LCQ18: Maintenance and repairs of fresh water mains

Following is a question by the Hon Abraham Shek and a written reply by the Secretary for Development, Mrs Carrie Lam, in the Legislative Council today (March 16):

Question:

It has been reported that on the first day of this month, a burst underground fresh water main at Wong Nai Chung Road in Happy Valley had brought gush of fresh water from underground, and it took staff of the Water Supplies Department (WSD) nearly six hours when they succeeded in turning off all relevant valves for isolation of the burst main, after which they carried out emergency repair works.  Fresh water supply in the vicinity of Wan Chai and Causeway Bay was suspended for 15 hours, which affected hundreds of thousands of residents, thousands of eateries and several hospitals.  Regarding the maintenance and repairs of fresh water mains, will the Government inform this Council:

(a) whether the records and plans of the underground water mains in Hong Kong are comprehensive, accurate and readily accessible at present; if they are, of the details; if not, the reasons for that;

(b) whether WSD has adopted new technology for inspecting and maintaining underground fresh water mains as well as preventing sudden bursting of fresh water mains; if it has, of the details; if not, the reasons for that;

(c) whether abnormalities such as water seepage and decrease in water pressure will appear prior to the bursting of water mains; if so, whether WSD will conduct inspections and repairs on the basis of such abnormalities; if not, of the reasons for that;

(d) given that replacement of aged water mains takes time, whether WSD has put in place corresponding procedure for emergency repair works, stepped up inspection of fresh water mains at risk and arranged for expedient replacement of such water mains; if it has, of the details; if not, the reasons for that; and

(e) whether, in view of the aforesaid incident, WSD will adjust the priority of the various projects under the Replacement and Rehabilitation Programme of Water Mains and expedite their implementation; if it will, of the details; if not, the reasons for that?

Reply:

President,

The water distribution network of Hong Kong has developed gradually in line with growing water demand over the years.  The network is huge, complex and measures 7,800 kilometres in total length.  Given the continual upgrading and expansion of the distribution network over the years and the congested state of public utilities and pipes underground (especially in the urban areas), the task of keeping comprehensive and accurate information on water mains is a very challenging one.

The Water Supplies Department (WSD) has always been looking for, researching into and adopting sophisticated technology for leakage detection in water mains network to improve its service and efficiency.

In general, to isolate a burst water main requires turning off not more than five valves.  But in the case of the fresh water main burst incident at Happy Valley, the distribution network involved is more complicated and requires turning off 22 valves, including the valves of many branch pipes, in order to isolate the burst main.  All these valves are recorded in the drawings.

My reply to the five parts of the question is as follows:

(a) The existing records of WSD are sufficient for the daily operation and maintenance of water supply systems on the whole.  Since 1998, the WSD has implemented a digital information system on water mains networks.  This information system is based on the Geographical Information System to record information on water mains installations and ancillary facilities, such as the locations of the valves, the level, size and materials of the mains.  The System captures all the water mains plans and is readily accessible by staff.  The WSD also takes every opportunity to ascertain and update the information in the course of their maintenance works on water mains.

(b) The WSD has adopted many measures to reduce leakage from water mains, including proactive leakage detection, water pressure management and establishing small district metering areas (DMAs).

The WSD has also adopted a risk management strategy for continual surveillance of water mains under busy trunk road sections that are pending replacement.  To date, the WSD has installed about 1,200 noise loggers at these water mains to detect and record noises generated by water leakage to facilitate timely repairs.

The WSD is currently exploring a probe detection technology that allows surveillance cameras or equipment to be inserted into water mains for observing and monitoring the mains conditions without disrupting water supply.  However, there is yet to have a cost-effective detection technology that can be adopted across the territories to prevent sudden bursting of water mains.

(c) Water pressure fluctuates with changes in water demand at different times of the day.  As such, leakage cannot be concluded from changes in water pressure alone.  The leakage detection technology primarily relies on detecting the noise generated by leaking water.  As mentioned above, the WSD has adopted various measures to detect leakage and reduce bursts of water mains, including proactive leakage detection, water pressure management and establishing small DMAs as well as the 15-year Replacement and Rehabilitation (RR) Programme of Water Mains which has commenced since 2000.  These measures have reaped certain success.  For instance, the number of burst water mains incidents dropped from 2,479 in 2000-01 to 988 in 2009-10.  The WSD expects the figure to drop further to about 600 in 2010-11.

(d) The WSD has stepped up monitoring mains leakage.  Apart from traditional leakage detection devices, noise loggers have also been installed to monitor water mains under busy trunk road sections that are pending replacement.  In the course of replacing water mains, the WSD will also install additional valves wherever necessary and practicable to reduce the area of suspension of water supply as a result of burst water mains.

(e) The water main involved in the Happy Valley incident is already included in the RR Programme.  But in light of the burst water main incident, the WSD will expedite the replacement works of the water main section concerned.

In addition to regular review of the overall situation of burst water mains, the WSD also monitors the progress of water mains replacement and repair works to coordinate prioritisation of specific water main replacement works.  Where necessary, water mains that are not covered by the RR Programme may be included in the current or pending RR works contracts to accord the problematic water main section a higher priority for replacement or repairs.  In case timely adjustment to works under the RR Programme is not possible, the WSD will consider deploying district resources for early commencement of RR works for the problematic section.

Ends/Wednesday, March 16, 2011
Issued at HKT 18:15

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