Mission: • Stormwater Management

Technology• Pilot Projects, Monitoring,

Modeling, Manuals, Training, Education

The Low Impact Development Center, Inc.

Balancing Growth and Balancing Growth and Environmental IntegrityEnvironmental Integrity

LID ModelingLID Modeling

Why are We Modeling?

• Determine Effectiveness• Predict/Project (Pre-Post)• Calibration• “It’s Cheaper than Doing anything”• NC State needs more PhD’s

Regulatory Requirements

Resource Protection

Hard Stuff

• Peak Flow

• Water Quality

• Energy (Light, Thermal, Stream Power)

• Habitat

• Optimization

• Maintenance

• Optimization

Easy Stuff

How well do we maintain the ecological integrity How well do we maintain the ecological integrity (functions) of aquatic systems (small streams)?(functions) of aquatic systems (small streams)?

Chemical Chemical

VariablesVariables

Flow Flow

RegimeRegime

Habitat Habitat

StructureStructure

EnergyEnergy

SourcesSources

Biotic Biotic

FactorsFactors

Nutrients Nutrients Temperature Temperature

D.O. pH D.O. pH Turbidity Turbidity

Organics Organics ToxicsToxics

Disease Disease Reproduction Reproduction

Feeding Feeding Predation Predation

CompetitionCompetition

Sunlight Sunlight Nutrients Nutrients

Seasonal Cycles Seasonal Cycles Organic Matter Organic Matter

1&2 Production 1&2 Production

Canopy Canopy Siltation Siltation Gradient Gradient Substrate Substrate Current Current Instream Cover Instream Cover

Sinuosity Sinuosity Width/Depth Width/Depth

Channel Morphology Channel Morphology Soils Stability Soils Stability

Riparian VegetationRiparian Vegetation

Velocity Velocity Frequency Frequency

Runoff Runoff Evaporation Evaporation

Ground Water Ground Water Flow Duration Flow Duration Rain IntensityRain Intensity

Scale / Spatial / Temporal / SpeciesScale / Spatial / Temporal / Species

Ecosystem Ecosystem IntegrityIntegrity

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

3/2ARn

K

Simple WQ Stuff

72.212

ACRPP

L vj

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

dttQ

dttQtCC

)(

)()(

Bioretention

)())((

))((f

ff

rvf t

dhk

dWQA

RECHARGE

HYDROLOGIC CYCLE:

P+R+E+T

Optimization

A bioretention pond costs $2,000 to construct for a ½ site. So it costs $4,000 per acre.

First, it’s a cell not a pond!!

RJ

IJIJ QmcMC *

2

Region of Feasibility

Gazillions of Acceptable Solutions

Conventional Pipe and Pond Centralized Control

““Efficiency”Efficiency”

LID Uniform Distribution of Micro Controls

McCuen 2002

III

II

I

Runoff Hydrograph is Sensitive to Bioretention Placement

in II only

7

3

I

II

III

Hoffman and Crawford, 2000

Existing Problems and Future High Risks

Hoffman and Crawford, 2000

Remove Large Impervious Areas

Oversize Pipes

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 Defining LID Technology

Major Components 1. Conservation (Watershed and Site Level )

2. Minimization (Site Level)

3. Strategic Timing (Watershed and Site Level)

4. Integrated Management Practices (Site Level)Retain / Detain / Filter / Recharge / Use

5. Pollution PreventionTraditional Approaches

“Initial” Low-Impact Development Hydrologic Analysis and

Design

“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

Q

T

Developed Condition, Conventional CN(Higher Peak, More Volume, and Earlier Peak Time)

Existing Condition

Hydrograpgh Pre/ Post Development

Losses

Q

T

Developed Condition, with Conventional CN and Controls

Existing

Additional Runoff Volume

Developed

Existing Peak Runoff Rate

Detention Peak Shaving

Q

T

Developed Condition, with LID- CNno Controls.

Existing

Reduced Runoff Volume

Developed- No Controls

Reduced Qp

Minimize Change in Curve Number

Q

T

Developed, LID- CN no controlssame Tc as existing condition.

Existing

More Runoff Volumethan the existing condition.

Developed,LID-CNno controls Reduced Qp

Maintain Time of Concentration

Q

T

Provide Retention storage so that the runoffvolume will be the same as Predevelopment

Retention storage needed to reducethe CN to the existing condition= A2 + A3

A3

A2

A1

Reducing Volume

Q

T

Provide additional detention storage to reduce peak discharge to be equal to that of the existing condition.

Existing

Predevelopment Peak Discharge

Detention Storage

Q

T

Comparison of Hydrographs

A2

A3

LID Concepts

Conventional Controls

Existing

Increased Volumew/ Conventional

Q

T

2

3

4

1

5

6

7

Hydrograph Summary

2

3

4

1 Existing

Developed, conventional CN, no control.

