Following is a question by the Dr Hon Priscilla Leung and a written reply by the Secretary for Development, Mr Paul Chan, in the Legislative Council today (October 14):
The Water Supplies Department commenced the Water Mains Replacement and Rehabilitation Programme in 2000 to comprehensively replace and rehabilitate about 3 000 kilometres of aged water mains in phases. The programme is expected to be substantially completed within this year. In this connection, will the Government inform this Council:
(1) regarding those water mains covered by the aforesaid programme, of the respective total lengths of those water mains in various District Council (DC) districts for which works have yet to start at the present moment, and the relevant work schedules;
(2) of the details of each incident of fresh water main bursting since January 2014, broken down by DC district, including (i) the location of the burst water main, (ii) the duration of the resultant fresh water supply suspension, and (iii) the number of years for which the burst water main had been used; among such incidents, the number of those involving water mains which had been used for less than 30 years; and
(3) whether the authorities will, upon the completion of the aforesaid programme, gradually replace and rehabilitate water mains with relatively shorter years of usage; if they will, of the manpower and expenditure involved; if not, the reasons for that?
The Replacement and Rehabilitation Programme of Water Mains involves the replacement and rehabilitation of some 3 000 kilometres of aged water mains in stages. 96 per cent of the works has been completed and the programme is anticipated to be substantially completed by the end of this year. Replies to the three items of the question are given here below:
(1) Up to September 2015, the respective total length of water mains of which relevant works are still in progress within each district of the DC under the programme are shown in Table 1. The programme will be substantially completed by the end of 2015.
(2)(i) The summary of fresh water main bursts in 2014 and 2015 within each district of the DC is shown in Table 2.
(ii) Among the 128 fresh water main burst incidents, 84 incidents (about 66 per cent) affected fresh water supply to premises.
For the 84 incidents which affected fresh water supply to premises, there were 60 incidents (about 71 per cent) with the duration of suspension within eight hours, and an average duration of 5.7 hours. For the remaining 24 incidents, the average duration of suspension was about 16.5 hours. The latter needed more time to repair because (a) it was required to confine the road closure area in order to minimise the impact on road traffic during repair; (b) hand tools were required for excavation to avoid damaging the congested underground utilities; and (c) the removal of underground concrete structures or blocks took considerable time.
(iii) Among the 128 main burst incidents, 23 cases (about 18 per cent) were related to water mains which had been used for more than 30 years; 19 cases (about 15 per cent) were related to water mains which had been used for less than 30 years; and the remaining 86 cases (about 67 per cent) were related to water mains with "unknown" age. (Note: In the past, all water mains record plans were prepared by hand and the year of construction of the water mains was not recorded. In the early 80s, the Water Supplies Department (WSD) started recording the construction year when preparing water mains record plans. In the late 90s, the WSD commenced digitising water mains record plans and classified all the water mains without the year of construction as water mains with an "unknown" construction year. These water mains should have been put into service for more than 30 years.)
According to analysis, among the 19 main burst incidents involving water mains which had been used for less than 30 years, 18 incidents were caused by external factors, such as accidental damages by other roadworks projects or ground movement or settlement due to construction activities in the vicinity of the burst mains, causing pipe damages or dislocation of pipe joints.
(3) Following the substantial completion of the Replacement and Rehabilitation Programme of Water Mains by the end of 2015, the condition of the water supply network will be improved significantly. Thereafter we will adopt a multi-pronged strategy to maintain the condition of the water supply network.
With reference to overseas advanced technology and experience, we have planned to progressively establish the Water Intelligent Network (WIN) by setting up some 2 000 District Metering Areas (DMAs) over the territory with monitoring and sensing equipment installed within the network of each DMA to collect network data. We will make use of an intelligent network management system to analyse the data collected for continuous surveillance of the condition of the water supply network. When the WIN is fully implemented, it will help us determine the most effective network management measures (including pressure management, active leak detection, re-provisioning of water mains in poor condition, etc.) according to the condition of the supply network in each DMA, so as to maintain the condition of the water supply network.
Prior to the full implementation of the WIN, the existing water supply network will continue to age and deteriorate. Therefore it is still necessary for us to consider the replacement and rehabilitation of aged water mains with relatively high risk of failure during the transitional period. Apart from the age of water mains, we will continue to consider other relevant factors, e.g. the pipe material, burst and leakage records, current conditions of the water mains, etc., to determine the probability of occurrence of burst failure of water mains and at the same time assess the seriousness of consequences arising from main bursts (e.g. number of users affected, interruption to traffic, etc.) in identifying water mains with relatively high risk of failure for replacement and rehabilitation as a transitional arrangement, in order to sustain the condition of the water supply network.
Ends/Wednesday, October 14, 2015
Issued at HKT 11:38