Changes In Shoreline Position Research Articles

Video observation of megacusp evolution along a high-energy engineered sandy beach: Anglet, SW France

Birrien, F., Castelle, B., Dailloux, D., Marieu, V., Rihouey, D. and Price, T.D., 2013. Video observation of megacusp evolution along a high-energy engineered sandy beach: Anglet, SW France.We present an 18-month period of video monitoring of both the nearshore sandbars and the megacusps at Anglet Beach, SW France. The study site covers a 2-km long stretch of beach that is constrained to the North by a groin that extends 400 m seaward. The beach is high-energy intermediate, mostly double-barred, with a steep beach face (~1/10) favouring the formation of cusps at a large range of lengthscales, from beach cusps (O(10 m)) to megacusps (O(100 m)). A megacusp is systematically observed against the groin as a result of the persistent presence of a topographic rip. Further away from the groin, about 4–5 megacusps are typically observed. The shoreline dynamics are strongly controlled by the geometry of the surfzone sandbar. In-phase shoreline-sandbar coupling was commonly observed, that is, megacusps in the alignment of the rip channels and seaward bulges in the shoreline facing the surfzone sandbar horns. Megacusps at Anglet Beach have a typical cross-shore amplitude of O(10 m). During a severe storm with significant wave heights over 7 m, a very erosive megacusp (hotspot) formed in the alignment of the rip channel. Prior to this storm, a seaward bulge in the shoreline was observed in this location. Accordingly, 40 m cross-shore variation change in shoreline position at this location was the signature of megacusp dynamics only. This hotspot was systematically observed at the same location during 7–8 months after the storm event, before the fair weather conditions in summer resulted in an overall accretion of the beach. Megacusps were smoothed out during rapid alongshore migration of the sandbar or for high-energy wave conditions. In addition, the evolution of the alongshore-averaged shoreline position shows the exact opposite trend as that of the alongshore-averaged sandbar position, yet with less pronounced cross-shore variations. Overall, our results highlight once again the strong links between shoreline and surfzone sandbar dynamics.

Probabilistic prediction of barrier‐island response to hurricanes

Prediction of barrier‐island response to hurricane attack is important for assessing the vulnerability of communities, infrastructure, habitat, and recreational assets to the impacts of storm surge, waves, and erosion. We have demonstrated that a conceptual model intended to make qualitative predictions of the type of beach response to storms (e.g., beach erosion, dune erosion, dune overwash, inundation) can be reformulated in a Bayesian network to make quantitative predictions of the morphologic response. In an application of this approach at Santa Rosa Island, FL, predicted dune‐crest elevation changes in response to Hurricane Ivan explained about 20% to 30% of the observed variance. An extended Bayesian network based on the original conceptual model, which included dune elevations, storm surge, and swash, but with the addition of beach and dune widths as input variables, showed improved skill compared to the original model, explaining 70% of dune elevation change variance and about 60% of dune and shoreline position change variance. This probabilistic approach accurately represented prediction uncertainty (measured with the log likelihood ratio), and it outperformed the baseline prediction (i.e., the prior distribution based on the observations). Finally, sensitivity studies demonstrated that degrading the resolution of the Bayesian network or removing data from the calibration process reduced the skill of the predictions by 30% to 40%. The reduction in skill did not change conclusions regarding the relative importance of the input variables, and the extended model's skill always outperformed the original model.

