Rivers are great collectors. As freshwater molecules flow along the landscape, gravity forces them to seek the lowest possible ground, where they gather with other water molecules. The collected water soon becomes a trickle.
There are many factors, such as the identification of the source, the identification or the definition of the mouth, and the scale of measurement of the river length between source and mouth, that determine the precise meaning of "river length". As a result, the length measurements of many rivers are only approximations.
A watershed is an area of land that drains all the water in a particular area to a single point: the place where a river meets the ocean. The size of a watershed can be big or small, depending on the landscape, and some watersheds can be massive.
Where a few creeks and streams running together end and a river begins is difficult to determine, but in order to rank rivers by their length, they've got to start somewhere and a bit of arbitrary fudging has to happen in order to measure them.
Even when detailed maps are available, the length measurement is not always clear. A river may have multiple channels, or anabranches. The length may depend on whether the center or the edge of the river is measured. It may not be clear how to measure the length through a lake or reservoir. Seasonal and annual changes may alter both rivers and lakes.
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Other factors that can change the length of a river include cycles of erosion and flooding, dams, levees, and channelization. In addition, the length of meanders can change significantly over time due to natural or artificial cutoffs, when a new channel cuts across a narrow strip of land, bypassing a large river bend. These points make it difficult, if not impossible, to get an accurate measurement of the length of a river.
The varying accuracy and precision also makes it difficult to make length comparisons between different rivers without a degree of uncertainty. For most rivers, different sources provide conflicting information on the length of a river system.
When the length of a river is followed by an asterisk, it is an average of multiple information sources. If the difference in lengths between given information sources is significant, all lengths are listed.
Let's delve into a comparison of two iconic rivers: the Mississippi and the Nile.
The Mississippi River
The largest river in North America, the Mississippi river rises at Lake Itasca in Minnesota and flows south, meeting its major tributaries, the Missouri and the Ohio rivers, on its way to southeast Louisiana, where it enters the Gulf of Mexico.
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The Mississippi River got its name from the Native American Chippewa tribe's words "mici zibi," meaning "great river," while the Missouri River was named after the Missouri Indian tribe and means "town of the large canoes." Hernando de Soto, a conquistador, or Spanish explorer, was the first European to discover the river in 1541 during an expedition in search of gold.
Its major tributaries, the Missouri and the Ohio rivers, meet on its way to southeast Louisiana, where it enters the Gulf of Mexico.
Mississippi River Watershed Map
The Nile River
Considered to be the longest river in the world, the Nile flows northward through the tropical climate of eastern Africa and into the Mediterranean Sea.
The Nile's energy is harnessed by the Aswan High Dam, which was completed in 1970 and provides hydroelectricity and controls summer flooding.
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Originally called Iteru by the Egyptians and represented by hieroglyphics, the Nile's name is derived from the Greek word Neilos, which means "river valley." Since the Stone Age, human civilizations have prospered along the banks of the Nile.
In fact, the Greek historian Herodotus called Egypt "the gift of the Nile". The Nile runs through Egypt, as well as nine east and North African nations Sudan, Eritrea, Ethiopia, Uganda, Kenya, Tanzania, Rwanda, Burundi and the Democratic Republic of Congo.
The Nile has two major tributaries - the White Nile and the Blue Nile, which meet up in Khartoum, the capital of Sudan.
Since the Stone Age, human civilizations have prospered along the banks of the Nile. The Nile also is recognized by the Guinness World Records as the world's longest river.
Nile River Map
Comparative Analysis
Length
The longest river in the world is different, depending on who you ask. Is it the Nile in Africa or the Amazon in South America? They're comparable in length, but in 2009, a study in the International Journal of Digital Earth determined the Nile to be a bit longer at 4,132 miles (6,650 kilometers).
The Mississippi River is not the longest river in the world. It is the fourth longest, following the Nile, Amazon and Yangtze.
Traditionally, the Nile is considered longer, but recent information suggests that the Amazon may be longer. Scientists debate whether the Amazon or the Nile is the longest river in the world.
