Recent Coastal Dune Development: Effects of Sand Nourishments

www.cerf-jcr.org

Recent Coastal Dune Development: Effects ofSand Nourishments

Marcel A.J. Bakker{, Sytze van Heteren{, Laura M. Vonhogen{, Ad J.F. van der Spek{,and Bert van der Valk1

{TNO Geological Survey of the NetherlandsP.O. Box 80015, NL-3508 TA Utrecht,The [email protected]

{DeltaresUnit Subsurface and Groundwater SystemsP.O. Box 85467, NL-3508 AL Utrecht,The Netherlands

1DeltaresUnit Marine and Coastal SystemsP.O. Box 177, NL-2600 MH, Delft,The Netherlands

ABSTRACT

BAKKER, M.A.J.; VAN HETEREN, S.; VONHOGEN, L.M.; VAN DER SPEK, A.J.F., and VAN DER VALK, L., 2012. Recentcoastal dune development: effects of sand nourishments. Journal of Coastal Research, 28(3), 587–601. West Palm Beach(Florida), ISSN 0749-0208.

Much of the Dutch coast has been subject to structural erosion. From 1990 onward, sand nourishments have been usedunder a government policy of dynamic preservation. Annual monitoring and field inspections show that the structuralerosion has decreased or even turned into coastal progradation after 1990. The monitoring data concern onlymorphodynamics and thus supply limited information on system-related geological processes driving the observedchanges. Recently acquired ground-penetrating radar (GPR) data help establish the origin of sedimentary elementswithin the beach-foredune area, determine their decadal-scale preservation potential under the present nourishmentpolicy, and demonstrate temporal and spatial accretion/erosion variability along nourished coasts. GPR images from anonnourished retrograding barrier section show historical storm surge deposits within the eroding foredune andaccumulations of natural eolian sediment farther landward. GPR images from a heavily nourished, prograding site showthat the accreted foredune and beach consist of nourishment embankments (20%), wind-blown units derived fromnourished sand (70%), and progradational beach deposits (10%). The net volume of accretion at this site is approximately200 m3/m. Remarkably, almost all sand nourished before 2000 has been washed away, except for embankmentsconstructed in 1990. Analysis of meteorological data suggests that 1999 storm surges are responsible for this erosion. Therelative longevity of post-2000 nourishments can be attributed to a combination of shoreface nourishment and favorablemeteorological conditions. During a storm surge in 2007, water-lain embankments proved to be more resistant againstwave erosion than nourished sand redistributed by wind, indicating the importance of grain size, roundness and packingin the durability of nourishments.

ADDITIONAL INDEX WORDS: Foredune, beach, coastal zone management, storm surge, meteorology, sedimentdynamics.

INTRODUCTION

The Dutch coast has been subject to persistent erosion and

landward retrogradation throughout at least the last centuries,

presumably for up to 1500 years. The long-term erosional trend

and the damage caused by a series of storm surges in 1990

prompted the definition of the ‘‘Reference Coast Line,’’ which

corresponds roughly with the position of the coastline at that

moment. The Reference Coast Line concept defines a minimum

sediment volume in the beach-foredune area that is to be

maintained. Maintenance takes place in the form of sand

nourishments. Locations and volumes of these nourishments

are determined on the basis of year-to-year trends as derived

from coastal monitoring. A precondition is that, in controlling

structural erosion, the natural behavior of the sandy coastline

is maintained as much as possible. The so-called ‘‘dynamic

preservation’’ of the coastline is achieved by the application of

shoreface and beach nourishments (Rijkswaterstaat, 1990). At

places where safety is not at risk, nourishments are rarely

or not applied, and limited breaching, scarp formation, and

blowout of foredunes is allowed or even stimulated. On an

annual basis, about 12 Mm3 of sand has been nourished at

selected places along the Dutch coastline since the year 2000.

Before 2000, this volume was about 6 Mm3. This sand was used

for raising and widening the beach itself and for constructing

embankments (erosion buffers or ‘‘shoulders’’) up against the

foredunes. After later insights (evaluated by Nourtec, 1997),

sand has since also been placed on the shoreface around the

5–6-m isobath (adjoining the outer beaker bar), allowing

currents, waves and wind to redistribute the sand to adjacent

areas.

Since 1965, the development of the coastal zone has been

monitored by means of coastal profiling (called Jarkus).

Decadal shoreface, beach, and foredune development can be

analyzed using this morphometric database. The Jarkus

database contains elevations for cross sections spaced 250 m

apart (corresponding with the beach-pole grid). These eleva-

tions are measured annually along the entire Dutch coast (cf.

Arens and Wiersma, 1984). The profiles stretch from about

1000 m seaward of the low-tide line up to and including the

DOI: 10.2112/JCOASTRES-D-11-00097.1 received 20 May 2011;accepted in revision 24 October 2011.Published Pre-print online 19 March 2012.’ Coastal Education & Research Foundation 2012.

Journal of Coastal Research 28 3 587–601 West Palm Beach, Florida May 2012

frontal dune. The supratidal part of the profiles has been

measured by airborne laser altimetry (LIDAR) since 1996.

Earlier profiling of the land part was achieved by topographic

levelers and aerial photography. Annual measurements extend

landward to at least the top of the (fore)dune. Year-to-year

variability in measuring and processing techniques occasion-

ally complicate straightforward analyses of the annual net

changes in profiles (Arens, 2009). Additionally, the Jarkus

database solely represents annual registrations of the topog-

raphy of the beach–dune profile. Hence, little can be said on

the actual processes resulting in the observed year-to-year

variability.

This paper addresses these processes by linking Jarkus

with ground-penetrating radar (GPR) and meteorological

observations. This approach was applied to data from a

nonnourished beach that has been subject to long-term net

erosion and from an actively and frequently nourished beach

that has experienced recent coastline progradation. The

primary aims of this study are to determine (1) the origin of

sedimentary elements within the upper beach and foredune

area, (2) the fate of the sand volumes nourished in the past,

and (3) the decadal-scale preservation potential of sand in

the dune foot and on the adjacent backshore in light of the

established nourishment policy. A secondary aim is to

demonstrate temporal and spatial accretion and erosion

variability along nourished coasts.

