The document discusses green infrastructure implications for the state of Tennessee. It provides definitions of green infrastructure and describes how green infrastructure can infiltrate, evapotranspire, or capture and reuse stormwater runoff to maintain natural hydrology. The document focuses on potential urban ecosystem benefits of green infrastructure such as increased infiltration, decreased erosion, and improved water quality. It examines how factors like soils, rainfall patterns, and hydrology vary across different regions in Tennessee and concludes that statewide green infrastructure policies can work if sufficient flexibility is allowed for individual sites. The document also models the impact of green infrastructure approaches like bioretention and disconnection of impervious surfaces. It finds that properly designed green infrastructure can help reduce runoff to pre-development

1. Green Infrastructure Implications
for Tennessee
Curt Jawdy, PE
865-310-4727

2. New MS4 Permit Language

3. Green Infrastructure is…
• “An approach to wet weather management that is cost-effective,
sustainable, and environmentally friendly. Green Infrastructure
management approaches and technologies infiltrate,
evapotranspire, capture and reuse stormwater to maintain or
restore natural hydrologies."
• “The interconnected network of open spaces and natural areas,
such as greenways, wetlands, parks, forest preserves and native
plant vegetation, that provide wildlife habitat, natural drainage,
recreational opportunities and help to sustain our Nation’s cities..."
• “A cost effective and environmentally friendly approach to
mitigating sewer overflows and works by diverting stormwater from
the sewer system and directing it to areas where it can be
infiltrated, evapotranspired or reused.

4. I will be focusing on…

5. Potential Urban Ecosystem Benefits
•Increased infiltration contributes
to reliable base flows.
•GI treatments decrease channel
erosion potential.
•Infiltration allows filtration of
suspended pollutants, resulting in
better water quality.
•GI is able to cool urban runoff by
allowing the ground media to
moderate temperatures.

6. • Infiltrate
– Bioretention/rain gardens
– Pervious pavement
– Vegetated swales
• Evapotranspire
– Bioretention/rain gardens
– Tree planters
– Vegetated swales
• Harvest and reuse
– Cisterns
– Rain barrels
Primary GI Pathways

7. Hydrograph
Pre-
developed
Urbanized
Urbanized
w/detention
Channel
Eroding
Flow

8. Flow Duration Curve
Storm Flows Mid Range Low FlowsMoist Conditions Dry Conditions
Pre-
developed
Decreased
Baseflow
Urbanized
Urbanized w/detention
Increased Erosive VolumeChannel
Eroding
Flow

9. Question 1:
• Do statewide hydrologic differences require
custom GI policies?
• a la Delaware

10. Median = 1.5%
Median = 7.0%
Median = 8.5%
Slopes

11. Hydrologic Soil Groups
Memphis HSGs
A
B
C
D
Nashville HSGs
A
B
C
D
Knoxville HSGs
A
B
C
D

12. Surface Soils
Knoxville
Nashville
Memphis

13. Soils at 36” Depth
Knoxville
Nashville
Memphis

14. 24-hr Rainfall Depth Exceedance
0
1
2
3
4
5
6
7
0 10 20 30 40 50 60 70 80 90 100
Exceedance Frequency (%)
RainfallDepth(in)
Memphis
Nashville
Knoxville
Rainfall Patterns

15. Surface Ponding Runoff
Surface Evaporation
Pre-Development SWMM Model
Infiltration per Green & Ampt
Unsaturated Soil
Saturated Soil
Water Table per moisture relations
Deep Percolation
Evapotranspiration • Goal
– Determine the water
balance prior to
development
• Parameters
– Soil physical
properties from
texture
– Slopes from GIS
– 3’ deep soil matrix
• Forcings
– Rainfall and PET for
1971-2006
Rainfall

16. Pre-developed Water Balance
Knoxville Water Balance
Evaporation
Direct
Runoff
GW
Recharge
Evapo-
transpiration
Memphis Water Balance
Evaporation
Direct
Runoff
GW
Recharge
Evapo-
transpiration
Nashville Water Balance
Evaporation
Direct
Runoff
GW
Recharge
Evapo-
transpiration
• Small differences for “average” conditions
• Some portion of GW recharge eventually becomes
quickflow and baseflow

17. State Hydrology Conclusions
• The variability of GI factors is greater within
counties than across the state, therefore
– Statewide policies make sense
– Significant flexibility must be available for
individual sites

