Numerical and physical modelling of different nourishment designs

1. 9 juli 2015
Physical and numerical modelling of
different nourishment designs
Alessio Giardino, Yorick Broekema, Jebbe van der Werf,
Arnold van Rooijen, Michalis Vousdoukas

2. 9 juli 2015
Why studying nourishments?
 Coastal erosion is becoming a common threat to
most of the countries (e.g. anthropogenic action,
sea level rise)
 Advances in dredging techniques  Sand deposits
easier accessible
 More attention towards flexible and environmental-
friendly type of solutions to coastal erosion problems

3. Nourishment designs (1)
 Beach nourishments
- Compensate local erosion
- Mainly used in areas with narrow and low dunes
- Lifetime: 1-5 years (relatively low)
- Expensive solution (require pumping line to the beach)
9 juli 2015

4. Nourishment designs (2)
 Shoreface nourishments
- Compensate erosion at larger scale
- Mainly used in regions with relatively wide and high dunes
- Lifetime: up to ≈ 10 years
- Cheap solution
- Large nourishment volumes required (efficiency ≈ 0.3 - 0.5)
9 juli 2015

5. Objective of this research
Nourishments designs around the world often carried out based on
experience and practical guidelines.
Objectives:
- Better understanding of the physical processes (i.e.
hydrodynamics, waves and sediment transport) related to different
nourishment designs, based on physical and numerical modelling.
- Results to be used in practical recommendations for the design of
nourishments.
9 juli 2015

6. Physical modelling (1)
9 juli 2015
Beach nourishment:
Large Wave Channel Hannover (GWK)
L = 307 m, W = 5 m, d = 7 m
D50 = 300 µm
Vn = 1.3 m3/m
Tests:
2 h accretive wave conditions
Hs = 0.51 m; Tp = 7 s
Ω = Hs / (Tp x wss) = 3.6
3 h erosive wave conditions
Hs = 0.9 m; Tp = 5.17 s
Ω = 8.7

7. Shoreface nourishment (2 designs):
Deltares Scheldt flume
L = 56 m, W = 1 m, d = 1.2 m
D50 = 134 µm
Vn = 0.37 m3/m
9 juli 2015
Physical modelling (2) (Walstra et al. 2011)
Tests:
24 h accretive wave conditions
Hs = 0.10 m; Tp = 3 s
Ω = Hs / (Tp x wss) = 2.3
16 h erosive wave conditions
Hs = 0.17 m; Tp = 2.3 s
Ω = 5.1

8. Numerical modelling (1)
Delft3D model (Lesser et al., 2004; Reniers et al., 2004)
9 juli 2015
(1) Propagation of short wave energy
(2) Wave energy dissipation due to wave breaking
(3) Roller energy propagation
(4) Roller energy dissipation
Shallow water equations
(1) Continuity equation
(2) Momentum equations
Waves (Instationary Roller model) Hydrodynamics
Wave, roller
forces
Water levels
Sediment transport computed with TRANSPOR2004
formula (Van Rijn 2007a,b,c) (bedload + suspended load)
Sediment transport
Morphological bed update
Exner equation
θ θ∂ ∂∂
+ + =−
∂ ∂ ∂
cos( ) sin( )w g w gw
w
E c E cE
D
t x y
α
γ
  
   
= − −    
   
  
2
2
2 1 exp
dn
w
w p w
ref
E
D f E
E
θ θ∂ ∂ ∂
+ + =− +
∂ ∂ ∂
2 cos( ) 2 sin( )r r r
r w
E E c E c
D D
t x y
β
=
2 sin( ) r
r
g E
D
c

9. 9 juli 2015
Beach nourishment

10. Beach nourishment: hydrodynamics
9 juli 2015
 Accretive conditions: Hs = 0.51 m and Tp = 7 s
 Erosive conditions: Hs = 0.9 m and Tp = 5.17 s

11. Beach nourishment: concentrations
9 juli 2015
 Accretive conditions: Hs = 0.51 m and Tp = 7 s
 Erosive conditions: Hs = 0.9 m and Tp = 5.17 s

12. Sediment sorting on a cross-shore profile (reference profile)
9 juli 2015
Broekema et al. (in preparation)
- 8 sediment fractions
- 12 layers in the bed

13. Beach nourishment: effect of grain sorting
9 juli 2015

14. 9 juli 2015
Shoreface nourishment

15. Bathymetry evolution measurements (Walstra et al. 2011)
9 juli 2015
Low nourishment design
High nourishment design

16. Beach erosion measurements
9 juli 2015

17. Shoreface nourishments: waves
9 juli 2015
ReferenceLownour.Highnour.
Erosive tests: Hs = 0.17 m and Tp = 2.3 s

18. Conclusions
Measurements and model results for different nourishment scenarios have
been compared.
To conclude:
- Higher velocities and concentration can be seen in proximity of the beach
nourishment
- The model is capable of reproducing the sorting processes along the
profile (Broekema et al., in preparation)
- Using larger grain size for the beach nourishment contribute to the
formation of a armour layer which can lead to a reduction in erosion
- Different shoreface nourishment designs respond differently to different
wave conditions (i.e. erosive vs. accretive)
- Shoreface nourishments higher in the profile are more effective in
reducing beach erosion due to larger reduction in wave height
- More work is being carried out to: improve sediment transport formulations
for small-scale laboratory tests, assess alongshore vs. cross-shore
effects, validation with field data
9 juli 2015

19. 9 juli 2015
Alessio.giardino@deltares.nl