Rhode Island Stormwater Design and Installations Standards Manual - - PowerPoint PPT Presentation

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Rhode Island Stormwater Design and Installations Standards Manual - - PowerPoint PPT Presentation

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Rhode Island Stormwater Design and Installations Standards Manual Public Workshop Acceptable Water Quality BMPs and S election Criteria January 13, 2011 Horsley W itten Group, I nc. Horsley W itten Group, I nc. Water Quality BMPs Larger

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Rhode Island Stormwater Design and Installations Standards Manual

Public Workshop Acceptable Water Quality BMPs and S election Criteria January 13, 2011

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Community Planning LID Site Design LID BMPs Larger Conventional BMPs Receiving Waters

Water Quality BMPs

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3.2.3 Minimum Standard 3: Water Quality

  • The WQv must be treated by at least one of the

structural BMPs listed in Chapter Five at each location where a discharge of stormwater will occur.

  • Minimum average pollutant removal efficiencies: 85%

removal of total suspended solids (TS S ), 60% removal of pathogens, 30% removal of total phosphorus (TP) for discharges to freshwater systems, and 30% removal of total nitrogen (TN) for discharges to saltwater or tidal systems.

  • Excludes LID credits allowed under S

ection 4.6

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Acceptable BMPs

  • 5.2 Wet Vegetated Treatment S

ystems (WVTS )

  • 5.3 S

tormwater Infiltration Practices

  • 5.4 Permeable Paving
  • 5.5 Filtering S

ystems

  • 5.6 Green Roofs
  • 5.7 Open Channel S

ystems

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Minimum Design Criteria

  • Required Elements and Design Guidance

– If required elements can’ t be met, select a different BMP

  • S

ix Categories

– Feasibility – Conveyance – Pretreatment – Treatment – Landscaping – Maintenance

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Wet Vegetated Treatment S ystems

  • Designed t o st ay wet !
  • Veget at ion –key component
  • S
  • me rest rict ions near coldwat er st reams
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Gravel WVTS

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Gravel WVTS

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Infiltration

  • S
  • il t est ing required
  • S

eparat ion t o S HGT and bedrock

  • Rest rict ions in fill
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Permeable Paving

  • Two main cat egories
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Porous Pavements

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Permeable Pavers

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Filtering Practices

Sand/organic filters Bioretention areas/Tree filters

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Sand Filters

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Bioretention

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Bioretention Schematic

Planting Soil - Primarily Sand Underdrain System Vegetation on Surface Vegetation on Surface Runoff

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Bioretention Planting Soil and Mulch

  • Loamy S

and to a S andy Loam – 85-88 % sand – 8-12 % silt – 0-2 % clay

  • Well-aged graded compost (25%
  • f soil mix)
  • Layer of well-aged, shredded hardwood mulch (aged 6

months, if possible)

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Bioretention –Many Applications

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Tree pits

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Green Roofs

Extensive Intensive

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Open Channels

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Dry Swale

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Wet Swale

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Swales

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Practices Approved for Other Criteria

  • S

torage Practices – Chapter 7

S

tormwater Basins

Underground

S torage Devices

  • Pretreatment Practices

– Chapter 6

Grass Channel Filter S

trips

S

ediment Forebay

Deep S

ump Catch Basins

Proprietary Devices

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  • II. S

electing the Most Effective and Appropriate S tormwater Practices

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  • 1. Land Use
  • 2. Physical Feasibility
  • 3. Watershed
  • 4. S

tormwater Management Capability

  • 5. Community and Environmental

Five Selection Factors to Consider

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#1. Land Use

The land use of the contributing drainage area influences the stormwater strategy:

  • Rural areas
  • Residential sites
  • Roads/ highways
  • Commercial sites
  • LUHPPLs
  • Urban sites

(e.g., redevelopment)

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Cul-de-Sac Application

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Commercial Application

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Municipal Application

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Retrofit Application

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# 2. Physical Feasibility

S

  • me Practices Cannot Be Used Because of S

ite Constraints:

  • S
  • ils
  • Groundwater
  • Drainage Area
  • Minimum S

urface Area

  • S

lope Restriction

  • Head
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Wet Swale

  • Used when water

table is close to surface

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#3. Watershed Factors

Different Receiving Water Management Obj ectives S hape S tormwater S trategies:

  • Groundwater (Aquifer protection)
  • Freshwater streams and Rivers
  • Other Freshwaters (Ponds/ Lakes/ Wetlands)
  • Coastal Waters (shellfish/ beach areas
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#4. Stormwater Management Capability

No single practice achieves all stormwater management obj ectives. A combination of practices is often needed to provide desired level of:

  • Groundwater recharge
  • Water quality treatment
  • Channel protection
  • Flood control
  • Ability to treat LUHPPLs
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To Offline Facility for Water Quality Treatment To Discharge Pipe

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#5. Community and Environmental Impacts

Other community and environmental impacts should be considered when selecting BMPs:

  • Ease of maintenance
  • Affordability
  • Community acceptance/

aesthetics

  • S

afety

  • Habitat
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S tormwater Practice Maintenance Burden

Maintenance Burden is a function of the type

  • f facility as well as the design and

implementation

  • WVTS
  • Medium to Easy
  • Infiltration* ---------

Medium to Difficult

  • Filters --------------

Medium to Difficult

  • Green Roofs ---------

Medium

  • Open Channels ------------

Medium to Easy *Except drywells - Easy

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Pollutant Removal Capability

Important when higher removals are required (see list in S ection 3.2.3). Table H-3/H-4 compares removal efficiencies for:

  • Total S

uspended S

  • lids
  • Total Phosphorus
  • Total Nitrogen
  • Bacteria
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Questions?