Changes In Shoreline Position Research Articles

Seasonal and Interannual Influences on the Patterns of Shoreline Changes in Rio Grande do Sul, Southern Brazil

Changes in shoreline positions along the Rio Grande do Sul coast, southern Brazil, are analyzed to determine the spatial and temporal variability of shoreline movements at a regional scale. Using a kinematic Differential Global Positioning System (DGPS) survey method, the 618-km long shoreline of Rio Grande do Sul has been mapped on five occasions between November 1997 and April 2002. These data show that the coastline responds differently to hydrodynamic and meteorological forcing along the three major coastal sectors. The observed differences occur especially in the magnitude of changes, in the time interval in which the shoreline returns to a previous position, and in the length scale of dominant shoreline changes. Here changes in shoreline position are examined with respect to grain size, shoreline orientation, storms, El Nino–Southern Oscillation (ENSO) events, and gradients of longshore sediment transport. Data analyses and modeling indicate that the alongshore variability in the patterns of shoreline change through time is closely related to shoreline orientation and the associated gradients of longshore sediment transport. Results indicate also that variability in wave energy and storminess influence seasonal changes, whereas ENSO events influence interannual changes. This study demonstrates the importance of understanding the drivers of shoreline change at a regional scale and has applications in studies concerned with coastal engineering and shoreline response to climate change.

Monitoring changes in shoreline position adjacent to the Hadera power station, Israel

The paper focuses on the shoreline changes following the construction of a power station cooling harbor in Hadera, Israel, and uses a statistical analysis method capable of mitigating the effect of short-term changes on the measurement of long-term changes. The changes in shoreline position detected 25 years after the harbor's construction were compared with forecasts of the Central Lab for Hydraulics of France (LCHF) in 1976, which correctly predicted the effects of the construction on the nearby coast and with studies conducted a few years after the construction. A comparison between later studies and the study described herein shows a spatial effect of the harbor on shoreline position of 750 m north of the northern breakwater. No effect was found south of the harbor. The harbor's temporal effects extend over a few years from the beginning of the construction until the coast reaches a new sedimentary equilibrium. The statistical analysis method employed was found useful for the detection of long-term changes in shoreline position such as those caused by the construction of coastal structures; it will not be suitable for the detection of long-term changes resulting from a rise in sea-level.

Response of reef island shorelines to seasonal climate oscillations: South Maalhosmadulu atoll, Maldives

The Maldives experience seasonal shifts in monsoon winds from the west‐northwest to northeast. The morphologic response of reef island beaches and shorelines to these predictable shifts in climate was examined on eight islands in South Maalhosmadulu Atoll based on global positioning system surveys of island shoreline planform in January and June 2002 and February 2003. Surveys show that islands exhibit large gross changes (31–120% of beach area) in shoreline position between seasons. Such changes reflect large reversals in sediment flux of 9–23 × 103 m3 on a biannual basis driven by seasonal reversals in wind and wave conditions. Annual net change is small (2–15%), suggesting islands spatially exhibit a dynamic equilibrium. An island oscillation index (Io) is defined that describes the spatial extent of shoreline change around islands. Island shape (ellipticity, e) is found to be positively correlated with Io in the expression Io = 1.021e − 0.275, suggesting island shape is a better indicator of the susceptibility of island shorelines to morphological change than wave energy exposure.

A Study Of Hydrodynamic And CoastalGeomorphic Processes In Küdema Bay,The Baltic Sea

The aim of the paper is to analyze relationships between hydrodynamic and geomorphic processes in a small bay in the West-Estonian Archipelago. The area consists of a Silurian limestone cliff exposed to storm activity, and a dependent accumulative distal spit consisting of gravel and pebble. Changes in shoreline position have been investigated on the basis of large-scale maps, aerial photographs, topographic surveys and field measurements using GPS. Waves and currents were investigated using a Recording Doppler Current Profiler RDCP-600 deployed into Kudema Bay in June 2004 and the rough hydrodynamic situation was simulated using hydrodynamic and wave models. The main hydrodynamic patterns were revealed and their dependences on different meteorological scenarios were analyzed. It was found that due to exposure to prevailing winds (and waves induced by the longest possible fetch for the location), the spit elongates with an average rate of 14 m/year. Major changes take place during storms. Vitalization of shore processes is anticipated due to ongoing changes in the regional wind climate above the Baltic Sea.

Changes in shoreline positions on the Harilaid Peninsula, West Estonia, during the 20th century

Changes in shoreline positions on the Harilaid Peninsula, West Estonia, during the 20th century

Formation of Deep Incisions into Tide-Dominated River Deltas: Implications for the Stratigraphy of the Sego Sandstone, Book Cliffs, Utah, U.S.A.

