Berm Crest Research Articles

INVESTIGATION INTO THE MECHANISMS OF CREST GROWTH ON GRAVEL BERMS

The continual sea-level rise predicted over the next century poses a significant threat to coastal regions. Preserving the coastline will require innovative coastal protection techniques and structures. A potential defence is to introduce artificial gravel beaches (Loman et al., 2010), or dynamic revetments (Bayle et al., 2020), a gravel berm placed at the high tide berm(Bayle et al., 2020). A key feature of these types of defences is their ability to maintain the berm elevation relative to the water level. As the water level rises, the structure is overtopped by waves which drives sediment up and over the berm crest peak. This leads to elevation gain for the berm and limits the landward excursion of waves. Berm crest behaviour has only been recorded at frequencies that do not allow wave-by-wave analysis of the process and the resultant ‘snapshot’ profiles may not be representative of the true variability of gravel berms. Through application of continuous 2-D Lidar monitoring on several active gravel berms this paper addresses this gap. It presents new findings related to sediment transport at the berm crest, the morphodynamic behavior under wave attack and a conceptual model for berm state.

Observation and Modeling of the Equilibrium Slope Response of a High-Energy Meso-Macrotidal Sandy Beach

Beach slope is a critical parameter to, e.g., beach safety, wave reflection at the coast and longshore transport rate. However, it is usually considered as a time-invariant and profile-average parameter. Here, we apply a state-of-the-art equilibrium model to hindcast beach slope variability from the time scales of days to years at the high-energy meso-macrotidal sandy beach of Truc Vert, southwest France. We use 9 years of bimonthly beach surveys to compute beach slope time series at different elevations. Results show that beach slope exhibits an equilibrium response with contrasting behaviors along two distinct areas of the beach profile. From 0 to 2 m above mean sea level, which is located under the berm crest, a slope response predominantly at the storm time scale is observed. The beach slope steepens under low energy waves, with the equilibrium model explaining up to 40% of the observed beach slope variability. In contrast, from 2.5 to 4 m above mean sea level, which is above the berm crest, the beach slope steepens under high-energy waves. Within this region of the beach profile, the response time scale increases upwards from seasonal (~2.5 m) to seasonal (~4 m), with the model explaining up to 65% of the observed beach slope variability. Such behaviors are found to be enforced by the berm dynamics developing from the end of the winter to early autumn, providing new perspectives to model and predict beach slope on sandy beaches.

Beaching and Natural Removal Dynamics of Pelagic Sargassum in a Fringing‐Reef Lagoon

AbstractMassive quantities of the pelagic brown macroalgae Sargassum spp. (sargassum) have been invading the Caribbean and West African shores since 2011, causing devastating effects on the coastal ecosystem and local economy. Little is known about sargassum beaching dynamics and the capacity of the coastal system to naturally remove beached sargassum. Here, we characterize the temporal variation in arriving and beached sargassum in a reef lagoon using a 5.2‐year data set of hourly optical imagery, and identify the governing hydrometeorological conditions. Image classification reveals interannual variability in the start, duration, and intensity of the sargassum arrival season. Arrivals are associated with relatively low energy onshore directed winds and waves, and offshore abundance of sargassum. Furthermore, nearshore sargassum mat size is found to decrease with decreasing wave/wind energy. Once sargassum beaches, a berm of wrack is formed. Natural wrack removal was observed under elevated water levels and increased wave action. Three types of wrack removal were distinguished, depending on the water level with respect to the berm crest height and berm crest toe : gradual berm destruction with gaps developing in the seaward berm edge that grow larger with time (Type I; ) and abrupt berm destruction with part of the wrack depositing on the upper beach (Type II; ) or in the dunes (Type III; ). Higher energy waves activate the reef circulation, which is suspected to flush part of the wrack out of the reef lagoon. We propose a conceptual model of nearshore sargassum dynamics in a reef lagoon system.

