Journal of Coastal Research SI 39 1801 - 1803 ICS 2004 (Proceedings) Brazil ISSN 0749-0208
ANGULO, R. J.; SOUZA, M. C. de and LAMOUR, M. R., 2006. Coastal erosion problems induced by dredging activities in the navigation channel of Paranaguá and São Francisco do Sul harbor, southern Brazil. Journal of Coastal Research, SI 39 (Proccendigs of the 8th International Coastal Symposium), 1801 - 1803. Itajaí, SC, Brazil, ISSN 0749-0208.
In southern Brazil, sectors of navigation channels of Paranaguá and São Francisoco do Sul harbors were dredged on ebb tidal delta. The dredging activities have been interfering in the sediment transport and seem to be responsible for accelerated coastal morphologic changes and serious erosion problems along the coastal zone.
ADDITIONAL INDEX WORDS:ebb tidal delta, coastal changes, beach erosion.
ABSTRACT
Coastal Erosion Problems Induced by Dredging Activities in the Navigation Channel of Paranaguá and São Francisco do Sul Harbor, Southern Brazil
Rodolfo José Angulo†; Maria Cristina de Souza† and Marcelo Renato Lamour†
Journal of Coastal Research Special Issue 39, 2006,
† Department of Geology, University Federal do Paraná, Curitiba, Paraná, 81531-990, Brazil.
angulo@ufpr.br
INTRODUCTION
RESULTS AND DISCUSSION
In the southern region of Brazil there are two important harbors, Paranaguá and São Francisco do Sul, located inside estuaries. Within both harbors, dredging activities on the navigation channels have reached a design water depth of 15 and 11 m respectively necessary for larger load-displacement.
These navigation channels interfere in the sediment transport along the coast and seem to be responsible for the serious erosion problems in the coastal zone.
The coasts of Paraná and Santa Catarina states are characterized by large coastal plains, ocean straight sandy beaches, different size estuarine complexes and ebb tidal deltas 1999) (Figure 1). The coastal zone is surrounded by high mountain ridges named Serra do Mar that can reach 1,800 m high. The coastal plain can reach 55 km wide and is characterized by Pleistocene and Holocene barrier systems (L ., 2000). The barrier is composed by beach and inner platform sandy sediments and muddy estuarine sediments . The estuarine complexes are characterized by sandy coastal bottom sediments on the outer part and muddy sediments on the middle part. On the estuarine heads there are coarse to fine sediments and estuarine head deltas (B
and Figure 2).
The region is characterized by two main wave systems from ENE and SSE/SE (P 1983). The wave period varies between 6 and 10 s and the significant wave height between 0.5 and 1.5 m 1983). At the mouth of the Paranaguá bay the mean spring tide range is 1.7 m and the mean neap tide range is 1.4 m (M and 1997). Geological and geomorphological evidences indicate a net longshore sediment transport to the north that has been acting, at least, since the late Holocene and has been inducing the migration of estuarine inlet northward ., 2000).
(ANGULO,
ESSA
(SOUZA 2003)
IGARELLA
., 1970, SOARES BARCELOS, 1995,
ORTOBRAS,
ARONE JAMIYANAA,
(LESSA
et al et al.,
et al
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The ocean beaches and the ebb tidal deltas seem to have significant sediment interchange. In natural conditions the ebb tidal delta terminal lobes have depths between 3 and 5 m, therefore the waves are able to transport sediments on these lobes and promote the interchange of beaches sediments located on the margins of the estuarine inlets. As a result of this all the ocean beaches and ebb tidal delta of the study area function as a system with sedimentary interchange.
Sectors of the navigation channels of the harbors of Paranaguá and São Francisco do Sul have been dredged on the ebb tidal delta terminal lobes interfering on coastal sediment transport (Figure 3). Sediments transported from the south and from the north by longshore currents, are trapped in the
Figure 1: Estuarine complexes of Paraná and north Santa Catarina state. Sector with sedimentary deficit (white rectangle).
0 25 50 75 25° 17'
25° 31'
48° 39' 48° 24'
Mel island
Peças island
Pontal do Sul Paranaguá Bay
Antonina Bay
0 3 6
Laranjeiras bay
km
S
W PR
z
Sand %
100
Journal of Coastal Research Special Issue 39, 2006, navigation channels. On the Paranaguá navigation channel
sector dredged on the ebb tidal delta terminal lobe 2.3x10 m to 2.8x10 m /year of sediments were trapped (L ., 2003). The main part of these sediments came from the south.
Part of sediments trapped in the navigation channel can be transported offshore by the strong ebb tidal currents, that can
reach 20 m/s and another part silted
up the channel.
It is important to point out that sand and coarser continental sediments that come from the mountain ridges have been trapped in the estuary heads. Most part of these sediments can not pass through the low energy middle estuarine sector (Figure 2). Therefore, there is almost no continental sediment supply to
the ebb tidal deltas.
The channel is frequently dredged and the sediments are disposed in the near inner platform (Figure 3). These processes probably cause a sedimentary deficit in the delta and adjacent beach systems. This sediment deficit probably cause a decrease in the volume of the deltas as well as erosion on the beaches and adjacent coastal plains. These processes can have distinct temporal scales, depending on the relationship between the sediment volumes of the delta and longshore drift.
The net longshore drift in the Paraná coast was estimated to be 2 to 3 x 10 m /year to the north 1997).
On the other hand, Paraná and north Santa Catarina ebb tidal deltas have estimate volumes from 10 m in the Paranaguá southern inlet ( and São Francisco do Sul inlet to 2 x 10 m in the Mar de Ararapira inlet (Figures 1 and 4).
