Search

A rigorous program of coastal monitoring of vital signs has been initiated in three Federal Agencies in the northeastern United States. Shoreline position and subaerial coastal topography, both products of sediment budget, have been selected as targets for monitoring and contributing to an Agency regional database. Science-based protocols have been developed and implemented to periodically collect and track one-dimensional shorelines, two-dimensional beach-dune profiles, and three-dimensional landform elevation models in the agency coastal land holdings. The use of the resulting datasets and their accompanying scientific analyses provide an understanding of the geomorphological evolution at the scales of seasons, years, and longer terms. Further, the analyses establish a firm scientific foundation and allow for the use of applied coastal geomorphology for management decisions related to the natural and cultural resources within the coastal units. The establishment of consistent protocols meets the agency needs of ease of application, is based on a firm scientific foundation, and is appropriate to the management issues at the sites. [ABSTRACT FROM AUTHOR]

The trend and episodes of erosion at Great Kills Park, part of the National Park Service, are products of the origin of the park's location and the impact of a negative sediment budget. Management response to the impacts of erosion is somewhat limited by National Park Service philosophy, but some options remain because the negative sediment budget is a product of barriers to sediment transport updrift of the Park. The erosional situation is exacerbated by an exposure of an antecedent backmarsh feature within the Park that is affecting the inshore pattern of incident waves. Recent monitoring data indicate planform conformity to an updrift log-spiral erosional bluff that extends downdrift to a site with beach and dune features. Despite a general net negative sediment budget in the profile, the dune feature is increasing in volume as it shifts inland, fitting models of foredune development. Seasonal monitoring of the topography records that storms cause a stepwise inland displacement of an updrift portion of the Park and a more linear displacement in the downdrift portion. Among the options consistent with management policy responding to the negative sediment budget issue is an opportunity to work within the scale of the small sediment transport cell and backpass sediment toward the updrift margin of the cell. [ABSTRACT FROM AUTHOR]

The geomorphological map offers a snapshot of the landforms generated through topographical response to physical process drivers within a given landscape. A comparison of geomorphological maps with consistently and objectively identified landform boundaries allows for the assessment of spatiotemporal variations in process-response dynamics that represent the fundamental nature of geomorphological evolution, and form a basis to derive quantitative metrics of landform development. Two geomorphological maps of Fire Island National Seashore created from LiDAR datasets and orthophotography collected prior to and immediately following Hurricane Sandy were compared according to consistent and objective criteria. The mapped geomorphology and the LiDAR elevation data facilitated the use of regional-residual separation methods to assign sediment volumes to specific processes and landforms. This led to the calculation of sediment volumes deposited as beaches, foredunes, and washover deposits before and after the storm and to the quantification of the changes associated with the storm across the entire 50 km stretch of barrier coastline that comprises Fire Island. The temporal comparisons indicated that different portions of Fire Island exhibited variable geomorphological responses to a major storm. Notably, the central and western portion of the island, from 6 km to 36 km from the mouth of Fire Island Inlet, experienced substantial losses to coastal dunes — on the order of 2.9 × 106 m3 of sediment. The beaches in this segment of the coastline gained volume (~86,000 m3) in the storm indicating that the dunes provided a source of sediment to the beach, both buffering erosion and supplying sand to the littoral system. The eastern third of the island experienced beach erosion (~540,000 m3) and erosion of the dunes (~350,000 m3), as well as a significant amount of overwash deposition (~250,000 m3) that represents a transfer of sediment from the beach/dune reservoir to the backbarrier. This mode of geomorphological evolution adds elevation to the backbarrier at the expense of sediment available to buffer the shoreline position. Two 6 km strecthes of Fire Island coastline, Bellport/Old Inlet and Talisman/Watch Hill, exemplify the geomorphological response of the eastern and central potions of the island to the impact of Hurricane Sandy: 1) at Bellport/Old Inlet, overwash deposition was partially sourced from beach deposits adding elevation to the backbarrier at the expense of the shoreline position; and 2) at Talisman/Watch Hill, sediment stored in dune systems was transferred to the beach to slow storm induced shoreline retreat, and the dune buffer and its associated resilience was reduced. In quantifying the system response of a barrier island to a major storm event like Hurricane Sandy, we demonstrate the feasibility and utility of deriving metrics of geomorphological change from geomorphological maps. This approach of quantifying process-response outcomes through mapping is broadly applicable to a variety of geomorphological settings and timescales given a consistent means of boundary determination and using regional-residual separation. [ABSTRACT FROM AUTHOR]

