Like all the river basins in Kerala, the Pamba basin also can be divided into three natural zones based on elevation, consisting of low land or seaboard, midland and high land. The coast for a short distance along the borders of lakes is flat, retreating from it the surface roughens up into slopes which gradually combine and swell into mountains on the east. The low land area along sea coast is generally swampy and liable to be flooded during monsoon inundation. The plains/midlands succeed low land in gentle ascents and valleys interspersed with isolated low hills. The high land on the eastern portion is broken by long spurs, dense forests, extensive ravines and tangled jungles. Towering above all their slopes are Western Ghats that form eastern boundary of the basins.