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HomeMy WebLinkAboutGoldsmith Inlet: Draft Report 2010Prepared for: Town of Southold 53095 Route 25 Southold, NY 11971 Prepared by: eDesign Dynamics 338 West 39th Street, l0th Fl. New York, NY 10018 BACKGROUND This report has been prepared to provide the Town of Southold, NY, (Town) with recommendations regarding the dredging scheduled for January 2011 at Goldsmith Inlet (Inlet) on the North Fork of Long Island. Goldsmith Inlet is a tidal pond with direct connection to Long Island Sound by means of a channel that has been chronically at risk of closure due to the natural movement of large volumes of sand and stone by storms and littoral drift. This report is not intended as a complete analysis of the conditions at Goldsmith Inlet nor does it intend to address long-term solut ions to the problems of accumulation, beach erosion or jetty maintenance. Rather, the report seeks to advise the Town on its current strategy of dredging and removal of material that accumulates in the channel. A wealth of research and information has been published regarding the portion of coastline that includes Goldsmith Inlet and Mattituck Inlet to the west, but with little conclusive insight into the processes that appear to be leading to channel closure at the Inlet. The bulk oftbe investigative work has been performed to address beach erosion and shoreline change that may occur due to natural processes or as a consequence of the jetty immediately west of the Inlet and other shore protection structures. Additionally, some effort has been directed toward the channel mechanisms and the process of flood shoaling at the inland mouth of the channel. The most detailed work was reported by Offshore and Coastal Technologies in the 2005 report, "An Assessment of Jetty Shortening Alternatives: Goldsmith Inlet, Bay, and Adjacent Shorelines." The 2005 report describes the process by which high-energy flood tides carry sand and sediment inland and into Goldsmith Pond at a faster rate than the Iow-energy ebb tide can carry it back out to Long Island Sound. eDesign Dynamics (EDD) believes that it is this process ofcrcating a net depositional zone that extends several hundred feet into the Pond which will be the eventual cause of Inlet closure. Regular dredging of the channel and the accretion zone to the east of the jetty does not appear to be improving these conditions. Specifically, EDD was asked to review the dredging plans along with existing literature to determine if altering or even canceling the dredging operation scheduled for January 2011 could achieve better results. EDD also reviewed the 2007 NYSDEC permit under which the dredging has been performed, and contacted George Hammarth (Deputy Regional Permit Administrator, NYSDEC Region 1) regarding regulatory flexibility and the requirements for altering the plans as described in the permit. Mr. Hammarth stated that any changes to the planned course of the dredge, final cross-sections of the channel, or locations for depositing fill material would have to be approved by the NYSDEC through the permit modification process. This would involve submission of materials showing intended changes to the plan and reasoning behind the request. Mr. Hammarth understands the limited timeframe involved and his office would make every effort to review the request for modification before the end of the dredging window. This report is limited to review and recommendations for technical changes to the dredging operation. Permit modification would be the responsibility of the Town. The Town and its residents should be clear that the recommendations included in this report may not result in a net positive effect on the Inlet. The forces that cause coastal erosion and deposition are highly complex and highly dependent on individual storm events. EDD is offering its best engineering judgment based on a review of the existing literature, conversations with long-term residents, and a visit to the site on 11/30/10. METHODS EDD was contracted by the Town to perform several tasks related to the issue of sedimentation within the channel at Goldsmith Inlet and the annual dredging that is performed to avoid potential channel closure. The first task involved the identification and review of existing documents related to the geomorphology of the Inlet and the adjacent beach areas (see Bibliography). The second task was composed of a site visit by hydrologists Eric Rothstein and lan Lipsky with time for meetings with residents and stakeholders. Task 3 involved any further communications with other stakeholders and residents who wished to be heard in the course of this investigation, and Task 4 involves the writing of this report. Task 5, a second site visit, will be performed during the dredging operation if the Town wishes for EDD to make comment or offer guidance while the operation is underway. EDD reviewed each of the documents in the bibliography with special attention to sections related to the channel, its historical configurations, and the processes governing the deposition and erosion of adjacent beaches. As it was not in the scope of this project to perform any new engineering study of the area, EDD attempted to formulate a thorough understanding of the specific coastal conditions through consideration and interpretation of existing reports. While at the site, Rothstein and Lipsky spent several hours at the Inlet including the period of low tide and the transition in the channel from ebb flow to flood flow. During the day, EDD also met with James Richter, James McMahon, Hugh Switzer, Lillian Ball and Aaron Virgin. EDD was able to reach an understanding of the methods and intentions behind the past several dredging efforts, the resources that have been available for dredging, and the difficulties in meeting the goals outlined in the dredging permit. EDD was also recounted many separate stories and impressions of the process by which sand quickly accretes to the east of the jetty after storms, how sand formations change l~equently throughout the year, and were shown visible signs ofblufferosion along the beach to the east. Subsequent to the site visit, EDD informed Town Supervisor Scott Russell of our intended recommendations. As part of the contract language, EDD was to inform the Town if our recommendations were not going to differ significantly from the existing dredge plan, allowing the Town an