Abstract
The declared depth in port access channels is often maintained by dredging and monitored by regular bathymetric surveys. However, at remote sites these activities are not cost-effective and the channel depth would need to be defined based on the surveyed depth plus an allowance for sedimentation and variability in bed levels. This allowance can especially be significant in estuaries with strong tidal currents, where mega bedforms, including sand waves, develop on the seabed due to the prevailing strong current flows. The mega sand waves are highly mobile and fluctuate in height as they migrate over the seabed. Mega sand waves and mega ripples with a height up to approx. 3.2 m were observed in multi-beam bathymetric survey undertaken in the offshore entrance to the Geba River estuary in Guinea Bissau. Supramax bulk carriers with a draft of 11-12 m are planned to transit this area on departure from a proposed phosphate export terminal located further upstream in the estuary.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/5Gmy9yQkfno
Highlights
ANALYSIS OF MEGA BEDFORMS Sediment composition data in conjunction with water depths and tidal currents from a calibrated MIKE HD FM model were analysed to identify the areas potentially suitable for the formation of mega bedforms
Mega sand waves and mega ripples with a height up to approx. 3.2 m were observed in multi-beam bathymetric survey undertaken in the offshore entrance to the Geba River estuary in Guinea Bissau
A bedform allowance amplitude above the mean depth was determined based on the observed sand waves in the bathymetric survey and the Yalin & Da Silva (2017) formula for mega bedform formation, which best represented the dimensions of the observed features
Summary
ANALYSIS OF MEGA BEDFORMS Sediment composition data in conjunction with water depths and tidal currents from a calibrated MIKE HD FM model were analysed to identify the areas potentially suitable for the formation of mega bedforms. 3.2 m were observed in multi-beam bathymetric survey undertaken in the offshore entrance to the Geba River estuary in Guinea Bissau. Supramax bulk carriers with a draft of 11-12 m are planned to transit this area on departure from a proposed phosphate export terminal located further upstream in the estuary.
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