Mission:
• Stormwater Management
Technology
• Pilot Projects, Monitoring,
Modeling, Manuals,
Training, Education
The Low Impact
Development Center, Inc.
Balancing Growth and
Environmental Integrity
LID Modeling
Why are We Modeling?
Regulatory Requirements
Resource Protection
•
•
•
•
•
Determine Effectiveness
Predict/Project (Pre-Post)
Calibration
“It’s Cheaper than Doing anything”
NC State needs more PhD’s
Easy Stuff
• Peak Flow
• Water Quality
Hard Stuff
•
•
•
•
•
Energy (Light, Thermal, Stream Power)
Habitat
Optimization
Maintenance
Optimization
How well do we maintain the ecological integrity
(functions) of aquatic systems (small streams)?
Scale / Spatial / Temporal / Species
Nutrients
Temperature
D.O.
pH
Turbidity
Organics Toxics
Chemical
Flow
Variables
Regime
Ecosystem
Integrity
Biotic
Habitat
Structure
Factors
Disease
Reproduction
Feeding
Predation
Competition
Energy
Sources
Sunlight
Nutrients
Seasonal Cycles
Organic Matter
1&2 Production
Velocity
Frequency
Runoff
Evaporation
Ground Water
Flow Duration
Rain Intensity
Canopy
Siltation
Gradient
Substrate
Current
Instream Cover
Sinuosity
Width/Depth
Channel Morphology
Soils Stability
Riparian Vegetation
Performance Measures
• Volume (Seattle Sea Streets)
• Prescriptive or Presumptive
• Load vs. Percentage
• Flow Rate (Discrete or
Continuous)
Taxonomy and Classification
Design Models
Calibration Models
Coordinating Needs Critical
Early Models
K

n
AR
2/3
Simple WQ Stuff
L
P  Pj   Rv
12
 C  A  2.72
L = Load, P=Precipitation
Courtesy Geoanalysis
Today
• Moving towards Tributary
Strategies
• Loadings and Limits
(303d)
• Site Design Models don’t
link to Watershed Models
• Rapid Assessments that
may have significant data
or science gaps
• Costs and Predictability
unknown
Civil to Environmental
Q = CIA
C (t )Q(t )dt

C
 Q(t )dt
Bioretention
(WQv )(d r )
Af 
(t f )
(k )(h f  d f )
HYDROLOGIC CYCLE:
P+R+E+T
RECHARGE
Optimization
A bioretention pond costs $2,000
Region
to construct for
a ½ofsite. So it
Feasibility
costs $4,000 per acre.
Gazillions
of
Acceptable
First, it’s a cell not a pond!!
Solutions
MC  cIJ  mIJ Q
*
2
RJ
Conventional Pipe and Pond Centralized Control
“Efficiency”
LID Uniform Distribution of Micro Controls
Runoff Hydrograph is Sensitive to
Bioretention Placement
in II only
I
II
III
I
II
III
7
3
McCuen 2002
Hoffman and Crawford, 2000
Existing Problems and
Future High Risks
Hoffman and Crawford, 2000
Oversize Pipes
Remove Large
Impervious Areas
Comparison of
Conventional and
LID Strategies
An estimate of imperviousness can be derived directly from the satellite image for
developed areas. (Water bodies from the USGS topographic maps are overlaid for
orientation, and areas identified as undeveloped in the National Land Cover dataset are
left white.)
Soil moisture maps can be generated using the vegetation and surface
temperature data with a surface climate model. The gray-scale image is dark
for surfaces with a dried out top layer and bright or white for surfaces that are
wet. This information can be used to locate areas with very moist surface
layers near identified wetlands that can be easily converted to wetlands
themselves.
woody wetlands classified by
the National Land Cover
Dataset (NLCD)
forested, non-tidal wetlands
classified by the Army Corps
of Engineers
Defining LID Technology
Major Components
1.
2.
3.
4.
