CONTINUING TO SORT THROUGH THE SPIN: MORE FREQUENTLY ASKED - TopicsExpress



          

CONTINUING TO SORT THROUGH THE SPIN: MORE FREQUENTLY ASKED QUESTIONS, AND ANSWERS Q: Is it possible to replicate the natural erosion process? A: No. The erosion which feeds neighboring beaches — Sesachacha, Quidnet, Squam and Wauwinet to the north, Codfish Park, Low Beach Road and round to Tom Nevers to the south — is related to storm events, which cannot be accurately predicted. The coastal processes that make Nantucket Island Nantucket are all interrelated: interrupt the system in one place, and there will be consequences in others. Attempts are now being made through the ConCom hearing process to calculate the amount of sediment that would be necessary to replace what would be lost by walling off the bluff. SBPF estimates 40,000 cubic yards a year, while the consultant for the Land Council, using previously-submitted SBPF figures, comes up with an amount over double that, 90,000 cubic yards a year. Discussion is also ensuing about the grain size of the replacement sediment and whether or not it can replicate the grain size of the naturally eroding buff. In addition, SBPF states it will monitor beaches nearby and farther away to see if there is any variation from what would have been expected, “caused by the revetment.” If an impact is observed, the amount of sand delivered will be adjusted. However, Dr. Young points out, “It has been my experience that mitigation requirements based on any clause requiring that the structure must be demonstrably proven to be the cause of increased erosion or the cause of a downdrift sand deficit are problematic. Proving an increase in erosion on a shoreline is straightforward. Demonstrating direct, indisputable cause and effect in a court of law is almost impossible. Coastal monitoring plans simply can’t account for that level of detail, and monitoring the impacts of storms is particularly problematic. In my opinion, one cannot assume that mitigation sand will be ordered for downdrift property owners if it MUST be demonstrated that the revetment is the primary cause (even if the revetment IS the primary cause).” Q: So, replacement sand would have to be in introduced into the system every year going forward, if the rock revetment were to be installed, in an attempt to “mitigate” for any adverse impacts on adjacent areas? A: Yes, that is what SBPF is proposing to do: to replace the sediment that would have naturally eroded on an annual, or bi-annual basis. Q: For how long would SBPF do this? A: It has not been determined. But, realistically, such mitigation would have to take place in **perpetuity** to protect adjacent coastal areas. Quidnet Squam attorney Dirk Roggeveen, using figures provided by SBPF, estimates that the two island sand pits will run out of sand in 20 years, and SBPF will have to buy and import sand from off-island to dump over the bluff in Sconset. Questions have been raised about the sustainability of such a plan, both in terms of the availability of sand and the cost. Q: If SBPF uses up all of the sand in the two island sand pits, sand Nantucketers need for other purposes than mitigation of a revetment project, where will islanders get sand? Will SBPF be required to replace the sand they took from these pits for the general sand needs of the island? A: At the August 28 hearing, SBPF stated that when demand increased “market forces would create new on-island pits.” Q: How much would such mitigation cost? A: Mitigation cost has not been discussed so far during the ConCom hearings, although Mr. Roggeveen has asked the Commission to consider this aspect of the proposal. According to figures previously provided to the BOS by SBPF, the cost of “sand replacement” would be $400 per linear foot. For a 4,200-foot revetment, that would be $1.68 million annually, for a 3,400-foot revetment, $1.36 million annually.
Posted on: Tue, 24 Sep 2013 21:02:03 +0000

Trending Topics



Recently Viewed Topics




© 2015