CHAPTER
83
COASTAL
SAND
MANAGEMENT
SYSTEM
by
Birchard
M.
Brush
Scripps
Institution
of
Oceanography,
University
of
California
La
Oolla,
California
92037
ABSTRACT
Interruption
of
sand
transport
is
the
most
persistent
worldwide
coastal
problem.
Wave
action
produces
sand
transport
which
is
not
a
problem
in
some
areas
but
in
others
results
in
coastal
erosion,
obstruction
of
harbor
entrances,
and
permanent
loss
of
sand.
Conflict
between
saving
sand
and
bypassing
it
is
caused
by
a
lack
of
methods
to
manage
this
valuable
resource.
Separate
elements
of
control
have
been
used
with
varying
degrees
of
success;
now
it
is
proposed
to
incorporate
subsystems
into
an
integrated
system
for
management
of
the
littoral
transport.
A
coastal
sand
management
system
is
to
be
evaluated
using
three
principal
subsystems:
(1)
a
mobile
jet
pump
for
use
with
a
crater
sink
and
fluidization
accessories;
(2)
interlocking
inertial
modules
which
simulate
structural
materials
because
of
high
intergrain
stresses;
and,
(3)
the
tactical
deployment
of
phase
dependent
roughness
elements
to
direct
(or
reverse)
the
net
transport
of
sand.
A
coherent
sand
management
system
promises
to
make
a
start
toward
true
control
of
littoral
sand
transport.
In
addition,
there
is
the
prospect
of
eventually
establishing
the
first
self
maintaining
harbors.
It
is
attractive
to
consider
systems
which
would
be
operative
within
reasonable
cost,
which
may
be
entirely
submerged,
and
which
are
capable
of
operating
without
regard
to
surface
seakeeping
problems.
Some
aspects
of
the
system
indicate
possible
use
of
the
mobile
jet
pump
as
a
means
for
estimating
longshore
transport
in
the
field,
use
in
archaeology,
and
as
a
dredging
and
maintenance
tool
for
small
nations
whose
investment
capital
could
not
support
massive
dredging
operations.
INTRODUCTION
Everything
in
the
coastal
zone,
as
with
life
in
general,
turns
into
a
system.
It
can
be
a
system
at
the
outset,
or
through
insufficient
planning,
become
one
at
a
less
convenient
time.
An
example
is
the
construction
of
a
coastal
feature
which
may
have
been
erected
without
regard
to
all
of
the
factors
bearing
upon
the
problem,
and
which
then
possibly
caused
new
problems
by
its
presence.
Historically,
there
did
exist
unique
and
systematic
means
of
coping
with
littoral
drift
around
1500
B.
C.
Two
types
of
harbors
are
known
to
have
existed
during
those
times;
continuous
self-flushing
harbors,
which
accomodated
large
numbers
of
ships
even
by
today's
standards,
and;
flushable
harbors,
which
were
periodically
flushed
in
the
manner
of
a
modern
tank
toilet,
for
the
removal
of
sand
and
silt.
Exemplary
were
the
harbors
of
Tyre
(rhymes
1503
1504
COASTAL
ENGINEERING
with
fire)
and
Sidon
(rhymes
with
widen)
on
the
coast
of
Phoenicia,
locations
that
on
modern
maps
are
on
the
southern
coast
of
Lebanon.
In
332
B.
C,
a
year
before
his
death,
Alexander
The
Great
laid
seige
to
Tyre.
To
gain
access
to
the
walled
city
which
was
on
a
small
offshore
island,
he
built
a
causeway
which
interrupted
the
current
flow
through
the
harbor,
and
the
divided
portions
of
the
harbor
began
to
accrete;
the
causeway
became
a
tombolo
through
continued
accretion
of
sand.
The
method
of
cleaning
the
harbor
was
lost
at
the
time
of
the
Romans
and
the
harbor
remains
sand
covered
today.
The
harbor
at
Sidon
was
flushed
by
a
system
of
two
large
sea
water
storage
tanks
filled
by
wind
driven
swell
in
the
absence
of
large
tidal
range
which
when
discharged
into
the
harbor
could
cause
enough
current
to
entrain
sediment
and
thus
make
it
available
to
bypass
along
the
coast.
While
wise
enough
not
to
resist
Alexander,
this
knowledge
of
the
harbor's
manner
of
operation
was
lost
in
about
the
second
century
A.
D.
In
spite
of
the
fact
that
the
resourceful
methods
of maintaining
these
harbors
were
rediscovered
in
the
1930's
by
a
remarkably
astute
French
priest-
archeologist,
Pere
A.
Poidebard,
a
harbor
built
by
modern
engineers
in
T958
at
Tyre,
to
provide
a
Mediterranean
terminus
for
the
Saudi-Arabian
petroleum
pipeline
during
the
Suez
crisis,
silted
up
in
four
months
(McKee,
1969).
Modern
techniques
were
not
available
to
the
ancients,
and
because
of
that
fact,
they
were
quite
resourceful
and
innovative.
