Lab 7 Coastal Hazards 2023 (1)

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Dec 6, 2023

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Geol. 116 Fall 2023 Lab 7: Coastal Hazards You’re the vice president and senior principal for insurance company Denyallclaims in their San Mateo, California, office. You were able to buy a really nice house in Moss Beach, across the mountains on the coast, back before real estate prices went completely crazy in the San Francisco Bay Area. But the company wants to transfer you to their suburban New York office in Westhampton, Long Island. You’re really torn on this, because, despite the fact that you grew up in New York, you’ve become very comfortable with the California lifestyle, especially your house overlooking the ocean. So you’d like to be able to live on the coast if you do move to Long Island. After careful review of the value of your Bay Area house (Zillow lists it at $4.1 million) and comparison with similar prices on Long Island, you’ve identified the community of Westhampton Dunes as an option were you to move. But being the wise insurance executive that you are, you want to further explore the risks associated with living on the south shore of Long Island, particularly in this location, compared to your current West Coast abode. You’ve decided to supplement what you can learn about the science and policy issues at Westhampton Dunes with analysis of information about erosion and deposition along the south shore of Long Island—and compare what’s been happening there with what has been occurring at the town you currently live in, Moss Beach California. You find particularly useful information from NOAA (the National Oceanographic and Atmospheric Administration at noaa.gov), the New York Times, and other sources. And you learn there have been significant issues at Westhampton Dunes, as well as where you live in Mass Beach. Westhampton Dunes Your goal is to identify how stable the Westhampton Dunes location is. a. How do coastal processes work here—role of longshore transport, large storms, extent of beach, etc.? Note the first of the accompanying photos, which shows the effects of groins at Westhampton Beach, which is immediately east of Westhampton Dunes. The waves that hit the beaches with oceans may have occurred due to hurricanes or storms from the Caribbean by long and low swell saves. Long Island has 2 high and 2 low tides every day. When nor’easters or other storms occur, storm surges are a possibility and can lead to major flooding. In situations where water levels rise, the sand is pushed into the bay. On the south shore of long island, the waves hit the beach at an angle that leads to sediments being moved from one side to the other from a push and pull of a sediment of waves. The direction of the waves determines the way the sediment is pulled. Winds blowing west are usually stronger than the east so longshore transport in southern long island moves the sand east to west. The bigger the wave, the most sand and large sediment pieces are moved. Groins were built in an attempt to control erosion and the amount of sand being pushed around. Sand can be moved from the shore temporarily which will create sandbars, so purchasing a boat should be done with caution. b. You’ve discovered a major event that occurred in the early 1990s: the island was breached, and the breach was closed and refilled. You’ll find lots of information about it online. What happened, and why? Examine the photos on the following pages; note especially the relationship between the groins and the breach. Among the sources of information: https://seagrant.sunysb.edu/cprocesses/pdfs/LIDynamicSouthShore.pdf (hint: focus on descriptions of the 1992 opening of Little Pikes Inlet/Westhampton). New York Times articles from August 27 and December 23, 1993 (see below) . The text on page 5 provides additional information. The New York Times article from 2003 provides an excellent update. The Nor’easter that occurred in 1992 caused an increased level of water and flooding. The storm was 30 years because statistically they happen once every 30 years. This led to a new inlet being

created and changed existing ones. This caused water to enter the bay and flooded and eroded new areas. To fix the inlet, money was spent to fill it in by the town. ` c. What mitigating measures have been taken since this event? How effective were they? Answer this by first examining the impacts of Hurricane Sandy in 2012. Using Google Earth and the history function, go to Westhampton Dunes and examine changes in the coastline that occurred in 2012 by comparing images before and after the storm; use Dune Road (county route 89) as a constant marker and measure the distance from the road to the beach front. The history of interventions since 1992 is briefly summarized in this short report from the Army Corps of Engineers. After the hurricane had occurred, west of the Westhampton dunes, where no housing or infrastructure was, had a breach so there was erosion on the beach. No measures had been put in place to protect the coastline which caused the erosion to be more severe. Westhampton only receded a little. The distance from Dune Road to the beachfront was 0.03 miles. Before the hurricane the distance was 0.7 miles from beachfront to shoreline. It moved to 0.04 after the hurricane. d. What is the current situation in Westhampton Dunes? How has the beach changed as a result of the groin system and recovery efforts? Look at recent images in Google Earth and summarize the differences between the coastline in 2013, 2016, 2019, and 2021. Overall the shoreline is slowly receding, but the change is less significant by the groins because they are working. e. Is this a good place to live, in terms of the potential for future events like the one you’ve learned about? Explain your answer with information about the recovery of the area as well as the risk for future events (such as the potential for storms to damage the area). There is a great risk and potential for future events to cause flooding, erosion, storm surge, and hurricanes. Lots of people have very expensive homes and are able to afford insurance as well as beach repair, one major storm could destroy all of the homes. This isn’t cost effective due to the possibility of breaches, inlets, and erosion. Moss Beach, California a. Time to look at your current location in California to get a better idea about the stability of this coastline. Your house at 201 Nevada Ave., Moss Beach, has a spectacular ocean view. But you are well aware of the issues along this coast. Your house has been protected by the large boulder accumulation that a previous owner emplaced to harden the base of the cliff, but cliff erosion has continued immediately north and south of your house. Use Google Earth and the history and path functions to estimate the amount of coastal erosion around your house. a. First establish a “baseline” along the coast using the 1993 photo. You should be able to mark the coastline (specifically, the crest of the coastal bluff), although the image isn’t sharp. b. Mark the edge of the coastal bluff in May 2022. Describe the changes. Then measure the amount of retreat (i.e. distance between the two lines) at 2 points, one just north of your house and another just to the south. c. How rapid has cliff retreat been? To what extent is it greater or lesser in the developed area north of your house versus the undeveloped area south of your house? The cliff retreat is 20 meters which is pretty rapid. South of the house is 3.40. It is greater in the developed area north.

