Stormwater Bmp Sizing: bioretention
Stormwater Best Management Practice (BMP) and green infrastructure sizing criteria, pollutant removal efficiencies, and design parameters for 12 BMP types per EPA, International Stormwater BMP Database 2020, MDE, Virginia DEQ, and Minnesota Stormwater Manual
| bmp type | bmp variant | TSS removal pct (%) | applicable HSG | design storm in (in) | expected lifespan years (years) | infiltration rate in per hr min (in/hr) | maintenance frequency | max contributing drainage acres (acres) | media depth in (in) | nitrogen removal pct (%) | notes | peak flow reduction pct (%) | phosphorus removal pct (%) | ponding depth in (in) | relative cost index | sizing ratio bmp to drainage area (dimensionless) | underdrain required | volume reduction pct (%) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| bioretention | road_shoulder | 80 | A,B,C,D | 1 | 20 | 0.5 | twice_yearly | 1 | 24 | 35 | Road shoulder bioretention cell. Higher sediment loading — pretreatment forebay required. Sizing ratio 3% for road drainage. | 55 | 45 | 6 | medium | 0.03 | yes | 35 |
| bioretention | tree_box_filter | 80 | A,B,C,D | 0.5 | 20 | 0.5 | annually | 0.5 | 30 | 30 | Tree box filter (urban tree trench). Ultra-urban application. 0.5 in design storm. Sediment chamber pretreatment critical. | 50 | 40 | 6 | medium | 0.01 | yes | 30 |
| bioretention | with_underdrain | 85 | A,B,C,D | 1 | 20 | 0.5 | twice_yearly | 2 | 24 | 40 | Sizing ratio 5% of contributing drainage area (CDA). Ponding depth 6-12 in, media depth 18-30 in typical. Underdrain discharges to storm sewer. TSS from International BMP Database median 85% (Geosyntec 2020). P removal variable; higher with P-sorbing media. | 60 | 50 | 6 | high | 0.05 | yes | 40 |
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