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.

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

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

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

Horsley Witten Group, Inc.Horsley Witten Group, Inc.

Horsley Witten Group, Inc.Horsley Witten Group, Inc.

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.

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.

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).

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.

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.

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.

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?

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.

Infiltration

Wet Swales, typ

Horsley Witten Group, Inc.Horsley Witten Group, Inc.

Existing Swale Maintenance

Bioretention and Wet Swale

Horsley Witten Group, Inc.Horsley Witten Group, Inc.

Swales

Horsley Witten Group, Inc.Horsley Witten Group, Inc.

Wet Swale

Horsley Witten Group, Inc.Horsley Witten Group, Inc.

Infiltration

W S lWet Swales, typ

Horsley Witten Group, Inc.Horsley Witten Group, Inc.

Dry Swale

InfiltrationWet Swale

Horsley Witten Group, Inc.Horsley Witten Group, Inc.

Infiltration

Horsley Witten Group, Inc.Horsley Witten Group, Inc.

Diversion Manhole

InfiltrationInfiltrationBasinBasin

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Horsley Witten Group, Inc.Horsley Witten Group, Inc.

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.

Wet Swale

Horsley Witten Group, Inc.Horsley Witten Group, Inc.

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

Horsley Witten Group, Inc.Horsley Witten Group, Inc.

information.

Horsley Witten Group, Inc.Horsley Witten Group, Inc.

Horsley Witten Group, Inc.Horsley Witten Group, Inc.

Horsley Witten Group, Inc.Horsley Witten Group, Inc.