The Selangor government's decision to privatize three rivers in the state to three companies to undertake management and development is totally unwise vis-à-vis the serious water shortage in Selangor which is expected to occur from next year.

Of the three rivers, Sg Langat and Sg Selangor serve as significant sources of drinking water to more than 50% of consumers in Selangor.

The fresh water inflow into a river comes from two sources. One is the surface runoff during rainfall in the river basin. This is normally referred to as fast flow. The other fresh water source is from the soil water and ground water system, which is normally referred to as base flow or dry weather flow.

During raining seasons, the river will always have an abundance of surface runoff. However during prolong droughts, the river relies mainly on the base flow. Therefore, this base flow is the one used to determine the safe yield of river for water supply purposes in Malaysia.

In Malaysia, water supply is designed according to a 50-year return period of drought, which is based on historical statistics of hydrological behavior of the river basin. So it is expected that if a water treatment plant is built drawing raw water from a river, the hydrological behavior of that river basin should substantially remain unchanged in order to ensure the sustainability of the safe yield of the river.

For Sg Langat and Sg Selangor, the two rivers have already been fully exploited for water supply purposes. To privatize these two rivers and allowing the concessionaires to extract sand as well as carry out development, albeit on limited scales, will invariably alter their already fragile hydrological behavior and reduce their safe yields.

Sand mining activities will cause deterioration of raw water quality. Commercial development will lead to increase in surface runoff to the river thus leaving only little water to enter the subsoil layer to be utilized during dry spells for base flow generation. Therefore under such hydrological conditions, the safe yields of the two rivers would not be sustainable and Selangor would then experience more frequent water shortage events such as low water levels in dams and rivers.

The reduction of base flow in Sg Selangor could be one of the reasons for the low water level in Sg Selangor dam during the last quarter of last year. Water had to be released from the dam to compensate for the low base flow in the river.

Note:
An edited version of the above was published in The Star on 14/02/06.