Engineering of Dunes
Protection Benefits of Coastal Sand Dunes
In addition to providing habitat for a variety of species,
coastal sand dunes are an integral part of a wellplanned coastal defense system. Coastal sand dunes act
as reservoirs of sand that help the beach maintain its
equilibrium and preserve the ability of the beach to
respond naturally to storm events. Beaches evolve
during a storm by taking on a more dissipative state
that causes waves to break farther offshore, reducing
the wave energy near the shoreline. During this
transition, the beach slope is reduced and one or more
sand bars may form. e bars are formed as sand is
transported offshore during the peak of the storm and
is deposited near the region of most intense wave
breaking. During smaller storms, the waves don’t reach
the base of the dune, and the erosion is limited to the
beach face (berm) itself. e dunes only become active
during moderate to large storms when the dissipation
created by the bars is insufficient to prevent the waves
from attacking the base of the dune. As a dune erodes,
it releases a portion of its built-up reservoir of sand
into the littoral system, where it contributes to bar
formation and the development of a more dissipative
profile, ultimately reducing damage to inland
infrastructure. Larger dunes can withstand more wave
activity and therefore provide more protection to areas
behind them. In the simplest terms, the sand stored
in a dune buys time and provides protection from
severe storms.
FEMA Dune Standards
Although dunes of nearly any size are beneficial, in
order to be considered as a barrier to coastal flooding
for flood insurance purposes, coastal sand dunes need
to meet the size criteria established by the Federal
Emergency Management Agency (FEMA). Based on
an analysis of hurricane-related dune erosion, FEMA
identified the amount of sand stored within the crosssectional area of the frontal half of the primary dune
above the 100-year stillwater elevation (Figure 10A) as
the critical parameter for protection against a 100-year
storm event. It has been established that a dune that is
predominantly below the 100-year stillwater elevation
will be rapidly overwashed and eroded and will not
provide significant protection. As the dune erodes,
sand is transported both seaward into the littoral drift
and landward into the backdune, resulting in a
landward migration of the dune. Along developed
12 Dune Manual
shorelines, this process will ultimately cause the loss of
the dune. A dune that is only slightly above the
100-year stillwater elevation will typically undergo
significant erosion and will deflate, reducing in height
and width. Studies by Hallermeier and Rhodes (1986)
and by Dewberry & Davis, LLC (1989) found that
540 cubic feet of sand per linear foot of dune
(equivalent to 20 cubic yards per foot) was required to
resist the 100-year storm. FEMA’s current V-zone
mapping procedures (FEMA 1995) are based on these
observations and require this quantity of material be
present in the cross-sectional area of the frontal half of
the primary dune, above the 100-year stillwater
elevation (Figures 10A and 10B), to be considered
substantial enough to withstand erosion during a base
flood event. is criterion is commonly referred to as
the FEMA 540 rule.
Dune Removal
1’
100-Year Stillwater Elevation
Erosion
50’
Dune Toe
Erosion
Dune Retreat
100-Year Stillwater Elevation
D
o
siti
o
p
e
n
Initial beach profile
Changed Segment
(Eroded Profile)
Figure 10A. FEMA's current determination of dune retreat and removal.
Figure 10B. Factors to be considered in determining dune failure and V-Zone mapping.
More recently, post-storm surveys have indicated that an
even larger volume of sediment is necessary to withstand
significant erosion events. e revised FEMA Coastal
Construction Manual (FEMA 2000) recommends a
minimum frontal dune volume (measured the same way
as the 540 rule) of 1,100 cubic feet per linear foot
(equivalent to 40.7 cubic yards per foot) above the 100-
year stillwater level. Since the National Flood Insurance
Program (NFIP) regularly encourages communities to
establish standards above the minimum NFIP standards,
New Jersey has taken the proactive step of referencing
this higher standard in its Coastal Zone Management
Regulations, although it is not yet required in the rules.
Currently, very few communities in New Jersey even
Dune Manual 13
meet the lower standard. However, federal beach
nourishment programs are authorized for the majority of
New Jersey's Atlantic coast communities. In Ocean,
Atlantic, and Cape May counties, the approved federal
projects include construction and maintenance of dunes
of specific dimensions, with the dune crest typically 12
to 22 feet above sea level (U.S. Fish and Wildlife
Service 2005). ese approved dunes, along with the
associated beach berm, have been determined by the
Army Corps of Engineers to provide sufficient storm
protection. Projects to enlarge or modify a Corps-built
dune should be reviewed by the ENSP and the U.S.
Fish and Wildlife Service before starting any work.
Likewise, any proposals for dune building in
Monmouth County should be reviewed by the ENSP
and the U.S. Fish and Wildlife Service, since the
Corps-approved beach nourishment program in
Monmouth County does not include any dunes.
