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Stream Ordering & Bifurcation Ratio
Stream Ordering & Bifurcation Ratio
Author:
Syed Ali
Edu Level: Unit1
Date: Aug 31 2025 - 2:18 AM
⏱️Read Time: 2 min
Stream Ordering
Stream ordering is a system used to classify and number the tributaries of a river to determine the complexity or simplicity of its drainage network. It is a morphometric method (measurement of form and structure) that helps compare rivers within a drainage basin.
This method, introduced by A.N. Strahler, is commonly used by hydrologists, biogeographers, and GIS specialists to categorize streams based on their position in the network. It is an essential step for understanding and managing different types of waterways.
Stream order classification:
- First-order streams: Streams with no tributaries are classified as first-order streams.
- When two streams of the same order meet, their combined flow creates a stream of the next higher order.
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- Example: Two first-order streams join to form a second-order stream.
- When two streams of different orders meet, the higher order is retained.
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- Example: A first-order stream joins a second-order stream, remains second order.
- A drainage basin is often described by its highest order stream (e.g., third-order or fourth-order basin).
Bifurcation Ratio
The bifurcation ratio represents the ratio of the number of streams of a given order to the number of streams of the next higher order in a drainage network. It indicates the degree of branching in the basin and is a key parameter in drainage basin analysis, linking the hydrological regime to topography and climate.
Key Points:
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Formula:
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A low ratio (≈2) is typical of flat or rolling terrain.
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A high ratio (3–4) indicates mountainous or highly dissected terrain.
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Higher bifurcation ratio = faster runoff and higher flood risk, as water reaches the outlet more quickly, increasing peak discharge.
Positively correlated with drainage density higher ratio often means higher drainage density.
