International Journal of Geosciences, 2011, 2, 111-119
doi:10.4236/ijg.2011.22012 Published Online May 2011 (
Copyright © 2011 SciRes. IJG
Beach Morphology and Sediment Budget Variability Based
on High Quality Digital Elevation Models Derived from
Field Data Sets
Mohammed Taaouati*, Abdelmounim El Mrini, Driss Nachite
Department of Geology, Abdelmalek Essaâdi University, Tétouan, Morocco
Received January 11, 2011; revised February 17, 2011; accepted March 22, 2011
The morphological and volumetric changes of a sandy beach were investigated through a series of two-
monthly filed surveys carried out over a 2-year period from April 2005 to January 2007. This paper discusses
the ability of 3-D digital elevation models (DEMs) derived from high accurate data to assess and quantify
beach morphodynamics in relation with wave forcing. The methodology and data acquisition are described
and consist mainly in the production of interpolated DEMs from which a variety of representations can be
made, including as elevation change maps, two-dimensional cross-sections of the beach, and calculation of
net volume. The results of the analysis highlight seasonal changes in beach morphology due to variations in
wave energy. This behavior is characterized by beach erosion and bar decay under high-energy waves and
net accretion and bar formation during relatively fair weather conditions. The sand budgets adjustments show
that the loss of volume in the winter months is compensated for by accumulation to the beach during summer.
This trend suggests that waves are the main forcing which controls the beach evolution. The correlation be-
tween beach changes and wave energy variations highlights a strong relationship between them and supports
the suggestion previously made. The results from this investigation state the value of DEMs utilized and
demonstrate the efficiency of the 3-D approach employed here to assess the erosion and accretion patterns
which would not be visualized using 2-D profiles.
Keywords: Moroccan Coast, Beach Change, Wave Forcing, Digital Elevation Model, 3-D Approach
1. Introduction
Sandy beaches are difficult landforms to study because
of the complex interaction between morphology, sedi-
ment and hydrodynamic forcing, which makes these en-
vironments very dynamic and moving systems.
Many authors have worked on the spatial and temporal
evolution of beach morphology using several models,
classification and indices [1]. Unfortunately, little suc-
cess has been obtained when using such models because
of the complexity of beach systems [2]. An alternative
approach is to repeatedly measure the beach topography
over time to evaluate the changes that have taken place
Nowadays, high-resolution techniques (satellites, ae-
rial photographs, LIDAR, etc.) allow for improved
monitoring and provide coverage of large sections of
coastal systems. Although the excellent resolution of the
data obtained, some limitations (cost, enormous data sets)
restrict the use of such techniques. Field surveys remain
the best way to frequently collect topographic data. The
most common technique used is beach topographic pro-
filing or 3D surveying [3], which is the case of the pre-
sent work.
On the other hand, the data collected must be repre-
sented appropriately in order to keep as much as possible
the field reality. The digital elevation model (DEM) is a
numerical representation of beach topography, which is
widely used throughout geomorphologic and environ-
mental studies [4,5]. In coastal areas, DEMs have been
utilized in many analyses such as topographic distribu-
tion, slope variations, estimation of scour and/or fill
The present work aims to apply DEMs, derived from
accurate topographic data, to identify seasonal morpho-
logic change in a mesotidal high-energy beach, located
on the northwestern coastline of Morocco in order to
derive patterns of erosion and deposition within the sys-
tem. The specific objectives of this paper are: 1) to gen-
erate Digi- tal Elevation Models from high-quality field
data, 2) to produce elevation contour maps and determine
areas of accretion and erosion, 3) to calculate cut and fill
volumes and 4) establish the relationship between beach
changes and hydrodynamic forcing. This approach al-
lows us to assess and predict the morphodynamic behav-
ior of the studied beach over time and space.
2. Field Site Description
Charf el Akab is a sandy beach located on the Atlantic
side of Tangier Peninsula in the northwestern of Mo-
rocco (Figure 1). It is an interesting sector showing a
progressive increase in human activities during the last
few years, and well-known for high energetic waves
during winter months [6,7].
