Page 22 The Earth Scientist
aB S T r a c T
This article present a project developed by Portuguese high school students.
They have manufactured an analogical model that demonstrates how sedi-
ment is transported alongshore. The model also illustrates the anthropogenic
interference with the sand drift as a result of the implementation of coastal
engineering structures like groins (a hard, man-made stabilization built
perpendicular to the beach intended to prevent the migration of sand during
alongshore drift). From the results, students have concluded that the groins
are not the solution to the problems of coastal erosion; on the contrary, they
enhance and transfer it to the adjacent areas.
in T r o d u c T i o n
Along most of the world’s coastal areas one can observe the increase of erosion and
shoreline retreat. In Portugal, as in many other countries, this situation has been
recognized as an important problem.
The main factors contributing to this growing problem are: (a) sea level rise, (b)
decrease in the amount of sediment that reaches the coastal areas, (c) the human
occupation and deterioration of natural landforms and (d) the deployment of coastal
engineering structures. The recent evolution of the coastal stretch along Vilamoura
and Quarteira towns (Algarve, Southern Portugal) (Fig.1) is a paradigmatic example of
The most signiﬁcant
structures in this area
are the Vilamoura
Marina jetties (600
and 500 m long); the
Quarteira ﬁshing boat
harbour and the groins
(140 m long) built to
protect the oceanfront
of Quarteira. These
the ﬂow of sand along-
Bu i l d i n g a m o d e l in T h e
c l a S S r o o m T o i l l u S T r a T e
h u m a n i n T e r F e r e n c e w i T h
S a n d d r i F T
Figure 1 - Location of
the study area near
the coastal towns of
Vilamoura and Quarteira
By Hélder Pereira
Grupo de Biologia e Geologia,
Escola Secundária de Loulé,
Page 23Volume XXV, Issue 2
shore, causing the increase of the erosion rates of the cliffs located eastwards. This
situation led to the construction of more groins, which require regular maintenance
and enhancement, without solving the problem.
After a ﬁeldtrip to the study area three students, from our school’s Earth and Space
Sciences Club, developed this project with the main purpose to demonstrate the ﬂow
of sand along a beach, and the interference of human engineered structures in the
alongshore sand drift.
ma T e r i a l a n d
m e T h o d S
The ﬁrst step of the model
manufacture was making an
aquarium from acrylic glass
plates; silicone was used
to join glass plates. Then
polyurethane foam and sand
were used to make the beach
proﬁle; gravel allowed making
a groin like structure perpen-
dicular to the shore. A wave
generator mechanism was
developed using an electric
motor attached to an acrylic
glass plate (Fig. 2 and 3).
re S u l T S
The model built in this project
illustrates the movement of
sediment parallel to shore
when waves strike the shore-
line at an angle. After turning
on the wave generator, one
can see waves hitting the
shoreline and changing direc-
tion, becoming nearly parallel
to the shoreline (wave refrac-
tion). Refracted waves hit the
coastline at a small angle,
pushing water and sand
parallel to the coastline in the
form of an alongshore current.
Consequently, sand has a net
movement down current. This
net movement of the sand is
known as alongshore sand
The model also demonstrates
the interference of human
engineered structures in the
alongshore sand drift. Groins
interrupt sand ﬂow along the coast and one can see that the beach up current widens
due to sand accumulation, but as sand continues to move the beach down current
erodes severely (Fig. 4).
Figure 2 – General view of
the model manufactured
by the students.
Figure 3 - Students
making ﬁnal adjustments
in the wave generating
mechanism of the model.
Figure 4 – Aspect of the
model after the generated
waves hit the shoreline:
deposition up current
(left) and erosion down
Page 24 The Earth Scientist
di S c u S S i o n a n d c o n c l u S i o n S
With this project an analogical model was built, that demonstrates the alongshore
sand drift. The model also illustrates the effect of human interference with the sand
drift, as a result of the construction of coastal engineering structures like groins.
From the results obtained, the students have concluded that shorelines are very
dynamic and that the groins do not minimize, nor are they the solution to the prob-
lems of coastal erosion; on the contrary they enhance and transfer it to the adjacent
During the ﬁeldtrip to the study area, students realized that the other approach of
coastal management – beach nourishment – has contributed to the decrease of the
erosion of the coastal cliffs located east of Quarteira, induced by the groins interfer-
ence with the sand drift.
ac k n o w l e d g e m e n T S
The author would like to thank the enthusiasm and commitment of the 3 students –
that developed the described model and Óscar Ferreira for his suggestions on how
to build and improve it. The author would like to thank the editor, Tom Ervin, who
provided his very useful comments for this article.
Bi B l i o g r a P h Y
Bettencourt, P. (1985) Géomorphologie et Processus d’Évolution Récente de la
Côte Sotavento (Algarve, Sud Portugal). Ph.D Thesis, Univ. de Bordeaux I: 92p.
Correia, F., Dias, J.M.A. and Boski, T. (1994) The retreat of eastern Quarteira cliffed
coast (Portugal) and its possible causes. In: Jones, P.S.; Healy, M.G. and Williams,
A.T. (Eds.) Studies in European Coastal Management: pp.129-139.
Dias, J.M.A. (1988) Aspectos Geológicos do Litoral Algarvio. GEONOVAS, 10: pp.113-
Dias, J.A. (1990) A Evolução Actual do Litoral Português. GEONOVAS, 11: pp.15-28.
Dias, J. A. and Neal, W.J. (1992) Sea cliff retreat in Southern Portugal: proﬁles,
processes, and problems. Journal of Coastal Research, 7 (3), pp. 839-852.
Dias, J.A. and Taborda, R.P.M. (1988) Evolução Recente do Nível Médio do Mar em
Portugal. Anais do Instituto Hidrográﬁco, 9: pp. 83-97.
Gomes, F.V. and Pinto, F.T. (2004) Vale do Lobo (Portugal). EUROSION, Case Study.
time accessed, 15 Jan 2009).
Kraus, N.C. and Galgano, F.A. (2001) Beach erosional hot spots: types, causes and
solutions. Coastal and Hydraulics Engineering Technical Note CHETN II-44, U.S.Army
Engineer Research and Development Center, Vicksburg, M.S.: 17p.
Oliveira, S. Cruz de; Catalão, J.; Ferreira, Ó. and Dias, J.M.A. (2008) Evaluation of
cliff retreat and beach nourishment in southern Portugal using photogrammetric
techniques. Journal of Coastal Research, 24(4c): pp. 184-193.
Pereira, H.; Guerreiro, V.; Dias, J.M.A. and Ferreira, Ó. (1998) Short term cliff retreat
at Quarteira-Vale do Lobo (Algarve - Southern Portugal). Proceedings of Littoral’98
-Fourth International Conference: pp. 397-403.
Pilkey, O.H. and Wright III, H.L. (1988) Seawalls versus beaches. Journal of Coastal
Research, SI (4), pp. 41-64.
aB o u T T h e
u T h o r
Hélder Pereira (1)
Grupo de Biologia
e Geologia, Escola
Loulé, Av. Laginha