Silveira, T.M., Carapuço, A.M., Sousa, H., Taborda, R., Psuty, N.P., Andrade, C. and Freitas, C., 2013. Optimizing beach topographic field surveys: matching the effort with the objectives In any study design, the surveying approach should match the objectives, thereby limiting the effort to focus on the purpose of the inquiry. Often, in beach geomorphological research, study design is based on expert judgment, that does not assure the optimization of the field surveys. In this study, several dimensions of survey strategies were evaluated to compare the outcomes and uncertainties associated with field data collection. The objective of this work is to assess the accuracy of the derived volumes achieved by different survey strategies, including cross- and alongshore lines, with varying density and spatial distribution, to optimize the field survey effort. A number of survey strategies are simulated, covering a range of data resolutions and configurations, replicating a number of possibilities for field data gathering. Topographical data from different field surveying approaches were analyzed for a 4 km long coastal stretch in Portugal. Measures of beach volume were computed from cross-shore as well as alongshore information, and the errors associated with each approach evaluated. Results show that beach volume varies with the adopted survey strategy. As an example, beach volume change can be adequately portrayed and survey effort minimized either through the surveying of 3 alongshore lines, or through 200 m spacing beach profiling. This work highlights the importance of the study design in beach contexts because of its inevitable influence on the results of volumetric change analyses. [ABSTRACT FROM AUTHOR]

Abstract: A century of human manipulation of sediment transport and sediment supply at Sandy Hook spit has generated an evolving suite of geomorphological responses and shoreline management approaches at this public coastal resource. Eventually a major erosion problem was created in a portion of the Gateway National Recreation Area knows as the “Critical Zone”, a location immediately downdrift of the end of a lengthy seawall. In the last three decades, the management approach was to apply beach nourishment to replace the eroded volumes. Projects emplacing from 20000 m3 to 1.7 million m3 of sand in the Critical Zone attempted to counter the erosional trend. However, evolving Park policy sought to identify alternatives to the massive emplacements of sand from offshore sources. Starting in 1997, detailed topographical surveys were begun to track sediment budget in the eroding Critical Zone, and subsequently at Gunnison Beach, a site of sediment accumulation. A new management philosophy of smaller scale restoration of sediment supply in the Critical Zone has emerged. At present, the Gunnison Beach area on Sandy Hook is being monitored to determine its potential for sediment backpassing to the Critical Zone as a means to balance its local sediment budget, create a relatively consistent topography, and maintain the recreational resources. [Copyright &y& Elsevier]

Beach nourishment was applied at three fetch-restricted sites along the estuarine margin of Delaware Bay, New Jersey. Evaluation of geomorphological performance of the nourishment project was conducted through seasonal monitoring to track linear features (shoreline, dune crest, peat edge) and to create digital elevation models (DEMs). Comparisons of the DEMs yielded sediment budgets of the updrift, fill area, and downdrift zones as well as the spatial and temporal evolution of the tidal flat, beach, and dune features within the zones. Through four years, Moore's Beach lost all of the emplaced fill as well as an additional −5446 m3 from the fill area. The shoreline position shifted inland −12.78 m, and the foredune crest shifted inland −9.23 m. The fill area at Pierce's Point lost all of the fill and an additional −3810 m3. The shoreline and dune crest shifted inland −7.35 m and −1.17 m, respectively. The Reed's Beach study area benefited from beach fill updrift that more than offset the losses in the fill area, a net gain of 2107 m3. There was a major contrast in volumetric change between the updrift and downdrift portions. Sediment budget calculations established alongshore transport was an important factor in the fetch-restricted estuarine environment driving the variable geomorphological responses in the updrift, fill, and downdrift zones. [ABSTRACT FROM AUTHOR]

Coastal overwash is one of the most important hazards affecting the coastal zone and therefore has been the focus of several studies related to the establishment of setback lines. However, studies of extreme overwash (EO) events along urban beaches backed by a seawall or structure are scarce, and reveal the difficulties associated with its assessment, measurement and validation. The Nazaré coastal urban area (located on the west coast of Portugal) is developed adjacent to an embayed reflective beach and is subject to frequent and localized inundation due to EO events capable of overtopping the protection seawall. The current work develops a methodological approach to simulate total water levels (TWL) and seawall overtopping occurrences in time and space, with the ultimate goal of identifying the factors that govern the extreme overwash regime. The method uses multi-decadal time series of site-specific wave and tide, and high-resolution topo-bathymetric data, and recreates the TWL time series for a 36-year period. The model is successfully validated against video imagery and maximum swash line data that provide information on the reach of the water levels measured during modal and extreme TWL conditions along the studied beach. This study establishes the importance of the interaction of the modal and extreme hydrodynamic processes with the beach and backshore morphology. The Nazaré embayment is in equilibrium with the alongshore-varying modal wave conditions, resulting in higher vulnerability of the most sheltered sector during extreme events. [ABSTRACT FROM AUTHOR]