Search

Sandy coastlines in Chile currently have strong erosive tendencies. However, little is known about the morphodynamics of these coastlines; such knowledge would allow us to understand coastline changes and incorporate this knowledge into coastal management. Accordingly, the historical scale of coastal erosion and the morphodynamic characteristics of six beaches of the Arauco Gulf, central-southern Chile (36° S), were analyzed to determine the prevailing wave conditions during winter and summer. Historical changes in the relative position of the coastline were determined using DSAS v5.1. The coupled WAVE-FLOW-MOR modules of the Delft3D 4.02 software package were used for the morphodynamic analysis. Using image processing, it was established that erosion predominates in winter seasons for almost every beach analyzed. However, the Escuadrón beach presents this trend both in winter and summer, with rates of up to −0.90 m/year (2010–2021). In addition, accretion was observed in both stations at Tubul beach. On the other hand, numerical models for the dominant conditions predict accretion in the beaches of Escuadrón, Chivilingo, and Arauco, stable conditions for Coronel beach, and erosion in Llico.

Coastal boulder deposits (CBD) provide what are sometimes the only remaining signatures of wave inundation on rocky coastlines; in recent decades, CBD combined with initiation of motion (IoM) analyses have repeatedly been used as primary evidence to infer the existence of ancient tsunamis. However, IoM storm wave heights inferred by these studies have been shown to be highly inaccurate, bringing some inferences into question. This work develops a dimensionless framework to relate CBD properties with storm‐wave hindcasts and measurements, producing data‐driven relations between wave climate and boulder properties. We present an elevation‐density‐size‐inland distance‐wave height analysis for individual storm‐transported boulders which delineates the dynamic space where storm‐wave CBD occur. Testing these new relations against presumed tsunami CBD demonstrates that some fall well within the capabilities of storm events, suggesting that some previous studies might be fruitfully reexamined within the context of this new framework., Key Points Size, elevation, and distance inland in storm‐wave‐generated coastal boulder deposits are all functions of climatological wave heightsClear data ranges exist where storm wave coastal boulder deposits do/do not existSome coastal boulder deposits previously identified as having tsunami origin may have been generated by storm waves

A user-friendly system designed to understand local littoral processes and design/evaluate coastal interventions, named the Coastal Modeling System (SMC e ) is presented. The system, which comprises a set of numerical models, state-of-the-art methodologies and numerical databases, is prepared to provide a method for coastal practitioners, researchers and decision-makers to address coastal issues, such as erosion and flooding or to evaluate coastal defense structures. The system incorporates a method to transfer numerically generated, calibrated and validated wave series to the surf zone; to estimate the sediment littoral drift by means of up-to-date formulations; and to estimate the flooding level and impacts such as those produced by climate change. In this paper, these skills are detailed. The system, which is adaptable to any coastal region, was implemented for the Brazilian coast (SMC-Brasil). The implementation includes databases and methodological adaptations to local characteristics, a dissemination plan and the development of several study cases.

The present paper presents aspects of the morphological behavior of Rio das Pacas Beach, situated in the Southeast portion of the Island of Santa Catarina - SC. The methodology adopted consisted in the monitoring of three beaches profiles, every twenty days, during the period of one year. Besides the topographical survey, there were also carried out observation on height and wave periods, wind direction and intensity and current direction. The results indicated a great variation on the profiles throughout the monitored period, especially evidenced in the values of width and sedimentary supply of the beach (highest variations reaching 30m and 40m3/m between two consecutive expeditions), where it was possible to identify seasonal behavior characterized by accretion during the end of spring and summer and erosion in autumn and winter. The erosive periods were of bigger magnitude than the accretion, and in the extremities of the beach, the complete recovery of sediments was not reached during the monitored period. Events of high energy (undertows) that reached the beach revealed capacity to modify the morphology of the beach system, also eroding frontal dunes settled for vegetation and partially destroying anthropic structures – such as walls, poles, props and fences - constructed on the frontal dune and backshore.

