Lab 7 Coastal Hazards 2023
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Dec 6, 2023
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Geol. 116
Fall 2023
Lab 7: Coastal Hazards
Nicholas DeNobrega
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.
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.
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.
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. 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).
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? 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?
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.
Putting It All Together Response: Westhampton Dunes
When trying to determine if Moss Beach or Westhampton Dunes is safer to live in, one of
the main factors to consider is the coastal processes of each location. Coastal processes at Westhampton Dunes are influenced by both natural factors and human interventions such as groins. Groins are structures built parallel to the shore with the goal of limiting erosion on one side and accumulating sand on the opposite side. Even though groins can help stable shorelines, they also have the possibility of disrupting natural longshore transport, which can lead to erosion in other areas. Also, when discussing the stability of the Westhampton Dunes, other factors besides groins influence this stability such as longshore transport, large storms, and the extent of beach. Longshore transport helps shape the coastline by carrying sand primarily in a west-east direction, which is important for maintaining the beach and dune system. Large storms which bring high winds and rainfall can cause coastal erosion and damage to coastal structures, which can affect Westhampton Dunes as the dunes are mainly influenced by the balance of sediment deposition and erosion. Two major events to consider in this location are the nor’easter of the 1990s which mainly hit the south shore of Long Island, and Hurricane Sandy in 2012. During the nor’easter event, hurricane-force winds and storm surges lasted in this area for nearly 4 days. At one point, the barrier island was breached near the westernmost groin, which was most likely due to a design flaw of the groin. This created an inlet that gradually grew wider and wider, which allowed the destruction of a majority of the land and houses on the western end of the breach. This event was included in the “"Top 10" most expensive known New York beach "disaster repair" or modification projects”, with a cost of around 50,000,000 dollars. As a result of this event, response measures were taken such as pumping sand back onto the beach, using bulldozers to help rebuild dunes, and most importantly filling in the breach zone caused by the event. Another significant event at this location was Hurricane Sandy. To understand the effects of this hurricane, we can look at the coastline and how it changed before and after the hurricane. In 2011, the distance between the coastline and Dune Road was roughly 171 meters. In 2013, after the hurricane, the distance between these two points was roughly 162 meters. This distance fluctuates the closer we get to the present year, but there is an overall decline in the coastline.
Overall, I do not feel that this is a good place to live. There is a high potential for similar events such as the nor’easter of the 1990s, which devastated homes near the coastline due to high winds
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and storm surges. Even though there are recovery efforts to mitigate the effects such as pumping sand back onto the beach, which can be seen in this photo.
However, this is just an expensive and temporary solution as the coastline is still on a general decline as the years go on.
Moss Beach, California
When discussing the potential of choosing this area to live in, the key factors to consider is the stabilization and cliff erosion near the house we live in. In this area, one of the attempts to mitigate the cliff erosion are large accumulations of boulders that were put in place, with the goal
of hardening the base of the cliff the house is located on. The location of where the county approved these accumulations can be seen in the image below.
However, cliff erosion has still continued near the north side of the house. General cliff erosion can be attributed to several factors, primarily slope over-steepening and slope overloading Also, shocks and vibrations from earthquakes, water saturation, and removal of natural vegetation play
a role in the erosion. Specifically in regions like ours, marine erosion, high storm waves, and subaerial erosion can lead to the erosion of the cliff. While the retreat of the cliff isn't always catastrophic, it is important for states with areas like these to identify hazard-prone areas and the probabilities of future failure The cliff erosion specifically near our house can be more closely looked at in Google Earth. The line that connects the 1993 placemarks is the rough location of the cliff in 1993. The line that connects the 2023 placemarks is the rough location of where the cliff lies today. Directly in front of the house, the distance between the 1993 cliff and the 2023 cliff is roughly 10 meters. Further to the right of the house, the cliff erosion is slightly greater, with a distance of around 15 meters between 1993 and 2023.
In my view, Moss Beach seems like the better choice mainly because of its location, which means it's less exposed to storms. Both sites have limited options for mitigation, making the decision challenging. However, I believe Moss Beach is more stable than Westhampton Dunes. Unlike Westhampton Dunes, Moss Beach isn't notorious for severe storms, resulting in less beach erosion. While options like pumping sand back into the beach offer some protection, they aren't long-term solutions. Building up the sea cliffs is another technique, but it also provides temporary relief. Considering these factors, Moss Beach appears to have a lower risk of
flooding damage due to its cliffside location, making it the safer option in my opinion.
New York Times, August 27, 1993
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New York Times, Dec. 23, 1993
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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