Due to coastline orientation, the beach is mainly af-
fected by waves (both sea and swell wave conditions),
approaching from western directions especially the ones
that approach the coast from west-northwest quadrant.
Significant wave height is usually within 1 to 3 m and
can reach 7 to 9 m during large storm events [8]. Then,
this area can be classified as a high-energy environment
[9]. Not surprisingly, the impact of these high energetic
events on flat sandy beaches in the region is very impor-
The coastline, NNE-SSW aligned, is dominated by
long and wide sandy beaches, such as Charf el Akab
(studied beach), Haouara and Briech; it is characterized
by vegetated dunes which protect humid (marshy) zones.
Last, the coastal zone between Cape Spartel and Tahad-
Figure 1. Atlantic coast of Tangier peninsula showing study area.
Copyright © 2011 SciRes. IJG
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dart is drained by rivers, notably Tahaddart, which carry
terrigenous sediments towards the continental shelf [6].
Charf el Akab is an approximately 2 km long and
200 m wide beach. Throughout this beach is present a
wide vegetated foredune and rocky outcrops in many
places along the backbeach (Figure 2(a)). The study area
(200 × 250 m) is characterized by many features formed
by wind, tide and wave processes. Sand shadows are
usually found on the backshore of Charf el Akab beach,
especially when strong offshore winds prevail in the
studied area. They are associated with pebbles, shells and
considerable heavy minerals fractions (Figure 2(b)). The
foreshore zone exhibits a wide variety of beach features
such as swash marks, ripples, etc. The most usual are the
rill marks which are formed by water drainage in the rip
channels. One of the main features of Charf el Akab site
is an intertidal bar which is provisionally present at the
mid- and upper beach (Figure 2(c)).
3. Data and Methods
Below, we present the data analysis methods used herein
in order to characterize the hydrodynamic (wave) condi-
tions, beach morphology and sediment budget variability.
The data analysis involved mainly 1) seasonal charac-
terization of beach morphology and offshore wave forc-
ing, and 2) exploring for evident correlation between
3.1. Wave Data
Wave data provided by Puertos del Estado (Ministry of
Public Works, Spain).were utilized to characterize the
wave conditions during survey period. Data are collected
from an offshore point “WANA43” (35°45' N, 6° W)
located near the study beach at approximately 70 m
depth (Figure 1). These data are daily wave forecast
output from the WAM wave model [10] and do not come
from direct measurements. However, the data are useful
and reliable since the objective is to analyze the wave
climate at seasonal time scale. The wave data sets ana-
lyzed cover a two-year period from 2005 to 2007 and
consist of sig- nificant wave height (Hs), wave period (Tp)
and wave direction (θ). The WANA data analysis was de-
Figure 2. Ground photographs of beach morphologies in Charf el Akab site.
Copyright © 2011 SciRes. IJG
signated to characterize the general offshore wave condi-
tions in the study area throughout the period of beach
monitoring. The wave data are represented by frequency
histograms for the 2-year period.
Additionally, the significant wave height and the cor-
responding period were identified and compared with the
beach changes for correspondence analysis. The under-
lying question was what value should be used to properly
represent the wave forcing as it pertains to morphologi-
cal evolution. Thus, considering that the morphology
responds more rapidly to the more energetic events, the
significant wave height and the corresponding wave pe-
riod were chosen. These values were then used to calcu-
late the wave energy flux or wave power “P” using the
following expression [11]:
32 π
with, ρ is the sea water density 1025 kg/m3 and H and T
are the offshore wave height and period, respectively.
3.2. Topographic Data
Almost two years of beach surveying was conducted on
Charf el Akab site. A 3D topographic mapping was made
using GTS-TOPCON 225, a high resolution laser total
station, at two-monthly and/or seasonal intervals through-
out the study period. In this study, we obtained highly
accurate vertical (±2 cm) as well as horizontal (±5 cm)
position estimates, which allow us to recommend GTS-
TOPCON 225 as a highly effective tool for beach moni-
toring. Previously, many authors [12,13] stated that
ground survey, using GPS and Total Station techniques
give the best accuracy in elevation measurements. Then,
the DEMs established from such data sets seem to be
more representative of the field reality and the calcula-
tion of sediment budget is reliable [2].