ABSTRACT The Upper Cretaceous Sego Member of the Mancos Shale in east-central Utah is composed of tidally deposited sandstones interbedded with intervals containing marine shales and thin wave-deposited sandstones. The tidal sandstones have been interpreted to comprise multiple amalgamated estuarine valley fills above a major sequence boundary that is incised into distal marine deposits of the underlying Buck Tongue Shale. According to this interpretation, the deposits constitute the base of a thick transgressive succession within the Sevier foreland clastic wedge. Alternatively, lower Sego sandstones have recently been interpreted by the authors to be tide-dominated river delta deposits in an overall regressive interval of the foreland succession. A cross section showing facies variations and stratigraphic surfaces within the lower Sego Member along 100 kilometers of the eastern Book Cliffs is used in this paper to refine depositional and sequence stratigraphic interpretations of these tidal deposits, particularly the origin of deep incisions within the Sego sandstones. A strike-oriented section of the lower Sego Member reveals tidal sandstone lenses, 40-50 kilometers wide and tens of meters thick, separated laterally by areas tens of kilometers wide that have no tidal sandstones. Facies variations within the tidal sandstones reflect depositional processes on tide-dominated deltas that prograded obliquely into the shallow intracratonic Western Interior Seaway of North America. Two major episodes of delta progradation and subsequent transgressions are interpreted to have formed tidal sandstone layers within the lower Sego Sandstone. Thinner tidal sandstone layers, of more local extent, are interpreted to reflect changes in tidal current strength but not necessarily shifts in shoreline position or major changes in water depth. Multiple origins are suggested for incised erosion surfaces within the lower Sego sandstones. Firstly, the tide-dominated deltaic sandstones are floored by laterally discontinuous erosion surfaces. These basal surfaces, marking abrupt vertical changes in depositional process and coarsening of grain size, are interpreted to record tidal scouring of the sea floor during shoreline progradation. Secondly, sharp-based upward-coarsening deltaic sandstones are cut by numerous deep incisions with tens of meters of relief, and locally they are entirely removed by erosion. Some of this deep erosion within the lower Sego Sandstone may reflect the upstream avulsion of incised distributaries during forced regression of deltas into the basin, whereas others may have formed by tidal erosion of abandoned distributaries during more gradual progradation and subsequent retrogradation of deltas. Highly variable facies trends within incision fills are related to pronounced changes in sediment supply to different distributaries on the delta, to differences between incisions cut during delta regression versus those cut during the start of transgression, and to varying distances from delta axes. When the entire coast was transgressed, the influence of tides waned and wave-generated currents ravined delta tops. Depositional interpretations of the Sego Member indicate that the Buck Tongue to Neslen interval lies in a broadly regressive part of the foreland basin fill.

Wavelet analysis of shoreline change on the Outer Banks of North Carolina: an example of complexity in the marine sciences.

The horizontal, shore-perpendicular change in shoreline position along the Outer Banks of North Carolina is found to be a self-affine signal. We measure shoreline change by determining the horizontal change in position of the 0.8-m contour sampled from shore-perpendicular profiles spaced at 20-m intervals along the coast. The profiles are obtained from two light detection and ranging surveys performed in September 1997 and September 1998. For six selected sections of coast, wavelet analysis of the shoreline change signal indicates the signal is self-affine with a scaling exponent that varies from 1.2 to 2.1. This self-affine behavior indicates that the shoreline change signal is nonstationary with long-range persistence. A stochastic diffusion model of sediment transport replicates the observed self-affine behavior observed south of Cape Hatteras (scaling exponent between 1.2 and 1.6) whereas a random walk model replicates the signal observed north of Cape Hatteras (scaling exponent approximately 2.0). Because of the finite nature of the data set, there are limits in space and time to the power law behavior of the system. Characteristics of such systems can be described by upper-truncated power laws, which yield the upper limits of power law behavior. Applying an upper-truncated power law to the data for one section of coast, we find an upper limit of 7 km for the maximum continuous alongshore distance eroding or accreting. For the same section of coast, we find upper limits of 25 m for the maximum shore-perpendicular erosion and 11 m for the maximum shore-perpendicular accretion during the study period.

