*AKA: Green Infrastructure (GI) and other aliases
Paul Wagner, USACE IWR Lisa Hair, USEPA, Office of Water Roger Lindsey, Nashville Metro Water Services Tom Palko, Nashville Metro Water Services Dan Medina, Atkins Global Definition and Introduction Riverine and Coastal Application Future Needs Riverine and Coastal Federal Mechanisms to Encourage Change
Natural and Nature-based Infrastructure Natural: Naturally occurring systems that provide services, i.e. natural dunes or forests Nature-based: Engineered systems to mimic or restore natural functions, i.e. floodplain restoration Green Infrastructure Large scale (Benedict and McMahon) or Site-scale for Stormwater Management practices that reduce runoff volume via infiltration or capture and use Site-scale is also called Low-Impact Development (LID) Terminology is evolving, overlapping
2007: EPA Commissioned National Research Council to review Stormwater Program Result: Current methods not effective Finding: Runoff volume control needed - not just concentration of pollutants in runoff
Low Impact Development (LID) Natural approaches - infiltration and evapotranspiration and harvest-and-use Distributed small-scale hydrologic controls retain rainfall close to the source Replicates the pre-development hydrologic regime: reducing runoff volume compared to impervious surfaces Modified from Prince George's County, Maryland. Larry Coffman et al. (1999).
Eco-Roof (green roof or blue roof)g Underground: Infiltration Vaults and Expanded Tree Pits Infiltrating swales
Examples: Tulsa, OK; Charlotte-Mecklenburg, NC Future increases in imperviousness = increased development set-backs by local code, at a high cost to existing river-front landowners. But we can t set back existing riverfront development for future upstream imperviousness, it s too costly. Land for more reservoirs is too costly. Levees are not always a desirable option. Small storm retention ordinances are a feasible and relatively low-cost option.
Typical LID design retains 0.5 to 2 ; or more Not noticeable at major storms (i.e. 50 yr) BUT 80% to 90% of annual rainfall is <1.5 AND - 80% to 90% of annual pollution is reduced Replicating predevelopment runoff rate and duration assures water quality protection and integrity of stream channels and floodplain connectivity. Restoration may be too costly. On a watershed scale, flood reduction benefits can accrue, as studied in future conditions study EPA recently prepared.
NE: Omaha, Papio Creek Watershed Plan - LID adoption multi-jurisdiction for flood control; WQ side-benefit MN: Capital Region Watershed District - LID cheaper flood control option; water quality improvement for popular lake CA: Los Angeles Sun Valley Watershed - LID flood control benefits changed LA s approach to overall stormwater management NC: Asheville Flood Task Force Ordinances recommending LID for flood control as part of comprehensive approach
-Improved water quality -North Carolina Coastal Federation cites shellfish bed protection - Stream channel and habitat protection - Nashville LID could reduce repetitive flood losses and maintain baseflow in summer for endangered species, per USACE -Puget Sound Biological Opinion to protect salmon includes LID - Groundwater recharge for water supply - Protecting Florida s Springs: An Implementation Guidebook, State of FL - Lower costs for water treatment and dredging -Streambank erosion is the major sediment contributor - Lower costs for stream/floodplain restoration - Greener towns: self-watering landscapes
Small storm retention is required for redevelopment and/or new development: State-wide: CA, NY, PA, NJ, MN, MD, DE Retention requirement varies from about 85 th percentile to over 95 th percentile ( about 0.75 to 1.8, varies) www.epa.gov/npdes/pubs/sw_state_summary_standards.pdf MS4 permitted cities in MA, MT, NH, WV, TN, DC Adopted in regions for specific issues, examples: Maricopa County (Phoenix), AZ: LID for flood management since 1985; 100-yr, 2-hr event Kane and Lake Counties, IL; LID adopted for flood management US Navy in 2007: Pioneers policy that is now a requirement for new and redevelopment of federal facilities
FEMA model ordinance for Puget Sound: Stormwater and drainage features shall incorporate low impact development techniques, if technically feasible, that mimic predevelopment hydrologic conditions, such as stormwater infiltration, rain gardens. If more than 10 percent of the portion of the lot in the Regulatory Floodplain is covered by impervious surface, the applicant shall demonstrate that there will be no net increase in the rate and volume of the stormwater surface runoff that leaves the site Because western Washington State LID standards are similar, most NFIP communities are adopting it in local ordinances to comply with NFIP. 5 communities have adopted the FEMA Model Ordinance, and 10 have modified their ordinances to match it (per FEMA) Floodplain Management and the Endangered Species Act, A Model Ordinance, FEMA Region 10, January 2012