Each of the 9 surveys covered most of the beach from
the dune to just below the waterline. The elevation points
measured are referenced to a benchmark installed at the
foot of the dune. The collected data were interpolated
using triangulation with linear interpolation (TLI) and
converted into a grid with 2 m cell spacing. The grids are
used to produce the DEMs for which the quality (preci-
sion) is assessed. Precision is usually evaluated by indi-
ces with no spatial dimension such as the mean error or
the root mean square error [4]. In this study, In this study,
estimated height from the selected interpolation tech-
nique was compared at each point to observed height
using a cross-validate option in a basic mapping software
program SURFER® (Golden Software, Golden, CO). An
empirically derived error margin of 5 cm, covering both
field measurement and data interpolation, was applied to
the raw data.
4. Results
4.1. Hydrodynamic Characterization
Wave climate for the period 2005 – 2007 was character-
rized by conducting a statistical analysis of the data sets
corresponding to the “wana43” point. Results shown in
Figure 3 indicate that the most likely waves come from
the W quadrant, with almost 90% of the incident angle of
the incoming waves range between SW and NW. The
most frequent wave directions are WNW and W, which
represent approximately 60% and 24%, respectively.
With respect to the wave energy, the most frequent (45%)
significant wave height is between 0.5 m and 1 m, and
93.5% of the time the wave height is below 2 m. During
the study period the significant wave energy exceeded
rarely (6.5%) 2 m, but the occurrence of such “storm”
events can affect strongly the beach morphology. The
most likely wave periods are within 8 to 12 s and 65% of
the time the wave period is above 8 s.
In order to characterize energy conditions just before
the surveying times, significant events were identified
and the wave height and period were chosen to determine
the corresponding energy level (Table 1). The results
show that the offshore waves are characterized by a
mean significant wave height and period of 2 m and 9 s,
respectively. However, considerable annual variation in
the wave conditions is experienced (Table 1). Mean sig-
nificant wave conditions in winter (January - March) are
characterized by a wave height of 2.85 m and a period of
13.4 s. Mean significant wave conditions in summer
(June - September) are characterized by a wave height of
1.6 m and a period of 6.7 s, which remain, however, rela-
tively energetic conditions.
Table 1. Offshore wave energy conditions.
Survey times Hs (m) Tp (s) P (kgms3)
23/04/2005 1.8 13.4 42 618
22/06/2005 2 9.4 36 915
24/09/2005 1.4 6.3 12 124
07/01/2006 2.5 12.3 75 472
04/03/2006 3.2 14.5 145 767
29/04/2006 1.2 7 9 896
27/06/2006 1.3 5.3 8 792
09/09/2006 2 6.5 25 526
20/01/2007 2.5 7.5 46 019
Mean 1.99 9.13 44 792
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Figure 3. Histograms of wave direction, significant wave height and peak period for the 2-year period.
In summary, results from wave climate analysis prove
that Charf el Akab beach was subjected to seasonal
variation in incident wave conditions during the survey
period. This seasonality is characterized by more ener-
getic waves in winter than in summer.
4.2. Beach Morphology
The beach morphology is described herein by represent-
ing the main changes occurred the survey period. The
DEMs illustrated in Figure 4; show two contrasting pro-
files where the morphology is affected by the accretion
and/or decay of an intertidal bar. The profile during
summer “accreted profile” was characterized by a non-
permanent feature (swash bar) aligned in the longshore
direction (Figure 4(a)). The formation and onshore mi-
gration of the swash bar is induced by low-energy condi-
tions prevailing during the summer season (Table 1).
These conditions favored onshore sediment transport by
swash processes; the sand is then accumulated in the
upper beach (Figure 4(a)). Following this calm period,
significant increase in wave energy (Hs > 2.5 m) re-
corded in winter (Table 1 ) caused a total decay of the bar
and yielded an “eroded profile” (Figure 4(b)). Such
evolution permitted us to suggest that Charf el Akab
beach present a cyclic behavior mainly modeled by wave
energy variations during the study period. It should be
stated; however, that beach slope remained gentle with a
mean gradient of tanβ = 0.02, and exhibited low variabi-
lity throughout the different surveys.
