LCQ18: Incidents of fresh water mains burst

Following is a question by the Hon Kam Nai-wai and a written reply by the Secretary for Development, Mrs Carrie Lam, in the Legislative Council today (June 1):

Question:

In recent months, there were a number of incidents of fresh water mains burst in Hong Kong which affected the supply of fresh water.  In particular, the areas affected by the incident of the sudden burst of an underground fresh water mains at Wong Nai Chung Road in Happy Valley which occurred in the early morning of 1 March 2011 were the most extensive, covering Wong Nai Chung Road, Blue Pool Road, Leighton Road, Leighton Hill and the Causeway Bay area, and included Ruttonjee Hospital as well as a number of hotels and eateries in Causeway Bay.  In this connection, will the Government inform this Council:

(a) of the particulars of the detailed contingency plan of the Water Supplies Department (WSD) in response to an incident of fresh water mains burst;

(b) of the time WSD needs to make deployment for the provision of temporary water supply following an incident of fresh water mains burst;

(c) of the total number of fresh water mains burst incidents handled by WSD in each of the past three years, together with a breakdown by the 18 District Council districts; among such cases each year, of the information of the 10 cases with the longest duration of water supply suspension, including the date and time of the incident, time taken to isolate burst mains upon receipt of report, duration of suspension of water supply, whether temporary water supply was provided, and the time taken by WSD to start to provide temporary water supply after the burst;

(d) among the cases of fresh water mains burst reported in the past three years, of the number of those in which the performance target regarding the time taken to isolate burst mains was not met, and the reasons for failing to do so;

(e) among the cases of fresh water mains burst reported in the past three years, of the number of those in which the performance target regarding the duration of water supply suspension was not met, and the reasons for failing to do so;

(f) of the respective numbers of water tanks and water wagons used for providing temporary water supply in each of the four operational regions of WSD, and the location for storing these tanks and wagons; and

(g) given that the Government has indicated that it might be necessary to increase the number of water wagons for providing temporary water supply to meet the need in emergency situations, of the details and the amount of funding required?

Reply:

President,

The water distribution network of Hong Kong has developed in line with growing water demand.  It is massive and complex measuring 7 800 kilometres in total length.  Given the hilly terrain of Hong Kong, the water supply pressure is relatively high.  Service reservoirs are usually situated at high level for optimal use of scarce land resources.  Together with ground movements and external disturbances, bursts and leaks are inevitable in our aged water distribution network.  We fully understand that water supply suspension and, in some cases, the associated traffic disruption would cause inconvenience to the public.  To tackle the problem, the Water Supplies Department (WSD) is taking a multi-pronged approach, including proactive burst prevention by leakage detection, replacement/rehabilitation of aged water mains under the Water Mains Replacement and Rehabilitation (R&R) Programme and implementation of pressure management.  With these measures being put in place, the number of water mains burst incidents has dropped from a peak of about 2,500 in 2000-01 to 609 in 2010-11.  The water mains leakage rate has also declined from 25% in 2001 to 20% in 2010.  We anticipate that the leakage rate will further decrease to 15% upon completion of the R & R programme.

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

(a) WSD has established procedures for handling water mains burst incidents.  Upon receipt of reports on mains burst incidents, WSD's designated teams will be mobilised　to the sites immediately to identify and isolate the water mains concerned.  The contractors will also be called to the sites to undertake repair work.  Should the incident affect existing traffic, WSD will liaise with the concerned parties, including the Police, Transport Department and Highways Department for necessary traffic diversion arrangement to facilitate the carrying out of the repair work.  WSD will also liaise with other utility undertakers for protection of their existing utility services, which may be affected by the repair work.

After isolation of the burst main, the emergency repair work may affect water supply to consumers. WSD will take the following steps to mitigate the impact on consumers:

(i) Whenever possible, WSD will maintain uninterrupted water supply for the affected areas by arrangement of alternative water supply from other water supply zones wherever possible.

