Above ground and below grade storage and settling - system and component sizing
Link to this table

Device Land use Downstream BMP (type) Enhancement opportunity Sizing calculations Inlets/oulets Flow diversion structures
StormTech Isolator Row Residential, Urban, Commercial StormTech detention/ infiltration arc storage chambers [1] Yes Volume-based for sites with good infiltrative soils, or more commonly rate-based using a water quality flow <= 2.5 gpm/sq ft of bottom area using two layers of woven geotextile, see Table 2. See design tool from manufacturer (does not require registration). [2] Manhole with overflow weir before pretreatment row
Settling chamber/vault Urban, Construction, Agricultural [3] Infiltration, Media Filtration [4]; [5] No Volume equivalent to at least 25% of water quality volume, surface area calculated from flow and particle settling velocity [6] Overflow weir at end of chamber
Oil/water/grit separators Ultra-high density, Industrial, Commercial [7] Yes Size device to pass 2-year 24-hour storm without interference and then provide bypass for larger storms [8] 8-inch diameter minimum [9] Inlet chamber (sediment trapping), oil separation/storage chamber, inverted elbow pipe to bypass chamber [10]; [11]
Hydro Dry Screen Residential, Commercial Yes Rate-based, 80% TSS removal based on 25 gpm/sq ft settling area, treatment flow rate based on 150 gpm/sq ft settling area. Download the manufacturer’s sizing tool here (requires registration) Max pipe diameter = 30-60 in [12] Vertical screen weir [13]
Suntree Nutrient Separating Baffle Box (NSBB) Rainwater harvesting, Wet or dry detention [14] Yes Q = ciA (runoff coeff. * intensity * area), then see Table 1 (NJCAT) [15] See tables for inlet and outlet placement depending on manhole and pipe diameters Three chambers/stages [16]
Manhole Baffle Box Yes Precast boxes: can be used for pipes up to 48 in diameter, up to 60 in if cast in place [17] Weir height = 3 ft, set at same level as pipe invert [18]
Environment 21 StormPro No Rate-based sizing Model V510: inlet/outlet diameter = 15 in diameter [19] Baffle wall, bypass pipe [20]
BaySeparator by BaySaver Yes Rate-based sizing Surface skimming weir, flow to and from offline manhole storage [21]
Sump Manhole with SAFL Baffle Residential, Commercial Yes Sizing with SHSAM [22] Top of SAFL baffle roughly 2-6 in above top of inlet, Sump depth below outlet >= 3 ft, bottom of SAFL baffle at 1 ft below invert of outlet . Max inlet diameter: 15-54 inches Baffle wall [23]; [24]
Deep sump catch basin Residential, Office, Retail [25] No Rate-based sizing, flow not to exceed capacity of inlet grate [26] Outlet below water surface level to allow floatables to remain on top. Inlet 4 ft above water surface level. Hooded outlet to prevent floatable materials and trash from entering storm drain system, weep hole above outlet pipe [27]; [28]
Forebay/pre-settling basin Wet Pond, Storm Water Treatment Wetland [29] No V with 1-2 ac imp area = 0.01* WQV; Max depth = 12 in; V with 2-5 ac imp area = 0.02 * WQV; Max depth = 18 in; V with 5-10 ac imp area = 0.03 * WQV; Max depth = 18 in; V with >10 ac imp area = 0.03 * WQV; Max depth = 24-30 in [30] Size outlet based on avg release rate and average head (elev. diff. between permanent pool water surface elev. and water quality volume elev.), non-erosive conditions. [31]; [32] Rip rap channel, pipe outlet or concrete channel with a notch outlet can be constructed between forebay and downstream practice [33] Anticipate overflow of forebay basin. Adequate protection of downstream structure or berm is necessary along with appropriate erosion control measures. If piped flows are used in the design, minimum recommended pipe diameter is 8 in, and recommended only for larger catchments.

This page was last edited on 19 December 2020, at 14:36.

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