STUDY SITES

The two study sites discussed in this paper are located along

the west coast of the Netherlands, in a region where the coast is

orientated roughly north–south (Figure 1). The tidal range is

,2 m, with spring tide around 1.2 m above mean sea level

(+MSL). Prevailing winds, mostly moderate in strength, are

from the southwest. Strong winds, occasionally gale force or

stronger, reach the coastline from southwesterly to northwest-

erly directions. Storm surges, with significant water level set-

up, accompany westerly to northwesterly storm wind regimes.

Water level monitoring shows extremes of 3.50 to 3.85 m +MSL,

with associated offshore significant wave heights of approxi-

mately 7 m.

Site 1. Nonnourished Beach (Heemskerk aan Zee)

Longshore redistribution of past nourishments has likely

influenced any stretch of beach in one way or another, even

when beaches and the adjacent shoreface have not been

nourished themselves. This is the case for the Heemskerk site

(Figure 1). Nourishments were carried out just south of the

study site in 1996–97 and just north of the site in 2005.

However, the first nourishment at the study site itself was not

put into place until after completion of our study. In a situation

of limited sediment availability, coastline retrogradation has

Figure 1. The study sites of Heemskerk and Bergen along the southern North Sea coast.

588 Bakker et al.

Journal of Coastal Research, Vol. 28, No. 3, 2012

taken place, resulting in narrowing and steepening of the

foredune (Figure 2) and, thus, in landward exceedance of the

local Reference Coast Line. Because no economically valuable

built structures or infrastructure are present near the coastline

at this site and because the total dune area is wide and high

enough to ensure safety, this coastline recession has not been

considered a problem to date. During and immediately after

each storm surge event, erosion is taking place in the form of

bluff formation and slumping, exposing older eolian and storm

surge deposits that date from the 17th and 18th century

(Cunningham et al., 2011; Van Heteren et al., 2008).

The coastline recession near Heemskerk aan Zee and the

formation of large blowouts in the foredune are a consequence

of the nonnourishment policy at this beach section and of the

practice of dynamic preservation. It opens up the dune area to

sand being blown inland from the present-day beach and from

the exposed foredune (Figure 2).

Site 2. Heavily Nourished Beach (Bergen aan Zee)

The coastal resort of Bergen aan Zee (see Figure 1 for

location) experienced strong and prolonged coastal erosion in

the past. Twentieth century aerial photographs of Bergen

typically show a distinct escarpment along the foredune, most

pronounced after the impact of storm surges (Figure 3). The

historical development of the coastline near Bergen is best

demonstrated by the reconstructions published by Schoorl

(1990) showing the retrogradation of the coastline at Egmond

aan Zee, a village about 5 km south of Bergen aan Zee.

The storm surges of early 1990 destroyed part of the Bergen

aan Zee boulevard (Figure 3). Sand nourishments were applied

shortly after these erosional events. They include a large

embankment (dune face nourishment). Additional nourish-

ments were put into place in 1992, 1995, 1997, 1999, 2000, and

2005 (see Table 1 for details). The nourishments before 2000

were carried out solely on the beach, whereas those of 2000 and

2005 were placed in part on the shoreface. Although the main

goal of the nourishments is maintenance of the position of the

coastline, they also result in a wider beach for the benefit of

recreational activities.

METHODOLOGY

This paper focuses on data from two main methodologies.

GPR data from transects perpendicular to the coast, starting at

the upper beach and extending into the area behind the frontal

dune, are compared with Jarkus profiles across the same

environments. The resulting dataset is analyzed to understand

Figure 2. Foredune near Heemskerk aan Zee (view to the north on November 22, 2007). In the absence of nourishments, erosion has caused a steep,

slumping foredune front that is subject to wind erosion and wave attack during water levels above 2 m +MSL. The back-dune drop has become oversteepened

because of sand entrapment in the marram grass tussocks.

Recent Coastal Dune Development 589


the role of actual processes in nourished beach-foredune

environments.

Ground-penetrating radar has proven to be a significant

technique in coastal studies, as demonstrated in many papers

(e.g., Jol, Smith, and Meyers, 1996; Van Heteren et al., 1998).

In this study, GPR data were collected using PulseEkko PRO

equipment (Sensors & Software Inc.), using unshielded 100-

and 200-MHz antennae and 250-MHz shielded antennae. The

acquisition settings are listed in Table 2.

The velocity of the radar signal in the sediment, needed to

convert the measurements (conducted in two-way travel time)

to depth, was established in various ways. Velocity information

was obtained directly by analyzing the shape of diffraction

hyperbolae. This information was supplemented by data from

indirect comparisons of reflection travel time and reflector

(reflecting feature) depth. The depth to prominent reflecting

features (lithological units and the groundwater table) was

determined by hand augering. Common-midpoint surveys

were not conducted. The unsaturated zone was marked by

signal velocities of 0.11–0.12 m/ns. Below the groundwater

table, the velocity typically dropped to 0.07–0.08 m/ns.

Penetration depth was generally on the order of 12–15 m for

the unshielded 100-MHz profiles, 7–8 m for the unshielded 200-

MHz profiles, and 6–7 m for the shielded 250-MHz profiles. In

very steep terrain, the penetration depth was reduced. In the

processing of radar data, topographic correction is needed to

assess the geometry and depth of subsurface units. Position

and elevation data were gathered by a real-time kinematic

global positioning system (RTK-GPS) with centimeter accura-

cy. Additional processing steps included dewowing, horizontal

and vertical filtering, and the application of an automatic gain

control to better view deeper reflections.

Figure 3. Oblique aerial photo of Bergen aan Zee looking north, taken shortly after the storm surges of 1990 (source: photo archive Rijkswaterstaat). Part of

the boulevard was destroyed. At the beach, in front of the boulevard, Roman-age peat beds were exposed (dark patches). The positions of images and cross-

sections shown in Figures 6–8 are indicated; Jarkus transect 32.750 is represented by the line labeled Figure 8.