4.3. Net Beach Change and Sand Budget
Quantifying the net beach change between successive
surveys permitted us to assess both visual and quantita-
tive patterns of erosion and deposition within the system.
In this way, we used different grid commands of a soft-
ware program (SURFER®), and subsequent grid was
subtracted from previous grid to produce altimetry change
Copyright © 2011 SciRes. IJG
(a) (b)
Figure 4. Examples of beach profile during the survey period. Elevations are in meters relative to the Moroccan General
Leveling (N.G.M).
map and calculate sand budget adjustments. The esti-
mated error of about ±5 cm on the data utilized corre-
sponds to an uncertainty of ±2000 m3 in the computed
Results shown in Figure 5 provide information on
portions of the beach that had eroded, remained un-
changed or accreted between survey times and show the
net volume corresponding to each period. The main
morphologic changes observed and the volumes involved
are described briefly below.
1) Jun 22nd to Sep 24th, 2005
Low-energy conditions prevailed during this period
(Table 1) and beach accretion is more pronounced than
erosion yielding a significant deposition, the highest re-
corded over the 2-year survey period (Figure 5(a)). The
accretion was mostly observed in the intertidal zone,
whereas the erosion predominated on the backbeach.
This accretion phase is associated with a build up and
onshore migration of the swash bar. The sediment vol-
ume deposited was larger than that eroded, and the net
beach gain was of +8809 m3 of sediments.
2) Sep 24th, 2005 to Jan 7th, 2006
Relative increase in wave energy was observed
throughout this period and several high events (Hs > 2 m)
were recorded. This time was marked by net erosion,
especially in the lower and middle intertidal zones where
the bar was eroded causing an important beach flattening
(Figure 5(b)). In addition, minor spatially areas of net
deposition were observed on the backbeach. As a result,
the eroded volume was very important and a net beach
loss of -6593 m3 was recorded.
3) Jan 7th to Mar 4th, 2006
During this period, many high-energy events (Hs > 2 m,
Tp > 10 s) were recorded (Table 1). Accordingly, the
beach underwent the major erosional episode which
cause the bar destruction and/or offshore bar migration
resulting in a flatter beach profile (Figure 5(c)), whereas
a weak sediment deposition occurred on the backshore.
As a result, the beach developed a relatively flat and
featureless profile. Since the beach underwent dramatic
erosion, lost volume was the greatest and reached
–14302 m3.
4) Mar 4th to Jun 27th, 2006
This was a period when significant net deposition oc-
curred (+6746 m3). There was 0.25 - 0.75 m of accretion
that extended from 80 to 180 m cross-shore distance
(Figure 5(d)). The most significant occurrence during
this time was the formation of a swash bar in a parallel
direction of the shoreline. This was a relatively low-en-
ergy period; a maximum wave height of only 2 m was
recorded once. There was a long-duration event when Hs
< 1.25 m. Additionally, there was a moderate and spa-
tially minor area of erosion, notably on the backbeach.
This erosion can be ascribed to the dry eastern winds
which moved sediment in offshore direction.
5) Jun 27th to Sep 9th, 2006
Persistence of relative calm conditions during this pe-
riod (Table 1) induced swash bar growth and onshore
migration. The beach was significantly accreted com-
pared to the eroded backbeach (Figure 5(e)), always pro-
bably due to the eastern winds. This summer period was
characterized by a small sediment gain (+3666 m3) com-
paratively to the previous summer. This can be ascribed
to few separate energetic events (Hs > 1.8 m) which seem
moved offshore some sediment accumulated in the inter-
tidal zone.
6) Sep 9th, 2006 to Jan 20th, 2007
Almost minor net changes were recorded during this
period due to alternation of high- and low-energy events.
As a result, the swash bar moved till the backbeach and
formed a planar berm; whereas spatially minor zones of
erosion were located on the lower beach (Figure 5(f)).
