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Beach response to high energy wave climate. A case study in...
Beach response to high
energy wave climate.
A case study in the
portuguese west coast
Jorge Manuel do Rosario
Trindade
C e n t r o de E s t u d o s G e o g r á f i c o s
F a c u l d a d e de Letras d a
U n i v e r s i d a d e de L i s b o a
j o r g e t r d @ u n i v - a b . p t
Ana Paula Ribeiro
Ramos-Pereira
C e n t r o d e E s t u d o s G e o g r á f i c o s
F a c u l d a d e de Letras d a
U n i v e r s i d a d e d e L i s b o a
anarp@fl.ul.pt
Mario Rui Nunes Neves
C e n t r o d e E s t u d o s G e o g r á f i c o s
F a c u l d a d e de Letras da
U n i v e r s i d a d e de L i s b o a
inario.neves@ceg.ul.pt
Territoris (2007-2008). 7:
21-38
Territoris
Universitat de les Illes Balears
2007-2008. Núm. 7. pp. 21-38
ISSN: 1139-2169
BEACH RESPONSE TO HIGH ENERGY
WAVE CLIMATE. A CASE STUDY IN THE
PORTUGUESE WEST COAST
J o r g e M a n u e l d o R o s a r i o T r i n d a d e
A n a Paula Ribeiro R a m o s - P e r e i r a
M a r i o Rui N u n e s N e v e s
ABSTRACT: Portugal's vvestern coast is a wave-dominated rocky coast with a semidiurnal mesotidal regime. The
wave climate is highly conditioned hy the Atlantic Ocean's atmospheric circulation. which results in a seasonal
change in wave patterns. Storms arc freqüent during winter and can reach 10-m wave heights with a 5-year recurrence
period. Four profile monitoring campaigns were carried oul in December 2005. January and May 2006 using a dGPS
and a total station to evalúate the response of three differem beach systems to high wave climate events. comparíng
pre-storm wave. morphology and sediment characlerislics with the modifications induced in the system after the storm
event. A series of 64 beach profiles is analysed in terms of sediment textural propenies. volume. slope. surf similarity
Índex and dimensionless full velocity parameters' variability. Each beach system's modal and límit morphological
behaviours are established according to Wright and Short's morphodynamic model.
KEY WORDS: Beach profile. storm event. system morphodynamic range.
RESUMEN: La costa oeste de Portugal es una costa rocosa dominada por olas y con un régimen mesomareal
semidiurno. El clima marítimo está altamente condicionado por la circulación atmosférica del océano Atlántico y
presenta una variabilidad estacional en el régimen de oleaje. Las tormentas son frecuentes durante el invierno y
pueden alanzar alturas de ola de 10 m con una recurrència de 5 años. Se han hecho cuatro campañas de control en tres
playas, mediante el uso de GPS diferencial y estación total con el objetivo de evaluar su respuesta a sendos episodios
de alta energía. Se comparan los cambios en la morfología y en la textura sedimentaria antes y después de cada
temporal. Para ello se realizaron 64 perfiles de playa y se han analizado las variaciones en la textura del sedimento, el
volumen, la pendiente, el índice de surf similarity y el parámetro adimensional de caída del sedimento. Con todo ello
ha podido establecerse el comportamiento morfológico modal y extremo de dichas playas según el modelo de Wright
y Short.
PALABRAS CLAVE: Perfiles de playa, temporales, variaciones del sistema morl'odinámico.
T r i n d a d e . J.. R a m o s - P e r e i r a . A. y N e v e s . M .
Beach response to high energy wave climate.
1. Introduction
d o m i n a n t w a v e p a t t e r n s a l o n g t h e c o a s t
occur in 265 days of the year (Costa, 1994)
B e a c h e n v i r o n m e n t s a r e t h e r e s u l t of
a n d t h e m e a n o f f s h o r e s i g n i f i c a n t w a v e
s e v e r a l f o r c i n g f a c t o r s w h i c h act p e r -
height is 2,5m in winter and I.Om in s u m m e r
manently changing profile m o r p h o l o g y and
( O l i v e i r a P i r e s . 1 9 8 9 ) . C a r v a l h o ( 2 0 0 4 ) ,
b e a c h s h a p e . W a v e s , t i d e s a n d s e d i m e n t
u s e d t h e w a v e n u m è r i c m o d e l M A R 3 G
properties are amongst the main factors that
( O l i v e i r a P i r e s & C a r v a l h o . 1 9 9 6 ) a n d
e x p l a i n t h o s e c h a n g e s . W h i l s t b e a c h m o -
applied it to a 1998/2001 o c e a n - a t m o s p h e r i c
p h o d y n a m i c s c a n b e d e f i n e d t h r o u g h
c l i m a t e d a t a s e r i e s . H e e s t i m a t e d 8
seasonal cycles. the dramàtic c h a n g e s occur
s t o r m s / y e a r in t h e w e s t - c e n t r a l c o a s t of
frequently during high energy events. T h e s e
P o r t u g a l w i l h w a v e h e i g h t s a b o v e 4 m ,
c h a n g e s a r e v e r y s i g n i f i c a n t for l o c a l
m o s t l y b e t w e e n O c t o b e r a n d A p r i l . T h e
c o m m u n i t i e s b e c a u s e o f t h e i m p o r t a n t
main directions of high w a v e climate fnund
d a m a g e costs, namely in beach facilities.
by C a r v a l h o ( 2 0 0 4 ) w e r e W ( 6 7 , 3 % ) and
T h e m a g n i t u d e of m o r p h o l o g i c a l
N W ( 2 7 , 4 % ) . Considering storms with w a v e
c h a n g e s in wave d o m i n a t e d e x p o s e d beach
heights over 6m. the W direction was found
systems are closely related to the capacity of
in 89,3'/f of t h e o c c u r r e n c e s . H o w e v e r ,
t h e o u t e r b a r s u b - s y s t e m to a b s o r b a n d
storm w a v e s from S W are less freqüent but
d i s s i p a t e w a v e e n e r g y b e f o r e it r e a c h e s
they usually h a v e a h i g h e r m a g n i t u d e and
beach face. This capacity can be e x c e e d e d if
c a n r e a c h h e i g h t s of 10 - 12m ( P e r e i r a ,
t h e f r e q u e n c y of s t o r m o c c u r r e n c e o v e r -
1999: T a b o r d a et al. 1992). E x t r e m e w a v e
c o m e s t h e t i m e n e e d e d f o r t h e s y s t e m
h e i g h t s a b o v e lOm can be r e a c h e d with a
recovery.
r e c u r r e n c e p e r i o d of 5 y e a r s ( C a r v a l h o .