Developed, conventional CN and control.

Developed, LID-CN, no control.

Developed, LID-CN, same Tc.

Developed, LID-CN, same Tc, same CN withretention.

Same as , with additional detention tomaintain Q.

6

5

6

7

Pre-developmentPeak Runoff Rate

Disconnecting Impervious Areas to Reduce CN

CNc = CNp + (Pimp/100) (98-CNp) (1-0.5 R)

Disconnecting Impervious Areas to Reduce CN

CNc = CNp + (Pimp/100) (98-CNp) (1-0.5 R)

Where: CNc = Composite Curve NumberCNp = Pervious Curve NumberPimp = Percent ImperviousR = 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

Comparison of Conventional and L I D Curve Numbers (CN)

for 1- Acre Residential Lots

Conventional CN

20 % Impervious80 % Grass

Low Impact Development CN

15 % Impervious25 % Woods60 % Grass

Curve Number is reduced by using LID Land Uses.

8% BMP

Determining LID BMP Size

Basic Idea: If you can maintain Tc, storage capacity can be based on curve number difference only.

LID Manual

H and H Process

Comparison of Conventional and L I D Curve Numbers (CN)

for 1- Acre Residential Lots

Comparison of Conventional and L I D Curve Numbers (CN)

for 1- Acre Residential Lots

Conventional CN

20 % Impervious80 % Grass

Low Impact Development CN

15 % Impervious25 % Woods60 % Grass

Curve Number is reduced by using LID Land Uses.

Q

T

Developed Condition, with LID- CNno Controls.

Existing

Reduced Runoff Volume

Developed- No Controls

Reduced Qp

Minimize Change in Curve Number

Source Node

Gross Pollutant Trap

Buffer Strip

Vegetated Swale

Vegetated Swale

InfiltrationDry & Wet Detention Pond

Wetlands

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

HSPF LAND SIMULATION

– Unit-Area Output by Landuse –

BMP Evaluation Method

Existing Flow & Pollutant Loads

Simulated Flow/Water Quality Improvement Cost/Benefit Assessment of LID design

0

50

100

150

200

250

2/20/99 6/20/99 10/20/99 2/20/00 6/20/00 10/20/00

Time

Flo

w (

cfs)

0

1

2

3

4

5

6

7

8

9

10

Tota

l Rai

nfal

l (in

)

Total Rainfall (in) Modeled Flow

BMP DESIGN– Site Level Design –

SITE-LEVEL LAND/BMP ROUTINGSimulatedSurface Runoff

N.B.: Good design may need to go beyond period of record.

b. Lead

0

20

40

60

80

100

0 20 40 60 80 100 120 140

Bioretention Depth (cm)

% R

emov

al

Box S1 Box S2 Box L

Greenbelt Landover

Phosphorus

0

20

40

60

80

100

0 20 40 60 80 100 120 140

Bioretention Depth (cm)

% R

em

ov

al

Box S1 Box S2 Box L

Greenbelt Landover

Phosphorus

LeadCalibrated BMPs!!!

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

Overflow Spillway

Bottom Orifice

Evapotranspiration

Infiltration

Outflow:

Inflow:

Modified Flow &Water Quality

From Land Surface

Storage

BMP Class A: Storage/Detention

Underdrain Outflow

BMP Class B: Open Channel

Outflow:Inflow:

From Land Surface

Overflow atMax Design

Depth

Open Channel Flow

Evapotranspiration

InfiltrationUnderdrain Outflow

Modified Flow &Water Quality

Modified Flow &Water Quality

Holtan Infiltration Model

veg. parameter

void fraction

soil porosity

soil fc D u

(A)

background f c

D s

f G I A S fa c 1 4.

General Water QualityFirst Order Decay Representation

Mass2 = Mass1 x e – k t

Pollutant Removal is a function of the

detention time

Underdrain Water QualityPercent Removal

Massout = Massin x (1 - PCTREM)

Underdrain percent Underdrain percent removal is a function removal is a function of the soil mediaof 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 2USER 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 DESIGNCN 83 Area-weighted average for the NoLID site design.Tc 15 minutes Cannot be less than 5 minutes.

LID DESIGNStandard CN Determination

CN 76 Area-weighted average for the LID site.

Optional CN Determination If option not used, enter zeroes in Lines 4b-4d.CNp 74 Composite CNp for pervious areas alone.

Pimp 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)

Selected CN 81 Enter the value from Line 4a or Line 4e.Tc 30 minutes Cannot be less than 5 minutes.

LID Retention Features

Rain Garden Capacity6.0 inches Average ponding depth.

