rh d i l d srhode island stormwater design and
TRANSCRIPT
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Rh d I l d SRhode Island Stormwater Design and InstallationDesign and Installation
Standards Manual
RIDOT W k hRIDOT WorkshopCase Study Exercises
July 13 2011July 13, 2011
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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Introduction• Three case study exercises :
1. Route 138: Major Intersection2. East Main Rd, Portsmouth: Sidewalk and Parking3. Waterfront Dr, East Providence: New Road
ConstructionConstruction
• Real project examples – but we’ve made some assumptionssome assumptions
• Thanks to designers for allowing us to use h i l !their plans!– BETA Group, GRA Designers/Green International,
Maguire Group
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
Maguire Group
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Case Study No. 1: Route 138
R t 138 (b/ R t 2 d R t 108)R t 138 (b/ R t 2 d R t 108)Horsley Witten Group, Inc.Horsley Witten Group, Inc.
Route 138 (b/w Route 2 and Route 108)Route 138 (b/w Route 2 and Route 108)A Redevelopment ProjectA Redevelopment Project
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Route 138 Reconstruction
• Redevelopment Project– Approx 3 mile stretch;Approx. 3 mile stretch;– New Roundabouts;
Drainage and Stormwater Improvements;– Drainage and Stormwater Improvements;– Drains to both Cold and Warm Water Fisheries;
Design is being modified to meet new – Design is being modified to meet new requirements.• 75% design was done based on early draft of revised • 75% design was done based on early draft of revised
manual;• 90% design is now being finalized using final version
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
– Still a work in progress
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Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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Stormwater Management CriteriaImportant Questions/Informationp Q
• Redevelopment Project– Need impervious cover analysis (existing vs proposed);p y ( g p p )
• Define Site Area (for Redev. Criteria)– If > 40% I, then need to manage 50% of existing I + all of
Inew I;
• Required Design Criteria;– Recharge (50% of exist + all new Imp );Recharge (50% of exist. + all new Imp.);– Water Quality (50% of exist. + all new Imp.);– Channel Protection (only new development where
)necessary);– Overbank Control (Qp) – 10 and 100 Yr Storms (only new
dev where necessary)
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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Stormwater Management Criteria(continued)(continued)
• Channel Protection Criteria:N if I 1 0 d – Necessary if new Imp area > 1.0 acre and > 2.0 cfs peak inflow rate;
– No practical way to separate new from No practical way to separate new from existing impervious cover.
• Overbank Flood ProtectionOverbank Flood Protection– Compare peaks to existing, not natural
conditions;– Downstream analysis may allow for
elimination of practices.
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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LID Site Planning and Design Criteria
• Avoid ImpactsG di / l d ll t id di t b– Grading/slopes and walls to avoid disturbance;
– Maximize protection of waterways and wetlands (crossing locations, angle, location of BMPs);(crossing locations, angle, location of BMPs);
– Minimize clearing and grading/soil compaction (location of sidewalks, construction access/staging, l ti f BMP )location of BMPs).
• Reduce ImpactsP id l i t g t ti– Provide low maintenance vegetation;
– Minimize impervious surfaces (Pervious Pavements –alternatives for traffic islands);
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
);– Maximize runoff time of travel (tc).
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LID Site Planning and Design Criteria
• Manage Impacts– Infiltrate precipitation near the source;– Disconnect impervious cover; – Smaller drainage areas to practices; and– Source controls to minimize or prevent
exposure of pollutants
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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Additional Considerations
• Cold Water Fishery– No WVTS for treatment within 200’ (special ( p
outlets beyond);– No WVTS or detention basins for CPv & QP
within 200’ (special outlets beyond);• Warm Water Fishery
N t i ti– No restrictions• High Groundwater Table
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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BMP Selection Criteria
• Cold Water FisheryS l Hi h G d T bl• Seasonal High Groundwater Table– Recharge: (infiltration, filtering, open
h lchannels);– Water Quality: (infiltration, filtering, open
h l )channels);– Conveyance, Channel Protection and
Overbank Flood Protection (may not be Overbank Flood Protection (may not be necessary)
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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New Manual Considerations
• Water Quality Swales:– Pretreatment forebay?y– Adequate treatment area?– Slopes (< 4%)?Slopes (< 4%)?– Dry Swales: Soil (bio soil mix) spec & depth above
gw (3 feet)?gw (3 feet)?
• Infiltration:Separation distance to gw (3 feet)?– Separation distance to gw (3 feet)?
– Pretreatment?Design infiltration rate?
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
– Design infiltration rate?– Groundwater mounding?
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New Manual Considerations(continued)(continued)
• Bioretention:P t t t f b ? G h l ?– Pretreatment forebay? Grass channels?
– Adequate treatment area?– Soil (bio soil mix) specs & depth above gw (3 feet)?– On-line design
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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Infiltration
Wet Swales, typ
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Existing Swale Maintenance
Bioretention and Wet Swale
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Swales
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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Wet Swale
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Infiltration
W S lWet Swales, typ
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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Dry Swale
InfiltrationWet Swale
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Infiltration
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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Diversion Manhole
InfiltrationInfiltrationBasinBasin
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Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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Large TreesLarge Trees
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Diversion Manhole
Bioretention? Bioretention? Work around existing treesWork around existing trees
Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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Wet Swale
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Lessons Learned
• Project shifted from dry detention to the WQ BMPs in Chapter 5WQ BMPs in Chapter 5
• WQ BMPs actually allowed more flexibility in some cases (High gw) and fit in the same in some cases (High gw) and fit in the same footprint or even smaller
• WQ BMPs worked better with the natural contours (less grading)
• Critical to set up design templates at the beginning of project to keep track of
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information.
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Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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Horsley Witten Group, Inc.Horsley Witten Group, Inc.
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Horsley Witten Group, Inc.Horsley Witten Group, Inc.