Slip Slidin’ Away is being prepared for its move to the lot next door. This will buy some time for it – how much is to be seen. Swept Away remains a few feet from the edge and we have seen the edge behind the Claudy house, the one closest to the lighthouse, degrade further.
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The NLC is a 501 (c)(3) non-profit dedicated to protecting Nantucket’s natural world and rural character by holding and enforcing conservation restrictions, commissioning scientific research, monitoring development proposals, engaging in legal proceedings to protect natural resources, and educating the public on local environmental issues.
After each “weather event”, no matter how insignificant, there is a rush to judge the impact of the geotubes recently installed below Sankaty Bluff. If they remain intact, they are declared a success by some, while others express surprise that they have not been lost to the tides. The tubes’ own survival is not their purpose. Their success or failure can only be judged by their effect on the erosion of the bluff and the impact on the beach.
The winter weather during and after the installation of the tubes has not been a true test of the durability of the structure. Unremarkable tides, wind and rain have exposed the north end of the second tier of tubes, and one 24 hour period has seen the erosion of the beach to a point that appears to be near the top of the first tier. There has been no opportunity to evaluate the effectiveness of the tubes in protecting the toe of the bluff or to measure a potential loss of beach, but one thing is clear; the tubes will have no effect on the erosion of the bluff from above. Photos taken on the morning of 2/15/14 show significant new fissures in the face of the bluff and in the sand covering of the tubes. Large amounts of sediment have spread across the top and run down the south end and the front through crevices 2½ to 3 feet deep. Clumps from near the top have landed on the tube “deck”. Photos taken 24 hours later show new avalanches of dirt and several boulder-sized chunks, with much of the edge of the bluff looking ready to fall at any time. It would be fair to conclude that the bluff is eroding as quickly as ever from rain run-off and wind even if the tides are not reaching the toe.
We acknowledge that those with differing points of view will judge by different criteria. We feel that it can be called a success when it halts the erosion of the bluff and preserves the beach as well.
We have a new folio titled What is There to Lose – The Future of Sankaty Beach. This folio contains photographs we have taken over the past five years. Our hope is that Baxter Road is soon moved and this beautiful beach can be restored to its natural state.
The geotube installation below the Sankaty Bluff is nearly complete. Work is being done to cover the tubes in the envelope of sand required to keep them intact. It is difficult to imagine that they can be kept covered without frequent replenishment, a job that will entail numerous heavy truck deliveries and one or more conveyor systems on Baxter Road for the duration of each recovering.
The photo below shows the second and third tiers of tubes prior to their first covering. It also shows that a less than extraordinary tide has washed away recently placed sand to a point similar to the face of the first exposed tube. This suggests that the maintenance will need to be more frequent than the proposed spring and fall replenishments, and more than the before and after storm maintenance that has been mentioned.
Dirck and I have spent a great deal of time the past month covering the geotube installation on Sconset Beach. The tubes are now installed and work will begin covering them. Most of the sand allocated for this project will be used in covering the tubes. It will be interesting to see how much truck traffic this generates. Twin Chimney has not been moved onto its new foundation and Slip Slidin’ Away awaits its move to the lot next door. The photo below is of Slip Slidin’ Away. We have added a new slideshow to Nantucket Erosion. The link is listed below.
A night of rain brought a significant amount of run-off from the top of Sankaty Bluff. Numerous rivulets of rainwater carried fine sediment down the face until it collected behind the second tier of geotubes. A wetland on the landward side of Baxter Road continues to drain under the road toward the bluff hours after the rain.
The crew installing the geotubes below Sconset Bluff suspended work today to clear out their equipment and backfill behind the tubes already in place. As sand cascaded down the face of the bluff from the conveyor on Baxter Road, a bulldozer spread it down the length of the excavation. The new fill will support the third row of tubes and more immediately, keep storm driven tides from washing out behind the work before it’s completed.
The crew will take the next two days off except to check the site periodically during the storm.
The laying out of the first row of geotubes is complete and the next phase is ready to begin. The bluff side of the excavation has been backfilled and the scour apron for the second row is being sewn to the first. The pump and sand hopper have been moved into position along with their ancilliary equipment, and rolls of apron have been brought up to the site.
The first row was filled with material excavated from the trench but the subsequent rows will be filled with sand trucked to the top of the bluff and poured over the edge via conveyor belt.
The dig continues. The installation of the first level of tubes is nearing the end of the 900′ run. Given the tight schedule, it’s a job of long hours, rain or shine. As the work progresses southward,the ocean is washing away the machine tracks at the northern end of the excavation.
After approval by a split decision of the Nantucket Conservation Commission, an emergency erosion mitigation project has started below the Sankaty Bluff. The effort involves the installation of geotextile tubes and jute bags along a 900′ stretch where the retreating edge of the bluff most threatens Baxter Road, its infrastructure and the houses on its landward side.
The top of the first layer of tubes will be flush with the Mean High Water level, and the additional tubes will be stacked like stair steps back toward the bluff face. A smaller diameter tube will run across the face of the lowest level to anchor the stack in place. In addition, a broad scour apron will cover the bottom of the excavation to prevent undermining of the tubes by incoming waves.
The viability of the geotextile tubes will be determined by their maintenance. In the words of one of the men on the site, “You have to keep them covered.” The plan calls for a minimum of 2′ of sand for cover, suggesting the need for perpetual replenishment. It’s possible that the system will remain untested during the life of the 30 day emergency certification, so its future is unclear.
The slide presentation that follows shows some of the excavation, scour apron deployment and filling of the first tube on the north end of the site.
The construction has begun to install the massive geotubes on Sconset Beach. The cement blocks we were told were part of the house moves further south are actually part of this construction. Sand is being trucked to the site on Baxter Road and transported to the beach via a large conveyor belt system.
Stakes mark the line of proposed work to slow the erosion of the Sankaty Bluff as “Swept Away” finds itself on the edge for the second time since 2010. Runoff from the top, rather than a battering ocean, has opened a large cut that has dumped a considerable amount of top and subsoil down onto the beach.
Concrete forms are being assembled at three of the houses to be moved and large concrete blocks used to counterbalance asymmetrical building masses have been stacked in the open space to the north of the work sites. That stretch was once filled with houses that have already been moved or demolished.
We photographed “Slip Slidin’ Away” in June of 2013 from below the bluff, not entirely sure of which house it was as seen from Baxter Road. It’s now evident that the house is being prepared for a move immediately adjacent to its current site. At first glance it’s not clear what is to be gained by the lateral move, but looking from above and below shows that the bank has eroded considerably more where the house sits now than the short way toward the lighthouse. There are heavier clay deposits near the new site which probably contribute to the slower decay there. Looking at the stakes marking the new excavation, it can be seen that the house will sit approximately 14′ closer to the road in a spot that has an additional 5 or 10′ to the bluff’s edge.
A collection of railings and trellis sits on the edge of the property, waiting for the house to follow.
We took an after hours trip to Baxter road to see if Twin Chimney or House of Cards had moved any since yesterday. Twin Chimney is still up on the edge of the bluff, waiting for the completion of the excavation, while House of Cards is poised over its new location in anticipation of its foundation.