Bart Schultz
On the Asian continent, I have identified 21 countries with polders with an identified area of 49.1 million hectares. The total area of polders must be considerably larger, but is very difficult to determine.
By far the majority of the polders consist of reclaimed low-lying land. Land gained on the sea are also found in various countries. These include: China, India, Japan, Myanmar, North Korea, the Philippines, Singapore, Sri Lanka, Taiwan, and South Korea. I have only encountered drained lakes in India. These concern several polders in Lake Vembanad with a total area of 719 hectares.
As I described earlier in my article The polders of ancient Mesopotamia, the oldest polders were probably located in the vicinity of Ur, northeast of present-day Baghdad, as early as the fourth millennium BC. The lowest polder in the world is also probably located in Asia, specifically at 210 metres below mean sea level on the northern side of the Sea of Tiberias. The possibly largest polder on Earth is also probably located in Asia. At 680,000 hectares, this concerns the Hetao Irrigation District in China.
Land use in the vast majority of the polders is agriculture, a significant proportion of which consists of rice polders. Polders with ponds for shrimp farming are located in Bangladesh (various polders), Indonesia (a few polders), and Thailand (probably a few polders). Polders with nature reserves are located in Bangladesh (Sunderbans) and India (Kuttanad and Western Sunderbans). In Malaysia, there are a number of polders with palm trees.
Urban polders are located in Cambodia (Beng Tempen and North Phnom Penh), China (Sangyuanwei), Indonesia (many urban polders, especially in Jakarta, but also in Semarang and Surabaya), Japan (various polders), Myanmar (Rangoon Reclamation Scheme), the Philippines (Kamanava Polder), Taiwan (various urban polders), Thailand (Laem Chabang Polder), and South Korea (Samsan).
Polders with industry are located in South Korea: Hangdong, Jungang, Sowalmi, Suknam and Walmi. Polders with multiple land use are located in Cambodia (Muk Kampul), China (Dongxihu and Jianghan Plain), Japan (several polders), Vietnam (Trieu Dong Polder), and South Korea (Namdong, Sihwa and Saemangeum).
The polders on the northeast coast of the Caspian Sea in Kazakhstan deserve a special place. These are polders used for oil extraction. Also special is the polder in Thailand where Bangkok's Second International Airport is located.
For agricultural polders, pumping capacities range from 35 to 335 millimetres per day. For urban and industrial polders, this is 66 to 173 millimetres per day. The Shanhua Polder in Taiwan, where the Tainan Science Park is located, deserves special mention. The pumping station of this polder has a pumping capacity of no less than 2 metres per day.
Values found for flood protection range from a probability of flooding of once every 20 years for rural areas to once every 200 years for major cities in China. However, in the vast majority of urban polders in Asia, flood protection is not higher than once every 100 years.
As I described earlier in my article Subsidence in polders, many polders are dealing with subsidence. This certainly also applies to polders in Asia, which can amount to about 20 centimetres per year for some polders. For agricultural polders, this is primarily caused by oxidation and compaction of peat soils. For urban and industrial polders, it is generally due to the extraction of groundwater beneath thick clay layers, causing them to subside.
