Flood irrigation involves spreading water on the ground and letting it soak in. In its pure form, this method is used in parts of the country with extreme summer heat to water lawns. It’s also sometimes used to water orchards and other agricultural crops, such as rice.
In flood irrigation, the ground must be absolutely level to keep the water from running off. Earth dams are built to contain the water, then each section contained by dams is flooded.
A variation of flood irrigation commonly used in home gardens is basin irrigation. It works just the same as flood irrigation, but the dam is around only one plant or small group of plants. Basin irrigation is commonly used to water trees and other large plants until they are established.
Another form of flood irrigation is furrow irrigation, used with row crops. In this case, furrows are dug alongside rows of plants (usually vegetables), then flooded with water.
Flood irrigation wets the soil thoroughly and evenly. The amount of water applied can be easily controlled, and there is less evaporation than with sprinkler irrigation (but more than with drip irrigation).
However, the land must be carefully leveled and dams must be built. Also, the source of water must have a flow rate large enough to fill the dammed section fairly quickly, or water will soak in more deeply at the end where the water is applied. For this reason, flood irrigation works best in soil with a fairly slow infiltration rate.