Human-Induced Modifications of Dune Systems
e ability of a dune to withstand the extreme forces of a
severe storm event can be either enhanced or diminished
by human modifications to the dune system. Dunes are
dynamic features that naturally erode during extreme
storm events and then recover when storm conditions
subside. Although robust dunes have been shown to be
extremely effective in minimizing damage during even
very large storm events (Barone et al. 2014), several New
Jersey communities have sought to supplement the
protection provided by these natural systems by
incorporating a non-erodible core to their existing or
planned dunes. Some of the materials that have been
utilized and/or proposed include geotextile cores, rock,
and steel/vinyl sheet pile. e objective is to combine the
aesthetic and habitat benefits of a dynamic beach and
dune system with the robust storm protection provided
by a structural core.
Although constructing a dune core can have significant
benefits from a storm-protection standpoint, there are
several important factors that must be considered. Hard
structures that are routinely exposed to wave activity
have been shown to accelerate erosion in front of and
along the edges of the structure; therefore, dunes with a
structural core must be properly maintained. After storm
events, the beach fronting a dune with a structural core
should be restored as soon as possible to ensure that the
exposed core does not create additional erosion. When
constructed on eroding beaches, dune cores should only
be considered within the context of a larger beach
management strategy that addresses the long-term
sustainability of the beach in front of the dune, including
the potential impacts to habitat for rare and listed species
(evaluated in coordination with the ENSP and the U.S.
Fish and Wildlife Service).
Examples of Engineered Dune Stabilization Methods
Geocore
Geocore refers to one of several approaches in which
the natural beach sand is encased in a geotextile fabric.
Geotextile is a synthetic woven product that is used in
many soil-stabilization projects to increase the strength
of the soil and maintain proper drainage. e two
most popular forms of geocores used in beach
stabilization projects are geotubes (Figure 11) and
geocubes (Figure 12). In both cases, the geotextile
containers are manufactured offsite and are shipped to
14 Dune Manual
the installation location where they are filled
mechanically with sand from the beach on which they
are being deployed. Geocores are frequently viewed as
a quasi-soft approach to shoreline stabilization and in
some locations may be preferred over rock and/or
sheetpile.
Geotubes come in a variety of shapes and sizes;
however, the most common for dune-core applications
is an oval-shaped tube with a diameter of between 4
generally preserved. Currentl t
imental system
ed in Oce
ity a
wn ge u
rsto
installation in New Jersey is
dy.
excavator (Figure 12). e manufacturer of the
product suggests that one of the advantages of the
product compared to geotubes is that if a single unit or
compartment fails, the integrity of the structure as a
whole is generally preserved. Currently, the only
known geocube installation in New Jersey is an
experimental system deployed in Ocean City after
Superstorm Sandy.
Rock
Superstorm
Figure 10Figure
. pose11.
d geExposed
otube geotube
e uperstoafter
rm Sandy
in Oce Sandy
t Nin
ew Je ey.
Ocean City, New Jersey.
and 8 feet. e geotube casing is typically filled by
pumping a water and sand mixture, known as a slurry,
into the casing through a fill port. As the geotextile
material is porous, the water percolates through the
fabric, leaving behind a large-diameter, sand-filled
17 | P a g e
tube. Geotubes have been used in several locations in
New Jersey, including Strathmere, Atlantic City, and
Ocean City on the ocean coast, and at Mordecai Island
in Barnegat Bay. e installation in Ocean City was
completed just prior to Sandy, and although the most
Figure 13. Exposed dune rock core after Superstorm
Sandy in Bay Head, New Jersey.
severe impacts of the storm were experienced well
Figure 12. posed dune rock core e upe torm Sandy in B
New Jerse
north of the project site, the geotube core performed
SheetthePile/BulkheadGenerally, rock dune cores are constructed as rock
its intended function and successfully absorbed
Most modern sheet pirevetments
ts already
are co existing beach.
d us e
steel or v l
le dune corbacking
e projecan
et
wave impacts.
structures
are
usually
covered
in
sand,
and
in
some
however, many of the older bulkhea
ects were c nstructed out of timber. tee
cases,
planted
with
dune
thetroverall
li grass
ndto
eaimprove
se
uction. Similar to o
sheet piused
le is typically used due to its
Geocubes are a relatively new and less commonly
aesthetic
appeal
of
the
project.
