Beach Crest Research Articles

Experimental beach reconstruction-renourishment on mixed sand and gravel beaches, Washdyke Lagoon, South Canterbury, New Zealand

A novel experimental solution to a very severe erosion and inundation hazard complex at Washdyke beach is presented. Erosion and inundation at Washdyke are the most severe coastal hazards in New Zealand whether measured in physical terms or in terms of the assets threatened by rapid barrier beach regression and eventual breach. The Washdyke shore was naturally eroding prior to harbour construction at Timaru but has been divorced from the (also eroding) updrift feeder coast to the south since 1879 when construction began. Thus Washdyke Beach has a zero coarse sediment input and is progressively exhausting itself as it abrades coarse sands and gravels to finer sizes and transports sediments northward and/or offshore. Reduced grain size lowers berm heights and increases washover to the backshore, so “rolling over” the beach volume and accelerating the rate of shoreline retreat. An experiment with combined beach reconstruction and renourishment was commissioned in June 1980 after extensive analysis of erosion hazards in 1978 and 1979. The experiment was monitored for 5 years and ran for 6 years to provide interim protection for an ocean sewage outfall, and to evaluate the method for the full 3km of Washdyke barrier. Beach crest heights were raised 2.0–2.5 m to cut down overtopping and washover sediment from the backshore. Washover sediment was used to fill the body of the 300 m long site before a coarse capping of river gravels was added to the beach crest. Design specifications called for 4–7% volume loss per year and a fill “life” of 16–25 years. These were met and a considerably longer fill life has been obtained (53.6 years indicated). The overall reduction in erosion rates was about 55% over 5 years with no crest retreat, no overtopping and nil washover of sediment. The neighbouring untreated coasts retreated between 11.5 and 22.5 m during the experiment. The project presents new methods of performance assessment and fill “lifetime” estimation. These use repeated profile survey data subjected to normalised excursion distance analysis. NED plots were fitted with regression models to distinguish short term “noise” in the beach related to changing sea-states from underlying erosional trends. This was done with high degrees of precision both for the treated section of shore and the “control” sites surveyed on two untreated areas, one updrift and the other downdrift of the site. Linear models reliably estimate the time trends of erosion on both the treated and untreated shores, rather than negative exponential models thought to apply to sand beach fill bodies.

Crestal Overtop and Washover Sedimentation on a Fringing Sandy Gravel Barrier Coast, Carnsore Point, Southeast Ireland

ABSTRACT Storm sedimentation on a fringing. sandy gravel barrier system in southeast Ireland is examined. Recent wave overtopping and overwashing during severe onshore storms have resulted in a distinctive pattern of crest and backbarrier sedimentation. This is not easily matched with available models of washover sedimentation drawn from the barrier islands of the eastern United States. Beach crest overtopping occurs at heights up to +6 m MHWS and is related to the development of upper beach swash ramps that are plastered against storm-wave-eroded dune scarps located at the barrier crest. Ramp sediments comprise coarse basal beach gravels overlain by coarsening-upward units and finally topped by distinctive seawarddipping fine grit/coarse sand couplets. In places where ramps reach the dune cre t, overtopping swash has deposited a fine marine gravel veneer (

A proposed mechanism for storm beach sedimentation

One of the major problems of shingle beach dynamics is the method by which coarse gravel is transferred from beach face to storm beach, the latter often lying several metres above high spring tidal levels. The mechanism which is usually proposed, cites the action of plunging breakers as being central to this problem of sediment transfer. However, the nature of net residual fluid force of plunging breakers is deemed unsatisfactory for any substantial upbeach (onshore) sediment transport during storm conditions on gravel beaches. A mechanism is proposed by which high still water levels due to high astronomical tides, onshore storm force winds and allied wave surge, promote shoaling characteristics and beach profile changes which are conducive to spilling breaker development at tidal extremities. It is the net onshore fluid force vector of the spilling breaker overtopping the beach crest which may be the cause of extreme sedimentation events on the storm beach. An example of such sediment transfer is given for a known storm beach sedimentation event at Llanrhystyd gravel beach, West Wales, during February 1974. Process variables were monitored on several days allowing the use of an inshore breaker steepness criterion, to indicate positions in the tidal regime where plunging breakers give way to spilling forms. This example serves to suggest that more attention should be given to the nature and characteristics of shoaling waves, especially in respect of breaker type, when examining problems of shingle beach dynamics and sedimentation.

