What Is Stream Order In Hydrology?

The stream order or waterbody order is a positive whole number used in geomorphology and hydrology to indicate the degree of branching in a river system. Rather than “river,” the words “stream” and “branch” are commonly used as terminology.

Therefore, Stream order is a hydrological term used to distinguish between rivers or streams on the basis of their size. The stream order or waterbody order is a positive whole number used in geomorphology and hydrology to indicate the degree of branching in a river system.

The stream order is a function of the density of tributaries in relation to the main stem. A first-order stream has one tributary, a second-order stream has two, and so on. Streams of higher order display high channel complexity, with numerous islands and side channels that contribute to the overall network density.

The concept of stream order was first used by geomorphologist W. H. Schwartz in 1925 based on his observations from the American rivers. Since then, it has been widely used in applied and natural science research

Types of Stream Orders in Hydrology

Stream order is used to describe the branching of river systems. It is also used in describing which rivers are more important or “higher order”.

Stream order is a measure of the magnitude of streams in relation to one another. The tiniest tributaries are known as first-order streams, whereas the world’s longest river, the Amazon, is a twelfth-order waterway.

First- to third-order streams are commonly referred to as headwater streams. Streams classed as fourth- to sixth-order are referred to as medium streams.

A river is defined as a stream of the seventh order or above.

Scientists begin by identifying the first-order streams in a watershed when diagramming stream order.

Perennial streams (streams that carry water all year) with no permanently running tributaries are examples of first-order streams. This implies that they are not “fed” by any other streams.

Scientists begin by identifying the first-order streams in a watershed when diagramming stream order.

Perennial streams (streams that carry water all year) with no permanently running tributaries are examples of first-order streams. This implies that they are not “fed” by any other streams.

Stream orders are thus roughly categorized as follows:

Stream orders of 1 to 3: 1st order: perennial, mainly single channel and no tributaries. 2nd order: mostly single channel but may have some tributaries. 3rd order: more complex than 2nd order
Stream orders of 4 to 7: 4th-order stream is known as the medium stream. It has a steady flow but not much water and muddy during rains, with an average depth between 0.6 and 2 meters.
5th-order stream is normally a small river. It has a steady flow but not much water, with an average depth between 0.6 and 2 meters.
6th- and 7th-order stream are known as large rivers. They have a steadier flow and more water, with an average depth between 1 and 3 meters.
Stream orders above 7: tributaries may merge into each other without losing their identity, forming an overall channel. They are known as confluent streams.
Stream orders are also based on the sizes of the individual tributaries, and the number of tributaries that feed into the main river channel.

For example, a 3rd order stream with 10 tributaries is going to have a larger flow than the same size 2nd order stream with 5 tributaries because they carry more water.

Stream Types

Streams are classified into three types:

Streams that are perennial- In a well-defined channel, water flows at least 90% of the time in the stream.
Sporadic streams- Flow occurs only during the wet season (50 percent of the time or less).
Ephemeral rivers- Flow usually occurs for a short period of time following severe storms. Typically, the channel is not well defined.

Importance of Stream Ordering In Hydrology

The concept of stream order is important in the study of hydrology. It is used to classify and compare rivers.

Also, the stream order is used to determine which streams are more important (higher-order) and which have a larger influence on other streams (exceptional economic or environmental values).

Stream orders also help in identifying biogeochemical patterns. For example, small streams are very sensitive to changes in neighboring land use, whereas large ones are much less so due to their increased size and length of their watersheds.

It is also used to determine which tributaries contribute most to the flow of a river.

Stream order is also used in determining the flow of rivers. The higher the stream order, the more tributaries contribute to a river.

The importance of stream ordering methods in hydrology has led some scientists to suggest many different types of stream orders, such as “stream order index”.

Stream order in Hydrology characteristics

Stream order is one of the most important hydrological indices used in environmental and future planning. The value of stream order is determined by the density of tributaries in relation to the main stem, and whether they change over time or not.

