The Gulf Coast Prairie is a nearly level area with low local relief. Average annual precipitation -625 to 1,400 mm, increasing from west to east. Precipitation is fairly evenly distributed, but it is slightly higher in midsummer and late in summer in the west and slightly higher in winter in the east. Rainfall and perennial streams provide abundant water. Water for irrigating rice is obtained from streams and in some places from wells.
Ground water is abundant.
Most of the soils must be drained for optimum growth of general farm crops. Uderts are dominant in the western and central parts. They are deep, clayey soils that have a very slowly permeable subsoil and montmorillonitic mineralogy. Aqualfs are dominant in the eastern part. They are deep and loamy and have a clayey, very slowly permeable subsoil, an aquic moisture regime, and montmorillonitic mineralogy.