LID and Flood Control Presented by: The Low Impact Development Center, Inc. A non-profit water resources and sustainable design organization .

LID and Flood Control

Presented by:

The Low Impact Development Center, Inc. A non-profit water resources and sustainable design organizationwww.lowimpactdevelopment.org

Presented by:

The Low Impact Development Center, Inc. A non-profit water resources and sustainable design organizationwww.lowimpactdevelopment.org

The Low Impact Development Center, Inc. has met the standards and requirements of the Registered Continuing Education Program. Credit earned on completion of this program will be reported to RCEP at RCEP.net. A certificate of completion will be issued to each participant. As such, it does not include content that may be deemed or construed to be an approval or endorsement by RCEP.

COPYRIGHT MATERIALS

This educational activity is protected by U.S. and International copyright laws. Reproduction, distribution, display, and use of the educational activity without written permission of the

presenter is prohibited.

© Low Impact Development Center, 2012

The purpose of this presentation is to discuss how Low Impact Development fits into flood control programs.

At the end of this presentation, you will be able to:• Explain where LID fits into flood control• Discuss how LID can reduce flooding

Purpose and Learning Objectives

Multi-Objective Solutions Improve Cost Effectiveness

• Flood mitigation activities are FEMA, USACE• Protection of Water Quality is EPA’s goal• Stormwater management affects both

Small storm retention in local ordinances for new development and redevelopment can help achieve both.

Stormwater ordinances

Local drivers vary: water quality, flooding, beach and shellfish contamination

LID is the most reliable approach to reduce pollutant loading via volume reduction and soil filtration

EPA Commissioned NRC in 2007 to review NPDES Stormwater Program

Result: Current methods not effective

Stormwater is #1 growing quality concern

Impairment wide-spread; increasing

Volume control needed not just concentration

Stormwater Rulemaking Underway

Why Detention Does Not Work

t

Q

Post-Development Condition

Pre-Development Condition

Increased rate and volume runs off an impervious site

Limiting flow rate with the same volume extends the duration of flow impact on the stream

LID Practices: Infiltration, evaportranspiration, harvest and use to restore the runoff volume of predevelopment

conditions Does not replace treatment where needed

Watershed-wide LID can reduce small storm flood losses from development – less runoff

Corps of Engineers: Nashville Mill Creek 2007

Papio Creek Partnership Watershed Plan, Omaha, 2007; LID adoption multi-jurisdiction

Braden and Johnson, University of Illinois, ASCE 2006; LID adoption in Kane and Lake Counties

Maricopa County, adopted for flood control since 1985

Capital Region Watershed District, Minnesota, Arlington-Pascal Project 2003 saw cost savings for LID flood control; ordinance

Los Angeles’ Sun Valley Watershed, LID flood control project changed county approach to stormwater management

Asheville, North Carolina, Flood Management Task Force 2007, LID Ordinances

Findings in Nashville Corps Mill Creek Study

• Continued urbanization would cause:o Increased flooding, most noticeable in small storm events in Mill Creeko Tributaries to run dry, an ecosystem problem

• Threat to endangered species• Sedimentation and habitat alteration

Photo Credit: The Conservation Fund

Findings in Nashville Study

• Infiltration basins added 10 weeks of baseflow during summer: If only half achieved, significant improvements in water quality and habitat survival would occur

• LID reduces peaks flooding in small storms, maintains needed baseflow, eliminates need for regional detention (opposed locally)

• Pollutant loading not a part of study• LID only solution that maintained stream base flow,

protecting endangered species

Examples of LID in Flood Management and Flood Modeling

• Papio Creek Partnership: Omaha 2007 – Flooding and WQ Benefit Modeled: LID Only solution to both flooding and impairment

• Capitol Region Watershed District: MN 2004 to 2011 – Flooding, WQ, Capital Cost Benefits Realized in 190 acre watershed

• Sun Valley, Los Angeles - Flooding, WQ, amenities, cost/benefit optimized 2004 – 2011

How Much Flooding Can be Reduced?

