The Entrenchment Ratio Calculator helps determine how confined or connected a stream channel is to its surrounding floodplain. It’s commonly use in fluvial geomorphology, watershed planning, river restoration, and environmental impact assessments. The entrenchment ratio provides insight into the degree of channel incision and potential for overbank flooding, making it an important tool for hydrologists, civil engineers, and environmental scientists.
This calculator belongs to the Hydrology and Geomorphology Analysis category and supports decision-making for sustainable river management.
Formula of Entrenchment Ratio Calculator
Entrenchment Ratio = Flood-Prone Width / Bankfull Width
Detailed Breakdown:
- Entrenchment Ratio: A dimensionless number showing how wide the flood-prone area is compare to the bankfull channel.
- Flood-Prone Width: The width of the channel at a height equal to 2 times the bankfull depth. This represents how far floodwaters can spread during major flow events.
- Bankfull Width: The width of the stream when it is just full, right before water begins to spill into the floodplain.
Interpretation of Results:
| Entrenchment Ratio | Interpretation |
|---|---|
| < 1.4 | Highly entrenched, confined channel |
| 1.4–2.2 | Moderately entrenched |
| > 2.2 | Well connected to floodplain |
This helps planners assess how easily a river can flood its surroundings and whether interventions are need to restore floodplain function or manage erosion risks.
Quick Reference Table
| Flood-Prone Width (m) | Bankfull Width (m) | Entrenchment Ratio | Channel Type |
|---|---|---|---|
| 28 | 20 | 1.4 | Confined |
| 44 | 20 | 2.2 | Moderately connected |
| 60 | 20 | 3.0 | Well connected |
| 18 | 15 | 1.2 | Entrenched |
| 80 | 25 | 3.2 | Floodplain-active |
This table helps users quickly compare ratios for different channel widths and assess entrenchment levels.
Example of Entrenchment Ratio Calculator
Let’s say a river has a bankfull width of 15 meters, and the flood-prone width at 2× bankfull depth is 36 meters.
Entrenchment Ratio = 36 / 15 = 2.4
This result shows the stream is well connect to its floodplain, with a lower risk of channel entrenchment.
Now consider a smaller stream with a bankfull width of 10 meters and a flood-prone width of 12 meters.
Entrenchment Ratio = 12 / 10 = 1.2
This channel is entrench, indicating limited access to the floodplain and potential issues with erosion or flow confinement.
Most Common FAQs
A low ratio (below 1.4) means the stream is deeply incised and confined to its channel. This often reduces floodplain interaction and increases erosion risk.
This level is considered a standard approximation of significant overbank flow. It represents the elevation where the river begins to influence its broader valley floor during floods.
Yes. It is helpful in both natural and urban environments to evaluate channelization effects, restoration needs, or potential for flooding.