18. Question 2:
• What impact will the 1” runoff reduction
requirement have on land use and runoff
volume?

19. Define “inch”
• Capture runoff from a 1” storm
• What intensity of storm?
– Assume 1” in 1 hr
Runoff Bed Depth Bed Area Bed Area Bed Area
(in) (ft) (sf) (% of total) (% of pervious)
Knoxville Exurbs (2 acre) 0.112 3 3388 0.8% 0.9%
Knoxville Suburbs (1 acre) 0.187 3 5656.75 1.3% 1.6%
Knoxville Residential (1/4 acre) 0.355 3 10738.75 2.5% 4.0%
Knoxville Townhomes (1/8 acre) 0.61 3 18452.5 4.2% 12.1%
Knoxville Commercial 0.794 3 24018.5 5.5% 36.8%
Knoxville Exurbs (2 acre) 1 3 30250 6.9% 7.9%
Knoxville Suburbs (1 acre) 1 3 30250 6.9% 8.7%
Knoxville Residential (1/4 acre) 1 3 30250 6.9% 11.2%
Knoxville Townhomes (1/8 acre) 1 3 30250 6.9% 19.8%
Knoxville Commercial 1 3 30250 6.9% 46.3%
ScenarioCriteria
1"overan
hour
1"pure
runoff
Location

20. Urbanization Effects on Land
Landuse
%
Impervious
Flow
Length (ft)
Ponding
Depth (in)
Pre-developed 0 300 0.35
Exurbs (2 acre lots) 12 200 0.3
Suburbs (1 acre lots) 20 150 0.25
Residential (1/4 acre lots) 38 100 0.2
Townhomes (1/8 acre lots) 65 75 0.15
Commercial 85 50 0.15
• Pre-development models were altered to represent
conditions after settlement
• Impervious areas were routed directly out to
represent a piped conveyance system

21. Surface Evaporation
Infiltration per Green & Ampt
Evapotranspiration
Unsaturated Media
Saturated Media
Water Table per moisture relations
Deep Percolation
Surface PondingSurface Ponding Runoff
Surface Evaporation
Runon
3’ Deep Bioretention Model
Infiltration per Green & Ampt
Unsaturated Soil
Saturated Soil
Water Table per moisture relations
Deep Percolation
Evapotranspiration
Source Area GI Facility
Rainfall Rainfall

22. Memphis Bioretention
Memphis 1" Runoff Bioretention
0%
10%
20%
30%
40%
50%
60%
70%
80%
12 20 38 65 85
Imperviousness (%)
Runoff(%)
Developed
Developed w/Bioretention
Pre-development target
Pre-Development
Level

23. Nashville Bioretention
Nashville 1" Bioretention
0%
10%
20%
30%
40%
50%
60%
70%
80%
12 20 38 65 85
Imperviousness (%)
Runoff(%)
Developed
Developed w/Bioretention
Pre-development target
Pre-Development
Level

24. Knoxville Bioretention
Knoxville 1" Bioretention
0%
10%
20%
30%
40%
50%
60%
70%
80%
12 20 38 65 85
Imperviousness (%)
Runoff(%)
Developed
Developed w/Bioretention
Pre-development target
Pre-Development
Level

25. Question 3:
• How much does soil infiltration rate affect GI
performance?

26. Infiltrating
flow w/o
runoff
Media has
saturated and
begun to
create a water
table
Runoff occurs
only when
media and
ponding depth
are both full
Causes of
Runoff
• Flow out of
the cell is
the limiting
factor
• VERY few
storms can
overwhelm
the inflow
capacity

27. 0
5
10
15
20
25
30
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
SiteRunoff(in/yr)
Bioretention Percolation Out Rate (in/hr)
3' Deep BioretentionatCommercial Site in Knoxville

28. Importance of Testing
• Infiltration rates can vary
significantly over small
areas
• Tests must be performed
at the bottom of proposed
facilities
• Siting facilities well is
crucial

29. Question 4:
• Do I have any alternatives to putting in
constructed GI facilities at sites with tight
soils?

30. Impervious Disconnection
• Is the practice of directing
runoff from impervious
areas to flow over pervious
areas and thus allowing
infiltration
• Goal: check for possibility
for maintaining pre-
development hydrology
• Method: model various
levels of development with
disconnection

31. Memphis Disconnection
Memphis Disconnection
0%
10%
20%
30%
40%
50%
60%
70%
80%
12 20 38 65 85
Imperviousness (%)
Runoff(%)
Developed
Developed w/Disconnection
Pre-development target
Pre-Development
Level

32. Nashville Disconnection
Nashville Disconnection
0%
10%
20%
30%
40%
50%
60%
70%
80%
12 20 38 65 85
Imperviousness (%)
Runoff(%)
Developed
Developed w/Disconnection
Pre-development target
Pre-Development
Level