LATE CENOZOIC DEPOSITIONS PALEOENVIRONMENTS OF SOUTHEAST FLORIDA INTERPRETED FROM CORE LOGS

The use of core logs from water wells and engineering-geological site investigations permitted spatial refinement of known paleodepositional environments along the southeastern coast of Florida where the narrow continental shelf was influenced by changes in sea level and shoreline position during the late Cenozoic. Lithological materials have been formalized in terms of the Tamiami Formation (early Pliocene), Fort Thompson Formation (late Pliocene), Anastasia Formation (Pliocene-Pleistocene), Miami Limestone (late Pleistocene), and Pamlico sands (Pleistocene) in southeastern Florida. The lack of good exposures, scarcity of biostratigraphically important microfossils, similarity of sedimentary deposits, and pervasive diagenesis of fossiliferous sections have mitigated against a consensus of interpretation for late Cenozoic stratigraphic sections. Inspection of more than 18,300 m of unpublished core log data combined into cross-sections that crisscrossed the Broward County study area, permitted mapping of vertical and horizontal relationships for Miocene, Miocene-Pliocene, early Pleistocene, and late Pleistocene/Holocene time frames. These lithostratigraphic interpretations of changing paleoenvironments formed the basis of a preliminary model for the coastal geological framework of Broward County. This study confirmed general late Cenozoic trends in sedimentation from marine conditions (Tamiami Formation) to nearshore (Anastasia Formation, Fort Thompson Formation) settings to very shallow marine environments (oolitic facies of the Miami Limestone) and eolian materials in the upper Pamlico sands. Late Pleistocene to Recent trends showed a shore-parallel pattern of shallow paleobathymetries that included barrier bars and tidal passes (paleoinlets). Erosional unconformities (interpreted as irregular karstified groundsurfaces with low paleotopographic relief) in the sections were frequently capped by dense subaerial weathering crusts of calcite which today act as semi-impermeable barriers to groundwater flow. Knowledge of this coastal geological framework is relevant to increased understanding of submarine groundwater discharges, modes of saltwater intrusion, boundary conditions for groundwater models, and has practical implications for optimized water management along the southeast coast of Florida.

Short-term shoreline changes due to cross-shore structures: a one-line numerical model

The proposed numerical model simulates the short-term temporal changes in shoreline position due to a structure interrupting the longshore sediment flux. The impacts of both the groin-type construction and underwater trench of arbitrary orientation relative to the shore are discussed. In order to estimate the sediment mass trapped by the structure, a submodel of the longshore sediment transport induced by a random wave field is developed. The contribution of the surface roller in momentum balance as well as in sediment suspension is included. The shoreline changes are computed from the equation deduced from the mass conservation. The perturbations in the longshore sediment discharge caused by a structure are assumed to concentrate within some boundary area of which the spatial scale is proportional to the structure's length until the latter is exceeded by the width of the sediment flux. It is shown in particular that the total effect of a long trench (channel) and a pier in its nearshore part results in general shoreline recession except for the vicinity of a pier. The model is tested against the laboratory data of Baidei et al. (1994) and applied to the Baidara Bay coast (Kara Sea) where a pipeline would be designed.

Some Notes on Design Method of Sluce Flood Way on Coast Dominating Longshore Sand Transport

Relation between the function of sluce flood way and beach erosion on its downcoast was investigated through the field observation at Showa sluce flood way located on the Fuji coast facing Suruga Bay. Beach survey data were analyzed to investigate temporal and spatial change in shoreline position around the flood way. Shoreline change was compared with the theoretical results. This flood way was partly destroyed by wave action associated with the beach erosion and scouring. Succesive beach erosion around this structure was made clear by comparison of aerial pictures.

Geomorphic response-type model for barrier coastlines: a regional perspective

Based on quantitative documentation of historical changes in shoreline position between 1847 and 1991, eight geomorphic response-types were established for classifying megascale changes along barrier coastlines: (1) lateral movement, (2) advance, (3) dynamic equilibrium, (4) retreat, (5) in-place narrowing, (6) landward rollover, (7) breakup, and (8) rotational instability. Long-term (decades to centuries) monitoring of shoreline position over a spatial scale of 10 to 100 km provides a scientific basis for documenting process-response relationships that shape regional coastal morphodynamics. Although megascale shoreline change studies often are lacking, this type of information is critical for developing realistic research and management strategies regarding form/process relationships in coastal depositional systems. The spatial distribution of geomorphic response-types is delineated along the barrier coastlines of Louisiana, Mississippi, and southern Georgia/northern Florida. At megascale, the rate of relative sea level rise along these barrier coastlines appears to be one of the major factors controlling the occurrence of geomorphic response-types; however, sediment supply exerts significant influence on shoreline response as well.

