A river is a natural stream of water that flows to another water body such as a lake, ocean or another river. Rivers can be found on every continent but there are at least 18 countries that don’t have any river at all. Russia has the most number of rivers with around 100,000 while the United States has the oldest one which is ironically called the New River.
The world’s longest river is the Nile River at 6,853 kilometers long, followed by the Amazon River at 6400 kilometers in length. The third is the Yangtze River with a length of 6,300 kilometers while the Caño Cristales river in Colombia is referred to as the world’s most beautiful river because of its stunning multiple colors.
Table of Contents
- How Rivers are Classified
- Glossary of River Terms
- Interesting Facts About Rivers
- How Are Rivers Formed?
Whenever snow melts quickly or there is an exceptionally heavy downpour, it can result in an ephemeral river. The river’s temporary quick flow can be found in desert areas where flash flooding occurs on a very irregular basis. For most of the year, these rivers’ beds remain dry because the water table is below the surface and therefore, base flow does not happen.
Although they are rare, episodic rivers are formed from run-off channels and found in areas with very dry climates. They may have some permanent areas, and they usually only flow fervently after very heavy rain. In the desert, episodic rivers are very important sources of water. They can also be thought of as seasonal or occasional rivers, and they are known as episodic because they only exist after an episode of a heavy downpour of rain.
Any river that flows through a very dry region is called an exotic river. Most commonly, exotic rivers flow through the desert and are found in places such as Saudi Arabia and the countries that surround it. The Tigris and Euphrates rivers are perfect examples of exotic rivers, and they flow from the Persian Gulf into northern Iraq. Essentially, a river is called exotic because it stands out on the landscape, so a river that sits in the middle of an otherwise dry, barren region such as a desert is always called an exotic river.
These are rivers that have a semi-permanent nature and are known because of their seasonal flow. During wet periods when runoff is related to both heavy rain or a temporary rise of the water table, the rivers will flow fully. In the summertime, which is considered a dry period, the river bed may be dry because of a falling water table and reduced rainfall.
A mature river is not very steep and has a slow flow when compared to youthful rivers. Youthful rivers have several tributaries feeding into it, and they have less of a sediment deposit than youthful rivers. Examples include the River Thames, the St. Lawrence River, and the Ohio River.
Old rivers have a low gradient and they depend on floodplains. The Nile, Euphrates, and Ganges rivers are perfect examples of old rivers.
Periodic rivers have dry spells throughout the year, especially if they are located in very dry climates where the precipitation is less frequent than the amount of evaporation. Also called nonperennial rivers, they usually flow best right after a heavy rain.
Permanent rivers are those which have water all year around. These are also called perennial rivers, and the water comes mostly from groundwater. Also contributing to the water flow is surface water runoff. The only time these rivers do not have water is during periods of extreme drought, which is seldom.
With a steep gradient and only a few tributaries, youthful rivers flow swiftly and quickly. Examples include the U.S. rivers of Trinity and Brazos and the Ebro River in Spain.
How Rivers are Classified
Biotic classification refers to each river’s ecosystem type, and it includes everything from the purest and cleanest rivers to the most contaminated ones. Biotic classification is broken down into three different zones, described below.
- Crenon zone. This is the area right near the source of the river. In other words, it is the zone where the river gets its start. It is broken down into two main zones – the eucrenon, which encompasses the spring zone; and the hypocrenon, also known as the headstream zone. The Crenon zone has flow speeds that are slower than speeds found in the Rhithron zone, and it has lower oxygen levels and colder temperatures as well.
- Rhithron zone. This is the upstream area of the river, characterized by quicker and more intense flowing speeds. The Rhithron zone has very cool temperatures and a higher oxygen level than the Potamon zone.
- Potamon zone. The Potamon zone is the downstream area of the river. It has slower flowing speeds and is usually warmer than other areas of the river. It also consists of a lower oxygen content and a very sandy river bed.
Experts use the biotic classification system to identify recovery time from and sensitivity to the surrounding habitat’s environmental disturbances. In this example, wetlands are not very sensitive to disturbance but need longer recovery times from environmental disturbances. Microhabitats, on the other hand, have fast recovery times but are also extremely sensitive to any type of disturbance.
Chronological classifications go by the river’s age, which experts can study by researching its patterns of erosion. They can be classified further into these three types of rivers:
- Mature rivers. Mature rivers have grades that are not very steep, and they have several tributaries, along with a fast discharge speed.
- Old rivers. You can identify old rivers with their floodplains.
- Rejuvenated rivers. These rivers have various gradients, and they are raised by tectonic movement.
- Young rivers. Young rivers flow quickly, have deep instead of wide channels, and no tributaries.
Strahler Stream Order
This classification was developed in 1952 and is based on a number – called the Strahler number – that shows how difficult it is to branch numbers. The numbers range from the first order to the twelfth order. For example, headwaters belong to the first order, while the Amazon River belongs to the last one. Experts claim that approximately 80% of the world’s rivers belong in the first and second orders. The larger the number, the slower and bigger the river.