590 Bakker et al.


After processing, the GPR images were interpreted on the

basis of radar facies identified on the profiles, following the

concept of Van Heteren et al. (1998). In this concept, radar

facies are defined as spatial units within GPR profiles in

which the reflection configuration is uniform. The lithological

characteristics of the radar facies were verified by hand

augering and are listed in Table 3, which includes a short

description of their appearance, indications of their position

and an environmental interpretation.

The second research methodology involves analysis of Jarkus

coastal profiles through time and comparison of the observed

changes with the sedimentary architecture visible on GPR

images. After this comparison, the observations are linked to

processes—driven largely by meteorological conditions—that

are known to have an effect on sand-nourished beach-foredune

environments.

RESULTS

Site 1. Nonnourished Beach (Heemskerk aan Zee)GPR Observations

A steep dune scarp, the result of a significant storm surge in

November 2007 that created a local water level of 3.13 m +MSL,

provided a (laterally discontinuous) exposure of older beach

and eolian sediments (Cunningham et al., 2011; Van Heteren

et al., 2008). Over a length of about 1 km, relatively coarse-

grained, shell-bearing paleostorm surge deposits were exposed

at various elevations, intercalated with wind-blown sand. At

beach pole 49.500 km (52u309570 N, 4u359400 E) near Heems-

kerk aan Zee, the foredune scarp was partly cut into a large

blowout in the frontal dune, facilitating access for GPR

surveying on top of the exposed sequence. This enabled direct

comparison between the GPR images and exposed strata. The

exposures were used to ground-truth the corresponding GPR

images, linking subsurface reflections and reflection configu-

rations (facies) with exposed boundaries and strata. This

information supported the interpretation of GPR transects

perpendicular to the shoreline. GPR profiles measured per-

pendicular to the escarpment start at the scarp and extend

across the steep foredune, to a maximum elevation of 18.5 m

+MSL, and landward down into the adjacent blowouts with

lowest points around 3 m +MSL. The seaward side of the

foredune is dominated by bare sand and was temporarily

oversteepened as a result of the scarp formation. The vegetated

lee side of the foredune is particularly steep, with angles up to

37u (Figure 2). The steep slope reflects strong fixation by

European marram grass (Ammophila arenaria).

Inclined and listric (spoon-shaped) reflections occur in the

higher parts of the foredune (Figure 4, right-hand part). Radar

facies at the lee sides are dominated by subparallel, inclined

reflection sets (facies FDL, Table 3, Figure 4 in yellow) dipping

landward. Locally, diffractions are visible. High-amplitude,

continuous and subparallel reflection sets (facies SB, Table 3,

Figure 4) are indicated in red. Below this unit a continuous

subhorizontal reflection at ,1.5 m +MSL (facies WT, Table 3,

Figure 4 in blue) is present.

GPR Interpretation

The inclined and listric reflections in the higher parts of the

profile are attributed to eolian bounding surfaces within the

foredune (facies FDC). Unit FDL is interpreted as an eolian

deposit that formed in the wind shadow of the migrating

foredune, deposited at the angle of repose. Local diffractions

can be caused by debris that washed up on the shore and was

transported farther inland by storm winds. The scarp exposure

revealed a link between unit SB and convoluted shell-bearing

beds deposited in storm surge conditions (cf. Cunningham

Table 1. Overview of sand nourishments at Bergen aan Zee (source: Rijkswaterstaat, Waterdienst). Volumes are given both per kilometer (as an indicator of

nourished sand in the kilometer bordering the study site) and per nourishment, as a typical nourishment extends along the coast for several kilometers. The

maximum elevations (top surface) of embankments are given; the elevations of the beach nourishments are unknown. No nourishments were carried out in

Bergen before 1990. Beach nourishment 3 (June 1994) was placed only along the southern part of Bergen aan Zee. Dates of Jarkus profiling refer to the onshore

part of the monitoring.

Number Type Volume (m3) Volume (m3/km) Elevation (m +MSL) Date of Placement

Date of Jarkus Profiling in

Year of Placement

1a Beach 386,000 257,000 May–Jun 1990 Apr 14

1b Embankment 60,000 40,000 6.00 May–Jun 1990 Apr 14

2 Beach + embankment 1,473,000 115,000 3.50 May–Nov 1992 Apr 25

3 Beach 101,000 168,000 Jun 1994 Apr 25

4 Beach 306,000 306,000 May 1995 Mar 30

5 Beach 352,000 144,000 Jun 1997 May 22

6 Beach 206,000 165,000 Apr–May 1999 Apr 17

7a Beach 225,000 450,000 Jun 2000 Nov 4

7b Shoreface 994,000 497,000 — Apr–Aug 2000 Nov 4

8a Beach + embankment 300,000 200,000 3.75 Apr 2005 Apr 24

8b Shoreface 1,500,000 320,000 — Aug–Sep 2005 Apr 24

Table 2. Overview of GPR settings applied.

Frequency Antennae Spacing Pulser Voltage Step Size Stacks Time Window

100 MHz 1.0 m 400 V 20 cm 16 300

200 MHz 0.5 m 400 V 10 cm 16 480

250 MHz 0.4 m 165 V 5 cm 16 350



et al., 2011). Hand augering at the landward dune foot confirmed

the lateral, landward continuation of this unit. Additional GPR

surveying showed that this unit extends more than 750 m

inland. Reflection WT is interpreted as the groundwater table.

Jarkus Analysis and Comparison with GPR Imaging

Jarkus profiles from selected years demonstrate a distinct

landward shift of both the seaward foredune foot and foredune

crest and a general oversteepening and narrowing of the

foredune (dashed lines in Figure 4). Over the period 1965–

2008, the dune crest migrated ,0.5 m/y and the dune foot

(beach side) ,1.0 m/y. It is interesting to note that the dune

crest remained more or less on the same topographical level.

