Tables: Grass Swales (Small-Scale GI)¶
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1. Table 1¶
| N.J.A.C. 7:8 Stormwater Management Rules – Applicable Design and Performance Standards | ||
|---|---|---|
| Green Infrastructure | Yes | |
| Stormwater Runoff Quantity | Not Allowed | |
| GR | Groundwater Recharge | Not Allowed |
| % | Stormwater Runoff Quality | ≤ 50% TSS |
| Stormwater Runoff Quality Mechanisms and Corresponding Criteria | ||
| --- | --- | |
| Settling | ||
| Minimum Length | 50 feet | |
| Manning’s n value | 0.25 for the Water Quality Design Storm | |
| Vegetative Uptake and Filtration | ||
| Minimum Density of Vegetation | 95% | |
| Grass Height | Between 3 and 6 inches | |
| Maximum Longitudinal Slope | 10% | |
| Minimum Separation from the Seasonal High Water Table | ≥ 1 ft, when the swale is designed with a slope ≥ 2% ≥ 2 ft, when the swale is designed with a slope < 2% | |
| Minimum Required Length | For 50% TSS Removal Rate: 50 Feet - singular point of inflow 200 Feet - continuous inflow along entire length | |
| Flow Characteristics for the Water Quality Design Storm | Maximum 2 inch depth of flow Maximum flow velocity 0.9 feet/second Must fully drain within 72 hours |
Source context and notes
Source revision: March 2021. # 9.3 GRASS SWALES [Figure: img-0.jpeg (original PDF, p. 1)](SOURCE.pdf#page=1) A grass swale is a stable, parabolic or trapezoidal channel that is lined with turf; it is used to improve water quality and convey stormwater runoff. Grass swales do not rely on the permeability of the underlying soil for pollutant removal; instead, pollutants are removed by settling and filtration through the grass. The maximum total suspended solids (TSS) removal rate is 50%. | N.J.A.C. 7:8 Stormwater Management Rules – Applicable Design and Performance Standards | | | | --- | --- | --- | | | Green Infrastructure | Yes | | | Stormwater Runoff Quantity | Not Allowed | | GR | Groundwater Recharge | Not Allowed | | % | Stormwater Runoff Quality | ≤ 50% TSS | | Stormwater Runoff Quality Mechanisms and Corresponding Criteria | | | --- | --- | | Settling | | | Minimum Length | 50 feet | | Manning’s n value | 0.25 for the Water Quality Design Storm | | Vegetative Uptake and Filtration | | | Minimum Density of Vegetation | 95% | | Grass Height | Between 3 and 6 inches | | Maximum Longitudinal Slope | 10% | | Minimum Separation from the Seasonal High Water Table | ≥ 1 ft, when the swale is designed with a slope ≥ 2% ≥ 2 ft, when the swale is designed with a slope < 2% | | Minimum Required Length | For 50% TSS Removal Rate: 50 Feet - singular point of inflow 200 Feet - continuous inflow along entire length | | Flow Characteristics for the Water Quality Design Storm | Maximum 2 inch depth of flow Maximum flow velocity 0.9 feet/second Must fully drain within 72 hours |Images on table pages¶
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