Transcript No Slide Title

Basics of ESD
and the New Design Sequence
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Agenda
1. Why ESD is Important to the Bay
2. The New Design Sequence and Spreadsheet
3. Using Alternative Surfaces and Credits
4. Design of Micro- ESD Practices
The Bay Stormwater Problem
Stream habitat and biodiversity
degraded in 10,000 stream miles in
the Bay watershed
Major ecological impacts in small
estuaries and coastal creeks
Fastest growing nutrient load source
in the Bay watershed
Pesticides detected in 95% of
urban streams and fish tissues
sampled
Metals, PCBs and
hydrocarbons in tidal
sediments
Bacteria violations in runoff close
streams, beaches and shellfish beds
Our traditional stormwater
practices have not solved
these problems
Our Traditional Stormwater BMPs Have Not Worked
Piney Branch - WBPB203A
100
Excellent
Percent of Best Possible BIBI Score
90
80
Good
70
60
Fair
50
40
30
20
Poor
10
0
Avg Pre-development IBI
Avg Post-development IBI
Avg During-construction IBI
The New Maryland ESD Regulations
You are not alone..tougher stormwater regulations
are on the horizon in all Bay states:
Maximum Extent Practicable is defined as maintaining
predevelopment site runoff to “woods in good condition.”
The resulting ESD volume typically ranges between 1.7
and 2.6 inches, depending on soils and development
intensity
Features of the CSN
ESD to MEP Compliance Spreadsheet




Automatically Calculates ESD Target
Volume
Accounts for all of the credits, alternative
surfaces, micro-ESD practices and
conventional practices in a step-wise
fashion
Simultaneously tracks ESD volume and
Critical Area 10% requirements
Easy to verify compliance
Status of Compliance Spreadsheet




Spreadsheet and Users Guide are available
at www.chesapeakestormwater.net
Has undergone significant testing
Version 2.0 was released in June, 2010
Version 2.1 released in July 2010
Before You Get Started





Site Recon (understand the site)
Environmental mapping (protected areas)
Define small drainage areas and flow paths
ID locations of most permeable soils
Develop site plan that shows impervious
and pervious cover footprints
Site mapping and stormwater concept plans are
mandated at the earliest stages of development
plan review
– Natural Resource Inventory and
Mapping
– Better Site Design to Minimize
Impervious Area
– Disconnection and Filter Strips
– Integrate ESD Practices into
the Best Soils
– Using Natural Flow Pathways for
Stable Conveyance
Site mapping and stormwater concept plans are
mandated at the earliest stages of development
plan review
Mapping Requirements
•
•
•
•
•
•
•
•
Wetlands
Major Water Ways
Floodplains
Critical Areas
Wetland Buffers
Perennial Streams
Stream Buffers
Forest Stand
Delineation
•
•
•
•
•
•
•
Steep slopes
Springs and seeps
Highly erodible soils
Topography
Existing drainage
area
Hydrologic Soil
Groups
Zero-order streams
Start By Reducing Clearing and
Preserving Highly Permeable Soils
Step 1
ESD Site Planning Checklist




Must answer 12 questions related to ESD
site and stormwater planning
Should be able to answer “Yes” or “does
not apply”
Show on the site plan
If answer is “No”, must provide a written
narrative
. as to why it could not have been
used
The basic idea is that a compliant plan is one without
any no’s (either a yes or not applicable)
ESD Implementation Checklist
Check all of the Following ESD Practice That Were Implemented at Site
Environmental Mapping Was Conducted at Site Prior to Layout
Natural Areas Were Conserved (e.g., forests, wetlands, steep slopes,
floodplains)
Stream, Wetland and Shoreline Buffers Were Reserved
Disturbance of Permeable Soils Was Minimized
Natural Flow Paths Were Maintained Across the Site
Building Layout Was Fingerprinted to Reduce Clearing and Grading at Site
Site Grading Promoted Sheetflow From Impervious Areas to Pervious
Ones
Site Design Was Evaluated to Reduce Creation of Needless Impervious
Cover
Site Design Was Evaluated to Maximize Disconnection of Impervious
Cover
Site Design Was Evaluated to Identify Potential Hotspot Generating Area
for Stormwater Treatment
Erosion and Sediment Control Practices and Post Construction
Stormwater Management Practices Were Integrated into a
Comprehensive Plan
Tree Planting Was Used at the Site to Convert Turf Areas into Forest
Yes
No
N/A
X
X
X
X
X
X
X
X
X
X
X
X
Step 2 Calculate Site IC and WQv
Four Basic Inputs:




