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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. - PowerPoint PPT Presentation
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ENSC 202 – 2004Impervious Cover
Impacts of Impervious Cover
Lecture 6 – ENSC 202
ENSC 202 – 2004Impervious Cover
Urban Sprawl
Sprawl is dispersed, automobile-dependent development outside of compact urban and village centers along highways and in rural countryside.
ENSC 202 – 2004Impervious Cover
Sprawl &Impervious
Cover
0 20 40 60 80
Commercial
Light Industry
Residential (multifamily)
Residential (townhouse)
Institutional
Residential (1/8 acre)
Residential 1/4 acre)
Residential (1/2 acre)
Residential (1 acre)
Residential (2 acre)
Open urban land
Parks, golf courses, cemetaries
Agriculture
Impervious area (%)
MeanSE
Center for Watershed Protection 2003
ENSC 202 – 2004Impervious Cover
Sprawl and Water Quantity• Higher highs/lower lows• Intensification/flashiness
Center for Watershed Protection (2003)
ENSC 202 – 2004Impervious Cover
Runoff as a function of Imperviousness
Center for Watershed Protection (2003) after Schueler (1987)
ENSC 202 – 2004Impervious Cover
Stream Enlargement due to IC
ENSC 202 – 2004Impervious Cover
Fine Sediment Deposition due to IC
ENSC 202 – 2004Impervious Cover
Center for Watershed Protection (2003)
Impacts of Deposited Sediments
ENSC 202 – 2004Impervious Cover
Center for Watershed Protection (2003)
Impacts of Suspended Sediments
ENSC 202 – 2004Impervious Cover
Stormwater contains
more than sediments
State of Maine (1995)
…note the wide ranges
ENSC 202 – 2004Impervious Cover
Pollutant concentrations differby land use
Burton and Pitt (2002) Stormwater Effects Handbook
A measure of variance in the data.
ENSC 202 – 2004Impervious Cover
National Event Mean
Concentrations
Center for Watershed Protection (2003)
ENSC 202 – 2004Impervious Cover
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 coefficientIA = impervious area (%)
from Impacts of Impervious Cover on Aquatic Systems, p. 61 (CWP 2003)
ENSC 202 – 2004Impervious Cover
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!
ENSC 202 – 2004Impervious Cover
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 lbsU = unit conversion = 0.226R = runoff (inches, Step 2)
C = concentration (EMC, mg/L)A = area (acres)
Can be modified for bacteria
ENSC 202 – 2004Impervious Cover
Loss of LWD due to IC
ENSC 202 – 2004Impervious Cover
Biotic Impacts of
ImperviousArea
Center for Watershed Protection (2003) as noted.
ENSC 202 – 2004Impervious Cover
Sprawl, impervious area, & impairment
Center for Watershed Protection 2003
ENSC 202 – 2004Impervious Cover
Impaired Rivers
Burton and Pitt (2002) Stormwater Effects Handbook
ENSC 202 – 2004Impervious Cover
Impaired Lakes
Burton and Pitt (2002) Stormwater Effects Handbook
ENSC 202 – 2004Impervious Cover
Imperviousness and habitat qualityVariation within a watershed
0 10 20 30 40 50 Percent watershed impervious cover
Inde
x of
Bio
tic I
nteg
rity
(IB
I)100
80
60
40
20
0
Fairfax County (2001) in CWP (2003)
ENSC 202 – 2004Impervious Cover
Variation among watersheds
Total watershed impervious cover
Inde
x of
Bio
tic I
nteg
rity
(IB
I)
Horner and May (1999) in CWP (2003)
ENSC 202 – 2004Impervious Cover
Measuring Impervious Cover
Total versus Effective or Net IC
• Direct measurements• Inferred measurements
– from land use– from road density– from population
ENSC 202 – 2004Impervious Cover
Stormwater management matters
ENSC 202 – 2004Impervious Cover
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 – 2004Impervious Cover
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 – 2004Impervious Cover
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 – 2004Impervious Cover
Extra
ENSC 202 – 2004Impervious Cover
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.
ENSC 202 – 2004Impervious Cover
Why focus on scale?
Effectiveness: uncertainOrientation: local protectionCost: known - mediumRisk: uncertain - medium
Effectiveness: unknownOrientation: source controlCost: uncertain – low?Risk: unknown – medium/high
Effectiveness: known – dependsOrientation: downstream protectionCost: known - highRisk: known - low
ENSC 202 – 2004Impervious Cover
Why focus on scale?
Clearly, a mix of interventions is desirable. But what mix? For what purpose? Located where?
ENSC 202 – 2004Impervious Cover
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 – 2004Impervious Cover
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 – 2004Impervious Cover
Project Focus Area
ENSC 202 – 2004Impervious Cover
ButlerFarm
Subdivision
ENSC 202 – 2004Impervious Cover
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 – 2004Impervious Cover
National and Vermont StandardsComparison 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
VT Stormwater Manual, Vol 2 VT Water Quality Standards