Design and management aspects of a coastal protection system. A

Journal
Journalof
ofCoastal
CoastalResearch
Research
SI 64
pg -- pg
492
495
ICS2011
ICS2011 (Proceedings)
Poland
ISSN 0749-0208
Design and management aspects of a coastal protection system.
A case history in the South of Italy
F. D’Alessandro†, G.R. Tomasicchio†, F. Frega‡, and M. Carbone‡
†Engineering Dept., University of Salento,
Lecce, 73100, Italy,
[email protected]
[email protected]
‡ Dept. for Soil Conservation, University of Calabria,
Arcavacata di Rende, 87036, Italy,
[email protected]
[email protected]
ABSTRACT
D’Alessandro, F., Tomasicchio, G.R., Frega, F., and Carbone, M., 2011. Design and management aspects of a
coastal protection system. A case history in the South of Italy. Journal of Coastal Research, SI 64 (Proceedings
of the 11th International Coastal Symposium), 492 – 495. Szczecin, Poland, ISSN 0749-0208.
A case history concerning the design and management aspects of a coastal protection system built by the Italian
National Railway Authority (NRA) during the 80’s is reported. The intervention was built in order to protect the
main national railway line to Sicily from the severe damages induced by the wave action. In particular, the impact of a breakwater/groin system, based on a T-shaped structure, along the Tyrrhenian coast from Paola to San
Lucido, in the South of Italy, has been considered. In 2005, the local Administration (San Lucido Municipality)
promoted a lawsuit against the NRA. The local Administration denounced the negative effect of the intervention
arguing that the presence of the defense structures caused an accretion of sediments in the protected area and
interrupted the long-shore sediment transport, determining a relevant downdrift beach erosion. The case of a
lawsuit evoking a loss of beach induced by maritime works represents the first case in Italy. The Court decision
stated that the shore protection structures built along the coast between Paola and San Lucido represent an obstacle to the long-shore sediment transport in the north-south direction. The sentence obliged the NRA to pay a sum
of money per year in favour of the San Lucido Municipality to be invested for the construction of new coastal
protection structures. The present paper describes the local wave climate, the intervention, its monitored effects
on morphodynamics, and the technical discussion which was held in front of the Court in 2006.
ADDITIONAL INDEX WORDS: T-shaped structures, Breakwaters, Physical Model, Lawsuit
INTRODUCTION
The Tyrrhenian coast of Calabria (Italy) has been affected by
strong erosion phenomena in the last thirty years. In particular, the
area between the towns of Paola and San Lucido was exposed to
severe wave attacks determining significant damages to the Battipaglia-Reggio Calabria railway line; this caused frequent interruptions of the railway service during major surges.
In 1982, the Italian National Railway Authority (NRA), drewup the “Executive and 1-st stage General Project for the protection
of the Battipaglia-Reggio Calabria railway line between the stations of Diamante and Campora San Giovanni”.
In 1983, 7 detached breakwaters and 3 groins were initially designed to protect the railway line along a limited segment of the
coast between Paola and San Lucido. A 3D movable bed physical
model experiment, with 1:200 and 1:100 scale for horizontal and
vertical dimensions, respectively, was carried out at the ESTRAMED laboratory in order to verify and to improve the designed intervention (Italian Ministry of Public Works, 1992). The
experimental results indicated the need to extend the intervention
to a longer coastal area, together with the opportunity to replace
the foreseen detached breakwaters with a different coastal protection system allowing people to enjoy the beach, still giving a safe
defense of the storm-exposed railway. In this path, a new physical
model experiment was performed. In this case, a non-distorted
physical model, with 1:40 scale, was built using mono-granular
sand having 0.135 mm diameter; it reproduced a beach nourishment protected by detached submerged breakwaters. However, the
large amount of longitudinal losses of sediments, measured during
the experiments, prevented the adoption of this solution.
After the discussion of the experimental results, in order to obtain more effective retention of the nourishing material, the capability of a breakwater/groin system, based on a T-shaped structure,
was verified and thus selected as the intervention to be built (Figure 1).
Figure 1. The physical model at the ESTRAMED laboratory
In 1986, the construction of the T-shaped structures between the
southern zone of Paola and northern zone of San Lucido started.
The construction ended in 1995.
In order to verify and to improve the designed intervention, additional 3D physical model tests were carried out during the con-
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Coastal Engineering
struction, before the end of the works. In particular, two experiments were conducted with the scope to investigate the opportunity of covering, with natural stones, the T-shaped structures made
by 19 ton, Antifer type, concrete units. In the first experiment,
with scale 1:50, a layer of natural stones was placed on the entire
T-shaped structure (groin/breakwater) starting from the water
depth -3.0 m; the results were negative and the structure appeared
considerably damaged. A second experiment, with 1:35 scale, was
performed in order to verify the stability of a T-shaped structure
made by 19 ton, Antifer type, concrete units with an additional
layer of natural stones placed only in the emerged back-side of the
structure, with the scope to reduce the visual impact from the
concrete units; in this case, the performed physical model test
showed the efficiency of the structure and this solution was
adopted.
