Linking Wetland Alteration to Coastal Flooding: predictors, consequences, and policy implications

Transcription

1 Linking Wetland Alteration to Coastal Flooding: predictors, consequences, and policy implications Samuel D. Brody Sammy Zahran, Wesley Highfield, & Himanshu Grover Environmental Planning & Sustainability Research Unit Hazard Reduction & Recovery Center Department of Landscape Architecture & Urban Planning Texas A&M University, USA

2 Increasing Costs of Floods Remain the costliest of all hazards in U.S. Flood losses between 1975 and 1994 alone estimated at $67.5 billion (Peilke, 1996). $22 billion in flood losses from in the U.S. compared to $80 billion in from (Kunreuther and Roth, 1998). Presence of the built environment exacerbates losses.

3 Study Area: Why Texas? Consistently has the most deaths and damages from flooding of any state. Of the 42 flood events listed as causing more than $1 billion in damage between 1980 and 1998, 4 were in Texas. From 1978 to 2001, Texas suffered $2.25 billion dollars in property loss - more than California, New York and Florida combined.

4 Beaumont Houston Corpus Christi

5 Section 404 Permits:

6 Houston Area Wetland Alteration

7 WETLAND TYPE Texas Permit & Wetland Types PERMIT TYPE FIP LOP NWP GP TOTAL ESTUARINE SUBTIDAL % 6.73% 13.77% 8.45% 35.67% ESTUARINE INTERTIDAL % 1.06% 3.49% 1.31% 7.24% LACUSTRINE LINMETIC % 0.08% 1.50% 1.40% 3.47% LACUSTRINE LITTORAL % 0.06% 0.66% 0.08% 0.82% MARINE SUBTIDAL % 0.02% 0.07% 0.02% 0.17% MARINE INTERTIDAL % 0.03% 0.25% 0.02% 0.42% OUT % 0.00% 0.03% 0.02% 0.19% PALUSTRINE % 1.32% 33.11% 3.87% 41.97% RIVERINE TIDAL % 0.66% 1.21% 1.69% 3.73% RIVERINE LOWER PERENNIAL % 0.54% 2.98% 2.30% 6.21% RIVERINE INTERMITTENT % 0.00% 0.09% 0.00% 0.11% TOTAL Percent of Total 13.18% 10.50% 57.16% 19.16% %

8 Texas Permits Granted: Nationwide Letter of Permission Individual General Denied Permits Total: 40 Percent: 0.03% Nationwide Total: 5116 Percent: 47% General Total: 3512 Percent: 31% Letter of Permission Total: 1237 Percent: 11% Individual Total: 1284 Percent: 11%

9 Research Questions To what degree do features of the built environment affect flood damage in Texas? Do preparedness measures make a significant difference in reducing flood damage? What is the price of a wetland permit and what are the economic tradeoffs of various mitigation measures?

10 Research Methods Selected 37 counties in eastern Texas. 423 spatially repetitive damaging flood events. Time period: Measure and map wetland alteration permits, changes in impervious surfaces, and dams for the study period. Analyzed data using multiple regression analysis using robust standard errors.

11 Cumulative Flood Damage from

12 Descriptive Results 423 flood events caused over $320 million in reported property damage among coastal counties. Average amount of damage per flood was $423, Majority of this damage occurred during a twoday tempest beginning October 17, Between , 5,922 persons were either killed or injured in a flood event.

13 Conceptual Model Biophysical Baseline Conditions Flood Property Damage Built Environment Variables -Wetland Alteration -Impervious Surfaces -Flood Control Structures Socioeconomic/ Policy Controls

14 Factors Influencing Flood Damage Natural environment variables Precipitation day of event Precipitation day before event Floodplain overlap Duration of flood Built environment variables Impervious surface Wetland alteration Number of dams Socioeconomic/Policy variables FEMA CRS rating Median household income

15 Factors Influencing Flood Damage Natural environment variables Precipitation day of event (+) Precipitation day before event (+) Floodplain overlap (+) Duration of flood (+) Built environment variables Impervious surface (+) Wetland alteration (+) Number of dams (-) Socioeconomic variables FEMA CRS rating (-) Median household income (+)

16 Conclusions: Factors influencing flooding Timing and duration of precipitation is important. Alteration of naturally occurring wetlands is the most important built environment indicator of flood damage: Large development projects (>.5 acres) Cumulative impacts from small scale wetland alteration Increased impervious surfaces

17 Change in Impervious Surfaces NOAA Coastal Change Analysis Program

18 Conclusions: Factors influencing flooding Structural solutions to flood mitigation significantly reduce flood damage, but Mitigation measures under FEMA s CRS program reduce property damage (both property and human life).