T h e aim of this vvork is to evalúate the
1992).
r e s p o n s e of S t a . R i t a . A z u l a n d F o z d o
C o a s t a l drift is u s u a l l y d i r e c t e d to the
L i z a n d r o b e a c h e s to h i g h w a v e c l i m a t e
south along the West coast. although Pereira
e v e n t s t h r o u g h m o r p h o s e d i m e n t a r y v a -
( 1 9 9 1 ) r e f e r s that in c a s e s of s t r o n g S W
riability analysis and to establish modal and
w a v e c l i m a t e the s o u t h w a r d s c o a s t a l drift
l i m i t m o r p h o l o g i c a l b e h a v i o u r s o f t h i s
may invert locally its direction. Several field
systems.
and numérica! based estimates of longshore
t r a n s p o n r a t e in t h e w e s t e r n c o a s t o f
Portugal have been m a d e a range b e t w e e n
2. Study site framework
1.0 x l O and 2.3x10" mVyear (Oliveira et al.
6
1982; B e t t e n c o u r t . P. & A n g e l o . C . 1992;
T h e western coast of Portugal, b e t w e e n
T a b o r d a . 1 9 9 3 : V i d i n h a et al. 1 9 9 7 :
P e n i c h e and C a s c á i s , is a w a v e d o m i n a t e d
L a r a n g e i r o . 2002). Most of those estimates
r o c k y coast with a s e m i - d i u r n a l m e s o t i d a l
are related lo the central-northern sector of
r e g i m e . Tidal w a v e p r o p a g a t e s n o r t h w a r d s
the P o r t u g u e s e c o a s t . b e t w e e n N a z a r é and
and reaches its m á x i m u m amplitude at circa
O p o r t o (Fig. 2).
4 m . The Cascáis tidal gauge data s h o w s that
T h e c o a s t l i n e b e t w e e n P e n i c h e a n d
in 1998 the e x t r e m e w a t e r l e v é i s r e a c h e d
Cascáis is a limestone cliff d o m i n a n t with a
4.03()m and the mean spring tide amplitude
lack of sediment supply from local sources
w a s 3,075m (Fig. 1). W a v e climate is highly
and from longshore drift sediment d y n a m i c s .
c o n d i t i o n e d by the A t l a n t i c O c e a n a t m o s -
S o u t h w a r d s longshore drift is interrupted by
p h e r i c c i r c u l a t i o n r e s u l t i n g in a s e a s o n a l
the s u b m e r g e d N a z a r é c a n y o n and by the
c h a n g e of t h e w a v e p a t t e r n s . N o r t h w e s t
Peniche headland (Fig. 2).
24
Territoris, núm. 7. 2 0 0 7 - 2 0 0 8
Beach response to high energy wave climate.
T i ï n d a d e . J.. R a m o s - P e r e i r a . A. y N e v e s , M .
T h e Peniche - Cascáis continental shelf,
T h e e x p o s e d beach s y s t e m s are n a r r o w ,
between Om and - 5 0 m , is mainly c o m p o s e d
e m b a y e d or a s s o c i a t e d w i t h small infilled
of r o c k o u t c r o p s a n d c o a r s e s e d i m e n t
valleys as a result of the Holocene sea level
d e p o s i t s w i t h h i g h l e v é i s of b i o g e n i c
rise. and their importance in the overall costal
remains. Fine sands and m u d s are found in
systems of the study area decrease southwards.
v e r y c o n f i n e d a n d s h e l t e r e d a r e a s in t h e
T h r e e b e a c h - d u n e s y s t e m s , different in
E r i c e i r a s e a . T h e r e f o r e . l o c a l s e d i m e n t
size and shape. bul similar in the exposure to
sources are scarce due to (i) continental shelf
W s t o r m y w a v e c l i m a t e . w e r e c h o s e n to
m o r p h o l o g y a n d d e p o s i t s , ( i i ) l i t t l e
¡ I l ú s t r a t e t h e b e a c h - s y s t e m s ' m o r p h o -
c o n t r i b u t i o n f r o m t h e s m a l l r i v e r b a s i n s
d y n a m i c s . T h e y a r e a l s o i n c l u d e d in a
(Pereira, 1987) and (iii) the carbonate nature
monthly monitoring p r o g r a m m e being held
of the rocks that constitute the cliff systems
at the «Centro de Estudos Geográficos» for
(Neves, 2004).
over two years.
H i g h ( m )
L o w (m)
e s T
4.030
0.070
m s T
3.672
0.597
m n T
2.902
1.447
Figure 1. Tidal range in the Cascáis tide gauge ( 3 8 ° 4 1 ' 3 9 , 1 7 1 " N ; 0 9 ° 2 5 0 5 , 2 2 9 " W - heights
-
above chart d a t u m ) , 0 1 - 0 1 - 1 9 9 8 / 3 1 - 1 2 - 1 9 9 8 . esT - e x t r e m e spring tide: msT - m e a n spring
tide; mnT- m e a n neap tide: msl - m e a n sea level.
T h e Sta. Rita b e a c h is a m i x e d b e a c h -
2 0 0 m in w i d t h and has a v e r y small d u n e
d u n e / b e a c h - c l i f f s y s t e m ( F i g . 2 - a ) . T h e
field. highly d a m a g e d by h u m a n trampling.
b e a c h - d u n e c o m p o n e n t of t h e s y s t e m is
Azul b e a c h (Fig. 2-b) is the largest b e a c h -
55()m l o n g and 1 5 0 - 2 0 0 m w i d e , w h i l e the
d u n e s y s t e m . 19()0m long and 9 7 5 m w i d e
b e a c h - c l i f f part is lOOOm l o n g a n d lOOm
and is the only one of the three affected by
wide. F o z do Lizandro beach (Fig. 2-c) is a
o v e r w a s h e s .
b e a c h - d u n e s y s t e m 6 0 0 m in l e n g t h a n d
Territoris, n ú m . 7. 2 0 0 7 - 2 0 0 8
2 5
T r i n d a d e , J.. R a m o s - P e r e i r a , A. y N e v e s , M .
Beach response to high energy wave climate.
Figure 2. The study área, a - Sta. Rita beach: b - Azul beach: c - Foz d o Lizandro beach; Le -
Leixòes offshore w a v e buoy; Sn - Sines offshore w a v e buoy.
