One of the major components of the Flood Prevention Strategy is a set of flood protection standards for the planning and design of the public stormwater drainage systems. Factors such as land use development scenarios, economic growth, socio-economic needs, consequences of flooding and benefit-cost analysis of flood mitigation measures have been considered in developing the standards. As a result, there are different standards for different elements of the drainage systems.
All stormwater facilities in new developments have to be designed to withstand a severe flood event, which will occur at the Average Recurrence Interval (approximately once within the period) stated below:
| Types of Drainage |
Years |
|
Urban drainage trunk systems |
200 |
|
Urban drainage branch systems |
50 |
|
Main rural catchment drainage channels |
50 |
|
Village drainage |
10 |
|
Intensively used agricultural land |
2-5 |
The definition of flood events is based on the combination of rainfall intensity and tide levels.
It is recognized that it will not be always possible or practical to upgrade the existing drainage systems, especially those within the old urban areas, to the current standards. In these special circumstances, a pragmatic approach is necessary in order to determine the best possible flood protection levels that can be achieved having regard to the constraints imposed by the existing highly intensive development.
What is a 10-year rainstorm? (PDF format, 21KB)
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