figures (pg 59-70) · figure 6 - beach protection measures . direct dumping at nearshore pumping by...
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Coastal Area
Nearshore Zone
Inshore Offshore or shore face
Surtlone
Shore or beach
HWL--------+--7~r-~~~----~~
Ordinary LWL ____ ___;:;;..._+-----------;.==::;_,,.r _____ , I I
Plunge Point Breaker Line
HWL LWL
Coas1
High water level Low water level
59
Figure 1 - Schematic View of Shore Profile
Vx
J
I Waves v. : Long shore current
y Sx : Longshore sediment transport
Figure 2 - Longshore Current and Longshore Sediment Transport
MWL
-""'• "'"- '""""' \ /
- Profile during intense wave condition --Sy: Cross-shore transport
60
Figure 3 - Beach Profiles
/
---~ ............ --:...- .... - .... _,!',_~,.-- ., -- .': ___ ,~ ~ ,· ~ .,.- .• ~
Accretion Zone
Impermeable structure
Longshore transport direction
Initial beach plan shape (before construction of Impermeable structure)
- - - Beach plan shape after 1 year - --- Beach plan shape after 2 years
I j 1\ "·;· - __ ,- ,_ ., --..... -~ --;,;;.,;.· ,· ~ -,........ /
/
· ·- · · ..... ·.Erosion Zone
Figure 4 - Effect of Coastal Structure on Beach Plan Shape
Wl2
I ~-----------------WU
Wl2>WL1
Water level change
WL: Water level
Ds0: Grain diameter
d : Water depth
L,
D6o2 < D5o1
Grain diameter change
61
Figure 5 - Variation of Equilibrium Beach Profiles
Net longshore transport
Beach alignment following redistribution of recharge
Net longshore /Detached breakwaters transport ~
if (Plan View)
Detached Breakwaters
,-Bea,ch crest
(Section View) Underwater sill
Minimum required beach width
Figure 6 - Beach Protection Measures
Direct Dumping at Nearshore
Pumping by Floating Pipeline
Rainbow Method
62
Figure 7 - Sand Placement Methods
N
Wave climate
above 1.5 1.0 - 1.5 0.5 - 1.0 0.1 - 0.5 below 0.1
63
Figure 8 - Wave Rose
Berm width of construction profile
Design beach width at mean low water level
Upper slope of construction profile
Mean low water level
Lower slope of construction profile
Equilibrium profile affer reshaping
Existing beach profile
rEquilibrium . profile I af!er reshaping
Note: Beach fill in hatched Area A placed during construction moved to lower portion of the profile at hatched Area B by wave action.
Figure 9 - Construction Profile
)-
%,. "'
z
~os~shore profile
d Measured water depth from mean sea level
64
Figure 10 - Coordinate System for Longshore Transport Computation
Net Longshore Transport
m3 /year
Southward
Northward
Plot of net longshore transport versus shoreline orientation
~----~------------------------~------------~-------x Shoreline orientation (Angle with respect to north)
Orientation of net zero longshore transport (Shoreline orientation perpendicular to resultant incoming wave direction)
Figure 11 - Variation of Net Longshore Transport with Shoreline Orientation
(a) One-line Approach
S2(x) S(y)
------------==r=~'-~ S1 (x)
Original shoreline
Plan
Groin
Zone 1
Profile
(b) Two-line Approach
S(x)
S(x) : Longshore transport rate atx
Breaker zone
Groin
81 (x),S 2(x): Longshore transport rates at x
S(y) : Cross-shore transport rate aty
S 2(x){direction perpendicular fo the page)
Zone 2
65
Figure 12 - One-line Approach and Multi-line Approach
Net longshore transport
Spacing between Groins
f---Groin
New shoreline gradually aligned with incident wave direction
Spacing between Groins
Note: Length of groin should be extended beyond the toe of the cross-shore equilibrium beach profile to avoid loss of sand.
