Microbiological water quality at non-human influenced reference beaches in southern California during wet weather

Although urban wet weather discharges may have elevated concentrations of fecal indicator bacteria impacting water quality at swimming beaches, not all of these bacteria may arise from human sources. In this study, the contribution of non-human fecal indicator bacteria was quantified by sampling coastal reference beaches in southern California. Samples were collected at beaches near stormwater discharges from undeveloped watersheds and analyzed for total coliform, Escherichia coli, and enterococci. Surfzone samples exceeded water quality thresholds >10 times more frequently during wet weather than dry weather. Exceedences were greatest <24 h following rainfall, then steadily declined on successive days. Early season storms exceeded thresholds more frequently, and by greater magnitude, compared to late season storms. Large storms exceeded thresholds more frequently than smaller-sized storms, partly due to the breaching of sand berms. When discharges did reach the surf zone, bacterial concentrations in the wave wash were correlated with watershed bacterial flux.     

Impact of erosion and accretion on the distribution of enterococci in beach sands

Bacterial pathogens in coastal sediments may pose a health risk to users of beaches. Although recent work shows that beach sands harbor both indicator bacteria and potential pathogens, it is neither known how deep within beach sands the organisms may persist nor if they may be exposed during natural physical processes. In this study, sand cores of approximately 100 cm depth were collected at three sites across the beach face in Kitty Hawk, North Carolina, before, during, and after large waves from an offshore hurricane. The presence of DNA from the fecal indicator bacterium Enterococci was detected in subsamples at different depths within the cores by PCR amplification. Erosion and accretion of beach sand at the three sites were also determined for each sampling day. The results indicate that ocean beach sands with persisting enterococci signals could be exposed and redistributed when wind, waves, and currents cause beach erosion or accretion.     

PAH concentrations in Coquina (Donax spp.) on a sandy beach shoreline impacted by a marine oil spill

The BP MC252 well failure in the Gulf of Mexico, April 2010 caused concern for crude oil and polycyclic aromatic hydrocarbon (PAHs) exposure along the sandy beaches of the Florida Panhandle. We began collections of Coquina clams (Donax spp.) from the surf zone of Florida Panhandle beaches to monitor PAH contamination to compliment analysis of surf zone sand samples. These clams had higher levels of PAHs relative to ambient sand, and this allowed us to continue to monitor PAH levels after sand concentrations fell below limits of detection. PAH levels in the Coquina tissues were highly variable, perhaps indicative of the heterogeneous distribution of oil and tar on the beaches and exposure to tar particles. Overall, PAH levels decreased continuously in both sand and Coquina tissues, reaching limits of detection within one and two years respectively after oil landed on Florida Panhandle beaches. Our work suggests these surf zone molluscs may be used to monitor pollutant exposure along high energy sandy beach shorelines.     

Analysis of water quality and circulation of four recreational Miami beaches through the use of Lagrangian Coherent Structures

Four popular, recreational beaches in Miami, FL are Hobie Beach, Virginia Key Beach, Crandon Park Beach, and Bill Baggs Cape Florida State Park. While all of the beaches are within a few miles of each other in Biscayne Bay, they have greatly differing water qualities, as determined by the testing for fecal indicator bacteria performed by the Florida Department of Health. Using the geodesic theory of transport barriers, we identify Lagrangian Coherent Structures (LCSs) in each area. We show how these material curves, which shape circulation and mixing patterns, can be used to explain the incongruous states of the water at beaches that should be comparable. The LCSs are computed using a hydrodynamic model and verified through field experimentation at each beach.     

Modelling aeolian sand transport and morphological development in two beach nourishment areas

The aeolian sand transport model SAFE and the air flow model HILL were applied to evaluate cross‐shore changes at two nourished beaches and adjacent dunes and to identify the response of aeolian sand transport and morphology to several nourishment design parameters and fill characteristics. The main input of the model consisted of data on the sediment, tide and meteorological conditions, and of half‐yearly measured characteristics of topography, vegetation and sand fences. The cross‐shore profiles generated by SAFE–HILL were compared to measured cross‐shore profiles. The patterns of erosion and deposition, and the morphological development corresponded. In general, the rates of aeolian sand transport were overestimated. The impact of parameters that are related to beach nourishment (namely grain size, adaptation length and beach topography) on profile development was evaluated. Grain size affected the aeolian sand transport rate to the foredunes, and therefore the morphology. Adaptation length, which is a measure of the distance over which sediment transport adapts to a new equilibrium condition, affected the topography of the beach in particular. The topography of a beach nourishment had limited impact on both aeolian sand transport rate and morphology. Copyright © 2000 John Wiley & Sons, Ltd.     

