The Dynamic History Of The Popponesset Spit
By: Brian Kehrl
The Popponesset spit is a shadow of its former self.
Over the past six decades it has withered from a massive beach running across the mouth of Popponesset Bay and covering seven-tenths of a mile of the Cotuit shoreline, down to sliver of a sandbar, less than half its previous height and a quarter of its previous width.
Without nourishment piped over to its shores from dredging around the entrance to the bay, some experts say it could breach, even permanently, at any of several points in the next big storm.
The evolution of the spit has been watched closely by officials and residents over the past several decades, and the concerns about its integrity are nothing new.
In many ways, the issues have not changed since a drastic reduction in the size of beach in the 1950s and 60s led to a series of detailed reports by scientists at Woods Hole Oceanographic Institution in the early 1980s. Public concern has ebbed and flowed, often rushing forward after some natural event, like Hurricane Bob in 1991, illustrates how precarious the spit can be.
One constant, however, through the thick and thin of recent decades, has been concerns voiced by Save Popponesset Bay, a little-known nonprofit that owns the majority of the spit and is dedicated to preserving the beach, maintaining navigation in the Popponesset area, and protecting the property of homeowners in Popponesset and New Seabury.
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But those ongoing concerns, which are now focused mainly on several unvegetated, low points along the spit, have led to two new efforts this winter to protect the barrier beach. With the Mashpee Waterways Commission and town officials working in conjunction with SPB, dredged material from the outer channel will be deposited directly onto the low points in an effort to build them back up. And SPB will then be installing an erosion control system known as “sand drift fencing,” meant to hold the new sand in place.
The spit is a defining feature of the bay and of Mashpee’s environment: it is host to hundreds of beachgoers on any given summer day, shelter for coastal property owners, home to two endangered bird species, and key to creating the productive estuarine ecology of Popponesset Bay. Yet it is also one of the most dynamic landscapes on Cape Cod, a sort of mini-Nauset that has proven as unpredictable as it is beloved.
“It’s almost like it’s alive, the way it moves and does what it wants,” Harbormaster Perry F. Ellis said in a recent interview.
Protected, But Not Completely
The forces shaping the Popponesset spit are fundamentally similar to those that shape Nauset and the coastline of much of the Cape and Islands, according to coastal geology books about the region.
But a crucial difference here is the protection offered by Monomoy Island, Nantucket, and Martha’s Vineyard from the brunt of Mother Nature. That protection comes from both blocking direct waves and wind, as well as restricting the tides from pushing and pulling water and sediment.
Protected as the Great Neck between Waquoit and Popponesset is, however, Mother Nature is still at work. Watching an outgoing tide rip through the mouth of the bay, running along the knuckles at the first of the spit, shows the strength of even the most regular of the forces that shape the beach.
The tides and wind move sand along the shore, predominantly in a northeasterly direction, from Succonesset Point out to the tip of the spit, and exchange sand from the bluffs above the beach, the bottom of the sound, and the coastline itself.
But it is storms that account for most of the drastic changes to the spit over the years, not the everyday wear and tear of tides. Major storms are responsible for more than half the shoreward migration of the spit over the past six decades, according to the WHOI reports.
Growth And Contraction
The history of the spit can be broken down into three general time periods: before the 1850s, the century between the 1850s, and post-1950s. In that time period, according to the three WHOI reports and a 1993 Army Corps of Engineers study, the spit has gone from short to long to short again.
Maps and charts between 1779 and mid-1800s show the spit to be generally stable and in a similar location as it is now. The maps are imprecise, however, so little is known about the exact condition of the spit in terms of stability, according to the WHOI reports, by authors David G. Aubrey, Arthur G. Gaines Jr., and Margaret R. Goud.
In the mid-19th century, however, the federal government began to prepare and print more precise maps of the shoreline here.
And beginning in the 1850s, the spit began to elongate, growing past Meadow Point on the western side of the bay’s mouth, past Oregon Beach and Rushy March Pond in Cotuit. It maxed out at more than 260 feet wide, more than 13 feet high, and about 1.8 miles long.
For the next 100 years, the spit appears to have been relatively stable in size but also subject to numerous breaches at different locations.
Then came the 1950s, a period of revolution for the spit, both at the hand of man and Mother Nature, according to the WHOI reports. The decade saw the first heavy development of the shoreline and construction of the first groins along New Seabury and Popponesset Beach and a series of three strong hurricanes that split the once massive barrier beach into two sections.
