Transcript (en)

If you cut a small opening in a riverbank, water can flow downhill and irrigate fields below. But when the fields sit above the river, people have to lift the water by hand. That takes a lot of work and moves very little water. To make the job easier, you build a wooden trough up the slope. Then you tie a bucket to a rope and pull river water up along the trough. But moving one bucket at a time is too slow, so you attach several containers to the rope and keep them moving one after another. The problem is weight. Once the buckets fill with water, pulling them uphill quickly wears you out. Then you think about a well pulley. You place one wheel at the top and another near the river. A rope loops around both wheels, creating a continuous system. Replace the heavy buckets with lighter containers, turn the upper wheel, and water keeps moving uphill. This works well for small height differences. But if the fields are much higher, lifting water becomes harder. So instead of using muscle, you use the river itself. You build a large wooden wheel in the current and attach bamboo tubes around its rim. A water channel is built beside the wheel and lined up with the unloading point. The current turns the wheel. Each tube fills at the bottom, rises with the wheel, then dumps its water into the channel. From there, the water flows straight toward the fields. As long as the river keeps moving, the wheel keeps lifting water automatically. That's how ancient farmers turned flowing water into a simple irrigation machine.