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Sitework & Earthworkaka: drainage swaleaka: bioswaleaka: grassed waterway

Swale

In Plain English

A shallow, grass-lined drainage channel that directs rainwater away from buildings and filters it as it flows.

Definition

A shallow, vegetated or lined channel designed to convey stormwater runoff while providing filtering and slowing of flow. Swales can be grass-lined (traditional drainage) or bioretention swales (designed to infiltrate runoff). They serve both drainage and water quality functions by filtering sediment and pollutants before runoff reaches waterways.

Why It Matters in Bidding

Swales appear in the grading and stormwater scope, and whether one is a simple grass channel or an engineered bioretention swale dramatically changes the takeoff for excavation, soil amendments, underdrain, and plantings. Misreading the detail can leave a bid missing filter media or check dams, and swales often tie into permit and SWPPP requirements that carry inspection and maintenance obligations.

Example

Reading the civil details, an estimator prices a bioretention swale with engineered soil, an underdrain, and native plugs rather than a basic grass-lined channel, adding the cost of imported filter media that a generic grading line item would have missed.

Related Terms

Erosion ControlSediment ControlFrench DrainGrading

Frequently Asked Questions

Take off the channel length and cross-section from the grading plan and civil details to compute excavation volume, then price any liner, riprap, check dams, engineered soil, underdrain, and seeding or plantings. Bioretention swales cost far more than grass channels because of filter media and landscaping, so the detail drives the number.
Both convey runoff, but a swale is typically shallow, vegetated, and designed for water quality and infiltration, while a ditch is a simpler conveyance channel. The distinction matters because vegetated and bioretention swales add soil amendment, planting, and establishment costs that a plain excavated ditch does not.
Often yes. Swales are common stormwater best management practices tied to the project's drainage permit and erosion control plan, so the bid may need to carry SWPPP measures, inspections, and a maintenance or establishment period. Estimators should check the specs for warranty and plant-establishment obligations before final pricing.

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