2010 tn green infrastructure

986 views

Published on

Published in: Education
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
986
On SlideShare
0
From Embeds
0
Number of Embeds
3
Actions
Shares
0
Downloads
17
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

2010 tn green infrastructure

  1. 1. Green Infrastructure Implications for Tennessee Curt Jawdy, PE 865-310-4727
  2. 2. New MS4 Permit Language
  3. 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. 4. I will be focusing on…
  5. 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. 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. 7. Hydrograph Pre- developed Urbanized Urbanized w/detention Channel Eroding Flow
  8. 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. 9. Question 1: • Do statewide hydrologic differences require custom GI policies? • a la Delaware
  10. 10. Median = 1.5% Median = 7.0% Median = 8.5% Slopes
  11. 11. Hydrologic Soil Groups Memphis HSGs A B C D Nashville HSGs A B C D Knoxville HSGs A B C D
  12. 12. Surface Soils Knoxville Nashville Memphis
  13. 13. Soils at 36” Depth Knoxville Nashville Memphis
  14. 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. 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. 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. 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. 18. Question 2: • What impact will the 1” runoff reduction requirement have on land use and runoff volume?
  19. 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. 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. 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. 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. 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. 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. 25. Question 3: • How much does soil infiltration rate affect GI performance?
  26. 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. 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. 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. 29. Question 4: • Do I have any alternatives to putting in constructed GI facilities at sites with tight soils?
  30. 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. 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. 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. 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. 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. 35. Question 5: • Can we plan GI well with event storm techniques?
  36. 36. Benefits of Event Storm Design • Good at designing facilities to handle flood flows • Simple • Well-known
  37. 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. 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. 39. Event Storm Shortcomings • False: GI facilities are always empty at the beginning of a storm • True: GI facilities may be partially full
  40. 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. 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. 42. FDC Standard Storm Flows Mid Range Low FlowsMoist Conditions Dry Conditions Disallow flow increases here
  43. 43. I’m not sure we’re ready for that…
  44. 44. Question 6: • Is there any way to make this easier for my local designers?
  45. 45. Are the current methods really that simple?
  46. 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. 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. 48. SWMM Define Prototypes 1. Generic Section 3. Layer Specifics 2. Each prototype has different layers
  49. 49. SWMM Place BMPs • Simply define the area for each BMP in each subcatchment
  50. 50. Question 7: • What about those difficult sites?
  51. 51. • Money for watershed projects!
  52. 52. Question 8: • Great, where do I put them?
  53. 53. Difficulty of Location Choice Channel Improvement Regional Detention Multiple Bioretention Cells Pervious Paving Stormwater Wetland Flooding Abatement Volume/Quality Abatement
  54. 54. GI Optimization • Optimization routines perform 1,000s of runs to find the best mix
  55. 55. 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
  56. 56. Let’s talk about: Questions?

×