3. Methodology
c o n s i d e r e d r e p r e s e n t a t i v e of t h e l o c a l
h y d r o d y n a m i c i n f l u e n c e in s e d i m e n t
Four monitoring c a m p a i g n s were carried
t r a n s p o r t d u r i n g t h e h i g h w a v e c l i m a t e
o u t in p r e - s t o r m a n d r i g h t a f t e r s t o r m
event.
conditions ( D e c e m b e r of 2 0 0 5 , January and
Total station and d G P S units were used to
M a y of 2 0 0 6 ) on t h e t r e e b e a c h s y s t e m s ,
m e a s u r e e m e r g e d b e a c h v o l u m è t r i c a n d
resulting in 64 survey profiles (table 1). T h e
m o r p h o m e t r i c c h a n g e s . T h e d i f f e r e n c e s
s t o r m m o r p h o l o g i c a l a n d s e d i m e n t p a r a -
b e t w e e n t h e t w o t e c h n i q u e s p r o v é to b e
m e t e r s m e a s u r e d 3 or 4 d a y s after s t o r m
negligible in this dynamic context (Trindade
p e a k s in e a r l y J a n u a r y a n d l a t e M a y a r e
et al, 2007). As part of a beach monitoring
26
Territoris, núm. 7. 2 0 0 7 - 2 0 0 8
Beach response to high energy wave climate.
T r i n d a d e . J.. R a m o s - P e r e i r a , A. y N e v e s . M .
p r o g r a m m e , b e a c h p r o f ï l e n u m b e r a n d
c o r r e s p o n d s to a b o u n d a r y b e t w e e n marine
spacing were initially defined to record data
and aeolian d y n a m i c s . This boundary point.
f r o m t h e b e a c h f a c e a n d b e r m m o r p h o -
that we can call a knick point, was accessed
dynamics.
b y t h e d i r e c t o v e r l a p of all t h e o b t a i n e d
B e a c h p r o f i l e s a r e a n c h o r e d in f i x e d
beach profiles.
p o i n t s a w a y from the h y d r o d y n a m i c area,
S e v e r a l i n t e r p o l a t i o n m e t h o d s w e r e
e n s u r i n g o v e r l a p p i n g b e t w e e n c a m p a i g n s
tested with the field data of M a y c a m p a i g n
(Trindade et al, 2006).
in order to calcúlate beach profile v o l u m e .
Beach m o r p h o d y n a m i c s w a s accessed by
namely inverse distance to a p o w e r of two,
v o l u m e variability a l o n g e a c h profile with
k r i g i n g . n e a r e s t n e i g h b o u r a n d m o v i n g
an a s s u m e d width of 0, l m . T h e v o l u m e of
a v e r a g e . T e s t results e x p r e s s e d in T a b l e 2
each profile w a s calculated a b o v e m e a n sea
r e v e a l e d that K r i g i n g is the m o s t a c c u r a t e
l e v e l ( m s l ) a n d b e l o w t h e p o i n t of n o
t e c h n i q u e , w i t h the l o w e s t r e s i d u a l v à l u e s
r e l a t i v e h y d r o d y n a m i c s a n d m o v e m e n t .
b o t h in h e i g h t a n d v o l u m e c a l c u l a t i o n s
usually associated with the inland backshore
( A R H = 0 , 3 0 0 m ; A R V = - l , 6 8 5 m ) a n d
3
or backshore/foredune limit (Ferreira. 1998:
t h e r e f o r e t h e m o s t s u i t a b l e f o r t h i s
B a p t i s t a . 2 0 0 6 ) . T h e i n l a n d b e a c h profile
c a m p a i g n s profile volumetry.
limits is not e a s y to e s t a b l i s h and often it
Table 1. Monitoring c a m p a i g n s .
S". Rita beach
Azul beach
Foz do Lizandro beach
1
Sediment
Sediment
Sediment
Date
Profiles
Date
Profiles
Date
Profiles
Satnples
Samples
Samples
17,12.05
5
4
16.12.05
6
4
15.12.05
5
4
i Pre-storm)
04.01.06
5
3
02.01.06
6
.ï
03.01.06
5
4
(Storm)
14.05.06
5
4
15.05.06
6
4
12.05.06
S
4
(Pre-storm)
28.05.06
5
4
26.05.06
6
3
25.05.06
5
3
(Storm)
T a b l e 2. R e s i d u a l v à l u e s of h e i g h t and v o l u m e . A R H - A v e r a g e residual h e i g h t : A R V -
A v e r a g e residual v o l u m e .
A R H height (ni)
A R V (m')
Inverse distance
0.069
-2.716
Kriging
0.030
-1.685
Nearest neighbour
0.048
-3.308
Moving average
0.965
-74.352
Territoris, n ú m . 7. 2 0 0 7 - 2 0 0 8
2 7
T r i n d a d e , J.. R a m o s - P e r e i r a . A. y N e v e s , M .
Beach response to high energy wave climate.
S e d i m e n t o l o g i c a l a n a l y s e s of b e a c h
l i m i t of t h e s u r v e y e d p r o f i l e . in e a c h
s a n d s w e r e c a r r i e d o u t w i t h 4 4 s a m p l e s
c a m p a i g n ;
(Table 1) taken from the berm. beach face,
H is the breaker w a v e significant height.
h
base of the beach face and low tide terrace
expressed in meters a b o v e cel, obtained from
( w h e n e x i s t e n t ) d u r i n g e a c h c a m p a i g n , in
the K o m a r and G a u g h a n (1972) expression
order to evalúate grain size distribution and
based on the Leixòes offshore w a v e data:
statistical p a r a m e t e r s . A p p r o x i m a t e l y 6 0 g
H = 0,39g (T * H*)°
b
02
(2)
f r o m e a c h s a m p l e w e r e w a s h e d , w i t h o u t
c a l c i u m c a r b o n a t e d e s t r u c t i o n , a n d d r y
W h e r e :
s i e v e d b e t w e e n -2.0<j) ( 4 , 0 m m ) a n d 4,5<ji
H is t h e o f f s h o r e w a v e s i g n i f i c a n t
ü
( 0 , 0 4 4 m m ) . in 0,5<p intervals, and w e i g h e d
height. expressed in meters above cd;
w i t h a 0 , 0 1 g a c c u r a c y . T h e S E D M A C / -
0,39 is the empirical coefficient based on
S E D P C w o r k s h e e t ( H e n r i q u e s , 2 0 0 4 ) w a s
laboratory and field data from M u n k (1949)
u s e d t o c a l c ú l a t e t h e m e a n . S t a n d a r d
a n d c o n f i r m e d l a t e r as a g o o d p r e d i c t i v e
d e v i a t i o n a n d s k e w n e s s of e a c h s a m p l e .
coefficient by W e i s h a r and Byrne (1978);
a c c o r d i n g to the M e t h o d of M o m e n t s of
L„ is the deep water wave-length which.
