Contract C is one of the major contracts managed by Drainage Projects Division of Drainage Services Department. It is one of the contracts for constructing the Main Drainage Channels System in Yuen Long and Kam Tin area. The HK$316 million contract mainly involves the straightening and widening of Kam Tin River middle reach by forming a 2.3km long concrete lined trapezodial channel from Castle Peak Road (Hung Mo Bridge section) to Ko Po Tsuen north. The channel then splits into two branches to Kam Tin north and Kam Tin Road.
 

A special feature of the Contract is the construction of two rubber dams, which are the third and fourth rubber dams under Drainage Services Department's management. Located at the confluence of the two tributaries of the drainage channels in Ko Po Tsuen north, the rubber dams are to prevent the polluted tidal water at downstream from backflowing upwards, and can, therefore, significantly improve the environment in the upstream area.
 

During fine weather, the rubble dams are inflated to exclude the tidal water from Deep Bay. The dry-weather-flow in the rivers is diverted through the desilting basins and screen chambers to segregate the silt and rubbish. The flow is then pumped by four screw pumps in the pumping station to downstream.
 

When the heavy rainstorm comes, the flow in the rivers will become very heavy and the water level in the rivers may rise. When the upstream water reaches a threshold level and is detected by electric sensors, the rubber dams will subsequently be deflated and flat on lay the bottom of the channels to allow full flow within the channels.

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