DROPS • LIVABILITY
Drainage Services Department

Exemplary Services@Gov
2017
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GOING THE EXTRA MILE WITH FLOOD PROTECTION

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.

INNOVATIVE AND SUSTAINABLE DESIGN

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.

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. 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”.

SERVICE-DRIVEN CUSTOMISED DESIGN FOR THE COMMUNITY

Constructing the underground stormwater storage tank required the temporary closure of certain parts of the heavily-used Happy Valley Recreation Ground facilities. Residential buildings, schools, places of worship, etc. are all located near the area. During race days, there are also heavy people and traffic flows. The project team maintained very close communication with various stakeholders through visits, presentations, workshops, on-site interviews, etc. to gather their views and understand their needs for better construction arrangement.

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.

During the construction of the stormwater storage tank, relevant departments considered that the recreational facilities at the Happy Valley Recreation Ground needed to be refurbished. DSD was requested to take on this task, which would be a sizeable and unfamiliar project for the department. It also would significantly increase DSD’s overall workload. However, by accepting this request DSD was able to minimise public inconvenience from repetitive construction works on the recreation ground, and also provide people with the refurbished facilities earlier. Going the extra mile for the benefit of the public, the project team took on the work and completed it to everyone’s satisfaction.

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.

The movable weir only opens during heavy rains to better utilise the storage tank’s capacity. The tank is designed to be relatively shallow.After it stops raining, the weir is opened again, allowing one-third of the stored stormwater to be discharged using the water’s gravity.  This reduces the need for pumps and saves energy.
The movable weir only opens during heavy rains to better utilise the storage tank’s capacity. After the rainstorm has subsided, the weir can be further lowered. This coupled with the shallow tank design, allows one-third of the stored stormwater to be discharged by gravity. This reduces the need for pumping and saves energy.
The underground stormwater storage tank has a capacity of 60,000 m3, which is equivalent to the volume of 24 standard-sized swimming pools.
The underground stormwater storage tank has a capacity of 60,000 m3, which is equivalent to the volume of 24 standard-sized swimming pools.
The brown building is the fan room.  The pump house is situated under the slanting lawn.
The brown building is the fan room. The pump house is situated under the slanting lawn.