Changes in Shoreline Position Along the Northern Gulf of Mexico Between 1847 and 1994: Sabine Pass, Louisiana to Dauphin Island, Alabama: ABSTRACT

Changes in Shoreline Position Along the Northern Gulf of Mexico Between 1847 and 1994: Sabine Pass, Louisiana to Dauphin Island, Alabama: ABSTRACT

Wave Climate and Nearshore Lakebed Response, Illinois Beach State Park, Lake Michigan

The Lake Michigan outer nearshore zone (water depths ≈5 to 25 m) off Illinois Beach State Park is subjected to a spectrum of wave conditions, including those generated by major storms. Only under these major storm conditions is there a realistic potential for wave-lakebed interaction (and associated wind-driven currents) to cause a significant net modification to the outer nearshore lakebed, which, in turn, may promulgate change in the inner nearshore (surf) zone. Analysis of bathymetric and sediment grain-size data, used in conjunction with published wave hindcast data, wave propagation modeling, and previous studies in the area, indicates that this potential occurs, most likely, on a scale of years. Although such storms can generate bottom currents well in excess of what is required to mobilize the fine to very fine sands that are present, little compelling evidence was found, on the basis of gross comparisons with previous studies (1946, 1973, 1978), that there have been rapid or pronounced changes in the outer nearshore lakebed. Nonetheless, grain-size data suggest that sands are episodically transported in a net southerly direction. At least over the time period represented by this and previous studies, any modification of the outer nearshore zone lakebed would seem to be modest and gradual. If so, whereas the outer nearshore zone may be a factor in the long-term adjustment of the shoreline, any rapid change in shoreline position, or any conspicuous change in the rate of shoreline adjustment, is more likely controlled by factors other than those linked to the outer nearshore zone.

A discussion of alluvial sandstone body characteristics related to variations in marine influence, Middle Jurassic of the Cleveland Basin, UK, and the implications for analogous Brent Group strata in the North Sea Basin

Abstract The pattern of deposition in the Middle Jurassic Cleveland and North Sea basins was complicated by spatial and temporal variations in the amount of marine influence. These variations ranged from major changes in shore-line position resulting in the alternating deposition of marine and non-marine formations to minor shore-line movements, incursions, tidal back-up, saline wedge intrusion and storm/tide/rain-induced flood events. The fluctuating extent of marine influence resulted from the interplay of factors including sedimentation rate, compaction, local tectonic activity and eustatic variations. The extent of marine influence on the alluvial environment affected the nature and architecture of sandstone bodies and the nature of early diagenesis. It is probable that within the North Sea area local and regional relative sea-level fluctuations during Ness Formation deposition would have resulted in a range of alluvial sandstone body types similar to those of the Middle Jurassic of Yorkshire seen in outcrop. Major changes in sea-level relative to surface subsidence resulted in changing sandstone body architectural styles, while minor changes in marine influence resulted in significant changes in internal sandstone body characteristics.

LONG-TERM BEACH CHANGES AND THEIR CAUSES AT AJIGAURA BEACH, IBARAKI PREFECTURE, JAPAN

Long-term beach changes and the topographic responses to the wave climate were analyzed based on the field data of the wave characteristics, grain size of the bed materials and beach profiles measured every week in a 11-year period between 1976 and 1986 at Ajigaura Beach in Ibaraki Prefecture. For the wave characteristics wave direction, wave height and wave period were observed. Eigenfunction analysis was carried out using the profile data. It was found that distinctive changes were observed before and after a period of 1982-83 in the moving average value of one year regarding shoreline position, wave climate and foreshore slope, and the periodic fluctuations of wave direction and shoreline position had totally changed since this time. It was concluded that the changes in shoreline position and foreshore slope were caused by the offshore sediment transport associated with the extraordinary high waves. In addition, the abrupt changes of the periodic fluctuations in wave direction and shoreline position closely correlated to the long-term changes of the oceanic and meteorological changes associated with the climate anomalies such as El Nino.

BEACH EROSION-ACCRETION AT TWO TIME SCALES

Erosion and accretion on the beachface have been studied at two time scales on the central and south coast of New South Wales, Australia. This research aims at providing a temporal perspective to contemporary problems of beach erosion in areas where the historic map record of changes in shoreline position is poor. Field work has been concentrated at two localities Moruya (lat. 35° 53'S long. 150°09'E) and Newcastle Bight (lat. 32°48'S long. 151°55'E)(Fig. 1).

Coastal changes at Kaikoura, 1942–74, determined from air photographs

Abstract Changes in shoreline position at 100 locations along 45 km of the Kaikoura coastline have been determined for the 32-year period from 1942 to 1974 by comparison of air photograph sequences. The areas studied in detail comprise the mixed sand-pebble beaches to the north and south of the Kaikoura Peninsula and the raised beaches and shore platforms of the peninsula itself. Both pronounced erosion and progradation of sectors of the shoreline have occurred and there are large variations in the rate of change within small distances. These variations are thought to reflect local differences in the availability of sediments in the littoral zone and the longshore distribution of dominantly high energy wave action. Maximum accretion was more than 40 m (weighted mean = 12.65 m) and maximum erosion was 47.6 m (weighted mean = 8.23 m). Both mixed sand-pebble beaches are dominantly accreting whereas the major zones of erosion occur along the northern and southern flanks of Kaikoura Peninsula and along the nor...