Thus, in a small ebb tidal delta like Mar do Ararapira, any sedimentary deficit in the ebb tidal delta will cause an immediate response at the nearby beaches. On the other hand, the sedimentary volume of the large ebb tide delta like Paranaguá and São Francisco do Sul are about 30 to 50 times larger than the net annual longshore drift. As a result of this higher sedimentary stock which act as a source of sediments to the adjacent beaches, the response of the sedimentary deficit caused by dredging can take years.
In the north coast of Santa Catarina the navigation channel of the São Francisco do Sul harbor was dredging up to 11 m deep in the 80's (APSFS, 2003).
Comparing nautical charts of 1979 and 1994 a decrease of 7.7 x 10 m in the volume of the north part of the terminal lobe of the São Francisco do Sul Bay tidal delta was estimated (Figure 5). These changes seem to be associated to the dredging of the navigation channel of São Francisco do Sul harbor. Moreover a sedimentary deficit of 5.7 x 10 m of sand or 10 m /year was verified on the 16 km-down drift beach from 1996 to 2002 (Figure 1). This deficit has been causing a 2,3 m mean coastline retreat and serious coastal erosion problems on this coastal sector (Figure 6).
Other coastal erosional problems can be related to the dredging sediment disposal. In December 2002, 3.5 x 10 m of sediments trapped in São Francisco do Sul navigation channel were dredged and disposed in the inner platform at about 15-18 m deep (APSFS, 2003) (Figure 3B ). Then the most part of these sand was probably lost from the beach system increasing the sedimentary deficit and the beach erosional problems.
Sediments dredged from ebb tidal delta sector of the Paranaguá harbor navigation channel have been disposed in the neighbor inner shelf shallow areas (Figure 3A). These sediments can be transported by induced wave currents. In Ilha do Mel, located northward the navigation channel, there were verified sudden changes on coastal morphology. In Farol beach there was about 400 m progradation in the southern sector and more than 100 m retrogradation in the northern sector, B 1980 and 1999 (Figure 7). A heavy mineral study indicates that the sand source is from the inner platform
from a neighbor area when dredged
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5 3
6 3
8 3
5 3
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ETWEEN
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.,
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Figure 2. Sand percent of surficial bottom sediments of Paranaguá estuarine complex.
26º10’ S
48º30’W Depths
São Francisco island São Francisco do Sul harbor Itapoá
municipal district
ATLANTIC OCEAN
0 to 5 m 5 to 10 m > 10 m access channel
Superagui island
disposed area 25º30’S
48º20’W Galheta island
Palmas island Mel island
Cobras island
Paranaguá harbor
Peças island
Pontal do Sul
ATLANTIC OCEAN Paranaguá bay
A
0 2km
B
0 5km
Figure 3. Paranaguá (A) and São Francisco do Sul (B) bays inlets, bathimetry, harbor access channels and sediment disposal areas.
Figure 4. Ararapira ebb tidal delta.
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Journal of Coastal Research Special Issue 39, 2006, sediments were disposed. The sediment input caused changes
on the wave refraction pattern and longshore currents circulation that induced coastal erosion in the northward beaches.
Therefore, it would be possible to diminish significantly the coastal erosional problems choosing better places to dispose the dredged sediments. The dredged sediments would be disposed down drift on the ebb tidal delta terminal lobe or on the down drift beaches with erosional problems. This by passing could restore the longshore drift and diminish significantly the environmental impacts caused by the harbor navigation channel dredges.
ACKNOWLEDGEMENT
To CNPq and CAPES for the research and PhD scholarship.
LITERATURE CITED
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BIGARELLA, ALESSI, BECKER, DUARTE,
GIANNINI, ANGULO, SOUZA, KOGUT, DELAI,
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LESSA, ANGULO, GIANNINI, ARAÚ JO,
MARONE JAMIYANAA,
NOERNBERG, MARONE, ANGULO,
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SOUZA, DE; ANGULO, ASSINE, DISARÓ, PESENDA, ARAUJO, A. D.; ODRESKI, L. L. R.;
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, Curitiba, 11(1-2):95-107.
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(submitted).
O.J., 1989. Littoral drift along some beaches in Brazil.In: Magoon, O.T.; Converse, H.; Miner, D.; Tobin, L.T.; Clark, D. (Eds.), Proc. Sixth Symp. Coast. Ocean Manag., Charleston, USA, vol. 4. American Society of Engineers, pp. 3638-3746.
C.R.; J.H., 1995. Considerações sobre os sedimentos do fundo das baías das Laranjeiras e de Guaraqueçaba - Complexo estuarino da baías de Paranaguá (Paraná, Brasil). Bol. Par. de Geociências, n. 43, p. 41-60.
M. C. R. J.; M. L.; S. T.;
L. C. R.;
, F. A. and S. H. M., 2003. Evolução da barreira holocênica no litoral do Estado do Paraná, sul do Brasil. In. Congresso da Associação Brasileira de Estudos do Quaternário, IX. Recife, in print.
Anais Academia Brasileira de Ciências.
Rev. Inst. Biol. Pesq. Téc.,
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Journal of Coastal Research
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Nerítica
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7
APSFS - Administração do Porto de São Francisco do Sul 2003.
http://www1.apsfs.sc.gov.br accessed on 09/01/2003.
Coastal Erosion
26º10’ S
48º30’W
(4) (5) 0 2km
Itapoa municipal
district
São Francisco island
(1) (2) (3)
Figure 5: São Francisco do Sul ebb tidal delta areas that became deeper between 1979 and 1994. (1) 0 to 5 m; (2) 5 to 10 m; (3)
>10 m; (4) areas that became deeper and (5) shalower, between 1979 and 1994.
Figure 6: Coastal erosion problem at Itapoá municipal district, located northernward São Francisco do Sul inlet.
Figure 6: Coastal erosion problem at Itapoá municipal district, located northernward São Francisco do Sul inlet.
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