The splitting breach resulted in the whole northeastern section, more than 1 kilometer long, separating from the rest of the spit and eventually eroding into the Cotuit shore. It set the stage for the configuration that in essence remains to this day, remarkably similar to the configuration that existed up until the 1850s.
“The breach occurred near the base of the main inlet channel and provided a very short alternative channel for water exchange between the bay and Nantucket Sound, bypassing the much longer pre-existing inlet channel (nearly 1 km long). The new breachway quickly became the prime conduit for tidal exchange between the two bodies of water,” according to the 1982 WHOI report.
Since the 1950s, the spit has not changed much in length, but it has changed drastically in width, height, and location.
The arm of the spit has rotated counterclockwise, migrating between 150 and 200 yards in toward the bay.
The barrier beach has breached numerous times in recent years, most notably in the early 1990s, when a 30-foot-wide cavity opened up near the southern tip of Popponesset Island. The breach was quickly refilled with dredged material cleaning up the results of the storm.
Perhaps no other contemporary physical feature illustrates the migration of the spit better than the remains of a beach club built by New Seabury on the spit in the 1960s. The spit shrank right out from underneath the development, which included a large paved parking lot, cabana, dock, and restrooms, so by the early 1970s the club had to be abandoned and eventually torn down.
“If you hadn’t seen it when it was what it was, and seeing it now, you wouldn’t recognize it,” Mr. Ellis said.
Pilings from the dock that was inside the spit now stick out on the sound side of the beach. So while the remains of the dock have stayed put, the spit has shifted inward, folding completely over itself.
The same phenomenon holds true with what was known as Big Thatch Island, a small mass of beach grass and small trees that once lay well inside the spit. The peat and soil from Big Thatch can now be seen along the Nantucket Sound shoreline about three-quarters of the way down the spit.
What The Groins Have Wrought
Conventional wisdom, from the 1960s through today, holds that the groins to the southwest of the spit, along the coast of New Seabury and the Popponesset neighborhood, are robbing the spit of the sediment that once kept it thick and healthy. Residents and officials alike point their fingers at the large groin near the staircase down from the parking lot at Wading Place Road, a feature known as the “terminal groin.” A look at a map shows the beach curving in behind the rocky groin, feeding the perception that it is to blame for starving the spit of needed sand.
The scientific reports, however, tell a more complicated, somewhat different story. The groins do prevent sand from moving along the shoreline, a phenomenon known as “littoral drift,” but they do not appear to be detaining enough sand to account for the shriveling of the spit.
“The net effect of the groins appears to be minimal,” according to a survey of all the shoreline structures between Waquoit and Cotuit bays. “Though the beach has remained stable since the construction of the groins, its width is not substantially different from beaches to the southwest, where there are no groins.”
The Army Corps of Engineers report states, “The groins have probably limited sediment supply to Popponesset Spit to some degree; however, most of the groins are short and sediment is likely to bypass them under storm conditions because of the wider surf zone.”
However, while the WHOI reports make clear that while the groins are not solely to blame for the loss of the spit, armoring the shoreline has had consequences. Construction of seawalls, for example, prevents the exchange of sand between the beach and the dunes above, which also serves to starve the beach of a source of natural nourishment.
“Beach stability at any point in the cell can be affected by changes in any element of the sand budget elsewhere in the littoral cell, a lesson learned at great expense in past decades through man’s attempt to modify or stabilize beaches,” according to the 1982 report.
The changes over time demonstrate the difficulty in establishing a baseline. What is the natural state of the spit? According to the reports, there is not one. There are different configurations that are more or less stable, but the natural state is one of change.
Richard J. Bailey, executive director of Save Popponesset Bay, said he holds no illusions about humankind’s ability to effectively sculpt the shoreline.
“Preserve and protect is how we describe our goals,” Mr. Bailey said. “We are not egotistical enough to even contemplate that we could move it out to some location that it was in before.”
The nonprofit aims to preserve the spit for the next generation, so it can then take up responsibility to preserve it for the generation after it, he said.