Assessing Oregon's twenty-six coastal beach areas for recreational water quality standards

Water samples from 26 Oregon beaches were analyzed for Escherichia coli (E. coli) and enterococci concentrations by the Oregon Department of Human Services (ODHS) Public Health Laboratory. Nine Oregon beaches exceeded US Environmental Protection Agency's (USEPA) single sample maximum density of 104 enterococci colony forming units (cfu) per 100 mL with levels ranging from 121 to 4325 most probable number (MPN)/100 milliliters (mL). Otter Rock at South Cove had the highest enterococci concentration at 4352 MPN/100 mL. The results from two Oregon beaches exceeded Oregon Department of Environmental Quality's (ODEQ) estuarine E. coli standard of 406 organisms/100 mL. Otter Rock at South Cove had the highest E. coli concentration at 1850 MPN/100 mL while Road's End had an E. coli density of 771 MPN/100 mL. Results of this study suggest that adopting USEPA's marine enterococci standard in lieu of the ODEQ's estuarine standard will lead to increased Oregon beach water standard failures.     

Spatial variability in beach biogeomorphology in a tropical archipelago

Beaches of tropical island coasts exhibit high levels of diversity in composition and form in comparison with their continental counterparts. To investigate the nature and origin of this diversity, individual beach morphology and sedimentology was investigated in the British Virgin Islands (BVI), a Caribbean archipelago of > 60 high volcanic and low reef islands. The islands exhibit a diversity of orientations (some facing the Atlantic and some the Caribbean), elevation and gradient, rock type and wave energy. An examination of 100 beaches in the archipelago revealed a first-order division into sand (70 beaches) and coral rubble (30 beaches). These beaches occur in seven planform types (determined by the antecedent geological framework) and are further subdivided according to shoreface type (seagrass, sandy shoreface, or reef). Mainland-attached headland-embayment beaches are the most common form of sand beach while coral rubble beaches usually occur as barriers that enclose salt ponds and wetlands. Among sand beaches, carbonate content is greatest on Atlantic-facing beaches, and coral rubble beaches are more common on Caribbean-facing beaches. Grain size characteristics on sandy beaches are highly variable and range from fine to very coarse sands while coral rubble beaches range up to boulder-sized clasts. The local source material is a primary determinant of sediment composition. The local factors such as the underlying geology, source and availability of sediments are the primary determinants of beach form, composition and texture in the BVI. Oceanographic and climatic conditions such as the prevailing easterly trade winds and waves which seasonally range in direction from east-northeast to southeast as well as beach orientation to Atlantic- or Caribbean-facing waves also contribute to the variability, but in a secondary role. © 2019 John Wiley & Sons, Ltd.     

The behaviour of beach elevation contours in response to different wave energy environments

Within the context of a warming climate, there are wide and increasing concerns about the way beaches respond to different wave energy environments. However, behavioural differences in changes in beach elevation contours (including shorelines) in different wave energy environments remain unknown. Thus, it is unilateral to evaluate the changes in beaches based on a single elevation contour (e.g. shoreline) in coastal engineering and management applications. In this study, based on the collected shoreline and wave energy data of two international beaches, as well as the measured beach elevation contour data from Yintan Beach and the corresponding wave energy data simulated by Xbeach, our results show that frequency distributions of beach elevation contour changes exhibit distinct features under different wave energy environments. Under high wave energy environments, the frequency distributions of beach elevation contour changes show a Gaussian distribution. However, frequency distributions of beach elevation contour changes present a power law, intermediate between the logarithmic and Gaussian distributions under low and moderate wave energy environments, respectively. Furthermore, the conceptual model of beach elevation contour changes constructed by this study indicates that the relative importance of the wave energy and sediment resistance determines this phenomenon. © 2020 John Wiley & Sons Ltd     

Storm response of a mixed sand gravel beach ridge plain under falling relative sea levels: A stratigraphic investigation using ground penetrating radar

