Stream Patterns
Streams meet each other and they merge together, the smaller stream
is known as a tributary. A river will have a large number of tributary
streams. Rivers grow larger as more water joins from other tributaries.
The point at which they join is known as the confluence.
Tributary stream entering creating a confluence
There is a method of grading streams using the tributary patterns
known as Stream Order. Stream order is a measure of the relative
size of streams. Stream sizes range from the smallest, first-order,
to the largest, the twelfth-order (the Amazon River). Over 80% of
the total length of Earth's rivers and streams are first- and second-order
streams. Streams gradually increase their width and depth.
Establishing stream order from a map of a stream network.
The diagram shows a sample stream pattern. The first-order streams
are the smallest and represent the start of the stream course. When
two first-order streams come together, they become a second-order
stream. When two second-order streams come together, they form a
third-order stream. However, if a first-order stream joins a second-order
stream, it remains a second-order stream. It is not until a second-order
stream combines with another second-order stream that it becomes
a third-order stream. Similarly when two third-order streams meet
they become a fourth-order stream.
This example shows the catchment area of
the River Exe i.e. the area of land that is drained by the Exe and
all its tributaries.
Task: Stream Order Activity
Identifying stream order:
- Use the map of the Exe and draw a dotted line to join up the
source of each of the tributary streams. The area you have enclosed
may be shaded lightly and this area will represent the catchment
area. All precipitation falling on this area will potentially
drain into the River Exe.
- Use another map or atlas to identify a major river near to
where you live, and use tracing paper to identify and draw its
treelike structure from the source (where it begins) to and its
mouth (where it ends). Identify the catchment area of that river.
- Label the tributaries to identify their 'stream order'
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