Crucial for survival and production of the rice crop are the age of plants at the start of inundation, the rate of water rise, and the duration of the flood. Many parts of the tidal, deepwater and rainfed lowland rice areas are subject to sudden increases in water level, commonly called flash floods. These floods occur after heavy rain, local or remote, and may completely submerge the crop for several days. The water is often heavily laden with silt which covers the leaves of the plants. Deepwater and floating rice are mainly grown in unbunded fields on the flood plains and deltas of rivers such as the Ganges and Brahmaputra Rivers of India and Bangladesh, the Irrawaddy of Myanmar, the Mekong of Vietnam and Cambodia, the Chao Praya of Thailand, and the Niger of West Africa.
Flooding occurs in the later stages of plant growth and can last for several months.
Tidal wetland rices are cultivated during the wet season in scattered areas along the coastal plains of Bangladesh, India, Indonesia, Myanmar, Thailand, Vietnam, and West Africa. Tidal rices can tolerate submergence due to flash floods or tidal fluctuations. Salt-tolerant tidal rices are grown in areas where there is salt water intrusion from the sea. The soils are of various ages and are complex and diverse, particularly in river floodplain areas. Many of these alluvial sediments have undergone little soil formation.