The resulting constructed coastal defense presented the seaward
parallel breakwaters with the toe on a water depth ranging between -4 m and -8.4 m; these values are more appropriate in the
case of a port, and in fact some of the cells between two adjacent
groins have become fishery and recreational ports (Figure 2).
Mountains higher than 1500 m lay 6 km from the coast. The
Lao and the Savuto rivers and many steep streams, well known as
“fiumare”, flow on the coast. The mean beach grain size, D50, is
equal to 3.51 mm at the swash zone and is 0.84 mm and 0.20 mm
at -3.0 m and -10 m water depth, respectively. The emerged beach
is characterized by a 0.07 mean slope. The submerged and the
foreshore mean beach slopes are 0.05 and 0.03, respectively
(Guiducci and Paolella, 2004).
Severe storms affect the coast. In January 2000, a 8.9 m significant wave height, Hs, and 13.3 s peak period, Tp, with return period = 50 years, was recorded at the wave buoy of the National
Wave Network (http://www.idromare.it) located offshore Cetraro
since 1999 (Figure 3). The direction orthogonal to the coastline is
255°N, while the most frequent and intense wave attacks present a
mean direction 280°N. The net long-shore sediment transport is
southward directed; it has been estimated equal to 20.000 m3/year
(Guiducci and Paolella, 2004).
In 1955 the minimum width of the emerged beach in San Lucido was 30 m, up to 70 m in some sections, thus providing a
flourishing tourist activity (Fiorini Morosini et al. 2008).
From 1955, soil conservation, water control and dam construction began and sediment excavation from the beds of the “fiumare” grew. Consequently, the beach erosion, due to a reduced
sediment supply, started and it is still active.
From 1970, protection structures were built consisting of rubble
mound revetments to protect the main southern railway and the
national road n° 118, that alternatively lay behind the beach.
From 1985, part of the emerged beach eroded and the railway
was exposed to the directly impinging waves. Many damages to
the railway occurred and the service was often interrupted.
RESULTS AND ANALYSIS
Description of the works
Figure 2. The port in the north zone of the San Lucido promenade
METHODS
The coastal protection system, designed and built with the scope
to protect the main railway line to Sicily from the severe damages
induced by the wave action, consists of 18 cells with 19 T-shaped
structures. Figure 4 shows an aerial view of the intervention along
the Paola-San Lucido coastline.
Study area and environmental conditions
A physiographic unit 90 km long, from Capo Bonifati to Pizzo
Calabro, comprises the two towns of Paola and San Lucido where
the coastal protection intervention has been built (Figure 3).
Figure 4. Aerial view of the T-shaped structures along the PaolaSan Lucido coastline
Figure 3. Corography of the Calabria region
The T-shaped structure is composed by a groin 140 m long in
the cross-shore direction, linked with a breakwater lying parallel
to the coastline for a length of 120 m; spacing between 2 successive groins varies from 230 m to 320 m (Figure 5).
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D’Alessandro et al.
Figure 5. An example of the as-built T-shaped structure
Both groins and breakwaters are well known protection structures and their use is well documented in scientific literature and
in professional practice (USACE, 1984; Tomasicchio and Tomasicchio, 2011).
As a result, the coastal defence system had an apparent success,
at least in Paola, along the northern coastline, where the effect of
the intervention has been positive not only for the protection of the
railway line but also because a wide enjoyable beach was created.
On the contrary, the T-shaped structures determined a strong
erosion in San Lucido. In this area the natural beach disappeared
and significant damages occurred.
In order to face this problem which was not fully foreseen by
the designers, in 1995 the NRA entrusted the construction of a
submerged continuous breakwater parallel to the shoreline (500 m
long, 1.5 m submergence, 35 m from the shoreline) immediately
south of the T-shaped system, aiming to contain the losses of
sediments (Figure 6).
Figure 7. The southern T-shaped structure and the induced
erosion at the San Lucido promenade
Morphodynamics effects
The presence of the T-shaped structures caused the accretion of
sediments in the protected area and interrupted the long-shore
sediment transport, inducing a relevant downdrift beach erosion.
In a previous study, Fiorini Morosini et al. (2008) analyzed the
historical shoreline evolution at San Lucido using data from maps
and aerial photographs available from 1955 to 1998.
Table 1 summarizes the results of the study in terms of shoreline average variation (erosion/accretion) and eroded volume.
Table 1: Historical shoreline evolution at San Lucido
Average variation (m)
Eroded volume (m3)
Erosion
Accretion
1955 - 1986
-8
19
-23312
1986 - 1998
-30
0
-714458
In the area of San Lucido, from 1955 to 1986, the shoreline retreated about 8 m in some zones, while it increased in some others.
