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Impacts of Impervious Cover

Impacts of Impervious Cover. Lecture 6 – ENSC 202. Urban Sprawl. Sprawl is dispersed, automobile-dependent development outside of compact urban and village centers along highways and in rural countryside. Sprawl & Impervious Cover. Center for Watershed Protection 2003.

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Impacts of Impervious Cover

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  1. Impacts of Impervious Cover Lecture 6 – ENSC 202 ENSC 202 – 2004 Impervious Cover

  2. Urban Sprawl Sprawl is dispersed, automobile-dependent development outside of compact urban and village centers along highways and in rural countryside. ENSC 202 – 2004 Impervious Cover

  3. Sprawl &ImperviousCover Center for Watershed Protection 2003 ENSC 202 – 2004 Impervious Cover

  4. Sprawl and Water Quantity • Higher highs/lower lows • Intensification/flashiness Center for Watershed Protection (2003) ENSC 202 – 2004 Impervious Cover

  5. Runoff as a function of Imperviousness Center for Watershed Protection (2003) after Schueler (1987) ENSC 202 – 2004 Impervious Cover

  6. Stream Enlargement due to IC ENSC 202 – 2004 Impervious Cover

  7. Fine Sediment Deposition due to IC ENSC 202 – 2004 Impervious Cover

  8. Impacts of Deposited Sediments Center for Watershed Protection (2003) ENSC 202 – 2004 Impervious Cover

  9. Impacts of Suspended Sediments Center for Watershed Protection (2003) ENSC 202 – 2004 Impervious Cover

  10. Stormwater contains more than sediments …note the wide ranges State of Maine (1995) ENSC 202 – 2004 Impervious Cover

  11. Pollutant concentrations differby land use A measure of variance in the data. Burton and Pitt (2002) Stormwater Effects Handbook ENSC 202 – 2004 Impervious Cover

  12. National Event Mean Concentrations ENSC 202 – 2004 Impervious Cover Center for Watershed Protection (2003)

  13. The ‘Simple Method’ for calculating runoff loading from stormwater Step 1 – What portion of the ‘effective’ rainfall becomes runoff? Rv = 0.05 + (0.9 * IA) where Rv = runoff coefficient IA = impervious area (%) from Impacts of Impervious Cover on Aquatic Systems, p. 61 (CWP 2003) ENSC 202 – 2004 Impervious Cover

  14. The ‘Simple Method’ for calculating runoff loading from stormwater Step 2 – How much total runoff is there in a typical year? R = P * Pf * Rv where R = runoff (inches) P = precipitation (inches) Pf = fraction of rain events that produce runoff (~0.9) Rv = runoff coefficient (Step 1) ENSC 202 – 2004 Impervious Cover Note unfortunate mix of English and Metric units!

  15. The ‘Simple Method’ for calculating runoff loading from stormwater Step 3 – How much total loading occurs due to this runoff? L = U * R * C * A where L = loading in lbs U = unit conversion = 0.226 R = runoff (inches, Step 2) C = concentration (EMC, mg/L) A = area (acres) Can be modified for bacteria ENSC 202 – 2004 Impervious Cover

  16. Loss of LWD due to IC ENSC 202 – 2004 Impervious Cover

  17. Biotic Impacts ofImperviousArea Center for Watershed Protection (2003) as noted. ENSC 202 – 2004 Impervious Cover

  18. Sprawl, impervious area, & impairment Center for Watershed Protection 2003 ENSC 202 – 2004 Impervious Cover

  19. Impaired Rivers Burton and Pitt (2002) Stormwater Effects Handbook ENSC 202 – 2004 Impervious Cover

  20. Impaired Lakes Burton and Pitt (2002) Stormwater Effects Handbook ENSC 202 – 2004 Impervious Cover

  21. 100 80 60 Index of Biotic Integrity (IBI) 40 20 0 0 10 20 30 40 50 Percent watershed impervious cover Imperviousness and habitat qualityVariation within a watershed Fairfax County (2001) in CWP (2003) ENSC 202 – 2004 Impervious Cover

  22. Index of Biotic Integrity (IBI) Total watershed impervious cover Variation among watersheds ENSC 202 – 2004 Impervious Cover Horner and May (1999) in CWP (2003)

  23. Measuring Impervious Cover • Direct measurements • Inferred measurements • from land use • from road density • from population Total versus Effective or Net IC ENSC 202 – 2004 Impervious Cover

