Figure 12 – Shifting course of river Kosi in last 250 years

3.2.1. The Bhabar Plain

Bhabar is a narrow belt ranging between 8-10 km parallel to the Shiwalik foothills at the break- up of the slope. Its width is, however, more in the western plains than in the eastern plains of Assam. The streams and rivers coming from the mountains deposit heavy materials of rocks and boulders, and at times, disappear in this zone due to high porosity. These rivers carry very coarse load with them. This load becomes too heavy for the streams to be carried over gentler gradients and gets dumped and spread as a broad low to high cone shaped deposit called alluvial fan ath the foothills of Shiwalik. Usually, the streams which flow over fans are not confined to their original channels for long and shift their position across the fan forming many channels called distributaries. The Bhabar tract is not suitable for cultivation of crops. Only big trees with large roots thrive in this region. The inhabitants are largely the cattle keeping Gujjars.

3.2.2. The Tarai Tract

South of the Bhabar is the Tarai belt, with an approximate width of 10-20 km where most of the streams and rivers re-emerge without having any properly demarcated channel, thereby, creating marshy and swampy conditions known as the Tarai. Unlike Bhabar tracts, Tarai is wider in the eastern parts of the Great plains, especially in Brahmaputra valley due to heavy rainfall.

This has a luxurious growth of natural vegetation and houses a varied wild life. Many parts of the Tarai, especially in Uttarakhand, Uttar Pradesh, Haryana, Punjab and Jammu, have been reclaimed, for agricultural crops such as sugarcane, rice, wheat, maize etc. This marshy tract is infested with mosquitoes and infamous for Japanese Encephalitis (JE) disease.