• Typical LID design retains 1.0 to 1.5” storm; could be much higher if feasible

• Effect is large for small events, say 3” storm• Effect is not noticeable at major storms• BUT – 80% to 90% of annual rainfall is <1.5”• 80% to 90% of pollution reduced with a side benefit of

reducing small storm flooding• Typically requirements are for new development or

redevelopment; retrofits more costly

Benefits of LID for Floodplain Management

• “Stormwater Magazine” Fall 2011 article by Daniel E. Medina et. al.

• Case study; LID & watershed scale hydrology; Hydraulic modeling; flood damage analysis

• Modeled 13.2 sq mi urbanized watershed in Atlanta Georgia

• Looked at flood loss reduction with 1.2” LID retrofits throughout watershed

Study Models Inundation Reduced

Medina et al. 2011

Medina et al, 2011

Study does not model water quality benefits, the primary objective from EPA perspective. Flood loss reduction is a side benefit of this water quality approach.

LID Can Help Meet Watershed Water Quality Regulations

• NPDES Antibacksliding provisions• TMDLs: Applies in Urban, Suburban, Exurban• Source Water Protection for Drinking Water• Endangered Species Act• NPDES Phase I and Phase II permit requirements• Shoreline bacteria contamination (North Carolina)

LID can help protect floodplain services including habitat

- Floodplain/stream connectivity maintained

- Connected floodplain absorbs floodwaters

- More natural hydrology and habitat maintained

- FEMA Region X per NMFS ESA Biological Opinion

- ESA Habitat Conservation Plans (Etowah, GA)

Excess runoff volume from impervious area scours streams

Not New Concept for USACE

PLG 52, Floodplain Management Plans

PLG 52, Floodplain Management Plans

Watershed LID Consistent with FEMA Flood Insurance Credits

• FEMA’s Community Rating System (CRS) has had credit for stormwater retention ordinances in the past, key example Maricopa County (Phoenix)

• The New Draft CRS scoring has more credits for stormwater retention ordinances and LID

• The New Draft CRS Scoring has credits for flood control projects only if future conditions (build-out) are studies

• Credit for natural areas as part of large-scale, contiguous Green Infrastructure Plan

Consistent with Professional Floodplain Management Community

• ASFPM, NAFSMA concepts: Holistic management• Natural and Beneficial Floodplain Functions: Floodplain

Management—More than Flood Loss Reduction, White Paper Adopted by ASFPM Board 2008

• No Adverse Impact Initiative by ASFPM, 2004• “If current land development patterns, minimum floodplain

requirements, and standard stormwater practices remain, no doubt flooding and flood losses will worsen.” ASFPM

Flooding from Development Well-Established – Mitigation New

• Tulsa, Oklahoma early application of future build-out planning, set-back development as a result (“Flood Wars”). Now development has higher % impervious than was planned in the 1980’s.

• Charlotte-Mecklenburg Stormwater Services also modeled future build-out, set-back development as a result (increased floodway 45%)

• What if your town is already built to water’s edge, you can’t set-back development, but watershed continues to develop? One answer: ordinances from no increased runoff from development

Example Watershed Strategic Plan Goals Comprehensive: Pollution, Flood, Drought, Water Supply, Geomorphology andHabitat

Stormwater as a Resource: How to Manage it that way?Identify Infiltration Opportunities – soil mapping (“Green Seams”)

Prioritize: Development , Retrofit Areas, Floodplain PreservationMimic pre-development hydrology where feasibleRunoff reduction by local ordinance, water quality treatmentDevelopment /Redevelopment Issues (Where and How to develop)

- Preserved open space, parks - Low impact development techniques – rural, suburban, urban

- Early involvement of regulatory agencies and stakeholders- Smart Growth: walkable, livable cities

Stormwater management planning has a role in all of these, affecting water quality degradation and increasing flood potential.

Conclusion

• Be aware of state or local partner’s stormwater management requirements, water quality issues, water supply needs, long-range development plans in the watershed

• Encourage adoption of LID ordinances to prevent increases in flood potential, maintain healthy stream baseflow, assure regulatory compliance, earn FEMA NFIP CRS credit, comply with Corps PLG 52.

• Include watershed LID alternatives when modeling flood mitigation alternatives

Thank you for your time.

QUESTIONS?

Low Impact Development Center, Inc.www.lowimpactdevelopment.org

301.982.5559