–
Site Area
Existing Site Impervious Cover Area
Proposed Site Impervious Cover Area
WQv Rainfall Depth (0.9 or 1.0)
Impervious cover is measured as any area
without vegetative or pervious cover
Step 2: Calculate Site Imperviousness and Water Quality Volume, WQv
Site Area, A (acres)
Existing Impervious Surface Area (acres)
Proposed Impervious Surface Area (acres)
.
Existing Imperviousness, Ipre
Proposed Imperviousness, Ipost
Development Category
Rainfall Depth, P (in)
Runoff Coefficient, Rv
Water Quality Volume, WQv (ac-in)
Water Quality Volume, WQv (cf)
38
0
13.8
0.0%
36.3%
New Development
1.0
0.38
14.32
51,982
CSN Tip: Break sites up into 2 to 5 acre sub-drainage
areas, define natural flow paths, and make best
estimate of IC (and increase it by 15%)
Step 3 Compute MD Critical Area
Phosphorus Removal Requirement *

Automatically calculates the phosphorus removal
requirement, depending on whether the site is
classified as new development or redevelopment
(>15% IC)
.
* This requirement applies to Intensely Developed Areas in the
1000 ft Critical Area
Step 4
Enter Pre-development Soil Data



Enter Percent Site Area in Hydrologic Soil
Group A, B, C or D
Automatically computes ESD rainfall
Target Volume, and the Recharge Volume
Your HSGs will determine your ESD
strategy
.
Output From Spreadsheet in this Step
% Soil Type A
% Soil Type B
% Soil Type C
% Soil Type D
Pre-Developed Condition, RCNwoods
0%
60%
40%
0%
61
New Development
Soil Type A ESD Rainfall Target, PE (in)
Soil Type B ESD Rainfall Target, PE (in)
Soil Type C ESD Rainfall Target, PE (in)
Soil Type D ESD Rainfall Target, PE (in)
0.00
1.08
0.72
0.00
Site ESD Rainfall Target, PE (in)
1.80
ESD Runoff Depth, QE (in)
ESD Runoff Volume, ESDv (cf)
0.68
93,567
Required Recharge Volume, Rev (ac-ft)
Required Recharge Volume, Rev (cf)
0.25
10,812
Step 5 Select Alternative Surfaces



Look at areas at Site where Green Roof or
Permeable Pavers Can be Used
Enter area and thickness
The spreadsheet then reduces the ESD
Rainfall Target volume and adjusts the
Phosphorus removal rate accordingly
Alternative Surfaces
Green Roof (on Soil Type A)
.
Green Roof (on Soil Type B)
Green Roof (on Soil Type C)
Green Roof (on Soil Type D)
Permeable Pavement (Soil Type A)
Permeable Pavement (Soil Type B)
Permeable Pavement (Soil Type C)
Contributing
Drainage Area (ac) Thickness
Effective RCN
0
0
0
0
0
0
0
Permeable Pavements
Alternative Surfaces: Green Roof
CSN Tip: Design spec available on CSN website –
www.chesapeakestormwater.net
Step 6
Utilize Disconnection and Filtering
Credits

Three broad credits
 Rooftop Disconnection
 Non-rooftop Disconnection
 Expanded Conservation Area


