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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

Impacts of Impervious Cover

Lecture 6 – ENSC 202

ENSC 202 – 2004

Impervious Cover

urban sprawl
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

sprawl impervious cover
Sprawl &ImperviousCover

Center for Watershed Protection 2003

ENSC 202 – 2004

Impervious Cover

sprawl and water quantity
Sprawl and Water Quantity
  • Higher highs/lower lows
  • Intensification/flashiness

Center for Watershed Protection (2003)

ENSC 202 – 2004

Impervious Cover

runoff as a function of imperviousness
Runoff as a function of Imperviousness

Center for Watershed Protection (2003) after Schueler (1987)

ENSC 202 – 2004

Impervious Cover

stream enlargement due to ic
Stream Enlargement due to IC

ENSC 202 – 2004

Impervious Cover

fine sediment deposition due to ic
Fine Sediment Deposition due to IC

ENSC 202 – 2004

Impervious Cover

impacts of deposited sediments
Impacts of Deposited Sediments

Center for Watershed Protection (2003)

ENSC 202 – 2004

Impervious Cover

impacts of suspended sediments
Impacts of Suspended Sediments

Center for Watershed Protection (2003)

ENSC 202 – 2004

Impervious Cover

stormwater contains more than sediments
Stormwater contains more than sediments

…note the wide ranges

State of Maine (1995)

ENSC 202 – 2004

Impervious Cover

pollutant concentrations differ by land use
Pollutant concentrations differby land use

A measure of variance in the data.

Burton and Pitt (2002) Stormwater Effects Handbook

ENSC 202 – 2004

Impervious Cover

national event mean concentrations
National Event Mean Concentrations

ENSC 202 – 2004

Impervious Cover

Center for Watershed Protection (2003)

the simple method for calculating runoff loading from stormwater

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

the simple method for calculating runoff loading from stormwater1

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!

slide15

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

loss of lwd due to ic
Loss of LWD due to IC

ENSC 202 – 2004

Impervious Cover

biotic impacts of impervious area
Biotic Impacts ofImperviousArea

Center for Watershed Protection (2003) as noted.

ENSC 202 – 2004

Impervious Cover

sprawl impervious area impairment
Sprawl, impervious area, & impairment

Center for Watershed Protection 2003

ENSC 202 – 2004

Impervious Cover

impaired rivers
Impaired Rivers

Burton and Pitt (2002) Stormwater Effects Handbook

ENSC 202 – 2004

Impervious Cover

impaired lakes
Impaired Lakes

Burton and Pitt (2002) Stormwater Effects Handbook

ENSC 202 – 2004

Impervious Cover

imperviousness and habitat quality variation within a watershed

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

variation among watersheds

Index of Biotic Integrity (IBI)

Total watershed impervious cover

Variation among watersheds

ENSC 202 – 2004

Impervious Cover

Horner and May (1999) in CWP (2003)

measuring impervious cover

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

stormwater management matters
Stormwater management matters

ENSC 202 – 2004

Impervious Cover

mission of the vermont water resources board
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

the wrb stormwater docket

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

key questions in the wrb docket
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

extra
Extra

ENSC 202 – 2004

Impervious Cover

slide29
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

why focus on scale

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

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why focus on scale1
Why focus on scale?

Clearly, a mix of interventions is

desirable. But what mix?

For what purpose?

Located where?

ENSC 202 – 2004

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primary goal
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

key objectives
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

project focus area
Project Focus Area

ENSC 202 – 2004

Impervious Cover

butler farm subdivision
ButlerFarmSubdivision

ENSC 202 – 2004

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key collaborations
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

national and vermont standards
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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