Sam.S.L HETTIARACHCHI1, Saman. P SAMARAWICKRAMA1, Harsha RATNASOORIYA1, Joe FERNANDO2
1University of Moratuwa, Sri Lanka, Democratic Socialist Republic of; 2Universiy of Notre Dam, USA
TỔNG ÔN TẬP THI VÀO LỚP 10 MÔN TIẾNG ANH NĂM HỌC 2023 - 2024 CÓ ĐÁP ÁN (NGỮ Â...
Investigating the performance of coastal ecosystems for hazard mitigation
1. Investigating the performance of coastal
ecosystems for hazard mitigation
Sam Hettiarachchi H.J.S.Fernando
S.P.Samarawickrama University of Notre Dame
A.H. R. Ratnasooriya Indiana
University of Moratuwa USA
Sri Lanka
9. Measured currents offshore of Colombo
80
Current Speed
70
Velocity Magnitude (cm/s)
60
50
2.5
km/hour Tsunami
40
30
20
10
0
12/26/04 0:00 12/26/04 6:00 12/26/04 12:00 12/26/04 18:00 12/27/04 0:00
Time
360
315
270
Current Direction (deg)
225
180
135
90
45
Current Direction
0
24-Dec 25-Dec 26-Dec 27-Dec 28-Dec 29-Dec
Time
10. Sediment Transport by the 2004 tsunami at Sri Lanka
Ongoing Study (Tohoku University)
Sounding surveys were conducted before
(December 2004) and after (December
16. Coral reefs are severely
affected and damaged
by the debris and sand
transported during the
inland and shoreward
movement of the
tsunami waves.
From Prof. H.Fernando
17. Natural Methods for Mitigation
Coral Reefs & Sand Bars
Sand Dunes
Coastal Vegetation and Mangrove Forests
Hybrid Solutions
Combination of Natural /Artificial Methods
18. Coral Reefs
Submerged natural breakwaters
Hi
H
t
h τb ub
Submerged depth (h)
d
Coral Reefs –
act as submerged
natural breakwaters
L Length (L)
19. Small submerged depth (h)
Significant length (L)
Coral Reefs
Kenyan Coastline –From J. Tychsen
20. The influence of Wave Reflection from Maldive Islands
Reflection of waves
Sri Lanka
Maldive Islands
24. Theoretical Considerations
Wave Parameters (U0 , λ, a) U0
Reef Parameters (M, P, L, H)
Reef Gap (ω)
Depth of water (H0)
Location (x, y, z) UC UG
UC
UG
Gap
M
z
P
x
y
H
ω L
Wave Parameters Uo , λ, a
25. The velocity in the gap at a location (x, y, z) is given by
U G = f {[ P, M , L, H ], [ω ], [ H 0 ], [ x, y, z ], [U 0 , a, λ ]}
reef parameters gap location wave
parameters
Reef Parameters: Height H, Length L, Porosity P and other hydrodynamic and
physical characteristics of the ridge represented by the dimensionless parameter M.
Gap in the reef ω
Depth of water at the location is H0
Oncoming wave parameters: Velocity amplitude U0, the Wave length λ and
Wave amplitude a.
26. On dimensional grounds equation (1) can be written as
L H x y z ω a λ
U G = f 1 P, M , , , , , , , ,
×
H H0 L H H H H0 H0
(2)
Since the interest here is the velocity just at the lee edge of the reef or
x
= 1 and the velocity distribution at the centerline ( y = 0)
L
L H z ω a λ
U G = f 2 P, M , , , , , , (3)
H H0 H H H0 H0
27. ω
When the gap is absent =0
H
and this is equivalent to the condition far away from the gap where the effects of the
gap are hardly felt. Therefore the lee-side velocity far away from the gap (or that in
the absence of the gap) can be written as
L H z a λ
U C = f 3 P, M , , , , , (4)
H H0 H H0 H0
Since the present experiments are designed to demonstrate the possibility of large
velocity amplifications and their dependence on the porosity of the barrier
L H λ
M, , and were kept Thus (3) and (4) yields:
H H0 H0 constant.
∆U U G − U C a z
= = π P, , (5)
UC UC H0 H
28. a z
In the experiments the dependence on P, and are investigated
H0 H
Porosity P = 20% and 50%
Amplitude a = 20, 30 and 40 cm for H0=30 cm
Measurements at z = 5, 10, 15, 20 cm for H=20 cm
∆U U G − U C a z
= = π P, ,
UC UC H0 H
U0 UC UG
29. Schematic diagram of the experimental set-up
(all values are in cm s)
86 cm
W
60 cm
30 cm
20 cm
ADV Positions
26 cm
(a) Plan view (b) Elevation
30. Simulation of Coral Reefs in 2D Physical Modelling
Representation of high dense (20% porosity) and
low dense (50% porosity) structures
31. Collaborative Research
Arizona State University / University of Moratuwa
(May/June 2005 and Nov/Dec 2006)
PIV method
Large flume studies
ADV method
Simulated reefs
40. Hikkaduwa Case Study
Key areas of investgation
(i) Discontinuity in the Continental Shelf-
Edge waves
(ii) Coral Mining
(iii) Negative Slope
41. (ii) Coral Mining
Illegal coral mining has created a
defenseless “low resistance path”
Ilegal Coral mining over the
last few decades
Presence of
Corals and Rocks