Fluorescent tracers have been used in a field assessment at Tres Piedras beach (Chipiona) in order to characterise morphodynamic processes, disturbance depth and longshore transport during a single tidal cycle. Native sand was marked with a fluorescent dye without any chemical fixer. The tracers and the rods and plugs, to record the disturbance depth, were inserted in the foreshore during low tide. The sampling area was established using a fluorescent lamp. Beach accretion as well as the landward dispersion of tagged sand, confirmed the constructive work of swell waves

Source: https://erdc-library.erdc.dren.mil/jspui/ The Coastal Engineering Research Center (CERC), under a multiagency program initiated in 1966, has developed a synoptic sand tracing system capable of operating on the beach, in the surf zone, and offshore. This system has application in determining sediment movement along coastal areas. Some specific problems to which the system can be applied are: (a) mechanisms of sediment movement; (b) improving beach fill criteria; (c) relation of engineering structures to sediment transport; and (d) movement of disposal materials. Sand of the desired size characteristics is plated with gold 198-199 isotopes and sealed in water soluble packets. The packets are injected in the water as either line or point sources by extrusion from the carrier-injection device. Surveying is conducted from an amphibious vehicle (LARC) which tows a ball-like device containing four scintillation detectors. Signals from the detectors are transmitted by cable to the onboard data collection system. The system also collects other data (e.g., navigation, fathometer, etc.) pertinent to surveying; this data are telemetered to a shore-based PDP-8 computer system for field processing. Processed data are plotted on the cathode ray tube (CRT) real-time data display and stored on magnetic tape for further analysis. Data obtained with the RIST system represent nearly synoptic observation of sediment transport within one or all of the nearshore environmental zones over a wide area. Field tracing experiments are designed toward the solution of particular problems. Some of the factors considered in planning the experiment include: selection of the tracer, tidal state, predicted environmental conditions, available support, and acceptance (or licensing) of the use of isotopes. After the isotope is injected, surveys are conducted for several days depending upon dispersion and isotope half-life. Results of recent tracer experiments demonstrate the utility of RIST in research and engineering studies. RIST studies synoptically cover a wider area both offshore and alongshore than is obtainable with other tracer systems such as fluorescent and stable isotope tracers. Since differences in sediment transport exist between the various nearshore environmental zones, RIST studies provide data more indicative of total transport on a scale previously unobtainable.

Source: https://erdc-library.erdc.dren.mil/jspui/ A field experiment was conducted to develop correlations between wave characteristics and longshore sediment transport. The waves were measured by two near-bottom mounted pressure transducers and by visual observation when pressure transducers were not in operation. The average longshore sediment transport rates were determined from sequential volumetric surveys behind an offshore breakwater which was regarded as a total trap. The data analyzed encompass a period of 2 years, 1 year after each dredging cycle. Spectral analyses of the pressure gage wave data were conducted and yielded one direction per frequency. The correlations include immersed weight sediment transport rate, I, versus longshore component of wave energy flux at breaking, P£s· The most widely used correlation constant, K, in the, relationship I= KP£s is 0.77. The value determined from the data was K = 0.98, based on the P£s values directed toward the trap. One feature of this type of trap is the potential for overtrapping if the waves are directed nearly normal to shore.

