Transcript Building Green in Bowling Green (and Beyond) Low Impact Development and Green Infrastructure Construction Site Stormwater Management Future Trends in Construction Stormwater Regulations Barry Tonning Tetra Tech.

Building Green in
Bowling Green (and Beyond)
Low Impact Development and
Green Infrastructure
Construction Site Stormwater Management
Future Trends in Construction Stormwater Regulations
Barry Tonning
Tetra Tech
Low Impact Development and
Green Infrastructure
Integrating the built environment into
stormwater management
Increased Run-off due to Impervious Surfaces
Sidewalks
Roads
Driveways
Parking
Buildings
Center for Watershed Protection
Polluted
Runoff
Water
Quality Impacts: Pollutants
Trash
Nutrients
Heavy
Metals
Pathogens
Oil
Sediment
and Grease
Effects of Development on
Stormwater Runoff
Increases:
• Impervious
surface area
• Stormwater
volume
• Stormwater
velocity
• Deposition of
pollutants
Decreases:
• Stormwater
quality
• Ground water
recharge
• Base flow
• Natural drainage
systems including
riparian
vegetative cover
Land development and
management practices that
reduce water quality impacts
What we’ve learned . . .
• Runoff from impervious surfaces
is the leading cause of water
pollution in developed areas
• We’ve made matters worse by
designing streets, parking lots,
& etc. as stormwater collection
systems
• BUT!! Low-impact site design
can improve water quality . . .
and aesthetics . . . and value!
Basic Premise of Low Impact Development
Maximize infiltration of precipitation
where it hits the ground:
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Prevents stormwater contamination
Promotes ground water recharge
Minimizes flooding concerns
Minimizes stream bank erosion
Eliminates or minimizes curbing, storm drains, piping, etc.
Implementing low-impact development
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Reduce storm pipes, curbs and gutters
Reduce impervious surfaces
Reduce building footprints
Preserve sensitive soils
Reduce road widths
Minimize grading
Limit lot disturbance
LID Site Planning Process
• Identify key desirable natural features
• Delineate building footprints & clusters that
minimize environmental impacts and
infrastructure costs, and maximize views of
natural features
• Design road layout, sidewalks and lot lines
to minimize impervious cover and create
opportunities for dispersal of runoff.
Conservation
Subdivision
Typical
Subdivision
LID Best Management Practices
• Site planning techniques (e.g., narrower roads,
conserved natural areas, preserved natural
depressions/topography)
• Bioretention areas / rain gardens
• Grassed (vegetated) swales
• Permeable pavers
• Filter / buffer strips
• Green roofs
Porous
• Dry wells for rooftop runoff
Asphalt
Standard
• Rain barrels and cisterns
Asphalt
• Stormwater planters
Infiltration
Practices:
Rain Gardens
Lots of applications
Do Rain
Gardens
Really
Work?
Blue: Runoff
from control
neighborhood
Red: Runoff from
neighborhood
retrofitted with
rain gardens
Barr Engineering
Vegetated Filter Strips
Pretreatment and Attenuation
• Mild vegetated slopes
• Adjacent to small parking
lots and roadways
• Another opportunity for
snow storage
Vegetated Swales
Conveyance, Treatment, Infiltration
• Roadside swales (country
drainage) for subdivisions,
commercial, institutional
development projects;
• For small parking lots;
• Mild side slopes and flat
longitudinal slopes;
• Provides area for snow
storage & snowmelt
treatment
Permeable and Porous
Pavements
Permeable
Paving
Runoff Reduction
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Grass pavers
Paving stones
Porous asphalt
Pervious concrete
Reinforced turf
Permeable
Paving
Applications
• Parking stalls
• Overflow parking
• Driveways
• Walkways and plazas
Better Site Design of
Roadways & Driveways
• Narrower streets
• Alternative cul-de sacs
• Shared driveways
Source: CWP
Better Parking Lot Design
• Incorporate green strips & buffers
• Alternative pavers in overflow areas
• Reduce requirements near transit
• Create multiple small lots
• Allow shared parking
• Require compact spaces
• Set parking maximums
Source R. Droll
Parking lot retrofit
Reducing Runoff Volume: Connected Surfaces
Downspouts Connected to
Driveway = More Runoff,
Less Infiltration
Reducing Runoff Volume: Disconnect It!
Rain Barrels, Cisterns
and Storage Tanks
Green Roofs
Green
Infrastructure
looks OK . . .
but does it really
work?
Typical Pollutant Removal
International BMP Database
(October 2007)
BMP Type
TSS
Bay Runoff Reduction Report
(April 2008)
TP
TN
TP
TN
(influent/effluent (mg/l))
(% Removal)
Detention Pond 72/31
.19/.19
1.3/2.7
15
Wet Pond
34/13
.21/.12
1.6/1.4
50-75
30-40
Constructed Wetlands
38/18
.27/.14
2.1/1.2
50-75
25-55
Biofilter (biofiltration)
52/24
.25/.34
.9/.8
25-50
40-60
Media Filter
43/16
.2/.14
1.3/.76
60-65
30-45
Porous Pavement
NA/17
NA/.09
NA
25
25
10
Raingarden Performance
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Infiltration reduces
peak discharge rate
Vegetative uptake of
stormwater pollutants
Pretreatment for
suspended solids
Groundwater recharge
Aesthetic Improvement
Porous Pavement Performance
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16 year old porous
pavement in Philadelphia
reported zero discharge
during Hurricane Floyd in
1999 (10” rain/24 hours)
Functions in cold weather
75% reduction in salt use
(Toronto & NH) from
reduced surface freezing
What about costs?
