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Advanced technologies to rehabilitate pipes

There are more than 4500 kilometres of underground stormwater drains and sewers across Hong Kong. Many of those in the old districts have been in use for over 30 years. The sewers, in particular, are more prone to ageing and deterioration due to prolonged exposure to corrosive gases brought by sewage. Drainage Services Department (DSD) has gradually rehabilitated the high-risk underground pipes by adopting a pipe repair method that requires no excavation of pipe trenches or road surfaces in order to alleviate inconvenience caused to the public during the works. Gradual rehabilitation of old pipesSerious wear and tear will cause pipe collapse and road subsidence, bringing adverse impact on traffic, environment and public safety. Since 2017, the DSD has initiated comprehensive planning for the phased investigation and rehabilitation of pipes that have been assessed to be of high risk and formulated a territory-wide replacement and rehabilitation programme. However, we have to face a number of challenges in carrying out drainage improvement works in urban areas. Hong Kong is congested not only with people and vehicles, but also with various underground utilities such as gas pipes, communication facilities and water pipes. The traditional “open trench” rehabilitation technology may inevitably affect traffic and residents. The benefit of the new trenchless technology introduced by the DSD in recent years is that pipes can be replaced and rehabilitated without the need to open up an entire road section. Only a temporary shaft is neededAccording to Engineer of the Project Management Division of the DSD, Mr CHEN Ka-yin, the trenchless pipe rehabilitation works only need to excavate a temporary shaft at an individual location to facilitate the insertion of new pipe material into an old pipe to form a new pipe. Under this method, the excavation requires less open space and a shorter duration of works, allowing traffic to resume quickly after the completion of works to minimise impacts to the public. Currently, subject to the damage of the pipes and on-site situations, the DSD mainly employs three trenchless technologies, namely cured-in-place-pipe (CIPP) lining, spirally-wound lining and slip-lining. CIPP lining technologyAccording to Mr CHEN Ka-yin, under the CIPP lining technology (that is commonly referred to as the “insertion into pig intestines” in Chinese), a soft polyester liner with a thickness of 10 to 40 millimetres is pulled into the host pipe through a “launch shaft”. The liner is then expanded and cured by steam or hot water until it hardens and forms a new pipe. This technology can be used on pipes under dry condition. In rehabilitating trunk sewers that still has water flow, we have to employ the spirally-wound lining technology instead. In this technique, a special winding machine is placed inside the pipeline to helically wind steel-reinforced polyethylene strips into circular shape to form a new pipe in the original pipe. Alternatively, the slip-lining method can also be used. As both methods are designed for the rehabilitation of running pipes, no interception is required. Slip-lining methodStanding at the construction site on Bailey Street in To Kwa Wan, Mr CHEN Ka-yin introduces the use of the slip-lining method at the site. First, a temporary shaft will be set up at an appropriate location. Part of the old pipeline will then be cut and exposed. After cleaning and inspection of the pipe, a 1.5-metre long fibreglass plastic liner will be pushed into the old or damaged pipe section by section. Then, with cement slurry filling the gap between the new and the old pipelines, a new pipe is formed. He points out that although a fibreglass plastic liner looks relatively thin, its structural strength is equal to that of a concrete pipe and its lifespan is up to 40 to 50 years. Planning for stage 2 worksAs the rehabilitation works of all stormwater drains and sewers in Hong Kong involves 18 districts, over the course of four months, colleagues of the DSD visited each of the districts to consult the relevant District Council committees and explain project details to stakeholders, so as to give an early start to the projects. Stage 1 works had begun and are scheduled for completion in 2022. Stage 2 works are scheduled to start in 2020 to conduct condition survey and rehabilitation of stormwater drains and sewers in six districts, including Tsuen Wan, Sham Shui Po and Yau Tsim Mong. (The video is broadcasted in Cantonese) (The video is provided by Development Bureau)

Father’s Day Series: Drain Chargeman Mr KOO Wai-ming of the Drainage Services Department

