Can you imagine earth without rivers? It would be difficult. If you flip through pages of history books, you will find that almost all great civilizations took shape along rivers.

A river, an integral part of hydrologic cycle, is a water body flowing in a natural channel confined to well-defined banks. It may originate from a glacier, lake, or spring and empty into a lake, another river or sea. Water volume in a river is more than in a brook or creek. The level of river energy depends on its velocity and volume. Energy is required to transport load and overcome friction. The channel, gradient and volume decide velocity of the river. With increase in its velocity its transportation capacity also rises tremendously.

The source of river water could be precipitation, spring, and seeps. Birth of a stream could be traced in a group of rivulets which merge to form a main river like the Amazon, the Ganga, and the Nile. Sheet wash may be indication of formation of a river. Sheet wash is a thin layer of water that does not flow in a channel.

River System

A tributary is a river/stream that joins a main river on either side at any place. All tributaries increase water volume and speed of flow but do not always make it wider. An area drained by a major river and its tributaries is called water shed.

A distributary is a stream / branch that leaves the main river and never merges again with it. It empties in a lake or sea. A river branches into several channels, distributaries, in its delta.

River Parts

A place on the earth where river originates is termed as its source. Bed is the bottom of the river. Lateral limits are called river banks. Path of the river is referred to as its course. Headwater is segment of river near its source. Smooth flowing part of river is called run. Pool is section of a river where water depth is high and movement is slow. The part of a river featuring turbulent and shallow flow is called riffle. The point where it empties into another water body is called mouth.

The point where a tributary joins a major river is confluence. Confluence is called a fork when size of both merging rivers is same.

Upstream part of river is generally rocky and rapidly flowing. In downstream, it flows slowly.

River Channels

A wide range of river channels including straight, anabranching, anastomosing, braided, and meandering can be found.

The braided river channels feature islands and bars. The islands broader than the width of bankfull water discharge divide anabranching channel. These channels result in the islanded braided pattern. The peculiar feature of anastomosing channels is distributaries joining the main channel again.

Types of Rivers

Arroyos/ temporary streams flow only in heavy rainy season.

A river that follows dip direction i.e. initial slope of the land is called a consequent river. A tributary of consequent river is called subsequent river, which follows strike direction. Subsequent river generally carves out a wide and deep valley. A tributary of consequent river following an opposite direction to that of the consequent river is referred as obsequent river. Resequent river follows direction of consequent river though at a lower level. Insequent river flows on homogenous terrain.

Perennial rivers, common in humid regions, always have water in their channels.  Intermitten rivers are seasonal in nature and flow only for a few months every year. 

Some rivers have water only after snow melting or heavy rains. These are called ephemeral rivers. These rivers can go dry any time of the year.

Stable river / graded river does not continuously modify its cross sectional profile. Unstable river continuously erode / deposit due to external factors.

Whitewater / brown water rivers appear muddy and carry large amount of sediments. Rivers that look like tea due to decaying plant matter, which releases tannic acid are referred to as blackwater rivers. Cleanwater rivers, generally originating from springs, do not have sediments.

Sediment Load

Load is material/sediments transported by a river. Rivers carry three types of sediment load including chemical / dissolved, suspended and bed load. Suspended load consists of fine particles such as clay, mud and silt in suspension. Bed / traction load features coarser particles like sand and gravels on or near the bed. The traction load is transported by jumping, rolling and sliding movements. The river banks are composed mainly of fine sediments such as clay, silt and sand. The size of sediments in river bed decreases in downstream. Both suspended and traction load are responsible for erosion. The capacity of a river, the total sediment load that river can transport, increases with discharge. Competence of a river increases with velocity.

Drainage Pattern

Drainage pattern, disposition and arrangement of streams, depends on various factors such as climate, diastrophism, initial slope, geological and geomorphological history, lithology, rainfall and structure.

Streams flowing away from a dome shaped upland / central elevated area (such as volcano and dome) form radial drainage pattern. Dendtritic drainage pattern, an irregular / tree like arrangement of tributary streams, is very common on rocks of uniform resistance. The pattern can be found on almost flat sedimentary rocks and huge igneous rocks. In Greek Dendros means tree. Streams could be at any angle but generally less than 90 O.  Structure does not play any significant role in its formation.

Consequent and subsequent rivers produce trellis drainage pattern that looks like a trellis or a rectangle. It is a parallel or sub parallel stream network following dip and strike of the slope. Primary tributary is generally at 90 O to the main river and secondary tributary joins primary at 90 O. As a result, secondary tributary drains parallel to the main river.

Damming rivers for electricity and irrigation is very common in our modern world.

Rivers, the life lines of our society since antiquity, are also used as waterways, but a creek generally can not be navigated. The basic features of a river/stream are a bed, banks, water with visible current.