Enter the CIDA (contributing impervious drainage
area) and a few simple design parameters
.
Must also enter the predominant pre-development
HSG of the filter path to compute the TP
reduction
CSN Tip: Connect CIDA “blobs” with pervious “blobs”
on plan and check distances/slopes. OK to aggregate
acceptable credits in the spreadsheet
Step 6: Select Nonstructural Practices to Treat the ESD Rainfall Target
Nonstructural Practices
PE Credit
Description
ESDv
from
Contributing Direct ESDv Upstream
Impervious Received by Practices
Cover (ac) Practice (cf)
(cf)
Disconnection of Rooftop
Runoff (A/B Soils)
Up to 1 inch credit
provided based upon
disconnection flow
length.
Disconnection of Rooftop
Runoff (C/D Soils)
Up to 1 inch credit
provided based upon
disconnection flow
length.
Disconnection of Non-Rooftop
Runoff (A/B Soils)
Up to 1 inch credit
provided based upon
disconnection and
contributing flow
lengths.
0
0
Disconnection of Non-Rooftop
Runoff (C/D Soils)
Up to 1 inch credit
provided based upon
disconnection and
contributing flow
lengths.
0
0
Sheetflow to Conservation
Areas (A/B Soils)
Up to 1 inch credit
provided based upon
conservation area
width.
3
18,622
0
0
0
Practice Specific
Parameter(s)
Flow Path (ft)
East/West
75
Western
Shore
Runoff Enhance
PE
ESDv Volume d Filter
Credit credit Remaini Volume Rev
(in)
(cf) ng (cf)
(cf)
(cf)
1
10,346
8,276
10,346
0
0
0
0
0.4
0
0
0
0
0
0
0
1
7,465
-7,465
7,465
Contributing
Disconnection Length (ft)
Length (ft) (Impervious)
75
150
Minimum
Width (ft)
0
13437
100
Credits Are Easy to Show on Plan
But Will They Actually Show Up
at the Site?
Four Stage Review:
1.
Evaluate Feasibility During
Concept Design
2. Confirm Area in Final Design
3. Protect During Construction
inspection
4. Verify as Part of Final
Stormwater Acceptance
Step 7
Apply ESD Micro-Practices




100% IA to micro-practices
Enter CIDA, and specific design
parameters for each micro-practice
selected
Can select a downstream practice to which
runoff will flow to
HSG are. used to make sure that the Micropractices are properly applied to the right
soil, and adjust TP removal rate
Micro-ESD Practices










Rainwater Harvesting
Submerged Gravel Wetland
Micro-Infiltration (Dry Well)
Micro-bioretention *
Rain farden
Landscape Infiltration
Grass Swales
Bioswales*
Wet Swales
Enhanced Filters are add on to * practices
It seems complex, but only a few inputs are needed
Step 7: Select Micro-Scale Practices to Treat the ESD Rainfall Target
Micro-Scale
Practices
Rainwater
Harvesting
Submerged
Gravel
Wetlands
MicroInfiltration
PE Credit Description
0
PE = 10" x Surface Area /
Drainage Area
PE = 10" x Surface Area /
Drainage Area
Bioretention
(A/B Soils)
Bioretention
(C/D Soils)
PE = 15" x Surface Area /
Drainage Area
PE = 15" x Surface Area /
Drainage Area
Landscape
Infiltration
PE = 20" x Surface Area /
Drainage Area
Grass Swales
(A/B Soils)
Grass Swales
(C/D Soils)
PE = 10" x Surface Area /
Drainage Area
PE = 10" x Surface Area /
Drainage Area
Bio-swales (A/B PE = 15" x Surface Area /
Soils)
Drainage Area
Bio-swales (C/D PE = 15" x Surface Area /
Soils)
Drainage Area
PE credit is based on design
volume
0
Surface Area
(sf)
PE credit is based on design
volume
PE credit is based on design
volume
Practice Specific
Parameter(s)
Enhance
d Filter
Volume
(cf)
Rev (cf)
PE
ESDv
credit
(cf)
0.00
0
0
0
0.00
0
0
0
Downstream
Practice
Design
Volume (cf)
PE credit is based on design
volume
Rain Gardens
(A/B Soils)
Rain Gardens
(C/D Soils)
Wet Swales
CDIA
(ac)
Direct ESDv ESDv
Received from Up
by Practice Practice
(cf)
s (cf)
0
5
5
0.8
0
31,037
0
0
0
0
0
31,037
0
0
0
0
0
4,966
7287
0
0
0
0
0
0
0
0
Depth* (ft)
2.2
Surface Area
(sf)
11,000
Surface Area
(sf)
Depth* (ft)
1.6
0
Surface Area
(sf)
20,000
1.02
17,600 13,437
17,600
0.00
0
0
0
0.00
0
0
0
1.38
23,750 7,287
23,750
0.00
0
0
0
0.00
0
0
0
0.49
3,325
1,641
3,325
0
Surface Area
(sf)
0
0.00
0
0
0
0.00
0
0
0
0
Surface Area
(sf)
0
0.00
0
0
0
0.00
0
0
0
Surface Area
(sf)
0
Surface Area
(sf)
4,200
Depth* (ft)
1.0
Sheetflow to
Conservation Areas
(A/B Soils)
Grass Swales (A/B
Soils)
Step 8
Check for ESD Compliance and Go Back

