smp sizing in redevelopment projects scenarios are countless tools –simple method –cn back...
TRANSCRIPT
SMP Sizing in Redevelopment Projects
• Scenarios are countless
• Tools– Simple method– CN back calculation– Peak Discharge Rate
• Chapter 10 Criteria
• List of Verified Practices
Site Description
• Total area = 4 acres
• Disturbed are = 1 acre
• Impervious area = .6 acre
• Precipitation = 1”
• Storm Type 2
• Justification
• Sizing and SMPs selection– 4 scenarios
Justification
Bethlehem, NY
• Site information– approximately 29.2% Imp– florist, green houses, parking, planting beds
• Proposed development – 54% impervious – condominium complex, 9 buildings and 4 covered garages
• Constraints– relocating a sanitary sewer– maintaining setbacks
• Proposed practice– CDS units– Underground storage
25% Impervious Cover Reduction
Scenario 1•Reconstruction of existing impervious area not exceeding footprint.•Selected Practice: Reduction of Impervious area by 25%•Plan appropriately•Document footprint reduction•Ensure adequate infiltration
•Soil amendment•Decompaction
Redevelopment Project with an Existing Detention Pond
Keep the detention pondAddress WQ treatment
WQv Calculation -1
WQv Calculation –2100% Impervious
Reduce upstream drainage and control an area that is all impervious.
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WQv Calculation –3Rv Constant
25% Standard practice
Scenario 2•Reconstruction of existing impervious area not exceeding footprint.•Selected Practice: Infiltration Trench•Calc. WQv x 25%•Locate sub-catchment & diversion structure• Check feasibility & limitations•Document maintenance plan, etc.
Site DescriptionEddy Greenhouses
• Nursing facility in Cohoes• Area encompass 22 acres• Northwestern portion of the property undeveloped
(wetlands)• Remainder is buildings and parking areas• Existing impervious area 8.29 acres• Proposed construction 16 Greenhouses
– New construction 7.8 acres– Reconstruction 6.17 acres
Redevelopment Project with an Existing Detention Pond
May modify the pond to meet pond design standards
Redevelopment Project with Increased Footprint
Proposed PlanEddy Greenhouses
• Reduce impervious area by 25%• Design a P-1 Pond• Maintain existing water quantity controls in pond• Provide treatment for all the new disturbance• Provide treatment for a portion of the existing
imperviousness• Allow sheet flow for ½ of the site that did not have
detention in existing condition• Did not restore soil property• Increase HSG for new pervious area
75% Alternative practice
Scenario 3•Reconstruction of existing impervious area not exceeding footprint.•Selected Practice: Hydrodynamic System•Back calc. CN
•If only imp. Connected, CN = 98•Define flow rate•Locate sub-catchment, flow splitter•Look up the corresponding model from table 1•Check all the requirements for suitability of the practice, feasibility, limitations (head, soil, separation distance, etc.)•Document calculation method, manufacturer’s recommendation, maintenance plan, etc.
Redevelopment Project with Increased Footprint
Inputs Parameter Redevelop. UnitsNew Construction
Site Acreage A 2 acres 0.5
Impervious Area IA 1.5 acres 0.5
Impervious Cover% I 75 % 100
Runoff Coefficient Rv=.05+.009*I 0.73 constant 0.95
Min. Rv Rv 0.2 constant 0.2
90% Rainfall P 1 inches 1
Water Quality Volume WQv = [PRvA]/12 0.1216667 Acre-Feet 0.0395833
5299.8 ft^3 1724.25
Alternative Practice, sized to 75% of WQv, define priority areas that generate a runoff volume equivalent to the target WQv. Rv constant. 0.75 3974.85 Total (ft^3) 5699.1
EquationsWQv = [PRvA]/12Rv=.05+.009*I
I = imperviousness
P= precipitation (inch)
A= area
CN Back-CalculationPeak Discharge Rate
http://www.dec.ny.gov/chemical/29089.html
Hydrodynamic SystemsVortechs System
http://www.dec.ny.gov/chemical/29089.html
Hydrodynamic Systems
WQv VSM + VDL + (DP x ARG)
VSM = ARG x DSM x nSM
VDL (optional) = ARG x DDL x nDL
where:VSM = volume of the soil media [cubic feet]
VDL = volume of the drainage layer [cubic feet]
ARG = rain garden surface area [square feet]
DSM= depth of the soil media, typically 1.0 to 1.5 feet [feet]
DDL = depth of the drainage layer, typically .05 to 1.0 feet [feet]
DP = depth of ponding above surface, maximum 0.5 feet [feet]
nSM = porosity of the soil media (≥20%)
nDL = porosity of the drainage layer (≥40%)
WQv= Water Quality Volume [cubic feet], as defined in Chapter 4 of the New York Stormwater Management Design Manual
Alternative PracticesRain Garden
Redevelopment Project with Increased Footprint