Figure 4 also shows a profile recorded with RTK-GPS shortly

after the storm surge of November 2007 (marked A). Compar-

ison with the Jarkus profiles of spring 2007 and spring 2008

(marked S) shows that the severity of scarping is not captured

in the annual monitoring series.

Site 2. Nourished Beach (Bergen aan Zee)GPR Observations

GPR transects collected on the heavily nourished beach-

foredune system of Bergen aan Zee reflect a complex nourish-

ment history. The positions of these transects are indicated on

Figure 3, which shows the presence of a prominent scarp after

a 1990 storm surge. The present-day situation is visible in

Figure 5: a generally gentle seaward slope covered with

marram grass. The remains of the 1990 scarp can still be

recognized locally as a subtle morphological break in the slope.

Near the base of the current slope, sparsely vegetated,

ephemeral, and hummocky dunes are present. The GPR data

show shore-perpendicular transects from the dune foot over the

gentle slopes toward the hinterland in the immediate vicinity

of the Jarkus profile at beach pole 32.750 km (52u399 580 N

4u379460 E, situated in the northern part of the town).

Figure 6 presents a 100-MHz transect from the dune

foot over the foredune crest (see Figure 3 for location). At

Table 3. Overview of radar facies visible on GPR profiles of beach and foredune deposits at Heemskerk and Bergen aan Zee.

Unit Facies Description Position Interpretation

WBN Long, subparallel reflections, dipping seaward;

erosive lower boundaries; diffractions

On beach against foredune and

embankment

Wind-blown sand (nourishment-derived), brown,

diffractions from modern debris incorporated

in the sand

WBS Long, subparallel reflections, dipping seaward;

erosive lower boundaries

On beach against foredune and

embankments

Wind-blown, white, fine-grained sand

EM High-amplitude, subparallel reflections Against former scarp, below unit WBN Embankment

FDC Subparallel, landward-dipping reflections;

bounding surfaces; diffractions

Foredune core, diffractions from root concentrations

(marram grass) and debris (in top part only)

FDL Steeply dipping, subparallel reflections; local

diffractions

On lee side of foredune ‘‘Avalanche’’ deposits of drifting wind-blown

sand, diffractions from modern debris

TR Mostly transparent facies; blanket At the surface behind foredune ‘‘Fall-out’’ of wind-blown sand, derived from beach

(nourishments) and from exposed foredune

scarps

SB High-amplitude, continuous and subparallel

reflection

About 3–6 m +MSL Shell-bearing storm surge beds

WT Subhorizontal, single reflection From 1–2 m +MSL Groundwater table

P Tabular top-and-bottom reflection set; horizontal;

transparent

Near MSL/groundwater table Peat beds

PF Westward-dipping low-angle reflections, locally

hummocky

Between 0.5 and 2 m –MSL. Prograditional upper (storm) beach deposits,

local eolian deflation and infilling

Figure 4. Combined image of GPR profile (200 MHz, unshielded) across the foredune at beach pole 49.500 near Heemskerk aan Zee and corresponding

Jarkus profiles from selected years. Profiles marked S are standard Jarkus profiles recorded in spring; the profile marked A (solid line) was recorded with

RTK-GPS shortly after the storm surge of November 2007. The dune crest has migrated ,0.5 m/y and the dune foot (beach side) ,1.0 m/yr, resulting in

narrowing and oversteepening of the foredune. The groundwater table (in blue) and historical storm surge beds (in red) are clearly visible on the GPR profile.

A set of strong and inclined subparallel reflections marks eolian deposits on the landward side of the profile.

592 Bakker et al.


,1.0–2.0 m +MSL, a continuous subhorizontal reflection is visible

(reflection WT, Table 3). On the seaward side, it is situated near

the top of westward-dipping, low-angle oblique reflections (unit

PF). Farther landward, the subhorizontal reflection is masked by

a set of high-amplitude reflections (unit P). Farthest inland,

subparallel, mostly landward-dipping reflection sets and bound-

ing surfaces (unit FDC) occur. This unit can also be recognized

in Figure 7. Unit FDC is generally bounded on its seaward side

by a sharp, seaward-dipping discontinuity at an angle of about

32u. This erosional boundary is commonly characterized by a

continuous reflection that is caused by a marked change in

lithological and sedimentological properties. The discontinuity

is covered with several sedimentary units. These units are

marked by a dominance of long, subparallel reflection sets,

dipping seaward and exhibiting erosive lower internal bound-

aries. Situated against the base of the discontinuity, unit EM

(Table 3) shows high-amplitude, subparallel reflections across a

limited lateral distance. The overlying unit WBS is dominated

by long, subparallel reflections, generally dipping seaward.

The facies succession discussed above is also visible on

additional GPR profiles, such as in Figure 7. Hand-augered

cores were used to assign lithological characteristics to GPR

facies EM, WBS, WBN, and FDC. The sequence is similar to

that presented in Figure 6: unit EM resting against a dipping

discontinuity, topped by unit WBS.

GPR Interpretation

An extensive hand-augering campaign was conducted to

establish the sedimentary character of the radar facies units.

Reflection WT is interpreted as the groundwater table. Unit PF

was correlated to shell-bearing sand and is interpreted as

progradational beach deposits. Unit P was positioned too deep

to be sampled by hand augering but is believed to consist of

remnants of a peat bed that was partly exposed at the beach

after the storm surges of 1990 (Figure 3).

Hand augering unit EM was difficult because of the pres-

ence of very dense compacted (sub)angular brown sands with

Figure 5. Situation at Bergen aan Zee in October 2007. The position of the 1990 scarp is indicated in black, along with the position of the GPR profile (in

light gray) shown in Figure 7. Most striking is the gentle slope from the former scarp toward the present-day foredune foot.



abundant shells (mostly Donax sp.) and shell fragments. Unit

EM is interpreted as the remains of the embankment, or dune

face nourishment, that was put up as a quick fix to repair the

storm surge damage of 1990. Hand augering has proven two

overlying units to be eolian in origin (judging from the well-

sorted character of the little-compacted sand and the presence

of fine wind-blown debris). Patchy unit WBS (Table 3) was

correlated to fine subrounded white-yellow sands, and unit

WBN to subangular brown sand. The white-yellow and brown

wind-blown sands produce identical radar facies that could

only be distinguished by augering. Unit FDC was linked to

white-yellow, fine-grained, and subrounded sands of Baltic

(northern) origin poor in, or devoid of, CaCO3.

