Estudo da deriva litorânea em Fortaleza/Ce: análise quantitativa do transporte longitudinal para gestão costeira e portuária

Abstract

The study of littoral drift is very important to coastal zone management and harbors for coastal, such as Fortaleza city. The lack of knowledge of sediment dynamics during the construction of the Mucuripe Harbor generated serious problems for the sedimentary balance of the region. The harbor’s jetty has barred the natural transport of sediment from the Futuro beach, which resulted in severe erosion in west beaches. Climatological studies indicate that from December to April, due to influence of northeast trade winds, there is a higher incidence of waves in this direction, generating greater transport in the west beaches of the harbor and transport of sediments on the contrary to the predominant direction on the Futuro beach, due to natural coastline inclination. While from May to November, due to a higher incidence of the trade winds from the southeast and east locations, the Futuro beach presents an intense sediment transport, on the other beaches the transport is very slow. In this study, it tried to estimate the longitudinal transport from an experimental methodology compared with a theoretical study in order to assess the quality of results. It was used the software ACES (Automated Coastal Engineering System) to calculate the theoretical transport on the Futuro, Meireles and Leste-Oeste, from data of direction and significant wave height. While experimentally, it was analyzed suspended sediment and the discharge with an ADCP (Acoustic Doppler Current Profiler) on the Futuro and Leste-Oeste beach, to calculate the sediment transport. Through the ACES program, it was calculated a rate of sediment transport of 1,3 million m³/year for the Futuro beach, 0,6 millions m³/year for the Meireles beach and 0,4 millions m³/year for the Leste-Oeste beach. While experimentally, it was calculated an average rate of sediment transport 2,3 million m³/year for the Futuro beach and 4,2 million m³/year for the Leste-Oeste beach. The values were very close between the theoretical and experimental studies considering only transport in July for the Futuro beach, about 0,22 milion m³, showing a 90% correlation between the variation of water level and discharge recorded. The big difference in the annual results is due to experimental study has used only 2 months of data to estimate the annual transportation. Moreover, the west beaches of the harbour, the experimental study have been conducted near the mouth of the outfall of the city, 3 km off the coast, overestimating the transport calculations.