Minimum
 ESD For Full WQv
 Entire Rev
 Zero TP removal requirement

Must Attempt to Provide ESD for Full ESD
Target Volume
.
Several iterations are needed to get to compliance
ESDv Treated (cf) 62,485
PE achieved (inches)
1.20
WQv Requirements Met Through Environmental Site Design?
YES
WQv Remaining? (cf)
Entire ESDv Treated Through Environmental Site Design?
0
NO
ESDv Remaining? (cf) 31,082
Rev Requirements Met Through Environmental Site Design?
Rev Remaining? (cf)
YES
0
Total Rev (cf) 62,485
Strategies to Achieve Compliance



Adjust site layout to reduce IC or
increase forest cover. Make sure that all
the ‘No’s “ are addressed
Consider more alternative surfaces (most
designers will have skipped this step
initially)
Expand site area subject to credits (e.g.,
more disconnection, improve soil and slope
conditions within filter strip, accept
concentrated flows w/ level spreader)
Strategies to Achieve Compliance
(continued)



Add more Micro-ESD practices to pick up
addl. untreated CIDA
Change ESD practices to get higher
runoff reduction (e.g., go from grass
channel to bio swale, or from rain garden to
micro-bioretention
Add an Enhanced Filter to the bottom of
select micro-ESD Practices
Strategies to Achieve Compliance
(continued)




UPGRADE: Substitute Larger ESD
practices such as Bioretention, Dry Swales
and Infiltration that pick up more CIDA or
have higher runoff reduction
Do more soil infiltration testing to find
best sites
ESD basins Use bioretention within ED or
flood control pond (at smaller sites)
Subarea Over-control As long as they
drain to same area, OK to over control in
one DA to compensate for under-control in
another
Step 9 Compute reduced RCN for CPv
Calculations


Automatically calculates a new runoff curve
number (RCN) to calculate the remaining storage
volume needed for channel protection that
reflects the final combo of ESD practices
employed.
The RCN can also be used in hydrologic models for
peak discharge calculation
.Reduced RCN for Type A Soils
Reduced RCN for Type B Soils
Reduced RCN for Type C Soils
Reduced RCN for Type D Soils
42
63
77
81
Composite Reduced RCN
69
Q (in)
CPv Treatment Required (cf)
0.45
62,511
Step 10
Apply Structural Practices for
remaining Compliance




Only after you have exhausted your ESD
opportunities
Conventional practices can be used to
obtain any remaining Rev, Cpv, WQv or TP
removal for site compliance
Simplified List: Ponds, Wetlands, Filters
These practices
are independently sized
.
and designed
Note Level 1 and 2 Design for Critical Area
Structural Practices
Stormwater Ponds (Level 1)
Stormwater Ponds (Level 2)
Stormwater Wetlands (Level 1)
Stormwater Wetlands (Level 2)
Stormwater Filtering Systems
(Level 1)
Stormwater Filtering Systems
(Level 2)
Stormwater Infiltration (Level 1)
Stormwater Infiltration (Level 2)
Contributing Direct ESDv
ESDv from
Impervious Received by
Upstream
Cover (ac)
Practice (cf) Practices (cf)
0
0
0
0
0
0
0
0
Treatment
Volume (cf)
Enhanced
Filter
Volume
(cf)
Rev (cf)
0
0
Phosphor Load
ous
Reducti
Removal
on
Efficiency (lbs/yr)
50%
0.00
75%
0.00
50%
0.00
75%
0.00
0
0
0
60%
0.00
0
0
0
0
0
0
0
65%
60%
90%
0.00
0.00
0.00
Total structural CPv
provided
CPv Requirement Met?
CPv Remaining
0
NO
62,511
Total Load Reduction (lbs P / year) 24.12
Total Load Reduction Remaining (lbs P / yr) 0.00
Total Rev provided (cf)
Rev Requirement Met?
Rev Remaining? (cf)
62,485
YES
0
Step 11
Additional Concept Design Work




