Flood irrigation is mainly used in arid areas. In this type of irrigation, water is allowed to flow over the surface of the soil to wet the plants. This is a very old and simple method of irrigation that is still used today in areas where there is not enough water for other types of irrigation systems. Flood irrigation is effective in arid areas because it allows water to be distributed over a large area, and the water can seep down into the soil to reach the roots of the plants.