Conservation (Watershed and Site Level )
Minimization (Site Level)
Strategic Timing (Watershed and Site Level)
Integrated Management Practices (Site Level)
Retain / Detain / Filter / Recharge / Use
5. Pollution Prevention
Traditional Approaches
“Initial”
Low-Impact Development
Hydrologic Analysis and
Design
• Based on NRCS technology, can be applied
nationally
• Analysis components use same methods as
NRCS
• Designed to meet both storm water quality
and quantity requirements
Hydrograpgh Pre/
Post Development
Developed Condition, Conventional CN
(Higher Peak, More Volume, and Earlier Peak
Time)
Q
Existing Condition
Losses
T
Detention Peak
Shaving
Developed
Developed Condition, with Conventional
CN and Controls
Q
Existing Peak Runoff Rate
Additional Runoff Volume
Existing
T
Developed- No Controls
Reduced Qp
Minimize
Change in
Curve
Number
Developed Condition, with LID- CN
no Controls.
Reduced Runoff Volume
Q
Existing
T
Maintain Time
of Concentration
Developed,
LID-CN
no controls
Reduced
Qp
Developed, LID- CN no controls
same Tc as existing condition.
Q
More Runoff Volume
than the existing condition.
Existing
T
Reducing Volume
Q
Provide Retention
storage
so that the runoff
volume will be
the same as
Predevelopment
A1
A2
A3
T
Retention storage needed to
reduce
the CN to the existing condition
= A2 + A3
Detention Storage
Provide additional detention
storage to reduce peak discharge
to be equal to that of the existing
condition.
Q
Predevelopment Peak Discharge
Existing
T
Comparison of
Hydrographs
Increased Volume
w/ Conventional
Conventional Controls
Q
LID Concepts
A2
A3
Existing
T
Hydrograph Summary
4
Q
5
Pre-development
Peak Runoff
Rate
1
Existing
2
Developed, conventional CN, no control.
3
Developed, conventional CN and control.
4
Developed, LID-CN, no control.
5
Developed, LID-CN, same Tc.
6
Developed, LID-CN, same Tc, same CN with
retention.
7
Same as 6 , with additional detention to
maintain Q.
2
7
3
6
1
T
Disconnecting Impervious Areas
to Reduce CN
CNc = CNp + (Pimp/100) (98-CNp) (1-0.5 R)
Where:
CNc = Composite Curve Number
CNp = Pervious Curve Number
Pimp = Percent Impervious
R = Ratio of Disconnected to Total Imperviousness
Comparison of Conventional
and LID Site Conditions
Comparison of Conventional and L I D
Curve Numbers (CN)
for
1- Acre Residential Lots
Conventional CN
20 % Impervious
80 % Grass
Low Impact Development CN
15 % Impervious
25 % Woods
60 % Grass
Curve Number is reduced by using LID Land Uses.
Determining LID BMP Size
Basic Idea: If you can maintain Tc, storage capacity
can be based on curve number difference only.
8% BMP
LID Manual
H and H
Process
Comparison of Conventional and L I D
Curve Numbers (CN)
for
1- Acre Residential Lots
Conventional CN
20 % Impervious
80 % Grass
Low Impact Development CN
15 % Impervious
25 % Woods
60 % Grass
Curve Number is reduced by using LID Land Uses.
Developed- No Controls
Reduced Qp
Minimize
Change in
Curve
Number
Developed Condition, with LID- CN
no Controls.
Reduced Runoff Volume
Q
Existing
T
Vegetated Swale
Infiltration
Buffer Strip
Dry & Wet
Detention Pond
Gross
Pollutant Trap
Wetlands
Source
Node
Vegetated Swale
BMP Evaluation Computer
Module
Prince George’s County, Maryland
Target Pollutants
• Suspended Solids
• Nutrients
– Nitrogen (nitrate, ammonia, organic nitrogen)
– Phosphorus
• Metals (copper, lead, zinc)
• Oil & Grease
BMP Evaluation
Method
HSPF LAND
SIMULATION
Existing Flow &
Pollutant Loads
– Unit-Area Output by Landuse –
SITE-LEVEL LAND/BMP ROUTING
Simulated
Surface Runoff
Total Rainfall (in)
Modeled Flow
250
0
1
2
Flow (cfs)
3
150
4
5
100
6
Total Rainfall (in)
200
7
50
8
9
0
2/20/99
BMP DESIGN
– Site Level Design –
10
6/20/99
10/20/99
2/20/00
6/20/00
10/20/00
Time
Simulated Flow/Water Quality Improvement
Cost/Benefit Assessment of LID design
N.B.: Good design may need to go beyond period of record.