Coastal environments and oil spill residues in Chedabucto Bay, Nova Scotia

Investigations following the oil spill from the tanker ARROW in Chedabucto Bay, Nova Scotia, in 1970 have focussed on the physical and chemical degradation of the Bunker C oil in different littoral environments and on the effects of sediment removal to restore polluted beaches. Natural processes have restored the beaches effectively on coasts exposed to wave activity. In sheltered, low-energy areas, the oil has undergone relatively little change over the 3-year period and is still present in the littoral zone. The removal of contaminated sediments from exposed beaches has not caused major changes but has resulted in permanent retreat of the beach crest in areas of limited sediment supply.

Changes in Beach Profiles at Chedabucto Bay, Nova Scotia, Following Large-scale Removal of Sediments

The effects of sediment removal on three beaches have been monitored during a one year period following attempts to clean up an oil spill in Chedabucto Bay, Nova Scotia. Profiles of these beaches are compared with those surveyed on a high energy beach on Crichton Island which was not affected by cleaning operations. It is apparent on beaches affected by cleaning operations that sediments removed from areas beyond the limit of normal wave action have not been replaced. Excessive sediment removal can seriously alter the equilibrium of a beach and this was demonstrated by a 20-m retreat of the beach crest at the eastern end of Indian Cove.

Permeability-Porosity Patterns and Variations in Some Holocene Sand Bodies

Sandstone reservoirs are the results of long and commonly complex histories of geologic evolution. The combined processes of deposition, burial, compaction, diagenesis, and structural deformation yield final reservoir bodies of widely varied geometries, permeability-porosity characteristics, and structural configurations that are difficult to predict. In unraveling the evolution of sandstone reservoirs it is necessary to have detailed knowledge of their initial depositional characteristics and of the postdepositional modifications impressed upon them. This knowledge can provide a rational basis in predicting the characteristics of reservoir bodies away from areas of data control. Little information pertaining to the reservoir characteristics of freshly deposited sand bodi s has been available. In an API sponsored study, permeability, porosity, and textural parameters were derived from 992 oriented and undisturbed sand samples of river bars, beaches, and dunes undergoing active sedimentation. River point-bar samples have permeabilities ranging from 4 md to more than 500 darcys and average 93 darcys. Porosities in the river point-bars range from 17 to 52 percent and average 41 percent. Beach sand samples have a permeability range of 3.6 to 166 darcys and average 68 darcys. Porosities in beach sands range from 39 to 56 percent and average 49 percent. Permeability values in dune sands range from 5 to 104 darcys and average 54 darcys. Dune sand porosities range from 42 to 55 percent and average 49 percent. Permeability values in river-bar sands are extremely varied in comparison to those of beaches and dunes. In river bars, permeability decreases systematically downstream and bankward. Although of low variability, permeabilities on beaches are low on the beach faces, high on t e beach crests, and variable on the beach-berm areas. Both river-bar and beach sands have well organized directional permeabilities, parallel with the length of the bodies in river bars and perpendicular to the length of the bodies in beaches. Dunes are characterized by low variability in permeability and porosity and show no significant patterns or trends. There is greater variability within bedding and lamination packets than between them. In addition the boundary conditions between bedding and lamination packets are important factors in determining the effective reservoir characteristics of sand bodies, to the extent that a bedding unit of higher permeability completely surrounded by units of lower permeabilities will not demonstrate its ultimate through-flow capabilities, but will have an effective permeability influenced by and largely determined by the lower permeabilities of the bounding units. River-bar sand bodies have significantly different arrangement and variability between bedding units from those of beaches or dunes. The ideal relations between permeability-porosity and textural parameters that have been set forth by various authors for artificially packed particles are demonstrated only slightly by these natural sands from different depositional environments. In all three depositional environments permeability increases with increase in grain size and porosity increases with increase in grain sorting. However, in river-bar sands permeability increases as grain sorting increases and porosity increases as grain size increases, just the opposite of the relations in beach-dune sands and in the artificially packed grain experiments. The underlying cause of these deviations is the different style of grain packing in the river-bar sands.