Friedman and Sanders (1978).
b a s e d o n l i n e a r w a v e t h e o r y , c a n be
O f f s h o r e w a v e s i g n i f i c a n t (//,) a n d
calculated as:
m á x i m u m (//„„„.) height. expressed in meters
a b o v e chart d a t u m (cel « -2m msl), p e r i o d
(T) and wave direction (r7 ) w e r e provided
2n
(3)
í / / r
by the Leixòes buoy, one of the two offshore
w a v e buoys available on the west coast of
T h e D i m e n s i o n l e s s fall v e l o c i t y
Portugal (Fig. 2).
p a r a m e t e r (Q) w a s calculated a c c o r d i n g to
W a v e breaker type and m o r p h o d y n a m i c
the Wright and Short (1984) formula:
classification w a s accessed with widely used
p a r a m e t e r s . n a m e l y t h e s u r f s i m i l a r i t y
(4)
p a r a m e t e r o r I r i b a r r e n N u m b e r (£[,,) f o r
b r e a k e r w a v e c o n d i t i o n s a n d t h e
d i m e n s i o n l e s s fall velocity (Q) ( M a s s e l i n k
W h e r e :
& H e g g e , 1 9 9 5 : B e n a v e n t e et a l , 2 0 0 2 ;
\\\\\\ is t h e s e d i m e n t fall v e l o c i t y .
B e n e d e t . F i n k l & K l e i n . 2 0 0 4 : B e n e d e t ,
e x p r e s s e d in m / s . H a l l e r m e i e r ( 1 9 8 1 a.b)
Finkl. Campbell & Klein. 2004; Goodfellow
e m p i r i c a l f o r m u l a s for w w e r e u s e d to
s
& Stephenson, 2 0 0 5 : Anfuso & B e n a v e n t e ,
o b t a i n t h e fall v e l o c i t y of t h e s e d i m e n t
2006).
samples:
T h e s u r f s i m i l a r i t y p a r a m e t e r w a s
calculated according to Battjes, 1974:
0.7
(Ps-P)g 1
_
0
( ) M
W. =
P
(5)
(D
W /L ?
(Ps-P)gü
(6)
3
b
0
A =
51)
pv2
W h e r e :
tan/3 is the beach slope calculated from
W h e r e :
t h e a v e r a g e s l o p e of t h e b e a c h p r o f i l e s ,
p is the sediment density (=2,648 g / c m
s
3
b e t w e e n the b e r m c r e s t a n d the s e a w a r d
for quartz grains and =2,8 for shell material).
28
Territoris, núm. 7. 2 0 0 7 - 2 0 0 8
Beach respon.se to high energy wave climate.
Trindade. J.. Ramos-Pereira, A. y Neves. M.
p is t h e d e n s i t y of t h e s e a w a t e r ( = 1.026
H o w e v e r . the beach is c o m p o s e d of '-everal
g / c m at l 5 C - 33 p p t ) , u is the s e a w a t e r
c o n s t a n t s l o p e a n g l e s a s s o c i a t e d to t h e
3
a
kinematic viscosity (=0.0119 c m 2 / s at 15 C
d i f f e r e n t d y n a m i c s u b u n i t s of t h e b e a c h .
a
- 33 ppt), g is gravity acceleration (981cm/s)
Because the s u b m e r g e d profile is absent in
a n d D is t h e P a s s e g a ( 1 9 5 7 ) s e d i m e n t
this study, m e a n b e a c h slope is c a l c u l a t e d
S(I
median size, in centimetres. The Hallermeier
for t h e m o s t d y n a m i c a t e a s of t h e b e a c h
f o r m u l a t i o n for w ( e q . 5) w a s t e s t e d on
profile. including berm crest. beach face and
s
p r e v i o u s l y p u b l i s h e d s e t t l i n g v e l o c i t y
low tide terrace, when present.
m e a s u r e m e n t s of s a n d s w i t h a d i a m e t e r
range between 0 , 1 2 5 m m and l.Omm.
T h e quartz/shell content of the s a m p l e s
4. Results
was used to calcúlate the final result for the
w e i g h t e d a r i t h m e t i c a l m e a n o f W .
s
January and May c a m p a i g n s were prece-
concerning the different valúes of p .
s
ded by two high w a v e climate events recor-
T h e s e types of d i m e n s i o n l e s s p a r a m e t e -
ded entirely or partiallv. in the two existing
rizations are fully related to beach behavior
w a v e b u o y s (Leixòes and Sines). Despite the
and are useful tools to first access the range
p r o x i m i t y to t h e s t u d y á r e a , it w a s
o f b e a c h m o r p h o d y n a m i c s t a t e s . b u t
impossible to use data from the Sines buoy
c h o o s i n g the right p a r a m e t e r s to c a l c ú l a t e
because of the several g a p s registered in the
f o r m u l a e is d i f f i c u l t d u e to t h e i r r e g u l a r
January and late M a y records. This m a d e it
nature of the beach system d y n a m i c s .
unable to correlate and interpólate the Sines
T h e r a n g e of v a l ú e s a s s u m e d for Q in
d a t a w i t h t h e L e i x ò e s b u o y to fu 1 Ti 1 d a t a
one system depend on the measured range of
loss.
s e d i m e n t s i z e . w h i c h u s u a l l y c o n t r o l s the
T h e L e i x ò e s offshore w a v e data before
i n t e r t i d a l s l o p e . a n d on c h a r a c t e r i s t i c s of
the January 2 0 0 6 monitoring c a m p a i g n s w a s
incident w a v e s w h i c h are the main driving
very similar to the M a y 2 0 0 6 (Fig. 3). M e a n
factor of beach d y n a m i c s .
H valúes w a s 3.89m in January and 3.67m
s
Incident w a v e can be d e s c r i b e d by the
in M a y . T r e g i s t e r e d a r a n g e of 16,3s in
r a n g e of b r e a k e r t y p e s (t,,) that can o c c u r
J a n u a r y a n d 14.6s in M a y . r e a c h i n g Tnun
within a beach system. which are controlled
21,1 Os a n d 18.80s at the m á x i m u m s t o r m
by beach slope and w a v e height and length
strength (Table 3). H w a s p r e d o m i n a n t l y
Jir
( K o m a r , 1998; Masselink & H u g h e s . 2003).
from the N W quadrant with resultant vectors
Table 3. High w a v e climate event data from Leixòes w a v e buoy.
