We humans are supposed to number about 7.8 billion by 2050. Feeding every one of those mouths demands food production in new, less-than-"optimal" areas. Like the Sahara. And if these monstrous irrigations work there, they can work virtually anywhere.
Irrigation is essentially the application of water to soil using non-natural methods. It's been around about as long as farming - like as far back as the 6000 years BCE. Archaeological evidence suggests the use of irrigation to grow barley in parts of ancient Mesopotamia, Egypt and Persia that wouldn't otherwise support it. In the 2nd century BCE, the Chinese constructed the Dujiangyan Irrigation System to irrigate huge swaths of farmland. It still supplies water today. And, by the 2nd century CE, the Han Dynasty had instituted the use of chain pumps to lift water to higher elevations. From these and subsequent innovations, modern irrigation practice now consists of over 689 million acres of agricultural land.
There are four major types of irrigation systems in use today: surface irrigation, where you basically flood the field like a rice paddy; sub-irrigation, which artificially raises the water table to moisten soil from below the root zone; drip irrigation, which continuously drops minute amounts of water on specific plants or areas; and sprinkler irrigation, which shoots water from pressurised spigots.
Among sprinkler irrigation, the centre pivot system is king. Far more common than its lateral-movement cousin, centre pivots are electrically or hydraulically driven wheeled towers that connect long expanses of trusses which, in turn, support long lengths of supply pipe. These pipes are normally constructed from corrosion-resistant galvanised steel or aluminium. The centre pivot design is most commonly 1/4 mile long (400m) though some designs exceed a 500m radius.
The machine circles a central point which supplies the water source and acts as the pivot. Water flows from a pumping station out to the pivot at around 60,000psi, where it's pushed out along the supply pipe to the sprinkler heads for distribution before eventually exiting from the end boom, which is essentially a high-pressure water gun for watering lulz. Newer designs have forsaken the traditional high-flow sprinkler head in favour of low-energy precision application (LEPA) heads which hang just above the ground suspended from the supply pipe. This reduces the amount of water wasted through wind drift and evaporation.
The system is typically propelled by a series of 480-volt electric motors which power the wheels of each tower. The outermost tower sets the pace for the sweep, while angle and GPS sensors mounted on the inner towers keep everything moving in unison. As the trellis system moves around the field, an on-board water pressure regulator adjusts the flow to maintain an even and sufficient amount of moisture is reaching the plants. This entire setup is monitored and controlled from a remote workstation using satellite imagery and GPS data from the towers.
The centre pivot became king of the industrial sprinklers due to its versatility. They can work with many types of soils and don't require perfectly flat ground to work (like surface irrigation would) but are effective even on mild slopes. That's why you can find them on virtually every continent. And in deserts.
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