Assessment of offshore sand and gravel bodies for dredging

Abstract

Abstract Reliable assessment of offshore sand and gravel resources permits efficient dredging, the maintenance of cargo quality control and the effective mitigation of environmental impacts. Site investigation should be based on the interpretation and correlation of high resolution seismic profiling and CPT/sampling data. A preliminary interpretation of the seismic data reveals the geological setting of the sand bodies and leads to the selection of appropriate sampling methods and the recognition of key sampling positions. Geologically complex sand bodies demand phased data acquisition to delineate geometry, physical properties and compositional variability. The alternative approach, of grid-based sampling using a predetermined sampling density, is costly at best and probably misleading. A three-dimensional model is created from the integration of acquired data and a resource volume calculated. Dredging constraints and overflow losses are applied to the model resulting in the determination of a reserve volume and critical dredging parameters. It is advisable to carry out a wide-ranging testing programme on the recovered samples to ensure compliance with relevant standards or requirements. The potential penalties for superficial site investigation include delay, unpredictable cargo quality and unforeseen environmental problems.