| Runoff Measurement (contd..) |
| Rational Method |
| Assumptions of rational method |
- Steady flow and uniform rainfall rate will produce maximum runoff when all parts of a watershed are contributing to outflow .
- Runoff is assumed to reach a maximum when the rainfall intensity lasts as long as tc
- Runoff coefficient is assumed constant during a storm event .
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| Drawbacks of rational method |
- The rational method is often used in small urban areas to design drainage systems and open channels .
- For larger watersheds, this process is not suitable since this method is usually limited to basins less than a few hundred acres in size .
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