Souza, Priscila Emerich; Nicolodi, João Luiz

doi:10.1590/S1679-87592016124106403

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Brazilian Journal of Oceanography

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Original Articles • Braz. j. oceanogr. 64 (3) • Jul-Sep 2016 • https://doi.org/10.1590/S1679-87592016124106403 copiar

Coastal Vulnerability Assessment using geoindicators: case study of Rio Grande do Sul coastline

Autoria SCIMAGO INSTITUTIONS RANKINGS

Resumo

Geoindicadores são medidas de processos e fenômenos geológicos que ocorrem perto ou sobre a superfície da Terra e que variam significantemente durante um período de até 100 anos. Nas últimas três décadas, o uso de geoindicadores foi direcionado para avaliações de impactos e riscos geológicos. Seu uso, porém, ainda é pouco difundido e explorado em relação aos demais indicadores ambientais. Este estudo tem por objetivo contribuir à difusão de informação e aplicabilidade dos geoindicadores. Definimos como geoindicador um parâmetro ou aspecto comumente estudado ou monitorado nos ambientes costeiros. Os geoindicadores aqui propostos foram testados com vistas à avaliação da vulnerabilidade física costeira das praias do Rio Grande do Sul, Brasil. Quatro geoindicadores foram definidos e aplicados: altura e estado morfo-ecológico de dunas frontais, posição de linha de costa e concentração de sangradouros. Além destes indicadores de caráter físico, outro de caráter socioambiental foi incluído, qualidade sanitária. Os indicadores foram agregados para gerar um Índice de Vulnerabilidade Física para sete localidades ao longo do litoral costeiro do Rio Grande do Sul. Um mapa cartográfico de linguagem acessível ao público comum e aos tomadores de decisão foi gerado a partir dos indicadores e do Índice.

Descritores:
Indicadores ambientais; Vulnerabilidade física; Avaliação ambiental

Name	Height and Morpho-ecological State of foredunes
Brief description	Foredunes are defined as shore-parallel dune ridges formed on top of the backshore by aeolian sand deposition within vegetation. The two main types of foredunes include incipient and established foredunes, which can have wide morphological and ecological variations (HESP, 2002HESP, P. Foredunes and blowouts: initiation, geomorphology and dynamics. Geomorphology, v. 48, n. 1-3, p. 248-265, 2002.). Foredunes mainly occur on dissipative beaches dominated by waves (CARTER et al., 1990CARTER, R. W. G.; NORDSTROM, K. F.; PSUTY, N. P. The study of coastal dunes. In: NORDSTROM, K. F.; PSUTY, N. P.; CARTER, R. W. G. (Eds.). Coastal dunes: form and process. Chinchester: John Wiley & Sons, 1990 p. 1-16.) and can be formed on any coast that presents favorable and determinative factors for dune formation. These factors include wind competence and intensity, low precipitation, sand supply, obstacles to aeolian transported sand deposition, and the ability to stabilize plant cover. The vegetation determines the morphological development of the dune, with taller plants corresponding to taller dunes that are shorter in length (VAN DIJK et al., 1999VAN DIJK, P.; ARENS, S.; VAN BOXEL, J. Aeolian processes across transverse dunes. II: modelling the sediment transport and profile development. Earth Surf. Process. Landf., v. 24, n. 4, p. 319-333, 1999.).
Significance	Dunes are areas of permanent preservation, according to the National Coastal Management Plan (Law 7661/88) and Decree No 5300/2004. The balance of the dune system directly influences the depositional and erosional processes of the beach, protecting the coast against wave attack and tidal flooding. Dunes work as groundwater storage, serve as habitats for different species of flora and fauna, and form landscapes.
Human or Natural Causes	Usually natural but can be manipulated by man.
Environment where applicable	Any coast that presents favorable conditions for dune development, including beaches, estuaries, lakes or lagoons.
Types of monitoring sites	On the backshore
Spatial scale	Local or regional
Method of measurement	Height: measured with a topographic ruler from the dune base at the georeferenced points; Morpho-ecological State: visual classification of the dune state based on its vegetation cover density and its morphological state (HESP, 1988HESP, P. Morphology, dynamics and internal stratification of some stablished foredunes in Southeast Australia. Sediment. Geol., v. 55, n. 1-2, p. 17-41, 1988.).
Frequency of measurement	Seasonally due to variations in rainfall and predominant wind regimes (intensity, frequency and direction), which interfere with vegetation cover and sand supply.
Limitations of data and monitoring	Although it does not limit monitoring, subjective factors might interfere in the qualitative evaluation of the dunes' morpho-ecological state.
Applications to past and future	The vulnerability of dunes may result from several factors on different spatiotemporal scales, including sea level rise, increases in storm frequency and magnitude, negative sediment balance, and human activities. Monitoring and management of dunes are practices that are recommended for structurally controlling erosion and flooding. Efficient dune management plans in coherent urban planning minimize conflicts in land use and the natural risks inherent to coastal environments.
Possible thresholds	Foredune Height (h):
	Height: h > 2 m
	Intermediate: 1 > h > 2 m
	Low or absent: < 1 m
	Morpho-ecological State:
	Well established: dunes showing simple topography, were laterally continuous or were slightly interrupted with 75-100% vegetation cover.
	Erosive-stable: wider lateral variation of density and lower vegetal cover (20-75%); topography characterized by a morphology that is more fragmented, irregular, asymmetrical, hummock type, which favors blowouts.
	Erosive: most portions of the foredunes were removed through wind and/or wave action, leaving only mounds and ridge segments.
Key references	Law 7661 of May 16, 1988;
	Decree No 5300 of (2004)
	CALLIARI et al. (2005)CALLIARI, L. R.; PEREIRA, P. S.; DE OLIVEIRA, A. O.; FIGUEIREDO, S. A. Variabilidade das dunas frontais no litoral norte e médio do Rio Grande do Sul, Brasil. Gravel, v. 3, p. 15-30, 2005.
	CARTER et al. (1990)CARTER, R. W. G.; NORDSTROM, K. F.; PSUTY, N. P. The study of coastal dunes. In: NORDSTROM, K. F.; PSUTY, N. P.; CARTER, R. W. G. (Eds.). Coastal dunes: form and process. Chinchester: John Wiley & Sons, 1990 p. 1-16.
	CARVALHO et al. (2008)CARVALHO, R. V.; SILVA, K. G.; CRIVELLARIO, C. V. L. Gestão ambiental das dunas costeiras: manejo e conservação. Cassino: NEMA, 2008. 28 p.
	DAVIES et al. (1995)DAVIES, P.; WILLIANS, A. T.; CURR, R. H. F. Decision making in dune management: theory and practice. J. Coast. Conserv., v. 1, n. 1, p. 87-96, 1995.
	HESP (1988, 2002)HESP, P. Foredunes and blowouts: initiation, geomorphology and dynamics. Geomorphology, v. 48, n. 1-3, p. 248-265, 2002.
	SEELIGER (1992)SEELIGER, U. Coastal foredunes of Southern Brazil: physiography, habitats, and vegetation. In: SEELIGER, U. (Ed.). Coastal Plant Communities of Latin America. New York: Academic Press, 1992. p. 367-381.
	TABAJARA et al. (2005)TABAJARA, L. L.; GRUBER, N. L. S.; DILLENBURG, S. R.; AQUINO, R. Vulnerabilidade e classificação das dunas da praia de capão da canoa, litoral norte do Rio Grande do Sul. Gravel, v. 3, p. 71-84, 2005.
	VAN DIJK et al. (1999)VAN DIJK, P.; ARENS, S.; VAN BOXEL, J. Aeolian processes across transverse dunes. II: modelling the sediment transport and profile development. Earth Surf. Process. Landf., v. 24, n. 4, p. 319-333, 1999..
Related environmental and geological issues:	Sediment supply, grain size and nature, platform width, beach stage, wave energy, energy flow in the surf zone, longshore transport;
	Erosion/accretion; foredune scarp;
	Shore orientation in relation to the predominant wind; direction, intensity and frequency of the predominant wind; aeolian transport effectiveness;
	Anthropic pressure: real estate speculation, opening of paths (trampling of vegetation), mining, engineering structures, etc.;
	Areas of Permanent Preservation, Conservation Units, and Dune Monitoring Programs: Coastal Management.
Overall Assessment	Studying and monitoring the “height” and “morpho-ecological state” parameters of foredunes under geoindicator aggregates with relevant and accessible information (easily and cheaply obtained) for managers of areas that already use some sort of Dune Monitoring Program and for those who are unaware of the degree of vulnerability and importance of these coastal features.