Very small streams that have a year-round flow, but no tributaries are classified as first-order streams using the Strahler Stream Order. If two second-order streams flow into one another, a third-order stream is formed, and so on.
Topographic classification involves the shape, physical makeup, and specific features of the river, and all rivers fall into one of the three separate categories that are described below.
- Alluvial rivers. Alluvial rivers have floodplains, which is land found next to the river that is flooded quite often; and channels, or river routes, that are formed in sediment that is consolidated loosely. Because of flooding, alluvial rivers maintain a primary route filled with water and they form side channels, wetlands, and oxbow lakes. When the water in this type of river rises, the banks are eroded, and the resulting sediment is deposited into the sandbars or floodplains, usually in the middle of the river. Alluvial rivers contain habitats that range from shallow to deep pools and very turbulent waters, and they are further broken down into types that include braided, straight, meandering, wandering, and anastomose.
- Bedrock rivers. Bedrock rivers are formed when water cuts through new levels of sediment, resulting in the bedrock below. They are more commonly found in areas where the earth’s surface has experienced an upward shift – including uplands and mountainous regions. Bedrock rivers have a lot of alluvium, or loose sediment and soil. This alluvium moves with the water and shapes and erodes the river while moving along. The Colorado River in the United States is a perfect example of a bedrock river.
- Mixed bedrock-alluvial rivers. Just as the name implies, these rivers have a characteristic that falls into both of the above categories. They usually flow through different bedrock layers and areas with alluvial deposits.
Rivers contribute to healthy ecosystems and provide fresh water, but they can also be important aspects of a recreational activity. If you’re boating or whitewater rafting, becoming familiar with the whitewater classification is crucial, and the International Scale of River Difficulty has determined six different whitewater classifications, described below.
- Class I: easy river to navigate with fast flow and small waves
- Class II: good for novices and has medium-sized waves, though the rivers can be wide
- Class III: intermediate difficulty level; has irregular waves that are able to turn over a canoe
- Class IV: advanced difficulty level; powerful holes, waves, and restricted passages; this is the type of water that calls for fast boat handling, and there is a risk of injury to swimmers nearby
- Class V: requires an expert because of violent waves and complex passageways; the rapids also continue for long periods of time before you reach calmer pools
- Class VI: extreme difficulty; considered extremely dangerous; these are the types of rapids that come with a high risk of error and are so difficult to maneuver that to be rescued may be impossible
Glossary of River Terms
Alluvial: When something is alluvial, such as a river, it is deposited by running water.
Banks: The sides of a river; or the stream that the water normally flows between.
Bed: The very bottom of a river or other type of water is called the bed.
Brackish: When water is brackish, it is saltier than river water, yet not as salty as seawater.
Channel: This is an area with flowing water and which is confined by banks.
Channeled: When something is channeled, it is grooved or cut deeply.
Delta: A large silty area at the mouth of a river and which then splits into two or more different slow-flowing channels with muddy banks. They are often triangular in shape, and they are the basis for new land to be developed.
Effluent: Effluent is wastewater flowing from a commercial or industrial facility, such as a sewage plant or a factory of some type.
Estuary: The spot where a river meets an ocean or a sea; for example, the spot where fresh water from the river meets salt water from the ocean.
Headwaters: Streams or rivers which are the source of other streams or rivers.
Hydrologic Cycle: Also called the Water Cycle, this term refers to water’s journey as it goes from the land to the sky and back again.
Meander: If something meanders, it follows a winding path.
Mouth: The very end of a river; the point at which a river spills into a large body of water.
Oxbow Lake: This term refers to a stagnant lake developed alongside a winding river. It occurs when a river changes its path due to the erosion of soil because it leaves an abandoned stream channel that is cut off from the rest of the river.
Rill: A very small channel of water. A rill is caused by runoff water that resulted in the erosion of soil.
Riparian: This is a term used to describe an area right next to a body of water; for example, a river, stream, or lake.
River: A large, flowing body of water that usually flows into a larger body of water, such as a sea or an ocean.
Riverbed: The bottom of a river or any other large body of water.
Riverine: This term refers to anything that is formed by, is similar to, or is related to a river.
Runoff: This is simply water than runs into a river or other large body of water, and which is normally caused by drains, sewage lines, or uncontrolled streams. Runoff water can include water from melted snow, storms, or even agricultural irrigation.
Salinity: Salinity refers to the amount of salt found in a body of water.
Sediment: Small pieces of rock or soil that is transported by the wind or even water.
Silt: This is extremely small pieces of soil or rocks, usually no more than 60 micrometers in diameter.
Siltation: The accumulation or deposit of silt, or small pieces of rocks and soil.
Source: The very beginning of a river or stream.
Tributary: A tributary is a river or stream which flows into another stream, lake, or river.