Holocene paleoshorelines, water levels and submerged prehistoric site potential of Rice Lake (Ontario, Canada)

Rice Lake, located in the eastern Great Lakes of North America, has a high density of prehistoric (11–0.5 ka BP) terrestrial archaeological sites. It has been speculated that a large number of sites are submerged on the lakebed, as lake levels have risen >9 m since the arrival of Early Paleoindian peoples (∼11 ka BP). In order to better understand the submerged landscape and its archaeological potential, a detailed bathymetric survey and sediment-coring program was conducted across a 30-km2 area of northeastern Rice Lake. Changes in Holocene water levels and shoreline positions were reconstructed by integrating core data with a digital elevation and bathymetric model (DEBM) that accounted for differential isostatic uplift and basin sedimentation. The DEBM was used to generate a series of maps showing changes in the lake paleobathmetry and paleogeography and areas of prehistoric archaeological potential.Isostatic uplift of the eastern basin outlet (>30 m) had a dramatic influence on water levels and shoreline positions since the inception of Rice Lake (∼12 ka BP). During the Early Paleoindian occupation phase (∼11–10.5 ka BP), water levels were at a maximum lowstand (10 m bpl) and much of the present lakebed was an exposed lake plain with extensive wetlands. At the time of the Late Paleoindian/Early Archaic occupation (9.5–8.7 ka bp; 11,150–9560 cal. BP), the lake was about half its modern extent and during the second lowstand phase (<6000 cal. BP) water levels dropped to >4 m bpl and the lake became hydrologically closed. After 4000 cal. BP, water levels recovered and the lake approached its modern extents. An archaeological potential map based on the reconstructed paleoshorelines identified four areas with archaeological potential: these include drowned river mouths, submerged wetlands and an area of uplifted Early Holocene lakebed in northeast Rice Lake. The results illustrate that isostatically driven changes in lake paleobathymetry can be substantial and must be accounted for when attempting to reconstruct paleoshoreline positions. The approach can be applied more broadly to other basins within the Great Lakes and elsewhere to assess prehistoric site archaeological potential.

Looking for evidence of climate change impacts in the eastern Irish Sea

Abstract. Although storminess is often cited as a driver of long-term coastal erosion, a lack of suitable datasets has only allowed objective assessment of this claim in a handful of case studies. This reduces our ability to understand and predict how the coastline may respond to an increase in "storminess" as suggested by global and regional climate models. With focus on 16 km of the Sefton coastline bordering the eastern Irish Sea (UK), this paper analyses available measured datasets of water level, surge level, wave height, wind speed and barometric pressure with the objective of finding trends in metocean climate that are consistent with predictions. The paper then examines rates of change in shoreline position over the period 1894 to 2005 with the aim of establishing relationships with climatic variability using a range of measured and modelled metocean parameters (with time spans varying from two to eight decades). With the exception of the mean monthly wind speed, available metocean data do not indicate any statistically significant changes outside seasonal and decadal cycles. No clear relationship was found between changes in metocean conditions and rates of shoreline change along the Sefton coast. High interannual variability and the lack of long-term measurements make unambiguous correlations between climate change and shoreline evolution problematic. However, comparison between the North Atlantic Oscillation winter index (NAOw) and coastline changes suggest increased erosion at times of decreasing NAOw values and reduced erosion at times of increasing NAOw values. Erosion tends to be more pronounced when decreasing NAOw values lead to a strong negative NAO phase. At present, anthropogenic changes in the local sediment budget and the short-term impact of extreme events are still the largest threat likely to affect coastal flooding and erosion risk in the short- and medium-term. Nevertheless, the potential impacts of climate change in the long-term should not be ignored.

An integrated approach to coastal erosion problems in northern Tuscany (Italy): Littoral morphological evolution and cell distribution

