5 Drainage System of Nepal Nepalese rivers are not only cross the ranges of different altitudes but also cut deep gorges and valleys. Most of these originate from Boarder Range, which cross the main Himalayas and flow down to Ganga River in India. Some rivers like Kali, Humla, Arun and Sunkosi are older than Himalayan Mountain itself (Antecedent River) Kali has formed the deepest gorge in the world (7000m +-) Nepal has in total 6000+- rivers with the length of 4500 km. The ultimate destination of each river of Nepal is the Indian Ocean through Ganga River. 3 major River Basins (Gandaki, Kosi and Karnali) These are snows – fed rivers also known as First category Rivers. Mechi and Mahakali also fall in this category.
6 First Category Rivers: Kosi River System (Sapta Kosi). Major Tributaries: Tamor, Arun, Dudh Kosi, Likhu Koshi, Tama Kosi, Sun Kosi and Indravati. Catchments area- 33,000 sq. km. Hydro Power Capacity _ 22 million kW. Biggest river of Nepal Ii was known as ‘sorrow of Bihar’ before the construction of Kosi- Barrage. Ethnically this basin is called as Kirat or Limbuwan Region.
7 Gandaki River System (Sapta Gandaki) Gandaki River System (Sapta Gandaki) Flows between Gosainthan (Langtng) in the east to Dhulagiri in the west. Catchments area- 26,000 sq. km. Capacity of Hydropower – 21 million km. It is also known as Narayani in Chitwan and Gandak in India. Major tributaries: Trisuli, Buddhi, Marsyangdi, Madi, Kali, Seti and Daraundi. Ethnically this basin is known as Magarat Region.
8 Karnali River System. Karnali River System. This is the longest river flowing inside Nepal Flows between Dhaulagiri (east) and Byas – Rishi Himal (west). Catchments area 49,000 sq. km. It is called Ghagra in India. Hydro Power Capacity 10 billion KW (UN survey 1961) Major Tributaries: Humla, Mugu, Seti, Tila, Bheri, Babai within Nepal and Rapti in India. Ethnically this basin is known as Khas Region.
9 Second Category Rivers Second Category Rivers Most of these rivers originate in the hilly areas of the Mahabharat Lekh. Among them Kankai, Trijuga, Kamala, Bagmati, Tinau, Rapti, Banganga, Babai etc. are major ones. These are comparatively low in length and volume than First Category Rivers, but these rivers swell during monsoon period. During winter season the volume and velocity of water decrease.
10 Third Category Rivers Most of the third Category Rivers originate from Churia Range. These are helpful only for local level irrigation works especially in the Terai region. Catchments area of these rivers is about 40,000 sq km. The names of the major third category rivers are Mohana, Balan, Hardinath, Mawa, Ratuwa, Lohandra, Bheraha, Kothi, etc.