A private property next to Tisbury Great Pond, permitted to truck in sand from off-Island and dump it in perpetuity in an effort to mitigate erosion, is concerning local environmental officials, who are already worried about sand accumulation at pond coves. Local officials say the sand buildup is affecting water flow and quality, even leading to cyanobacterial blooms.
At a recent West Tisbury conservation commission meeting, town herring warden Johnny Hoy asked the commission whether a permit that they granted to a Middle Point Road property could be altered. The permit allows for sand to be dumped at least once a year as an anti-erosion measure.
The sand dumping supports what conservation commission member Whit Griswold called a “soft revetment.” The system is made of coir logs and gabion baskets, an increasingly more common and natural way of preventing erosion compared with rock walls. The logs, typically made of an organic material, are supported by the gabion baskets, which are cages with rocks roughly the size of a softball. Together, they absorb shocks from waves in order to combat erosion.
“Part of the deal with these [coir logs] is that they need to be covered with sand,” said Griswold. “Sand will absorb the first shocks [from waves] … over time, the sand gets washed away, and these two elements, the coir logs and the gabion baskets, will get exposed. And then the whole [soft revetment] doesn’t break down, but it doesn’t work as efficiently.”
But Hoy, who is also one of the pond’s three riparian commissioners, stated that sand dumping at the property is a small contributor to a long-standing and much larger problem of buildup at Tisbury Great Pond coves.
“Wind marches that sediment to the coves, and nourishes opposing sandbars. They are getting bigger and bigger. It’s not subtle. It’s kind of closing the coves off,” Hoy said, adding that all the sand dumped last year at the soft revetment is gone already.
Though the riparian commissioners open the pond to the sea approximately four times per year, sand buildup restricts the flow of water into the coves that branch off from the Great Pond. As a result, water quality suffers.
Hoy is also concerned about increased development in areas like Middle Point Road that release nitrogen from septic systems and fertilizer use. “There’s lots of development at the tips of the coves, and cyanobacteria are starting to bloom. The coves aren’t getting the flushing that they once did,” he said.
According to Hoy and commission member Griswold, the mouths of both Deep Bottom Cove — located north of the permitted dumping — and Tiah Cove are particularly affected.
The conservation commission initially told Hoy that only the permit grantee could move to alter the permit. However, Griswold says that the commission has found multiple ways that it might be able to act to alter the permit. Griswold does add that the commission would need to further review the permit conditions before any action is taken. “It won’t happen very quickly,” says Griswold. “We won’t do this as an emergency.”
Another impact of sand accumulation, though more minor, according to Hoy, is that getting boats out of the water has become more difficult: “I have to physically drag my clamboat over the sandbar. Sometimes I have to physically carry clams over the sandbar.”
Hoy, who identified himself as a layperson, not a scientist, acknowledged that managing the Great Pond requires balancing many complex issues, and accommodating the many species that rely on the ecosystem. “It would be great to have some genius take all [the] information and figure out what it all means,” he said. “I think all that I can do is just do my bit, and try to reach [out] to what I’m seeing.”
Hoy said that poor water quality at the coves has the potential to impact key pond functions, like the spawning of herring, a population that has suffered due to offshore commercial activities. Deep Bottom Cove is one location that herring use to spawn after the pond is opened in the spring. “Herring spawn in Deep Bottom … bad water quality at coves might have an effect on herring,” Hoy said.
Hoy is also reluctant to dredge the pond in order to deepen its waterways: “I don’t really want to get into dredging, because there is such a delicate ecosystem along those bars, where herring go to spawn. You could totally [mess] it up if you look at it cross-eyed.”
Removing sand from cove mouths also poses salinity issues, as herring and perch require freshwater environments to spawn. “If you took too much [sand] out, the salinity level above those bars might increase to the point where the herring don’t want to spawn there anymore, and perch might not spawn anymore.”
“I’m old. I’ve caught … plenty of fish, plenty of dough from the pond,” said Hoy. “I’m now trying to help things for the next generation.”
Armoring our coast, with massive rock revetments or even so-called “soft” solutions, has so many negative consequences. Every alternative needs to be considered.