The Indus, the Ganges with the tributary Brahmaputra, the Tigris and the Euphrates belong to the large rivers of the Indian Ocean basin. The Indus and the Ganges with the Brahmaputra originate in the Himalayas. Ganges and Brahmaputra, merging, form a large delta, because they take out from the mountains a lot of small particles of the rock. By area, it can only be compared to the Amazon delta. It is believed that the Indo-Gangetic lowland was formed from river sediments. The Indus and the Ganges, like the rivers of East Asia, are deep in summer and low in winter. The water level in them fluctuates throughout the year. Thus, in the Ganges during the high water period, water is 30 times greater than during the period of intergeneration. This is due to the prevailing sources of nutrition. The rivers are replenished with water due to monsoon rains and the melting of mountain glaciers. Often they are flooded. The rivers are navigable. Their water is used to irrigate fields.
The Tigris and the Euphrates are the largest rivers of Western Asia. They originate in the Armenian Highlands and feed on thawed snow and winter subtropical rain. In the lower reaches merge into one river Shatt-el-Arab, which flows into the Persian Gulf. The water of rivers is used to irrigate fields on the Mesopotamian lowland.