For discussion PWSC(96-97)65
on 20 November 1996


New Territories North Development
(Civil Engineering - Drainage and erosion protection)
70CD - Yuen Long bypass floodway

Members are invited to recommend to Finance Committee -

  1. the upgrading of part of 70CD, entitled "Yuen Long bypass floodway - advance works at intersection with Route 3 (Country Park Section)", to Category A at an estimated cost of $64.3 million in money-of-the-day prices; and
  2. the retention of the remainder of 70CD in Category B.


A section of the proposed Yuen Long bypass floodway ("the floodway") will cut underneath Route 3 (Country Park Section) ("R3(CPS)") which is now under construction. Unless we construct the part of floodway at the intersection point as part of the Route 3 construction works now, there will be serious disruption to the traffic on R3(CPS) in future.


2. The Director of Territory Development (DTD), with the support of the Secretary for Planning, Environment and Lands, proposes to upgrade part of 70CD to Category A at an estimated cost of $64.3 million in money-of-the-day (MOD) prices for the advance works for a section of the Yuen Long bypass floodway at its intersection with R3(CPS).


3. The scope of 70CD comprises the construction of a 3.6-kilometre floodway running along the south facing side of the Yuen Long Highway from the upstream of Yuen Long nullah to Kam Tin floodway. The project also includes the construction of maintenance access roads alongside the drainage channels.

4. The part of the project we now propose to upgrade to Category A comprises the construction of a 100-metre long multi-cell box culvert at the intersection of the floodway with R3(CPS).


5. After almost 30 years of continuing and rapid development of Yuen Long Town and its adjacent areas, the capacity of the existing Yuen Long nullah drainage system, completed in the 1960s to serve Yuen Long Town, has become inadequate to protect Yuen Long Town from periodic flooding. As a result, flooding in the area occurs from time to time causing economic loss and disruption in traffic and communication.

6. The "Territorial Land Drainage and Flood Control Strategy Study - Phase II", which was completed in August 1993, recommended the construction of a bypass floodway to divert part of the flow from Yuen Long catchment into Kam Tin floodway (which is at present under construction), as the best option to reduce the flooding risk of Yuen Long Town. The Study also identified the need to proceed with the floodway project, otherwise a significant portion of Yuen Long Town and its adjacent low-lying areas would be flooded by rainstorms. This situation is not acceptable according to the current flood protection standards for urban areas.

7. The proposed floodway will be a trapezoidal-shaped flood relief drainage channel. It will intercept a portion of runoff from the areas to the south of Yuen Long Town and convey the runoff to the Kam Tin floodway and then to Deep Bay. This would bring the existing Yuen Long nullah system to pass a 50-year return period flooding and would relieve Yuen Long Town from unacceptable flooding risk.

8. A section of the floodway will intersect R3(CPS) near Small Traders New Village. The construction of R3(CPS) by the R3(CPS) Company, Limited ("the Company") is now under way and is scheduled for completion in 1998. According to the original programme, the construction of the whole floodway will commence almost three years after the completion of R3(CPS).

9. However, if we do not construct the section of the floodway in the form of a multi-cell box culvert at the intersection with R3(CPS) now, we envisage that during the construction of the floodway in future, it will cause serious disruption to the traffic on R3(CPS). The traffic diversion will also be costly as it involves the acquisition of additional land. To avoid the traffic disruption and any interface problems, we need to advance the floodway construction works at the intersection point and entrust the works to the Company. To tie in with the construction programme of the R3(CPS) project, the proposed works are scheduled to commence in December 1996 for completion in mid 1997.


10. We estimate the capital cost of the project to be $64.3 million in MOD prices (see paragraph 11 below), made up as follows -

$ million

(a) Construction of about 100- metre long multi-cell box culvert including supervision of works (based on the rates of similar works in existing contracts)


(b) Project management and design services during construction


(c) Contingencies


(at December 1995 prices)


(d) Inflation allowance


(in MOD prices)


11. Subject to approval, we will phase the expenditure as follows -


$ million
(Dec 1995)


$ million

1996 - 97




1997 - 98






12. We have derived the MOD estimate on the basis of the Government’s forecasts of trend labour and construction prices for the period 1996 to 1998. We will pay the Company, in phases, a fixed lump sum in MOD prices for the entrustment works upon negotiation under the terms of the R3(CPS) Project Agreement.

13. We estimate the annually recurrent expenditure of the proposed works to be $202,000.


14. We consulted the Environmental Improvement Committee of the Yuen Long District Board on the proposed advance works in October 1996 and the Committee supported the proposal.

15. We also consulted the Environmental Impact Assessment (EIA) sub-committee of the Advisory Council on the Environment (ACE) in October 1996. Members have no objection to the proposed advance works.


16. The proposed advance works will be carried out in conjunction with the construction of R3(CPS). We will adopt environmental mitigation measures recommended in the Route 3 Tai Lam Tunnel and Yuen Long approach Northern Section EIA to control the impacts arising from the construction of the advance works to conform with established standards and guidelines.

17. The long term implication of the advance works is that they will set a constraint for the future floodway alignment and the full EIA for the floodway project scheduled to commence in early 1997. We consulted the EIA subcommittee of the ACE on 14 October 1996. The subcommittee agreed to the proposed advanced works and its implication on the EIA study.


18. The proposed project does not require land acquisition.


19. We upgraded 70CD to Category B in September 1995.

20. We have entrusted the detailed design of the proposed advance works to the Company and charged the cost of $1.5 million to the block allocation Subhead 7100CX "New towns and urban area works, studies and investigations for items selected in Category D of the Public Works Programme". The construction works at the intersection point with R3(CPS) have been scheduled to commence in December 1996 for completion in mid 1997.

21. We will carry out the site investigation and detailed design work for the remaining section of the Yuen Long bypass floodway and an EIA for the whole project in March 1997 for completion in February 20011 . We will commence the construction of the remaining section of the floodway in March 2001 for completion in March 2004.

1 -- This is the subject of a separate PWSC paper PWSC(96-97)66 "Yuen Long bypass floodway - site investigation and consultants' fees" to be discussed at this same meeting.

Last Updated on 16 August 1999