Reservoir Inhomogeneities of Some Recent Sand Bodies

Abstract Sandstone reservoirs are the results of long and frequently complex histories of geologic evolution. The combined processes of deposition, burial compaction diagenesis and structural deformation yield final reservoir bodies of widely varying geometries, permeability-porosity characteristics, and structural configurations that are difficult to predict. In unraveling the evolution of sandstone predict. In unraveling the evolution of sandstone reservoirs, it is necessary to have detailed knowledge of their initial depositional characteristics and of the post-depositional modifications impressed upon them. This knowledge can provide a rational basis in predicting the characteristics of reservoir bodies away from areas of data control. To present, little information pertaining to the reservoir characteristics of freshly deposited sand bodies bas been available. In an API-sponsored study, permeabilities, porosities, and textural properties were derived from 992 oriented and properties were derived from 992 oriented and undisturbed sand samples of river bars, beaches and dunes undergoing active sedimentation. River point-bar samples have permeabilities ranging from 4 md to more than 500 darcies and average 93 darcies. Porosities in the river point bars range from 17 to 52 percent and average 41 percent. Beach sand samples have a permeability percent. Beach sand samples have a permeability range of 3.6 to 166 darcies and average 68 darcies. Porosities in beach sands range from 39 to 56 Porosities in beach sands range from 39 to 56 percent and average 49 Percent. Permeability values percent and average 49 Percent. Permeability values in dune sands range from 5 to 104 darcies and average 54 darcies. Dune-sand porosities range from 42 to 55 percent and average 49 percent. Permeabilities in river-bar sands are extremely Permeabilities in river-bar sands are extremely variable compared with those of beaches and dunes. In river bars, permeability decreases systematically downstream and bankward. Although of low variability, permeabilities on beaches are low on the beach faces, high on the beach crests, and variable on the beach berm areas. Both river-bar and beach sands have well organized directional permeabilities, parallel to the length of the bodies permeabilities, parallel to the length of the bodies in river bars and perpendicular to the length of the bodies in beaches. Dunes are characterized by low variability in permeability and porosity and show no significant patterns or trends. There is greater variability within bedding and lamination packets than between them. In addition, the boundary conditions between bedding and lamination packets are important factors in determining the effective reservoir characteristics of sand bodies, to the extent that a bedding unit of higher permeability completely surrounded by units of lower permeability will not demonstrate its ultimate through-flow capabilities, but will have an effective permeability influenced by and largely determined by the lower permeabilities of the bounding units. River-bar sand bodies have a significantly different arrangement and variability between bedding units than do beaches or dunes. The ideal relationships between permeability-porosity and textural characteristics permeability-porosity and textural characteristics that various authors have set forth for artificially packed particles are only weakly demonstrated by packed particles are only weakly demonstrated by these natural sands from various depositional environments. In all three depositional environments, permeability increases with increase in grain permeability increases with increase in grain size and porosity increases with increase in grain sorting. However, in river-bar sands permeability increases as grain sorting increases and porosity increases as grain size increases, just the opposite of the relationships in beach-dune sands and in the artificially packed grain experiments. The underlying cause of these deviations is the different style of grain packing in the river-bar sands.

Significance of pebble size and shape in sorting by waves

This paper compares means, standard deviations and standard errors for length, breadth, thickness and weight of samples of 500 quartzite and flint/chert pebbles from six beach crest sites on the shingle beach at Chesil Beach, Dorset, England. Because of the conditions prevailing, grading alongshore is especially well developed but the principles apply elsewhere. The data are used in examining various shape ratios and indexes including LÜTTIG 's (1956) sigma (σ) and pi (π), the W entworth (1922)-C ailleux (1945) flatness index, K rumbein's (1941) sphericity index, and the maximum projection index of S need and F olk (1958). It is shown that the only comparable dimension or index between the quartzite and flint/chert population is thickness. Since the specific gravity of both lithological types is the same it would appear that over the range of pebble sizes and shapes present on this beach, thickness is the critical dimension in determining the overall sorting of pebbles by wave action.

Comparison of Modern and Ancient Beaches, Central Georgia Coast: GEOLOGICAL NOTES

Although not many ancient beaches have been described from the geologic record, they are environmentally significant and worthy of diligent search. Characteristics of a modern beach at Sapelo Island, Georgia, as seen in section are illustrated and compared with a similar Pleistocene beach 5 mi inland. In general the stratification of the beach conforms to the slope of the beach surface. Individual laminae are thin, parallel, and may be traced for several feet. Departures from parallelism of surface and stratification occur in areas of bar and trough development and near the beach crest. In general, the seaward dip of beach stratification in this area is less than 4 degrees . The upper limit of the diagnostic burrow features made by the marine decapod Callianassa major Say marks the approximate position of mean sea level in both the modern and Pleistocene beaches.

Statistical designs for sampling beach sand

The sampling of beach sand involves questions of sample size, depth of penetration; sample spacing, and sampling for seasonal variations. These problems can be studied by analysis of variance, in which experiments are designed to explore several relations at a time. The experimental design is controlled in part by natural subdivisions of the beach. These subdivisions include backshore, foreshore, and a nearshore submerged zone. Each displays certain “population” characteristics in terms of bedding, particle‐size distribution firmness, and other attributes.Sampling experiments conducted over the past several years are described and summarized in terms of observed variations which occur on Lake Michigan beaches. In general, it was found that most beach characteristics are normally distributed within limited areas of the beach, and that the beach crest (berm) is an important dividing line between different populations of many beach attributes. A tentative design for sampling beach sand is submitted as a result of the studies.