3 0 - 1 2 - 2 0 0 5 - 16h
2 1 - 0 5 - 2 0 0 6 - 0 6 h
to
to
0 1 - 0 1 - 2 0 0 6 - 2 l h
2 3 - 0 5 - 2 0 0 6 - 12h
T i m e (h)
53
54
//, (m-cd)
3.89
3,67
£ / ( m - cd)
9.77
10.77
m a x
T(s)
8.54
8,38
21.10
18.80
Territoris, n ú m . 7. 2 0 0 7 - 2 0 0 8
29
T r i n d a d e . J.. R a m o s - P e r e i r a . A. y N e v e s . M .
Beach response to high energy wave climate.
of 310° in January and 309° in M a y (Fig. 3)
m e a n of t h e d i f f e r e n c e s b e t w e e n t h e v o -
w h i c h u s u a l l y m e a n s a s t r o n g s o u t h w a r d s
luntes of all e m e r g e d beach profiles in each
l o n g s h o r e d r i f t in t h e w e s t e r n c o a s t of
s y s t e m a n d in t w o s e q u e n t i a l c a m p a i g n s .
Portugal. T h e registered H is also perpen-
M e a n v o l u n t e s a n d t h e s e d i m e n t b u d g e t
d i r
d i c u l a r t o t h e S . R i t a a n d A z u l b e a c h
v a r i a b i l i t y ( m e a n and m á x i m u m ) b e t w e e n
l a
systems. The two high w a v e climate events
c a m p a i g n s are expressed in Table 4.
l a s t e d 5 3 h ( J a n u a r y ) a n d 5 4 h ( M a y ) a n d
V a l ú e s of m e a n s e d i m e n t b u d g e t v a -
H
r e a c h e d 9 , 7 7 m a n d 1 0 , 7 7 m . r e s p e c -
riability b e t w e e n c a m p a i g n s r a n g e from a
m a x
ti vely (Table 3).
m á x i m u m e r o s i v e s e d i m e n t d y n a m i c s (-
The m o r p h o d y n a m i c s of a beach system
3 9 9 , 5 1 9 m / m 3 ) in Foz do Lizandro beach to
a m á x i m u m a c c r e t i o n a r y b e h a v i o u r in S ".
c a n b e e x p r e s s e d in t e r m s of t h e m e a n
1
Rita beach ( 3 4 9 , 8 1 3 m / m 3 ) . both registered
sediment budget ( S B in T a b l e 4) w h i c h . in
m
in January data.
this study. is a s s u m e d to be the a r i t h m e t i c
Figure 3. W a v e parameters from Leixòes w a v e buoy preceding monitoring c a m p a i g n s .
30 Territoris, n ú m . 7. 2 0 0 7 - 2 0 0 8
Beach response to high energy wave climate.
T r i n d a d e . J.. R a m o s - P e r e i r a . A . y N e v e s . M .
Table 4. Slope, v o l u m e and mean sediment size in the three beach systems. S m - slope (x 102
= % ) ; V m - mean v o l u m e ( m / m 3 ) ; S B m - mean sediment budget ( m / m 3 ) ; S B m a x - m á x i m u m
variability of sediment budget ( m / m 3 ) ; T T s e d - m e a n sediment size of the tidal terrace ( m m ) ;
B B F s e d - mean sediment size of the base of the beach face ( m m ) ; BFsed - mean sediment
size of the beach face ( m m ) ; Bsed - mean sediment size of the berm ( m m ) ; Csed - c a m p a i g n
average sediment size ( m m ) ; N p - not present.
Date
S„,
V,„
SB
TT„„
BUF,.,,
BI'„„
c_
17.12.2005
0,0512
806.133
Np
0.370
0.348
0.602
0.440
( p r e -storm )
349.81 3
1.093.261
04.01.2006
0.0472
1155,946
Np
0.537
0.363
0.400
0.433
S". Rita
(storm)
Beach
14.05.2006
0.0988
0.466
(pre-storm)
1648,873
0.715
0.542
0.571
0.573
-149.044
298.097
28.05.2006
0.0596
1499.829
0.551
0.475
0.517
0.484
0.507
(storm)
16.12.200?
0.0514
1391.846
0.417
0.549
0.580
Np
0.515
(pre-storm)
-101.497
504.541
02.01.2006
0.0567
1290.348
0,473
0.434
0.428
Np
0.445
Azul
(storm)
Beach
15.05.2006
0.071 1
1033.670
0.746
0.742
0.437
Np
0.642
(pre-storm)
89.769
122.212
20.05.2006
0.0340
1123.439
0.525
0.855
0.506
Np
0.628
(storm)
15.12.2005
0.0725
2782.981
(1.714
0.443
0.498
0.544
0.550
(pre-storm)
-399.519
1.289.503
03.01,2006
Faz (t
z o
(t
0.0444
2383.462
0.400
0.410
0.426
0.398
0.409
(storm)
I.iznndro
Beach
12.05.2006
h
i
0.0826
2344.240
Np
0.544
0.42S
0.458
0.477
pre-storm)
-90,591
1.523.128
25 1)5 2l«Ki
0.0601
2253.649
Np
0.536
0.364
0.395
0.431
(storm)
Sa
S .a Rita Beac
a
h
0.509
(1.524
0.445
0.514
Azul Beac
l
h
0.540
0.645
0.4SS
Np
I-'oz
I-'o d
z o Lizandr
o
o Heuc
o
h
0,557
0.483
0.429
0.449
Azul beach have the smallest variation in
T h e s e d i m e n t c o l l e c t e d d u r i n g the four
sediment budget variability. January erosión
c a m p a i g n s is c h a r a c t e r i s e d b y m i d d l e
( - 1 0 1 . 4 9 7 m / m 3 ) is a l m o s t e q u i v a l e n t to
m e d i u m to m i d d l e c o a r s e s a n d s ( T a b l e 4 )
May accretion (89.769 m / m 3 ) .
w i t h s i z e s t h a t r a n g e f r o m 0 , 3 4 8 m m t o
Differences in s y s t e m s r e s p o n s e s to the
0 , 8 5 5 m m . T h e l o w r a n g e o f m e a n s a n d
s a m e energètic event can be m e a s u r e d also
sizes, a p p r o x i m a t e l y 1 . 2 5 0 . m a y be a s s o -
with m á x i m u m sediment budget variability
ciated to the high selectivity of the transport
( T a b l e 4 ) . T h e h i g h e s t m á x i m u m b u d g e t
a g e n t a n d t o t h e h o m o g e n e i t y o f t h e
value in January (1289.503 m / m in Foz d o
sediment source.