Drainage Basin
Although the Nile is officially the longest river in the world, many disagree with that assessment and insist the Amazon is longer. Certainly, it's the world's largest river based on the enormous volume of water it deposits into the Atlantic Ocean every day; it has a greater output of fresh water than the next seven largest rivers combined. It also has the largest drainage area - 2,400,000 square miles (6,300,000 square kilometers) - which occupies almost 40 percent of the entire continent of South America.
Historical Significance
Since the Stone Age, human civilizations have prospered along the banks of the Nile. In fact, the Greek historian Herodotus called Egypt "the gift of the Nile".
The Mississippi River got its name from the Native American Chippewa tribe's words "mici zibi," meaning "great river," while the Missouri River was named after the Missouri Indian tribe and means "town of the large canoes."
Hernando de Soto, a conquistador, or Spanish explorer, was the first European to discover the river in 1541 during an expedition in search of gold.
Delta Formation
Why Do Rivers Have Deltas?
Let's take a moment to talk about how deltas form and grow. A delta is the only river in the world that has such an elegant delta; it's the result of sediment deposited at the mouth of a river where it flows into a standing body of water.
The Mississippi River carries a tremendous amount of sediment. Why? Rain flows into the river and down the Mississippi River towards the Gulf of Mexico, but these heavy particles settle to the bottom rapidly when the water stops flowing. The stream itself stops moving and falls to the bottom, and thereby form a large delta.
Deltas feature distributaries, smaller streams that traverse the growing delta. There is a similar pattern in the Nile as well as in our own Mississippi River delta, and the Nile and Mississippi deltas are very similar in size and shape.
Images of the Nile Delta (left) and Mississippi Delta (right)
Internal Structure of a Delta
The Mississippi delta is growing. Over the past 10,000 years, the Mississippi delta is growing. At one point, the delta became too large and the river needed to find a new course, where the Atchafalaya River runs into the Gulf of Mexico. Engineers work to control and maintain the current river channel, but control using levees is not always easy.
A growing delta consists of particles (which travel farthest) that form the horizontal bottomset beds. The foreset beds overlie the bottomset beds, and these flow downhill (because they cannot flow uphill) and in so doing generate new lobes for the delta. As a result, the delta itself is an environment of physical change.
The gradient and flow regime of distributaries change as the sediments thicken. Deltas are often affected by unusually high tides and storms, impacting the delta's position relative to sea level. Cities that are built on deltas face a problem, and as a result the major delta cities of the globe are in trouble. New Orleans, Venice, and Alexandria are all examples of delta cities that are losing the long-term battle between land and sea.
Ancient Cities in the Nile Delta
Three ancient cities in the Nile Delta no longer exist, sinking from view entirely: Heralkeion, Menouthis and Eastern Canopus. Divers have found traces of them on the floor of the Mediterranean Sea, near the mouth of the Canoptic distributary of the Nile.
Herakleion controlled entry into Egypt from the 1st through 6th centuries AD. All trade entering the River from the Mediterranean paid taxes in Herakleion, as well as hosting extravagant religious festivals.
One interpretation is that a powerful earthquake shook the area, causing soil liquefaction and subsidence of the silt-rich delta sediments. The date of the destruction is reasonably well-constrained. The cities were still vibrant centers of trade at that time, and the destruction was not mentioned by travelers of that same era.
An earthquake in 749 A.D. could have caused the soil failures observed in the ancient delta, and a tsunami (earthquake at sea transform?) would have produced the soft-sediment deformation configuration often associated with earthquake damage. Historical records indicate anomalously high Nile floods in 741-742 AD, which would have made the delta sediments water-laden. This combination of physical instability led to the ultimate and final demise of the two cities.
Quick Comparison
Here is a quick comparison of some key facts about the Mississippi and Nile Rivers:
| Feature | Mississippi River | Nile River |
|---|---|---|
| Continent | North America | Africa |
| Length | 3,902 miles (6,275 kilometers) | 4,135 miles (6,650 kilometers) |
| Mouth | Gulf of Mexico | Mediterranean Sea |
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