Current
practice
is kto
c
o
r
e
s
ta
bi
l
nt
e
h
pi
l
e
w
l
o
bul
head is to funct
i
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n
a
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o
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c
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,
t
he
i
approach for stabilizing coastal dunes. A single
independently
last line of defense dudesign rock
recores
storms
.
el s ast traditional
p walls revetments
n or bulkheads ha
geocube consists of a series of interconnected
the event
become
during lalsstorm.
widwith
ely uansed throug in N
ersthey
y. M
an exposedlde
re
ber bulkheads w
rectangular compartments that can be filled
intended to serve a thDesign
ctiorevetments
n f r t e canmmu
oasguidance
tal pro efor
n inloboth
catethe
d behind them
be found
e Engineering
utilize heeManual
t pile (U.S.
heArmy
ads toCorps
formofa dune core to prev
communities have decCoastal
breaching o
torm. TCUR;
his technique has b
achEngineers
a
systand
em theriRock
ng Manual
se ere s(CIRIA;
2002)
incorpo ted
eraCETMF
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,
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After Superstorm Sandy, many g Sandy Hook and
Mant lok g. The procommunities
a direct result of the ca
ct Ma oinl New
kingJersey
was pointed
rtaktoentheaseffectiveness
hed in multiple loca
ndyrelict
damage ex rienced of
duBaygHead’s
, rock
re tseawall
he barrie
spit breac
in rprotecting
the
community (Walling et. al. 2014; Irish 2014) as rationale
for their own proposed dune enhancements. During the
2015-2016 winter, several sections of the Bay Head
seawall were undermined, illustrating a potential
shortcoming in the traditional design philosophy and
highlighting the importance of maintaining a wide beach
Figure 12. Trapbag geotextile (geocube) container
Figur
e
11
.
apbag
ge
o
t
x
(
ge
o
cube
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ns
al
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at
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.
installation in Ocean City.
in front of proposed dune core projects.
ock
enerally, rock dune cores are constru e as ck
covere i and,
each. The structures e usu
Dune Manual 15
etmen
ome
d
king an already existing
, planted with dune grass
These flat berms which can be 150 to 300 feet wide contain an ample
natural dune development (Figure 15). The rate at which the dunes w
rategeast tiwohi
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y sdmsaelcl ovn
eent,
borethtaainipr
ya
fosraarth
pl
cporimary
nda
du
edar
of theofvseagnd
etpl
atiaocen,mfe
ncbo
ingth
, aand
e
its
lrfyindu
an
/Crossovers
foredudune
nes pcore
reviously eare
xistedf.oredunes previously existed.
sheet
ve beus
en. Afony
und
esize(mulprojects
tiple dunune
e lisne
e fepile
ataur
ive value o Most
coamodern
staldun
xim
arse) cha
onti
breo
akn nourished beaches because of the
constructed
steel
in
uriello, 2001).
dism
up
y t(oNromrd
tro
example, an 8.6 million yd
nha
et dorsevinyl
dune become
s an aree
ausing
w enc
ro
ivsheet
eenptospile;
er pl
ohowever,
susrg
em
andanwdavM
esaare
New
Jersey
there
are
many
older
timber
bulkheads
that
ot welid
bewa
rm
nO
te a 1
ekasch fill proojectasto
t recre
s aan
ed. Typically, water sebe
an0d0 isfofunn
ede to
rdian
y cean ity, ew Jersey, successfully reessentially
perform
the
same
function.
Steel/vinyl
sheet
rodwibth
(Noerds
alnceyscle of duene
uriello, 2001). Within 5 years
stabl
d tehe na
pot in a dune. Unforetuna
teishe
, nc
u turdu
o gro
le mat
rial,tro and
pile
is
typically
used
due
to
its
durability
and
ease
of
ration of t flow ac oflesraand
tes plraoce
iom
n ent, bothflaow
voidry du
ve
n regions were only small
primaryInaonrddesreto
coanda
construction.
Similar
to
other
dune
core
stabilization
s hazar us onditi f,oredeuw
co exis
detred. the preferred means of
neasl pvrervsioausly
approaches,
the
intent
of
the
sheet
pile
wall
or us.
s, since
low the d e line
e ain continuo
dunes system er a
Figure 15. A phot et howi
he development
bulkhead is to function as a last line of defense during
severel roded beach.
tairs and/or ramps on both the
ypsevere
ic storms.
t
ere
strusheet
c pile
s ctechnique
o s ting has
o sbeen
across the dune crest. Ideally,
a
, at
ithseveral
a fla shoreline
c
tructuinreNew
incorporated
locations
n natural
er structureJersey,
c including
tr te Sandy
n such
a and Mantoloking.
s noCo
t inn
tecl
rfeuresiwoith
r that it doee
Hook
Coastal sand dunes make up a very important feature o ur beaches.