Units FDC and WBS are bounded by a sharply inclined

discontinuity, dipping seaward. Comparison with aerial imag-

ery and Jarkus data shows that it represents the 1990 scarp

(comparable to the recent Heemskerk aan Zee situation) that

is buried in the present-day foredune. Locally, the reflection

terminates at the position of a morphological break in the sea-

ward slope of the foredune. The indistinct nature of the

reflection marking the scarp could be due to slumping of the

steep slope during and immediately after the 1990 storm

surges. Additionally, the scarp could be obscured by secondary

slide planes within the foredune sand body. These slide planes

are created under storm wave attack, when entire blocks of

dune sand, held together by marram grass, slide into the surf

zone as the steep-sided frontal dune is undermined.

Bristow, Chroston, and Bailey (2000) encountered similar

subsurface scarps in a GPR study of the coastal foredunes at

north Norfolk (U.K.), attributing them to the 1953 and (likely)

older storm surges.

Analysis of the GPR profiles at Bergen aan Zee shows that

the net accumulation of post-1990 sand adds up to 180–210

m3/m. The toe on the North Sea side of the foredune has

migrated seaward over some 18 m during the period 2000–2008

and about 35 m in the period 1990–2008.

Jarkus Analysis and Comparison with GPR Imaging

The Bergen aan Zee GPR profiles are situated close to Jarkus

transect 32.750. Annual data for this transect are available

Figure 6. Section at beach pole 33.160 (100-MHz GPR) fronting Bergen aan Zee (see Figure 3). Seaward is to the left. Several GPR facies are visible (see

Table 1).

594 Bakker et al.


over the period 1965–present. Most profiling of the dry part,

relevant in the present study, has been done in spring. Beach

nourishment will usually take place during the summer

months, shortly after the annual Jarkus profiling. In 2000,

however, measurements were taken on November 4 after

substantial shoreface and beach nourishment earlier in the

year (Table 2). For 2002, no Jarkus data are available; the

profile was established by interpolation between 2001 and

2003.

When all Jarkus profiles of a selected location are analyzed,

it is possible to visualize stacked sediment volumes (deposited

in different years) making up the sand wedge that has

accumulated in front of the 1990 scarp. Figure 8 shows that

this sand wedge is composed of sand volumes from only a

limited number of years. The 1990 profile represents the most

inland position of the dune front in the recorded period. All

subsequent profiles are positioned farther westward (i.e., at a

higher position), except the western part of the 1993 profile.

Even though the profiles in the period 1990–99 were positioned

seaward of the 1990 line, only sediment deposited in front of the

scarp in 1990–91 has survived one or more erosive events that

took place before the Jarkus profiling of 2000. The GPR

surveying has shown that it concerns unit EM, the 1990–91

embankments. In the period 2000–08, gradual accumulation

pushed the profile seaward. Sand nourishments were conduct-

ed in 2000 and 2005 only, but all other post-2000 years have

contributed to the sand wedge that fronts the 1990 scarp

(mostly GPR facies WBN).

Figure 9 shows the data of Figure 8 in numerical form

(between positions 290 and 2145 m). Sediments from 1992 and

the period 1994–99 have not been preserved at Jarkus transect

32.750. The largest volumes that make up the sand wedge

fronting the scarp originate from 1990–91 (the 1990 poststorm

embankment), 1992–93, and 2000 (the large nourishment). The

gradual accumulation after 2000 is a result of redistribution

by wind of nourishment sand located on the dry beach, as

evidenced by field observations, GPR reflection configurations,

and sedimentology of hand-augered material.

Analysis of year-to-year gross volumetric changes at Jarkus

transect 32.750 provides important additional information on

system morphodynamics (Figure 10). Indicated are net chang-

es for each year in the period 1990–2008, compared with the

previous year, of the higher part of the beach plus the foredune

front (between positions 290 and 2145 m in Figure 8). Erosion

occurred primarily in 1989–90, 1991–92, and 1998–99. Major

accumulation occurred not only in 1990 (the 1990 poststorm fix)

and 2000 (the largest nourishment to date), but also in 1996

(second-largest beach nourishment to date).

According to the Jarkus data at transect 32.750, there is an

overall net growth of 233 m3/m during the period 1990–2008.

The acquired GPR surveys complement this information,

showing accreted volumes varying from 180 to 210 m3/m over

a lateral distance of 530 m. From the GPR data, it can be con-

cluded that 21% of this volume originates from the 1990–91 em-

bankments, 11% from 1993, 36% from the 2000 nourishments,

and the remaining 32% from the period 2001–08. The addition

of sand has resulted in an average seaward shift of the foredune

toe of about 35 m.

Understanding Processes ReworkingBeach Nourishments

It is relatively easy to determine the geometry, composition

(origin), and age of nourishment-related sand deposits at the

upper parts of the beach and the adjacent, windward part of the

foredune at Bergen aan Zee. Linking these observations to

actual processes in the coastal environment is more difficult.

Along coasts marked by frontal dunes, wind is the most

important parameter affecting erosion, transport, and deposi-

tion. It has an indirect effect on subtidal and intertidal areas by

driving waves and currents, and a direct effect on intertidal

and supratidal areas through various eolian processes. In the

study area, shore-parallel sediment transport prevails during

periods of strong southerly to southwesterly winds. Vast

amounts of sand are set in motion under these conditions.

