Like many coastal communities, the Town of Essex is vulnerable to the effects of global warming and climate change, conditions that are leading to an increase in the rate of sea-level rise (SLR) and a greater frequency and magnitude of coastal storms. During winter of 2018 the Massachusetts coastal zone experienced extensive flooding and wave erosion from intense Nor’easters. Numerous roadways in Essex and Ipswich became impassible, including much of the Essex downtown, and storm waves severely damaged the seawall protecting Conomo Point. Large magnitude storms are forecasted to become more prevalent in the future due to climate change. This project addressed three priority actions identified by the Essex Community Resilience Building Workshop and Report, with an overall goal quantifying vulnerability of natural and Town resources to changing climate, as well as determining how to work with the system to improve the resilience of the coastline around Essex via nature-based solutions. In Ipswich, the project was aimed at improving our understanding of the Castle Neck barrier system and particularly sand transport along Crane Beach and into Essex Bay.
OUTLINE OF MAJOR STUDIES
This was a multifaceted project with several seemingly disparate goals, but ultimately interrelated because of their focus on the effects of climate change and associated sea level rise and increased storminess
A. Castle Neck Barrier
The Castle Neck barrier is one of the major barriers along the Merrimack Embayment island chain. It is mostly an unfettered barrier consisting of an extensive beach, frontal dune and secondary dune system, fringing marsh, and a spit complex at the southeast end. In order to understand the overall extent of the island’s sand reservoirs and how their distribution has changed with time, an historical analysis was made in terms long-term areal changes and volumetric changes using the 2007 and 2017 Lidar data sets. This information is used to project the future evolution of the barrier translate those findings into management guidelines.
B. Crane Beach
Crane Beach is the most dynamic section of Castle Neck and with a visitor population of more than 350,000 each year, it is the most utilized part of the barriers and under the greatest human pressure. In order to understand the processes affecting the beach, we undertook field campaigns, laboratory analyses, and GIS studies to document historical shoreline changes and the erosional-depositional processes that produce these trends. Field campaigns consisted of collection of sediment samples and surveying the topography of the beach using RTK transects. Sediment transport trends were established from laboratory grain size and mineralogical determinations. Analysis of historical aerial photographs and GIS routines allowed a documentation of how sand is transferred through the system from southern Plum Island to Essex Bay. Various controlling processes include, 1) spit cycling at Sandy Point at the southern end of Plum Island, 2) meandering of the channel adjacent to the beach, 3) ebb channel deflection and breaching, 4) growth and decay of a mid-island beach protuberance, 5) erosion of the southeast spit, and 6) sand washed into Essex Bay.
C. Spit, Essex Inlet, and Essex Bay
These three morphological units are connected by sediment transport regimes. Sand eroded from the spit is fed into the inlet and from there transport seaward by ebb current to the ebb-tidal delta or moved landward by flood currents into the bay. In order to track this sand distribution system, we have conducted a detailed grain size analysis, historical image analysis, and hydrodynamic modeling. Together these studies reveal the sand circulation patterns and the morphological changes they produce. For example, we show that sand from the ebb-delta is transported back onshore rebuilding the spit, while other sand is transported into the bay causing channel shifting and the enlargement of sand shoals, which has important consequences to shell-fishing and eel grass beds.
D. Wave Energy inside Essex Bay
One of the recurring issues for the Town of Essex has been wave damage to Conomo Point region, particularly the seawall protecting the northern end of the coastal village. Storm dismantlement of the wall and erosion have been a hardship to the town both in terms of rebuilding costs as well as the expenditure of time and effort of town officials in seeking outside funding. Our coupled hydrodynamic and wave modeling scheme (Delft3D-Swan) has allowed us to identify shoreline hotspots where storm wave energy is concentrated and how this condition will be exacerbated in the future due to increased sea-level rise and greater storminess.
Tidal Current Measurements used for Input Data for Hydrodynamic Modeling
Velocity time-series for the 2-6 August 2019 period. The station was located inside Essex Bay in the channel west of Cross Island. The red line is the tide curve and the blue is the velocity curve. Note the strongly ebb-dominated current.
IN ASSOCIATION WITH THE TOWN OF ESSEX
Funded by The Commonwealth of Massachusetts Executive Office of Energy and Environmental Affairs, as part of the MVP funding program