It
would
appear
that
today
we
are
'hoist
by
our
own
technological
petard'
in
that
sand
handling
and
dredging
skills
are
available
only
in
single
expensive
remedies,
if
at
all.
At
the
Scripps
Institution
of
Oceanography,
a
coastal
sand
management
system
is
now
under
study.
Its
aim
is
to
establish
methods
for
remedial
sand
bypassing.
The
coastal
sand
management
system
consists
of
(but
is
not
limited
to)
three
principal
subsystems:
(1)
the
crater
sink
sand
transfer
system
with
optional
fluidization;
(2)
ballasted
interlocking
inertial
modules;
and,
(3)
the
tactical
deployment
of
phase
dependent
roughness
elements
to
direct
the
net
transport
of
sand
(Inman
and
Tunstall,
1972)
(Figure
1).
The
Crater
Sink
The
'jet
pump',
a
form
of
eductor
using
the
kinetic
energy
of
pumped
clear
water
to
entrain
sediment
laden
water,
has
undergone
design
and
perfor-
mance
improvements
in
recent
years.
Originally
used
in
the
1840's
for
water
wells,
and
more
recently
as
an
aid
in
maintaining
suction
lift
for
dredge
mounted
centrifugal
pumps,
it
now
promises
to
become
a
dredging
means
when
used
alone
(it
was
first
proposed
for
coastal
sand
handling
in
1911)
(Knowles
and
Rice,
1911).
The
jet
pump
may
be
used
to
form
and
maintain
its
own
crater
(Inman
and
Harris,
1971),
thus
maintaining
an
intentional
and
purposeful
sink.
A
header
of
flow
controlled
valves
may
be
used
as
an
adjunct
to
the
crater.
It
would
use
a
portion
of
the
driving
water
to
fluidize
the
sand
bottom;
the
increase
in
pore
pressure
reduces
the
coefficient
of
internal
friction
of
the
sand
and
permits
it
to
flow
freely
under
the
influence
of
currents
and
gravity.
The
current
which
feeds
secondary
flow
to
the
inlet
of
the
jet
pump
would
then
carry
additional
sand
to
the
crater
where
the
inlet
to
the
jet
pump
would
be
enriched.
COASTAL
SAND
MANAGEMENT
1505
QJ
CU
4_>
rt3
•
*->
IA
CU
fd
E
S-
.CI
fd
-M
O
S-
-M
4->
rd
S-
E
T3
>>
<U
C
cn
fO
S-
-a
V)
OJ
E
E
rd
j*:
cu
c
4->
>>
•.-
%-
E
x:
ISl
CU
OJ
ex
1
-C
E
ro
S_
+j
ai
s-
cu
o
>
Dl
+->
o
o
rd
s-
E
c
s~
o
to
u
•
a
a>
s-
E
u
d)
QJ
<o
o
JZ
+-»
v»
4->
rd
4-
:s
4-
O
m
.^
O
s-
ro
E
rd
OJ
c
o
s-
O
'1-
>i-Q
•
r-
-P
•
P
3
r—
fO
CJ
-P
O
O
i~
-P
x:
OJ-P
a
On-
a.
E
O
S-
E
ro
E
o
2
x
ow
O
0)
3
XI
i—
CD
o
E
-p
E
-
O
fd
at
ID
-p
•
p
cu
>>
VI
r—
"CJ
-O
>>JD
cu
^
t/i
E
>>-P
d)
O
i/l
•
P
Ulr-
C
U)
Q.Q)
ai
fd
cu
>
E
-O
—
CU
V)
l/>
ram
w
c
rflr-
+J
ai
E
rs
E
-P
ro
-a
cu
E
E
o
E
-r-
E
0)
-a
i—
s-
E
i—
CU
CU
fd
rd
T3
in
•!—(/)
c
•
p
in
3
r—
S-
CU
(O
ID
C
S
•
P
E
J=
O
to
•
>-
cn
sr
rd
13
o
cn
o
cu
u
E
s-
s-
•
r~
fd
ct
.^
-p
O
E
I/)
O
OJ
-t->
•
i—
-O
E
i—
S-
E
CU
<U
cu
E
CU
-P
Q-
CU
S-
E
CU
i—
cn
1506
COASTAL
ENGINEERING
A
portable
system
is
being
assembled
which
consists
of
a
trailer
mounted
power
supply
to
drive
a
jet
pump.
This
unit,
fully
instrumented,
will
be
transportable.
It
will
be
tested
in
the
Scripps
Hydraulics
Facility
especially
built
slurry
test
loop.
The
closed
loop
test
fixture
will
provide
baseline
data
on
carrying
capacity,
ability
to
maintain
crater
geometry
by
establishing
quasi-equilibrium
repose
angle,
ability
to
pump
the
crater
free
of
induced
cave-ins,
ability
to
pump
against
slopes,
and
will
continuously
record
the
parameters
of
interest
(Figure
2).
The
desired
information
will
include
hydraulic
head
differentials,
mass
transport,
flow
velocities
and
establishment
of
Newtonian
vs
Bingham-
plastic
relationships.
