Since 1995, the Drainage Services Department (DSD) has removed 127 flooding blackspots, with only four still remaining in Hong Kong. In that regard, the Drainage Improvement Works at Chatham Road South in Tsim Sha Tsui are scheduled to commence in the third quarter of this year, with a view to eventually removing the flooding blackspot from the list. This time, I have invited a colleague from the DSD to talk about details of the Drainage Improvement Works in Tsim Sha Tsui, as well as how to enhance the drainage capacity and mitigate the flooding risk in the area.

Minor drainage improvement works since 2009

At present, one of the flooding blackspots is the area along and adjacent to Chatham Road South between Granville Road and Austin Avenue in Tsim Sha Tsui, which is in a low-lying area and close to the coast, making the drainage outlets more susceptible to tidal effects. Besides, some of the stormwater drains in the area have insufficient capacity, resulting in major flooding incidents in the past. Since 2009, the DSD has carried out minor drainage improvement works in the vicinity of Chatham Road South to enhance the capacity of the stormwater collection system, and has stepped up inspections and clearing of debris from gullies in conjunction with other government departments. The situation has improved since then.

Construction of an underground stormwater storage tank and a stormwater pumping station

To reduce the flooding risk in Tsim Sha Tsui in the long run and meet the challenges posed by climate change, the DSD plans to carry out Drainage Improvement Works in Tsim Sha Tsui, including the construction of an underground stormwater storage tank and a stormwater pumping station at the Urban Council Centenary Garden, as well as to lay new stormwater drains. Senior Engineer (Project Management Division) of the DSD, KWOK Chi-kuen, Kenley, says that the proposed underground stormwater storage tank will have two levels, with the lower level for stormwater storage and the upper one near the surface for accommodating electrical and mechanical facilities, in order to minimise the above-ground space to be occupied. The two-level design will also optimise the use of land resources, thereby releasing more valuable urban land for other uses.

He adds that the improvement works have taken into account the impact of increased rainfall and sea level rise due to climate change, and will effectively improve the capacity of the existing drainage system and mitigate the flooding risk in the area, with a view to eventually removing Chatham Road South from the list of flooding blackspots. We will seek funding approval from the Legislative Council as soon as possible, hoping that the works will commence in the third quarter of this year for completion in 2027.

Optimising the use of land resources

Regarding the site selection for the stormwater storage facility, the department has not only considered whether the location can effectively achieve the required stormwater storage capacity, but also the available area and overall land use planning. The department has also considered the impact on the environment, traffic and other public facilities during the construction and operation of the facility, with the aim of optimising the use of land resources and minimising the impact on the public. Having taken into account the above factors, we consider that the underground space of the Urban Council Centenary Garden at Chatham Road South is the most suitable site.

Intelligent design and operation

Mr Kenley KWOK says that the proposed underground stormwater storage tank and stormwater pumping station will adopt an intelligent design for operation. Water level sensors installed in the upstream, downstream and inside the tank will provide real-time data, which, together with meteorological data from the Hong Kong Observatory, will allow effective monitoring and control of the operation of the tank and stormwater pumping station, and enhance the cost-effectiveness of the operation of the facilities. The works will also proactively adopt green design features and green building materials, as well as to put in place a water resource collection system to collect rainwater which can be treated and used for irrigation and other uses, in order to promote sustainable development.

A challenging project

However, given the busy commercial activities in the vicinity of Chatham Road South, one of the major roads to Tsim Sha Tsui, it is a very challenging task to carry out drainage works in such a bustling location. Furthermore, the complex network of underground pipes, limited above-ground space, and possible structural impact on the foundations of buildings nearby all add to the construction difficulties.

Trenchless excavation to minimise impact

To minimise the impact on local traffic and pedestrians, Mr Kenley KWOK says trenchless construction method will be adopted for most of the pipes in the project, and road works will be avoided during peak traffic hours as far as possible. The department will plan the temporary traffic management measures carefully with the relevant departments, conduct trial runs before carrying out the works, and minimise the duration and scope of the traffic management measures where practicable.

Currently, there are four large underground stormwater storage tanks in Hong Kong, located at Tai Hang Tung, Sheung Wan, Happy Valley and On Sau Road. The DSD is planning six underground stormwater storage schemes, including the Chatham Road South and the Sau Nga Road Stormwater Storage Scheme as mentioned earlier in this blog. It is believed that the flooding risk in the areas concerned will be more effectively reduced upon the completion of these major projects, further enhancing Hong Kong’s flood prevention capability.