wth of du
s s, includiMantoloking
ng e ovebulkhead
en fwas
sand
and the ginroresponse
constructed
to ne vegetation. Dune
ha
bita
fonrslo
cal vegetation and animal species, but they also
tur
tFiygur
picaeall15
dim
nstio
o en usthe
ed in
a that
whoccurred
er t rduring
e is heSandy
avy fothat
ot traffic, anadna
dunes system er a
. Aepho
t eare
t howi
he development
breach
p
ro
v
id
e
s
ig
n
i
f
ic
an
t
p
r
o
t
e
c
t
io
n
f
ro
m
s
e
v
e
re
c
o
as
t
a
l
s
t
rms
gur
enc
t ho
wri cons
hetrde
opm
ent
pr
je. Artificially
e e
fo
ucvtielng
weant
lkover dunes system esreaveno
on
tencompromised
ded us of the
strFi
uccoastal
turee15
. evacuation
A. Afupho
ll gtuida
reur
l hm
rode
d obe
ach.
a major
route.
venthe
po
os,d beoach.
viding even greater protection than naturally
veerte
raolede
n New rs project
ca successively
found inresisted
the Nethe
w Jerosive
ersey Cforces
oastal Zoneha
Ma
agseem
neltnti
Rul
pr
A.C.7:7E associated
al,with
r mu
iple fJoaquin
amily onor’easter
r public band
eacwinter
h acCo
ceospsneecl
sr,lytuhdsi
eesw
r maintained. However, both natural and man-m
oigalk
nneodveand
thelt2015
dto
ym
naseamic
sy
st
w’ille- cuopnsata
chaong
nvesir.o
u
oinenns
ust not excstorm
ee Jonas,
t whowever,
ide Co
in ovn
ecl
rabeach
ll dsiim
ionsof, athe
ndwall
musC
min
omak
tealt asan
d eim
dm
uun,m
easnd
ventl
ryyimp
rtaensthfap
eateuba
resoed ounr the
beaech
the
front
at tliry
he
seite
.trt
ofterfd
toreeporopeurly
decshiges
n and mai
ntain the
a healthoyvibde
each a
ce above theroded
e dunesignificantly.
crest. WCalk
ovtseveral
ealrssan
fordsdinugnlee15
are
mit
oIn
teatrw
oIn
as
sfamily
mak
euuspe aof
imp
a4nta
bea
onl
avena
tur
adl oha
bi
teefo
rulid
ocal vegreta
tion an. dNaonit m
alysdo
pecies,ybpr
ut they also
dunes system er a nour hment pr je
Figur
e 15.places,
A phot to
et 20hofeet
wi
he development
a minimumwall
of 3were
’ - 0exposed
” o cleaaran
cthe
e aab
ovbi
e ta
thhighlighting
dur nloeccare
set.geSpta
trrogur
uvcoid
tur
ensdaarenipho
im
nte
natur
l ha
tefo
l vthe
ti
neea15
alnd
sppe
echo
st,iobwnuti fro
the
ysaede
lvso
ha
easthe
itydune
to
an
rdeoedcbe
ttieto
mhe
evre
tant
l asbi
tolrms
. Arstifsic
y
ysial
telm
Fi
elocvo
pm
e
after
storms,
sesvige.nrAeiflic
rottde
ach.
ast possible amount of disruppti
o
n
to
t
he
na
t
ur
a
l
du
ne
,
a
nd
t
hu
s
a
r
e
r
e
qui
r
e
d
to
rovide saigwide
nificbeach
ant pin
rofront
tectioofn fha
rovme sthe
evepo
rete
conti
asatlaol storms
. ng
Arteifviceial
nehevarenrpece
nde
endsy
staneach.
m
ovidi
n glyreesat
ro
thbe
nas turally
l dtedrcuotio
importance of maintaining
t either 10 feet seaward of ha
theveline
o
f
pe
r
m
a
n
e
n
t
be
a
c
h
du
ne
v
e
g
e
ta
ti
o
n
,
o
r
at
t
he
tential o ovidingpreovpeenrlyredat
pro
c iomnatihnta
anine
nad.
turally
g dthunna
estur
, ifal and man-m
eseigr ne
dtaend
Howfeovremin
r, bo
the structure.
Co
nthe
clupo
sio
n
ontal dune. Support postspr
aroepneortlytodebe
e
nc
a
s
e
d
i
n
c
o
nc
r
e
t
e
,
s
ho
ul
d
h
a
v
e
a
signed and maintaidne
Hu
ow
ven
rm, ,bo
th na
l ata
ndntl
myacnha
-mad
nesba
are
ynd.amic
syest
and
willtur
coans
ngeesdhuap
sepdart
on othe enviro
si
a ven
rycl
imp
orto
ant feature o ur beaches. Not only do they provide
Coastal sand dunes make upCo
oil penetration of 5 feet, anddysnhamic
ould sy
allst
ow
fo
r
th
e
e
r
o
s
i
o
n
o
a
nd
dur
i
ng
a
s
to
r
m
em, and will consoata
edu
sohn
nrly
the
nv
onm
enta
fa
cto
rhsepr
tntl
they csha
iteng
. In
rap
deer mak
tba
o psereodpuoep
dveeesry
igniran
d mai
au
altehsyent
beach a
as
nnlttain
a natural habitat for local veC
geta
titoaln saan
nddani
mael sspe
cies, butathe
y alsimp
o haovrt
e athe
afebiat
lityre
to o ur bea
ch and Dune Walkover Guidaetlin
e
s
)
the site. In order to properly dtur
esign anbi
d mai
tain acahlevaletg
hy ta
beacohn an
d duni
nemsyasltsepe
m, itieiss, but the
t tnfo
provide significant protectioan fna
rom saelvha
ere cta
oas
alrstlorms
. Are
tificti
ially eannhdanace
d dune sycst
e ms
Figure
15.