100
Phosphorus
% Removal
80
60
Phosphorus
40
20
Box S1
Box S2
Greenbelt
Landover
Box L
0
0
20
40
60
80
100
120
140
Bioretention Depth (cm)
100
Calibrated
BMPs!!!
% Removal
80
b. Lead
Lead
60
40
20
0
0
Box S1
Box S2
Greenbelt
Landover
20
40
Box L
60
80
Bioretention Depth (cm)
100
120
140
HSPF Land Use
Representation
BMP Physical Processes
• Possible storage processes include:
–
–
–
–
–
–
–
–
Evapotranspiration
Infiltration
Orifice outflow
Weir-controlled overflow spillway
Underdrain outflow
Bottom slope influence
Bottom roughness influence
General loss or decay of pollutant
(Due to settling, plant-uptake, volatilization, etc)
– Pollutant filtration through soil medium
(Represented with underdrain outflow)
• Depending on the design and type of the BMP, any
combination of processes may occur during simulation
BMP Class A:
Storage/Detention
Inflow:
Evapotranspiration
Outflow
:
Modified Flow &
Water Quality
From Land Surface
Overflow
Spillway
Storage
Bottom
Orifice
Infiltration
Underdrain
Outflow
BMP Class B: Open
Channel
Inflow:
Outflow:
From Land Surface
Modified Flow &
Water Quality
Evapotranspiration
Overflow at
Max Design
Depth
Open Channel Flow
Modified Flow &
Water Quality
Underdrain Outflow
Infiltration
Holtan Infiltration Model
f  GI A S
1.4
a
 fc
veg. parameter
(A)
Ds
soil porosity
soil fc
Du
void fraction
background f c
General Water Quality
First Order Decay Representation
Mass2 = Mass1 x e – k
t
Pollutant Removal
is a function of the
detention time
Underdrain Water Quality
Percent Removal
Massout = Massin x (1 - PCTREM)
Underdrain percent
removal is a function
of the soil media
Massin = Surface conc * underdrain flow
Soil moisture maps can be generated using the vegetation and surface
temperature data with a surface climate model. The gray-scale image is dark
for surfaces with a dried out top layer and bright or white for surfaces that are
wet. This information can be used to locate areas with very moist surface
layers near identified wetlands that can be easily converted to wetlands
themselves.
woody wetlands classified by
the National Land Cover
Dataset (NLCD)
forested, non-tidal wetlands
classified by the Army Corps
of Engineers
Ground Truthing Image
Moving From Calibrated
“Sophisticated” Watershed
Models to Design Tools
Milwaukee Metropolitan
Sewer District (MMSD) LID
Model
• Ideas from LID awareness
conference/seminar
• Local Builder liked it and is using it
• School programs on planting trees and
reducing asphalt
• Keeper of the mega model liked idea
Model Highlights
• Need retrofit technologies for highly
impervious areas
• Need retrofit approach for build out of
conventional and centralized areas
• Need simple analysis tools for engineers
Highlights of approach
•
•
•
•
•
•
•
•
Volume based to control low peak rate (x cfs/acre)
Uses NRCS Methods
Outputs to NRCS Methods
Includes “Typical LID CNs
Limited Input
Graphical Output
Minimal Training
Transparent (No Big Black Box)
LID Site Hydrology
page 1 of 2
USER INPUT Enter data into the shaded boxes only.
PRECIPITATION and DRAINAGE AREA
100 years
Return period for this storm event.
qTarget
0.50 cfs/acre
Peak flow max.
