Land Conservation in the Floodplain

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1 Land Conservation in the Floodplain Assessing the Benefits and Costs of Green Infrastructure Investments Margaret Walls Resources for the Future

2 What is green infrastructure? Green infrastructure is strategically planned and managed networks of natural lands, working landscapes and other open spaces that conserve ecosystem values and functions and provide associated benefits to human populations. -- The Conservation Fund

3 Growing in popularity NYC Green Infrastructure Plan 2013

4 Using green infrastructure for flood control 1) Exposure reduction Removing structures in floodplain lowers damages. 2) Natural valley storage protection NVS areas are lands, often wetlands, that temporarily store floodwaters, reducing flood risk downstream. 3) Reconnect river to floodplain/increase floodway Expanding channel for conveyance in times of flood reduces flood stages upstream and downstream. 4) Stormwater management Expand pervious surface areas and hold water on lands.

5 Why choose green over gray? May be cheaper o Milwaukee: $27.7 million cost for 2,100 acres that hold 1.3 billion gals of water; Deep Tunnel System cost $3 billion to hold 405 million gals Can provide important co-benefits aesthetics, recreation, water quality But depends on specific case Many feel good stories but few quantitative analyses

6 The Meramec Greenway Network of lands in the floodplain along the Meramec River in Missouri Extends along 108 miles of the river Flood protection a major focus o Recreation (trails), water quality 28,000 acres of public protected lands so far

7 Greenway includes all lands within 300 of river + adjacent protected lands yr floodplain In St. Louis County Greenway = 25,988 acres Protected lands = 9,389 acres So ~64% of Greenway still unprotected

8 Estimating Benefits from the Greenway Flood damages avoided Compare estimated flood damages from current land use patterns to damages from a hypothetical counter-factual scenario in which the Greenway protected lands are developed (reduced flood exposure) Other benefits: recreation, aesthetics, water quality Hedonic property value analysis [future work] 2-year NOAA grant (Climate and Societal Interactions, Sectoral Applications Research Program)

9 Estimating Flood Damages Avoided Hazus: GIS-based FEMA model that estimates damages from flood events (version MH-2.1, run using ArcMap 10) Digital elevation model (1/3 arc sec) is input for delineation of stream network Hydrology/hydraulics model generates flood surface elevation layer, which gives flood depth for given return periods Depth-damage functions provide damage estimates Level 2 analysis Improved DEM Parcel-level property info (UDF tool)

10 Estimating Flood Damages Avoided (cont.) Our geographic focus: 5 sub-watersheds of Meramec River and its tributaries, within St. Louis County Flood damages estimated for 2, 10, 50, 100, 250 and 500-year floods for current scenario and for hypothetical scenarios. Average annualized loss calculated (AAL) from these estimates for each scenario.

11 Estimating Flood Damages Avoided (cont.) Hypothetical scenario: All protected lands in the 500-year floodplain of Greenway are developed approx 65% reduction in total protected acreage Single-family homes Property values based on current median values by area Total development calculated using current average lot sizes

12 Results: Benefits from Avoided Flood Damages Average Annualized Loss (AAL) Annual Benefits (avoided damages from reduced exposure) Current Land Use Hypothetical Land Use $29.65 million $33.69 million $4.04 million In hypothetical, 3,197 acres of public protected land in floodplain developed Annual benefits per acre = $1,264 Note: assuming no flood benefits on adjacent properties from altered hydrology. Probably OK as only 16% of developed parcels are next to these lands; 4-acre avg lot size.

13 Costs (approximately ) Costs = Foregone value of the land in its next best use, development Median appraised value in 2012 of singlefamily homes in the floodplain of Meramec River watersheds $203,000 Multiply by number of additional homes Annualize using 5% discount rate and 30-year time period Annual Opportunity Cost $27.5 million

14 Thinking about Co-Benefits Recreation, aesthetic, water quality, and other benefits from the Greenway need to $23.5 million per year to justify costs Population of St. Louis County 1 million Benefit per person per year needs to $23.50 For 3,197 acres of public protected lands this is < 1 cent/acre

15 Spatial Targeting Avoided flood damages are not distributed equally across the watershed ¾ of the total flood damages come from only 8.5% (177) of the parcels 10 parcels alone account for 30% of total damages Property value part of story, but flood depths vary greatly within the floodplain

16 Flood depths, 100-year flood June 2012

17 Flood depths, 100-year flood (cont.)

18 More on Targeting Back of the envelope. ¾ of the benefits = $3.03 million 8.5% of the costs = $2.3 million So with the right targeting of parcels to protect, avoided flood damages could have been > costs But co-benefits would be much lower; far fewer acres of public protected lands

19 Next Steps Co-Benefits from Greenway: Hedonic property analysis Thinking more carefully about BCA for green infrastructure flood protection projects What should count as a benefit? Spatial targeting when there are multiple benefits Second part of NOAA grant: Flood damages to county as a whole under future climate scenarios and alternative land use patterns Thinking about policy instruments to alter land use

20 Thank you! Comments/questions: More information at ological_wealth/pages/land-conservation-inthe-floodplain.aspx

DISCUSSION PAPER. Floodplain Conservation as a Flood Mitigation Strategy. Examining Costs and Benefits

DISCUSSION PAPER. Floodplain Conservation as a Flood Mitigation Strategy. Examining Costs and Benefits DISCUSSION PAPER Jul y 2013 ; revised October 2013 RFF DP 13-22-REV Floodplain Conservation as a Flood Mitigation Strategy Examining Costs and Benefits C a r o l yn K o u s k y a n d M a r g a r e t W