In the period 1986-1998 a retreat of about 30 m was observed.
This result confirms that before the construction of the structures
the beach was reasonably in equilibrium; after 1986, the erosive
process increased significantly.
In this paper the analysis of the historical shoreline evolution at
San Lucido has been extended until year 2009. The study was
conducted in order to allow more recent and comprehensive delineation in the shoreline configuration over the investigated period.
Figure 8 shows the comparison between the shoreline in 1986,
immediately prior the construction start, and in 2009, respectively.
The negative effect of the intervention on the erosion rate is still
evident.
Figure 6. The submerged breakwater along the San Lucido
coastline
However, even in this case, the result was not satisfactory and
the erosive process at San Lucido continued (Fiorini Morosini et
al. 2008). Today, the beach is about 5 m wide so that the shoreline
is close to the promenade of the town which is often damaged
during the frequent sea storms (Figure 7).
DISCUSSION
The relevant beach erosion occurred at San Lucido determined
significant damages to the coastal environment, strongly mining
the economy of this area greatly influenced by the touristic activity. Various are the causes to be investigated and discussed regarding both construction and design aspects.
With regard to the construction aspects, an up drift sequence of
the structures to be built, from south to north, was scheduled.
However, when the works started, the construction of the structures in the southern part of the coast was not authorized and the
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works proceeded northward from the groin 12, the last one in the
area under Paola administration. The works on the southern part
(T-groins 13-19) were authorized in 1991 based on experimental
tests on a 3D movable bed physical model. In the meantime, the
induced long-shore transport material was trapped into the
northern cells and, consequentely, this lack of material increased
the erosion along the downdrift coast.
With regard to the design aspects, it is remarkable that the chosen depth of the seaward breakwaters is larger than the closure
depth which is equal to 6-7 m for that area; the effect is that the
long-shore sediment transport has been strongly reduced.
This money has not been paid yet because the NRA appealed
against the Court decision.
In the meanwhile, the San Lucido administration tried to reduce
the negative effects from the limited long-shore sediment transport
with the construction of a series of 30 m long groins (year 2001)
covering a 800 m long coastline stretch and with an artificial
nourishing (8000 m3 in 2007).
CONCLUSIONS
The presented lawsuit concerning a coastal erosion process
induced by maritime works represents the first case in Italy. To
solve the problem of the ensuing erosion in Paola, large coastal
structures have been placed along the shoreline. The coastal intervention in Paola resulted in a good defence of the national railway; nevertheless, it induced a relevant beach erosion producing a
disaster downdrift of the sea works. The erosion deleted a natural
beach in San Lucido which is reported of 50 m width prior the
intervention.
The lesson from this experience is that the structures for the
coastal defence cannot be oversized like in this case, and that they
should be carefully designed according to simple practical rules
that, often, allow to overcome expensive physical model tests.
LITERATURE CITED
Fiorini Morosini, A., Pugliese Carratelli, E., and Veltri, P., 2008.
Management and planning aspects of the coastal defence
structures: a case history. Proceedings of the 3rd SCACR International Short Conference on Applied Coastal Research
(Lecce, Italy, IAHR), pp. 314-325.
Guiducci, F., and Paolella, G., 2004. Learning from 20 years of
design and realisation on coastal protection over the Tyrrehnian Calabrian coast. Proceedings of the 29th ICCE International Conference on Coastal Engineering (Lisbon, Portugal, World Scientific), pp. 3826-3838.
Italian Ministry of Public Works, 1992. Coasts, harbours and
lagoons protection works. Volume edited for the 23th ICCE International Conference on Coastal Engineering (Venice, Italy), pp. 151.
Tomasicchio, U., and Tomasicchio, G.R., 2011. Manuale di
Ingegneria Portuale e Costiera. Nuova Edizione. Napoli:
Hoepli, 1000 pp. In Italian.
USACE. US Army Corps of Engineers, 1984. 4th ed., U.S. Army
Engineer Waterways Experiment Station, U.S. Government
Printing Office, Washington, D.C.
ACKNOWLEDGEMENT
Figure 8. The San Lucido shoreline in 1986 (dashed line) and
in 2009 (full line)
The authors gratefully acknowledge prof. emeritus G. Corrado
Frega for the fruitful discussion and comments. The authors also
thank dr. Attilio Fiorini Morosini from University of Calabria for
providing the photographs included in the present manuscript.
The lawsuit
In 2005, the local Administration (San Lucido Municipality)
promoted a lawsuit against the NRA denouncing the negative
effects of the intervention. After a technical debate, the Court
decision stated that the shore protection structures built along the
coast between Paola and San Lucido has to be considered an
obstacle to the long-shore sediment transport in the north-south
direction. The sentence obliged the NRA to pay a sum of money
per year (€ 332.500) in favour of the San Lucido Municipality to
be invested for the construction of coastal defence structures;
payment is due until an emerged beach 15 m wide is obtained.
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