Green Stormwater. Flood Risk Reduction. Infrastructure for. June Presented by: Kari Mackenbach, CFM ms consultants Lynn Mayo, PE, CFM AECOM

Transcription

1 Green Stormwater Infrastructure for Flood Risk Reduction June 2016 Presented by: Kari Mackenbach, CFM ms consultants Lynn Mayo, PE, CFM AECOM

2 Topics 1. Proposed ASFPM Policy Paper 2. Background Why is the issue important 3. Policy Paper Proposed terminology Use of green infrastructure for flood mitigation Calculating benefits of green infrastructure for flood mitigation 4. Next steps and comments on ASFPM Policy Paper Green Stormwater Infrastructure for Flood Risk Reduction 2

3 Proposed ASFPM Policy Paper Consistent use of terms Effectiveness of Green Infrastructure for flood risk reduction Green Stormwater Infrastructure for Flood Risk Reduction 3

4 Background Green Stormwater Infrastructure for Flood Risk Reduction 4

5 Natural water cycle: Pre-development Green Stormwater Infrastructure for Flood Risk Reduction 5

6 Natural water cycle: Post-development Increased imperviousness increases flows Decreased water quality Increased erosion and sediment in streams Green Stormwater Infrastructure for Flood Risk Reduction 6

7 Distributed stormwater controls close to runoff sources Traditional Regional Technique Distributed Stormwater Features Integrated Stormwater Controls Green Stormwater Infrastructure for Flood Risk Reduction 7

8 Green Stormwater Infrastructure for Flood Risk Reduction 8 Is this green infrastructure?

9 Is this green infrastructure? Green Stormwater Infrastructure for Flood Risk Reduction 9

10 Green Infrastructure Technology Types

11 Why are consistent terms important? Green Stormwater Infrastructure for Flood Risk Reduction 11

12 Definitions of green infrastructure American Planning Association (first used term in 1994)*: Interconnected system of natural areas and open space that: conserves ecosystem values, helps sustain clean air and water, and provides benefits to people and wildlife EPA Definition (first used term in 2007)*: Preserving and recreating natural landscape features Minimizing effective imperviousness to create functional and appealing site drainage Treating stormwater as a resource rather than a waste product from Karen Firehock, 2010 Green Stormwater Infrastructure for Flood Risk Reduction 12

13 Definitions of green infrastructure US Army Corps of Engineers: Integration of natural systems and processes, or engineered systems that mimic natural systems and processes, into investment in resilient infrastructure ASFPM: No Adverse Impact Toolkit Green infrastructure is a proactive, systematic, multifunctional model that views open space on a large scale and better integrates open/green space planning with other efforts to manage growth and development. It essentially uses stormwater storage areas, water conveyance areas and other natural flooded areas as part of the community infrastructure for stormwater and flood damage reduction, as well as for parks, trails and other recreation areas. Green Stormwater Infrastructure for Flood Risk Reduction 13

14 Can green stormwater infrastructure really reduce flooding? Green Stormwater Infrastructure for Flood Risk Reduction 14

15 How is green infrastructure and flooding connected? Seeing the significance of the hydrologic impacts of urbanization over time Green Stormwater Infrastructure for Flood Risk Reduction 15

16 How is green infrastructure and flooding connected? In a 1 rainfall Potential Runoff: 7,040 gallons + Green Concrete Compacted Lawn 8,390 s.f. impervious x 1 rain (if infiltrates first ¼ of rain) = 3,923 gallons of runoff 1,500 s.f. house (& patio) x 1 rain = 935 gallons of runoff Stormdrain 2,500 s.f. impervious x 1 rain = 1,559 gallons of runoff 1,000 s.f. driveway x 1 rain = 624 gallons of runoff Street

17 Green infrastructure flood risk reduction potential benefits Depends on type of GI: Non-urban green infrastructure Urban green stormwater infrastructure New development Existing development Green Stormwater Infrastructure for Flood Risk Reduction 17