Stream orders are used to classify rivers according to their size and influence on other streams. Order 1 streams are the smallest and highest streams (i.e., with no upstream tributaries). Two streams of order 1 merge to generate a stream of order 2.

The confluence of two order 2 streams results in the formation of an order 3 stream. Each higher order of stream is generated by the confluence of two lower-order streams, and lower-order stream watersheds are included within higher-order stream watersheds.

Orders 10–12 relate to the major courses of the world’s major rivers. Individual streams get broader and longer as stream order increases.

Streams in the same stream order are classified as medium streams if they only have one tributary, shrinking to small streams if they have more tributaries.

What are the limitations of stream order?

Stream order is considered a practical way to classify streams. However, it has some limitations when used in real-world situations.

Stream order can change greatly over time in response to hydrologic events such as droughts, floods and salinity changes in the ocean.

Stream orders based on sequential tributaries that do not flow together will lead to inaccurate results when classifying streams of different stream order, or even when assessing the contribution of a single stream to a river’s overall flow.

Stream Order Classification

Other classification systems include:

There are three broad categories of stream orders that apply to streams with multiple tributaries:

The number of first-order streams = the sum of the number of first-order tributaries. This means that a stream order will not change as a stream grows longer.

If two second-order streams merge, they will automatically become a third-order stream because the number of first and second order streams is equal.

Stream order = number of first-order tributaries + 1. This means that a stream’s stream order will increase or decrease as first-order tributaries are added or subtracted from a stream.

How stream orders are calculated

The formula for calculating the ordering of streams with multiple tributaries is:

If you have 2 first-order streams and 3 second-order streams, then the stream order is:

You have 2 + 1 = 3 second-order streams and 4 third-order streams. So, your stream order is:

You can also use a “stream order calculator” to find the right stream order.

Stream order is defined by the number of first-order streams, which are confluent streams with more than one tributary.

If there are N first order tributaries and M second-order tributaries, then the stream order of the confluent streams is:

The number of second-order tributaries is equal to the sum of all first-order tributaries. It does not matter how many tributaries there are in the second-order streams. The same rules apply for streams of different order.

In a nutshell, the stream order of a confluent stream of N first-order tributaries is equal to the number of second-order streams that are formed by merging N first-order tributaries.

Difference between Horton and Strahler stream ordering

The difference is that Horton stream ordering considers the physical appearance of the streams. The basis is peninsulas and points.

Horton stream order is based on the confluence area between a system’s main stem and its tributaries. This method requires that you know both the main stem and tributary areas.

Strahler stream order mostly follows geomorphology, so it does not consider any other things such as side channels, ridges, islands or creeks.

The Horton stream order is based on a ratio between the main stem and the tributaries to be assessed, a method that is much more complicated than Strahler stream order.

The difference between Horton and Strahler stream ordering is:

Stream orders are used in hydrology to study the flow of streams within a river system while Horton and Strahler stream orders are used to classify it.

Strahler stream order is based on the coursing of a system’s tributaries into a main stem, while Horton stream order is based on the confluence area between a system’s main stem and its tributaries.

Strahler are used to identify river meanders and channel crossings while Horton stream order is used to assess the confluence area.

Stream order can be calculated using the formula C t = a / b, where Cn is the number of first-order streams and n is the number of second-order streams.

The derived stream order index is equal to stream order divided by 100,000.

Horton stream order is based on overall stream size, not just confluence size between tributaries. This means that stream order values are useful for all streams, not just confluent streams.

For stream orders of 10–12, Horton’s formulae give very different values than Strahler’s. The numbers are very close when you compare Horton with Strahler and between different orders.

FAQs

What is a steam order in Hydrology?

What is the difference between a steam order and a waterbody order?

A stream order and a waterbody order are not the same. A stream has a confluence with other streams and can be divided into numerous branches.

A waterbody (lake, pond, reservoir) does not have any tributaries, it has only one main channel that does not branch anywhere in its body.