opportunity to cut short the contract and forego a formal report. Mr. Russell decided that the recommendations being proposed did warrant the completion of the report and Tasks 3 and 4. EDD also made phone and/or email contact with Marisa Cardinale, Tom Foster, Peter Terranova and John Betsch. RECOMMENDATIONS The map references and cross-sections all refer to the drawings included in the 2007 permit. The drawings in the Appendix to this report demonstrate the intended alterations to the current permitted plan. Section l: 53+00-W to apx 51+00-W EDD believes that this "spit" which is attached to the jetty and extends eastward is an accumulation of material that is highly vulnerable to being washed inland during storm events. We recommend that as much of this spit be removed during dredging as is possible. While material will certainly return to accumulate at this location (either washed through the jetty or by other means), removal by dredging should reduce the volume of sand washed inland into the pond. Section 2: Apx 51+00-W to 49+00-W EDD believes that the sand that has been accumulating within this bend in the channel serves as an energy dissipater for waves and storm surges arriving fi.om the Sound. This accumulation of sand and stone should be lef~ in place during dredging, causing the channel to remain bent to the west. The channel should be dredged to be made deeper within this section oftbe course. Unfortunately, the channel currently scours close to the road bed. At some time, and under a separate project scope, the Town may wish to consider riprap or bulkhead to prevent further erosion and compromise of Mill Road. Depositing sand here fi.om the channel dredge is not recommended, as this will provide more material for deposition within the pond. Section 3: 49+00-W to apx 48+00-W EDD recommends that this section of the channel be excavated to create a deep and narrow channel leading as far into the pond area (south) as is practical and feasible. The narrower channel will cause ebb flow velocities of water draining fi.om the pond to increase, thus .promoting scouring and removal of material back to the sound. EDD believes it is important to increase the velocity of water leaving the pond in order to better balance the depositional processes resulting fi.om flood and ebb flows. However, the nature of the material composing the channel does not provide the proper conditions for achieving and maintaining a narrow and deep channel, and the material may quickly "slump" back into the hole from the sides. We recommend that to best approximate the desired result, the excavator should be located on the east side of the channel while dredging. Also, we recommend that during the several days that the dredging will be performed, the excavator should return to this section and again remove the sand and material fi.om the same locations. If it will become possible to create a narrower channel at this section, then higher ebb flow velocities could maintain the channel through scouring. While this does not pertain to the dredge planned for January 2011, EDD believes that creating a narrow and deep channel at this location could be the key to maintaining the connection between the Pond and the Sound. In conversations with local residents, and in references fi.om the literature (including photographs), we have learned that the channel embankments were once partly lined with bulkheads, and that regular dredging could be performed there with no risk of "slumping." Replicating those bulkheads may result in a low-cost and low-risk solution to this problem. Any future investigation of possible capital projects should include this notion. EDD has been very pleased to participate in this process of discovery through stakeholders and long-time residents. During this investigation we have had lengthy and useful conversations with Scott Russell, James Richter, James McMahon, Hugh Switzer, Lillian Ball, Marisa Cardinale, Tom Foster and Aaron Virgin. At this time we have reached out but have not made direct contact with Peter Terranova and John Betsch. Many of the stakeholders are very concerned about the long~term consequences of beach erosion and the role played by the jetty in the erosion/deposition process, and are also concerned about the possible effects on water quality and habitat health in Goldsmith Pond and Autumn Pond should channel closure occur. EDD's analysis was limited to evaluation of the dredging operation and not long-term improvements. BIBLIOGRAPHY Batten, B.K. and Kraus, N.C., (2006). 'Ev ' ' · aluat on of Downdrffi Shore Erosion, Mattituck Inlet, New York: Section 111 Study." US Army Corps of Engineers Coastal Inlets Research Program. Fields, L., Bosma, K.F. and Byrnes, M.R., (1998). "Historical Shorline Change Analysis: Western Town Line to Horton Point, Southold, NY." Aubrey Consulting, Inc., East Falmouth, MA. Morgan, M.J., Kraus, N.C. and McDonald, J.M., (2005). "Geomorphic Analysis of Mattituck Inlet and Goldsmith Inlet, Long Island, New York." US Army Corps of Engineers Coastal Inlets Research Program. Morgan, M.J. and Kraus, N ' . .C, (2007). Phys cai Processes Study of Goldsmith Inlet, New York." Proceedings Coastal Sediments '07 Conference, ASCE Press, Reston, VA 2331-2344. Newell, R.C., (1976). "Rose Remeinbers." Amereon House, Matt ituck, NY. Offshore and Coastal Technologies, Inc., (2005). "An ' Assessment of Jetty Shortening Alternatives: Goldsmith Inlet, Bay, and Adjacent Shorelines." Chadds Ford, PA. Rothstein, E. and Montalto, F., (2010). "Field Report of Visit to Goldsmith Inlet, April 7, 2010." eDesign Dynamics, New York City. APPENDIX Figure 1: Plan View of Recommeuded ami Permitted Dredge Areas Figure 2: Cioss-Sectmns of Recommended I)redge Area Figure 3: Cross-Sections of Permitted Dredge Area FIGURE i: PLAN VIEW OF RECOMMENDED AND PERMITTED DREDGE AREAS ~5o' ~ FIGURE 2: CROSS-SECTIONS OF RECOMMENDED DREDGE AREA STA 48+00-W STA 48+02-W STA 49+00-W STA 50+O0-W STA 51+O0-W STA 5a+O0 STA 53+00-W FIGURE 3; £R[]SS-SECTIONS OF PERMITTED DREDGE AREa (COPIED FR[3P1 PER~IT) STA 48~00-W STA ~8+02-W STA ~g+oo-w STA 50+O0--W STA 51+00-W STA 52+00-W STA53+OO-W NOTE: DRAWINGS PRESENTED ALIGN WITH PERMIT DRAWINGS AS BEST PDSSIDLE~ INACCURATE TRANSLAT]DN OF DRAW]NGS DOES RESULT FRON CONVERSION BETWEEN PDF AND AUTOCAD FORHATS. ABBITIONALLY~ BORE CROSS SECTIONS ~N ORIGINAL PERMIT CONTRADICT ]NFORNATION ON ORIGINAL PLAN VIEW OF DREDGE FOOTPRINT.