/88 5/8/88 4/10/88 3/12/88 1/2/89 2/4/89
Hsmax
Date
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2
4
6
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14/08/94 13/10/94 12/12/94 10/02/95 11/04/95
Hsmax(m)
Date
Storm clusters at Narrabeen Beach
(Karunarathna et al., 2014. Marine Geology 348, 13-112)

8. College of Engineering College of Engineering
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0 2000 4000 6000 8000 10000
Erosionvolume(m3/m)
Total Storm Power (m2hr)
R2 = 0.761
y = 0.0186x
Storm Clusters
0
40
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120
160
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0 2000 4000 6000 8000 10000
ErosionVolume(m3/m)
Storm Power (m2hr)
R2 = 0.804
y = 0.0081x
Storm Power 𝑃𝑠 = 𝐻𝑠𝑚𝑎𝑥
2
𝐷
Total storm power = Ps1 + Ps2 + Ps3 + ….
Isolated Storms
Do storm clusters erode more beach……
(Karunarathna et al., 2014. Marine Geology 348, 13-112)

9. College of Engineering College of Engineering
Modelling storm induced beach erosion
using XBeach
(a)
(b)
(c)
(d)

10. College of Engineering College of Engineering
Modelling storm induced beach erosion
using XBeach
(Pender and Karunarathna et al., 2013. Coastal Engineering, 81, 19-29)

11. College of Engineering College of Engineering
XBeach for beach recovery modelling
Wave skewness and
asymmetry is important for
onshore transport

12. College of Engineering College of Engineering
Modelling beach erosion from storm
clusters using XBeach

13. College of Engineering College of Engineering
2m contour
Zero Contour
(Pender and Karunarathna et al., 2013. Coastal
Engineering, 81, 19-29)
Modelling beach erosion from storm
clusters

14. College of Engineering College of Engineering
VERDICT
• XBeach did very well in simulating storm erosion– not a surprise!!
• Recovery simulations are satisfactory, but not quite
• Switching between ‘erosion’ and ‘recovery’ models was problematic
NOTE
• Measured profiles were not always ‘pre- and post-storm’ profiles.
So, model results may be better than we think they are..…
Modelling beach erosion from storm
clusters

15. College of Engineering College of Engineering
Modelling beach change from storm clusters
Sefton Coast, UK

16. College of Engineering College of Engineering
Modelling beach change from storm clusters
Sefton Coast, UK
- 36 km long concave shape beach
- Spring tidal range 8.2m
- Sandy beach
- Stormy winters/calm summers

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2013/2014 Winter storms at Liverpool Bay

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Modelled morphodynamic change
during 2013/2014 storm cluster
Red: pre-storm profile; Black: post-storm profile without recovery;
Broken black: post-storm profile with recovery
(Dissanayake, Brown, Wisse & Karunarathna, 2015. Marine Geology, 370, 63-75)

19. College of Engineering College of Engineering
Modelled morphodynamic evolution during
2013/2014 storm cluster
(Dissanayake, Brown, Wisse & Karunarathna, 2015. ECSS, 164, 301-312)

20. College of Engineering College of Engineering
Modelled morphodynamic evolution during
2013/2014 storm cluster
Cross-shore volume change vs. Longshore distance
P14

21. College of Engineering College of Engineering
Modelled morphodynamic evolution during
2013/2014 storm cluster
(Dissanayake, Brown, Wisse & Karunarathna, 2015. ECSS, 164, 301-312)

22. College of Engineering College of Engineering
POINTS TO NOTE
• Morphodynamic response of Sefton Coast to calm
weather is slow – beach recovery between closely
spaced storms was insignificant
• Water level at storm peak is more important than
peak storm wave height –tidal variation and surge
are the key
• Modelling Sefton was difficult…….complex sediment
characteristics & intertidal morphology, large tidal
range, aeolian transport

23. College of Engineering College of Engineering
SUMMARY
• XBeach successfully reproduced storm induced
beach/dune erosion of a variety of beaches
• Some success in recovery simulations. More work
is needed
• XBeachX may be a part of the solution

24. College of Engineering College of Engineering
Acknowledgement
• Dr. Douglas Pender
• Dr. Pushpa Dissanayake
• Sefton Metropolitan Borough Council
• Engineering and Physical Science Research Council

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Infragravity waves on reefs

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Thank You!