See User Manual to select the value.
NRCS Type II
Rainfall distribution. See RainDistribution sheet to change.
P
5.88 inches
Total precipitation.
A
10.0 acres
Drainage area.
CN minimum
25
CNs must be greater than this value to generate runoff.
NoLID DESIGN
CN
83 Area-weighted average for the NoLID site design.
Tc
15 minutes
Cannot be less than 5 minutes.
LID DESIGN
CN
Event and Area
Uncontrolled
Standard CN Determination
76 Area-weighted average for the LID site.
CN’s
Optional CN Determination
If option not used, enter zeroes in Lines 4b-4d.
74 Composite CNp for pervious areas alone.
30% Actual percent impervious.
0 Ratio of unconnected impervious area to total impervious area.
(Enter "0" as the ratio if total impervious area is greater than 30% of site.)
CN result:
81 (The "CNc" in TR-55 Appendix F)
CNp
Pimp
Selected CN
Tc
81 Enter the value from Line 4a or Line 4e.
30 minutes
Cannot be less than 5 minutes.
LID Retention Features
Rain Garden Capacity
6.0 inches
30.0 inches
0.1 (unitless)
Result:
9.0
Rain Garden
Coverage
55.0 gallons
400
Green Roofs
3.0 inches
0.50
100000 sq.ft.
Permeable
Pavement
Other
Design Volume
acregallons
feet
(thousand)
0.15
49
2.0% of drainage area used for rain gardens.
(average of top and bottom areas)
Rain
Barrels
Cisterns
Average ponding depth.
Average soil mix depth.
Average fillable porosity.
inches
Capacity per unit area.
Capacity of each rain barrel.
Number of rain barrels.
0.07
22
Maximum Water Capacity (MWC).
Multiplier between 0.33 and 0.67.
Area.
0.29
94
0.23
75
Storage depth, or capacity per unit area.
Area.
0.19
62
Additional storage not listed above.
0.02
7
0.95
309
10000 cu.ft.
5.0 inches
20000 sq.ft.
1000 cu.ft.
Total
IMP’s
Target
NoLID
LID
Detention
6
5
q (cfs/acre)
4
3
2
1
0
8
9
10
11
12
13
14
15
16
17
18
t (hours)
Instant Graphing of Results
(including detention/retention)
Multi-column hydrograph for
1
0.0
14.4
10.0
4.8
3.1
2.3
1.9
1.7
1.5
1.3
1.2
1.1
1.1
1.0
0.9
0.9
0.8
0.7
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.5
0.1
0.0
0.100 timestep
2
3
0.3
2.0
16.3
16.0
8.4
7.2
4.3
3.9
2.9
2.7
2.2
2.1
1.8
1.8
1.7
1.6
1.5
1.4
1.3
1.3
1.2
1.2
1.1
1.1
1.0
1.0
1.0
1.0
0.9
0.9
0.9
0.8
0.8
0.8
0.7
0.7
0.7
0.7
0.7
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.4
0.3
0.1
0.1
0.0
0.0
4
5.6
14.3
6.2
3.6
2.6
2.0
1.8
1.6
1.4
1.2
1.2
1.1
1.0
1.0
0.9
0.8
0.8
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.2
0.0
0.0
Readhyd Card for TR-20
5
10.4
12.0
5.4
3.3
2.4
1.9
1.7
1.5
1.4
1.2
1.1
1.1
1.0
0.9
0.9
0.8
0.7
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
0.2
0.0
0.0
Limitations
•
•
•
•
•
•
Accounting on a watershed scale
Link to WQ model and WQ calcs
ROUTING!!!
No groundwater recharge
End of pipe answer
Size (15 meg) no emailing here
Who else is doing this type of
Modeling Stuff
• New Jersey (includes groundwater recharge component,
YEAH!!!)