Methods for predicting berm height at Temporarily Open/Closed Estuaries

This study investigates the berm crest elevation at 20 Temporarily Open/Closed Estuaries (TOCEs) along the wave-dominated, microtidal coastline of South Africa and provides suitable methods of prediction. Several years of berm survey and estuary water level data were analysed for the selected estuaries, resulting in a relatively large record of historical berm crest elevations compared to previous regional datasets. The new dataset was utilised to test and develop multiple methods for the prediction of berm height and consequently flood levels within TOCEs. Long-term wave runup elevations (R2%) were simulated at the estuary berms using existing runup parameterisations to establish the exceedance probability threshold of R2% associated with the maximum berm height (BMAX). It was found that the 5% exceedance probability of runup provided consistent predictions of BMAX at the selected TOCEs with a mean absolute error (MAE) of 0.28 m. A Berm Height Criteria was developed to predict BMAX based on the wave height, beach face slope, sediment grain size and tidal range at the estuary. The criteria-based approach ensures ease of use and is intended as a first estimate of BMAX (with MAE of 0.23 m). Lastly, a stepwise berm growth model was tested according to its potential to track short-term berm growth during inlet closure to breach cycles. The model provides a simplified approach to predict berm accretion based on the overwash potential depth, which is defined as the elevation difference between R2% and the berm height. The use of a site-specific scaling parameter for berm accretion provided predictions of the berm height at breach with MAEs varying between 0.03 m and 0.17 m among estuaries for the short-term scenarios tested. The hydrodynamic and morphological variability displayed by the selected South Africa TOCEs increased the robustness of the results, potentially making the findings relevant to TOCEs in other parts of the world.

A Long-Term Coastal Evolution Model with Longshore and Cross-Shore Transport

Palalane, J. and Larson, M., 2020. A long-term coastal evolution model with longshore and cross-shore transport. Journal of Coastal Research, 36(2), 411–423. Coconut Creek (Florida), ISSN 0749-0208.This study encompasses the development of a long-term coastal evolution model with enhanced capabilities to simulate simultaneously the cross-shore and longshore evolution of the coast. The paper starts by reviewing the theory related to cross-shore and longshore sediment transport, which are the major components integrated in the model. Major advances were made by introducing modules to better account for dune erosion and overwash, dune buildup by wind, and exchange of sediment between the berm and the bar into an existing coastal evolution model. Then, the model performance was tested by simulating the evolution for a stretch of coastline corresponding to the conditions at Westhampton Beach (United States), first for a case with open boundaries representing a situation of dynamic equilibrium and then for the placement of a terminal groin causing advance of the shoreline, berm crest, and dune foot. Subsequently, the model was employed to simulate the combined cross-shore and longshore evolution along Macaneta Spit (Mozambique), and the results were compared with available data. Overall, the model succeeded in reproducing the expected combined cross-shore and longshore evolution at the selected case study sites. For the Westhampton Beach case, the model was able to qualitatively simulate the observed advance of the cross-shore dune system, following the placement of the terminal groin. For Macaneta Spit, the model reproduced the alongshore variation in cross-shore profile shape in response to the incident waves and water levels, as well as the net longshore sand transport pattern as identified in previous studies. In summary, the model produced reliable and robust predictions, showing the capability of running simulations for a period of decades in a few minutes on a personal computer.

Modes of Berm and Beachface Recovery Following Storm Reset: Observations Using a Continuously Scanning Lidar

AbstractFollowing the rapid and destructive impacts of storm erosion, beach recovery is a key natural process of restoration, returning eroded sediment to the subaerial beach and rebuilding coastal morphology. While the effects of storm erosion have commonly been investigated, detailed studies into poststorm recovery are currently lacking. This study investigates wave‐driven recovery processes of the berm and beachface on a microtidal, swash‐aligned sandy beach. Following complete removal of the berm by a significant storm event, the entire 76‐day rebuilding of a swash berm is analyzed at the timescale of every semidiurnal tidal cycle, utilizing high‐resolution (5 Hz) swash and subaerial beach profile measurements from a continuously scanning fixed lidar. Tide‐by‐tide rates of subaerial volume change during berm recovery were most frequently observed between 1 and 2 m3/m/day, including losses and gains an order of magnitude larger than the more gradual rate of net gain (0.7 m3/m/day) observed for the entire recovery period. Patterns of berm crest formation and vertical growth were found to be primarily governed by the neap‐spring tide variations in total water levels. Tide‐by‐tide beachface and berm volume changes were used to classify four principal behavioral modes of subaerial profile variability during recovery. Using decision tree classification, modes were differentiated according to nearshore dimensionless fall velocity, swash exceedance of the berm crest, and ocean water levels. The findings provide novel behavioral and parametric insight into the tide‐by‐tide rebuilding of the beachface and berm by swash throughout a complete poststorm recovery period.