Beach ridge stratigraphy can provide an important record of both sustained coastal progradation and responses to events such as extreme storms, as well as evidence of earthquake induced sediment pulses. This study is a stratigraphic investigation of the late Holocene mixed sand gravel (MSG) beach ridge plain on the Canterbury coast, New Zealand. The subsurface was imaged along a 370 m shore-normal transect using 100 and 200 MHz ground penetrating radar (GPR) antennae, and cored to sample sediment textures. Results show that, seaward of a back-barrier lagoon, the Pegasus Bay beach ridge plain prograded almost uniformly, under conditions of relatively stable sea level. Nearshore sediment supply appears to have created a sustained sediment surplus, perhaps as a result of post-seismic sediment pulses, resulting in a flat, morphologically featureless beach ridge plain. Evidence of a high magnitude storm provides an exception, with an estimated event return period in excess of 100 years. Evidence from the GPR sequence combined with modern process observations from MSG beaches indicates that a palaeo-storm initially created a washover fan into the back-barrier lagoon, with a large amount of sediment simultaneously moved off the beach face into the nearshore. This erosion event resulted in a topographic depression still evident today. In the subsequent recovery period, sediment was reworked by swash onto the beach as a sequence of berm deposit laminations, creating an elevated beach ridge that also has a modern-day topographic signature. As sediment supply returned to normal, and under conditions of falling sea level, a beach ridge progradation sequence accumulated seaward of the storm feature out to the modern-day beach as a large flat, uniform progradation plain. This study highlights the importance of extreme storm events and earthquake pulses on MSG coastlines in triggering high volume beach ridge formation during the subsequent recovery period. © 2019 John Wiley & Sons, Ltd.     

Pore water transport of enterococci out of beach sediments

Enterococci are used to evaluate the safety of beach waters and studies have identified beach sands as a source of these bacteria. In order to study and quantify the release of microbes from beach sediments, flow column systems were built to evaluate flow of pore water out of beach sediments. Results show a peak in enterococci (average of 10% of the total microbes in core) released from the sand core within one pore water volume followed by a marked decline to below detection. These results indicate that few enterococci are easily removed and that factors other than simple pore water flow control the release of the majority of enterococci within beach sediments. A significantly larger quantity and release of enterococci were observed in cores collected after a significant rain event suggesting the influx of fresh water can alter the release pattern as compared to cores with no antecedent rainfall.     

Estimation of enterococci input from bathers and animals on a recreational beach using camera images

Enterococci, are used nationwide as a water quality indicator of marine recreational beaches. Prior research has demonstrated that enterococci inputs to the study beach site (located in Miami, FL) are dominated by non-point sources (including humans and animals). We have estimated their respective source functions by developing a counting methodology for individuals to better understand their non-point source load impacts. The method utilizes camera images of the beach taken at regular time intervals to determine the number of people and animal visitors. The developed method translates raw image counts for week days and weekend days into daily and monthly visitation rates. Enterococci source functions were computed from the observed number of unique individuals for average days of each month of the year, and from average load contributions for humans and for animals. Results indicate that dogs represent the larger source of enterococci relative to humans and birds.     

Measurements and modelling of beach groundwater flow in the swash-zone: a review

This paper reviews research on beach groundwater dynamics and identifies research questions which will need to be answered before swash zone sediment transport and beach profile evolution can be successfully modelled. Beach groundwater hydrodynamics are a result of combined forcing from the tide and waves at a range of frequencies, and a large number of observations exist which describe the shape and elevation of the beach watertable in response to tidal forcing at diurnal, semi-diurnal and spring-neap tidal frequencies. Models of beach watertable response to tidal forcing have been successfully validated; however, models of watertable response to wave forcing are less well developed and require verification. Improved predictions of swash zone sediment transport and beach profile evolution cannot be achieved unless the complex fluid and sediment interactions between the surface flow and the beach groundwater are better understood, particularly the sensitivity of sediment transport processes to flow perpendicular to the permeable bed.The presence of a capillary fringe, particularly when it lies just below the sand surface, has influences on beach groundwater dynamics. The presence of a capillary fringe can have a significant effect on the exchange of water between the ocean and the coastal aquifer, particularly in terms of the storage capacity of the aquifer. Field and laboratory observations have also shown that natural groundwater waves usually propagate faster and decay more slowly in aquifers with a capillary fringe, and observations which suggest that horizontal flows may also occur in the capillary zone have been reported. The effects of infiltration and exfiltration are generally invoked to explain why beaches with a low watertable tend to accrete and beaches with a high watertable tend to erode. However, the relative importance of processes such as infiltration losses in the swash, changes in the effective weight of the sediment, and modified shear stress due to boundary layer thinning, are not yet clear. Experimental work on the influence of seepage flows within sediment beds provides conflicting results concerning the effect on bed stability. Both modelling and experimental work indicates that the hydraulic conductivity of the beach is a critical parameter. However, hydraulic conductivity varies both spatially and temporally on beaches, particularly on gravel and mixed sand and gravel beaches. Another important, but poorly understood, consideration in beach groundwater studies is the role of air encapsulation during the wetting of beach sand.     