(ii) If it is not possible to arrange alternative water supply from other supply zones, WSD will provide temporary emergency fresh water supply to meet the basic need of the affected consumers in the following descending order of preference:

(1) installation of standpipes at fire hydrants at convenient locations; and
(2) deployment of water wagons and placing of water tanks within the affected areas.

The public can obtain the latest information about mains burst incidents through WSD’s Customer and Telephone Enquiry Centre (CTEC) hotline.  For incidents affecting water supply to large numbers of consumers, the WSD will upload notifications on to the department's webpage.  For serious incidents, there will be radio announcement and press releases.  The CTEC staff will also maintain close coordination with the staff on site to keep abreast of the latest development of the incidents.

(b) If it is not possible to arrange alternative water supply from other supply zones, WSD will provide temporary emergency fresh water supply to meet the basic need of the affected consumers.

According to WSD's plan, arrangement of alternative water supply from other supply zones, installation of standpipes or deployment of water wagons and water tanks should be initialised at the target time for isolation of burst mains (i.e. 1 hour and 15 minutes for pipes up to 300 mm diameter or 2 hours for pipes above 300 mm diameter or complete isolation of the burst mains, whichever is the earlier).

(c) Table 1 shows a breakdown of the number of fresh water mains burst cases by 18 District Council districts in 2008-09, 2009-10 and 2010-11.

For the past three years, the average time required for isolation of burst mains upon receipt of report was about 0.95 hour and the average duration of water supply suspension was about 4.26 hours.  Provision of temporary water supply was required in 637 cases. The average lead time required for provision of temporary water supply in the past three years was as follows:

                  Average duration
                  from isolation
                  of burst mains to
                  provision of temporary
Year              water supply
----              ----------------------
2008-09              0.64 hour
2009-10              0.51 hour
2010-11              0.37 hour

Details of the 10 cases with the longest duration of water supply suspension are shown in Table 2.

(d) Table 3 shows the performance pledges and achievements of WSD in respect of handling mains bursts in the past three years.

Among the total 1 421 incidents of fresh water mains bursting in the past three years, 71 of them have taken a longer time to isolate the burst mains.  The main reasons are as follows:

(i) defective valves required shutting down other valves;

(ii) the emergency gang concerned was already engaged in dealing with other mains burst incidents; and

(iii) the remote location of burst mains required longer travelling time for the emergency gang to reach the site.

(e) Table 4 shows the performance pledges and achievements of WSD in respect of suspension of water supply in the past three years:

Among the 1,421 incidents of fresh water mains bursting over the past three years, 187 of them have taken a longer time to resume water supply.  The main reasons are as follows:

(i) only light duty machinery could be deployed in order to protect the congested utility services and installations adjacent to the burst water mains;

(ii) it was necessary to remove the concrete surround that encased the burst water mains; and

(iii) water supply could only be resumed after setting of the new concrete blocks for stabilising the water mains.

(f) At present, WSD has five water wagons, with capacities ranging from six to eight cubic metres each.  WSD also has 104 water tanks, most of which have a capacity of one cubic metre.  There are also a small number of one and half cubic metre tanks.  The distribution and locations of these water wagons and water tanks are shown at Table 5.  When the situation warrants, these water wagons and water tanks may be mobilised across regions.

(g) With cross-region deployment, the current stock of 104 water tanks is adequate for our needs.   In order to cope with the demand for the initial round of water supply and subsequent refilling of depleted water tanks in emergency situations, we are actively considering increasing the number of water wagons in individual WSD operational regions.  This is to ensure that a total of 10 water wagons can be mobilised, when necessary, by cross regional deployment to deal with individual burst incidents.  The estimated cost of the five additional water wagons is about $6.75 million.

Ends/Wednesday, June 1, 2011
Issued at HKT 16:28

NNNN

ATTACHMENT


Back