30.0 inches Average soil mix depth.0.1 (unitless) Average fillable porosity. Design Volume

Result: 9.0 inches Capacity per unit area. acre- gallonsfeet (thousand)

Rain Garden 2.0% of drainage area used for rain gardens. 0.15 49Coverage (average of top and bottom areas)

Rain 55.0 gallons Capacity of each rain barrel.Barrels 400 Number of rain barrels. 0.07 22

Green Roofs 3.0 inches Maximum Water Capacity (MWC).0.50 Multiplier between 0.33 and 0.67.

100000 sq.ft. Area. 0.29 94

Cisterns 10000 cu.ft. 0.23 75

Permeable 5.0 inches Storage depth, or capacity per unit area.Pavement 20000 sq.ft. Area. 0.19 62

Other 1000 cu.ft. Additional storage not listed above. 0.02 7

Total 0.95 309

IMP’s

CN’s

Event and Area

Uncontrolled

0

1

2

3

4

5

6

8 9 10 11 12 13 14 15 16 17 18

t (hours)

q (

cfs

/ac

re)

Target NoLID LID Detention

Instant Graphing of Results (including detention/retention)

Multi-column hydrograph for 0.100 timestep1 2 3 4 5

0.0 0.3 2.0 5.6 10.414.4 16.3 16.0 14.3 12.010.0 8.4 7.2 6.2 5.44.8 4.3 3.9 3.6 3.33.1 2.9 2.7 2.6 2.42.3 2.2 2.1 2.0 1.91.9 1.8 1.8 1.8 1.71.7 1.7 1.6 1.6 1.51.5 1.5 1.4 1.4 1.41.3 1.3 1.3 1.2 1.21.2 1.2 1.2 1.2 1.11.1 1.1 1.1 1.1 1.11.1 1.0 1.0 1.0 1.01.0 1.0 1.0 1.0 0.90.9 0.9 0.9 0.9 0.90.9 0.9 0.8 0.8 0.80.8 0.8 0.8 0.8 0.70.7 0.7 0.7 0.7 0.70.7 0.7 0.7 0.7 0.70.7 0.7 0.7 0.7 0.70.7 0.7 0.7 0.7 0.70.7 0.7 0.6 0.6 0.60.6 0.6 0.6 0.6 0.60.6 0.6 0.6 0.6 0.60.6 0.6 0.6 0.6 0.60.5 0.4 0.3 0.2 0.20.1 0.1 0.1 0.0 0.00.0 0.0 0.0 0.0 0.0

Readhyd Card for TR-20

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™)

PROJECT: NEW PROJECTHUNDRED: PENCADER COUNTY:SUBAREA: BYPASS SUBAREA STANDARD

BMP: FILTER STRIPS, BIOFILTRATION, BIOSWALE

TSS PP SP ON NH3 NO3 Cu Zn

175.8 0.83 0.56 1.98 0.23 0.49 0.013 0.24263,698 300 202 719 85 178 5 88

(112,065) 202 179 538 60 149 4 79

-64% 205% 788% 299% 244% 502% 1128% 922%

% IMPER. Q 25% LENGTH 800 WIDTH 15 SLOPE 1% SUM OK? OK

INPUT LOAD 15,965 75 51 180 21 45 1.17 21.97

OUTPUT CONC . 32.7 0.53 0.47 0.83 0.25 0.49 0.006 0.037

OUTPUT LOAD 2,081 33.5 29.8 52.8 15.9 31.0 0.38 2.33

PERCENT REMOVAL 87% 55% 41% 71% 26% 31% 68% 89% LINEAR LOAD (cu.ft./ft.) 3.22 TO BMP 3207 FROM BMP 2244 30%

% IMPER. Q 25% LENGTH 100 NET WIDTH 50 BIO WIDTH 20 LOAD OK? OK

INPUT LOAD 14,130 67 45 159 19 40 1.04 19.45

OUTPUT CONC . 5.3 0.04 0.23 0.90 0.23 0.47 0.003 0.002

OUTPUT LOAD 327 2.6 14.5 56.0 14.2 29.0 0.21 0.15

PERCENT REMOVAL 98% 96% 68% 65% 25% 27% 80% 99%HYDRAULIC LOAD (ft.) 1.29 TO BMP 2838 FROM BMP 2187 23%

% IMPER. Q 25% LENGTH 300 SIDES:1 4 BOTTOM 8 SWALE OK? -

SLOPE 2% COVER 4 0.28 0.16

INPUT LOAD 14,130 67 45 159 19 40 1.04 19.45

OUTPUT CONC . 14.02 0.07 0.39 0.68 0.25 0.31 0.005 0.043

OUTPUT LOAD 890 4.2 24.9 43.2 15.9 19.9 0.32 2.71

PERCENT REMOVAL 94% 94% 44% 73% 16% 50% 69% 86%

RESIDENCE TIME (min.) 17.95 TO BMP 2765 FROM BMP 2243 19%

PREDEV POSTDEVRUNOFF RUNOFF CU.FT. PERCENT AVERAGE PEAK

2.0 2,831 11,916 9,085 5053 56% 0.35 0.703.3 10,100 25,596 15,496 8285 53% 0.58 1.155.2 28,054 50,334 22,280 12847 58% 0.89 1.787.3 54,400 81,291 26,891 17765 66% 1.23 2.47