• North Carolina
• Delaware (DURMM)
• Virginia COE (Checklist)
• Puget Sound (HSPF)
• WinSlamm
• Proprietary Engineering
• Vendors (PCSWMM for Pavers Unilock™)
SIMPLIFIED DURMM BMP DESIGN
PROJECT:
HUNDRED:
SUBAREA:
BMP:
NEW PROJECT
PENCADER
COUNTY:
NEW CASTLE
BYPASS SUBAREA
HYDROGRAPH
STANDARD
FILTER STRIPS, BIOFILTRATION, BIOSWALE
POSTDEVELOPMENT LOAD DATA
PARAMETER
TSS
PP
SP
ON
INPUT CONCENTRATION
PREPARED BY
INTEGRATED LAND MANAGEMENT, INC.
DATE:
August 10, 2001
NH3
NO3
Cu
Zn
175.8
0.83
0.56
1.98
0.23
0.49
0.013
0.242
88
INPUT MASS LOADS (g)
63,698
300
202
719
85
178
5
INCREASE IN SUBAREA LOAD
(112,065)
202
179
538
60
149
4
79
% PREDEVELOPMENT LOAD
-64%
205%
788%
299%
244%
502%
1128%
922%
BMP DESIGN AND PERFORMANCE
% IMPER. Q
25%
INPUT LOAD
FILTER
STRIPS
OUTPUT CONC .
OUTPUT LOAD
PERCENT REMOVAL
LINEAR LOAD (cu.ft./ft.)
% IMPER. Q
25%
INPUT LOAD
OUTPUT CONC .
BIORETENTION
OUTPUT LOAD
PERCENT REMOVAL
HYDRAULIC LOAD (ft.)
BIOSWALE
QUALITY
800
75
WIDTH
51
15
180
SLOPE
21
1%
45
SUM OK?
1.17
OK
21.97
32.7
2,081
0.53
33.5
0.47
29.8
0.83
52.8
0.25
15.9
0.49
31.0
0.006
0.38
0.037
2.33
87%
3.22
55%
TO BMP
41%
3207
71%
FROM BMP
26%
2244
LENGTH
100
NET WIDTH
50
BIO WIDTH
20
LOAD OK?
14,130
67
45
159
19
40
1.04
19.45
5.3
327
0.04
2.6
0.23
14.5
0.90
56.0
0.23
14.2
0.47
29.0
0.003
0.21
0.002
0.15
98%
1.29
96%
TO BMP
68%
2838
65%
FROM BMP
25%
2187
SIDES:1
4
BOTTOM
% IMPER. Q
25%
LENGTH
300
SLOPE
2%
COVER
4
VELOCITY
67
45
159
19
14.02
890
94%
17.95
0.07
4.2
94%
TO BMP
0.39
24.9
44%
2765
0.68
43.2
73%
FROM BMP
0.25
15.9
16%
2243
EVENT
PRECIP.
PREDEV
RUNOFF
QUALITY
BANKFULL
CONVEYANCE
FLOODING
2.0
2,831
11,916
9,085
3.3
10,100
25,596
15,496
5.2
28,054
50,334
22,280
7.3
54,400
81,291
26,891
RESIDENCE TIME (min.)
POSTDEV
INCREASE
RUNOFF
31%
68%
RUNOFF REDUCTION
27%
80%
RUNOFF REDUCTION
89%
30%
OK
99%
23%
SWALE OK?
8
DEPTH
0.28
14,130
INPUT LOAD
OUTPUT CONC .
OUTPUT LOAD
PERCENT REMOVAL
BIOSWALE
VOLUME
LENGTH
15,965
40
1.04
0.31
0.005
19.9
0.32
50%
69%
RUNOFF REDUCTION
REQUIRED VOLUME
CU.FT.