Therefore, the beach net gain was only of +3020 m3 of
ediments. s
Copyright © 2011 SciRes. IJG
(a) (d)
(b) (e)
(c) (f)
Figure 5. Net DEMs beach changes and the sand budget involved for the survey beach. NBV = net beach volume. The plots
size is quite identical for all maps and is about of 40 000 m2. The area between yellow lines represents the elevation trench
considered as a negligible variation.
The overall net volume between the first and last sur-
vey highlighted the negligible changes in sediment
budget of Charf el Akab beach over the study period.
This stability leads to suggest a local distribution of
sediments; the sand eroded from beach during winter is
moved off-shore and deposited in the subtidal zone and
following a period of fair weather conditions (summer)
the beach is accreted by sediment supply from the sub-
merged area.
5. Discussion and Conclusions
The use of digital elevation models in beach morpho-
logical analysis has expanded throughout the decade of
the 1990s allowing a comparison between surveys from
different times [2]. However, the DEMs utilized in this
work allowed both visual and quantitative assessment of
beach changes. Accordingly, this study demonstrates the
usefulness of DEMs in the evaluation of morphological
and volumetric beach changes. In fact, the survey area is
highly exposed to swell events and beach morphody-
namics should be controlled by wave forcing. The results
obtained by both wave and morphology analysis support
this statement. It seems, therefore, that the sand removed,
during winter, is transported seaward and accumulates
mainly in the subtidal zone. The loss of volume is par-
tially compensated for by accumulation to the beach face
during fair-weather conditions in summer months.
In addition, a comparison between the beach change
maps and the sand volume adjustments showed that
greatest morphological and volumetric changes were
strongly associated with the accretion and erosion of an
intertidal bar. This result coincides with the findings of
Masselink and Hegge [14] who demonstrated that
changes in Nine Mile Beach morphology, on the Austra-
lian coasts, were mainly associated with the formation
and evolution of secondary morphological features, in
particular, swash bars in the intertidal zone. Therefore, it
appears that onshore and offshore bar migration, oc-
curred in response to low- and high-wave conditions,
In order to examine the role of wave forcing on beach
morphodynamics, we correlated net beach volume with
wave power variations during the survey times. The
Figure 6 shows that beach volume changes is inversely
proportional to wave power variations. In other words,
an increase in wave energy leads to a loss sediment stock
whereas a weak energy level permits to gain consider-
able quantities of sediment. This trend is supported by
the well correspondence between volume change and
wave power variations with a coefficient of correlation
of ap- proximately r2 = 0.9. This allows us to infer that
the beach changes occurred in Charf el Akab site during
the survey period were primarily caused and controlled
by wave forcing.
Summarizing, the use of DEMs based on high resolu-
tion filed data to quantify beach changes allow the fol-
lowing conclusions to be drawn from this study:
Figure 6. Beach volume and wave power variations during the survey period.
Copyright © 2011 SciRes. IJG
Copyright © 2011 SciRes. IJG
1) Charf el Akab beach presented almost seasonal be-
havior during the study period;
2) this trend consisted in net accretion during low- en-
ergy conditions (summer) and beach erosion and flatten-
ing due to high wave energy in winter months;
3) the sediment budget variations were found to be
strongly influenced by seasonal changes in wave energy;
4) the 3-D DEM employed here is valuable tool with
which morphological and volumetric changes can be
clearly visualized and quantified.
Finally, this investigation presents an effective method
of determining beach accretion and/or erosion from
high-resolution spatial data which enables accurate
three-dimensional DEMs production. The results from
the present work support this suggestion since the vol-
ume change calculated from DEMs, were highly corre-
lated to variations in wave forcing. These dynamics
would not be identifiable using two-dimensional profiles
and this em- phasizes the value of the three-dimensional
DEMs uti- lized in this study.
6. Acknowledgements
This work was funded by the Moroccan PROTARS III
D16/07 program research. The principal author was
sponsored by a PhD studentship provided by the Na-
tional Center for Scientific and Technical Research of
Morocco. Authors are grateful to the anonymous re-
viewers for their constructive remarks and suggestions
for improvement.
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