Restoring Hong Kong's Landfills
by Russ Canning, Landscape Architect & Director of Scott Wilson
As the site has been used as a landfill for 22 years, the Golf Centre is a positive enhancement of the site; particularly as there is a high demand for public golfing facilities in Hong Kong. The particular design objectives for the Golf Centre were to:
The Golf Centre is constructed above the landfill capping system, and the leachate and landfill gas extraction infrastructure installed by the landfill restoration contractor. The capping system on the platform comprises:
The sub-soil will be compacted to between 90% and 95% relative density under the golf course and landscaped areas, and to at least 95% relative density under buildings, pavements and utility services corridors, where settlements need to be minimised. The gradient of the finished surfaces of the golf course could be as flat as 2% and the subsoil will be covered by various types of growing media as described above.
Flexible pavements will have a surface wearing course of segmental concrete pavers overlying a compacted base, sub-base, and subgrade material. Pavement material thicknesses have been determined assuming that the California Bearing Ratio (CBR) of the underlying waste is less than 2%. The design will allow sections of pavement to be easily regraded if differential settlements over time results in unacceptable pavement surface profiles.
The careful use of pesticides, herbicides and fertilisers in the management of the golf course turf grass and planting is a key issue in ensuring that the water quality discharge standards are met. These aspects have been addressed by integrating the Landscape Management Plan with the Environmental Management Plan. Computer modelling to estimate pesticide concentrations in the runoff was carried out using a dedicated model - PESTRUN.
Drainage on the Golf Course area will merge and integrate inconspicuously with the finished landscape, and at the same time minimise opportunities for drains to claim misguided golf balls. The surface water drainage system is designed for a 1 in 200 year return period rainfall event to cater for the sub-tropical downpours that occur during Hong Kong's wet season and during typhoons. Typical design rainfall intensities are of the order of 325 to 375 mm/hr.
To minimise impacts arising from the consolidation and decomposition of the underlying waste, the following measures were considered in relation to the buildings construction:
Jordan Valley Ecology Park
Jordan Valley Landfill occupies the site of a small, high level, disused water storage dam having a site area of about 7ha on the northern edge of Kowloon, overlooking Hong Kong Victoria Harbour.
1.5 million tonnes of domestic, construction, commercial and industrial waste was received between 1986 and 1990. The depth of waste varies up to 50m. The Ecology Park will occupy about 4.3ha comprising the top platform of the landfill at an elevation of 120m above datum. The landfill is bounded by steeply wooded slopes rising from the northern and western boundaries whilst the southern and eastern sides slope away from the platform to the valley and urban Kowloon below.
The development concept is 'to promote the green campaign message and to educate visitors on the concept of ecology and the importance of environmental protection'. However, the ecology park includes, inter alia, a pedestrian plaza with shaded seating, a radio controlled model car racing circuit, gateball pitches, an environmental education centre, and management offices. The park is divided into an active zone, which contains the more formal and noisy or intrusive activities on the northern part of the site next to the busy Clear Water Bay Road, and a passive zone, providing an informal or natural environment away from sources of disturbance to allow quiet enjoyment of the ecology park.
The environmental education concept has been distilled into a design theme which stresses the historical and current importance of certain plant species and communities to Hong Kong, improves environmental awareness, reinforces the conservation message, and demonstrates how an old landfill can be transformed into an attractive and safe environment for public enjoyment. The plant species being established will demonstrate:
The Environmental Education Centre, located on natural ground, will include an exhibition hall, reception counter, refreshment kiosk, toilets, and a rooftop platform and viewing terrace overlooking Hong Kong harbour. An audio visual display will demonstrate to the viewing public the life cycle of both 'old' and 'new' generation landfills from initial site selection through site development, operation, landfilling processes and systems, aftercare and afteruse periods until the landfill is fully stabilised and poses no further threat to the environment. It will include features on options for utilising landfill gas and treating leachate. The display will also stress the need for improved environmental awareness, and encourage people to reduce waste generation to conserve landfill space.
The landfill restoration contractor has similar obligations to the Shuen Wan Landfill in respect of surface water drainage, leachate and landfill gas management, and landscape restoration. In the case of Jordan Valley, the existing soil capping material is at least 2.5m thick. Re-working of up to 1.5m depth of the upper part of the capping material is required to ensure a minimum compaction standard and a minimum surface gradient of 4%.
A new restoration capping system of geosynthetic components, including a LLDPE geomembrane liner, cushion geotextiles, and geodrains, with 850mm thickness of compacted soil cover material is being constructed. The geosynthetic capping system will segregate the afteruse from the underlying waste, and from migration of landfill gas.
The leachate and landfill gas extraction systems are installed beneath geomembrane liner. The drainage layer component of the capping system allows the collection of infiltration from the afteruse separately to the surface water runoff, and thereby separate collection and treatment, if any contamination from fertilisers, pesticides, and herbicides is detected. The capping system is designed to withstand the loading from an additional 3m depth of filling.
Soil depths for different types of planting are up to 2.5m for woodland, tree and shrub planting areas, 1.5m for herbaceous planting areas, and 0.5m for grassed areas and are achieved by placing additional fill above the 850mm deep soil cover of the capping system. The contours and slopes of the finished soil surface have been formed with consideration being given to:
A 'Fung Shui' water feature is incorporated into the design but it has been possible to locate this feature over natural ground to avoid potential problems with differential settlements and leaks causing unnecessary water infiltration into the capping system if it were located over waste. The Management Office building and Environmental Education Centre building are also located on natural ground and so no special foundation design was need to cater for differential settlement.
The restoration and after use development of the Shuen Wan Golf Centre and Jordan Valley Ecology Park demonstrate that with co-ordinated and innovative solutions to engineering and landscape issues, even recently closed sites can be transformed to safe and beneficial community use.
The authors would like to thank the Director of Environmental Protection, Hong Kong SAR Government, and the Construction Projects Controller of the Hong Kong Jockey Club for permission to publish this article.
Wastes Management April 1999