Inland sand transport occurs mostly when strong westerly

winds blow perpendicular to the coast. Numerous studies have

shown how these coastal processes act on beach sand (e.g., Van

der Wal [2004] for eolian sand transport and Pool [2009] and

Roelvink et al. [2009] for wave-induced erosion and associated

processes). Stuyfzand, Arens, and Oost (2010) additionally

demonstrated that the nourishment-derived sand has been

transported up to 300 m inland, affecting ecology. A complete

understanding of the effect of these processes on the coastal

profile requires analysis of meteorological and marine obser-

vations from the time period under consideration.

Water level data and marine observations are available for

two nearby sites (see Figure 1). The duration of water levels

above 2 m +MSL for each year in the period 1989–2008 at Petten

Zuid and IJmuiden Buitenhaven (Figure 11) is a relevant

parameter in understanding the direct impact of waves on the

coastal profiles of Heemskerk aan Zee and Bergen aan Zee.

Figure 7. Detail of a 250-MHz GPR section at beach pole 32.630 (see

Figure 3), with borehole data (A, B, and C) ground-truthing radar facies

SH, WBS, WBN, and FDC.



Although the exact water level at the dune foot is determined in

part by beach profile and breaker bar geometry, which affect

wave run-up, the 2 m +MSL water level, as measured at the two

monitoring stations, is a practical indicator for the threshold

that needs to be reached at both study sites before waves can

saturate and erode the dry beach and foredune.

Water levels above 2.0 m +MSL are reached only during

significant storm surges; the normal spring high-tide level is

around 1.05 +MSL (Petten) and 1.25 +MSL (IJmuiden). The

maximum levels reached during 1990–2008 at IJmuiden

Buitenhaven were 2.67 m +MSL in 1990 and 3.13 m +MSL

in 2007. The highest level recorded within the instrumental

monitoring time series is 3.85 m +MSL in 1953. Aside from the

surge-related water levels, wave run-up must be taken into

account. Under specific conditions, wave run-up can reach

elevations of more than 4–5 m +MSL (Pool, 2009).

Storm surge period 1 (Figure 11) occurred in 1990 and

caused the damage shown in Figure 3, creating the most

landward coastal profile to date. Storm surge 2, in 1993, eroded

the beach to even lower levels than in 1990, but the

embankments constructed in 1990 protected the dune foot

and stayed mostly intact. The 1999 storm surges eroded all

sediment accumulated between 1993 and 1999, including the

beach nourishments of 1994, 1995, and 1997. Storm surge 4, in

November 2007, resulted in the highest water levels since 1976

but had little effect on the profile at Bergen aan Zee.

The erosive effects of the storm surges, as indicated in the

volumetric balances of Figure 10, are more than offset by the

sand accumulation effects resulting from the nourishments. In

2000, the largest beach nourishment to date was carried out.

An even larger shoreface nourishment was put in place around

the same time. A 7-year period of marked meteorological

calmness followed; water levels above 2.0 m +MSL were very

rare and short-lived. Despite limited coastal erosion during this

time, additional beach (including embankment) and foreshore

nourishments were carried out in 2005. As a result of the period

devoid of significant storm surges, and reinforced by the 2005

nourishment that provided a new source of sediment, eolian

sand accumulation against the foredune has occurred ever

since the year 2000, without any significant intermittent

erosion.

Figure 12 shows wind frequencies for the period 1990–2008

at IJmuiden. Indicated are hours with wind speeds above 10

m/s, which are taken here as a measure of potential sand

transport by wind acting on a typical western Netherlands

beach. For natural and nourished sands with nonuniform grain

sizes, critical wind velocity is not a single value but a threshold

range (cf. Nickling, 1988). The threshold value of 10 m/s for

Bergen aan Zee gives an upper-end value of the critical range.

It is a function of grain size distribution of the local (nourished)

beach sediment (cf. Van der Wal, 1998). The frequencies in

Figure 12 are provided for winds from the 180u–270u quadrant

(shore-parallel sediment transport dominant), the 270u–360uquadrant (inland sediment transport dominant) and their sum

(180u–360u). Southeasterly to northeasterly winds are not

considered because these are rare and do not usually reach

10 m/s. Even when strong easterly winds occur, (seaward)

sediment transport is limited by vegetation on the landward

side of the foredune.

Figure 8. Analysis of Jarkus profiles for transect beach pole 32.750.

Preserved sand volumes originating from different years are shown in

different gray tones (situation 2008, derived from the Jarkus data). The

largest volumes originate from 1990 and 2000.

Figure 9. Post-1990 sand volumes present in 2008 and their year of origin at Jarkus transect 32.750. About 233 m3/m sand has accumulated since 1990.

596 Bakker et al.


Figure 10. Sediment dynamics at Jarkus transect 32.750. Indicated are interannual volume changes. Profiles from successive years are compared with

calculated volumes of erosion or sedimentation.

Figure 11. Duration (in hours) of water levels above 2.00 m +MSL for each year in the period 1990–2008 in Petten Zuid (north of the study areas) and

IJmuiden Buitenhaven (south of the study areas). Average high-water level at these locations is 0.80 (1.05) and 0.95 (1.25) m +MSL, respectively (maximum

spring tide levels in brackets). Highest levels are usually reached at IJmuiden. Significant storm surges occurred in 1990, 1993, 1999, and 2007. The

maximum water levels observed during these extreme events are indicated above the bars in the graph (m +MSL).



Potential sand transport occurs during 2000 hours (i.e., more

than 80 full days) in an average year. Two exceptionally calm

years were 1996 and 2003. Years with high potential wind

transport do not necessarily coincide with storm surge years,

which might explain why no direct links with the observed

interannual profile changes could be established. It is clear,

however, that given sediment availability on the dry beach and

in nonvegetated foredune parts, redistribution of sand by wind

will be significant almost every year.

