Dredging Conditions and Corals

Gregor Hodgson rcgregor at uxmail.ust.hk
Mon Apr 20 23:08:34 EDT 1998

The effects of dredging on corals depends on many factors e.g. type of
dredge, duration of dredging, depth of dredging, size distribution of
dredged material, typical water currents, typical background sediment
load, wave action, species and growth forms of corals etc so it is best
to set limits on dredging activities that match the specific conditions
at the site.

When faced with this situation in HK we have found that an exclusion
zone of 500 m, when carefully enforced, has prevented visually
observable damage to corals even with high volume discharges of very
fine materials. This can be carried out very safely if the dredging
contract limits dredging to periods when currents are moving away from
sensitive areas (if the configuration permits). The HK government has
often used a limit of 100 mg/l to control sediment load in plumes
impinging on sensitive areas and this seems to have worked well.
Gregor Hodgson, PhD
Institute for Environment and Sustainable Development
Hong Kong University of Science and Technology
Clearwater Bay, Kowloon, HONG KONG
e-mail: rcgregor at ust.hk
tel: (852) 2358-8568      fax: (852) 2358-1582
Reef Check: http://www.ust.hk/~webrc/ReefCheck/reef.html

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