Siwalik region

Siwalik is highland region in between the Mahabharat and Chure mountain range in Nepal.

This region has deposit of huge quantity of calcium carbonate and sub-economic grade of important minerals such as iron, sulfur, copper etc. The tectonically active zone of the Himalaya, Siwalik Hills are considered as the most dynamic formation where they annually rise up by 3 to 4 mm. Being very young in geological formation and tectonically active, the hills exhibit a very conspicuous fragile terrain. They stretch east west following a belt of merely 15-20 km in width, forming the north boundary of plains of Terai and southern boundary of Middle-hill Mountains.

The region is extremely important because of mainly two reasons: one is, it is the prime source of sediments, which a number of steep gradient torrents transport downstream to the plain of Terai. It leads to the rise of streambed level further aggravating the flooding and inundation problems in the plains. The other one is, the region is rich in a thick sub-tropical forest resource. The first reason is concerned over the need to protect the area from further degradation in order to protect the downstream low land plains, which serve more than 80% of the food supply to the country. The second one is concerned over the need to conserve the forest cover in order to mitigate the land degradation problems which is in increasing trend as a consequence of deforestation to meet the timber, firewood and litter needs of the local people. In spite of the thick vegetation cover, the Siwalik is characterized by the formation of numerous instabilities especially gullies and landslides. This is a result of weak geological formation and intense rainfall over the region. Tectonic uplifting phenomenon may also have contribution to the morphological developments of these instabilities, but the studies in this aspect are lacking. There are two distinct consequences of these instabilities: firstly, they are the main source of sediments, which produce sediment hazards such as debris flow. Secondly, their gradual expansion is leading to the decrease in forest resource.