Proposed dam may cause
soil erosion
Tuesday, March 2, 1999
By Esther Tan
KUALA LUMPUR, Mon. - The proposed Sungai Selangor dam
project in Hulu Selangor will cause significant soil erosion if
land-clearing is not strictly controlled.
According to the Detailed Environmental Impact Assessment for
the proposed project, the catchment area for the dam has been
categorised a "High Erosion Risk" area in a recent study.
SMHB Sdn Bhd, the consultant who carried out the EIA, did not
state which study was involved. However, the Agriculture Ministry
had drawn up a map of high-risk erosion areas for Peninsular
Malaysia.
The consultant warned that the duration and size of land left
exposed should be minimised.
This is because land-clearing will increase surface run-off rate
which can result in flash floods and even landslides during rainy
season.
The EIA report has been put up for public viewing in the
Department of Environment offices from today.
The EIA was commissioned by Consortium TSWA-Gamuda-KDEB
after it was given the rights by the Selangor Government to carry
out a technical feasibility study for the development of the
Sungai Selangor Water Supply Scheme Phase Three project.
The State Government is seeking new water resources because it
has been projected that by the year 2003, there would be an
acute shortage of water supply in Selangor and the Federal
Territory.
When asked about the EIA findings, Science, Technology and
Environment Minister Datuk Law Hieng Ding said the Department
of Environment would ask for more details from the consultant
before making any decision.
On the signature campaigns being organised to protest the
proposed dam, Law said it would be better if the people were to
provide their views and state their reasons after looking at the
EIA.
Asked if environmental consultants could be biased since they are
engaged by project proponents to carry out EIAs, Law said the
EIA approval was given by the DOE and not the consultant.
He said a technical committee set up by the DOE would review
the EIA taking into considerations public views.
"That is why we ask developers to only engage consultants
registered with the DOE," he added.
The proposed dam involves the construction of a dam in the
headwaters of Sungai Selangor to harness water for use in the
State's northern region and the Federal Territory.
It will comprise a reservoir of 600 hectares in surface
area and
will be located about five kilometres from Kuala Kubu Baru town.
A stretch of the existing Federal route 55 from Kuala Kubu Baru to
Fraser's Hill will be flooded.
The proposed project will displace two Orang Asli communities and
affect downstream activities besides bringing about environmental
problems.
Soil erosion and siltation of the watercourses are among the main
environmental impacts since the dam and road construction
involve significant land-clearing and earthworks.
Under the existing condition, the average annual rate
of soil
erosion is estimated at between 100 and 150 tonnes per hectare
per year.
Using Universal Soil Loss Equation based on the worst
case
scenario, the consultant believes the removal of vegetation cover
at steeper slopes during the construction of the dam may result
in soil loss of about 1,300 tonnes per hectare per year.
"Therefore, it is important to minimise the extent of areas cleared
at any one time," states the EIA.
All unnecessary land-clearing should also be avoided and selective
clearance should be adopted to prevent soil erosion.
The EIA states that all exposed areas must be covered
immediately either with geotextile or turfing and that a temporary
storm water diversion should be constructed to divert storm
water from exposed areas.
Since a stretch of the KKB-Fraser's Hill route will
be inundated,
the project proponent has to build a realignment road.
The new road will pass through undulating terrain, therefore,
construction will involve rock-blasting works and hill-cutting.
These can result in soil erosion and slope failures too.
Soil erosion will increase silt loading and affect the water quality
of the nearby Sungai Luit, a tributary of Sungai Selangor.
The EIA warns that sediment load from the construction
work can
settle within the reservoir which can reduce its storage volume.
This means the useful life of the reservoir will be affected.
Rock-blasting will cause vibration and air and noise pollution but
these will be temporary and localised.
The EIA states that most of the forested areas proposed for the
project are logged over or secondary forests or plantation sites.
There are no rare endemic or endangered plant species or
biodiversity attributes in the area.
As for dam safety, the consultant states that the dam is
designed not to fail and that the spillway is designed to pass the
Probable Maximum Flood.