Storm Surge Field Observations

During the storm surge of November 2007, field observations

were conducted in both Heemskerk and Bergen aan Zee. Along

the Dutch coast, the northwesterly storm winds were not

extreme along the coast (8–9 Beaufort, average wind speed

18–24 m/s). Nevertheless, the highest water levels since 1976

were recorded. The height of the storm surge was determined

in the northern part of the North Sea, far offshore, where

hurricane-force winds associated with a slow-moving depres-

sion were active across an extremely long fetch. These con-

ditions generated large and high swells that moved into the

southern part of the North Sea before reaching the coastline

(maximum wave heights of 7–8 m near IJmuiden).

During high tide, the water easily reached the dune foot,

saturating the sand. Waves attacking the dune front resulted

in large-scale scarping. In most places, the dune foot was

eroded back between 2 and 3 m (typical value for Bergen aan

Zee) and 10 m (maximum value for Heemskerk). The amount of

erosion depended on the presence or absence of nourishment

sand, nearshore bathymetry, height and width of the beach,

and other local conditions (e.g., Brodie and McNinch, 2009;

Houser, Hapke, and Hamilton, 2008; Pool, 2009).

In Heemskerk, the scarped dune face formed fresh exposures

of foredune sand with intercalated shell-bearing, paleostorm

surge deposits. In Bergen aan Zee, water-lain nourishment sands

(including embankments) could be recognized in fresh exposures

as generally subhorizontally stratified, densely packed sedi-

ments. The water-lain nourishment sands are subangular and

poorly sorted. They are marked by silty admixtures, shell

concentrations, and local clay balls and also contain plastic, rope,

and other types of anthropogenic debris. The subangular nature

and dense packing of these sands make them more resistant

against erosion than the loosely packed, well-rounded eolian

sands. This increased resistance could explain part of the

observed difference in dune foot erosion between Heemskerk

and Bergen aan Zee. It reduces slumping, which takes place at

relatively steep angles. Eolian strata are more easily washed

away and slump at considerably gentler angles. Although an

additional explanation for the difference in dune foot erosion is

the high elevation of the prestorm beach at Bergen aan Zee

(Figure 8), it is likely that type and composition of nourished

sediment and the way it is introduced into the beach system are

important elements in the durability of beach nourishments.

Figure 12. Duration (in hours) of wind speeds .10 m/s for southwest and northwest circulations (and their sum) in the period 1990–2008 (wind directions

indicated). Data from IJmuiden. Most hours with potential sand transport occurred in 1990, 1998–2000, and 2008. Calm years were 1996 and 2003. Note that

windy years do not necessarily coincide with storm surge years (cf. Figure 11).

598 Bakker et al.


DISCUSSION

Observations and analyses linking coastal profile changes to

natural processes and human interference on an annual to

decadal timescale are rare. Our study corroborates patterns

reported in the literature and supplements this knowledge by

providing quantified process-response relationships explaining

such patterns.

A regional study of foredune behavior in The Netherlands

was recently completed by Arens, Van Puijvelde, and Briere

(2010) using laser altimetric data and Jarkus profiling. To

quantify the effects of the nourishment policy on the dunes,

they analyzed total volumetric changes of the frontal dune

along the entire Dutch coast. They conclude that sand accretion

to the frontal dunes has shown an overall increase since the

establishment of the nourishment policy. Analysis of data from

the area just south of Bergen aan Zee (between beach poles

34.000 and 37.000, 1–4 km south of the GPR transects) shows a

trend break around 1997, from net erosion to net volumetric

growth. For beach pole 49.500 in the Heemskerk area, Arens,

Van Puijvelde, and Briere (2010) also observed a change

around 1997, from a net strong erosional state to a more or less

stable foredune volume. At this location, a landward shift of the

dune foot coincides with volumetric growth at the landward

side of the foredune, as confirmed and imaged by our data

(Figure 4). Arens, Van Puijvelde, and Briere (2010) see the

observed volumetric trend breaks as indirect proof of the

success of the nourishment policy. The overall pattern is

overprinted by local effects, such as sandbar migration,

blowout formation and—in general terms—a decrease of

storminess after 1990. Our study shows that the latter is true

for storm surges, but not for stronger winds in general

(Figure 12). As a result, sand loss through dune scarping has

been rare, whereas sand accumulation on the landward side of

the frontal dune has been significant.

The effects of dune scarps or bluffs, like the one at the

Heemskerk aan Zee, can be twofold. In a study on the influence

of coastal morphology on the transport of shoreface sediment in

the Canadian Beaufort Sea, Hequette et al. (2001) noted the

importance of downwelling, near-bottom currents. The numer-

ical model used in their study indicated that offshore sediment

transport is strongest where beaches are backed by bluffs.

Under these conditions, strong seaward-directed horizontal

pressure gradients drive powerful offshore bottom currents.

Low barriers that are easily breached experience lower set-up

and run-up during storm surges, and eroded sediment is

mainly transported obliquely offshore. Importantly, Hequette

et al. (2001) suggest that sediment eroded from bluff-backed

beaches might be transported offshore to depths that are

beyond the influence of fair-weather waves needed to return

the eroded material to the beach. Consequently, the presence of

coastal features that act as barriers to onshore-driven surface

water could result in a greater loss of sediment from the coastal

system than the absence of such features. In a study on the Gulf

coast of northwestern Florida, Houser, Hapke, and Hamilton

(2008) found the reverse to be true. They noted that in areas

with a relatively wide dune belt behind a foredune, most of the

sediment eroded from beach and dunes during storm surges is

deposited on the upper shoreface. This sediment is returned to

the beach during fair-weather conditions, when nearshore bars

weld to the coast. Areas with large foredunes and a wide dune

belt erode less rapidly than areas with smaller foredunes and

greater sediment fluxes through overwash. Houser, Hapke,

and Hamilton (2008) additionally suggested that the presence

or absence of transverse ridges in the nearshore zone affect the

storm surge level at the beach. In determining the response of a

stretch of coastline to the next extreme storm for coastal

management purposes, the differential influence of nearshore

bathymetry should be taken into account. In addition to beach

profiling and GPR imaging, field observations on sediment

transport on shoreface, nearshore zone, beach, and foredune

are needed, particularly during and after extreme events.

