reduction of wave overtopping by vetiver grass overtop .pdf · - reduction of wave overtopping by...
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- Reduction of Wave Overtopping by Vetiver grass -
1Introduction Objectives Model Set-up Result Case study Conclusions
Reduction of wave overtoppingby Vetiver Grass
Presentation: Vu Minh Anh
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- Reduction of Wave Overtopping by Vetiver grass -
2Introduction Objectives Model Set-up Result Case study Conclusions
Contents of presentation
Introduction
Physical model and model set-up
Results and Case study
Conclusions & Recommendations
Questions and Discussion
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- Reduction of Wave Overtopping by Vetiver grass -
3Introduction Objectives Model Set-up Result Case study Conclusions
Violent wave overtopping at the sea dikes
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4Introduction Objectives Model Set-up Result Case study Conclusions
Wave overtopping at the sea dikes
Dike
Wave Runup
Wave Overtopping
Waves
Initial profile Erosion profile on outer slope
Erosion profile on inner slope
Revetment
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- Reduction of Wave Overtopping by Vetiver grass -
5Introduction Objectives Model Set-up Result Case study Conclusions
Design Sea Dike
Reduce wave overtoppig
Traditional method:
‘’Hard’’ revetments like concrete blocks, big rocks, glacial stones
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- Reduction of Wave Overtopping by Vetiver grass -
6Introduction Objectives Model Set-up Result Case study Conclusions
‘’Hard’’ Revetments
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- Reduction of Wave Overtopping by Vetiver grass -
7Introduction Objectives Model Set-up Result Case study Conclusions
Design Sea DikeReduce wave
overtopping height
Traditional method:
‘’Hard’’ revetments like concrete blocks, big rock, glacial stone
Methods which are low-cost and readily available
Combination between ‘’Hard’’ revetments with Vegetations
or Bioengineering methods.
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- Reduction of Wave Overtopping by Vetiver grass -
8Introduction Objectives Model Set-up Result Case study Conclusions
‘’Soft’’ Solutions
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- Reduction of Wave Overtopping by Vetiver grass -
9Introduction Objectives Model Set-up Result Case study Conclusions
Vetiver grassIn a number of tropical countries Vetiver grass is well-known bioengineering. Vertiver grasses grow naturally in clump with thin, long, and erect leaves.
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- Reduction of Wave Overtopping by Vetiver grass -
10Introduction Objectives Model Set-up Result Case study Conclusions
Vetiver grassVetiver grasses as sea dike revetments
Lack of basic understanding for processes and propertiesLack of quantitative and qualitative knowledge of the protection on the outer slope of the sea dike by Vetiver
Addressing previous information: reduce wave overtopping by Vetiver grasses
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- Reduction of Wave Overtopping by Vetiver grass -
Introduction Objectives Model Set-up Result Case study Conclusions
Objectives
The hydraulics of flow with Vetiver grass
The interaction between flow velocity and flow depth in cases of Vetiver hedge in relation to the reduction of wave overtopping
Improving the guidelines in designing sea dike dimensions
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Introduction Objectives Model Set-up Result Case study Conclusions
Model set-up
R 1
B
ChB
vB
vc
h c
R 2
Full scale
Vetiver grass
Wave parameters in front of Vetiver hedge.
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- Reduction of Wave Overtopping by Vetiver grass -
Introduction Objectives Model Set-up Result Case study Conclusions
Model set-up
Overview of experimental set-up
Vetiver hedge
Reservoir
Slope
Flume
Gate
Root
Leaves
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- Reduction of Wave Overtopping by Vetiver grass -
Introduction Objectives Model Set-up Result Case study Conclusions
Model set-upLocations and instruments
EM S8 EM S12
S lope 1:30
W ater system
Reservo ir
G 27 G 26 G 25 G 24
Gate
Electromagnetic Flow Velocity Meter - EMSWave Gauge Height Meter - GHM
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- Reduction of Wave Overtopping by Vetiver grass -
Introduction Objectives Model Set-up Result Case study Conclusions
Model set-up
CaseDensity of grass
(Stem/m2)Water level inside reservoir
hr (cm)
Case 1 Without grass 50, 45, 40, 35
Case2 530 50, 45, 40, 35
Case 3 265 50, 45, 40, 35
Case 4 160 50, 45, 40, 35
The experiment scenarios
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- Reduction of Wave Overtopping by Vetiver grass -
Introduction Objectives Model Set-up Result Case study Conclusions
ResultsThe interactions
hr Vetiver hedges
Stem density
Individual stem strength
Stem moment of inertia
Modules of elasticity
hi
ui
In front of the
Vetiver hedges
ub
Behind the
Vetiver hedges
hb
Energy losses
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- Reduction of Wave Overtopping by Vetiver grass -
Introduction Objectives Model Set-up Result Case study Conclusions
Results
Flow through Vetiver hedges: Manning factor
Overtopping discharge
Practical application: Nam Dinh-Vietnam
Reduction of wave run-up
Guideline for designing dams and reduction of the cost for upgrading of the present sea dike
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Introduction Objectives Model Set-up Result Case study Conclusions
ObservationsOverview (film)
EMS8 EMS12
Slope 1:30
Water system
Reservoir
G27 G26 G25 G24
Gate
Water
system
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- Reduction of Wave Overtopping by Vetiver grass -
