Erosion: A Natural Process
The current rate of erosion on the ocean side of the Cape is estimated to be about 0.8 meters a year. This is an average for the entire length of the coastline since the amount of erosion happening in each area can be highly variable. While some areas consistently suffer from a greater amount of erosion like Nauset Beach and Wellfleet, some other areas like the backshore between Provincetown and Truro are exhibiting growth via accretion. Other areas along the seashore can be affected more sporadically by large storms that make dramatic changes to the coastline.
Like in any other coastal area, erosion has always been happening on the Cape as the longshore sediment transport system cyclically moves sand down the glacial escarpment. According to Graham Giese, the outer Cape has experienced around 7 km of erosion since its post glaciated formation, helping to establish the modern sediment deposits that make up the hook and elbow of the Cape:
The unconsolidated Pleistocene glacial outwash deposits forming the east-facing outer arm of Cape Cod have eroded some 7 km over the past 10,000 years in response to storm waves and rising sea level producing a 24 km-long coastal escarpment extending southward from Truro to Eastham.[i]
Within the National Seashore, there is an attempt to interfere as little as possible with natural coastal processes and to allow the coastline to change unimpeded, while trying to limit disturbances caused by human impact. This policy instituted by the NPS for the National Seashore sets Cape Cod apart from any other coastal areas that are reinforced by armored structures such as rip rap, seawalls, breakwaters and revetments that attempt to stabilize the coast line, making them more stable for development and general livability.
Despite the negative impact that erosion can have for residents, like necessitating expensive relocations to be carried out to save precariously placed homes, it is important to understand the essential role that erosion has in the context of a coastal system. Erosion related woes are the result of looking through an anthropocentric lens at its effect on our ability to live directly on the ocean but it should be understood as a positive and necessary process to maintain the equilibrium of the coastline. Erosion acts as a distributor of sand, bringing it from the toe of one glacial cliff or coastal bluff to be deposited on the shores of some other nearby area. In this way the beaches are continually replenished. The New York State Department of Coastal Resources teaches about erosion in the following way, which helps people understand why the manipulation of the shoreline has a negative consequence:
Shorelines are dynamic places. Weather systems generate wind, waves, rain, and other forces that affect shorelines. Accompanying the weather systems are environmental effects including storm surge, overwash, flooding and erosion creating a complex array of coastal hazards wherever development occurs near the shore. Remember that where they do not create risks to life and property these hazards are simply natural events with positive effects on the coastal environment. Natural protective features such as floodplains, wetlands, offshore bars, beaches, dunes and bluffs help to protect the shoreline by absorbing storm energy and flood waters. Unfortunately, the effectiveness of these natural protective features are impeded by structures and development.[ii]
By not seeing erosion as an oppositional phenomenon, we can focus on what strategies can be used to work with it to stabilize the beach instead of relying on hard engineered erosion solutions that aim to prevent it.
A sign warning visitors to stay clear of an eroding cliff face.
There is an assumption that over time erosion will continue to carve away at the beaches, enough to affect various structures and homes that are directly on the water as they recede and become less stable. For these buildings, erosion is an inevitable process, and it may eventually be necessary for the building to moved or demolished. As a result, numerous structures have been lost to this process when they have not been able to be moved in time for myriad reasons including a lack of available resources, dramatic cases of rapid erosion, an unviable project or lack of political or personal will. Confronting the effects of erosion is a reality for both the NPS and residents who face this problem every year at a frequency that will quicken with greater storm power from global warming and sea level rise. To help bring attention to this process and have beach goers understand how their individual interactions have an impact, the NPS invests heavily in trying to educate visitors through different means like erecting interpretive signage. In this way visitors are reminded by park signs to tread carefully along the beach and stay on established paths because of sliding cliffs or fragile dune grass.
Erosion does not just happen on the ocean side but happens on all sides of the Cape; on the bay side it erodes, but at a slower rate. On either side the process works the same way, whereby sand particles slough off the coastal bluffs otherwise known as glacial cliffs, settling on the toe where it is eventually washed away by incoming and outgoing waves. It is concerning that the rate of erosion on the bay side has changed in recent history. Prior to the 1950’s it was calculated that the rate of erosion was about ½ foot a year, but since the 1950’s as more hard engineered structures have been constructed to protect the coastal uplands, the erosion rate has increased to be about 1-1½ feet a year. This observation further emphasizes the concept that the wave power hitting the beach is not dampened by these structures but displaced, causing more wave impact and erosion to affect adjacent areas.
[i] Giese, Graham, and Mark Adams. Cape Cod Shoreline Change and Resource Protection. Prop. Provincetown Center for Coastal Studies and Cape Cod National Seashore (U.S. National Park Service).
[ii] “Natural Waterfront – Flooding & Erosion.” NYS DOS Coastal Online Resources. Web. 06 Nov. 2009. <http://www.nyswaterfronts.com/waterfront_natural_flooding.asp>.