Figure 13 - Groins
"' "'
Breakwater
Resulting salient
.. _:·
Updrift erosio:-~ -~' ~-,-- ,'"Zi:l~h~r:ine----~,;. :~::~;:erosion
1 0.9 0.8 0.7
m 0.6 ~ 0.5 -;::: 0.4
0.3 0.2 0.1 00~~~~~--T-~~
Dimensionless Salient Length Versus Dimensionless Distance Offshore
Source: Dean (2001)
I Breakwater I Gap I i::::::=::::J
Equilibrium shoreline after breakwater construction
Location of Breakwaters
67
Figure 14 - Detached Breakwaters
1.0 0.9 [\ ;,
0.8 1\ ~~l\
Diffracting Wave 0.7 l& ~ headland orthogonal
.B._ 0.6 \l'\l,( t'-..
I~ I'-I' ~ R 0.5 1\ \'!'-. I'- Ft.. '0.4
"I' I'- ~ ·'
0.3 ~, 0
0.2 I-~E E ....
0.1 Beach ,. ,. Transition 0.0
point 0 30 60 90 120 150 180 210 240 270 8'
Definition Sketch of a Static Equilibrium Bay R.fl 0 versus 8 for varying /3 Showing Variables Involved
Table - Arc ratios R/R, for a range of /3 and 8
N 30 45 60 75 90 120 150 180 210 240 270
10 0.37 0.26 0.20 0.17 0.15 0.12 0.10 0.10 0.08 0.08 0.08 15 0.53 0.38 0.30 0.25 0.21 0.17 0.15 0.14 0.12 0.11 0.11 20 0.70 0.50 0.40 0.33 0.28 0.23 0.20 0.17 0.15 0.13 0.13 25 0.85 0.61 0.48 0.41 0.34 0.27 0.24 0.21 0.18 0.16 0.16 30 1.00 0.72 0.57 0.48 0.40 0.32 0.28 0.23 0.20 0.18 0.17
35 - 0.82 0.65 0.55 0.47 0.37 0.31 0.26 0.22 0.19 0.19 40 - 0.91 0.73 0.62 0.42 0.41 0.34 0.28 0.23 0.20 0.20 45 - 1.00 0.80 0.68 0.58 0.46 0.38 0.29 0.24 0.21 0.20 50 - - 0.87 0.74 0.64 0.80 0.40 0.31 0.24 0.21 0.21 55 - - 0.94 0.80 0.69 0.54 0.43 0.32 0.24 0.21 0.20 60 - - 1.00 0.87 0.74 0.58 0.45 0.32 0.24 0.21 0.20
65 - - - 0.91 0.79 0.62 0.46 0.31 0.23 0.20 0.19 70 - - - 0.96 0.84 0.66 0.48 0.30 0.22 0.18 0.17 75 - - - 1.00 0.88 0.70 0.48 0.296 0.20 0.16 0.15 80 - - - - 0.92 0.74 0.49 0.27 0.18 0.14 0.13 85 - - - - 0.97 0.78 0.49 0.25 0.15 0.12 0.10 90 - - - - 1.00 0.81 0.49 0.23 0.12 0.09 0.07
Notes:
1. Waves are diffracted around the upcoast headland and the control line is defined between this headland and the transition point. At the transition point, the tangentto the beach is parallel to the offshore wave crests. The control line has length R, and is angled /3 to the wave crest line.
2. The relationship between R /R, and 8 for varying values of fJ as shown above can be used to determine the equilibrium bay shape.
Source: CIRIA (1996)
68
Figure 15 - Artificial Head lands
69
Figure 16 - Formation of Artificial Headlands by Groins and Detached Breakwaters
Rs = (..E.1_)312
A where A = 0.21D 0·411 and A is a dimensional factor with unit m 1/J
D = grain size in mm
~ I
A
Source: CIRIA (1996)
(a) Section A-A
Figure 17 - Configuration of Underwater Sill and Associated Sand Beach of Relatively Mild Slope
z
Berm v.1dth
Nourishment profile
Berm crest elevation
Beach slope
---------- ...... ' --+-----\-----------''c...:--'""':---f'-----------------High water
' ' ' ' Critical profile
' ' ------~--------~~~----------------~'~--~~~~------------------------X
Original profile
Figure 18 - Monitoring of Beach Profiles
.... 0
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