3
L i z a n d r o b e a c h ) w a s 2,5 times h i g h e r than
The D e c e m b e r - J a n u a r y sediments are in
the value of Azul beach (504,541 m / m ) . In
3
a v e r a g e l o w e r w h e n c o m p a r e d to a v e r a g e
May this relation rose to 12,5 times s h o w i n g
s e d i m e n t s i z e f r o m t h e M a y c a m p a i g n s .
t h e e x t r e m e d i f f e r e n c e s in t h e m o r p h o -
exception m a d e for F o z d o Lizandro where
d y n a m i c responses of this systems.
overall m e a n sand size is slightly higher in
M e a n beach slope variability (Table 4 ) is
D e c e m b e r - J a n u a r y c a m p a i g n s (Table 4 ) .
lower in Azul beach (3,717c). similar in F o z
S u p e r i o r valúes of m e a n sand sizes c a n
do L i z a n d r o b e a c h ( 3 . 8 2 % ) a n d h i g h e r in
also be found in the tidal terrace (0,540mm in
Sta. Rita beach ( 5 , 1 6 % ) .
Azul beach and 0.557mm in Foz do Lizandro
Territoris, n ú m . 7. 2 0 0 7 - 2 0 0 8
T r i n d a d e . J.. R a m o s - P e r e i r a . A. y N e v e s , M .
Beach response to high energy wave climate.
b e a c h ) a n d in the b a s e of t h e b e a c h face
a c c e s s i n g w a v e b r e a k e r c o n d i t i o n s a n d
( 0 , 5 2 4 m m in S . R i t a . 0 , 6 4 5 m m in A z u l
m o r p h o d y n a m i c s t a t e of t h e b e a c h by
t a
b e a c h a n d ( ) . 4 8 3 m m in F o z d o L i z a n d r o
formula and models is essential in order to
b e a c h ) . T h e s e m o r p h o l o g i c a l e l e m e n t s are
c o m p a r e t h e s y s t e m s r e s p o n s e to h i g h
placed w e r e the w a v e b r e a k e r point m o v e s
energy input during one or several episodes.
back and forward durin» the high tide cycle.
According to Wright and Short (1984) _
resulting in higher concentration of turbulence
c l a s s i f i c a t i o n ( < 1 Í 2 r e f l e c t i v e ; 2Q - 5Q
and wave energy dissipation. This differen-
i n t e r m e d í a t e ; > 6 Í 2 d i s s i p a t i v e ) , t h e t h r e e
tiation is not clear in the beach face and in the
b e a c h s y s t e m s lie b e t w e e n the d i s s i p a t i v e
berm where it would be expected a gradual
a n d i n t e r m e d í a t e s y s t e m s . T h e h i g h w a v e
decrease in the sediment size (Table 4).
climate events that occurred in January and
Sand samples are moderately well sorted
M a y of 2 0 0 6 (Fig. 4) are responsible for a
according to Friedman (1962) classification.
general c h a n g e in S '. Rita, Azul and Foz d o
u
S t a n d a r d d e v i a t i o n s h o w s little v a r i a t i o n
Lizandro beach systems towards dissipative
w h e n all c a m p a i g n s are a n a l y s e d ( 0 , 6 1 6 -
morphology (Fig. 4 . Tables 5 and 6).
0.779). Foz do Lizandro beach has the wider
D e c e m b e r - J a n u a r y r e s u l t s s h o w that
r a n g e in t h e s a m p l e d i s p e r s i ó n m e a s u r e
Sta. Rita evolved from low tide terrace with
(0.616 in the tidal terrace: 0.739 in the base
b e r m f o r m a t i o n to q u a s i - d i s s i p a t i v e
of the beach face: 0.755 in the beach face;
behaviour. T h e general decrease in ¡; vàlues
h
0,733 in the berm) in contrast with Sta. Rita
( T a b l e 5 ) f r o m t h e p r e - s t o r m t o s t o r m
which reveáis the highest h o m o g e n e i t y both
c o n d i t i o n s . e s p e c i a l l y d u e to H a n d L
h
ü
in m e a n ( T a b l e 4) and s t a n d a r d d e v i a t i o n
i n c r e a s e . reflects an a m p l i f i c a r o n of w a v e
measures (0,695 in the tidal terrace; 0,722 in
energy dissipation along s u b m e r g e d profiles
t h e b a s e of t h e b e a c h f a c e ; 0 . 7 4 5 in t h e
and an d e c r e a s e in the e n e r g y ' s reflection
beach face; 0.733 in the berm).
o v e r t h e b e a c h s y s t e m . as c l o s u r e d e p t h
m o v e s away from the shoreline.
T h e s a m e response w a s not observed in
5. Discussion
M a y c a m p a i g n s ( F i g . 4) as b e a c h p r o f i l e
r e a c h e d o n l y r h y t h m i c b a r a n d b e a c h
Although a wave breaker type and beach
behaviour. In fact, for similar offshore storm
profile c o n t i n u u m occur in natural beachcs.
v à l u e s ( F i g . 3) Q is m u c h l o w e r in M a y .
Table 5. Surf similarity index parameterization ), based on w a v e data from Leixòes buoy.
S P - spilling breakers: SG - surging breakers.
S"\\ Ritu beach
Azul l·i'iit'li
Foz du [.¡/andró htach
.v //, /..
•V H,. L„ ft,
i' H, L„ Çh
(U864
0.387!)
11.5472
Pre-storm
0.(1512 ().7.( 4 2 . Is
0.0514 0.74 4 2 . IS
0 . 0 7 2 5 0.74 4 2 . 1 5
January
SI'
SP
SG
S l u r m
0,2X08
0,3373
0.2641
0 . 0 4 " 2 2.02 71.SI
0 . 0 5 6 7 2.02 7131
0.11444 2.02 "1.51
SP
SP
SI'
0.6470
(1.4656
0,5409
Pre-storm
0.0988 1.09 4Í..74
0.0711 46.74 0.0826 1.0') 46.74
s o
M i n
SG
SG
0,3480
Storm
0 . 0 5 9 6 1,62 55.26
0,1985
0,3510
SP
0.0.140 1,62 5 5 . 2 6
0.0601 1.62 55.26
SP
SP
32
Territoris, n ú m . 7. 2 0 0 7 - 2 0 0 8
Beach response lo lügh energy wave chínate.
T r i n d a d e , J.. R a m o s - P e r e i r u . A. y N e v e s . M .