As Father’s Day is approaching, we would like to share with you a frontline worker and his little story as a father, so as to show our support for all good dads. Mr KOO Wai-ming has worked in the DSD for over three decades.  Starting out as a Workman II, he was promoted to Drain Chargeman 10 years ago.  He is not only a senior staff member in our department with total dedication, but also a guardian angel for his child. Currently, the DSD has 11 teams under the Direct Labour Force for clearing blocked drains, each with four to five Leading Sewermen or Workmen II led by a Drain Chargeman to discharge their duties.  More than clearing blocked drains Sharing his job experience, Mr KOO said that when an Amber/Red/Black rainstorm warning or a typhoon signal is hoisted, the DSD colleagues have to remain on standby on a rotational basis, 24 hours a day, at the Emergency Co-ordination Centre (ECC) to receive and handle public requests for assistance.  The frontline staff, once alerted by the ECC, will rush to the scene across the territory.  Upon arriving at the scene, the DSD workers will first use devices to test for any poisonous or explosive gas before opening manholes.  After that, they will desilt the blocked drains with rattan strips or high-pressure water jets. Handling emergency cases with a clear head Talking about his most memorable experience, Mr KOO recalled that he had once received an urgent request from a member of the public.  Arriving at the scene, he found the female caller emotionally unstable.  He did his best to comfort the lady, while at the same time he had to take prompt action with his colleagues to solve the blockage problem.  He later realised that the lady, being a new mother, had made incessant phone calls simply because she was worried that the foul water would affect her baby.  The incident tells him that there are always reasons behind the requests for assistance or complaints from the public or those in need, and therefore they should help them solve their problems as fast as possible with a positive attitude. A tough man’s tender love for his son Besides his work, our tough man Mr KOO also shared with us his family life.  When he talked about his family and his love for his son, his sentimental side shone through.  He has a 12-year-old son.  As he works shifts, he sometimes has to work on Saturdays and Sundays.  Whenever there is an emergency, he is required to go on duty at all hours and even has to work overnight.  At times, his son complains that he is often not at home.  As a father, he can only explain to his son with patience that his work is to serve the community and there is a public need for his service.  He hopes that his son will understand better as he grows up.  In the past, he read his son stories.  In the blink of an eye, his son will soon become a Secondary One student and the way they get along has changed a lot.  One thing is certain, however, he just cannot be too strict with his son and they need to communicate as friends to maintain their bonds. The name of Mr KOO’s son, KOO Chung-hang, carries a special meaning.  Mr KOO believes that all parents have expectations of their children.  He said the name he picked for his son comes from Confucius, whose second name is Zhongni (Chung-nei in Cantonese), with “Chung” meaning integrity.  Although he does not expect his son to have great achievements, he hopes his son will be a good, virtuous and righteous man.  Regarding his son’s future occupation, he said it will be up to his son. (The video is broadcasted in Cantonese) (The video is provided by Development Bureau)

