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Case Study No. 3: Waterfront Drive, East ProvidenceEast Providence
Background:• Over a mile of new road proposed to improve traffic p p p
circulation, sited in former railroad corridor• Immediately adjacent to Seekonk River in HSG B Soils• Portions of road will be underwater during 100-yr storm• Proposed roadway width varies between 32 and 40 feet: 2
12-foot travel lanes with varying shoulder widths12-foot travel lanes with varying shoulder widths• Curb-and-gutter drainage to extended detention ponds and
a proprietary device (Vortech)• Designed to meet requirements of 1993 Manual• Total drainage area to project is 44 acres, 29% impervious
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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Former RailroadW AWarren Ave
D t R dHorsley Witten Group, Inc.Horsley Witten Group, Inc.
Dexter Road
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Would this project meet new requirements?requirements?
• First question – Is any portion of this First question Is any portion of this project redevelopment?
• Our assumption: Yes Existing railroad • Our assumption: Yes. Existing railroad bed consists of a compacted dense-grade materialmaterial.
• However, the site has <40% impervious cover (assumed) so entire project would cover (assumed), so entire project would need to meet all standards anyhow.
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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Would this project meet new requirements?
• Standard 1?
requirements?
Standard 1?• Utilizing existing disturbed area,
minimum widths based on LOS Other minimum widths based on LOS. Other options?Standards 2 and 3?• Standards 2 and 3?
• No – extended detention and proprietary d i d id h devices do not provide recharge nor adequate water quality treatment.
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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Would this project meet new requirements?
• Standards 4 and 5?
requirements?
• Discharge to tidal waters – not needed.• Standard 7?• SWPPP needed.• Standard 8?• Standard 8?• N/A - Not a LUHPPL.• Standards 9, 10, 11?• Must confirm no illicit discharges, provide
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
g , padequate ESC, and O&M Plan.
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Focus Drainage Area
• 2.37 acres, 59.1% Impervious• Catchbasins collect road runoff, discharge to proposed , g p p
extended detention basin with sediment forebay• Soils are HSG B• Discharges to Seekonk River
Proposed Detention Pond #1Proposed Detention Pond #1Top of Pond: 16.00’ 100-year storm elevation: 13.57’
Bottom of Pond: 11.00’ 2-year storm elevation: 13.07’
WQCV and Sediment Storage elevation required:
11.41’ Emergency overflow elevation:
15.00’
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
WQCV and Sediment Storageelevation provided:
12.00’ Outlet control structure elevation:
13.00’
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Existing Area
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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Area As Proposed
Seekonk River
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Proposed Area
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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BMP Selection
• Which BMP could be used to meet Standards 2 and 3 for the focus drainage garea?
• WVTS?• WVTS?• Permeable Pavers?• Infiltration?• Open Channels?p• Filtration?No “right” answer but some wrong ones
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
No right answer, but some wrong ones
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Required Volume Calculations
• Compute required Rev based on B Soils and S t 3 3 2Sect. 3.3.2Rev = [(1”) (F) (I)] / 12
= [(0 35”)(1 4 ac)] (1ft/12in) = [(0.35 )(1.4 ac)] (1ft/12in) = 0.041 ac-ft = 1,800 cf
• Compute WQv based on Sect. 3.3.3WQ = [(1”) (I)] / 12WQv [(1 ) (I)] / 12
= [(1”)(1.4 ac)] (1ft/12in)= 0.117 ac-ft = 5,100 cf
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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Filter Sizing Equation
Af = (WQv) (df) / [(k) (hf + df) (tf)]
Af = surface area of filter bed (ft2)df = filter bed depth (ft)
k f f bili f fil di (f /d )k = coef of permeability of filter media (ft/day)
hf = average height of water above filter bed (ft)
t d ig filt b d d i ti (d ) (2 d i tf = design filter bed drain time (days) (2 days is recommended)
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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Bioretention Sizing Equation
Use sizing equation and values provided in Section 5.5.4:
Af = (WQv) (df) / [(k) (hf + df) (tf)]
A = surface area of filter bed (ft2)Af = surface area of filter bed (ft )df = filter bed depth (ft) (2–4 ft, depending on site constraints)k = coef of permeability of filter media (1 ft/day)hf = ave ht of water above filter bed (ft) (half ponding depth)tf = design filter bed drain time (days) (2 days recom.)
Af = (5,100 ft3) (4’) / [(1’/day) (0.25’ + 4’) (2 days)] (With df = 4’, k = 1.0'/day, hf = 0.25’, tf = 2 days)
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
( f , y, f , f y )Af = 2,400 sq ft
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Pretreatment?
• 25% of Water Quality Volume – Sediment ForebayForebay
• Sizing Calculation in Section 6.4.1As = 5,750 * Q
Where:As = Minimum sedimentation surface area (sf)Q = discharge from drainage area = %WQv/86,400 sec
As = 5,750 * (0.25 * 5,100 cf/86,400 sec) = 85 sf
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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Benefits:• Meets
Recharge Bioretention: and WQvrqmntsL
~2,500 sf
• Less clearingL
5,256 sf• Less
earthworkLower • Lower safety risk
Fl S littHorsley Witten Group, Inc.Horsley Witten Group, Inc.
Flow Splitter