Name	Shoreline position (SP)
Frequency of measurement	Seasonally before and after storm events, or according to usual interval of variability (if known).
Limitations of data and monitoring	Historical records are short, spatially discontinuous, and have been obtained using variable and limited methodologies.
Possible thresholds	Quantitative:
	Severe Erosion: > 2 m/year
	Erosion: 0.5 to 2 m/year
	Accretion or stability: < 0.5 m/year
	Qualitative:
	Severe erosion: lack of vegetation, clear beach escarpment, tidal channels exposed in surf zone, etc.;
	Erosion: dune escarpment or fragmented, narrow beach, peat, mud or tree pieces exposed on the beach;
	Accretion or stability: dune crest established by vegetation, laterally continuous with few or no breaks.

Period	Retreat rate (m/yr)	Rating
1947 – 1964	0.2	1
1964 – 1975	0.61	5
1975 – 1996	0.41	1
1996 – 2000	6.29	10
2000 – 2005	2.37	10
2005 – 2006	5.25	10
2006 – 2007	0.11	1
2007 – 2009	0.49	1
2009 – 2010	0.93	5
2010 – 2011	1.41	5
2011 – 2012	0.45	1

Name	Washout concentration (WC)
Method of measurement	Direct: georeferenced fieldwork observations of the number of washouts per kilometer covered
Method of measurement	Indirect: seasonal average calculations for stretches of 10 km through satellite image analysis (FIGUEIREDO; CALLIARI, 2005FIGUEIREDO, S. A.; CALLIARI, L. J. Sangradouros: distribuição espacial, variação sazonal, padrões Morfológicos e implicações no gerenciamento costeiro. Gravel, v. 3, p. 47-57, 2005.).
Frequency of measurement	Seasonal: during periods of higher and lower precipitation and preferably after the occurrence of storm surge events.
Limitations of data and monitoring	The transience of small washouts limits how they can be monitored, especially during periods of high evaporation or at sites with high permeability.
Limitations of data and monitoring	In addition, when taking indirect data measurements the monitoring process and development of the time series are restricted to the available images.
Possible thresholds	Considering the mean values of the washout number per kilometer:
	High: > 0.8/km
	Moderate: 0.5 to 0.8 per km
	Low: < 0.5/km

Universidade de São Paulo, Instituto Oceanográfico Praça do Oceanográfico, 191 , 05508-120 Cidade Universitária, São Paulo - SP - Brasil, Tel.: (55 11) 3091-6501, Fax: (55 11) 3032-3092 - São Paulo - SP - Brazil
E-mail: io@usp.br

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[1] *Corresponding author: pes@ign.ku.dk