Site plan showing CIDA and surface area
of individual ESD practices
Site testing to confirm feasibility of ESD
practices (e.g., water table, slopes, sheet
flow distances, infiltration rates, etc).
Analyze system of ESD practices for safe
conveyance
of the 10 year storm
.
ESC plan that shows how ESD practices will
be protected during construction
CONSTRUCTION CONSTRAINTS FOR
ESD MICRO-PRACTICES
ESD PRACTICE
Disconnect/Filter credits
Permeable Paver
Rainwater Harvesting
Gravel Wetlands
Micro-infiltration
Rain Garden
Bioretention
Landscape Infiltration
Grass Swales
Bioswales
Wet Swales
Enhanced Filters
Install
After Con.
X
X
X
X
X
X
X
X
X
X
X
X
Avoid or Do not use Restore
Protect
as ESC
Soil
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
Solution: Rain gardens or rainwater harvesting
Step 12
Final design and installation
This is where the rubber meets the road!
.
Alternative Surfaces and Credits
Alternative Surfaces
•


Alternative Surfaces
• Permeable Pavers
• Green Roofs
How they work
Dealing with design and installation issues
Select Alternative Surfaces



Look at areas at Site where Green Roof or
Permeable Pavers Can be Used
Enter area and thickness
The spreadsheet then reduces the ESD
Rainfall Target volume accordingly
Alternative Surfaces
Green Roof (on Soil Type A)
.
Green Roof (on Soil Type B)
Green Roof (on Soil Type C)
Green Roof (on Soil Type D)
Permeable Pavement (Soil Type A)
Permeable Pavement (Soil Type B)
Permeable Pavement (Soil Type C)
Contributing
Drainage Area (ac) Thickness
Effective RCN
0
0
0
0
0
0
0
Alternative Surfaces: Permeable Pavements
Design Scales for Permeable Pavers
Micro-Scale
Small-Scale
Large-Scale
Suitable Paver
PICP
ALL
ALL
Reservoir Size
Some or all of the
RRv or WQv
Full WQv, and as much of CPv and
design storms as possible
External DA?
No
Yes, Impervious cover up to twice the
permeable paver area may be
accepted
Observation
Well
No
No
Underdrain?
Rare
Depending on soils Back up
underdrain
Design Factor
Yes
Comparative Properties of the Three Major Permeable Paver
Design
Factor
Porous Concrete
(PC)
Scale of
Application
Small and Large
Small and Large
Scale Applications Scale Applications
Micro, Small and
Large Scale
Applications
Paver
Thickness
5 to 8 inches
3 to 4 inches
3 1/8 inches
Design
Permeability
10 feet/day
6 feet/day
2 feet/day
Construction
Cost
$ 2.00 to $6.50 sf
$ 0.50 to $1.00/sf
$ 5.00 to $ 10.00/sf
Min Batch
Size
Porous Asphalt
(PA)
~ 500 sf
Interlocking Pavers
(PICP)
NA
Longevity
20 to 30 years
15 to 20 years
20 to 30 years
Colors &
Texture
Limited Range of
Colors and
Textures
Black or Dark Grey
Color
Range of Colors and
Textures
Permeable Paver
ESD Sizing and Applicability
Effective RCNs for Permeable Pavements
Hydrologic Soil Group
Subbase
A
B
C
D
6”
76
84
93
─
9”
62
65
77
─
12”
40
55
70
─
Design shall include overdrain (inv. 2” below pavement base)
If sub-base is greater than 12”or under drains
are used on D soils, then skip this step, and enter
as an upgraded BMP later on
MDE Guidance on Permeable Pavers




Not allowed on D soils or Fill Soils
Porosity = 30%
More than 10,000 sf = must have tested
infiltration rate of more than 0.52 in/hr
Under-drain OK for smaller projects
CSN Tip: Detailed paver design spec available at
www.chesapeakestormwater.net
Paver Design Modification
Enhanced Filter
Source: Hunt and Collins, 2008
Enhanced Filters



The stone reservoir volume is equal to the
surface area multiplied by depth divided by
the porosity (n) of the stone
Used to address Rev for the contributing
impervious area using the percent volume
method.
When coupled with other properly designed
structural or micro-scale practices, the
combined system will address the ESD
sizing criteria.
Reinforced Turf
Post development RCN’s for reinforced turf
applications should reflect the surfacing
material used (e.g., “open space in good
condition” for grass).
Green Roof Sizing



