Grass Swale¶

Grass swales are governed by BMP Manual Chapter 9.3 in the live source corpus. This page now stays with the source-backed basics: a vegetated conveyance and treatment BMP whose use depends on geometry, maintenance, and whether the project is actually claiming infiltration-based credit.

Structured citation evidence for this page lives in the sibling claim manifest.

Overview¶

In the enrolled source set, a grass swale is a vegetated linear BMP used to convey runoff while also providing treatment and, where supported by the site evidence chain, some infiltration-based benefit. It is not a substitute for every storage BMP and it should not be treated as one.

Source Mapping¶

The live citations layer resolves this route directly to the following canonical source bundles.

Route type: canonical
2023 source bundle: Chapter 9.3 (2023_BMP_9_3) - Grass Swales
2026 source bundle: Chapter 9.3 (2026_BMP_9_3) - Grass Swales

Key verified claims already tied to this page manifest: - Grass swales remain vegetated conveyance and treatment BMPs in the live source set. - Grass swale geometry remains tied to the 3:1 side-slope rule and chapter-level slope management. - Grass-swale infiltration credit still depends on Chapter 12 support. - Grass-swale maintenance stays tied to vegetation, sediment, and erosion control.

Design Criteria¶

The reconciled design criteria below come from the live crosswalk and page-level claim set, not from the older narrative snapshot.

Parameter	2023 source value	2026 source value	Change
Maximum side slope	3:1 maximum (4:1 recommended)	3:1 maximum	unknown
Maximum longitudinal slope	10% maximum	10% maximum	unknown

Source-backed criteria that still control this route: - Grass swales remain vegetated conveyance and treatment BMPs in the live source set. - Grass swale geometry remains tied to the 3:1 side-slope rule and chapter-level slope management. - Grass-swale infiltration credit still depends on Chapter 12 support. - Grass-swale maintenance stays tied to vegetation, sediment, and erosion control.

Siting Constraints¶

The current source-backed siting review should focus on:

whether the site has the linear corridor and grade profile needed for a swale
whether the chapter's slope-management approach can be achieved
whether any claimed infiltration benefit is actually supported by the Chapter 12 evidence chain

Where those conditions are weak, the swale may still work as conveyance or pretreatment, but the project should not overclaim infiltration performance.

Maintenance¶

Grass-swale maintenance still turns on vegetation, erosion, and sediment control:

preserve vegetative cover and channel shape
remove sediment and debris before they reduce section capacity or infiltration opportunity
inspect grade-control features and repair erosion promptly

Source Bundles¶

Use these source bundles when checking the live extracted text or paired OCR evidence:

2023 bundle: Chapter 9.3 (2023_BMP_9_3) - Grass Swales
2026 bundle: Chapter 9.3 (2026_BMP_9_3) - Grass Swales