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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

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

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

ENSC 202 – 2004

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Stream enlargement due to ic
Stream Enlargement due to IC

ENSC 202 – 2004

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

ENSC 202 – 2004

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Impacts of deposited sediments
Impacts of Deposited Sediments

Center for Watershed Protection (2003)

ENSC 202 – 2004

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Impacts of suspended sediments
Impacts of Suspended Sediments

Center for Watershed Protection (2003)

ENSC 202 – 2004

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Stormwater contains more than sediments
Stormwater contains more than sediments

…note the wide ranges

State of Maine (1995)

ENSC 202 – 2004

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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

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National event mean concentrations
National Event Mean Concentrations

ENSC 202 – 2004

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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

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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

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Note unfortunate mix of English and Metric units!


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 stormwater

ENSC 202 – 2004

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Biotic impacts of impervious area
Biotic Impacts of stormwaterImperviousArea

Center for Watershed Protection (2003) as noted.

ENSC 202 – 2004

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Sprawl impervious area impairment
Sprawl, impervious area, & impairment stormwater

Center for Watershed Protection 2003

ENSC 202 – 2004

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Impaired rivers
Impaired Rivers stormwater

Burton and Pitt (2002) Stormwater Effects Handbook

ENSC 202 – 2004

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Impaired lakes
Impaired Lakes stormwater

Burton and Pitt (2002) Stormwater Effects Handbook

ENSC 202 – 2004

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Imperviousness and habitat quality variation within a watershed

100 stormwater

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

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Variation among watersheds

Index of Biotic Integrity (IBI) stormwater

Total watershed impervious cover

Variation among watersheds

ENSC 202 – 2004

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Horner and May (1999) in CWP (2003)


Measuring impervious cover

Measuring Impervious Cover stormwater

  • Direct measurements

  • Inferred measurements

    • from land use

    • from road density

    • from population

Total versus Effective or Net IC

ENSC 202 – 2004

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Stormwater management matters
Stormwater management matters stormwater

ENSC 202 – 2004

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Mission of the vermont water resources board
Mission of the Vermont stormwaterWater 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

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The wrb stormwater docket

The WRB Stormwater ‘Docket’ stormwater

“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

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Key questions in the wrb docket
Key Questions in the WRB Docket stormwater

  • 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

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Extra
Extra stormwater

ENSC 202 – 2004

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Redesigning the American Neighborhood stormwaterDeveloping 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

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Why focus on scale

Effectiveness: stormwater 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? stormwater

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 stormwater

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

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Key objectives
Key Objectives stormwater

  • 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

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Project focus area
Project Focus Area stormwater

ENSC 202 – 2004

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Butler farm subdivision
Butler stormwaterFarmSubdivision

ENSC 202 – 2004

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Key collaborations
Key Collaborations stormwater

  • 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

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National and vermont standards
National and Vermont Standards stormwater

  • 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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