Offshore aggregates in south-east Asia

Ceri James, British Geological Survey, Project R6840

The recent and continuing growth of coastal cities in south-east Asia has resulted in a major expansion in construction and strong demand for aggregates for building, roadstone and land reclamation. This demand has been met previously by land-based supplies but in recent years offshore aggregates have made an increasingly important contribution. The British Geological Survey has recently completed a study concerned with the effective development of offshore aggregates in south-east Asia. The study aims to:

· provide guidelines for planning and execution of offshore aggregate resource surveys

· encourage adoption of long-term planning, surveying and monitoring methods

· encourage environmentally sensitive and sustainable methods of offshore sand and gravel extraction.

The project report (The effective development of offshore aggregates in south-east Asia, BGS Technical Report WC/99/9 by James et al.) looks at marine aggregate extraction across south-east Asia, with a brief examination of the geological setting of areas of major extraction. It outlines the methods adopted for surveying and sampling aggregate resource areas and the specifications and uses of various types of aggregate. Examples of aggregate borrow areas are explained. Methods of dredging are also described.

Because of possible environmental impacts, offshore dredging is usually subject to licencing controlled by national or local government. The licence terms and procedures vary in detail from country to country but the best practices adopted are described.

Pearl Estuary building sand barged for use on tile Central Reclamation, Hong Kong.

Photo: Ian Selby

The report provides the reader with a description of the issues involved in the dredging of offshore aggregates, with a focus on the location, reserve estimation, licencing and monitoring aspects. It is hoped that this will provide an effective background to assist planners and dredging companies to develop a licencing and extraction policy which leads to the required supply of aggregate and at the same time limits the damage to the local offshore environment.

A trailing suction hopper dredger at a borrow area dredging marine aggregate, Hong Kong.

Photo: Ian Selby

Conclusions

i. Extraction of marine aggregates is likely to increase substantially in the years ahead as pressure increases to build at or near coastal locations and land based aggregate supplies become scarce.

ii. National or state licencing authorities need to locate, assess and quantify marine aggregate resources to formulate and administer long term sustainable extraction policies.

iii. Legislative frameworks need to be adopted to control indiscriminate extraction of marine sand and gravel and destruction of coral reefs for aggregate.

iv. Comprehensive site investigations and geological interpretations are essential in understanding the form and geometry of potential deposits of marine aggregates.

v. Environmental issues can only be addressed with a regional understanding of sea bed habitats, sedimentary environments and hydrographic conditions.

Workshops held in Thailand (3-8 May 1999) and in the Philippines (9-12 May 1999) helped disseminate the results of the project to a wide audience from the region. The latter workshop contributed significantly to the formulation of new Guidelines for Offshore Mining and Seabed Quarrying which was published as an Executive Order.