Occupation of the coast has significantly increased in recent decades, mostly due to a greater demand for recreation and tourism. Today, erosion threatens many human-made structures and activities, requiring an integrated approach for the understanding of coastal dynamics and identification of alternatives to associated problems. This study investigates a 64km-long coastal physiographic unit in the northern microtidal littoral of Tuscany (Italy). Vertical aerial photographs and direct field surveys were used to retrieve changes in shoreline position over 1938–1997 and 1997–2005 time intervals. Significant beach accretion was observed during the first period updrift of Carrara (84m) and Viareggio (280m) harbours and at Marina di Pietrasanta (100m), whereas severe erosion occurred downcoast of Carrara harbour (−130m, at Marina dei Ronchi) and on the northern side of Arno river mouth (−400m). Similar trends were observed between 1997 and 2005; beach slope between the 1997 shoreline position and the closure depth correlated well with the distribution of erosion/accretion patterns from the 1938–1997 period (slopes were lower in eroded areas than at sites under accretion). Longshore distribution of erosion/accretion patterns was controlled by coastal compartmentalisation. Three of the main littoral cells were mostly formed by natural limits (i.e., Punta Bianca promontory, Marina di Pietrasanta, the Arno river mouth and the port of Livorno). Several sub-cells were created within these cells due to the introduction of human-made structures (such as Carrara and Viareggio harbours), which formed artificial fixed limits that allowed the transport of sediments (exclusively fines) in one direction only. Results will help improve the understanding of coastal processes and manage littoral sediment transport in a sustainable manner. This will reduce the need for structural interventions, such as breakwaters and groynes, which in the past decades prevented coastal retreat at local scale but shifted erosion downdrift, leading to degradation of the investigated area and requiring continuous maintenance.

Observation of shoreline positions with X-band radars

Shoreline positions of southern Kashimanada coast facing Pacific Ocean have been observed with 4 X-band radars. The stretch is approximately 17 km long and extending from north to south with Kashima Port at the north and Tone River at the south. Half of the area is protected by coastal structures and the remaining is close to natural beach. Hourly-averaged radar images are processed to observe longshore distributions of shoreline positions and data collected for a year is discussed. The on- and off-shore migrations of shoreline positions are shown which are active for the protected areas and milder at un-protected areas. Waves were estimated with SWAN wave model and relationships between cross shore and longshore energy fluxes and observed changes in shoreline positions are discussed.

Decadal Behavior of Tidal Inlet-Associated Beach Systems, Northwest Ireland, in Relation to Climate Forcing

Abstract Shoreline and ebb channel evolution between 1834 and 2008 was recorded at three embayed beaches in northwest Ireland with historically stable relative sea level. The beaches are geologically constrained within bedrock valleys and have minimal contemporary sediment input. Their behavior is strongly influenced by tidal-inlet dynamics of adjacent estuaries; major observed changes in shoreline position are linked to fluctuations in inlet ebb-channel orientation. Comparison of the available historical record of geomorphological change with instrumental and proxy climate records suggests that inlet changes may be driven by fluctuations in average storminess: periods of high storminess perturb the inlet system, causing major changes in ebb-channel configuration, after which sediment redistribution returns the system to its former state over a prolonged period (years to decades).

Changing morphology of Ghana’s Accra coast

Coastal features in Ghana's Accra coast reflect both past and present processes that have been undergoing changes. These changes are influenced by a range of morphogenic factors such as geology and climatic conditions. These regimes have shaped the coastal geomorphic features through weathering processes that decompose and disintegrate the coastal rock. Sea level rise due to climate change is expected to increase coastal erosion and thus result in rapid changes in shoreline positions. Historic rate of sea level rise in Accra coast is about 2 mm/yr (Ibe & Quelennec, 1989) which is predicted to reach approximately 6 mm/yr in the next century since it conforms to the global change (Armah et al., 2005). This will result in flooding of vulnerable areas and enable waves to break closer inland. The effectiveness of the erosion process is aided considerably by the type of geology. Accra coastal zone has three types of rock in three identified geomorphic regions. They include unconsolidated and poorly consolidated rock along the western region, the Accraian series occupying the central region and the Dahomeyan series in the eastern region. The geology has thus influenced the extent to which the coastal features have changed and the type of cliff that is formed as a result of erosion within the regions. Generally, soft rock coastal features decay more rapidly than those of hard rock and tend to act as sediment sources. Human activities such as dam construction over the Densu River, engineering interventions to check the spread of erosion and sand mining has created sediment deficit which has exacerbated coastal erosion in Accra. Anthropogenic factors are estimated to account for 70-90% of coastal erosion problems in Accra.