33. Knoxville Disconnection
Knoxville Disconnection
0%
10%
20%
30%
40%
50%
60%
70%
80%
12 20 38 65 85
Imperviousness (%)
Runoff(%)
Developed
Developed w/Disconnection
Pre-development target
Pre-Development
Level

34. Additional Options
• Reuse BMPs
– Reuse water for toilets
• AMEC work in Nashville showed reasonably sized cisterns can
provide 40% - 80% runoff reduction
– Reuse water for irrigation
– Reuse water for cooling towers
– Reuse water for car washing
– Reuse water for ….
• Evapotranspiration BMPs
– Green Roofs
• AMEC work in Nashville showed ~55% runoff reduction
– Lush, shallow and large bioretention
– Trees

35. Question 5:
• Can we plan GI well with event storm
techniques?

36. Benefits of Event Storm Design
• Good at designing
facilities to handle
flood flows
• Simple
• Well-known

37. Event Storm Shortcomings
• False: A hypothetical
storm shape
represents actual
rainfall events
• True: Actual storm
shapes vary widely
– some runoff is caused
by saturation over a
long storm
– some runoff is caused
by overwhelming
rainfall intensity

38. Event Storm Shortcomings
• False: A 25-yr storm causes a 25-yr flood
• True: Existing soil moisture plays a large role
– especially for small storms (e.g. most storms)

39. Event Storm Shortcomings
• False: GI facilities
are always empty
at the beginning
of a storm
• True: GI facilities
may be partially
full

40. Event Storm Shortcomings
• False: Inter-storm periods aren’t important
• True: GI facilities mimic nature by evapotranspiring
and draining between storms
Nashville Water Balance
Evaporation
Direct
Runoff
GW
Recharge
Evapo-
transpiration

41. Single Continuous
Model Regulation
Regulate for outcomes:
– Baseflows, WQ & Channel Stability
Flow duration curve
– Flooding
Flow peaks for X, Y and Z real storms
– Infrastructure
Safe elevations for X, Y and Z real storms
Being used by several U.S. cities

42. FDC Standard
Storm Flows Mid Range Low FlowsMoist Conditions Dry Conditions
Disallow flow
increases here

43. I’m not sure we’re
ready for that…

44. Question 6:
• Is there any way to make this easier for my
local designers?

45. Are the current methods
really that simple?

46. Estimate BMP Area Required
Subcatchment Area 10 ha Bioretention Pervious Paving Veg. Swale Green Roof Cistern
% Impervious 50 % Media Depth (m) Media Depth (m) Media Depth (m) Media Depth (m) Storage Depth (m)
Capture Depth 25 mm 1 0.65 0 0.15 1
Porosity Porosity Porosity Porosity Porosity
0.4 0.4 0 0.58 1
Volumed Needed 1250 m3
Wilting Point Wilting Point Wilting Point Wilting Point Wilting Point
0.07 0.04 0 0.04 0
Effective Storage (m3
/m2
) Effective Storage (m3
/m2
) Effective Storage (m3
/m2
) Effective Storage (m3
/m2
) Effective Storage (m3
/m2
)
0.33 0.234 0.15 0.081 1
Area (m2
) Area (m2
) Area (m2
) Area (m2
) Area (m2
)
2000 2000 500 500 100
Total Storage (m3
) Total Storage (m3
) Total Storage (m3
) Total Storage (m3
) Total Storage (m3
)
660 468 75 40.5 100
Volume Supplied
1343.5 m3
• Should occur early in the planning process
and be easy enough for anyone to use
• Example above from AMEC work in
Edmonton

47. SWMM Municipal Water Template
• Free government software
with simple GI tools
• Handles all aspects of site
stormwater analysis
• Pre-load local data
– Long-term rainfall & PET
– Inlet grate parameters
– Soil and GI media parameters
– Pollutant generation by land use
– Pollutant removal by BMP
AMEC is preparing a
template for Knox Co.

48. SWMM Define Prototypes
1. Generic Section
3. Layer Specifics
2. Each prototype has
different layers

49. SWMM Place BMPs
• Simply define the area
for each BMP in each
subcatchment

50. Question 7:
• What about those difficult sites?

54. • Money for watershed projects!

55. Question 8:
• Great, where do I put them?

56. Difficulty of Location Choice
Channel
Improvement
Regional
Detention
Multiple
Bioretention
Cells
Pervious
Paving
Stormwater
Wetland
Flooding
Abatement
Volume/Quality
Abatement

57. GI Optimization
• Optimization routines
perform 1,000s of runs
to find the best mix

58. TN Optimization Trial
• SUSTAIN software
will be used to
optimize GI for a 600
ac. subdivision
• Results and lessons
learned will be shared
with MS4 Association
and AWRA

59. Let’s talk about:
Questions?