The flow that flows in the drain pipe or alternatively in the gutter.
Manning's numbers describe how rough the gutter is, less roughness results in greater Manning's number, which results in lower flow losses. Examples of Manning's figures can be seen in the table below.
| Type of gutter | Mannings tal |
|---|---|
| Rough concrete | 50-70 |
| Planed wood and ground concrete | 70-90 |
| Smooth plastic and the like | 100-120 |
| Strongly planted throughout the cross section | 10-20 |
| Overgrown bottom and overgrown slope | 20-30 |
| Overgrown bottom and slopes | 30-40 |
| Newly dug trench in clay | 40-50 |
| Canal through blasted mountain | 25-30 |
| Natural waterways | 10-40 |
Refers to the ratio between the wet cross-sectional area and the wet circumference of the drain.
Refers to the average velocity of water in the current drain.
Cross-sectional area on the wet part of the drain.
Refers to the slope of the drain.
Refers to the width of the bottom of the current drain.
Refers to the water depth in the gutter that flows unaffected by disturbances both upstream and downstream.
Refers to the slope of the slopes of the current drain.
| Mannings number: |  |
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