The morphodynamic responses of artificial embayed beaches to storm events

Abstract. The morphological changes caused by storm events in two Barcelona beaches were recorded using video monitoring techniques during the period 2001–2006. Changes in shoreline position and configuration and submerged bar position and shape were analyzed during the 25 major storm events that occurred during the study period. Beach responses to storms were grouped into three categories: shoreline advance or retreat (including rotation), sandbar migration and/or configuration change (linear or crescentic shape) and formation of megacusps. This work provides examples of the differential adaptation of both beaches to the same storm and of some unexpected morphological responses of both beaches. The response of the beach to storm events is not straightforward because wave conditions are not the only relevant parameter to be considered. In particular, in such embayed beaches it is crucial to take into account their specific morphodynamic configuration prior to the storm.

Shoreline changes and morphology of spits along southern Karnataka, west coast of India: A remote sensing and statistics-based approach

The changes in shoreline positions and morphology of spits along the Karnataka coast, western India, are investigated for the period from 1910 to 2005 using multi-dated satellite images and topomaps. The study area has been divided into four littoral cells, and each cell into a number of transects at uniform intervals. The rate of change in shoreline position has been estimated using the statistical linear regression method and cross-validated with regression coefficient ( R 2) and Root Mean Square Error (RMSE) methods. Past and future shoreline positions have been demarcated and future positions of shoreline are estimated for time periods of 10- and 24-years. The study reveals that (i) about 57% of transects exhibit ± 10 m RMSE values, indicating better agreement between the estimated and satellite-based shoreline positions, and (ii) transects closer to the cell boundaries exhibit about 50% uncertainties in shoreline change rate estimations. Based on RMSE values, the influence of natural processes and anthropogenic factors on shoreline changes has been evaluated. The cells/transects dominated by natural processes reveal low RMSE values, whereas the cells/transects influenced by anthropogenic activities such as sand mining, construction of coastal structures, exhibit higher RMSE values. However, the variation in RMSE values is not significant if the total number of transects is considered. Significant changes in morphology of spits have been recorded. Spits demonstrate variations in areal extent, i.e., length and area, if 1910 and 1967 are considered separately as base years. The present study demonstrates that combined use of satellite imagery and statistical techniques such as linear regression and RMSEs can be very useful in quantifying shoreline changes and spit morphology.

Evolution of a beach–dune system following a catastrophic storm overwash event: Greenwich Dunes, Prince Edward Island, 1936–2005

Greenwich Dunes, Prince Edward Island National Park, is a sandy mainland and barrier spit beach–dune complex stretching for about 10 km along the northeast shore of Prince Edward Island, Canada. In October 1923, surge associated with an intense storm produced catastrophic overwash along the whole length of the study area. Subsequent evolution of the system was quantified from historic aerial photographs taken in 1936, 1953, 1971, 1997, and 2005. Orthophoto mosaics were generated for each photo set using PCI Geomatica OrthoEngine, a digital photogrammetric software. Linear changes in shoreline position and areal changes in geomorphic units were evaluated for each photo set. In addition, digital elevation models (DEMs) were extracted from the 1953, 1971, and 1997 aerial photos, enabling analysis of topographic and volumetric changes. The 1936 photos show complete destruction of all foredunes, with overwash and transgressive dunes extending 300 to 600 m inland. A descriptive model of the stages of evolution of the system is proposed based on the processes controlling overwash healing and dune stabilization. Detailed topographic and volumetric changes associated with the development of an extensive transgressive dunefield and subsequent stabilization as a result of reduced sand supply due to the growth of a new vegetated foredune complex and vegetation colonization are doccumented for each stage. It was nearly 40 years before a continuous foredune system was re-established and a further 30 years before the inland transgressive dunes became completely stabilized.

