Storm Hazard Mitigation Structures 30.3 Shoreline Stabilization Structures 679
Part C | 30.3
Direction of net longshore
transport
Direction of net longshore
transport
Groin adjusted
shoreline
Groin
adjusted
shoreline
Groin adjusted
shoreline
Groin
shoreline
Original
shoreline
Beach
Ocean
Ocean
a)
Beach
b)
Nourished (MHW)
shoreline
MHW
shoreline
(dominant)
MHW shoreline
(dominant)
Bermline
Shore-passing
Over-passing
Through-passing
Q offshore
Q net
Q gross
Y min (MHW)
(Design storm)
Original shoreline (MHW)
Base (reference) line
Design
beach
width W Bermline
Waves (dominant) (H o , H b ) T, Θ
a)
X g
Original shoreline (MHW)
MHW
MHW
MLW
MTL
Base
(reference)
line
Protected
uplands
(cliffs,
dunes,
man′s
artifacts)
(Vegetation
line)
Y min (MHW)
design storm
Design
width W
e
Berm
Minium
section profile
Average, nourished, MHW shoreline
Crest
elev
Nourished, downdrift
Nourished, updrift
Gr oin
Y gd (downdrift)
Y gu (updrift)
b)
Z g (Y )
d g
Z b
Y g
d 50
d 50
Y gd
(downdrift)
Y gu
(updrift)
Bypassing
Y g
e
Fig. 30.26a,b Definitions of
variables in groin field design
Fig. 30.25a,b Schematic of (a) single groin and (b) groin
field displaying down drift impacts J
long-shore transport such that sand is deposited on the
up-drift side and consequently absent on the down-drift
side as illustrated in Fig. 30.25.
The net long-shore transport direction is revealed
(sand accumulates on the side of the groin from the updrift direction). How to maintain a minimum width of
beach at the down-drift side has always been of concern in coastal engineering design. As illustrated in
Fig. 30.26, the present-day philosophy of groin design
is to combine the structure with a beach nourishment
project to:
1. Minimize down-drift impacts
2. Maintain some basic level of coastal hazard mitigation as defined by Y min after storm erosion e, and
3. Allow some sand bypassing around the end.
The basic rule of thumb for the ratio of groin spacing X g to the groin length Y g is X g =Y g D 23 as found
from many years of experience to satisfy the three design goals listed above [30.88]. Note that the groin
Part C | 30.3
Direction of net longshore
transport
Direction of net longshore
transport
Groin adjusted
shoreline
Groin
adjusted
shoreline
Groin adjusted
shoreline
Groin
shoreline
Original
shoreline
Beach
Ocean
Ocean
a)
Beach
b)
Nourished (MHW)
shoreline
MHW
shoreline
(dominant)
MHW shoreline
(dominant)
Bermline
Shore-passing
Over-passing
Through-passing
Q offshore
Q net
Q gross
Y min (MHW)
(Design storm)
Original shoreline (MHW)
Base (reference) line
Design
beach
width W Bermline
Waves (dominant) (H o , H b ) T, Θ
a)
X g
Original shoreline (MHW)
MHW
MHW
MLW
MTL
Base
(reference)
line
Protected
uplands
(cliffs,
dunes,
man′s
artifacts)
(Vegetation
line)
Y min (MHW)
design storm
Design
width W
e
Berm
Minium
section profile
Average, nourished, MHW shoreline
Crest
elev
Nourished, downdrift
Nourished, updrift
Gr oin
Y gd (downdrift)
Y gu (updrift)
b)
Z g (Y )
d g
Z b
Y g
d 50
d 50
Y gd
(downdrift)
Y gu
(updrift)
Bypassing
Y g
e
Fig. 30.26a,b Definitions of
variables in groin field design
Fig. 30.25a,b Schematic of (a) single groin and (b) groin
field displaying down drift impacts J
long-shore transport such that sand is deposited on the
up-drift side and consequently absent on the down-drift
side as illustrated in Fig. 30.25.
The net long-shore transport direction is revealed
(sand accumulates on the side of the groin from the updrift direction). How to maintain a minimum width of
beach at the down-drift side has always been of concern in coastal engineering design. As illustrated in
Fig. 30.26, the present-day philosophy of groin design
is to combine the structure with a beach nourishment
project to:
1. Minimize down-drift impacts
2. Maintain some basic level of coastal hazard mitigation as defined by Y min after storm erosion e, and
3. Allow some sand bypassing around the end.
The basic rule of thumb for the ratio of groin spacing X g to the groin length Y g is X g =Y g D 23 as found
from many years of experience to satisfy the three design goals listed above [30.88]. Note that the groin