Swale calculator

Design drainage swales with proper depth and slope

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The Swale Calculator helps civil engineers and landscape architects design effective drainage swales for stormwater management. Calculate swale dimensions, slopes, and flow capacity to ensure proper site drainage.

Swales are shallow, vegetated channels that convey stormwater runoff while providing water quality treatment through filtration and infiltration. Proper swale design balances drainage capacity with landscape integration and environmental benefits.

Enter your drainage area, design storm intensity, and desired swale characteristics to calculate required swale dimensions, slope, and depth. The calculator uses Manning's equation to determine flow capacity and ensures swales meet both hydraulic and aesthetic requirements.

Features

Everything you need

Swale depth and width calculations
Slope determination using Manning's equation
Flow capacity verification
Multiple cross-section shapes
Design storm intensity inputs
Vegetation and roughness coefficients
Drainage area calculations

How it works

Simple workflow

1
Enter drainage area and design storm intensity
2
Specify desired swale shape and dimensions
3
Set vegetation type and roughness coefficient
4
Calculate required slope for design flow
5
Verify flow capacity meets drainage requirements

Use cases

Built for real-world scenarios

Site drainage design

Design swales to convey stormwater runoff while integrating with landscape design.

Low-impact development

Create vegetated swales as green infrastructure for stormwater management.

Erosion control

Design swales with appropriate slopes and vegetation to prevent erosion.

Permit applications

Generate swale design calculations for stormwater management permit submissions.

FAQ

Frequently asked questions

A swale is a shallow, vegetated drainage channel designed to convey stormwater runoff while providing water quality treatment. Swales are typically wider and shallower than ditches and are integrated into landscape design.

Swale slopes typically range from 1-4% (0.5-2 inches per 10 feet). Steeper slopes increase flow velocity and may require erosion protection. Flatter slopes promote infiltration but require more length.

Swale capacity is calculated using Manning's equation: Q = (1.49/n) × A × R^(2/3) × S^(1/2), where n is roughness coefficient, A is cross-sectional area, R is hydraulic radius, and S is slope.

Native grasses and sedges work well, providing good roughness coefficients (n=0.03-0.05) while requiring minimal maintenance. Avoid woody vegetation that could obstruct flow.

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We're always looking to improve our calculators. If you have ideas for new features, improvements, or found something that could work better, we'd love to hear from you.

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