The Sungai Selangor Dam is a crucial part of the SSP3 that will provide additional water supply for 2 million residents and industries in Selangor and Klang Valley. Works on building the dam commenced in the third quarter of 2000 and was completed two months ahead of schedule, in April 2003.

Aerial view of Sungai Selangor Dam

Highlights

• The Sungai Selangor Regulating Dam is a 110m high rockfill dam founded on solid granite bedrock. The rockfill type of dam is similar to the Kenyir Dam in Terengganu (155 m), Temenggor Dam in Perak (127m), Ahning Dam in Kedah (74m,), Batang Ai Dam in Sarawak (85m) and Pedu Dam in Kedah (61m).
• It is situated at the narrow gorge on massive granite bedrock just downstream of the confluence of Sungai Selangor and Sungai Gerachi.
• The dam embankment comprises an impervious earth core covered with an external rockfill. In between, there is a layer filter material consisting of 0.62 million cubic metres of granular material. The dam, 400m wide at the base, 800m long and 110m high, is built up of 1.2 million cubic metres of clay core and 6.4 million cubic metres of granite. At full supply level, the inundated areas is just 600 ha, making it the dam with the largest storage capacity relative to the area inundated.
• Dam impoundment commenced on April 25, 2003 and reached its full supply level which is 220 m (above sea leave) with a total storage capacity of 230 million cubic metres on 13 April 2004.
• The dam is designed as a regulating dam. During heavy rains, excess water from the catchment upstream is stored in the reservoir within the dam. On dry days when water level at the intakes is low, water is released into the river. The volume of release is dependent on the amount of the raw water to be abstracted downstream at Rasa and Batang Berjuntai.

The dam has several key components which enable the dam to function effectively:

• Draw-off Tower

The draw-off tower is a crucial and prominent structure of the dam, standing at a height of 110m with a diameter of 9m. This is the structure through which water is drawn from the reservoir for release into the river whenever discharges from the dam are required to augment low flows in the river, ensuring that sufficient water is available at the raw water intakes downstream. The twin discharge pipes leading from the draw-off tower have flow measuring devices and flow regulating valves installed to control and measure the volume of water released into the river. The draw-off tower has four service gates at various levels (RL131m, RL160m, RL190m and RL210m. Two emergency gates located at the beginning of the twin discharge pipes ensure that water discharges can be shut down whenever required for pipe maintenance.

• Spillway

The chute spillway with a flip bucket has a width of 30m and a length of 230.54m which are provided for overflow during the wet season. It is designed as an open chute, discharging excess water over the crest of the dam. When water overflows into the spillway, it creates a waterfall like scene at the downstream face of the dam. Visitors may experience scenario during the wet season. The spillway has a discharge capacity of 3000m³/sec (260,000 Mld), more than sufficient to route excess water during extreme floods.

• Plunge Pool

The plunge pool, located at the lower end of the spillway functions as an energy dissipator to dissipate the energy of any overflowing water from the spillway before the water is allowed to rejoin the river. This is to prevent turbulence and erosion of the riverbed and its banks. The plunge pool is 196m long and is 4m deep.

• Diversion Tunnel

The 480m long diversion tunnel which was blasted through solid granite at the start of the construction to divert the river to facilitate construction of the dam, is now used to house the twin 2200mm diameter discharge pipes coming out of the draw-off tower. The water drawn from the dam for release flows through these twin discharge pipes before being released into the river. The tunnel is 7m in diameter and has a horseshoe shape. It was constructed using the controlled drilling and blasting method.

• Coffer Dam

The coffer dam is a temporary water-tight enclosure that was built to divert the river to enable work to be carried out in the dry for the construction of the main dam. The coffer dam is required during the construction of the main dam. The coffer dam is required during the construction phase but has no specific function after the completion of the dam.

The dam is a necessity as demand for water in Selangor and Federal Territory has outstripped supply and this is the last viable source of raw water. Apart from performing its primary function to regulate the flow in the river, the Sg Selangor Dam is a man-made attraction which offers recreation and scenic view to the public at large.

Panel of Consultants Supervise Design, Construction and Operations of SSP3

The construction, operations and maintenance of the SSP3 regulating dam follows a series of guideline and procedures which also incorporate the environmental, ecological and social aspects imposed on by the dam project.

Significant advances in the design and construction of dams have been achieved nowadays. The construction material quality, construction techniques combined with new and improved construction equipment, better understanding of the science of soil mechanics and soil characteristics, and better quality control have also improved considerably.

Apart from this, independent dam safety reviewers are also being engaged by both SPLASH and the Government for SSP3. The qualified independent dam safety reviewers will conduct reviews throughout the design, construction and operational stages of the project.

Angkasa GHD, a joint venture between local consulting company and Australian company has been appointed by SPLASH and Mr. Douglas Galager (a dam expert from UK) has been appointed by Selangor State Government.

The panel of consultants:

Design and Supervision:

• Setia Sepakat Perunding (SSP)
• SMHB Sdn Bhd
• Universiti Kebangsaan Malaysia (UKM)
• Garis Architect
• Gunung Ganang (State appointed EIA Consultant)

Independent Engineering Consultants:

• Angkasa GHD
• KLIAB Berhad (Sate appointed supervising engineer for construction and operations)

The best site in the State

Comparison of potential sites

Dam site	Remark
Rening	Extensive inundation of private land, 1600ha with active storage of 92 MCM, Sg Selangor dam is still needed	Not necessary if Sungai Selangor Dam is constructed
Beletak	Will flood North-South Expressway and Lembah Beringin	Not feasible
Rawang	Will inundate the entire amenity area of Templer's Park and North-South Expressway	Not feasible
Batang Kali	High social impacts and flood many developments	Not feasible
Sungai Selangor	Small inundated area, high storage capacity and good bedrock foundation	RECOMMENDED

Note: Click the picture to enlarge

Sungai Selangor Regulating Dam site is most appropriate

• Biggest catchment and last major water resource available in the state
• Least area inundated with highest storage
• Least area of private land affected
• Low impact on environment
• Good bedrock foundation
• Affected private land area is small. Only 113ha private land is affected out of 600ha of inundated area for Sungai Selangor Regulating Dam.

Sungai Selangor Regulating Dam catchment area

The Sungai Selangor will only flood 3% (600ha) out of 19,700ha of the dam catchment area, compared with 7% for the other 5 dams in the State. The dam catchment area forms only 13% of the total Sg. Selangor river basin To protect the dam and the quality of reservoir water, the entire catchment of 19,700 ha is gazetted as a protected watershed

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Comparison of storage capacity with other dams

• Sungai Selangor Regulating Dam only floods one-third the area with same storage compared with other dams combined in the state

Note: Click the picture to enlarge