3,298 40.3 69.2 151.9 45.9 79.8 0.90 5.20

PERCENT REMOVAL 95% 87% 66% 79% 46% 55% 81% 94%

% BMP RUNOFF 50% WIDTH: 2.0 LENGTH: 300 DEPTH: 3.5 RATE OK? -

POROSITY 38% % CLAY 16% % SAND 35% TO SHWT 5 INFIL. RATE 0.27

OUTPUT LOAD 2,198 26.8 46.1 101.3 30.6 53.2 0.60 3.46

RESIDENCE TIME (hr.) 24 TO BMP 3337 FROM BMP 2224 33%

1,100 13.4 23.1 50.7 15.3 26.6 0.30 1.73

PERCENT REMOVAL 98% 96% 89% 93% 82% 85% 94% 98%1% 14% 102% 28% 62% 90% 79% 20%

SUMMARY OF TOTAL BMP PERFORMANCE

INCREASEPRECIP.

SIMPLIFIED DURMM BMP DESIGN

INTEGRATED LAND MANAGEMENT, INC.

August 10, 2001

PREPARED BY

DATE:NEW CASTLE

HYDROGRAPH

PARAMETER

POSTDEVELOPMENT LOAD DATA

FLOODING

INFILTRATION TRENCH

OUTPUT MASS LOADS (g)

% OVER PREDEVELOPMENT

RUNOFF REDUCTION

SUMMARY OF SURFACE FILTERING PERFORMANCE

OUTPUT MASS LOADS (g)

BANKFULL

CONVEYANCE

RUNOFF REDUCTION

VELOCITY DEPTH

RUNOFF REDUCTION

BMP DESIGN AND PERFORMANCE

REQUIRED VOLUME SWALE DEPTH

QUALITY

EVENT

RUNOFF REDUCTION

% PREDEVELOPMENT LOAD

INCREASE IN SUBAREA LOAD

INPUT CONCENTRATION

INPUT MASS LOADS (g)

FILTER STRIPS

BIORETENTION

BIOSWALE QUALITY

BIOSWALE VOLUME

RATE

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

LandSegment

Area (acres)

LULC SoilAnnual

Recharge(in)

AnnualRecharge

(cu.ft)

LandSegment

Area (acres)

LULC SoilAnnual

Recharge(in)

AnnualRecharge

(cu.ft)

1 1.4 landscape open space Woodstown 12.9 65,498 1 1.5 unlandscaped developed Keyport 0.0 -

2 0.3 unvegetated Woodstown 6.9 7,536 2 1.6 unvegetated Woodstown 6.9 40,191

3 3.5 wooded - general Woodstown 13.5 171,255 3 3.65 landscape open space Keyport 13.4 177,667

4 1.4 landscape open space Keyport 13.4 68,146 4 3.65 landscape open space Woodstown 12.9 170,762

5 0.5 unvegetated Keyport 7.5 13,657 5 0 brush Adelphia - -

6 3.3 wooded - general Keyport 13.9 165,963 6 0 landscape open space Adelphia - -

7 0 brush Adelphia - - 7 0 landscape open space Adelphia - -

8 0 brush Adelphia - - 8 0 landscape open space Adelphia Variant - -

9 0 brush Adelphia - - 9 0 landscape open space Adelphia - -

10 0 brush Adelphia - - 10 0 landscape open space Abbottstown - -

Total = 10.4

TotalAnnual

Recharge(in)

TotalAnnual

Recharge(cu-ft)

Total = 10.4

TotalAnnual

Recharge(in)

TotalAnnual

Recharge(cu.ft)

13.0 492,054 10.3 388,620

Procedure to fill the Existing Conditions and Proposed Conditions Tables % of Existing Annual Recharge to Preserve = 100%

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) = 103,435

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 RWC= 3.94 (in) DRWC= 3.94 (in)

select "unlandscaped developed" as the LULC. Soil type for impervious areas are only required if an infiltration facility will be built within these areas. ERWC = 0.93 (in) EDRWC= 0.93 (in)

Existing Conditions Proposed Conditions

Recharge Efficiency parameters Calculations (area averages)

Annual Recharge Requirements Calculation

Where to go from here?

• Multimedia and calibrated models

• Clearinghouses and Databases on effectiveness (ASCE)

• More rigorous calibrated models

• Optimization!!!

• Better CostingWWW.LID-Stormwater.net/Clearinghouse