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1 March 2002 Study of Harbour Infilling using Sand Tracer Experiments
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Abstract

The harbour of Fortaleza (Ceará - Brazil) is facing infilling processes by sand and fine-grained sediments. The influx of sand into the harbour resulted in the generation and growth of an internal beach (Praia Mansa), located on the sheltered side of the main jetty (Titan). Two tracer studies were performed in the harbour vicinity in order to understand sand transport patterns around the jetty and inside the harbour. For this purpose 1,410 kg (experiment FORT I), and 420 kg (experiment FORT II) of dyed sand were released from a boat at depths between 3.5–5 and 6–11 m below mean sea level, respectively. For FORT I a series of 23 surveys were carried out over a period of two months, including the collection of about 1,000 samples. Detailed maps of sand transport and dispersion were obtained for each survey. During the FORT II experiment only 45 samples were collected at different surveying days, giving an idea of the broad sediment dispersion patterns.

The general tracer dispersion and transport pattern observed at FORT II proved that the sediment arriving to the main jetty arrives by littoral drift from the Futuro beach, after bypassing the Titanzinho groin. The analysis of FORT I maps showed that the sand moved along the external part of the Titan jetty at rates about 30 m/day. Subsequently, due to wave refraction and diffraction around the jetty tip, the tracer started to be transported towards the internal part of the harbour. The computed average displacement rate of the tracer head was about 5 m/day. The last survey, 58 days after the tracer release, shows the existence of dyed sand inside the harbour, at the nearshore portion of Praia Mansa beach. This confirms that Praia Mansa is still slowly but continuously accreting, by addition of sediment transported around the jetty. The results also demonstrate the durability and the effectiveness of dyed sands for the study of sediment transport and harbour infilling.

Study of Harbour Infilling using Sand Tracer Experiments
©Coastal Education and Research Foundation, Inc. 2002
Óscar Ferreira, Sandra Fachin, A. Braga Coli, Rui Taborda, J. Alveirinho Dias, and Gustavo Lontra "Study of Harbour Infilling using Sand Tracer Experiments," Journal of Coastal Research 36(sp1), (1 March 2002). https://doi.org/10.2112/1551-5036-36.sp1.283
Published: 1 March 2002
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