Forecasting Hurricane Impact on Coastal Topography

Extreme storms can have a profound impact on coastal topography and thus on ecosystems and human‐built structures within coastal regions. For instance, landfalls of several recent major hurricanes have caused significant changes to the U.S. coastline, particularly along the Gulf of Mexico. Some of these hurricanes (e.g., Ivan in 2004, Katrina and Rita in 2005, and Gustav and Ike in 2008) led to shoreline position changes of about 100 meters. Sand dunes, which protect the coast from waves and surge, eroded, losing several meters of elevation in the course of a single storm. Observations during these events raise the question of how storm‐related changes affect the future vulnerability of a coast.

Evaluation of Effect of Beach Nourishment Using Imageries Produced from Photographs Taken from Fixed Point by Geometric Transformation

On the Chigasaki coast, beach nourishment using coarse material has been carried out since 2004 to recover the sandy beach. To investigate the daily changes of the nourished beach, photographs have been taken from a fixed point. The 51 photographs taken at 1 s intervals were selected under the conditions that the tide level is within M.S.L.±0.1 m, the significant wave height is less than 0.5 m, and the photograph was taken between 8 and 12 am. The weighted average of these photographs was obtained to clearly determine the shoreline position. The imageries were produced from these photographs by the geometric transformation method. The change in shoreline position after the beach nourishment was monitored using the imageries

Measuring and modelling longshore sediment transport

Field measurements of longshore sediment transport (LST) was undertaken on barred and non-barred beaches composed of fine, medium and coarse sands in Brazil, Denmark and Portugal. Measurements and predictions of vertical suspended sediment concentration profiles ( C-Profiles) and cross-shore hydrodynamic parameters were then combined in a new semi-empirical model for prediction of LST ( LT-MOD). Instantaneous LST predictions from LT-MOD and well-known bulk LST formulae were compared. Tests using LT-MOD to simulate measured changes in shoreline position in southern Brazil for periods of c. two years showed that LT-MOD gave more accurate predictions than existing bulk LST formulae. Results indicate that LT-MOD may have practical utility at sites where access to equipment is limited and where reliable estimates of LST are required over extended periods.

Mean sea-level rise impacts on Santos Bay, Southeastern Brazil – physical modelling study

The greenhouse effect and resulting increase in the Earth's temperature may accelerate the mean sea-level rise. The natural response of bays and estuaries to this rise, such as this case study of Santos Bay (Brazil), will include change in shoreline position, land flooding and wetlands impacts. The main impacts of this scenario were studied in a physical model built in the Coastal and Harbour Division of Hydraulic Laboratory, University of São Paulo, and the main conclusions are presented in this paper. The model reproduces near 1,000 km(2) of the study area, including Santos, São Vicente, Praia Grande, Cubatão, Guarujá and Bertioga cities.

Os Efeitos no Ambiente Marinho da Elevação do Nível do Mar em Regiões da Baixada Santista, Brasil

The greenhouse effect and resulting increase in the earth’s temperature may accelerate the mean sea level rise. Knowledge regarding the relative sea-level rise and its effects on coastal areas is reviewed here. Hydraulic processes, such as tidal forcing, prism, currents and storm surges, salinity intrusion and littoral processes, will be modified. The natural response of bays and estuaries to this rise, such as this case study on Santos (SP), will include change in shoreline position, land flooding and impacts on wetlands

Long-and Short-term Trends of Shoreline Position Change near the New Mouth of the Omono

Long-termt rendo f shorelinep ositionc hangen ear the new moutho f the Omonop ouringi nto the sea of Akita Southern Coast is discussed by using old map, topographicaml aps, field data collected in the last fifteeny ears and by examining accuracy of the old map (Inoul arge-scalem ap). Short-termt rend of shorelinep osition change on the same coast is also discussed to judge whethera remarkabler eceding of shorelinep ositiona t the Hamada-hamab athingp lace located near the mouth in July 2006 is a rare case. Through these discussions, it is concluded that 1) the shoreline position had basi cally advanced from 1800 to around 1900, and then it has gradually receded undulating and 2) the remarkable receding in July 2006 is not a rare case from the viewpoint of absolute shoreline position change

Process signatures in regional patterns of shoreline change on annual to decadal time scales