The overall trends at Bergen aan Zee (steady seaward

foredune migration) and Heemskerk (slow dune foot erosion),

as observed by Jarkus monitoring, are obscured by the effects of

major storm surges and by subsequent periods of relatively

rapid beach and foredune recovery. A limitation in separating

the erosive effects of storm surges from intervening recovery

periods and from the long-term trend is the low (annual)

temporal resolution of the Jarkus measurements. Pre- and

postsurge measurements will include not only storm surge

effects, but also the effects of all other coastal processes that

took place during the year between subsequent measurements,

including entrapment of sand by dune grass planted at the

dune foot. Earlier, Zhang, Douglas, and Leatherman (2002)

found a similar pattern as the ‘‘Heemskerk’’ scenario of slow,

long-term erosion in their analysis of shoreline data from the

U.S. East Coast. They noted that even after the most damaging

storms, such as the Ash Wednesday Storm of 1962, beaches

recover to positions matching their overall, century-scale

trend. Zhang, Douglas, and Leatherman (2002) concluded that

barrier beaches would not experience long-term erosion, even

when experiencing frequent major storms, if sediment supply

were sufficient to keep up with the effects of relative sea-level

rise. This conclusion is confirmed by our observations from

Bergen aan Zee, which show prenourishment erosion up to

1990 but slow nourishment-related foredune progradation

since then, interrupted, but not reversed, by brief erosive

events.

Although the two sites analyzed as part of this study

represent both a nourished and a nonnourished stretch of

coast, our results must be validated by observations from other

locations. Validation is possible where monitoring data of

nourished and natural foredunes within single coastal cells are

available. Where profile data are absent, GPR can be used

by itself to contrast the sedimentary record and behavior of

nourished and adjacent nonnourished beach-dune systems.

The resulting data need to be supplemented by meteorological

observations and by sediment transport measurements in the

entire coastal tract, particularly during extreme events.

Following this approach, morphological and ecological effects

of nourishment programs will become clearer, allowing fine-

tuning of nourishment strategy.

CONCLUSIONS

In revealing the internal architecture of foredunes, GPR

helps to establish the origin and preservation of stacked



sedimentary units that make up the foredunes. Thus, GPR

profiles are instrumental in explaining Jarkus profiling data in

terms of responsible coastal processes. The combination of GPR

and Jarkus can be used to optimize coastal management

policies.

At the Heemskerk aan Zee site, sand nourishment has never

been implemented. Jarkus profiling shows that during the period

1965–2008, the foredune foot migrated landward at an average

rate of 1.0 m/y. Scarp development has revealed bounding

surfaces in eolian strata resting on shell-bearing storm surge

beds. Both elements can be traced in a landward direction using

GPR surveying. Landward accretion of the foredune can also be

imaged. It is seen that the morphodynamics of the upper beach

and foredune are not captured by the lower temporal (i.e., yearly)

resolution of the standard profiling measurements.

At Bergen aan Zee, Jarkus and GPR data show a distinct,

nourishment-related net growth of the foredune volume over the

years, with high year-to-year variability. The dune foot has

migrated 35 m in a seaward direction over the period 1990–2008.

Integration of Jarkus and GPR data makes it possible to

establish the year of origin of sand volumes and to attribute

textural and compositional properties to these volumes. The data

show that 21% of the accreted volume originates from water-lain

embankments constructed in 1990, 11% from 1992–93 beach

sands, 36% from year 2000 nourishments (partly water-lain and

therefore in situ, mostly redistributed by wind), and the

remaining 32% from the period 2001–08 (entirely wind-redistrib-

uted nourishment sand). The net volume of accumulation ranges

between 180 and 233 m3/m over a shore-parallel distance of 530 m.

Almost all sand of the nourishments applied before 2000 has

been washed away. Analysis of meteorological and marine data

suggests that the 1999 storm surges are most likely responsible

for erosion of all post-1990 nourished material still present on

beach and foredune at that time. After 2000, structural

accumulation has taken place in the form of wind-blown

nourishment sand, not only in the nourishment years 2000 and

2005. This accumulation can be attributed to consistent, long-

term sediment supply from shoreface nourishments and to

favorable meteorological conditions.

Field observations during a significant storm surge in 2007

indicate that wind-blown nourishment sands are more prone to

wave erosion than water-lain nourishment sands. Type and

composition of the sand are very important and can be used not

only to predict the durability of nourished sediment volumes,

but also to assess ecological effects in the frontal dunes.

The analysis of process-response relationships governing the

behavior of the Dutch foredune system profits from the

combined power of Jarkus profiling and GPR surveying.

Whereas Jarkus profiling supplies volumetric data over long

time spans, GPR profiles visualize the net effects of profile

changes and reveal the contribution of natural processes and

specific nourishments to sand volume gained by nourished

coastal sections. Whereas the Jarkus profiling is restricted

to 250-m intervals and limited to measurements made each

spring, the GPR profiling can be carried out at any place and

time. Assessment of net variability along the coast at the

highest spatial and temporal resolution is essential when

understanding the behavior and preservation of nourished

sand volumes in light of meteorological conditions. Therefore,

combining a diversity of techniques and approaches, including

GIS based studies, Jarkus measurements, GPR, and meteoro-

logical reconstructions, in beach-nourishment evaluations

more often is recommended.

ACKNOWLEDGMENTS

Hoogheemraadschap Hollands Noorderkwartier and PWN

Water Supply Company North Holland gave us permission to

access the sites and provided logistical support; we especially

thank Menno van den Bos, Paul van der Linden, and Luc

Knijnsberg. Alastair Cunningham and Piet Kok provided

field assistance. Stijn van Puijvelde contributed to the

analysis of meteorological and marine data. Xavier Comas

and two anonymous reviewers are thanked for their critical

comments. This work was funded by Deltares projects Coastal

Maintenance (‘‘Kustlijnzorg’’) and Coastal Systems and is a

contribution to IGCP project 588 ‘‘Preparing for coastal

change: A detailed process-response framework for coastal

change at different timescales.’’

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