The district is divided into three well-defined parts - lowland, midland and the highland consisting of seaboard, plains and the hills and forests respectively. 20 percent of the total area is low land region. The midland consists mainly of plain land and group of islands having natural facilities of drainage via backwaters and canals. The hilly or eastern portion is formed by a section of Western Ghats. Muvattupuzha and Kothamangalam taluks which were initially parts of Kottayam district can be called the highlands. Muvattupuzhayar and Periyar are the main rivers of which the latter flows through Muvattupuzha, Aluva, Kunnathunad and Parur taluks. During rainy season these rivers are full and heavy floods affect the low-lying areas on the banks, but in the summer season they generally go dry and narrow. The Periyar is stretched over a length of 229 km.