19 The Price of Permits 1 wetland permit = an average of $ in added property damage per flood. $38,138 added damage per flood. 129 permits = flood reducing effect of dams. Real unit increase in CRS rating = $38,989 reduction in average cost per flood. Maximum premium discount reduces average flood cost to less than a quarter.

20 Social Vulnerability Analyzed 832 flood events at the county scale in Texas. 99 counties from 1997 to Do high percentages of socially vulnerable populations experience significantly more casualties from flood events? Analyzed data using Zero-Inflated Negative Binomial Model.

21 Social Vulnerability: Results Increase in composition of socially vulnerable populations increases the odds of casualty by 42.4 percent. For every real unit increase in FEMA premium discount, the odds of death and injury decrease by percent. An increase in the number of dams decreases the odds of a flood casualty by 21.6 percent. Precipitation the day of a flood event increases the odds of a casualty by 24.7 percent.

22 Research supported by the U.S. National Science Foundation Grant No. CMS

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24 Flood Damage & Wetland Permits Galveston County April 1997: 0.10 inches = $5,000 damage 546 permits Sept. 2000: 0.10 inches = $100,000 damage 921 permits Brazoria County June 1997:1.5 inches = $5,000 damage 356 permits Aug. 2001:1.5 inches = $500,000 damage 615 permits Harris County April 1997: 3.6 inches = $131,000 damage 685 permits May 2000:1.3 inches = $200,000 damage 1217 permits

25 Examining the Relationship Between Wetland Alteration & Watershed Flooding: Coastal Texas & Florida Samuel D. Brody & Wesley E. Highfield Environmental Planning & Sustainability Research Unit Department of Landscape Architecture & Urban Planning Texas A&M University

26 Study Area

27 Research Questions What is the spatial pattern of wetland development in Florida and coastal Texas from 1991 to 2002? To what degree does wetland alteration exacerbate coastal watershed flooding?

28 Research Objectives Geo-reference and analyze federal wetland permits within watersheds between 1991 & Measure flooding across 85 watersheds using stream gauge data provided by the USGS. Describe the spatial & statistical pattern of wetland development. Measure the impact of wetland alteration on watershed flooding while controlling for other factors.

29 Permit Types Individual Permits Letter of Permission Nationwide Permits General Permits - 36,465 geocoded permits -

30 Wetland Permits by Type Nationwide Individual Letter of Permission General Total Permits Texas Florida Total

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33 Factors Influencing Watershed Flooding Physical environmental Precipitation Topography Stream-length Watershed area Human-induced environmental change Wetland alteration permits Dams Land use change Socioeconomic & demographic Median household Income population density

34 Permit Types and Watershed Flooding Variable Coefficient Std. Error t-value Significance Nationwide Permits Individual Permits Letters of Permission General Permits State Constant R 2 = n = 85 F(5, 79) = 7.10 p = 0.000

35 Permit Types and Watershed Flooding with Contextual Controls Variable Coefficient Std. Error t-value Significance Nationwide Permits Individual Permits Letter of Permission General Permits State Area Slope Stream Length Precipitation Median Household Income Population Density Impervious Surface Change Dams Constant n = 85 F(13, 71) = 5.26; p = 0.000

36 Conclusions: Factors influencing flooding Large development projects (>.5 acres) Cumulative impacts from small scale wetland alteration Minor disturbances (<.2 acres) or restoration projects Precipitation remains the greatest predictor Increased impervious surfaces Wealthy communities

37 Future Research Position of wetland alteration: Proximity to water segment Upstream/downstream In/out of floodplain Improved flooding measures Gauge height Reported damages

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