HomeMy WebLinkAboutSE48_2824 NLC 2019 Annual Review comments RESEARCH AND ENGINEERING, INC.
Corporate Headquarters: 766 Falmouth Road, Suite A-1, Mashpee, MA 02649, (508) 539-3737 Gulf Coast Office: Executive Tower, 3500 North Causeway Boulevard, Suite 1480, Metairie, LA 70002 www.appliedcoastal.com
December 29, 2020 Emily Molden Nantucket Land Council, Inc. 6 Ash Lane PO Box 502 Nantucket, MA 02554 Re: Comments regarding SBPF’s 2019 Annual Review of Sconset Geotextile Tube Project Report
Dear Emily, Applied Coastal Research and Engineering, Inc. (Applied Coastal) has been providing
technical guidance and support to the Nantucket Land Council Inc. for more than 20 years concerning coastal processes and related scientific and engineering issues along the shorelines of Nantucket. As part of the on-going support of the Land Council, Applied Coastal has reviewed the supporting technical information supplied by the Applicant (Sconset Beach Preservation Fund (SBPF)) as part of the 2019 Annual Review of Sconset Geotextile Tube Project report developed by Epsilon Associates, dated March 2, 2020. The documents provide a wide range of data, analysis, and interpretation of the monitoring information collected on behalf of SBPF. The data in the Annual Review continues to confirm that erosion along the eastern coastline of Nantucket has increased since the geotube revetment was installed in the winter of 2013/2014. A number of the conclusions presented in the Annual Review are inaccurate and do not reflect an appropriate background in coastal processes which is required to accurately understand and interpret the data presented. Based on flawed interpretation of the data, the Epsilon’s review draws inaccurate conclusions regarding the severity of erosion being experienced along the unprotected shorelines, the impacts associated with inadequate performance of the mitigation template to provide
sediment to the littoral system as required as a condition of the project, along with inaccurate interpretation of data and analysis regarding how the mitigation volumes were determined based on SBPF’s own studies and reports. The following comments also include the information and
analysis presented in Mr. Berman’s review of the Annual Review dated December 8, 2020 and Epsilon’s response to Mr. Berman’s review dated December 21, 2020.
Mitigation Volume
The analysis of the mitigation volume delivered on an annual basis by Mr. Berman is very thorough and accurate based on data provided by SBPF. The accounting of sediment volumes illustrates that since 2016 SBPF has failed to provide the required volumes of mitigation to the littoral system and as of December 2019 is deficient is meeting the permitting conditions set by the Nantucket Conservation Commission and Massachusetts Department of Environmental Protection (MassDEP). The missing mitigation volume, 20,735 cubic yards, represents approximately an entire year of sediment contributions that were not available to mitigate for impacts on adjoining shorelines resulting from SBPF’s geotextile tube revetment. Epsilon’s response to Mr. Berman’s finding regarding the missing mitigation, the implication being drawn
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by project opponents that the volume of sand needed to protect the environment is not being provide is not true, is inaccurate and misleading. First, Mr. Berman is not a project opponent, he
is an independent review hired by the Town of Nantucket to review the analysis and data provided by SBPF. Second, the Annual Review Reports submitted by SBPF since 2016 do not offer any discussion or admission by SBPF or Epsilon that volumes of mitigation delivered were below the required volumes as condition by the local and state permits. The mitigation deficiency has been ongoing since 2016 which illustrates that the Conservation Commission’s order in the early winter of 2019 to stop the delivery of contaminated sediment or the onset of COVID-19 in March of 2020 were not causation for the reduced volumes of mitigation sediment being delivered.
The data clearly shows that the 23,236 cubic yards of mitigation missing from the template over the winter of 2018, would have minimized impacts on adjacent unprotected shorelines and bluffs during the repeated nor’easters experienced in March of 2020 when the mitigation delivery system failed to continue to supply sediment to the littoral system for a period of weeks when
mitigation would have been the most beneficial dissipate energy along the shoreline to minimize the erosion. Examination of the data provide in the Woods Hole Group Monitoring reports since the revetment was constructed continually shows that erosion rates have increased across a
majority of the monitored shoreline. It is inaccurate for Epsilon to state that the revetment structure is not having an adverse impact on the littoral system and adjoining properties, while the monitoring reports illustrate the opposite.
