Presenter Background
Nationally recognized expert in Low Impact
Development (Regulations and Applications)

Licensed Professional Engineer (CT)

Holds IECA certifications as CPESC &
CPSWQ

Over 27 years in the Land Development Field
and 10 years working with Low Impact
Development

9/8/2010 Copyright Trinkaus Engineering

What are problems with current
development philosophy?
Developments not respecting the
natural land form, forcing the site to
“fit” the development program
Excessive land clearing,
Massive amounts of earthwork,
Significant erosion & sedimentation issues,
Difficulty stabilizing the site,


What are problems with current
development philosophy?
Stormwater Issues
Large, interconnected impervious areas,
Handling of stormwater is an
“afterthought” in the design process,
Excessive use of structural systems,
Analyze for changes in peak rate only,
Emphasis on large, infrequent storm events,
No consideration of water quality impacts


What constitutes a Sustainable
Site?
Preservation of Natural Resources
Development which respects the
Natural Land Form
Minimize site clearing & grading
Rainfall is a resource to be embraced
and reused
Stormwater management is an integral
part of the site design


What constitutes a Sustainable
Site?
Focus of stormwater management:
Groundwater Recharge (Volumetric
Reduction)
Water Quality (Remove Pollutants from the
stormwater)
Source Control (Treat runoff where it is
first generated)
Implement “Treatment Train” approach to
stormwater


How do we create a Sustainable
Site?

Implement Low Impact
Development
Design Strategies


What is Low Impact Development?

LID is an ecologically friendly approach to
site development and storm water
management that aims to mitigate
development impacts to land, water, and
air. The approach emphasizes the
integration of site design and planning
techniques that conserve natural
systems and hydrologic functions on a
site.

How does Low Impact Development
work?
To manage rainfall at the source using
uniformly distributed decentralized
micro-scale controls. LID’s goal is to
mimic a site’s predevelopment hydrology
by using design techniques that
infiltrate, filter, store, evaporate, and
detain runoff close to its source
HYDROLOGIC TRANSPARENCY


What is Hydrologic Transparency?

The use of LID design strategies and
storm water treatment systems for a
development scenario which yields
hydrologic conditions matching or in
extremely close proximity to the
hydrologic conditions of the natural site
prior to development.


Low Impact Development
Five Basic Tools
Encourage Conservation Measures

Reduce Impervious Areas

Slow Runoff by using landscape features

Use Multiple measures to reduce and cleanse
runoff

Pollution Prevention


Regulatory Requirements (sample site)
Open Space Subdivision
Total Site Area = 104.50 acres
15% site area (roads) = -15.67 acres
Utility Easement = -5.12 acres
50% of Wetlands = -10.83 acres
50% of 25% slopes = -6.12 acres
NET AREA = 66.76 acres
Allowable Density = 66.76/1.9513 = 34.2 lots
(85,000 sq.ft. = 1.9513 acres)


A Typical Layout
Is this realistic?


What is Environmental Site Design?
Environmental Site Design (ESD) is considered part
of Low Impact Development Design Tools

It was development in Maryland to complement the
2000 Stormwater Management Design Manual for the
State of Maryland

The ESD approach is to design a site which protects
the natural resources on a site and maintains the
hydrologic characteristics of the site.


Environmental Site Design
The largest benefit of LID can be
achieved by implementing
Environmental Site Design Concepts

Preservation of critical natural resources

Places development on land most suitable
for development

Helps match pre-development hydrology


ESD Site Assessment – Primary
Conservation Areas
Inland Wetlands & Watercourses

Vernal Pools

Steep Slopes (>25%)

100-year Floodway and Floodplain

Upland Soil Types with Moderate to High
infiltration rates (Class A & B Soils)


ESD Site Assessment –
Secondary Conservation Areas
Upland areas adjacent to wetlands, watercourses, &
vernal pools (variable distance – suggested min. 25-
50’)

Habitat for sensitive species

Scenic views and areas

Vegetation systems, unusual tree species

Existing drainage patterns


Why should we protect these
resources?
Undisturbed woodlands provide great filtering
of overland flow, reduces runoff by rainfall
interception by canopy, provides
evapotranspiration, carbon storage

Wetlands provide trapping of TSS, and
attenuation of nutrients – provide
denitrification of Nitrogen, recharge
groundwater


resources?
Restricting construction on Steep Slopes
reduces soil disturbance, reduces or
eliminates erosion & sedimentation issues,
does not create stabilization issues

Well Drained soils have the ability to
infiltrate large amounts of runoff – dense
development on them should be minimized


resources?
Significant trees and unusual portions
of the site topography all provide
natural (habitat) and aesthetic benefits
to the end users and should be
preserved


ESD Site Assessment Process

Obtain Accurate Topographic information

Obtain delineation of inland wetlands &
watercourses by soil scientist

Determine presence of vernal pools or other
sensitive environmental areas (swamps,
marshes, ponds, flood prone areas, etc.)



