Flood irrigation is used for the cultivation of crops like swamp rice. This type of irrigation involves flooding a field with water and allowing it to slowly drain. The field stays submerged for a certain period of time, providing water and nutrients to the rice plants. This method is commonly used in low-lying areas where rice is grown and water is abundant. The flooded field also helps to control weeds and pests, making it an effective and efficient way to grow rice in these conditions.