Only used to reduce curve
number
No direct reduction of ESD
volume
Rev must be provided separately
Effective RCNs for Extensive Green Roofs
Roof Thickness (in.):
Effective RCN:
2
94
3
92
4
88
6
85
8
77
Disconnection and Filtering Credits

Three broad credits
 Rooftop Disconnection
 Non-rooftop Disconnection
 Expanded Conservation Area


Enter the CIDA (contributing impervious drainage
area) and a few simple design parameters
.
Must also enter the predominant pre-development
HSG of the filter path to compute the TP
reduction
CSN Tip: Connect CIDA “blobs” with pervious “blobs”
on plan and check distances/slopes. OK to aggregate
acceptable credits in the spreadsheet
Step 6: Select Nonstructural Practices to Treat the ESD Rainfall Target
Nonstructural Practices
PE Credit
Description
ESDv
from
Contributing Direct ESDv Upstream
Impervious Received by Practices
Cover (ac) Practice (cf)
(cf)
Disconnection of Rooftop
Runoff (A/B Soils)
Up to 1 inch credit
provided based upon
disconnection flow
length.
Disconnection of Rooftop
Runoff (C/D Soils)
Up to 1 inch credit
provided based upon
disconnection flow
length.
Disconnection of Non-Rooftop
Runoff (A/B Soils)
Up to 1 inch credit
provided based upon
disconnection and
contributing flow
lengths.
0
0
Disconnection of Non-Rooftop
Runoff (C/D Soils)
Up to 1 inch credit
provided based upon
disconnection and
contributing flow
lengths.
0
0
Sheetflow to Conservation
Areas (A/B Soils)
Up to 1 inch credit
provided based upon
conservation area
width.
3
18,622
0
0
0
Practice Specific
Parameter(s)
Flow Path (ft)
East/West
75
Western
Shore
Runoff Enhance
PE
ESDv Volume d Filter
Credit credit Remaini Volume Rev
(in)
(cf) ng (cf)
(cf)
(cf)
1
10,346
8,276
10,346
0
0
0
0
0.4
0
0
0
0
0
0
0
1
7,465
-7,465
7,465
Contributing
Disconnection Length (ft)
Length (ft) (Impervious)
75
150
Minimum
Width (ft)
0
13437
100
Lots of opportunity to boost the hydrologic
function of urban turf through ESD Credits
Our Turf Is Not Very Pervious and is Ineffective in Treating
Stormwater
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•
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Top Soil is Stripped
Soil Structure is Lost
Subsoils are Compacted
Reduced Water Holding
Capacity
• Low Infiltration Rate
• High Nutrient
Concentrations
• Runon to Impervious
Cover
Soil Restoration is Not Recommended When:
• Existing soils have high infiltration rates
(e.g., HSG “A” soils)
• The water table or bedrock is located
within 1.5 feet of the soil surface.
• Slopes exceed 10%.
• Existing soils are saturated or
seasonally wet
• They would harm roots of existing trees
• (stay outside the tree drip line)
• The downhill slope runs toward an
existing or proposed building foundation
• The contributing impervious surface
area exceeds the surface area of the
amended soils
MDE Simple Disconnection
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Min. 15 feet length
10 feet lateral setback to IC
Max Filter Path 0f 75 ft
Max of 500 sf of IC per disconnect (1000 for nonrooftop)
Max 5% slope w/o infiltration berms
A, B and C soils OK, soil amendments may be needed on
D soils or disturbed soils
Flows shall be non-erosive for two year storm
Rooftop Disconnection
MDE Sizing and Applicability
Applies to all development types of low to
moderate intensity
ESD Sizing Factors for Rooftop Disconnection
Disconnection Flow Path Length (ft.)
Western Shore
15
30
45
60
75
Eastern Shore
12
24
36
48
60
PE (in.) =
0.2
0.4
0.6
0.8
1.0
Disconnect to Grass Filter Strip
ESD Sizing
Non-Rooftop Disconnection
Ratio of Disconnection Length to Contributing Length
Impervious Ratio
0.2:1
0.4:1
0.6:1
0.8:1
1:1
PE (in.) =
0.2
0.4
0.6
0.8
1.0
CSN Design Guidelines for Grass Filter Strip
Soil and Ground Cover
Amended Soils and Dense Turf Cover
Construction Stage
Prevent Soil Compaction by Heavy
Equipment
Typical Application
Treat Small Areas of Impervious Cover
Close To Source (max of 5000 square
feet)
Compost Amendments
Yes
Boundary Spreader
Gravel Diaphragm at Top of Filter
Permeable Berm at toe of filter
Boundary Zone
