ENSC 202 2004

1
Impacts of Impervious Cover

• Lecture 6 ENSC 202

2
Urban Sprawl
Sprawl is dispersed, automobile-dependent
development outside of compact urban and village
centers along highways and in rural countryside.
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Sprawl ImperviousCover
Center for Watershed Protection 2003
4
Sprawl and Water Quantity

• Higher highs/lower lows
• Intensification/flashiness

Center for Watershed Protection (2003)
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Runoff as a function of Imperviousness
Center for Watershed Protection (2003) after
Schueler (1987)
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Stream Enlargement due to IC
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Fine Sediment Deposition due to IC
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Impacts of Deposited Sediments
Center for Watershed Protection (2003)
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Impacts of Suspended Sediments
Center for Watershed Protection (2003)
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Stormwater contains more than sediments
note the wide ranges
State of Maine (1995)
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Pollutant concentrations differby land use
A measure of variance in the data.
Burton and Pitt (2002) Stormwater Effects Handbook
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National Event Mean Concentrations
Center for Watershed Protection (2003)
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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)
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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)
Note unfortunate mix of English and Metric units!
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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
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Loss of LWD due to IC
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Biotic Impacts ofImperviousArea
Center for Watershed Protection (2003) as noted.
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Sprawl, impervious area, impairment
Center for Watershed Protection 2003
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Impaired Rivers
Burton and Pitt (2002) Stormwater Effects Handbook
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Impaired Lakes
Burton and Pitt (2002) Stormwater Effects Handbook
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Imperviousness and habitat qualityVariation
within a watershed
Fairfax County (2001) in CWP (2003)
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Variation among watersheds
Horner and May (1999) in CWP (2003)
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Measuring Impervious Cover

• Total versus Effective or Net IC

• Direct measurements
• Inferred measurements
• from land use
• from road density
• from population

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Stormwater management matters
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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).

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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 informationand to provide
  recommendations for developing clean up plans for
  Vermonts stormwater impaired waters

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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 cant attain the standards we want, what
  should we do?

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Extra
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Redesigning the American Neighborhood Developing
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.

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Why focus on scale?
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Why focus on scale?
Clearly, a mix of interventions is desirable.
But what mix? For what
purpose? Located where?
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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.

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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?

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Project Focus Area
35
ButlerFarmSubdivision
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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)

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, lt1 ug/L chronic
• 57 ug/L acute, 52 ug/L chronic
• ltlt1 mg/L as pesticides and PCBs
• No oil or grease causing impairment

VT Water Quality Standards
VT Stormwater Manual, Vol 2