Developing Long-Term Coastal Erosion Hazard Maps ASFPM Conference Seattle, WA

Transcription

1 ASFPM 2014 Annual Conference Developing Long-Term Coastal Erosion Hazard Maps ASFPM Conference Seattle, WA Jeremy Mull, P.E. Elena Drei-Horgan, Ph.D. June 5 th, 2014

2 Presentation Outline Overview of Great Lakes Coastal Erosion Study for NYDEC Data and Methods Long-Term Coastal Erosion Results Impacts of Climate Change and Sea Level Rise (SLR) on Coastal Erosion 2

3 Presentation Goals Discuss methods to analyze and map longterm coastal erosion Discuss simple framework to incorporate SLR into coastal erosion analysis Apply framework to illustrate how SLR can impact coastal erosion forecasts 3

4 Study Overview Coastal erosion threatens lives, properties, and natural resources NYDEC reduces risks to life and properties by regulating land use and development in vulnerable coastal areas Coastal Erosion Hazard Area (CEHA) Maps Structural Hazard Areas (SHA) Coastal Hazard Erosion Areas Permit Program Article 34 Part 505 NYS ECL 4

5 Study Overview 5

6 Study Overview Coastal erosion on Great Lakes is generated by waves (> 6ft), seasonal water level fluctuations, terrestrial processes, and human development Erosion puts residences, tourism facilities, natural resources, and port facilities at risk 6

7 Study Overview NYDEC analyzes erosion and maps vulnerable areas NYDEC restricts development in CEHAs CEHAs based on forecasted, long-term retreat (i.e., 40-yr time frame) Structural Hazard Areas (SHAs) have erosion rates greater than 1 ft/yr Last study completed and released in

8 Study Overview NYDEC asked AECOM to develop new approach to analyze 40-yr erosion and create new maps Update 1988 study results and maps Approach applied to NY open coast, Lake Erie shoreline, and Lake Ontario shoreline 8

9 Data and Methods airborne bathymetric/ topographic lidar data (USACE) geo-referenced aerial images (USACE) aerial images 4. Field site visits 9

10 Data and Methods Approximately 33 years between historic photographs and lidar survey To determine erosion rate and retreat we determine the change in shoreline position over this timeframe 10

11 Data and Methods 1-D Transect based approach with shore-normal transect spaced every 50 m Extracted cross-shore profiles from lidar data along each transect 11

12 Data and Methods Determine water level at time of historic photos in gage data Find location of water level on lidar profiles Determine shoreline position in historic photos 12

13 Data and Methods Current shoreline position found with linear regression fit to crossshore profile data Allowed us to assess error 13

14 Data and Methods Distance between points divided by 33 years to obtain erosion rate (ft/yr) SHAs are areas where erosion rate is greater than or equal to 1 ft/yr Erosion rate is projected over 40 year time horizon 1978 Shoreline 2011 Lidar Shoreline Projected 40-yr Retreat 14

15 Coastal Erosion The study found SHAs with erosion > 1 ft/yr Also areas with accreting sandy beaches 15

16 Coastal Erosion Dune Line SHA Example map 16

17 Coastal Erosion Baird (2006) found 2.9 ft/yr of erosion for the Town of Wilson AECOM (2012) ft/yr of erosion at inlet; 1.1 ft/yr to left and right of inlet 17

18 Coastal Erosion with SLR SLR can accelerate erosion rates and increase long-term retreat distances Increased risk to coastal communities Three components to coastal erosion (E) E H : historical erosion rate (already computed) E SLR : rate due to SLR E Storm : storm induced erosion E = E H + E SLR + E Storm 18

19 SLR Impacts on Coastal Erosion at Dunes Bruun (1962) Rule for sandy beaches and coastal dunes 19

20 SLR Impacts on Coastal Erosion at Bluffs Modified Bruun Rule for erodible coastal bluffs (Young et al., 2012) 20

21 Climate Change on the Great Lakes Climate Change Impact on Great Lakes Glacier melt and isostatic rebound may raise water levels on southern shore Changes in precipitation and river inflow Water levels are managed to maintain international shipping channels, hydroelectric power supply, and lake ecosystems 21

22 SLR Impacts on Coastal Erosion Water Level Scenario Current Conditions Plan Bv7 No Regulation ft (.1 m) 1.0 ft (0.3 m) Used proposed Lake Erie and Ontario water levels for proxy SLR scenarios 22

23 SLR increases retreat distances and number of eroding areas Retreat Distance Accretion Distance Alongshore Location (km UTM) 23

24 SLR decreases accretion rates, increases retreat rates and SHAs Retreat Rate Accretion Rate Alongshore Location (km UTM) 24

25 SLR Impacts on Coastal Erosion Number Eroding Transects Number Accreting Transects Number SHA Transects Number Alongshore SHA Miles Current Bv No Reg Total shoreline length = 35 miles 25

26 SLR Impacts on Coastal Erosion SLR decreases forecast time for CEHA 26

27 Conclusions Simple framework to assess how SLR will increase coastal erosion Similar approach used in FEMA pilot study of San Francisco, CA SLR can accelerate coastal erosion, erode coastal areas that were previously accreting SLR decreases retreat forecast times SLR creates increased risk to coastal communities 27

28 Acknowledgements Jeff Burm, Brent McCarthy, Erik Danielson, Abdulla Mohamed, Frankie Petit, Todd Monson, Ryan Storzbach, Marie Evens Esten (AECOM) Mathew Chlebus (NYDEC) Peter Ruggiero (OSU) Hilary Stockdon (USGS) Questions? 28