Resumo

PORTZ, Luana et al. Coastal dune management: the use of geographic information system (GIS) in the development of management plans in the coast of Rio Grande do Sul, Brazil. RGCI [online]. 2014, vol.14, n.3, pp.517-534. ISSN 1646-8872.  https://doi.org/10.5894/rgci445.

Foredunes are geomorphological features present in most of the sand beaches around the world. Under the Brazilian law, dunes are considered Permanent Protection Areas and, for conservation of these environments, it is necessary the establishment of plans, programs and measures by the government to discipline their use and management requirements. The development of projects for dune system management should include an environmental diagnosis (natural characteristics and human intervention degree), the trend of changes and the actions for maintenance or recovery of the system. The aim of this work is to evidence the potential of using a Geographic Information System (GIS) for the environmental diagnosis of dunes, as well as stress the importance of regional data integration within a GIS, for the purpose of obtaining better results to support decision making in the development of management plans for integrated coastal zone management. Study cases of two coastal cities in the State of Rio Grande do Sul, southern Brazil (Capão da Canoa and Arroio do Sal cities), are shown. The use of GIS allows updates at several time scales and also the joint analysis of multiple data from different sources. These characteristics assist work in coastal zones, an environment with highly dynamic forms and processes. For the characterization, diagnosis and planning of the two study areas, primary and secondary data were collected. Secondary data consists of bibliographic and cartographic search, and remote sensing data. Primary data consists of field observations, control points collected with GPS, photographic records (beach access, watercourses, irregular occupation, beach uses, dune uses, etc.), topographic data and vegetation identification. After collection, data were inserted in data layers and integrated in the GIS project. Using geoprocessing tools it was possible to calculate areas, measure foredune width and delimit the boundaries of Permanent Protection areas (using distance criteria), leading to further information to be obtained/added in the GIS. Distance criteria for delimitation of Permanent Protection areas were based in the law of the state environmental agency (FEPAM). For the city of Capão da Canoa, increases in sea level caused by storm surge were modelled in the GIS, in order to identify foredune areas susceptible to degradation. Results showed that water courses that cross the dune system are the preferential erosion zones in storm surge events. An evaluation based in the mapped elements and field observations, allowed the assignment of a coastal vulnerability index to each 500 meters beach segment. The higher the vulnerability index, the greater the fragility of the dune system. The areas with the highest index are the ones in which greater efforts are required (interventions/management). In the studied areas, these indexes allowed the planning of interventions required for each beach sector. Both cities have an extensive shoreline and dune areas affected by erosion (caused by storm surge effects, displacement of watercourses, planting of exotic vegetation and lack of planning for the shoreline - with disordered use of this natural system). A well developed urban area is present in Capão da Canoa city, where a discontinuous and highly segmented dune area exists. Preserved sections occur mostly in the non-urban areas. In Arroio do Sal city, there is an extensive and well preserved shoreline and dune system. The major problems affecting dune system in this city are erosion by storm surge and planting of exotic vegetation. With the environmental diagnosis and the vulnerability index for each beach sector, management proposals in different sectors of the shoreline were performed, and spatialization of the suggested actions/interventions was implemented in the GIS. This spatialization allowed visualization of all the beach sectors in maps, and this information was also added to the GIS project as new data layers. For dune system integrity maintenance/recovery in some sectors, some of the suggested interventions include pipe passing under the frontal dune crest (for controlled passage of watercourses), construction of walkways where the crosswalk is very intense (ordering the access to the beach), removal of exotic vegetation, etc. The results demonstrate the possibility of using GIS in coastal management studies, showing good results in the diagnosis and planning of the two study areas. As a final product of the management plans developed, all the collected and generated data are provided in GIS file format and in spreadsheets in a PDF report. At the municipal level, the advantages are ease of storage and availability of data, facilitating data modification in case of scenario alteration for the shoreline. The use of a GIS can also promote and facilitate the exchange of information between institutions and, in the long term, can allow the integration of all information into a single database to assist in decision making at the municipal, state and federal agencies.

Palavras-chave : coastal management; geospatial technology; database; coastal modelling.

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