In addition, huts built on piles formed villages along the rivers Sava and its tributaries. The Strahler Stream Order ranks rivers based on the connectivity and hierarchy of contributing tributaries. The Irrawaddy River has five major tributaries. Along the Colorado River and its perennial tributaries, a riparian community exists. Most of Hunan lies in the basins of four major tributaries of the Yangtze River. Zanskar is the main river of the region along with its tributaries. Most people live in valleys of the Mekong River and its tributaries. It is one of the upstream tributaries of the Indus River. The Celts also expanded down the Danube river and its tributaries. Most plantations were located directly on the Mississippi and other major navigable tributaries. Typically glaciers deepen their valleys more than their smaller tributaries. Over the next few years he explored much of the river and its northern tributaries. There are several reservoirs on Sabarmati and its tributaries. The city is at the confluence of two tributaries. The Tiber's three principal tributaries flow southward through Umbria.