18 Non-urban green infrastructure New development Green Stormwater Infrastructure for Flood Risk Reduction 18

19 Non-urban green infrastructure Land Preservation Wetland Preservation/Creation Floodplain and Stream Restoration (includes setback levees) Green Stormwater Infrastructure for Flood Risk Reduction 19

20 Non-urban green infrastructure success story Charles River USACE acquired 8,000 acres wetlands for flood control for $9M Average Annual flood damage reduction $17M Green Stormwater Infrastructure for Flood Risk Reduction 20

21 Urban green stormwater infrastructure New development Green Stormwater Infrastructure for Flood Risk Reduction 21

22 Urban green infrastructure (examples) Green roof Pervious pavers or pavement Rain garden or bioswales Infiltration trench Green Stormwater Infrastructure for Flood Risk Reduction 22

23 Green stormwater infrastructure used effectively for flood risk reduction City of Columbus, Blueprint Columbus Green Infrastructure Strategy Green Stormwater Infrastructure for Flood Risk Reduction 23

24 Urban green stormwater infrastructure success story Cuyahoga Falls green infrastructure mitigation park project FEMA grant to acquire 4 homes Space converted into green infrastructure Reduced flooding for remaining homes Green Stormwater Infrastructure for Flood Risk Reduction 24

25 Green stormwater infrastructure used effectively for flood risk reduction University of Louisville Belknap Campus Green Stormwater Infrastructure for Flood Risk Reduction 25

26 Green stormwater infrastructure used effectively for flood risk reduction Copenhagen, Denmark Climate Resiliency and Flood Mitigation Strategy On July 2, 2011, a cloud burst inundated Copenhagen with 6 inches of rain in less than three hours, flooding cellars, streets, and key roads. ($1.04 billion) in damage. Green Stormwater Infrastructure for Flood Risk Reduction 26

27 Proposed ASFPM Policy Paper Consistent use of terms Effectiveness of Green Infrastructure for flood risk reduction Green Stormwater Infrastructure for Flood Risk Reduction 27

28 Green infrastructure flood risk reduction potential benefits Depends on type of GI: Non-urban green infrastructure Urban green stormwater infrastructure New development or redevelopment Existing development Green Stormwater Infrastructure for Flood Risk Reduction 28

29 Urban green stormwater infrastructure New development Green Stormwater Infrastructure for Flood Risk Reduction 29

30 Inch rainfall Urban green stormwater infrastructure To be effective flood risk reduction, need to: Change land use to impact curve number (i.e., reduce runoff) or Have available storage at time of peak flow Rainfall Hyetograph Green Stormwater Infrastructure for Flood Risk Reduction 30

31 Urban green stormwater infrastructure GI can change land use to impact curve number and reduce flow GI can add storage so water detained at time of peak flow New Development a a Green Stormwater Infrastructure for Flood Risk Reduction 31

32 Urban green stormwater infrastructure GI can change land use to impact curve number and reduce flow New Development a Existing Development s GI can add storage so water detained at time of peak flow a s Green Stormwater Infrastructure for Flood Risk Reduction 32

33 Urban green stormwater infrastructure New development or redevelopment Green Stormwater Infrastructure for Flood Risk Reduction 33

34 EPA study on GI for flood loss avoidance (for new development or redevelopment) Assumed GI retained: Redevelopment: Approximately inch rainfall New development: Approximately inch rainfall Evaluated 20 HEC8 watersheds with and without GI retention out to year 2040 Benefits: Flood losses without GI / flood losses with GI Losses Avoided- HAZUS modeling results Present value 2020 to 2040 = $0.4 to $1 billion Average over 20 years = $30 to $65 million per year Source: EPA, Flood Loss Avoidance Benefits of Green Infrastructure for Stormwater Management, December 2015 Green Stormwater Infrastructure for Flood Risk Reduction 34

35 Urban green stormwater infrastructure Existing development Green Stormwater Infrastructure for Flood Risk Reduction 35

36 Existing Development Green Stormwater Infrastructure Typically limited land available to install green infrastructure Urban GSI Limitations: Limited impact for downstream large watershed Limited impact on large flood events Urban GSI Opportunities: Opportunities for localized flooding Opportunities for small flood events Green Stormwater Infrastructure for Flood Risk Reduction 36

