Impacts of Impervious Cover Lecture 6 ENSC

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

Urban 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 Center for Watershed Protection 2003 ENSC 202 – 2004 Impervious Cover

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 Center for Watershed Protection (2003) after Schueler (1987) ENSC 202 – 2004 Impervious Cover

Stream Enlargement due to IC ENSC 202 – 2004 Impervious Cover

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

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

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

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

Pollutant concentrations differ by 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 Center for Watershed Protection (2003) ENSC 202 – 2004 Impervious 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 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 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 – 2004 Impervious 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 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 ENSC 202 – 2004 Impervious Cover

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

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

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

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

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

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

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

Stormwater management matters ENSC 202 – 2004 Impervious Cover

Mission of the Vermont Water 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 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 • 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 ENSC 202 – 2004 Impervious 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 – 2004 Impervious Cover

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

Why focus on scale? Clearly, a mix of interventions is desirable. But what mix? For what purpose? Located where? ENSC 202 – 2004 Impervious 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 Englandscape and climate. ENSC 202 – 2004 Impervious 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 these approaches work? ENSC 202 – 2004 Impervious Cover

Project Focus Area ENSC 202 – 2004 Impervious Cover

Butler Farm Subdivision ENSC 202 – 2004 Impervious Cover

Key Collaborations • US-EPA/SNR-UVM (Mc. Intosh, 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 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/100 ml 3 x in 30 days (A 1 and A 2) 33 E. coli cfu/100 ml once (A 1 and A 2) 77 E. coli cfu/100 ml (B) • at hardness of 50 mg/L ENSC 202 – 2004 VT Stormwater Manual, Vol 2 Impervious Cover VT Water Quality Standards