Drainage Services Department

Overview of Overtopping Wave

During the passage of tropical cyclones, waves approaching shores may surpass the coping level of seawall forming “overtopping wave”. The rise in sea level by storm surge during passage of tropical cyclone results in easier seawater inundation at coastal areas due to overtopping waves.

Measures for Overtopping Wave Spots

Overtopping wave spots are located along coastal areas.  To handle the seawater inundation due to overtopping wave, construction of marine structures such as breakwaters and rock armours can reduce the intensity of waves, thus lowering flooding risk.

In response to the overtopping wave, government departments and citizens need to cooperate to reduce the impact.  Apart from the above measures, the government will consider non-structural measures, such as Early Alert System at the overtopping wave spots.  Upon the issuance of storm surge alerts on the spots by the Hong Kong Observatory, the DSD will, at the relevant locations, deploy pumping facilities, install water-stop boards, and/or provide sandbags for the residents' use.  DSD will also deploy emergency gangs to station at the sites prone to serious inundation, for implementing flood alleviation measures, such as removal of blockage at drains, to minimise the flooding risk arising from storm surge.  The government will arrange emergency and evacuation plans, if necessary.

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