Source: https://erdc-library.erdc.dren.mil/jspui/ Freshly formed small-scale washover deposits were examined along a section of the Atlantic coast (Outer Banks, North Carolina) and Lake Erie (Presque Isle Peninsula, Pennsylvania, to determine their stratigraphic properties, mode of placement and relationship to adjacent barrier (spit) morphology. Storm washover occurrence is a function of the degree of storm surge and backshore-foredune relief. The shape and dimension of the resulting washover sand body is largely controlled by surrounding topography. Overall textural distribution, modality, and skewness of sediment samples from the adjacent washover, foredune and beach show a strong similarity. Modality is related to texture subpopulation while skewness reflects subpopulation mixing. Normal and inverse grading as well as textural coarsening in the presumed direction of washover flow are distinctive trends. A characteristic structural trend from the washover neck toward the washover terminus consists of horizontal to very low angle, landward-dipping planar stratification merging into delta-foreset strata. Storm washover results from the deposition of sediment carried in a succession of unidirectional, discontinuous surges which flow past the berm or foredune line and downslope across the washover surface. Flow velocities imparted by the initial fluid surge coupled with downslope gravity effects facilitate the development of flow similar to sediment gravity flow. In some cases, added shear stress imposed on a sediment-concentrated bed layer by the overlying fluid results in the development of grain flow, a type of sediment gravity flow. Flow across the subaerial washover surface results in scouring and development of planar (horizontal) stratification. Flow into the more distal subaqueous (pond, lagoon) setting develops delta-foreset structures. Grain flow, in particular, leads to the development of normal and inverse textural grading and landward textural coarsening. Washover contributes to landward and vertical accretion of relatively coarse detritus in the barrier environment, thus serving as temporary sediment sink in an erosional (transgressive) littoral drift system.

Source: https://erdc-library.erdc.dren.mil/jspui/ Eighteen profile lines from Fort Story south to the Virginia-North Carolina State line were surveyed monthly for 27 months (September 1974 to December 1976). Net volume changes were moderate, with maximum rates of accretion at the north and south ends of the study area. A statistical analysis using earlier surveys going back to November 1956 confirms the pattern of accretion in the north and south separated by erosion in the middle. Maximum annualized accretion rate during the 27-month study was 18.9 cubic meters per meter of beach front per year at profile line 1 (Fort Story), and maximum erosion rate 11.6 cubic meters per meter per year at profile line 9 (Sandbridge). The ridge-and-runnel morphology typical of many active shorelines was not observed in the study area. Under present conditions, rates of erosion and accretion are independent of the four types of shore usage defined for this study area (commercial, natural, military, and residential). The narrow, erosional beaches are located at the center of the study area in Back Bay National Wildlife Refuge (natural area), Dam Neck (military), and Sandbridge (residential); the wide, accretion beaches are located at the north and south ends of the study area in Fort Story (military) and False Cape State Park (natural). Instead of beach usage, it is suggested that the observed differences result from a nodal zone of diverging longshore transport in the middle of the study area (approximately Dam Neck to Back Bay). North of this zone, net transport is to the north, and south of this zone, it is hypothesized that net transport is to the south. The net, but irregular, movement of sediment out of the middle area explains the narrow, relatively inactive, erosional beaches observed in the middle and the wide, more active, accretion beaches observed on the ends. This interpretation supports existing bypassing and sand nourishment procedures which place sand at the south end of the Virginia Beach commercial reach for natural longshore processes to distribute to the north. The measured volume changes of beach sand in this reach, especially when compared with adjacent reaches, strongly indicate that the bypassing and nourishment procedures are needed for the maintenance of the Virginia Beach commercial beach area. Results of reconnaissance inspections of the shores of Currituck County, North Carolina, are included to better relate the Virginia Beach study area to the CERC Field Research Facility at Duck, North Carolina.

Source: https://erdc-library.erdc.dren.mil/jspui/ This paper is a compilation of published longshore current data available from North American sources as of January 1966. The data comprise 352 separate observations; of these 225 were obtained from four laboratory studies and 127 from four field studies. Each observation includes (at least) measured longshore current velocity, in feet per second; wave direction; a wave height, in feet; wave period, in seconds; and beach slope. Values of breaker height and breaker angle were computed for those observations lacking measured values. Longshore current velocity is usually less than 2 feet per second under both field and laboratory conditions. The maximum velocity observation from the field is 5.5 feet per second; from the laboratory 3.8 feet per second.

Source: https://erdc-library.erdc.dren.mil/jspui/ A glossary of terms used by coastal engineers is presented. The terms apply to such subjects as waves, tides, littoral processes, shore protection, shore structures, and coastal geomorphology. Primary sources are cited.