Ingleses - Brazil: Urban problems due to coastal morphology

Ingleses - Brazil: Urban problems due to coastal morphology

Boeyinga, J.
Dusseljee, D.
Pool, A.
Schoutens, P.
Verduin, F.
van Zwicht, B.

da F. Klein, A.H. (mentor)
Verhagen, H.J. (mentor)
Stive, M.J.F. (mentor)
Storms, J.E.A. (mentor)

Civil Engineering and Geosciences

Hydraulic Engineering

2007-09-01

MSc Project Hydraulic Engineering - Delft University of Technology, Faculty of Civil Engineering and Geosciences, Section Hydraulic Engineering and Universidade do Vale do Itajaí, Centro de Ciências Tecnológicas da Terra e do Mar. - The town of Ingleses on Santa Catarina Island, in the state of Santa Catarina, Brazil, is threatened by nature at two different fronts. At the northern side of the town lies Ingleses Beach which appears to be subject to ongoing erosion. This forms a threat to the houses near the shore and diminishes the recreational value of the area. On the southern side, the town is threatened by a migrating dunefield, which is encroaching onto the houses and infrastructure. According to locals, dozens of houses have already been buried under the sand. The aim of this report is to give full insight in the situation and to find a number of possible solutions to the problems. There are, in fact, two dunefields in the area around Ingleses. The second dunefield does not pose a direct threat to the town, but passes the town on its eastern side. This dunefield is nevertheless very important, as it supplies a significant amount of sediment to Ingleses Beach. Research has been done to investigate how both dunefields migrate. An important result of this research is that the first dunefield (that is overwhelming the houses on the south side of the town) has never reached all the way to the beach. It had been previously assumed that the erosion of the beach was, wholly or partially, caused by the fact that sediment from the first dunefield could no longer reach the beach due to the urbanization between the dunefield and the beach. This assumption however has proven to be false. Another important result is the determination of the sediment influx rate from the second dunefield into the breaker zone of Ingleses Beach. This is an important factor in modelling the evolution of the beach. To be able to make predictions about the evolution of Ingleses Beach it is necessary to have nearshore wave data. Such data is not readily available and must, therefore, be obtained in another way. The available data consists of one year worth of measured wave data at a location about 35 kilometres offshore of Santa Catarina Island. To be able to translate this wave data to the nearshore of Ingleses Beach a thorough investigation of the bathymetry between the point where the wave data was measured and the beach has been carried out with the aid of the software package ArcGIS. With this bathymetry the available wave data can be translated to the nearshore of Ingleses Beach using the wave modelling program SWAN. The evolution of the beach has been modelled for two different scenarios using the computer program UNIBEST CL+. The first scenario represents a continuation of the present day situation. Simulation of this scenario has resulted in a trend prediction for the evolution of the beach. This prediction shows that, if no countermeasures are taken, some areas along the beach are indeed subject to erosion and houses in those areas will be severely threatened by the water. The second scenario represents a situation where the influx of sediment from the easterly dunefield is cut off from the sea. This may be due to ongoing urbanization between the dunefield and the sea, or fixation of the dunes by vegetation. If such a situation should occur the simulation shows that the erosion to be expected will be considerably more severe than in the first scenario. More houses will be threatened and a highly undesirable situation for people living near the shoreline, as well as economical damage due to loss of recreational areas, is the result. From the results of the dune study and the beach model simulation it is clear that action needs to be taken at both fronts. Several possible solutions to the problems have been produced based on the qualitative, and if possible quantitative, results of the research. It has been concluded that an extensive monitoring program and continued research are needed in order to quantify most of the suggested solutions. The monitoring can be done parallel to the excavation of the dunefield, which will give immediate results. While calculations and research are done on a suitable nourishment program, the sand of the Moçambique dunefield can be used for a small-scale nourishment. This will give extensive information about the way this sediment input will influence the morphology of Ingleses beach.

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