Trunk: The trunk is the main course of a river.
Water Cycle: This is the natural cycle that involves evaporation caused by the sun’s energy, the resulting water vapor condensation, and the next step, which is returning to Earth as rain, sleet, and snow. It is also called the Hydrologic Cycle.
Waterfall: A sudden drop in a river as it moves over a rock cliff. This can happen many different ways, including when the river passes from a hard-rock layer to a soft-rock layer, resulting in the water eroding away the softer form of rock.
Watershed: A piece of land that drains water into a specific lake, stream, or river.
Interesting Facts About Rivers
River of the Dead
There is a river in South Korea called the Imjin River that is also known as the “river of the dead,” because large numbers of dead North Koreans have been seen flowing down the river.
The Massiveness of the Amazon River
If the biggest eight rivers are measured by the volume of water, the Amazon River is larger than all of the other rivers combined.
Expensive River Photographs
A photograph of the Rhein River, named the Rhein II, was auctioned off for $4.3 million.
Safety and Danger Working Together
Juarez, Mexico, is one of the most dangerous cities in the world, but it sits right across the river from El Paso, Texas, which is one of the safest cities in the entire country.
Reversing River Flow?
The Chicago River’s flow direction was actually changed by engineers in the early 1900s, and it remains flowing in that direction today.
Countries without Rivers
There is a total of 17 countries that have no rivers. This includes the country of Saudi Arabia.
In the beginning, diamonds were not actually mined, but instead, they were found at the bottom or alongside of various rivers in India.
Underneath London, you can find almost 20 different hidden rivers.
Tombs in Rivers
At the bottom of the Delaware River sits more than 26,000 tombstones.
Everything Old Is New Again
A river called the New River is actually the oldest river in the United States. It runs through North Carolina, Virginia, and West Virginia. Many experts believe that only the Nile River is older than this one.
The Very Polluted Hudson River
The pollution in the Hudson River is so bad that evolution actually takes place in order to handle all of the toxins found there.
The Mekong River in Thailand is unique because each year, hundreds of fireballs erupt from the surface of the water. Known as the Naga Fireballs, the locals believe a mythical creature called Naga spits fire from the water in order to produce this effect.
Lightning Does Strike Twice
The Catatumbo River in Venezuela gets over 250 lightning strikes per hour. This occurs 10 hours a day for up to 160 days per year. No one can explain why, but it has been happening for centuries.
The Real Effect of Earthquakes
In the early 1800s, the New Madrid earthquake was so powerful that it cracked sidewalks in Washington, D.C., caused church bells to ring in Boston, and even reversed the flow of the Mississippi River.
Swimming Across the River
A man named Martin Strel from Slovenia has swum many different rivers, including the Mississippi River in the United States, the Danube River in Europe, the Amazon River in South America, and the Yangtze River in China.
There is evidence that roughly 2-1/2 miles underneath the Amazon is a hidden river that is as long as the Amazon – over 3,700 miles – and several hundreds of times wider.
Full Moon Effects
For three weeks a year, the full moon results in a tidal wave rolling up the Amazon River once a day and once a night. As a result, waves that are roughly 2-1/2 miles high are found continuously and can be surfed for up to eight miles.
Setting a River on Fire
At least 13 times, the Cuyahoga River in Cleveland has been set on fire.
Two Rivers Coming Together
When two rivers meet, the point at which they meet is called a confluence.
The Long and Short of it
The shortest river in the world is the Roe River, which runs between the Missouri River and Giant Springs, which is near Great Falls, Montana. It is approximately 200 feet long. The longest river in the world is the Nile, which runs for approximately 4,000 miles.
The Largest Rivers in the World
The eight largest rivers in the world are the Mississippi, St. Lawrence, Ohio, Columbia, Yukon, Missouri, Tennessee, and the Mobile.
How Are Rivers Formed?
- Springs and streams, known as headwaters, flow down to form large springs or streams. Stream beds lie between the banks of a river.
- Large streams are known as rivers, while smaller ones are known as rivulets, brooks, tributaries, brooks, and creeks.
- A river’s water source comes from the precipitation of groundwaters and through the release of water which is stored in natural reservoirs such as glaciers.
- All rivers have a starting point, and gravity is important when it comes to the direction that the river flows. In humid areas, this starting point usually comes from springs; however, other starting points include lakes, marshes, and melting glaciers.
- Rain is considered the main source of river water. Rainwater from the hills trickles down the slopes and flows into the riverbed. It usually flows in an evenly distributed manner and is called runoff.
- If the water flow travels a certain distance, it starts to flow in parallel rills and gains momentum with each step. Soon the rills unite and form a stream. After the rills unite with the stream, a brook is formed. Brooks flow into valleys and eventually becomes a river.
- Rivers are extremely important because they have been sources of water, food, and transport since prehistoric times. They supply water to farms that are being cultivated and are the main source of freshwater in the world. In addition, they can even sustain their own food chain.