Field observations revealed the presence of
M a y s t o r m e v e n t s are c o n s i s t e n t with the
one longshore bar in January whilst in May
m á x i m u m s e d i m e n t b u d g e t v a r i a b i l i t y
t h e r e w e r e at l e a s t t w o b a r s p r e s e n t .
e x p r e s s e d in T a b l e 4 . w h e r e h i g h e r
A c c o r d i n g to Battjes ( 1 9 7 4 ) classification.
v a r i a b i l i t y of J a n u a r y s t o r m
the wave type for the two high w a v e climate
( 1 . 0 9 3 , 2 6 1 m / m ) is c o n t r a s t i n g with l o w e r
3
conditions w a s the spilling breaker. given as
M a y v a l u e ( 2 9 8 . ( ) 9 7 m / m ) . F u r t h e r m o r e ,
,
s t o r m in T a b l e 5 . S p i l l i n g b r e a k e r s a r e
sediment size variations across beach profile
usually associated with steep incident w a v e s
c o n f i r m t h i s t e n d e n c y . A n i n c r e a s e in
(= H a L ) and low gradient beach profiles
J a n u a r y m e a n s e d i m e n t size b e t w e e n p r e -
h
h
that play a significant role in w a v e e n e r g y
storm and storm data (Table 4) is noted on
d i s s i p a t i o n . T h e p r e s e n c e of m u l t i - b a r r e d
the base of the beach face and on the beach
s u b m e r g e d p r o f i l e a n d v e r y well d e f i n e d
face ( B B F - ().37()mm to 0 , 5 2 7 m m ; B F -
crescentic b e r m s in S . Rita pre-storm M a y
0 . 3 4 8 m m to 0 . 3 6 3 m m ) . w h i c h d i r e c t l y
t a
m o r p h o l o g y ( F i g . 4 ) a c t e d as a buffer to
reflects a rise in the e n e r g è t i c levéis. M a y
w a v e e n e r g y a n d to o n s h o r e s e d i m e n t
results reveal the opposite tendency. with a
t r a n s p o r t , r e s t r i c t i n g b e a c h p r o f i l e p r o -
d e c r e a s e in m e a n s a n d s i z e b e t w e e n p r e -
gression towards fully dissipative behaviour.
storm and storm conditions.
The differentiated Q valúes for January and
Santa Rita beach
- - P M 7 . 1 2 - 2 0 0 5 i
i P2. 17.) 2-2005.
- , P3.17-12-2005.
^ ' v. P4.17-12-2005.
v" '-7», P5.17-12-2005.
- P l . 0 4 - 0 1 - 2 0 0 5 .
- P l . 1 4 - 0 5 - 2 0 0 6 .
2i04-01-2OO6i . ] O
4
^ S > f c ^ V i . P2-14-05-2006.
P3.04-01-2006' £l ' " ~ \\ \\ F3.14-05-2006.
• P4i04-0)-2006. ! ^ \\ P4.14-05-2006.
2
P5.04-01-2006. X V' P5.14-05-2006.
• - P l . 16-12-2005.
P:. i6-t;-roc6.
P 3.16-12-2005.
- - - P4i IÓ-I:-:C-05.
£ 3
p;>. 16-12-2005.
PÒ. 16-12-2005.
- - P l . 26-05- 2006*
V \\ P2.2S-05-2006.
^ P3< 28-05-2006.
\\ V P4,2S-05-2006'
\\ \\ P5.2S-05-2006^
Territoris, n ú m . 7. 2 0 0 7 - 2 0 0 8
T r i n d a d e . J.. R a m o s - P e r e i r a . A. y N e v e s , M .
Beach response to high energy wave climate.
Jü^. Azul beach
P 1.26-05-2006.
P 2 . 2 6 - 0 5 - 2 0 0 6 .
P 3 . 2 6 - 0 5 - 2 0 0 6 .
P 4 . 2 6 - 0 5 - 2 0 0 6 .
P 5 . 2 6 - 0 5 - 2 0 0 6 .
P6.26-05-200.3.
—-
40
6 0
80 100 120 140 160 ISO
I D
Foz do Lizandro beach
7 I _ ~\\__
- - P l . 15-12-2005.
6 •
P2. 15-12-20051
5 •
P 3 . 1 5 - 1 2 - 2 0 0 5 .
i i
P4. 15-12-2005.
i 3
•. - — \\
.»„ P 5 . 1 5 - 1 2 - 2 0 0 5 .
= 1 -
o •
-1 •
0
2 0
4 0 6 0 SO 100 2 0 140 160 ISO 2 0 0
m
~ \\ ^
- - P 1.03-01-2006.
P 2 . 0 3 - O I - 2 0 0 6 .
P 3 . 0 3 - 0 1 - 2 0 0 6 .
P 4 . 0 3 - 0 1 - 2 0 0 6 .
P 5 . 0 3 - 0 I - 2 0 O 6 .
0
2 0
4 0 6 0 SO tOO 120 140 160 ISO 2 0 0
m
„
7 -~~
- - P l . 1 2 - 0 5 - 2 0 0 6 .
6 •
P2. 1 2 - 0 5 - 2 0 0 6 .
5 •
~- >
P3. 1 2 - 0 5 - 2 0 0 6 .
- 4 1
" ^ ^
P 4 . 1 2 - 0 5 - 2 0 0 6 .
í 3 -
" "~ - X -^ P5. 12-05-2006.
\\
= 1
0 •
\\ ~ ~- -
-1 -
- - -
0
2 0
4 0 6 0 3 0 100 120 140 1 6 0 130 2 0 0
ni
—
- - P 1 . 2 5 - 0 5 - 2 0 0 6
P 5 . 2 5 - 0 5 - 2 0 0 6
P 3 . 2 5 - 0 5 - 2 0 0 6
P 4 . 2 5 - 0 5 - 2 0 0 6
'
P 5 . 2 5 - 0 5 - 2 0 0 6
. . .
— , — ^ ••,-*:•»..
0
2 0
4 0 6 0 SO 100 120 140 160 ISO 2 0 0
m
Figure 4, Beach profile sequence in Sta. Rita, Azul and Foz d o Lizandro.
34 Territoris, n ú m . 7. 2 0 0 7 - 2 0 0 8
Beach response lo high energy wave climate..
T r i n d a d e . J.. R a m o s - P e r e i r a . A. y N e v e s . M .
