Streams are important for several reasons Streams carry most of the water that goes from the land to the sea, and thus are an important part of the water cycle. Streams carry billions of tons of sediment to lower elevations, and thus are one of the main transporting mediums in the production of sedimentary rocks. Streams carry dissolved ions, the products of chemical weathering, into the oceans and thus make the sea salty. Streams are a major part of the erosional process, working in conjunction with weathering and mass wasting. Much of the surface landscape is controlled by stream erosion, evident to anyone looking out of an airplane window.
Streams are a major source of water and transportation for the world's human population.
Most population centers are located next to streams. The stream channel is the conduit for water being carried by the stream. The stream can continually adjust its channel shape and path as the amount of water passing through the channel changes The volume of water passing any point on a stream is called the discharge. Cross Sectional Shape - varies with position in the stream and discharge. The deepest parts of a channel occur where the stream velocity is the highest.