The Point of Concern
The most dire of the predictions in the old reports have not come to pass. The 1993 Army Corps of Engineers report, for example, predicted that another major breach was likely within 10 years and possible within two to five years. “The reduction in peak elevation indicates that a less severe storm can now completely submerge the spit. Whereas a 10-year event in 1966 could cause breaching to occur, a 10-year event now would probably submerge the entire spit allowing more energy to reach the interior shoreline. Diminished elevation and reduced width are key factors to the evolution of Popponesset Spit,” according to the Army Corps report.
For Save Popponesset Bay, however, the situation is still touch and go.
“We hold our breath during winter storms and hurricanes and any other major storm event,” Mr. Bailey said.
According to Norman Hayes, an engineer contracted by Save the Bay from the firm BSC Group, most of the concern is directed at three low-lying areas along the spit, and one area in particular: the section of the spit just south of Popponesset Island, where erosion from the Nantucket Sound side and a dredged channel in the bay have squeezed the spit down to a width of about 130 feet.
Mr. Hayes said since 2000, the spit has narrowed by about 12 feet at the point of the island.
Where the spit is at its skinniest and lowest, it is most likely to breach, Mr. Hayes said in an interview.
A breach at the point of the island would be the “doomsday scenario,” Mr. Bailey said.
The channel dredging, which is done about once every five years, is necessary to provide access to boaters in and out of Popponesset Creek and to maintain tidal flushing for water quality, Mr. Hayes said.
“The bottom line here is simple. The spit wants to migrate in and attach itself to Popponesset Island. And as the naturally occurring sand has been reduced, the spit has lowered and its width has been dramatically reduced,” Mr. Hayes said. “The difference is, before, if there was a hurricane, it would breach, but it could repair itself quickly. Now, because of a lack of sand, it can’t repair itself fast enough.”
The old reports likewise point to the island as the most likely location of a major breach. “A response to such a breach formation must be rapid, and based on a management scheme accepted by the Town of Mashpee. The implications of such a breach are profound, in terms of patterns of erosion and flushing of the estuary bay system,” according to the 1983 WHOI report.
James P. Hanks, former chairman of the Mashpee Waterways Commission who has studied the spit in detail, and Mr. Ellis both said the spit seems to be fairly stable these days.
“With the dredged material, it is pretty much maintaining itself. It is still trying to creep inland a little bit, but it is pretty much maintaining. But of course we haven’t had a hurricane. If there is a hurricane, all bets are off,” Mr. Ellis said.
There has been no shortage of ideas of how to fix the spit.
One of the more common recommendations through several studies was to let the channel between the Popponesset Island and the spit fill in and reroute the navigational channel from the south side of island to the north side, which would prevent some of the pinching effect that has made the section of the spit near the island such a concern.
In order to continue to allow large boats to continue to use the area, however, that approach would requiring building a new bridge to Popponesset Island to provide more clearance.
The Army Corps of Engineers studied that option, and the cost-benefit analysis resulted in a recommendation of “no action.”
Studies have also recommended pursuing a groin or set of groins along the spit and at the mouth of the bay, to keep the channel from filling in and hold sand at the spit.
Plans were kicked around in the 1990s to bring in 20,000 truckloads of sand, or 400,000 cubic yards of material, to either rebuild an entirely new spit or add to the ocean-side beach.
More recently, the idea of using an innovative erosion control structure invented by Mashpee resident Oskar H. Klenert has been raised, according to discussion at a December waterways commission meeting. The Earth Cell Modules, which were proposed but not permitted in front of the town parking lot at South Cape Beach, would be installed underground at the low point near Popponesset Island. The discussion, however, is preliminary.
To date, rather than pursuing a grand engineering project, the town and SPB have instead opted for one of the more low-key recommendations contained in several of the old reports: continue dredging and nourish the spit as much as possible. Pumping it in from elsewhere adds sand in lieu of what is lost to the seawalls and other structures up the beach.
There are at least three large dredging projects ongoing and planned inside the bay, in Popponesset Creek, and at the mouth of the bay in Nantucket Sound.
In an upcoming story, the Enterprise will report on the dredging of the mouth of the bay, scheduled to take place this month. The timing of the story will depend on the weather. The dredge was scheduled to arrive earlier this month, but poor weather and other issues delayed its deployment.
Dredging is tentatively scheduled to begin in the middle of next week, although poor weather predicted through the weekend may continue to put off the project. The next story will follow the commencement of the dredging.
A subsequent story will report on the sand-drift fencing that Save Popponesset Bay plans to install in three of the low-lying areas.
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