37 Urban green stormwater infrastructure Not going to affect May affect Green Stormwater Infrastructure for Flood Risk Reduction 37

38 Urban green stormwater infrastructure Not going to affect May affect Good News: Most flood reduction benefits come from addressing smaller, frequent events. Green Stormwater Infrastructure for Flood Risk Reduction 38

39 Example estimated damages from different storm events in Concord, MA Total expected dollar losses from flooded buildings and contents 10% (10 yr) 4% (25 yr) 2% (50 yr) 1% (100 yr) 0.2% (500 yr) $593 M $749 M $905 M $1,199 M $1,459 M Source: Concord, MA, Flood Risk Report Green Stormwater Infrastructure for Flood Risk Reduction 39

40 Example estimated damages from different storm events in Concord, MA Total expected dollar losses from flooded buildings and contents 10% (10 yr) 4% (25 yr) 2% (50 yr) 1% (100 yr) 0.2% (500 yr) $593 M $749 M $905 M $1,199 M $1,459 M 10% chance have $593M in damage any given year $593M x 10% = $59M Source: Concord, MA, Flood Risk Report Green Stormwater Infrastructure for Flood Risk Reduction 40

41 Example estimated damages from different storm events in Concord, MA Total expected dollar losses from flooded buildings and contents 10% (10 yr) 4% (25 yr) 2% (50 yr) 1% (100 yr) 0.2% (500 yr) $593 M $749 M $905 M $1,199 M $1,459 M 10% chance have $593M in damage any given year $593M x 10% = $59M 0.2% chance have $1,459M in damage any given year $1,459M x 0.2% = $3M Source: Concord, MA, Flood Risk Report Green Stormwater Infrastructure for Flood Risk Reduction 41

42 Average Annualized Loss Average Annualized Loss = estimated long-term weighted average value of losses to a property in any single year Green Stormwater Infrastructure for Flood Risk Reduction 42

43 Example estimated damages from different storm events in Concord, MA Total expected dollar losses from flooded buildings and contents 10% (10 yr) 4% (25 yr) 2% (50 yr) 1% (100 yr) 0.2% (500 yr) $593 M $749 M $905 M $1,199 M $1,459 M Total annualized losses from flooded buildings and contents 10% (10 yr) 4% (25 yr) 2% (50 yr) 1% (100 yr) 0.2% (500 yr) TOTAL Annualized (& / yr) $40 M $17 M $10 M $10 M $3 M $80 M Source: Concord, MA, Flood Risk Report Green Stormwater Infrastructure for Flood Risk Reduction 43

44 Commercial flooding- often most effective Addressing nuisance flooding in commercial areas Typically more dense development Loss of function, including loss of access to area Customers stay away High content value Vehicle detour time and mileage Potentially significant benefit of reducing flood elevation by less than a foot Green Stormwater Infrastructure for Flood Risk Reduction 44

45 Summary Non-urban green infrastructure Urban green stormwater infrastructure new development Urban green stormwater infrastructure existing development Potential flood benefits for large events Potential flood benefits for large events Potential flood benefits for small events Biggest long-term benefits are from small events Green Stormwater Infrastructure for Flood Risk Reduction 45

46 Next steps and comments on ASFPM Policy Paper Green Stormwater Infrastructure for Flood Risk Reduction 46

47 Green Stormwater Infrastructure for Flood Risk Reduction 47

48 Average Annualized Loss (AAL) AAL = estimated long-term weighted average value of losses to a property in any single year in a specified geographic area AAL = (10% - 4%) * (Loss 10% + Loss 4%) / 2 + (4% - 2%) * (Loss 4% + Loss 2%) / 2 + (2% - 1%) * (Loss 2% + Loss 1%) / 2 + (1% - 0.2%) * (Loss 1% + Loss 0.2%) / % * Loss 2% Green Stormwater Infrastructure for Flood Risk Reduction 48