Celebrating the 25th Anniversary of the establishment of the Hong Kong Special Administrative Region, the Drainage Services Department (DSD) has earlier held the San Tin Stormwater Pumping Station Open Day for the public to learn first-hand about its work on flood protection and the promotion of Hong Kong’s sustainable development. This time, I have invited colleagues from the DSD to introduce the Village Flood Protection Schemes, the San Tin Stormwater Pumping Station, as well as the Floating Photovoltaic (FPV) System and the Ecological Floating Island set up at the San Tin Stormwater Storage Pond, so that we can have a better understanding of the Department’s efforts in flood protection and combating climate change.

Completion of 27 Village Flood Protection Schemes

The open day spanned two days in the form of guided tours, introducing a series of long-term improvement measures implemented by the DSD to alleviate flooding problems in the Northwest New Territories. Apart from river training works, the DSD has also completed 27 Village Flood Protection Schemes to safeguard low-lying villages. Among them, the San Tin Flood Protection Scheme has covered seven low-lying villages, with a total area of approximately 51 hectares (around 2.5 times the area of Victoria Park), protecting about 3 500 residents from flooding risks.

Three major tools under the Village Flood Protection Schemes

Mr LAI Hong-ho, Engineer of the Special Duty Division of the DSD, explains that the Village Flood Protection Scheme generally involves three major tools – an embankment, a stormwater storage pond, and a stormwater pumping station. An embankment prevents the massive influx of rainwater into the village during heavy rainstorms, while the stormwater drainage system within the village collects and conveys the stormwater to a stormwater storage pond. When the water level in the pond reaches a pre-set level, the pumps in the stormwater pumping station will activate automatically, and pump the water in the pond to the rivers or large drainage channels outside the embankment.

Floating Photovoltaic (FPV) System at the San Tin Stormwater Storage Pond

Most DSD facilities need to operate round-the-clock. To reduce carbon emissions, apart from saving energy, it is even more important to create new energy sources. That is why the Department has been making good use of its facilities, hoping to develop more space for renewable energy and at the same time optimise land use. The stormwater storage pond under the San Tin Flood Protection Scheme, with a surface area of around 16 400 square metres (about the size of 13 standard swimming pools), is the largest stormwater storage pond under the Schemes, providing a suitable site for the Department’s first trial project of FPV System. Consisting of 70 photovoltaic (PV) panels, the system is expected to generate 37 000 kWh of electricity annually. In terms of net electricity generation, the FPV system at the San Tin Stormwater Storage Pond will produce sufficient electricity to power the operation of the San Tin Stormwater Pumping Station.

The intake of the San Tin Stormwater Pumping Station has also provided a suitable location for installing a flexible PV system and a steppable PV system. The Pumping Station is one of the visiting locations of the DSD’s Eco Tours, through which the Department hopes to promote the concepts of decarbonisation and sustainable development to the public.

Ecological Floating Island set up at the San Tin Stormwater Storage Pond

Besides, the San Tin Stormwater Storage Pond is adjacent to the Mai Po Nature Reserve. The DSD has set up an Ecological Floating Island at the pond to provide a roosting place for birds, thereby enriching the ecological environment of the pond as well as enhancing biodiversity.

Features of the FPV system

The FPV System at the San Tin Stormwater Storage Pond was completed at the beginning of this year, and the project team encountered many challenges in both design and construction. Mr CHIM Sai-shing, Engineer of the Land Drainage Division of the DSD, explains that the seemingly stationary FPV System involves complex mechanic principles. The project team had to consider many external factors such as wind load, rainfall intensity and forces due to water currents in the overall design. On the one hand, the project team aimed to minimise the weight of each PV panel so that the system could float more easily. On the other hand, there had to be enough tensile force to prevent the system from being blown up by strong wind under extreme weather and deviating from its designated position.

The project team also put a lot of effort into the design of the anchorage system at the pond, so as to prevent damage to the system due to impact, or breaking of electric cables caused by substantial displacement, etc. In addition, given the site constraints of the San Tin Stormwater Storage Pond, the project team had to overcome the challenge of transporting construction materials by making anchor blocks on-site through concreting. However, in-situ concreting inside the pond was not a simple task. The project team had to accurately estimate the concreting time and minimise the water level in the pond, at the same time minimising the duration of the works to avoid excessive impact on the landscaping area and the roosting of migratory birds. The project team also needed to keep a close eye on the weather forecast to reduce overall construction risks.

Considering the installation of FPV systems at other stormwater storage ponds

When Typhoon Chaba hit Hong Kong in early July, the Department closely monitored the system and concluded that its performance was satisfactory. This has given the Department more confidence to consider installing more FPV systems at other suitable stormwater storage ponds.

We will continue to follow the principle of sustainable development, proactively adopting renewable energy for reducing carbon emissions. We also hope to take the opportunity of the open day to let the public better understand how the DSD’s facilities can combine the four functions of flood protection, renewable energy development, education, and environmental improvement, in order to take the lead and set an example.