A
photo
set
showing
dune
s
s
y
s
t
Figur
e
15
.
A
pho
t
e
t
ho
w
i
he
de
v
e
l
o
pm
e
nt
e
m
e
r
a
no
ur
hm
e
nt
pr
p
ro
v
id
e
s
ig
n
i
f
ic
an
t
p
r
o
t
e
c
t
io
n
f
ro
m
s
e
v
e
re
c
o
as
t
a
l
s
t
o
rms
have the potential o oviding even greater protthe
ectio
n than naturally
ming dunes, if je . Artifi
development
of afordune
22 | P a g e
severte
el raolsystem
ded beoach.
after
ae
nourishment
haine
ved.the
v
i
di
ng
v
e
n
g
r
e
at
e
r
p
ro
t
e
c
properly designed and mainta
Hopo
weventi
r,20
bo|tohP na
tur
a
l
a
nd
m
a
n
mad
e
d
u
n
e
s
a
re
ptio
artnothan nat
a g e at a severely eroded
project
prta
op
erylycha
deng
siegne
dbeach.
ineed.
wenta
verl, fa
bo
thrsna
l and
dynamic system, and will cons
ntl
shap
eand
basm
edaointa
n the
nvirHoonm
cto
prtur
eseant
Conacl
u
si
o
n
yndamic
m, natnd
ha
baitseisd on the
t the site. In order to propedrly
esignsy
anstdemai
ainw
a ill
hecalotns
hyta
bentl
acyh can
dng
dueneshsyap
stem,
16 Dune Manual
Coastal sand dunes make up aavtetry
anot rfdeeatrutre
bea
Nd
otmai
onlnytdo
prtohvyidb
heimp
siteo.rtIn
o poropuerrly
decshigesn. an
ainthe
a hyeal
rs
22 | P a g e
uniform storm protection at the expense of the
creation of more natural dune forms. While there has
been some discussion recently about modifying project
design specifications to allow for the creation of more
natural features, there has been no formal adoption of
these suggestions. Beach nourishment projects
designed without a dune typically have higher and
wider berms to compensate for the absence of the
dune. ese berms, which can be 150 to 300 feet
wide, often provide a unique opportunity for dune
development in areas where the natural sediment
supply is scarce and the beaches are naturally narrow
(Figure 15). e rate at which the dunes will grow on
these constructed beaches depends on the rate at which
the placed sand is transported onto the dune from the
beach berm and on the effectiveness of the vegetation,
fencing, and/or the dune itself in retaining the sand.
Both primary and secondary dune features (multiple
dune lines) have been found on nourished beaches
because of the enhanced sediment supply (Nordstrom
and Mauriello 2001). As an example, a 6.6 million
cubic yard beach-fill project that created a 100-footwide berm in Ocean City, New Jersey, successfully reestablished the natural cycle of dune growth
(Nordstrom and Mauriello 2001). By following a
carefully crafted protocol that allowed the dune to
develop naturally, both a primary and a secondary
dune were developed within 5 years in regions where
only small foredunes previously existed.
Considerations to Dune Engineering
Ahl,ug
tho
rra
efbero
ramb
le
ctoro
etan
cntio
in
tehesar
ar
tioastructures
ns
Aug
ltho
,fpehrra
e, b
fpele
le
fro
ctoalaasp
alastpetal
ro
tpero
sdtpn
an
dtan
ptDune
thtar
e, re
seoetypically
msceoam
lo
alo
ticoaand
ns
ndand
AWalkways/Crossovers
ltho
prheug
am
cforoaasm
ctio
ncttsio
osin
,odtinhpteo,re
oreem
lo
tioecns
walkovers
are
timber
uwat
nhsdewurehnedre
deuw
noalk
evewrs
ootle
ary
uas
cand/or
haare
oon
f min
une and
sitiounsatitsio
nhsio
uwnalk
oalk
vare
eo
rsvneare
nost snpib
sspib
o
r enconsisting
enses,cary
,h
su
sramps
oafsimin
imal
undefront
situat
ew
re
orst are
p
orslesnib
ecle
soesrcary
seuscsof
asc, hsare
sasofaare
min
mal
d
unimal
edthe
stairs
both
Although stabilized dunes with no gaps degrade habitats
de
elt,oepm
seegtievoeta
gtieootarn,tiloown,
rotlo
fotrcoa.tffi
tr
.thIncease
tse
heof
se
thwith
esaereveaasral
re
edeck-type
veral structure
eloevpm
t,erssnpa
egervta
r lfo
oow
fo
csse
a, the
se
thsae, re
eflat
vesral
devede
lovpm
n
snpa
et,vrsespa
n,
trwoatffi
Inca.tffi
hIbackside
encse
thcsae,dunes,
re
for rare, threatened, or endangered (RTE) species, the
esrn
ivwhehsmay
icbhe may
tro
oevpac
roceveid
eatsdsgeacross
at
gera.ethe
dTh
e.as
ercrest.
