Considering Alternatives to Conventional Land Reclamation
International consultant Arcadis recently presented Hong Kong the option to create a polder as a mean to tackle the issue of land scarcity.
The Hong Kong Government is working on a project that calls for the construction of a group of islands and considers the usual reclamation by infilling with sand.
According to the government-appointed Task Force on Land Supply, Hong Kong needs to find 1,200 hectares of land for housing, and last year, Chief Executive Carrie Lam unveiled the government’s ‘Lantau Tomorrow Vision’ which looks to create 1,700 hectares through reclamation.
Hong Kong is no stranger to land reclamation with the first project undertaken by the British colonial authorities in 1851. Now around 6% of Hong Kong’s total area is reclaimed land, accommodating about 27% of the city’s population, and as much as 70% of Hong Kong’s commercial activities.
The Polder method offers an alternative to conventional reclamation. It originates from the Netherlands, where half the country is at or below sea level and over centuries, the Dutch have constructed about 3,000 polders. The method is also being increasingly adopted throughout the world, with Asian counterparts Singapore using this method.
Unlike the traditional method of reclamation, where filling has to be carried out to higher than sea level, the Polder method involves creating a tract of land by enclosing an area within the sea by dykes and pumping the water out. The polder is then kept dry with a network of drains, reservoirs and pumping stations.
When compared with traditional land reclamation, which involves filling and taking into account storm surges and se level rise, the Polder method substantially reduces the amount of fill material needed, lowering the upfront construction cost – especially in Hong Kong where fill resource is scarce and often has to be imported.
Polder development has higher long-term maintenance cost when taking into account the costs associated with operating and maintaining the flood protection system and the pumping stations. Nevertheless, such costs can be reduced by the adoption of renewable energy, such as the use of wind turbines, which has historically harnessed by windmills in the Netherlands.