Detection of antibiotic resistant bacteria inhabiting the sand of non-recreational marine beach

The present study examined the antibiotic resistance of heterotrophic bacteria, which were isolated from the sand of the beach located in the National Park of the southern Baltic Sea coast. The bacteria demonstrated low levels of antibiotic resistance. These microorganisms were the most resistant to cefaclor and clindamycin and the most sensitive to clarithromycin, doxycycline, gentamycin and oxytetracycline. The majority of bacteria inhabiting the sand of the studied beach were resistant to only one antibiotic out of 18 tested antibiotics in this study. The bacteria inhabiting the middle part of the beach and the dune were more antibiotic resistant than bacteria isolated from the seawater and the shoreline-seawater contact zone. Generally, there was no significant difference in antibiotic resistance between bacteria isolated from the surface and the subsurface sand layers. The bacterial antibiotic resistance level depends on the chemical structure of antibiotics.     

The role of wind direction in eolian transport on a narrow sandy beach

Comparison of eolian transport during five high-velocity wind events over a 29 day period on a narrow estuarine beach in Delaware Bay, New Jersey, USA, reveals the temporal variability of transport, due to changes in direction of wind approach. Mean wind speed measured 6 m above the dune crest for the five events ranged from 8·5 to 15·9 ms^?1. Mean wind direction was oblique to the shoreline (63° from shore-normal) during one event but was within 14° of shore-normal during the other events. Eolian transport is greatest during low tide and rising tide, when the beach source area is widest and when drying of surface sediments occurs. The quantity of sediment caught in a vertical trap for the five events varied from a total of 0·07 to 113·73 kgm^?1. Differences in temperature, relative humidity and moisture and salt content of surficial sediments were slight. Mean grain sizes ranged from 0·33 to 0·58 mm, causing slight differences in threshold shear velocity, but shear velocities exceeded the threshold required for transport during all events. Beach width, measured normal to the shoreline, varied from 15·5 to 18·0 m; beach slope differed by 0·5°. The oblique wind during one event created a source width nearly double the width during other days. Beach slope, measured in the direction of the wind, was less than half as steep as the slope measured normal to the shoreline. The amount of sand trapped during the oblique wind was over 20 times greater than any other event, even those with higher shear velocities. The ability of the beach surface to supply grains to the air stream is limited on narrow beaches, but increased source width, due to oblique wind approach, can partially overcome limitations of surface conditions on the beach.     

Fingered flow: The creator of sand columns in dune and beach sands

Sand columns, sand cones, sand mushrooms and other striking sand forms are frequently observed in the Dutch and German beach and dune sands. This paper aims to clarify the mechanism of sand column formation. Recently it has become evident that homogeneous beach and dune sands often become irregularly wetted by infiltrating rainwater. In otherwise dry sandy soils, wet preferential flow paths (‘fingers’) may develop. At two test sites the volumetric soil moisture content varied between 0·2 and 12·0 per cent. The wet fingers represent the premature state of sand columns. When the dry sand in between these fingers is blown away by the wind, the more resistant wet sand of the fingers will remain in its place and appear as sand columns at the surface. As a result of wind and erosive sand drifts, striking sand forms may be formed.     

Impacts of beach closures on perceptions of swimming-related health risk in Orange County, California

Following a major beach closure due to bacterial contamination, a survey of beachgoers was conducted in Huntington Beach, California in 1999 to assess perceived health risk from swimming. Responses were compared to those of beachgoers at the unaffected Laguna Main Beach. No significant differences were found in risk perception. Respondents were aware of the closures (83%), yet the majority (83%) felt the water was safe for swimming. Proximity of residence to the beach was strongly associated with closure awareness (Spearman's rho=0.427, p<0.0001). Although 83% of respondents felt that water quality was important in deciding to go to the beach, only 25% of respondents who did not plan to swim cited pollution or contamination as a reason not to swim. Most respondents (70%) trusted local health agency officials' decisions about when to open/close beaches. Surveyed beach visitors were likely to bathe (84%) and were not highly concerned with swimming-related health risks.     

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.     