At 25 feet of level grass
Concentrated Flow?
Not Recommended
Entrance Slope
Less than 2% in first ten feet of strip
Maximum Overall
Slope
5%
Sheet flow to Conservation Area (CA)
MDE Conservation Area Rules
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Max Slope of 5% in CA
Max IC length of 75 ft to CA
CA must be at least 20,000 square
feet in area
CA must have min. width of 50 ft
No managed turf in CA
Sheetflow to Conservation Area Sizing Factors
Min. Width (ft) =
50
75
100
PE (in.) =
0.6
0.8
1.0
CSN Supplemental Guidelines for Conservation Filters
Soil and Ground Cover
Undisturbed Soils and Native Vegetation
Construction Stage
Located Outside the Limits of Disturbance and
Protected by ESC Perimeter Controls
Typical Application
Adjacent Drainage to Stream Buffer or Forest
Conservation Area
Compost Amendments
No
Boundary Spreader
Infiltration Berm at Top of Filter
Boundary Zone
10 feet of Level Grass
Concentrated Flow?
Runoff should enter the boundary as sheetflow
for the one-inch storm or use concrete engineered
level spreader
Max Entrance Slope
Less than 4% in the first ten feet of filter
Site Reconnaissance
Site visit to confirm topography, slope, and soil
conditions prior to design
Infiltration Berm
Critical Area Buffer
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General rule is to keep stormwater treatment out of the
100 foot buffer
OK to use bioretention and filter strip at boundary
Exceptions:
 Use of regenerative conveyance wetlands through the
buffer in zero-order streams or ditches
 Use bioretention or other practices with trees in
buffer exception areas ?
CSN Tip: Provide a Credit for Soil Restoration and
Reforestation
Examples of Qualifying
Criteria
• Minimum area of 5000 sf
• Stormwater or conservation
easement
• Long term forest plan
• Achieve 75% forest canopy
in 10 years
• Show on all ESC drawings
Credits Are Easy to Show on Plan
But Will They Actually Show Up
at the Site?
Four Stage Review:
1.
Evaluate Feasibility During
Concept Design
2. Confirm Area in Final Design
3. Protect During Construction
inspection
4. Verify as Part of Final
Stormwater Acceptance
Design of ESD Micro-Practices
The List of Micro-ESD Practices
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Rainwater Harvesting
Submerged Gravel Wetland
Micro-Infiltration (Infiltration)
Rain Garden *
Micro-bioretention (Bioretention) *
Landscape Infiltration
Grass Swales
Bioswales) (Dry Swales) *
Wet Swales
Enhanced Filters are add on to * practices
Micro practices should be used to achieve entire ESD
volume, or at least the entire water quality volume
Your HSG’s Determine Which Micro-Practices
Are Feasible
ESD PRACTICE
HSG A
HSG B HSG C HSG D
Permeable Paver
X
X
X
Rainwater Harvesting
X
X
X
X
Submerged Gravel
X
X
Wetlands
Micro-infiltration
X
X
Rain Garden
X
X
X
Bioretention
X
X
X
Landscape Infiltration
X
X
Grass Swales
X
X
X
Bioswales
X
X
X
X
Wet Swales
X
X
Enhanced Filters
X
X
X= may be suitable depending on depth to water table, bedrock
and slope
Comparing the Micro-Practices
ESD PRACTICE
ESD
Max
Efficiency CDA (sf)
Rainwater Harvesting
20+
~20,000
Gravel Wetlands
~10
< 1 acre
Micro-infiltration
15
500
Rain Garden
10
2,000
Micro-Bioretention
15
20,000
Landscape Infiltration
20
20,000
Grass Swales
10
> 1 acre
Bioswales
10
> 1 acre
Wet Swales
15
> 1 acre
Enhanced Filters
~6
n/a
Upgrade
Size?
Yes
No
Yes
No
Yes
No
No
Yes
?
No
Landscape Infiltration
Four layer System
Surface ponding
12 inch of planting soil
12 inch of gravel
12 inch of sand
.
Landscape Infiltration
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Restricted to A & B soils
Max CDA of 10,000 sf (w/o soil testing and
pretreatment)
This has the best ESD reduction of any
micro-ESD practice per square foot of
practice surface area
.
Essentially an infiltrating bioretention
facility w/o underdrain
Submerged Gravel Wetland
Submerged Gravel Wetland
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C or D Soils
High Water Tables and Eastern Shore
Minimum CDA of 1 acre
18 to 48 inches of gravel
Pretreatment required
