Following is a question by the Dr Hon HO Chung-tai and a written reply by the Acting Secretary for Works, Mr Keith Kwok Ka-keung, at the Legislative Council meeting today (May 29) :
Regarding the conversion of open nullahs into underground drains, will the Government inform this Council:
(a) of the total number of open nullahs throughout the territory and the district with the largest number of such nullahs;
(b) of the number of open nullahs converted into underground drains in the past two years, and the reasons for such conversion; and
(c) whether it has considered converting all open nullahs into underground drains; if so, of the details; if not, the reasons for that?
(a) Currently there are 45 major open nullahs under the management of Drainage Services Department. The district with the largest number of such open nullahs is Yuen Long, which has nine open nullahs.
(b) Regarding the conversion of open nullahs into underground drains, there were works during the past two years to convert parts of three open nullahs into underground drains. The location of these nullahs and the reasons for converting them into underground drains are as follows:
(i) Part of the Tai Hang Tung Nullah in Tong Yam Street was decked to facilitate the construction of the Tai Hang Tung Flood Storage Scheme,
(ii) Parts of the Tuen Mun Nullah were decked to accommodate the new railway stations of the West Rail, and
(iii) Parts of the eastern section and the western section of the Yuen Long Nullah were also decked to accommodate a new railway station of the West Rail.
(c) From the flood prevention perspective, we do not currently have a comprehensive programme to convert all the open nullahs into underground drains. To convey the same flow, a closed culvert generally needs to be much wider than an open channel because of the obstructions to the flow caused by the interior columns and walls supporting the deck. Very few existing open channels and nullahs have sufficient spare capacity to allow for the adverse hydraulic effects of decking, and simply placing a deck over the channels would result in an unacceptable increase in risk of flooding. On the other hand, the widening of channels would result, in most cases, in considerable disruption to the community, additional land requirement and a large capital expenditure. Nonetheless, we will consider decking some of the nullahs when it is necessary to do so in order to cope with adjacent developments.
End/Wednesday, May 29, 2002