The required mitigation volume of 22 cy/lf/yr has been discussed at length numerous times prior and after construction to the geotextile tube revetment. The mitigation volume was determined utilizing SBPF’s previous studies and analysis which showed the coastal bank does indeed contribute at least a 22 cy/lf/yr (and potentially even greater volumes). This volume has been confirmed twice by MassDEP when issuing Superseding Orders of Conditions for the project and is consistent with mitigation requirements for similar projects permitted by DEP within Massachusetts. The suggestion that the mitigation volume is 1.5-1.8 times the average bank contribution is inaccurate and does not agree with SBPF’s own scientific findings. This is also why MassDEP and Conservation Commission have not approved the use of an adaptive mitigation program which would lower the annual mitigation contribution. The performance of the mitigation over the last 4 years highlights that when lower volumes of mitigation are provided, the erosional
pressures on unprotected shorelines is increased, and thus a mitigation approach of utilizing lower volumes has and will have an adverse impact on adjoining shorelines. Additionally, with SBPF not providing the required mitigation to the system for the last 4 years raises further questions
regarding any conclusions being made relative to reduced erosion volumes from mitigation template providing evidence that sediment is being oversupplied to the littoral system when 22 cy/lf/yr is mandated. The reduction in supplied sediment over a multi-year period would obviously
have a direct correlation to the reduced volumes of sediment eroding from mitigation template, therefore negating the arguments suggesting to much material is being provided.
A more through explanation of how the reduced volume of mitigation was not captured by the Applicants numerous steps to monitoring the template through the accounting of sand delivery slips, drone monitoring, quarterly topographic monitoring surveys, or even substantial reductions in anticipated mitigation costs (20,735 CY at $20-$25/CY is on the order of $400,000 to $500,000) should be requested to ensure similar oversites in the management of the mitigation are corrected and avoided moving forward.
Beach Monitoring
In Section 5.1 of the Annual Review SBPF requests that wading shots should be eliminated from the shoreline surveys. SBPF has not conducted wading shots as required in the Order of Conditions for the project since 2018. This lapse in required monitoring has been
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discussed during previous Conservation Commission hearings and has not been rectified by SBPF nor their consultant Woods Hole Group which is responsible for conducting the surveys.
This request should be denied and
The request to reduce the frequency of the monitoring surveys would jeopardize the value of the long-term dataset to evaluate the performance of the geotextile tube revetment project moving forward or potentially the expanded geotube project that SBPF has been proposing. Littoral systems are influenced on a variety of time scales. Shorter term or interrupted monitoring cycles can show the influence of shorter events (e.g., a passing sand wave, storm event, etc.). However, to accurately understand erosion rates and patterns on the scale of the eastern shoreline of Nantucket monitoring on a decadal time scale is crucial to understanding dynamics and impacts structures have upon the system. It would not serve the interests of Nantucket to reduce the frequency or requirements around the shoreline monitoring.
The aerial bluff monitoring by drone surveys should be expanded. The rapid nature of
being able to deploy a drone to capture post storm surveys along the bluff and aerial beach could provide insightful data regarding the performance of the geotextile revetment following major and minor storm events. This monitoring should include immediate quantification of the mitigation
supplied, severity of end effect erosion, any instabilities in the upper vegetated bank, and aerial photographs of the bluff and shoreline. At a minimum the surveys should occur on the same cycle as the larger scale shoreline monitoring.
To aid the residents of Nantucket in understanding the data provided by SBPF and the influence the Geotextile Tube Revetment has upon the Town owned shorelines, it is recommended that SBPF provide the historic and all future monitoring data to the Town of Nantucket in a format that can be readily displayed in Town’s online GIS system. All the data collected by SBPF is georeferenced and can be smoothly formatted to transfer easily into a GIS format to allow the residents greater access and understanding of the project influence.
Thank you for your time and if you have any questions on Applied Coastal’s comments please feel free to call me at 508-539-3737. Best,
Trey Ruthven