EPA GI Cost-effectiveness Study, 2007
EPA ‘Reducing Stormwater Costs through LID Strategies and Practices”
Overall Design Strategies
• Preserve natural systems
• Engineer systems to mimic natural functions
– Evapotranspiration ↑
• Plants (water uptake and transpiration)
• Surface water (evaporation)
– Infiltration ↓
• Soils
• Storage (provides additional time to infiltrate)
– Surface Runoff →
• Pipes, gutters, swales, ditches, underdrains
• Time of concentration (longer is better)
• “Treat” raindrop as close as possible to where it fell
• Lots of little BMPs instead of few regional systems
• BMPs in series not parallel
Design notes
• Base designs on:
– Unique features, such as vegetation, soil type,
and geology
– Regional water resource needs (water
conservation, reuse, and sustainable land use
management)
• Avoid using plants requiring irrigation
• Plan and design for sediment inputs
• Consider the seasonal high water table
when designing ponds
Design Details
• Test infiltration capacity,
don’t assume it
• Observation ports for
water levels
• Underdrains designed
with cleanouts
• Ponding depth in biosystems approximately
6-12 inch
• Extend time of
concentration
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Design for maintenance!
• Design BMPs with maintenance in mind
– Right-of-way, easements, vehicle access,
cleanouts, manholes
– At what depth should sediment be removed?
– Involve maintenance staff on BMP selection
and design
• Prepare a site specific maintenance guide
• Think about
– Staff gauges or offset points
– Dewatering pipes and valves
– Geese, mosquitoes, rodents, etc.
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Ideas to Consider
• Roto-till pervious surfaces before
topsoil/seed
• Amend soils
• Loosen up compacted soils with a
ditchwitch/auger and leaf compost
• Valves on underdrains
• If you need an underdrain, don’t
put it at the bottom
• Take every opportunity to educate
the public
• Adopt-a-rain garden
• Try something. Anything is better
than nothing.
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Operation and Maintenance of
Green Infrastructure
Management practices can be
damaged by . . .
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Excessive sedimentation
Fertilizers
Herbicides (e.g. Roundup)
Poor vegetation or mulch
maintenance
• Excessive mowing or
mowing too low
• Compaction
Common Construction Errors
Improper sequencing and erosion control
Common Construction Errors
Lack of Erosion Control
Irving St Images
P5240081 &
P4260061
Common Construction Errors
Unapproved Material
Substitution
Irving St Image (DSCN3901)
Construction inspection checklists
• Some common design elements
requiring inspection during construction
include:
– Storage volume
– Emergency spillway (location, design,
dimensions, lining, etc.)
– Pipes (material, joints, alignment,
compaction, etc.)
– Embankments (slope, compaction,
seepage control, etc.)
– Elevations – design plans vs. as-built
Maintenance Challenges
• Locating stormwater facilities
• Identifying responsible parties
• Lack of maintenance and
inspection staff
• Designs that do not allow for
easy maintenance
• Lack of enforcement authority
and access
• Owners are unaware of
maintenance responsibility
• Proliferation of BMPs that
require intensive
maintenance
Maintenance Agreements
Each agreement should contain:
• Routine Maintenance
Requirements – Who, What, How
• Maintenance Schedules – When
• Inspection Requirements
• Specifics on Access to BMPs
• Failure to Maintain Consequences
• Provisions for Recording the
Maintenance Agreement
Inspections
• When
– At regular intervals
– After significant rainfall
events
• Use a checklist
• Focus on preventative
measures to avoid
costly corrective
repairs
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Inspections
• Inspect each component (tributary area, inlet,
primary storage, outlet or overflow, downstream
of outlet)
• Vegetation management issues
– Too much or too little vegetation
– Invasive species
• Water storage management
– Infiltration/filtration capacity
– Standing water
– Water harvesting devices
• Trash and debris
• Sediment accumulation
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Example of BMP
Inspection
Checklist
Tasks and Schedule
• Observations (quick and simple) – monthly and after
significant rain events
• Trash removal – monthly (or more frequently) combine
with observations
• Inspections with measurements for sediment and
infiltration – annually
• Sediment removal – track accumulation with inspections,
• Vegetation Management
– Mulch – refresh yearly if needed, replace 3-inches or 3-years
– Weed/prune – monthly for new plantings, semi-annual once
established
– Plant replacement – anually as needed
– Water – check in droughts, water as needed
• Fertilizer applications – only if needed, soil test first
Structures
• Keep structures free and clear of debris
and in good working order
Vegetation Management
• Avoid scalping grass
• Encourage biodiversity
• Weeding: know which ones are weeds or
invasives (guide or manual)
• Soil test if vegetation problems: soil pH
may affect nutrient availability, root
growth and microbial population
• Mulch layer: prevents weeds, adds
organic matter, conserves moisture,
cools soil, should not float
• Watering requirements: usually
necessary during root establishment, but
not afterwards; adapted to local climate