Evaluating proxies for estimating subaerial beach volume change across increasing time scales and various morphologies

Proxies, such as changes in beach profiles and shoreline positions, are commonly used in management and research for estimating changes in subaerial beach volume; however, the accuracy of these proxies across increasing time scales and complex morphologies is unclear. Volume changes associated with along‐beach morphologic variability may not be captured well by changes in profiles, while volume changes associated with across‐beach morphologic variability may not be captured well by measuring shoreline change. This study assesses the impacts of morphologic variations, associated with beach cusps and nourishment material, on volume change estimates from profiles and shoreline change at 0.5 to 3.5 year time periods. Results indicate that profiles spaced ≥ 150 m apart and the shoreline‐change proxy will likely estimate volume change inaccurately over periods ≤ 1 year at beaches that are consistently eroding or accreting and contain cusps. However, over longer time periods (1–3.5 years), estimates of volume change from both proxies improved at those types of beaches. Volume changes at the edges of nourishment areas are not captured well by profiles. When the nourishment material is graded to a ramped morphology, which minimizes across‐beach morphologic variability, the shoreline‐change proxy does accurately estimate volume changes. Both proxies estimate volume changes inaccurately at beaches where volume changes oscillate between erosion and accretion on both short and long time scales because the magnitude of small‐scale changes in volume from the formation and erosion of morphologic features, such as cusps and berms, will always be similar to the longer‐term net volume change. This study suggests that decadal records of shoreline change, which are commonly developed using aerial photography, can be used to help identify the best proxy for estimating volume change; however, recent anthropogenic modifications that impact patterns of beach sedimentation, including nourishment, terminal groins, and inlet‐channel dredging, makes decadal records less useful. Copyright © 2013 John Wiley & Sons, Ltd.     

The use of video imagery to analyse groundwater and shoreline dynamics on a dissipative beach

Groundwater seepage is known to influence beach erosion and accretion processes. However, field measurements of the variation of the groundwater seepage line (GWSL) and the vertical elevation difference between the GWSL and the shoreline are limited. We developed a methodology to extract the temporal variability of the shoreline and the wet-dry boundary using video imagery, with the overarching aim to examine elevation differences between the wet-dry boundary and the shoreline position in relation to rainfall and wave characteristics, during a tidal cycle. The wet-dry boundary was detected from 10 min time-averaged images collected at Ngaranui Beach, Raglan, New Zealand. An algorithm discriminated between the dry and wet cells using a threshold related to the maximum of the red, green, and blue intensities in Hue-Saturation-Value. Field measurements showed this corresponded to the location where the water table was within 2 cm of the beachface surface. Time stacks and time series of pixels extracted from cross-shore transects in the video imagery, were used to determine the location of the shoreline by manually digitizing the maximum run-up and minimum run-down location for each swash cycle, and averaging the result. In our test data set of 14 days covering a range of wave and rainfall conditions, we found 6 days when the elevation difference between the wet-dry boundary and the shoreline remained approximately constant during the tidal cycle. For these days, the wet-dry boundary corresponded to the upper limit of the swash zone. On the other 8 days, the wet-dry boundary and the shoreline decoupled with falling tide, leading to elevation differences of up to 2.5 m at low tide. Elevation differences between the GWSL and the shoreline at low tide were particularly large when the cumulative rainfall in the preceding month was greater than 200 mm. This research shows that the wet-dry boundary (such as often used in video shoreline-finding algorithms) is related to groundwater seepage on low-sloped, medium to fine sand beaches such as Ngaranui Beach (mean grain size ∼0.27 mm, beach slope ∼1:70) and may not be a good indicator of the position of the shoreline.     

Aeolian sand strip mobility and protodune development on a drying beach: examining surface moisture and surface roughness patterns measured by terrestrial laser scanning

Ephemeral aeolian sand strips are commonplace on beaches. Their formation during high energy sand transport events often precedes the development of protodunes and their dynamics present interesting feedback mechanisms with surface moisture patterns. However, due to their temporary nature, little is known of their formation, mobility or the specifics of their interaction with beach surface characteristics. Similarly surface moisture has an important influence on sediment availability and transport in aeolian beach systems, yet it is difficult to quantify accurately due to its inherent variability over both short spatial and temporal scales. Whilst soil moisture probes and remote sensing imagery techniques can quantify large changes well, their resolution over mainly dry sand, close to the aeolian transport threshold is not ideal, particularly where moisture gradients close to the surface are large. In this study we employed a terrestrial laser scanner to monitor beach surface moisture variability during a three and a half hour period after a rain event and investigated relationships between bedform development, surface roughness and surface moisture. Our results demonstrate that as the beach surface dries, sand transport increases, with sediment erosion occurring at the wet/dry surface boundary, and deposition further downwind. This dynamic structure, dependent upon changing surface moisture characteristics, results in the formation of a rippled sand strip and ultimately a protodune. Our findings highlight dynamic mobility relationships and confirm the need to consider transient bedforms and surface moisture across a variety of scales when measuring aeolian transport in beach settings. The terrestrial laser scanner provides a suitable apparatus with which to accomplish this. Copyright © 2010 John Wiley & Sons, Ltd.