Drainage Swale Calculator
Design a drainage swale using Manning's equation to determine channel dimensions for a target flow rate.
Inputs
cfs
%
:1
Results
Bottom Width
2 ft
Swale Depth
0.31 ft
Flow Velocity2.26 ft/s
Cross-Section Area0.91 sq ft
Top Width3.9 ft
How to Use This Calculator
- Enter the drainage area in acres that drains to the swale.
- Set the design storm rainfall intensity in inches per hour and runoff coefficient for your surface type.
- Input the desired swale slope in percent and Manning's n for the channel material.
- Review the peak flow (CFS), required channel cross-section, and recommended dimensions.
- Verify velocity stays within non-erosive limits (< 3 ft/s for bare soil, < 6 ft/s for grass-lined).
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