Assessing Storm Damage: Hurricane Sandy, Future Hurricanes and Sea-Level Rise

Rhode Island has not always been so lucky. Large hurricanes in 1938 and 1954 hit the state directly and devastated the coast. Since then, sea level has risen. The barrier beaches have steadily eroded, and people continue to build on them. Looking at the damage that Sandy did to coastal areas closer to the storm center can show us what could happen to Rhode Island in the next storm.

Part 1. Barrier beach overwash and breaches

The south coast of Long Island has extensive barrier beaches with salt marshes and salt ponds behind them. Fire Island, when it was a single barrier island, was more than 30 miles long. It is in the central part of the south coast. Hurricane Sandy breached Fire Island, dividing it in two. In this exercise, you will examine aerial photos of Fire Island before and after the breach.

Note to instructor: The pre-storm image is a mosaic of aerial photos taken in 2010 by the New York Statewide Digital Orthoimagery Program (NYSDOP). You can preload this onto students’ computers or give them instructions to download it themselves.

Instructions for students or instructor, using ArcGIS 10.2.2:

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  Open a new blank map in ArcGIS.
  
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  Click the Add Data button and select GIS Servers, then Add ArcGIS Server. A box opens with a field for a Web address. Type in http://www.orthos.dhses.ny.gov/arcgis/services .
  
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  When a list of years comes up, choose 2010. The coordinate system for the data is WGS 1984 Web Mercator Auxiliary Sphere.
  

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  Open the Go To XY tool and type in the following coordinates: 40 43 26.92 N, 72 53 50.77 W. When the map zooms to the correct location, click on the Add Point icon (fourth from the left in the Go To XY box) to mark the location.
  

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  Use the Measure tool with the units set to feet. Measure the beach just south of your lat-long point from the ocean side to where the brown salt marsh begins.
  

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  Open a web browser and go to storms.ngs.noaa.gov/storms/sandy/ . This is a map that has an overlay of aerial photos taken in 2012 immediately after Sandy.
  
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  In the Search box, type in “Patchogue” and select “Patchogue” in the list that appears. The map zooms to the same section of Fire Island as in your 2010 image in ArcMap.
  
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  Find the breach in the barrier island.
  
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  Switch between the two images to answer the following questions.
  

3. In the 2010 image, there is a long boardwalk that ends in a T-shaped pier in Bellport Bay. What happened to the boardwalk when the storm breached the barrier island?

4. What happened to the island just northeast of the breach?

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  Save your New York map. You will be using it again.
  

Note to instructor: Recent aerial photos can be downloaded from the Rhode Island GIS website, www.edc.uri.edu/gis/. The photos can be preloaded onto student computers or the students can download it.

Instructions for students or instructor, using ArcGIS 10.2.2:

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  Open a new blank map in ArcGIS.
  
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  Click the down arrow next to the “Add Data” tool.
  
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  Choose “Add Data from ArcGIS Online”.
  
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  When the ArcGIS Online box appears, type “Rhode Island” into the search box.
  
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  Select “Rhode Island Aerial Photographs 2011”.
  

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  Open the Go To XY tool and type in the following coordinates: 41 19 32.32 N, 71 47 25.59 W. When the map zooms to the correct location, click on the Add Point icon (fourth from the left in the Go To XY box) to mark the location.
  
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  Use the Measure tool with the units set to feet. Measure the beach from the road to the ocean edge.
  

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  Save your Rhode Island map. You will be using it again.
  

Go to www.crmc.ri.gov/maps/maps_shorechange.html

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  In the first list, “Watch Hill to Narragansett Pier (South Shore)”, click on the “Westerly_Atlantic Beach” link (third from the bottom) to see the shoreline change for Misquamicut.
  
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  The maps are PDFs. You will have to zoom in to see them properly. Hover or click near the center of the bottom of the page and click on the magnifying glass with the plus sign in it.
  
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  The numbered black lines that divide the beach into sections are beach transects.
  
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  The yellow numbers show the average change per year in feet and meters. The red numbers show the total change from 1939 to 2004 in feet and meters. Negative numbers mean that the beach has retreated landward. Positive numbers mean that the beach has built seaward.
  
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  The red lines are the 1939 shoreline, based on aerial photos taken at the time, and the blue line is the modern shoreline.
  

7. Which beach transect line shows the greatest amount of beach change? What is the rate in feet per year?

8. Given the evidence, is it likely that Atlantic Beach could be breached by a hurricane more easily now than in 1938?

Breaches affect the salt ponds behind barrier islands. Salinity and currents can increase, and future storm surges will enter the pond, but better tidal flushing can reduce pollution. Breaches are natural and can be beneficial to salt pond life.

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  Save your New York map. You will be using it again.
  

Overwash is natural and gradually moves barrier beaches inland over time. Structures on a beach block overwash. Instead of washing over the beach to the salt pond, waves hit the structures, often damaging or undermining them, and erosion increases. Instead of being deposited in the salt pond, sand can be dumped out at sea. Over time this shrinks the barrier beach.

The storm surge from Sandy flooded structures in coastal areas and dumped sand around them. This can be seen in post-storm aerial photos of Rockaway Beach, Queens, at the west end of Long Island.

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  Open your New York aerial photo map in ArcGIS.
  
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  Open the Go To XY tool and type in the following coordinates: 40 34 51.17 N, 73 49 52.43 W. When the map zooms to the correct location, click on the Add Point icon (fourth from the left in the Go To XY box) to mark the location.
  

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  Open a web browser and go to storms.ngs.noaa.gov/storms/sandy/ .
  
