I refer to the letter You can solve flood problems? Come and see us which was in reply to my earlier letter Penang government not people-centric .

A new Urban Storm Water Management manual for Malaysia (MSAM) was completed in 2000 to replace the 1975 Urban Drainage Design manual. In January 2001, the Cabinet approved its application for all types of development projects in the country.

The new manual correctly pointed out that widening and channeling of rivers and drains to cater for increased discharges of storm water runoffs as urban areas develop is inherently defective from the environmental point of view. It also recognises the need to apply structural Best Management Practices (BMP) to control storm water from the aspect of quantity and quality runoffs to achieve zero development impact contribution.

It is hoped that this new strategy will be a sustainable solution to mitigate the existing flood problems and also to prevent the occurrence of such problems in the new areas developed.

I am really curious why this mandated approach enforced since 2001 is totally absent from Penang’s flood mitigation plans.

From feedback by developers and architects, I also realise that the Drainage and Irrigation Department has a strange way of interpreting the requirement of MSAM.

But using structural Best Management Practices to manage storm water runoff is a very cost- effective and efficient solution to mitigate the flash floods problem.

For example, in 1999, one maintenance station in Keary Mesa, California was selected for a retrofit pilot with the installation of the Storm-Filter™, a proprietary water quality treatment device that uses cartridges filled with different types of media to filter storm water runoff before channelling it into a storm water well.

The cost per unit for water quality volume treated is US$1572/m3. Total construction cost is US$305,356. This is a solution that can be deployed to manage storm water runoff for a tributary area of less than 8ha.

This is just one example of structural BMP that can be deployed to Georgetown areas which have land space constraints. There are other cheaper options that can be considered for use to manage storm water in ultra-urban areas.

Consider the cost involved and other side benefits like harvesting storm water for non-potable needs. With an average rainfall of 2000mm per annum, the volume of storm water harvested in Penang will be significant.

For a factory in the Free Trade Zone (FTZ) in Penang, the water yield is calculated as:

Total rainfall (water) yield = Roof area x Drainage coefficient (0.8) x annual rainfall

= 1000 m2 x 0.8 x 2505 mm per year

= 1000 m2 s x 0.8 x 2.505 m

= 2004.0 m3

= 2,004,000 litres per year

Based on the normal usage for 500 workers:

= 500 persons x 100 litres (Only for flushing toilets)

= 50,000 litres per day

= 18,250,000 litres per year

The rainfall harvested can fulfill about 11% of the total water needs of this factory. In monetary terms, based on the average rate of 78 sen per 1,000 litres of water (or 0.078 sen/litre), the factory will save RM156,312 per year.

The Penang government can use such kinds of solutions to solve the flash floods problems while at the same time harvesting rain water for sale in order to recover some costs.