Monday September1, 2008 11:26 am
Pahang-Selangor Raw Water Transfer
Interstate Water Transfer To Meet Future Water Demand For Selangor And Wilayah Persekutuan Kuala Lumpur
Malaysia has experienced substantial economic development since the 1980s, resulting in increasing water demands in the commercial and industrial development centres. The Selangor / Kuala Lumpur region which is the political, commercial and industrial centre of the nation is the most important focus for these high demands which are expected to continue their rapid growth into the 21st century. However, the water resources available within the Selangor / Kuala Lumpur region will not be able to meet the demands in the near future.
A scheme to transfer water from Pahang to Selangor has been proposed to cope with future water demand shortfalls in Selangor, Kuala Lumpur region and at a later stage, the western part of Negeri Sembilan. Pahang State which lies to the east of Selangor State, possess ample water resources compared with their local demand and has sufficient reserve for interstate transfer.
The Pahang – Selangor Raw Water Transfer Project is located in a central area of Peninsula Malaysia.
The Project is to convey raw water from the Semantan River through a transfer tunnel to the Selangor / Kuala Lumpur region for domestic and industrial uses to mitigate future water shortages.
Most of the urbanized areas of Selangor State and the federal territory of Kuala Lumpur receive domestic and industrial water from an integrated supply system with multiple water sources such as the Selangor, Semenyih, Klang Gate and Langat rivers.
The Project area in Pahang side is drained by a number of rivers, the principal ones being the Sg. Bentong, Sg. Telemong, and Sg. Kelau. Sg. Bentong is renamed as Sg. Semantan below the confluence with Sg. Kelau. The Project utilizes runoffs of these three rivers efficiently with provision of the reservoir in Sg. Kelau. The river flow including reservoir releases is abstracted at the intake in Sg. Semantan and is pumped up from the pumping station beside the intake to a connecting basin at the tunnel inlet through the pipeline.
The raw water from the connecting basin is transferred through the tunnel with gravity flow to an outlet connecting basin. The collected water is further distributed to receiving basins of a planned treatment plant through pipelines also with gravity flow. The outlet connecting basin and pipelines to the treatment plant will not be included in the Project but incorporated in the treatment works.
The implementation of the dam involves both environmental and social impacts and the project has been formulated based on a flexible project planning and design basis.
The Project will produce total reliable yield of 2259 Mld. The stage development plan with the associated treatment works has been established according to the water demand projection as follows:
SI + KD
SI + KD
SI + KD
Note: SI: Semantan Intake, KD: Kelau Dam, ( ): Pumping capacity
(1) Water Transfer Tunnel
The functions of the water transfer tunnel are to collect water from the Semantan intake and to transfer the water to the treatment plant. The transfer tunnel is planned to be 44.6 km in length, including the inlet connecting basin, inlet conduit and outlet conduit.
The inlet connecting basin is located on the hill about 300 m from the Karak-Telemong road and the outlet conduit ends about 3.5 km north of the existing Sg. Langat treatment plant. The tunnel route passes through the main central mountain range which typically has elevations exceeding EL. 1,200 m.
The tunnel has a diameter of 5.2 m in sections excavated by TBM and a longitudinal slope of 1/1,900. The tunnel will operate under free flow conditions with a design discharge of 27.6 m3/s.
The transfer tunnel is directly connected to the treatment plant with pipelines maintaining gravity flow. Thus the outlet water level is set at EL. 61.2 m.
Bedrock along the tunnel consists of metamorphosed rocks of the Karak Formation for the initial 3.5 km from the inlet. The remaining portion is in granites. Tunnel excavation will primarily be made by Tunnel Boring Machine (TBM) for 35 km. The upper and lower ends will be excavated with the conventional New Austria Tunneling Method (NATM). Four adits are provided for construction of the tunnel, and hence three TBM cutting-faces and four conventional cutting-faces are planned.
The inlet and outlet conduits are designed as cut-and-cover type culverts of horseshoe shape with vertical walls. They will be 4.0 m in width and 4.7 m in height.
(2) Semantan Intake and Pumping Station
The Semantan intake and associated pumping station will abstract raw water discharging from the Sg. Bentong and Sg. Kelau, including releases from the Kelau and dam. The raw water will be pumped through the pipeline to the tunnel inlet. The intake is located on the Sg. Semantan, 1.5 km downstream from the confluence of the Sg. Bentong and Sg. Kelau.
The weir, which is planned as a concrete structure with sluice gates, will divert the maximum discharge of 27.6 m3/s to the pumping station located on the right bank. The intake structure consists of intake grid chamber (sand settling basins), common well, and suction tank before pumping station. Pumps are of the fixed speed, vertical split casing double entry centrifugal type. The arrangement of pump-sets in the final development is as follows:
3.20 m3/s x 2 units (1 unit for standby) and 3.05 m3/s x 10 units (2 units for standby)
Two lanes of pipeline each with a diameter of 3.0 m are designed to convey raw water from the pumping station to the tunnel in Karak. The pipeline is approximately 11.8 km long. The pipe is designed largely to be below ground to minimize environmental and social impacts.
The route traverses the northern, left bank of the Sg. Bentong, passing through a disused rubber estate on the left bank where the terrain is undulating, and crosses the Sg. Bentong, the main highway, and Sg. Telemong.
Steel pipe with inside mortar lining is utilized. Where the pipeline crosses rivers, special pipes will be used across pipe beam bridges.
(4) Kelau Dam
The Kelau dam and associated reservoir will have an effective capacity of 299 million m3 for the storage of raw water. It will be located about 5 km upstream from the confluence of the Sg. Kelau and Sg. Bilut, at the site of a narrow gorge. The dam comprises a fill type dam, a spillway, and a river outlet with diversion facility.
Considering the availability of embankment materials, a homogeneous earth-fill dam 35 m in height with chimney drain is proposed. Foundation treatment with curtain grouting is planned for seepage control. Saddle dams are provided on the right bank ridge and reservoir rim where existing ground levels are below full supply level.
The spillway is located on the right bank. An ungated side channel type is proposed with sufficient capacity, in conjunction with flood storage in the reservoir, to discharge the Probable Maximum Flood.
A culvert used for river diversion during construction will be utilized as the outlet works. A draw-off tower is provided at the upstream end of the culvert.