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