The south of the house has more area of beach to erode before it reaches the house. b. You’ll find relevant information about cliff erosion and stabilization in the Moss Beach in the report available here ; the images at the end of this document show the situation at your house, with additional photos on p. 8-10 of the original document. What has been the effect of the armoring in front of your house? The effect on armoring in front of your house is that it prevents erosion. It has been shown to be successful because everything else around the armoring and house has been eroded. Putting It All Together Finally, which site is a safer location to live—Moss Beach or Westhampton Dunes? Justify your answer in terms of what you’ve learned. Your report should be brief, no more than a few pages. Include the measurements you made for Westhampton Dunes before and after Sandy, as well as a screen shot of your lines in Google Earth and the measurements from Moss Beach. Even though we’re asking a number of questions, you should be able to summarize everything in 2-3 pages of text. It is safer to live in Moss beach California because it has a high elevation whereas the location in Westhampton dunes is leveled to the sea so a singular storm could knock out a house. Houses in Moss beach are better protected from the shore and more capable of dealing with a storm. Many inlets and groins needed to be constructed to be able to deal with the water. There are 16 groins at Westhampton beach, 11 of which were constructed from 1965-1966 due to the breaching from the March northeaster in 1962. A couple years later in 1969, four additional groins were added to the west. Groins have been shown to work when it comes to accommodating water over a period,

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however they will not be so useful in preventing water damage during heavier storms. Big waves and elevated water levels can lead to significant erosion on sand from the shore. This can cause the bluffs or dunes behind the beach to get hit. These storms move adjacent to shore, and some sand that was eroded from the dune and/or the beach might be carried seaward and settle in water that is deep and not able to be brought back by more calm waves. This causes sand to be lost from the beach. If too much sand is taken into deeper water, the beach won’t be able to make a full recovery causing the shoreline to move towards land. Long term erosion or recession may be the result. This means that houses on shore level are significantly riskier when storms occur versus a better protected and higher elevated house. The Westhampton Dunes has houses on shore level. A large storm could cause serious damage to the area. Therefore, living on the Westhampton dunes is a greater risk. I would be more likely to have my house destroyed there. In Moss beach the houses are about 20 feet above sea level. The house being higher in elevation keeps it more protected from water damage during a storm. If the water level were to increase, it wouldn’t be a huge deal. If the water level were to increase in Westhampton dunes, the houses would flood much faster. Using armor would also lessen the amount of erosion caused by water. Hurricane Sandy led to the shore moving inland 24 meters. Before Sandy the road was 161 meters from the shore. After Sandy the road was 137 meters from the shore, proving how much impact a storm can have on the area. The shore moves back slower in Moss beach which will ensure that my house will remain safe over time. If a significant storm were to occur in Moss beach, the house would be better protected by the increased elevation which won’t allow for flooding if the water level were to rise. New York Times, August 27, 1993

New York Times, Dec. 23, 1993

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The Westhampton Beach groin field after initial construction From: Modeling long-term beach change under interacting longshore and cross-shore processes, by Hans Hanson, Magnus Larson , and Nicholas C. Kraus, 2011; Coastal Engineering Proceedings, no. 32, 11 p. Evaluation of Groin Shortening There are presently 16 groins at Westhampton Beach. The first eleven and easternmost (up-drift) groins were constructed over 1965-1966 in response to breaching during the March 1962 northeaster. Four additional groins were constructed to the west during 1969-1970. The rubble stone groins in this field of 15 structures were nominally 146 m long, tapering to the sea bottom and having spacing of approximately 365 m. Kraus and Batten (2006) provide the most recent summary of groin configuration and functioning at Westhampton Beach. The original groins functioned as intended (Nersesian et al., 1992) in protecting a once-vulnerable 5-km long segment of barrier beach that had experienced breaching during the September 1938 Great New England Hurricane, a 1958 storm, and the March 1962 northeaster. Although the ten groin compartments of the eleven original groins were not filled during initial construction, natural longshore transport eventually accomplished this. Over the years onshore-directed wind-blown sand has created a high and broad dune that is fronted by a wide berm. Beach fill accompanied construction of Groins 12-15. In December 1992, a northeaster opened two inlets (called Pikes Inlet and Little Pikes Inlet) directly west of the groin field. Pikes Inlet, located most westward, gradually shoaled and was readily closed manually (Bocamazo and Grosskopf, 1999), but Little Pikes Inlet enlarged in the eroding down-drift area directly west of Groin 15. In 1993, the U.S. Army Engineer District, New York (NYD) closed the breach by hydraulic fill placement. In 1996-1997, a tapered groin transition to the west was created by shortening Groins 14 and 15 and adding a short groin (called Groin 14A) between them. The groin tapering together with beach fill has been successful, and the planned renourishment of 3 years has been extended to 4 years.

Initial breaches, Westhampton Dunes. Full extent of Little Pikes Inlet breach, 1992 Pikes Inlet breach Filling in Little Pikes Inlet Breach. Note step-back in beach west of groin (in foreground)

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Lab 7 Coastal Hazards 2023 (1)

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