Bart Schultz
One of the large polders in China is the Hetao Irrigation District, with an area of 680,000 hectares. The area is not even referred to as a polder. The reason for this is, in itself, quite interesting. Just as in other countries in the temperate climate zone, the water management systems are primarily geared towards discharge of water, where flood protection is increasingly necessary in lowland areas, and quite recently, irrigation has also been used in various places to bridge dry periods. In most other countries, and certainly in ancient civilizations such as along the Nile, the Euphrates and Tigris, the Indus, and the Yellow River, irrigation was generally the starting point, with provisions for discharge only becoming a priority much later.
The Hetao Irrigation District is located in Inner Mongolia in northeastern China along the northern bank of the Yellow River. The average rainfall in the area is only 150 millimetres per year. By comparison, in the Netherlands it is more than 800 millimetres per year. Irrigation in the area originally started as early as the 3rd century BC. Since then, the system has been continuously expanded. For centuries, this was possible without a proper drainage system or flood protection, and excess water was returned to the Yellow River downstream through natural watercourses. However, due to significant sedimentation in the Yellow River, the river level along the Hetao Irrigation system rose steadily as well. According to a brochure from the Agency responsible for water management in the area – a kind of Chinese version of the Water Authorities in the Netherlands – construction of the drainage system and flood protection did not begin until the period 1960–1980.
In 2019, I was invited to participate in a forum in Beijing regarding the development of irrigation and drainage, as well as innovation aspects. A two-day field visit was also linked to the forum. The field visit turned out to be to the Hetao Irrigation District, about an hour's flight from Beijing. So, we departed early in the morning and flew north from Beijing over fascinating landscapes in beautiful, clear weather. If you go on an excursion like this in China, you never have to worry. Everything is arranged excellently.
We were picked up promptly at the airport and taken by bus to the area for the first day of the field visit, during which we primarily visited the water intake from the Yellow River and the upstream side of the area. The downstream section would be visited on the second day. As we drove through the area, I saw a substantial dike running along the Yellow River. I asked a Chinese colleague if that dike runs along the entire area, which he confirmed. It turned out that there was also a substantial drainage system in the area, consisting of one primary main drain, 12 smaller main drains, 59 sub-main drains, and more than 17,000 collector drains.
It turned out that nine of the twelve smaller main drains came together at a pumping station, which discharged the excess water into Lake Ulansuhai Nur, located downstream of the area. Three of the smaller main drains could still discharge excess water into the lake by gravity. On the south side of the lake was a discharge sluice with a capacity of 100 m³/s (cubic metres per second). The discharged water then flowed through a wide canal to the Yellow River, where drainage sluices and two pumping stations with a combined capacity of 60 m³/s were located. Part of the excess water could therefore flow through the sluices into the Yellow River. Thus, this was a genuine river polder, but my Chinese colleagues' attention was primarily focused on the irrigation system.