Determination of upland soil types in
the field by soil scientist

Determine the general infiltration rates
of the soils (NRCS data)

Define steep slopes (>25%)



Determine generalized types of
vegetation (meadows, brush, deciduous
woods, evergreen woods, etc)

Determine existing drainage patterns on
the site


Site Analysis Process

Remove wetland/watercourse/vernal
pools from potential development area

Remove the upland area immediately
adjacent to wetland/watercourse
systems to preserve the biological
integrity (width of area will vary,
suggested 25 - 50’, could be larger
depending upon quality of wetland)


Wetlands, Soils & Watershed
Boundaries


Site Analysis Process

Remove 25% slopes from development area

Highlight those soil areas with moderate to
fast infiltration rates (Soil Class A and B)

Highlight unusual vegetative features on the
site
(i.e. 200 yr old Oak tree in the middle of a field,
Ridge line, unusual scenic vista)


Slopes and Vegetation


Results of Site Analysis

Through the protection of the
environmentally sensitive features
noted previously, you will have
determined the optimum area for
development
NEXT STEP
Evaluate hydrologic patterns and think
about how storm water will be handled
on the site as part of the site design


Developable Area


LID Design Strategies Applied
Preserve Large Portions of Site

Reduce Connected Impervious Areas

Increase Time of Concentration by using landscape
features

Use Multiple measures to reduce and cleanse runoff
at the source

Remove Pollutants from Storm Water


LID Techniques
Apply Open Space or Cluster Development to preserve large
contiguous portions of the site

Layout the geometry of the road to follow the existing contours

How you will convey stormwater to the discharge point?

How will you meet Groundwater Recharge & Water Quality
requirements?

What treatment systems are available to meet these
requirements that will work on the site?


Road & Lot Layout
Road layout follows ex.
contours, lots are located
within “developable area”

Large extents of property
Density is
protected as Open Space
concentrated on Class 24 Lots – 64+ acres of
C soils, minimal preserved Open Space
density on Class B
soils


Stormwater Discharge Points
Intermittent
stream

Stormwater discharge
points to maintain pre- 24 Lots – 64+ acres of
development drainage
preserved Open Space
patterns
Intermittent stream


Stormwater Conveyance
Conventional curb & gutter

Vegetated swales
along both sides of
road
24 Lots – 64+ acres of


LID Techniques

Minimize direct impacts to wetlands & watercourses

Can you disconnect proposed impervious areas on the site?

Layout building lots to have construction (House, driveway, well,
sewage disposal system) on land most suitable for development

Implement “Site Fingerprinting” to minimize land clearing & soil
disturbance

Minimize soil compaction by limiting the area of grading.
Consider specifying measures to address soil compaction, if
unavoidable


Site Layout – LID Source Controls
Impervious area disconnection –
driveway runoff as overland flow
across 75’ of vegetated surface

Site Fingerprinting –
defined clearing area as
percentage of lot area

24 Lots – 64+ acres of
Meadow filter strip with Bioretention systems for
Micro-berm at edge of roof drains
development envelope


Hydrologic Issues

Groundwater Recharge
Bioretention for roof drains
Infiltration Trenches
Impervious Area Disconnection
Water Quality
Constructed Wetland
Subsurface Gravel Wetlands
Vegetated swales & Level Spreader


LID Treatment Systems
Constructed Wetland System
w/forebay & vegetated outlet
swale to wetland

Linear vegetated
level spreader

Subsurface flow gravel
wetland w/forebay &
vegetated outlet swale to 24 Lots – 64+ acres of
wetland preserved Open Space
Infiltration trenches for driveway
runoff


LID Treatment Systems


What Does the Project Look Like?