emfeedrre
is a
altat
ealt
rn
iv
ehsic
icwhhmay
teodvpid
id
ac
eac
ssgcra
ra
eTh
tfpas
etIdeally,
fpedrrre
modewalkover
hisoeadthisodastructure
altern
iveat
wat
ubsedubtseoedupsro
ssecat
. dTh
le
tlepas
ele
errre
tthe
h
dtm
dune
is
protective value of a coastal dune for human
ope
renr-di
rpe
at-resend
trt-eecend
t-ecnd
rpdlar
eicnconstructed
ensnin
tpcra
n
c
e
s
p
ro
v
i
d
e
mi
n
imal
re
s
is
t
a
n
c
e
rsh
er-pe
pecnul
diacrnul
Seh-opSreehr-popereenr-dpic
enu
uedlar
elar
ntcra
ero
s
p
ro
v
i
d
e
mi
n
imal
re
s
is
t
a
n
c
e
shorsh
e-ope
sditracreulestr
ut.
Sut.
hocrut.
nictura
v
i
d
e
mi
n
imal
re
s
is
t
a
n
c
e
such a manner that it does not interfere
infrastructure is maximized when the dunes are
s gasend
e,daythe
npr
d oythe
yovpr
ocoviande
feolwith
rinfu
eglh
i-nvigh
gedune
h-ivcgh
vcfelo
lo
ecthe
tdlylan
indlan
esavasend
ur
n
coantcdui
fonn
rt fu
nn
lhnatural
inigh
eitlo
itloywcfitlo
irlyedcinir
tly
in
. d.
to wto
avw
eto
saavw
nd
ur
, agsneur
d, agthe
vpr
ide
aide
dui
foonrtdui
fu
genn
lo
y-processes,
dyirwfeincluding
cdtw
lan
. movement
continuous. Any break or gap in a dune becomes an area
sm
us
be
ngrowth
ehshof
,picw
hvpicidro
hevegetation.
roele
vid
le
ere
,otfw
ob
re
fbesand
ra
chceaasccshcm
eascus
scem
us
tpr
be
ovpr
atdgeara
alt
rivnthe
,icw
h
vpat
id
at
as
t ast
pere
fpele
ra
le
If beIfacbe
hIfabe
t sbe
otvpr
ide
dide
aotvdgide
asetleat
ra
,ttdgwera
o, dtpw
ra
erb
nle
aetalt
eaestr,iv
waethsiv
ro
ofalt
and
dune
Dune
where the erosive power of storm surge and waves are
sdoit
me
n
sro
totprm
cnt,liuoinc
n,luianc
inntr
gewalkovers
th
e eantr
elesaattsotlused
trde
eisthwiisthheavy
soad
me
ad
italiodsnittal
stal
oprm
de
ing
negleth
eantr
snc
o
ea4at5sltede
4as5gareas
rw
eegitsrhewthere
some
iodnad
oiorm
ero
ctitpoero
nc,ttiieonc
de
nglulaide
nng
g alth
nc
snc
toeaare
atoften
e4e5gsde
in
where
concentrated. Typically, water seeks the path of least
rto
ecstpe
to rtsehe
rretl,ione
tocooin
nge aurt ethur
eonefdpa
rat
aasolm
ldi
l cbl
ckng
adiur
recstpe
toctsthe
ho
rseho
orin,tcoorin
pa
thpaoth
n onon
aeteethandimensions
etdth
eonfedth
thoare
efthth
aasellmbl
lcbl
kng
aodi
respe
he
ho
line
,lione
rp
oen
rrp
atcoerrp
aatosem
kaao
foot
traffic,
and typical
dependent
resistance and is funneled toward any gap or low spot in
the
sesaairde
w
d
de
,aittnpt
ttpt
ede
mtopt
to
ctgtsehe
froflng
m flo
aroigth
htrhoth
seaardw
d as, ride
inem
eam
easacscyew
asyw
. ay.
