Stormwater Bmp Sizing: hydrodynamic_separator
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) | 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 (%) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| hydrodynamic_separator | baffle_box | 45 | A,B,C,D | 0.25 | 25 | twice_yearly | 5 | 0 | 5 | Baffle box/trap: lower efficiency HDS. TSS 45% for fines, 80%+ for coarse sediment. Low maintenance cost. | 25 | 10 | 0 | low | 0.002 | no | 3 |
| hydrodynamic_separator | swirl_concentrator | 50 | A,B,C,D | 0.25 | 25 | twice_yearly | 5 | 0 | 10 | Swirl concentrator (CDS, Vortechs type). Peak flow-based sizing per manufacturer (typically 0.5-5 cfs). TSS 50-65% per NJDEP protocol. Primarily pretreatment device, not standalone WQ credit. | 30 | 15 | 0 | medium | 0.002 | no | 5 |
| hydrodynamic_separator | with_filter_insert | 65 | A,B,C,D | 0.25 | 20 | twice_yearly | 3 | 0 | 20 | HDS with filter insert for enhanced P and metals removal. TSS 65%, TP 30% per enhanced media testing. More frequent maintenance required. | 35 | 30 | 0 | medium | 0.002 | no | 5 |
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