Ridge top is part of
60% of the site preserved Open Space in center
as Open Space of loop road


What Does the Project Look Like?
When you
consider the
woods which
remain on the
lots, over 76%
of the site
remains
undisturbed


Actual Design
Meadow filter
strip Rain Garden for
roof drains

Defined tree
clearing limits
(site
fingerprinting)


Actual Design
Storm Water Controls for lots:
Utilize “site fingerprinting” to minimize the
extent of clearing on each lot
Utilize rain gardens for roof drains on
every lot (sized for Water Quality Volume)
Utilize a “meadow” filter strip with a 3”
‘micro-berm’ below the lawn area on each
lot to filter overland runoff & encourage
infiltration


Actual Design

Limit
development to
mild & moderate
slope areas

Preserve steep
slopes


Hydrologic Issues Conclusion

Pre-development infiltration rates are met
Water quality goal of 80% TSS removal will
be met, other pollutants also reduced
Pre-development Tc is closely approximated
by the use of vegetated swales and treatment
systems that will increase Tc (gravel
wetlands, level spreader)
Pre-development peak rates are matched for
post-development conditions


Other Sustainable Benefits of ESD

A resource for reductions of
atmospheric carbon dioxide

A resource for the long term storage of
carbon


The Carbon Cycle


Mixed Northern Hardwood Forests


Where is Carbon stored?
Forest – all above & below ground portions of live
trees

Soils – mineral horizons to a depth of 1 meter

Forest Floor – all dead organic matter above
mineral/sod horizons, including litter humus & coarse
woody debris

Understory Vegetation – all live vegetation which are
not tree (shrubs, herbaceous species)


Well Established Forest
w/understory layers


Carbon Dioxide Storage in Trees
Green WT above gnd: Wg=(0.25)(D)(D)H

Green WT (total w/roots): Wgt=120%*Wg

Dry WT: Wd=72.5%*Wgt

Weight of Carbon Stored: Wc=Wd * 50%

Weight of Carbon Dioxide stored: Wco=Wd*3.6663

Weight of Carbon Dioxide stored per year:
W = Wco/20


Example: 20yr old tree, 10” DBH,
30’ height
Green WT above gnd: Wg=(0.25)(10)(10)30 = 750 lb

Green WT (total w/roots): Wgt=1.20 * 750 = 900 lb

Dry WT: Wd=0.725 * 900 = 625.5 lb

Weight of Carbon: Wc=625.5 *0.5 = 312.75 lb

Weight of Carbon Dioxide: Wco=312.75*3.6663 = 1146.6 lb

Weight of Carbon Dioxide/year: W = 1146.6/20 = 57.3 lbs/yr


Actual Site Conditions
In NE U.S. – Mixed Northern Hardwoods have an
average density of 100 trees/acre

100 * 57.33 lb = 5,733 lbs of carbon dioxide
sequestered per acre/yr.

64 acres * 5,733 = 366,912 lbs per site area

Assume trees grow to 100 years, then a total of
29,352,960 lbs (14,676 tons) of carbon dioxide will
be sequestered from this site in the trees within the
Open Space


Carbon Storage in the Soils

Both Organic and Inorganic carbon will be
stored in the soils

Undisturbed soils will store more carbon than
disturbed soils

NE soils will store 144,703 lbs/acre of carbon
over the typical lifecycle of a mixed hardwood
forest


Actual Site Conditions

64 acres * 144,703 lb/ac = 9,260,992 lbs
(4,630.5 tons)

Between storage in trees and soils, the open
space on this parcel will store 19,306 tons of
carbon over the lifecycle of the forest (100
years)


Vegetated LID Treatment Systems

Bioretention systems, constructed wetlands,
and vegetated swales will provide additional
sources to sequester carbon

Plants have large stem or leaf areas, having
high rates of photosynthesis (retaining
carbon in the plant material)

Plants are fast growing, thus having high need
for carbon (high capacity for sequestering)

LID Vegetated Systems


Conclusion
Preservation of large extents of undisturbed
woodlands and native soils will continue to
provide valuable resources for sequestering
of carbon in the environment
The utilization of vegetated LID treatment
systems provide additional sources for the
storage of carbon


Contact Information
Steve Trinkaus, PE, CPESC, CPSWQ
Trinkaus Engineering, LLC
114 Hunters Ridge Road
Southbury, CT 06488
203-264-4558, Fax: 203-264-4559
Email: strinkaus@earthlink.net
Website:
http://www.trinkausengineering.com


QUESTIONS??


Environmental Site Design

Empfohlen

Empfohlen

Weitere ähnliche Inhalte

Was ist angesagt?

Was ist angesagt? (20)

Ähnlich wie Environmental Site Design

Ähnlich wie Environmental Site Design (20)

Environmental Site Design