Updated design guidance available from
UNH as Resource 5
Submerged Gravel Wetland Sizing
PE for the contributing drainage area is
based on the volume captured by
submerged gravel wetlands.
Assume about 10 inches
Dry Well = Micro-infiltration
Dry-Well (Micro-Infiltration) ESD Sizing
A PE value based on the ESDv captured and treated shall be
applied to the contributing drainage area.
The storage area for the ESDv includes the sand and gravel
layers in the bottom of the facility.
Assume about 15 inches
Dry Well = Micro-infiltration
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A and B Soils
Max CDA of 500 sf
Above this shift to normal infiltration
trench design
Pretreatment
Bottom sand layer
10 feet setback from foundations
Process for Investigating Infiltration
Feasibility at a Site
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Preliminary – Look at Soil Survey but don’t put too
much stock in it
Geophysics for Site – would also be good for
general site layout issues (e.g., best places for
infiltration, best places for wells)
On-Site Soil Test at Actual Facility Location:
– Bore Hole or Test Pit Drawdown Test (see Infiltration
Spec Appendix)
– Infiltrometer, controlled infiltration
test
Scale: Micro, Small, Conventional
Put a Max Limit on CDA or Require 100% IC in CDA?
Rainwater Harvesting
Rainwater Harvesting
ESD Sizing and Applicability
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Not a lot of design constraints
Spreadsheet available to determine the
ESD volume actually captured based on
indoor and outdoor demand
Rain barrels and cisterns shall be designed to capture at least
0.2 inches of rainfall from the contributing rooftop area.
A PE value based on the ESDv captured and treated shall be
applied to the contributing rooftop area.
Micro-Bioretention
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CDA should not exceed 0.5 acres
Must store at least 75% of ESDv
OK for all soil types
Temp ponding of 12 inches
Filter bed between 2 and 4 feet deep
Rain Garden
Rain-gardens
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CDA should not exceed
 2000 sf (residential)
 10,000 sf (other applications)
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Must store at least 75% of ESDv
Preferred for A & B Soils
Restricted for C & D Soils
Temp ponding of 6 inches
Filter bed between 12 and 18 inches deep
No underdrain
Grass Channels
At least its not a credit anymore!
ESD Sizing for Grass Channels
The maximum flow velocity
for the ESDv shall be less
than or equal to 1.0 fps.
Grass Channels
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OK for A, B & C Soils
For roads not parking lots
Swale length = road length
Max slope of 4% *
Max ESD flow depth of 4 inches
Checkdams or infiltration berms
Swale bottom at least 2% of CDA*
Max CDA of 1 acre *
* applies to all three designs
CSN Design Guidelines for Grass Channel
1.
2.
3.
4.
5.
6.
Explicitly prohibit for parking Lots
Minimum bottom width of 4 feet
One foot of restored soil along channel
bottom required for C and D soils and
mass graded B soils
No more than 3% slope in any 50 foot
segment (low check dams)
May need initial biodegradable geo-fabric
Be non-erosive for 10 year storm
Wet Swales
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For C and D Soils
Non-residential applications
Useful in flat terrain with high water table
Wet Swale
Sizing
Wet swales shall be designed to store
at least 75% of the ESDv.
A PE value equivalent to the volume
captured and treated shall be applied to
the contributing drainage area.
Assume about 8 to 12 Inches
CSN Wet Swale Design Criteria
1.
2.
3.
4.
5.
Average dry weather ponding depth no
more than 6 inches
Max. dry weather ponding of 18 inches
Multiple cell system, at least every 50 ft
Wetland planting plan (emergent or
forested)
Have hydraulic capacity for 10 year
storm
Bio-Swales = Dry Swales
Bio-Swale
ESD Sizing and Applicability
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OK for all soil types
Follow standard swale criteria
Surface area 2% of CDA