Stormwater runoff volume retention shall be achieved onsite in the amount equivalent to the runoff generated from one inch rainfall over the impervious surfaces of the development Alternative Compliance Sequencing. To the maximum extent practicable, the volume reduction standard shall be fully met onsite. If it is not possible because of site conditions listed above, the following steps shall be taken in the order shown: [as much on site as possible, then offset with banking, pay impact fee for remainder]
Rationale: smaller runoff volume leads to smaller floodplains and thus fewer flood damages Evaluate 20 HUC8 watersheds with and without GI-based retention out to the year 2040 Retention assumed: 85 th percentile storm on redevelopment; 90 th percentile storm on new development Approximately 0.5 for 85 th and 1 to 1.7 for 90 th Estimate monetary flood losses for each scenario Benefits = losses without GI losses with GI
At year 2040: $100 to $300 Million per year Would continue to increase over time Present Value 2020 to 2040 $0.8 to $2.3 Billion Hazus identified losses only, not damage from stream erosion or pollution i.e. avoided costs
Twenty HUC8 watersheds selected Publically available datasets Stream gage hydrology (PeakFQ) Hydraulic modeling (Rapid Flood Delineation [RFD] Atkins model) Damage estimation (Hazus) Nationwide scale-up (SAS regression)
When applied watershed wide, small storm retention is effective at reducing Peak flows for large events Flood elevations Flood losses Benefits can be quantified by the Average Annualized Losses Avoided (AALA) method (i.e. Hazus AAL with/without GI) Need to improve messaging about the link between runoff volume reduction and flood loss avoidance Watershed flood modeling should consider future conditions with runoff retention ordinances on new and redevelopment: As part of alternatives analysis; and To protect existing infrastructure To improve or maintain water quality and local water resources
Nashville Metro Water Services Discussion of Coastal Applications
FEMA CRS scoring has credits for: stormwater retention ordinances and LID flood control projects only if future conditions are studied large-scale, contiguous Green Infrastructure Plan USFWS has accepted LID in ordinances as one part of a Habitat Conservation Plan (HCP) under Endangered Species Act individual developers saved the headache. (Example: Etowah HCP, Georgia) FEMA has included LID in Model Ordinances in Puget Sound, and has funded pilots (Cuyahoga Falls, OH) because of repetitive losses EPA: Drinking water source protection, TMDLs, Combined Sewer Overflow Consent Decrees, etc., may allow LID credit or benefit from LID ordinances
WRDA 86 Section 402, as amended, requires non-federal interest to prepare a floodplain management plan (FPMP) to reduce impacts of future flood events Guidance for FPMP development in Policy Guidance Letter (PGL) 52 FPMP should include measures, practices, and policies to reduce loss of life, damages to property and facilities, public expenditures, preserve the level of protection provided by the Corps project, and enhance natural floodplain values Can include land use regulations, various preparedness activities, floodplain acquisition and easements, and preservation of natural resources and functions of the floodplain An example strategy highlighted in PGL 52 includes public development and redevelopment policies such as no net increase in runoff requirements for new development within its jurisdictions FPMP development is the project sponsor s responsibility; USACE can assist
The Energy Independence and Security Act of 2007, Section 438 (EISA 438) requires Federal facility buildings, both new development and redevelopment, to match predevelopment stormwater runoff rates, volume, and temperature. Storm water runoff requirements for federal development projects. The sponsor of any development or redevelopment project involving a Federal facility with a footprint that exceeds 5,000 square feet shall use site planning, design, construction, and maintenance strategies for the property to maintain or restore, to the maximum extent technically feasible, the predevelopment hydrology of the property with regard to the temperature, rate, volume, and duration of flow.
EPA Green Infrastructure website Local or state stormwater programs Industry news: Stormwater Magazine (free) EPA non-point source community list serve: Subscribe at: epa.gov/nps/npsinfo Green Highways Partnership (EPA/DOTs/ASCE and more) city and town announcements and reports searched from newspapers Subscribe at: greenhighwayspartnership.org Green Roof Design and News: Living Architecture Monitor (free)
Rapid Flood Delineation (RFD) model As accurate as HEC-RAS High speed hydraulic profile calculation (6,000 miles per CPU hour) Automatic cross sections Depth grids
1,200 1,000 800 Damages (millions) 600 Damages avoided with GI Without GI 400 200 0 0 20 40 60 80 100 Return period (years)
AALA = Average annualized losses avoided $60 AALA (per million dollars of exposure) $50 $40 $30 $20 $10 $- 02040205 12040104 12090205 12100301 03130001 12080005 02050306 02080201 01100004 03150201 2080205 10190003 10190004 05120208 02030201, 02030202 16040101 05140205 04080203 12080007 07010102