ehe
cfl
t sethe
urfrgsoeur
ngaigng
aith
gof
ht
ug
ascsecw
the sthe
e aw
n sa,itt
to
flede
eth
. sfor
ctfltde
ur
mfrgfloeom
ht
ug
throehug
athchceGuidance
the ointended
use
the
structure.
a dune. Unfortunately, since natural dunes are made of
Icnath
csa,sitenhe
ste
, tnihe
nto
t flisede
to
postttial
tsial
osrm
seun.rggOrean. de
grade
di
a, stehe
ntte
tteisde
ercfl
tosrm
gOrnade
tdieovcretdi
rtvfltehe
owconstructing
In boInthbo
sbo
ecsth
isinto
ctflode
pflotwpottial
orm
ustrg
eu. rgO
rotvrtehe
ortwtflhe
walkover structures in New Jersey can be
erodible material, the concentration of the flow
fooaths
tpa
alirm
lte
imd6ite
twin
idathe
th,
nde the
e nc nc
rne
sto
neaths
fooths
tpa
aim
reite
to
tfeindeth,
idaw
th,
ndaus
the
use usfound
ote
rne
so
topa
pa
are are
footpa
re lths
de ito
fede6to
tfe
in6ew
nd
te onc
rtesto
ths
rpa
e ths
in the New Jersey Coastal Zone Management
accelerates erosion along the flow path. In order to avoid
enetoial
oec gmin
ecdamin
torm
engeerally
neormit
t npoetrmit
epnootial
o ojoecotijlecsotiijnelecastiislnetosarim
sntoarsm
gngdagng
genegrally
nnoetrally
p
tepdermit
dteudetdteoudetdhtueoeirthtpoeoirtthepenoirttial
c min
odang
Rules, section N.J.A.C.7:7E. In general, for multiple
creating this hazardous condition, dune walkovers are
e
ve
n
t
.
T
h
e
u
s
e
o
f
g
e
o
t
e
x
t
ile
f
ab
ric
s
o
r
c
ab
le
d
o
o
p
la
n
k
s
s
h
o
u
ld
w
e
d
o
n
a
c
as
t xftab
ileric
fab
ricr scab
orle
cab
hould
evenetve
. Tnht.e Tuhse u
osf egeoof tgeexotile
so
d leodo opolanpkla
s snhkos usld
wedwoendaocnasaec-as
bye- -bye--byfamily or public beach accesses, the walkover structure
considered the preferred means of beach access, since
situa
eon.
sititua
afo
deoths
fooaths
tpa
ths
retbe
no
to
e eetw
tw
eun
ne th
e deune
ecasti
oOn.
tpa
aret ato
no
to tbe
haew
eenedth
casecsaistua
ntiogOn.
randgO
ernafodgoertpa
re no
edbe
wehdew
reed
nreheeasrn
ceaerasncaerescare tw
n eth
edun
must not exceed 6 feet wide in overall dimension, and
they allow the dune line to remain continuous.
und
cetur
eaacbnd
bcherm
abe
chisrm
be
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Figure 16A. Wooden dune walkover (preferred method); B. angled walkway through dune; C. shore-perpendicular
walkway through dune (least preferred method).
Dune Manual 17
must meet a minimum clearance of 3 feet 10 inches
above the dune crest. Walkovers for single family use
are limited to 4 feet wide and require a minimum of 3
feet of clearance above the dune crest. Structures are
intended to pose the least possible amount of
disruption to the natural dune, and thus are required
to terminate at either 10 feet seaward of the line of
permanent beach dune vegetation or at the toe of the
frontal dune. Support posts are not to be encased in
concrete, should have a minimum soil penetration of 5
feet, and should allow for the erosion of sand during a
storm event (Beach and Dune Walkover Guidelines).
Although dune walkovers are preferable from a coastal
protection standpoint, there are some locations and
situations where they are not possible or necessary,
such as areas of minimal dune development, sparse
vegetation, low foot traffic, or critical habitat value. In
these cases, there are several alternatives that may be
used to provide access at grade. e least preferred
method is a shore-perpendicular street-end cut. Shoreperpendicular entrances provide minimal resistance to
waves and surge, and they provide a conduit for
funneling high-velocity flow directly inland. If beach
access must be provided at grade, two preferable
alternatives, which provide at least some additional
storm protection, include angling the entrances to at
least 45 degrees with respect to the shoreline, or
incorporating a small blockading feature to deflect the
surge from flowing straight through the access way. In
both cases, the intent is to deflect or divert the
potential storm surge. State regulations require that
on-grade footpaths be limited to 6 feet in width, and
be constructed of materials other than solid concrete
or stone, which may become dangerous projectiles in a
storm event. e use of geotextile fabrics or cabled
wood planks is reviewed on a case-by-case basis. An
alternative that has been utilized with some success in
Avalon, as well as in several other communities, is the
construction of a mixed-sediment footpath. e mixed
sediments are selected to be more resistant to erosion
than the native sand, provide a stable base, preserve
natural aesthetics, and have a relatively minor
ecological impact. e mixed-sediment approach can
18 Dune Manual
also be used to construct footpaths over existing dunes
when walkovers are not possible. On-grade footpaths
are not considered appropriate in locations where an
escarpment exists between the dune structure and
beach berm (Beach and Dune Walkover Guidelines).