PERCENT
5053
56%
8285
53%
12847
58%
17765
66%
0.16
19.45
0.043
2.71
86%
19%
SWALE DEPTH
AVERAGE
PEAK
0.35
0.58
0.89
1.23
0.70
1.15
1.78
2.47
0.90
81%
5.20
94%
SUMMARY OF SURFACE FILTERING PERFORMANCE
OUTPUT MASS LOADS (g)
3,298
95%
PERCENT REMOVAL
INFILTRATION
TRENCH
RATE
40.3
87%
69.2
66%
151.9
79%
45.9
46%
79.8
55%
3.5
% BMP RUNOFF
50%
WIDTH:
2.0
LENGTH:
300
DEPTH:
POROSITY
38%
% CLAY
16%
% SAND
35%
TO SHWT
2,198
26.8
TO BMP
46.1
3337
101.3
FROM BMP
30.6
2224
OUTPUT LOAD
RESIDENCE TIME (hr.)
24
RATE OK?
INFIL. RATE
53.2
0.60
RUNOFF REDUCTION
5
0.27
3.46
33%
SUMMARY OF TOTAL BMP PERFORMANCE
OUTPUT MASS LOADS (g)
1,100
13.4
23.1
50.7
15.3
26.6
0.30
1.73
PERCENT REMOVAL
98%
1%
96%
14%
89%
102%
93%
28%
82%
62%
85%
90%
94%
79%
98%
20%
% OVER PREDEVELOPMENT
Annual Groundwater Recharge Analysis (based on GSR-32)
Select Township
↓
Average
Annual P
(in)
Climatic
Factor
MIDDLESEX CO., PERTH AMBOY CITY
47.8
1.53
Existing Conditions
Proposed Conditions
Area
(acres)
LULC
Soil
Annual
Recharge
(in)
Annual
Recharge
(cu.ft)
Land
Segment
1
1.4
landscape open space
Woodstown
2
0.3
unvegetated
Woodstown
12.9
65,498
6.9
7,536
3
3.5
wooded - general
4
1.4
landscape open space
Woodstown
13.5
Keyport
13.4
5
0.5
unvegetated
Keyport
6
3.3
wooded - general
7
0
8
Land
Segment
Soil
Annual
Recharge
(in)
unlandscaped developed
Keyport
0.0
-
unvegetated
Woodstown
6.9
40,191
landscape open space
Keyport
13.4
177,667
landscape open space
Woodstown
12.9
170,762
0
brush
Adelphia
-
-
6
0
landscape open space
Adelphia
-
-
-
7
0
landscape open space
Adelphia
-
-
-
-
8
0
landscape open space
Adelphia Variant
-
-
Adelphia
-
-
9
0
landscape open space
Adelphia
-
-
Adelphia
Total
Annual
Recharge
(in)
Total
Annual
Recharge
(cu-ft)
10
0
landscape open space
Abbottstown
Total
Annual
Recharge
(in)
Total
Annual
Recharge
(cu.ft)
Area
(acres)
LULC
1
1.5
2
1.6
171,255
3
3.65
68,146
4
3.65
7.5
13,657
5
Keyport
13.9
165,963
brush
Adelphia
-
0
brush
Adelphia
9
0
brush
10
0
brush
Total =
10.4
13.0
Total =
10.4
Annual Recharge Requirements Calculation
492,054
Procedure to fill the Existing Conditions and Proposed Conditions Tables
% of Existing Annual Recharge to Preserve =
For each land segment, first enter the area, then select LULC, then select Soil. Start from the top of table
The Required Annual Recharge Volume (cu.ft) =
and proceed downward. Don't leave blank rows (with A=0) in between your segment entries.
Rows with A=0 will not be displayed or used in calculations. For impervious areas outside of standard lots
select "unlandscaped developed" as the LULC. Soil type for impervious areas are only required if an infiltration facility will be built within these areas.
10.3
100%
103,435
Recharge Efficiency parameters Calculations (area averages)
3.94
(in)
DRWC= 3.94
(in)
ERWC = 0.93
(in)
EDRWC= 0.93
(in)
RWC=
Annual
Recharge
(cu.ft)
388,620
Where to go from here?
• Multimedia and calibrated models
• Clearinghouses and Databases on
effectiveness (ASCE)
• More rigorous calibrated models
• Optimization!!!
• Better Costing
WWW.LID-Stormwater.net/Clearinghouse