  24. Stormwater management matters ENSC 202 – 2004 Impervious Cover

  25. Mission of the VermontWater Resources Board “To ensure that rules which guide the management of Vermont's water resources and wetlands are adopted and (on appeal) are interpreted, by a citizen board which is independent of the Agency of Natural Resources (ANR).” ENSC 202 – 2004 Impervious Cover

  26. The WRB Stormwater ‘Docket’ “The purpose of the Docket is to create a forum for discussing the technical issues related to developing clean up plans for waters of the state impaired by stormwater in Vermont.” “The intended outcome of the Docket is …[to summarize] technical information…and to …provide recommendations for developing clean up plans for Vermont’s stormwater impaired waters…” ENSC 202 – 2004 Impervious Cover

  27. Key Questions in the WRB Docket • Is it feasible to use ‘source control’ as a primary option? • Can improvements be achieved in 5 years? • Can we separate and deal with natural vs man-made sources of pollutants? • Is a TMDL approach the best way to address clean up streams impaired by stormwater? • Are stormwater ‘offsets’ a reasonable approach to stormwater management? • Can we predict how ‘indicators’ of impairment will respond to stormwater treatment strategies? • What is the best way to evaluate progress toward desired goals? • What are the best ‘targets’ to judge when we have attained desirable goals? • If we can’t attain the standards we want, what should we do? ENSC 202 – 2004 Impervious Cover

  28. Extra ENSC 202 – 2004 Impervious Cover

  29. Redesigning the American NeighborhoodDeveloping an Ecological & Socioeconomic Framework for Effective Stormwater Management Purpose: To develop tools that will allow stakeholders, regulators, and researchers to visualize alternative future environmental states that they imagine collectively and then to optimize the mix of interventions at various scales, that will best balance environmental and social, as well as economic, criteria. ENSC 202 – 2004 Impervious Cover

  30. Effectiveness: unknown Orientation: source control Cost: uncertain – low? Risk: unknown – medium/high Effectiveness: uncertain Orientation: local protection Cost: known - medium Risk: uncertain - medium Effectiveness: known – depends Orientation: downstream protection Cost: known - high Risk: known - low Why focus on scale? ENSC 202 – 2004 Impervious Cover

  31. Why focus on scale? Clearly, a mix of interventions is desirable. But what mix? For what purpose? Located where? ENSC 202 – 2004 Impervious Cover

  32. Primary Goal Quantify the balances among environmental, economic, and social costs and benefits for storm water management at whole-watershed, neighborhood, and individual house scales in a typical New England landscape and climate. ENSC 202 – 2004 Impervious Cover

  33. Key Objectives • Assessment: What are the opportunities for intervention? • Evaluation: What are the comparative cost/benefits of these interventions? • Participation: How can we better involve community stakeholders to devise successful solutions? • Implementation: Can we demonstrate the these approaches work? ENSC 202 – 2004 Impervious Cover

  34. Project Focus Area ENSC 202 – 2004 Impervious Cover

  35. ButlerFarmSubdivision ENSC 202 – 2004 Impervious Cover

  36. Key Collaborations • US-EPA/SNR-UVM (McIntosh, Bowden, Todd, Voinov) • Partnership with South Burlington (JB Hoover) • Collaboration with key consultants (PEC, J Nelson) • Advice from key stakeholders (Project Working Groups) • EPA Demonstration grant (JB Hoover) • NRCD implementation grant (A. Willard, B. Gabos) ENSC 202 – 2004 Impervious Cover

  37. National and Vermont Standards • Comparison to selected VT Water Quality Standards • No TSS causing impairment • 0.010 – 0.054 mg/L total phosphorus • 2 and 5 mg/l nitrate for Class A and B waters • 10 ug/L acute, 8 ug/L chronic* • 23 ug/L acute, <1 ug/L chronic* • 57 ug/L acute, 52 ug/L chronic* • <<1 mg/L as pesticides and PCB’s • No oil or grease causing impairment • 18 E. coli cfu/100ml 3x in 30days (A1 and A2) • 33 E. coli cfu/100ml once (A1 and A2) • 77 E. coli cfu/100 ml (B) • at hardness of 50 mg/L ENSC 202 – 2004 Impervious Cover VT Water Quality Standards VT Stormwater Manual, Vol 2

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