In addition to their effects on the storm protection
functions of the dune system, dune crossings are
important in managing human disturbance and
trampling of rare, threatened, and endangered species,
because human density is strongly and inversely
correlated with distance from access points on
recreational beaches (Tratalos et al. 2013). e number,
spacing, and locations of dune crossings should be
carefully evaluated for their individual and cumulative
effects to rare, threatened, and endangered species.
Environmental Concerns
Any hard structure introduced into the beach
environment is likely to degrade habitat for wildlife in
general, but specific concerns about rare, threatened, and
endangered species are necessary to address. Proponents
of such projects should contact Endangered and NonGame Species Program (ENSP) and U.S. Fish and
Wildlife Service representatives early in planning. Even
in areas that do not currently support rare, threatened, or
endangered species, hard structures are likely to preclude
the formation of the most optimal habitats during future
storm events. In some locations, hard structures may be
the only cost-effective alternative to safeguard human
lives and property from future storms. However, the
adverse effects of such structures in precluding the
formation of optimal habitats for federally listed species
must be accounted for under the Endangered Species Act
through coordination with the U.S. Fish and Wildlife
Service. For example, for the recent installation of
sheetpile in Mantoloking, project proponents (in
consultation with Service representatives) provided
offsite compensatory mitigation.
All developed portions of the New Jersey coast
designated as piping plover nesting areas, including all
“protected zones” and “precautionary zones,” are
Adverse effects can be further reduced if conservation
commitments include periodic thinning of planted
beach grass (see targets in Table 1). Both mechanical and
chemical (herbicidal) thinning treatments can be
considered during those times of year when rare,
threatened, and endangered species are not present.
Managers should also avoid creating dunes that would
provide suitable den or burrow sites for predators such as
foxes (Vulpes vulpes) and ghost crabs (Ocypode quadrata),
and avoid installation of solid posts or other structures
that provide perches for avian predators such as crows
(Corvus spp.) and gulls (Laridae spp.). Woody species
should not be planted in or near rare, threatened, and
endangered species areas (not even in backdune areas), as
they provide perches for avian predators.
Figure 17. Portions of the New Jersey coast
designated as piping plover nesting areas. Based
on FWS NJ map.
Section 7(a)(2) of the Endangered Species Act (ESA)
requires Federal Agencies that authorize, fund, or carry
out projects within coastal ecosystems to consult with the
U.S. Fish and Wildlife Service if a proposed action may
affect any federally listed species. Section 9 of the ESA
applies to both Federal and non-Federal activities and
prohibits unauthorized taking of listed species, including
significant habitat modification or degradation that
results in the killing or injury of listed wildlife by
significantly impairing essential behavioral patterns, such
as breeding, feeding or sheltering. e U.S. Fish and
Wildlife Service and the ENSP assist local beach
managers in complying with the Endangered Species Act
and related laws and regulations. Most municipalities
have worked with the ENSP and the U.S. Fish and
Wildlife Service to develop a BMP for rare and listed
species.
delineated in the Beach Management Plans (BMPs)
(Figure 17). ENSP and the U.S. Fish and Wildlife
Service also recommend the following general
conservation measures as means for achieving the habitat
targets listed in Table 1. Where they are deemed essential
to protection of beachfront developments or other
infrastructure (and where overwashes or blowouts have
not formed), sand fences should be placed as far
landward as possible to minimize the amount of sparsely
vegetated and gently sloping beach that will be replaced
with steep dunes and dense vegetation. e number of
rows of sand fence should be minimized to decrease the
extent of habitat loss. Beach managers should work with
ENSP staff on siteDune Characteristic
Target
specific sand fence
Dune slope
< 13% (management intervention at > 17%)
configurations.
Dune height
< 1.1 m (management intervention at > 1.6 m)
Only native
Vegetative cover: primary dune
13% (management intervention at > 22%)
herbaceous
Vegetative cover: back beach
< 10% (management intervention at > 17%)
vegetation should
Shell/pebble cover: back beach
17-18%
be planted, and the
areal extent and
Table 1. Management targets for Dune Characteristics in all developed portions of the New Jersey
coast
designated as piping plover nesting areas (Figure17), including all “protected zones” and
density of plantings
“precautionary zones” (based on Maslo et al. 2011). Typically, these targets are best achieved by
should be
leaving the beach/dune system to evolve on its own without any vegetation planting or sand
fencing.
minimized.
Dune Manual 19