Nepal has three categories of rivers. The largest systems -— from east to west the Koshi, Gandaki/Narayani, Karnali/Goghra and Mahakali—originate in multiple tributaries rising in or beyond the high Himalaya that maintain substantial flows from snowmelt through the hot, drought stricken spring before the summer monsoon. These tributaries cross the highest mountains in deep gorges, flow south through the Middle Hills, then join in candelabra-like configuration before crossing the Mahabharat Range and emerging onto the plains where they have deposited megafans exceeding in area.