After
completion
of
the
laboratory
phase,
the
design
will
have
been
refined
in
such
a
manner
that
it
may
be
transported
to
a
field
location.
The
packaging
will
include
a
mobile
power
pack
consisting
of:
engine,
hydraulic
pump,
fuel,
and
instrumentation
panel.
Standard
process
electromagnetic
flow
meters,
an
important
adjunct,
will
be
used
both
in
the
test
loop
and
hopefully,
be
modified
for
underwater
use
in
the
field.
A
submerged
drive
will
power
the
pump
from
as
near
as
possible
to
the
water
pump
to
avoid
paying
the
hydraulic
head
penalty
associated
with
surface
pump-
ing
(Hammond,
1969).
An
air
boost
is
an
option
which
will
be
studied
to
determine
its
contribution
as
a
velocity
modulator,
and
as
a
means
to
augment
hydraulic
head
differential.
It
should
be
noted
that
this
method
holds
promise
for
use
in
shallow
water
dredging,
for
which
no
satisfactory
method
now
exists.
In
addition
to
a
static
application
such
as
a
crater
sink,
it
has
application
to
dynamic
methods
such
as:
1)
programmed
'sweeping'
of
a
river
channel
or
harbor
entrance,
or
in
response
to
wave
climate
information
from
sensors;
2)
riding
on
the
decks
of
ships
using
the
harbor
entrance
(the
hitch-hiking
feature
could
be
a
portion
of
the
harbor
fees)
for
tide
phased
agitation
dredging
(Figure
3);
3)
arrayed
in
fixed
grids
on
the
bottom.
Units
would
be
operable
singly
or
in
groups
in
response
to
storm
impulses
or
wave
climate
changes
either
by
operator
choice,
or
as
part
of
a
feedback
loop;
and,
4)
arrayed
in
series
along
a
channel
to
resuspend
sediment
and
eventually
direct
it
to
a
crater
sink.
In
addition
to
the
above
direct
applications
for
a
mobile
shallow
water
sediment
bypassing
system,
the
following
uses
should
be
studied:
1)
the
removal
of
sediment
from
dams
and
other
river
and
stream
obstructions;
2)
use
as
a
means
of
excavating
a
reference
crater
or
channel
along
a
sandy
coast
or
harbor
channel
for
the
purpose
of
estimating
littoral
drift
or
channel
accretion;
3)
use
for
dredging
sediment
containing
trapped
gas
(presently
considered
impossible
to
dredge
because
gas
pockets
break
the
suction
on
surface
mounted
centrifugal
pump
dredging
equipment);
4)
use
for
shallow
water
archaeology;
and
inland
excavation
by
wetted
crater
if
clear
water
may
be
pumped
to
the
excavation
(crater)
site.
H.
B:
The
only
present
options
available
to
underwater
archaeologists
are
the
air
lift,
which
requires
large
hydraulic
head
differences;
and
the
water
jet,
which
suspends
as
well
as
removes
sediment
thus
limiting
underwater
visibility
and
not
remotely
relocating
the
sediment.
5)
use
in
nations
whose
economic
capability
is
limited,
who
cannot
afford
monster-dredge
overkill.
Many
small
harbors
(for
example;
fishing
harbors
and
marinas)
could
benefit
by
a
small,
efficient
portable
machine
to
control
sediment.
Further,
the
possibility
of
enhancing
sediment
movement
by
the
use
of
two
pipes,
properly
sized,
with
no
machinery
or
external
energy
requirements
should
be
studied
COASTAL
SAND
MANAGEMENT
1507
zoo.o:a.
<c
i-s:
o>-
,,_
r>
XZ4-J
—
CTl
^~
n.
OJ
to
-a
4-
ci>
-P
^
t.
fO
<ii
-I
l+_
V
f/>
m
0
<=.
>
0
fl>
.n
-M
^
-n
>
c:
m
fW
m
0
0
n
fc-
-^
-1
m
4J
ft
+->
0)
m
l-
Cn-M
tj:
(TJ
c:
tlJ
-t->
m
(i
n
<3J
Cl)
e^:
•
>
(U
0
t.
0.
0
4->
o
-0
•*-*
*
<
s-
O
-n
(i>
m
T3
«*-
(/?
<
~i
0
>,
s_
OJ
**-
0
(Tl
.0
0
-a
<l!
<r
m
+-*
0
m
-s
0
c~
,0
cu
&
a.
Wl
.c
(ii
<r.
CD
t)
m
«J
c
t.
>
c
c:
O
x:
+J
\-
0
n
a.-a
%-
*-
?
•
•
<u
e
-*
<n
n
C1J
t
>
0
t/1
-0
a;
+J
15
^,
a.
>>
*>
CL
^
C
4-J
0
fsi
to
•
r-
0)
a
~s
-a
cr
>,
13
•
—
+J
c:
\~
m
\A
e
ai
4->
0
xz
TO
QJ
cu
O
S-
t/>
•
*-»