Drainage Services Department's remote-controlled desilting robot

In Hong Kong, the rainy season generally starts in April. In order to further reduce flood risks during rainstorms, the Drainage Services Department (DSD) has introduced the “just-in-time clearance” arrangement this year. It has also adopted new technologies in using a new remote-controlled desilting robot for silt clearing works at box culverts to enhance the efficiency of desilting works. Preventing silt accumulation from affecting the drainage capacityHong Kong faces an average rainfall of about 2 400 millimetres a year, one of the highest among cities in the Pacific Rim. According to Mr POON Tin-yau, an engineer of the DSD, when stormwater is discharged into the sea through box culverts, the washed-off sand, stones and dust will accumulate gradually at the drains to form silt, which will in turn affect the drainage capacity and may lead to flooding in the most serious cases. To avoid the above situation, the department inspects the box culverts on a regular basis and arranges the desilting works if necessary to ensure that the drains are functioning properly. Operating as a vacuum cleanerEarly this year, a new remote-controlled desilting robot was introduced into the DSD. The DSD conducted a pilot test on the use of the robot for desilting works at the box culverts in Sham Shui Po and Tsuen Wan with its functions monitored. The robot will be lifted up with a crane and sent into the box culvert concerned through its opening. With the help of closed-circuit television and sonic survey, the operator can then observe the conditions inside the box culvert and remotely operate the robot for desilting from his workstation. Mr POON Tin-yau says that the robot, measuring approximately 3 metres in length, and 1.5 metres in both width and height, works similarly to a vacuum cleaner. Once the silt is sucked by the robot, it will be pumped to a temporary silt container on the ground through a tube connected to the robot. The silt will be transported to a landfill only after dewatering. Enhancing work safetyAccording to the traditional desilting method, workers need to go into the box culverts for installation and operation of desilting devices. Given that box culverts are confined spaces, workers working inside will face certain safety risks. The traditional method also requires interception of water flow in the culverts to allow workers to work in an environment without water flowing through, which means the work is limited mostly to dry seasons. On the contrary, the remote-controlled desilting robot can take over diving tasks to spare workers from going into confined and submerged space of the box culverts. Apart from enhancing work safety, the use of the robot allows desilting works in rainy seasons, which in turn will expedite the progress of such works, lower the costs and significantly improve the desilting efficiency. Implementation of the “just-in-time clearance” arrangementFurthermore, the DSD had analysed more than 200 flooding cases between 2017 and 2019, finding that more than 60 percent of them were due to blockage of drains by litter, fallen leaves or other washouts carried by surface runoff. This year, the department will implement the “just-in-time clearance” arrangement. Before the onset of a rainstorm, staff will be deployed to inspect about 200 drain locations in the territory which are susceptible to blockage by litter, fallen leaves or the like, and will immediately arrange for clearance if necessary. The department will also send staff to inspect and clear all major drainage intakes and river channels to prevent blockage after a rainstorm or when a typhoon signal is about to be lowered so as to prepare for the challenges of further rainstorms. Constructing more underground stormwater storage tanksApart from strengthening the responsive management measures before and after rainstorms, the DSD will continue to press ahead with its flood prevention strategy, which includes constructing more underground stormwater storage tanks to collect and temporarily store excessive rainwater during rainstorms, thus reducing the loading at downstream drains and the consequential flood risks. At present, six locations are under planning, including Shek Kip Mei Park, Tai Hang Tung Recreation Ground (extension), the Urban Council Centenary Garden in Tsim Sha Tsui, as well as Sau Nga Road Playground, Kwun Tong Ferry Pier Square and Hoi Bun Road Park in Kwun Tong District. (The video is broadcasted in Cantonese) (The video is provided by Development Bureau)

Drops · Livability (Drainage Services Department)

Happy Valley and its neighbourhood are low-lying areas flanked by hills. In the past, heavy rains triggered frequent flooding, which had a significant impact on the public. To protect people from the risk of floods, the Drainage Services Department (DSD) developed an innovative scheme to enhance flood protection in the district. The project team installed a stormwater storage tank underneath the Happy Valley Recreation Ground. During heavy rains, the tank temporarily stores excessive stormwater. Conventional drainage improvement schemes in urban areas are normally upgraded in-situ and in a large scale. In comparison, building a storage tank and storing flood water below ground greatly reduces disruptions to traffic flows and the general public. Movable weir The stormwater storage tank features a movable weir, which is a mechanism deployed by DSD for the first time. The weir’s opening, closing and overall positioning are automatically adjusted according to the real-time information on tidal levels as well as the water levels in the drainage culvert upstream and downstream. This mechanism allows stormwater overflow into the storage tank at the optimal time. Harvesting system collects groundwater and rainwater The tank’s design also incorporates a sizeable water harvesting system that collects groundwater and rainwater. After undergoing some simple treatment, the water can be used for irrigating the Happy Valley Recreation Ground and for toilet flushing, thereby conserving water resources. These features ensure that the project is sustainable and in line with the concept of “Sponge City”. Fan Room and Lawn A stormwater storage scheme requires the construction of support facilities above ground such as a fan room and a pump house. The project team customised the design to make optimal use of the site in the interest of the public. With an environment-friendly design, the ground floor of the fan room is opened up as a public amenity. The pump house is covered by a lawn, providing a comfortable outside area for fun and game watching. Going the extra mile, drop by drop, the project team consolidates stakeholders’ support and the fruit of joint efforts, bringing the project smoothly towards the goal of “Smart Drainage•Green Living”: flood protection and a more livable environment in tandem.     Partnering for innovationCHENG Nga-see - Senior Engineer, Drainage Services Department (For more details, please visit Sevice Excellence Website)