Introduction Objectives Model Set-up Result Case study Conclusions
Wave Flow though the Vetiver hedgeObservations
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Introduction Objectives Model Set-up Result Case study Conclusions
Results (1)Flow through Vetiver hedge
Water level in front of Vetiver hedge and Grass density
Water level in front of grass ~ grass density
0,15
0,2
0,25
0,3
0,35
0,4
0,45
0 100 200 300 400 500 600
Grass density (stem/m2)
Wat
er le
vel i
n fr
ont o
f gra
sses
(m
)
h=35cm h=40cm h=45cm h=50cm
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- Reduction of Wave Overtopping by Vetiver grass -
Introduction Objectives Model Set-up Result Case study Conclusions
Results (1)Flow through Vetiver hedge
Variation of roughness coefficient with flow depth through Vetiver hedge
23
1
1 . .fn S hu
=0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.12 0.14 0.16 0.18 0.2 0.22 0.24 0.26
Average Water Depth (m)
Man
ning
's n
Case 4 - 160 stems Case 3 - 265 stems Case 2 - 530 stems Case 1 - no grass
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- Reduction of Wave Overtopping by Vetiver grass -
Introduction Objectives Model Set-up Result Case study Conclusions
Results (2)Overtopping Discharge
Reduction of overtopping discharge ~ Density
0
10
20
30
40
50
60
70
80
0 160 265 530
Grass density (stem/m2)
Red
uctio
n of
ove
rtop
ping
dis
char
ge
ΔV/
V [-
]
Reduction of overtopping
0
10
20
30
40
50
60
70
80
30 35 40 45 50 55
Water level inside reservoir hr (cm)
Dis
chag
re re
duct
ion Δ
Q/Q
(%)
Case 1 - w ithout grass Case 4 - 160 stem/m2Case 3 - 265 stem/m2 Case 2 - 530 stem/m2
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- Reduction of Wave Overtopping by Vetiver grass -
Introduction Objectives Model Set-up Result Case study Conclusions
Practical Application The reduction of wave run-up
Ru1 Ru2
Calculate wave run-up on the outer slope.
Re-calculate wave run-up in case of Vetiver grass are planted on the outer slope.
Find the reduction of wave run-up.
Define the influence factor for roughness of Vetiver grasses.
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- Reduction of Wave Overtopping by Vetiver grass -
Introduction Objectives Model Set-up Result Case study Conclusions
Practical Application - Results (4)The reduction of wave run-up
Nam Dinh province
Location
72km length of coastal line
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Introduction Objectives Model Set-up Result Case study Conclusions
Practical Application - Results (4)The reduction of wave run-up
Hs=(0.8-2.0)mT=(8-10)s
1:3
MSL
+5
Hs = 0.8-2mT = 8-10s
m:(3-5)
1:100 - 1:300
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Introduction Objectives Model Set-up Result Case study Conclusions
Practical Application The reduction of wave run-up
UnitRealvalue
Case1
Case4
Case3
Case2
Grass density stem/m2 - 0 160 256 530
Ration of wave height - - 0.886 0.501 0.422 0.406
Ru2% m 3.26 2.49 1.41 1.19 1.14
Reduction of wave run-up % - 23.73 56.85 63.64 65.1
γf - 0.95 0.75 0.410 0.345 0.332
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- Reduction of Wave Overtopping by Vetiver grass -
Introduction Objectives Model Set-up Result Case study Conclusions
Practical Application The reduction of wave run-up
Relationship between grass density and wave run-up
10
20
30
40
50
60
70
80
0 160 265 530
Grass density (stem/m2)
Red
uctio
n of
wav
e ru
-up
(%)
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- Reduction of Wave Overtopping by Vetiver grass -
Introduction Objectives Model Set-up Result Case study Conclusions
Practical Application - Case StudyUse the previous influence factor for roughness of Vetiver
grasses ( Result 4)
Allowed discharge of overtopping q=0.0001m2/s
(Dutch Guideline for the design dam )
Use Van der Meer formula (2001)
Calculation the total cost for upgrading the present sea dike
030 00
0, 06 1. . .exp 4, 7. .. . .tan.
cb
m b fm
RQHg H β
γ ξξ γ γ γα
⎛ ⎞= −⎜ ⎟⎜ ⎟
⎝ ⎠
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- Reduction of Wave Overtopping by Vetiver grass -
Introduction Objectives Model Set-up Result Case study Conclusions
Case StudyCrest height of sea dike
No Hedge One Hedge Two Hedges Three Hedges
6.606.706.806.907.007.107.207.307.407.507.607.70
1 2 3 4
Cres
t hei
ght (
m)
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Introduction Objectives Model Set-up Result Case study Conclusions
Case StudyTotal cost for one meter length
1:3
+7.6
MSLClay
Rock
+7.11
1:3
MSL
Vetiver hedges
Rock
Clay
Without Vetiver grass: $147,5
Two Vetiver hedges: $128,96
Reduction 12,6% total costs
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Introduction Objectives Model Set-up Result Case study Conclusions
Conclusions
The resistance of the slope with Vetiver grass is 2.5 times larger in comparison with the slope without grass.
The Vetiver hedges have ability to withstand flow which reaches depths up to 40cm.
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Introduction Objectives Model Set-up Result Case study Conclusions
Conclusions
The wave overtopping reduces with 45% in case of 200 stem/m2.
The influence factor for roughness of Vetiver grass varies from 0.33 to 0.41.
For upgrading sea dikes, the crest level would reduce 0.49m, and the total costs 12.6% if two Vetiver hedges are planted.
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RecommendationsThe influence factor of berm and angle of wave attack
Further research which includes these factors.
The accurate velocities in the middle of grass need more studies and investigations.
The living condition of Vetiver on the outer slope under saline condition.
A problem could appear because of grass’s roots.
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Thanks for your attention