To prepare for the rainy season, the Drainage Services Department (DSD) has been striving on flood mitigation to further reduce flood risks during rainstorms. This time, I have invited three DSD colleagues to share with us different flood prevention measures, including desilting, repairing and maintaining drainage facilities, the “just-in-time clearance” arrangement, and the use of new technologies to help monitor and analyse flood risks, with a view to reducing the impact of adverse weather on the public by enhancing flood prevention capacity in a comprehensive way.

Director of Drainage Services inspects various flood prevention facilities

With the rainy season approaching, all government departments have become more vigilant and are working hard to ensure that corresponding arrangements are in place. In mid-May, the Amber and the Red Rainstorm Warning Signals were issued in succession. The Director of Drainage Services, Ms Alice PANG, inspected several flood prevention facilities and visited the DSD’s Emergency Control Centre. During her visit, she was briefed on how the department coordinated with various parties to cope with situations in the rainy season and under unstable weather.

Large-scale flood prevention facilities

The flood prevention facilities managed by the DSD are massive in scale, including 2 400 kilometres of underground stormwater drains, more than 360 kilometres of engineered channels, four underground stormwater storage tanks with a total volume over 180 000 cubic metres (equivalent to the total volume of about 72 standard swimming pools) and four drainage tunnels totaling about 21 kilometres in length. In managing these facilities, the DSD has to handle daily reports of blockages of public drains, conduct regular electrical, mechanical and structural inspections, repair and rehabilitate ageing and damaged pipes, and desilt drainage facilities.

Repair and maintenance of drainage tunnels and stormwater storage tanks

Engineer of the Hong Kong and Islands Division of the DSD, Mr LAU Yiu-man, says that the desilting and maintenance works of drainage tunnels and underground stormwater tanks are particularly challenging. To avoid hindrance to the operation of these facilities during the rainy season, the DSD conducts the related works yearly during dry seasons (i.e. from November to March of the following year). However, affected by climate change in recent years, there is heavy rain at times in November and intense rainfall in as early as February. As a result, the department very often has only two to three months to complete the related work.

Working against time to prepare for rainy season

To complete the desilting and maintenance works of drainage facilities under such a tight schedule is by no means a simple task. Every year, the amount of debris and silt cleared from the four drainage tunnels and four stormwater storage tanks is as much as 500 tonnes, which is equivalent to the weight of about 34 double-decker buses. Moreover, structures of the facilities and their electrical and mechanical equipment also require inspections. Therefore, we have to work against time to prepare well for the rainy season.

Implementing the “just-in-time clearance” arrangement

In addition, the DSD will implement the “just-in-time clearance” measure during the rainy season (i.e. from April to October) every year. Before the onset of a rainstorm, staff will be deployed to inspect about 200 locations in the territory which are susceptible to blockages by litter, fallen leaves or the like. Clearance will be arranged immediately if blockages are found, so as to further mitigate flood risks in times of heavy rain.

Timely activation of the Emergency Control Centre

When a Red or Black Rainstorm Warning signal is hoisted, a special announcement on Flooding in the northern New Territories is issued, or the Tropical Cyclone Warning Signal No. 8 or higher is in force, the Emergency Control Centre (ECC) will be activated. Drain Chargeman of the Gang Management Team of the DSD, Mr LAI Yee-ming, says that colleagues will be on duty on a rotation basis around the clock to dedicate in handling public requests for assistance in regards to flooding, and will promptly arrive the scene to clear debris from drains. During the passages of Typhoon Lionrock and Kompasu in October last year, the centre operated consecutively for about 60 hours.

Flood prevention results obvious to all

Mr LAI Yee-ming says that, having worked in the DSD for 34 years, he has witnessed the department’s numerous achievements in flood prevention. Large-scale flooding used to be quite frequent decades ago, but it rarely happens nowadays. Although drainage clearance keeps them very busy, they get a strong sense of satisfaction out of helping the public and receiving recognition for their work.

Proactively adopting innovative technologies

To combat the extreme weather brought by climate change, the DSD has proactively adopted new technologies to better monitor and analyse flood risks. Engineer of the Land Drainage Division of the DSD, Mr MAK Shiu-wai, Maxwell, says that the department has set up more than 100 gauging stations in various districts and installed sensors at about 190 major flood control spots to collect real-time data on the water levels of major rivers and channels, rainfall and tide levels throughout Hong Kong round the clock. This year, the department has started to install CCTV at a number of major intakes to monitor their condition in real time.

With the application of new technologies, we can have a comprehensive understanding on the situation and can quickly analyse the flooding risks at various locations in advance, enabling us to deploy our teams in a timely manner. We can also coordinate with other departments to implement contingency measures promptly. The data will also facilitate long-term planning of flood prevention measures. I hope that all departments will continue to implement preventive measures to vigorously address the potential threats posed by the rainy season, giving the highest priority to public safety.