Gradients in wave-driven alongshore sediment transport influence the morphologies of sediment-covered coastlines on a range of spatial and temporal scales, affecting accretion and erosion patterns relevant to human development. Recent theoretical findings predict that a correlation between shoreline change and shoreline curvature results from patterns of alongshore sediment flux; the sign (positive or negative) of that correlation depends on whether high- or low-angle waves dominated the wave climate. Using lidar surveys of the northern North Carolina coast from 1996–2005 to document shoreline change and quantify alongshore patterns of erosion and deposition, we isolate these signals diagnostic of alongshore-transport processes. Our analyses show a persistent, significant negative correlation between shoreline-position change and shoreline curvature consistent with a low-angle-dominated incident wave climate over the last decade. At large spatial scales, convex-seaward promontories have eroded landward, while concave-seaward bays have aggraded seaward, resulting in an apparent diffusion of alongshore morphological features

Cenomanian Turonian Coastal Record in SW Utah, U.S.A.: Orbital-Scale Transgressive Regressive Events During Oceanic Anoxic Event II

Abstract The Cenomanian–Turonian interval of the Sevier foredeep, western U.S.A., is examined in order to (1) establish a high-resolution stratigraphic framework for marginal-marine strata of this interval and (2) test for the existence of high-frequency (tens of kyr-scale) cycles of continental runoff or sea-level change predicted by the hemipelagic record and climate models. High rates of sediment accumulation in marginal-marine environments of southwestern Utah (up to 210 m/Myr, compacted) and a northward translation of the major Sevier thrusting made possible the preservation of a highly detailed record of shoreline movements. The coeval Bridge Creek Limestone, linked with the study interval using biostratigraphic and bentonite-stratigraphic data of previous authors, provides an unprecedented, high-resolution orbital time scale. Three orders of transgressive–regressive cycles defined as genetic sequences are identified in the upper Cenomanian (S. gracile and N. juddii Zones) through lower Turonian (W. devonense through M. nodosoides Zones). The longest sequence (S. gracile Zone through V. birchbyi Zone) spans approximately 800 kyr and is penecontemporaneous with the δ13Corg positive excursion that defines Oceanic Anoxic Event II (OAE II). Medium-term and short-term sequences show durations of c. 65–160 kyr and c. 20–40 kyr, respectively. Features suggesting regression due to relative sea-level fall are described from some of the 20–40 kyr cycles in the lowermost S. gracile Zone (possibly including the uppermost M. mosbyense Zone). The data provide the first physical evidence globally of Cenomanian–Turonian changes in shoreline position and relative sea level, whose recurrence interval was as short as a few tens of kyr. These processes provide a viable depositional link between the rhythmic deposition of the Bridge Creek Limestone and the primary orbital forcing of insolation and climate. Although the possible tectonic influence is difficult to unravel, the study area represents an important reference point for climate and oceanographic modeling of the Cenomanian–Turonian greenhouse and OAE II.

Hurricane-induced beach change derived from airborne laser measurements near Panama City, Florida

This study used airborne laser data to investigate spatial variations in shoreline migration, beach width, subaerial volume, and subaqueous volume change due to a hurricane event. Five separate airborne laser data sets of Panama City, FL area beaches were collected during a seven-month period before and after landfall of Hurricane Ivan. Contour shorelines were extracted from digital elevation models interpolated from these laser measurements and were used to measure changes in shoreline position and beach width. The shoreline migrated 16 m landward due to Hurricane Ivan and migrated 10 m seaward following Hurricane Ivan. No significant spatial relationship was found between shoreline migration before and after the hurricane. Linear relationships between a time series of beach width and subaerial volume were found at many locations. However, utilization of a single coefficient to represent all relationships is problematic due to the spatial variability in the linear relationship. Differences in two bathymetric data sets for summer and fall show that only a small portion of sediments were transported beyond an active zone and most sediments remain within the active zone despite the occurrence of a hurricane.