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  In the Search box, type in “Beach 108^th Street” to see this area after Sandy.
  
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  Switch between the two images to answer the following questions.
  

A topographic map will clarify how vulnerable this area is to flooding in a hurricane.

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  In your ArcGIS map, click on the down arrow next to the “Add Data” tool and select “Add Data from ArcGIS Online”.
  
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  In the search box in the ArcGIS Online window, type “Topography”.
  
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  Select “USA Topo Maps” to download a layer of USGS topographic maps.
  
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  Drag the topography layer to the top of the Table of Contents so it is visible.
  
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  Zoom in to see the most detailed topographic map.
  

3. Did the floodwaters reach the sewage treatment plant on the north side of the barrier beach?

Rhode Island’s barrier beaches are not as densely developed as this one but they can still have a lot of houses and other structures on them. Let’s see how Atlantic Beach in Westerly compares in elevation to Rockaway.

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  Open your Rhode Island map.
  
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  Click on the down arrow next to the “Add Data” tool and select “Add Data from ArcGIS Online”.
  
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  In the search box in the ArcGIS Online window, type “Topography”.
  
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  Select “USA Topo Maps” to download a layer of USGS topographic maps.
  
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  Drag the topography layer to the top of the Table of Contents so it’s visible.
  
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  Zoom in to see the most detailed topographic map.
  

5. The storm surge from the 1938 hurricane was 10-12 feet high. Would Atlantic Beach be mostly inundated if a similar storm were to strike it now? Would the cottages along Atlantic Avenue escape flooding?

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  Save your Rhode Island map.
  

Salt marshes are part of the barrier beach system. They help to absorb the force of storms. A salt marsh can absorb more water when it is left in its natural state than when it is filled in and built on. Unfortunately, many of the salt marshes in the northeastern U.S. have been filled and built on or otherwise degraded by pollution, dredging, invasive species, and rising sea levels. Rhode Island has lost thousands of acres of salt marshes since the start of European settlement. Many have been filled with material dredged from navigational channels.

• 
  Open your New York aerial photo map in ArcGIS.
  
• 
  Open the Go To XY tool and type in the following coordinates: 40 47 59.19 N, 73 39 04.50 W. When the map zooms to the correct location, click on the Add Point icon (fourth from the left in the Go To XY box) to mark the location.
  

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  In the Table of Contents, put the 2010 aerial photo layer above the topographic map layer. Toggle the aerial photo layer on and off.
  

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  Make sure the topographic map layer is visible. In the toolbar, click on the Measure tool (the ruler). The Measure dialog box opens.
  

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  Click on the polygon, the second symbol from the left in the Measure box, for Measure an Area.
  

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  Click on the small triangle next to the . In the pull-down menu, choose “Area” and set the units to acres.
  

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  Click and drag to draw a polygon around the wetland area in Oneck. Double-click when you are done to make the polygon disappear. The Measure dialog box remains open and shows you the area of the polygon.
  

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  Look at the topographic map layer and draw another polygon around the undeveloped salt marsh close to the stream.
  

3. Does this area have the same capacity to absorb floodwaters in 2010 as it did when the topographic map was made in the mid-20^th century?

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  Open your Rhode Island map and go back to Atlantic Beach. Compare the area of salt marsh around Winnapaug Pond in the topographic map to the aerial photo.
  

It is easier to see salt marsh loss on parts of Long Island than in Rhode Island because much of it has been more recent and the old marsh can be seen on fairly new maps. Also, Long Island has more salt marshes on the mainland side of the salt ponds. These tend to be developed rather than those on the barrier beach side. Rhode Island’s south coast is more hummocky and has fewer salt marshes on the mainland side of the salt ponds.

The filling of coastal waters and wetlands began in Providence in the 1700s. Much of downtown was once a cove and marshland. Downtown was flooded to depths of more than 10 feet in places by hurricane storm surges in 1938 and 1954. The Fox Point Hurricane Barrier was built across the Providence River in the 1960s to keep this from happening again.

You can see the consequences of the city’s expansion into low-lying areas by looking at a hurricane inundation and evacuation map for Providence.

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  Open a web browser and go to
  

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  Open the hurricane evacuation map of Providence. Zone A (red) is likely to be inundated in a Category 1 or 2 hurricane. Zone B (yellow) is likely to be inundated in a Category 3 or 4 hurricane. An area that can be flooded in a Category 1 or 2 storm will also be flooded in a Category 3 or 4 storm.
  
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  The maps are pdf files. You can move around with the sliders at the edges of the browser window.
  

There is no easy answer to the problem of how we should handle rising sea levels, increasing population, and future hurricanes!

References

American Littoral Society. Assessing the Impacts of Hurricane Sandy on Coastal Habitats. American Littoral Society for the National Fish and Wildlife Foundation, December 17, 2012. crssa.rutgers.edu/projects/coastal/sandy/doc/ALS%20NFWF%20Final%20Assessment%20Report%20121712.pdf

Blake, E.S., T.B. Kimberlain, R.J. Berg, J.P. Cangialosi, and J.L. Beven II. Tropical Cyclone Report. Hurricane Sandy (AL182012), 22-29 October 2012. National Hurricane Center, NOAA, February 12, 2013.

www.nhc.noaa.gov/data/tcr/AL182012_Sandy.pdf

Tanski, J., H. Bokuniewicz, and C. Schlenk, Eds. Impacts of Barrier Island Breaches on Selected Biological Resources of Great South Bay, New York. Final Report, March 2001. New York Sea Grant (State University of New York and Cornell University), 2001.