What are the advantages of Strahler and Horton stream orders?

One advantage of Horton stream order over Strahler is that Horton can be applied to all streams, not just confluent streams.

Strahler and Horton stream orders are used to classify streams.

The number of fifth-order streams = the sum of the number of fifth-order tributaries, so there is a mathematical relationship between stream order and the number of tributaries.

For different Cs, the sum of all Cn always equals the sum of all An. This means that you can compare different channels using different parameters.

What are the disadvantages of Strahler and Horton stream orders?

Stream order = number of fifth-order tributaries + 1. This means that a stream’s stream order will increase or decrease as fifth-order tributaries are added or subtracted from a stream.

What is the difference between Strahler and Horton stream ordering?

Strahler stream order is derived from the relationship between tributary junctions and channels. The basis for this form of classification is the relationship between channel junctions and channel branching patterns of meandering streams.

Horton stream order is also based on channel patterns, but on the number of tributary junctions. In this classification method, you do not need any information about the channel segment length and size.

So, Strahler and Horton can be used together to work out the number of tributaries in a river system. Horton stream orders are derived from channels while Strahler streams are derived from junctions.

What is a stream order?

According to Poff, a stream order can be defined as: “a measure of the degree of difference in size among streams.”

How do you determine stream order?

The number of first-order streams = the sum of the number of first-order tributaries. This means that a stream order will not change as a stream grows longer.

How are streams and rivers classified in order?

A Rank Classification of Streams and Rivers A stream is a body of water that travels over the Earth’s surface as a current and is confined inside a small channel and banks.

The smallest of these streams are also known as brooks and/or creeks, depending on stream order and local language.

When does a stream have a second order?

For example, when a first and second order stream merge, the resultant stream is second order. When two streams with the same order merge, the new stream has the next higher order than the joining streams.

For example, when two second order streams merge, the new stream is of third order.

How is stream order used in the regulation?

The term’ stream order’ refers to the arrangement of streams in a watershed from top to bottom. Various approaches exist for describing stream order.

The Strahler system is used in the Water Management (General) Regulations (NWR ’97). The Horton-Frost system is used in the Water Management (Secondary) Regulations (NWR ’96).

What is Horton stream order?

Horton stream order is used to measure the overall distribution of stream size in a watershed. It offers a consistent way to compare streams of different orders and sizes.

How do you calculate Horton stream order?

The number of first-order streams = the sum of the number of first-order tributaries. This means that a stream order will not change as a stream grows longer.

When is a tributary considered a first-order stream?

When it is connected to the stream with the maximum number of first-order streams. For example, a tributary that connects to five first-order streams would be considered fifth-order in Strahler system and would be considered second-order in Horton system.

What is Strahler stream ordering?

Strahler’s (1952) stream order system is a straightforward approach for categorizing stream segments depending on the number of tributaries upstream.

A first order stream is one that has no tributaries (it is a headwater stream). A second order stream is a stretch downstream of the confluence of two first order streams.

How does Strahler stream ordering work?

Water that is formed by the junction of two or more streams flows into a single channel, and then spreads out over the channel floor. The mean flow on this channel then undergoes a period of maximum flow, after which it begins to flow in smaller channels.

What are the limitations of stream order?

The biggest disadvantage is that it requires prior Strahler’s ordering. In other circumstances, this may result in an unusual ordering in which the highest order is assigned not to the channel with the biggest accumulation but to the channel that leads to the most branching areas of the catchment.

What does stream order indicate?

The idea of stream order gives number designations that indicate where a certain stream segment is located in a watershed drainage system.

First-order streams are those with the lowest flows from upland areas, as well as springs and seep sources that retain defined stream beds throughout the year.

What is a first order stream according to Strahler stream order?

In the Strahler approach, all linkages with no tributaries are assigned an order of 1 and are referred to as first order. When streams of the same order collide, the order of the streams rises.

What Is Stream Order In Hydrology?

What Is Stream Order In Hydrology?