E x c e p t i o n m a d e f o r m o r e e n e r g è t i c
( 0 , 3 3 7 3 - J a n u a r y s t o r m : 0 . 1 9 8 5 - M a y
and/or durable storms it can be a s s u m e d that
storm) indícate high dissipative behaviour of
t h e i n t e r m e d í a t e m o r p h o d y n a m i c state of
t h e s u b m e r g e d b e a c h a n d w a s a m a j o r
longshore bar-trough is the limit response to
contribution to the lowest m e a n variability
high h y d r o d y n a m i c events. The modal state
of J a n u a r y (-1 0 1 . 4 9 7 m / m l a n d M a y
: ,
of m o r p h o d y n a m i c b e h a v i o u r d u r i n g low-
( 8 9 , 7 6 9 m / m - ) sediment budgets (Table 4).
e n e r g y w a v e c l i m a t e w a s f o u n d to be the
This fact d o e s n ' t necessary mean a less
low tide terrace.
d y n a m i c system w h e n c o m p a r e d to the other
Azul beach m o r p h o l o g y ranged from low
t w o b e a c h e s . D i m e n s i o n l e s s fall v e l o c i t y
tide t e r r a c e in p r e - s t o r m m e a s u r e m e n t s to
p a r a m e t e r v a l ú e s a n d i t ' s c o r r e s p o n d e n l
l o n g s h o r e b a r - t r o u g h in J a n u a r y and trans-
classification (Wright and Short. 1984) and
verse bar and rip in M a y . as a r e s p o n s e to
t h e o b s e r v e d b a r n u m b e r a l o n g t h e f o u r
the respective storm events (Table 6). Field
c a m p a i g n s d e n o t e h i g h m o r p h o l o g i c a l
o b s e r v a t i o n s r e v e a l e d a d e c r e a s e in t h e
d y n a m i c s of the s u b m e r g e d beach profile.
n u m b e r of b a r s f r o m p r e - s t o r m to s t o r m
A z u l b e a c h m o d a l s t a t e of m o r p h o -
m o r p h o l o g y . In D e c e m b e r . t h e p r e - s t o r m
d y n a m i c b e h a v i o u r ( l o w tide t e r r a c e ) and
s u b m e r g e d m o r p h o l o g y i n c l u d e d o n e b a r
l i m i t c o n d i t i o n s u n d e r s t o r m i n f l u e n c e
indirectly o b s e r v e d t h r o u g h the n u m b e r of
( l o n g s h o r e b a r - t r o u g h ) can be a s s u m e d as
consistent breaker lines present during low
being similar to Sta. Rita beach.
t i d e . T h i s b a r d i s a p p e a r e d a f t e r J a n u a r y
Unlike S . Rita and Azul beach. Foz do
I a
storm. A two bar system was also found in
Lizandro beach reached the fully dissipative
M a y pre-storm conditions. This bar system
m o r p h o d y n a m i c behaviour in January storm
w a s reduced to one transversal bar after late
event and the range of Q valúes indícate the
May high w a v e event.
full s p e c t r u m of i n t e r m e d í a t e t y p e s a r e
T h e existence of a barred system in M a y
present (Table 6).
o b s e r v a t i o n s a l o n g w i t h l o w v a l ú e s of
Table 6. Dimensionless fall velocity parameterization (Í3). D - dissipative: L B T - longshore
bar-trough: R B B - rhythmic bar and beach: T B R - transverse bar and rip: L T T - low tide
terrace.
S"'. Rila liiaih
A/.ul beach
Foz do Lizandro lu-ach
W„ T W. Q
H. T 11. Q «.. 7 11. í?
2,0160
1,8833
2.0744
lYe-Slorin
0.74 5.17 ().(I7|
0.-4 5.17 0.076
0.74 5.17 0.06»)
.lamían
LTT
LTT
LTT
Storm
5.4572
4.9205
5.8853
2.02 6.73 0.055
2.02 6.73 0.061
2.02 6 7 3 0.051
l.B!
LB 1
11
2.6716
2.4435
3.1307
I'rc-Slonn
| .09 5.44 0.075
1.09 5.44 0.082
1.09 5.44 0.064
Maj
LIT
LTT
TBR
Storm
4.1886
3.3307
5.1195
1.62 5.S6 0.1166
1.62 5.86 0.083
1.62 5.86 0.054
RBB
! BK
LUÍ
Territoris, n ú m . 7. 2 0 0 7 - 2 0 0 8
35
T r i n d a d e , J.. R a m o s - P e r e i r a . A. y N e v e s . M.
Beach response to high energy wave climate.
At Foz do Lizandro. the high variability
W r i g h t and S h o r t m o r p h o d y n a m i c m o d e l .
in m o r p h o d y n a m i c states is consistent with
S t a . R i t a a n d A z u l b e a c h h a v e t h e s a m e
the h i g h e r v a l ú e s of m á x i m u m s e d i m e n t
modal m o r p h o d y n a m i c b e h a v i o u r (low tide
b u d g e t c h a n g e s o v e r the four c a m p a i g n s
terrace) as well as the similar response limit
( 1 2 8 9 . 5 0 3 m / m i n J a n u a r y a n d to storm c o n d i t i o n s (longshore b a r - t r o u g h I .
I 5 2 3 , 1 2 8 m / m in M a y . ( T a b l e 4 ) . T h i s
F o z d o L i z a n d r o r e v e a l e d n o m o d a l m o r -
3
system is smaller and. unlike the other beach
p h o d y n a m i c b e h a v i o u r a n d r e a c h e d fully
s y s t e m s . beach m o r p h o l o g y is c o n d i t i o n e d
dissipative conditions during January storm
not only by wave climate but also by direct
event.
r i v e r h y d r o d y n a m i c s d u r i n g w i n t e r . T h e
T h e Q parameter s h o w e d good predictive
L i z a n d r o river flows in the s o u t h e r n m o s t
r e s u l t s w h e n c o m p a r e d to t h e o b s e r v e d
sector of the beach (Fig. 2) and in high water
beach m o r p h o l o g y .
episodes can flood and erode the beach and
Results reveal the high potential of beach
the backshore profile. This c o m b i n e u fluvial
monitoring p r o g r a m m e s in the prediction of
and marine h y d r o d y n a m i c s probably explain
local s y s t e m b e h a v i o u r s u n d e r h i g h w a v e
the higher volume and parameter variability
e v e n t s a n d . t h e r e f o r e . in p o t e n t i a l b e a c h
recorded in this system.
d a m a g e by storms.
B e c a u s e of this h i g h v a r i a b i l i t y in the
beach profile it w a s not possible to charac-
terize modal b e h a v i o u r of Foz do L i z a n d r o
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38
Territoris, núm. 7. 2 0 0 7 - 2 0 0 8