Aeolian sediment transport on a recovering storm‐eroded foredune with sand fences

AbstractStudies of sediment transport on developed coasts provide perspective on how human adjustments alter natural processes. Deployment of sand‐trapping fences is a common adjustment that changes the characteristics of the dune ramp and its role in linking sediment transfers from the backshore to the foredune. Fence effects were evaluated in the field using anemometer arrays and vertical sediment traps placed across a beach and dune at Seaside Park, New Jersey, USA during onshore and longshore winds. The foredune is 18 m wide and 4.5 m above the backshore. The mean speed of onshore winds at 0.5 m elevation decreased by 17% from the berm crest to the upper ramp and 36% in the lee of a fence there. Sediment transport during mean wind speeds up to 8.0 m s−1 at 0.5 m elevation was < 0.06 kg m−1 h−1 on the berm crest and backshore where fetch distances were < 45 m and surface sediment was relatively coarse (0.74–0.85 mm) but increased to 5.63 kg m−1 h−1 on the upper ramp aided by the longer fetch distances (up to 82 m) and finer grain size of the source sediment there (0.52 mm). Sediment transport along the berm crest and backshore during longshore winds, where fetch distances were > 200 m, was up to 58.69 kg m−1 h−1, about three orders of magnitude greater than during the onshore winds. Fences can displace the toe of the ramp farther seaward than would occur under natural conditions. They can create a gentler slope and change the shape of the ramp to a more convex form. A fence on the ramp can cut off a portion of sediment supply to the upper slope. Decisions about fence placement thus should consider these morphologic changes in addition to the effects on dune volume. Copyright © 2017 John Wiley & Sons, Ltd.

Coastal morphology and beach stability along Thiruvananthapuram, south-west coast of India

Shoreline changes are largely dependent on coastal morphology. South-west coast of India is a high energy coast characterised by monsoon high waves, steep beach face and medium-sized beach sand. Waves are generally from west and west south-west during rough monsoon season and from south-west during fair weather season. Shoreline change along this coast is studied with reference to coastal morphological features. Various morphological features, modifications and chronological positions of shoreline are analysed with the information derived from multidated satellite imageries, toposheets and GPS shoreline mapping along with extended field survey. Image processing and GIS techniques have been used for the analysis of data and presentation of results. Sediment accumulation on the leeward side of artificial structures such as harbour breakwaters and groynes is used as a sediment transport indicator. Artificial structures such as seawalls, groynes and harbour breakwaters modify morphology. Shoreline south of headlands/promontories and breakwaters are stable or accreting due to net northerly longshore sediment transport while erosion tendency is observed on the north side. Lateritic cliffs fronting the sea or with seasonal beach undergo slumping and cliff edge retreat as episodic events. Spits adjoining tidal inlets are prone to shoreline variations due to oscillations of inlet mouth. Interventions in the form of inlet stabilization and construction of coastal protection structures trigger erosion along adjoining coasts. Seawalls constructed along highly eroding coasts get damaged, whereas those constructed along monsoon berm crest with frontal beaches for protection against monsoon wave attack are retained. Fishing gaps within seawalls are areas of severe temporary erosion during rough monsoon season. Accretion or erosion accompanies construction of harbour breakwaters in a stable coastal plain. Close dependence of shoreline changes on morphology necessitates detailed understanding of impacts on morphology prior to introducing any intervention in the coastal zone.

Offshore aeolian sediment transport across a human‐modified foredune

AbstractConcepts derived from previous studies of offshore winds on natural dunes are evaluated on a dune maintained for shore protection during three offshore wind events. The potential for offshore winds to form a lee‐side eddy on the backshore or transfer sediment from the dune and berm crest to the water are evaluated, as are differences in wind speed and sediment transport on the dune crest, berm crest and a pedestrian access gap.The dune is 18–20 m wide near the base and has a crest 4.5 m above backshore elevation. Two sand‐trapping fences facilitate accretion. Data were obtained from wind vanes on the crest and lee of the dune and anemometers and sand traps placed across the dune, on the beach berm crest and in the access gap. Mean wind direction above the dune crest varied from 11 to 3 deg from shore normal. No persistent recirculation eddy occurred on the 12 deg seaward slope. Wind speed on the berm crest was 85–89% of speed at the dune crest, but rates of sediment transport were 2.27 times greater during the strongest winds, indicating that a wide beach overcomes the transport limitation of a dune barrier. Limited transport on the seaward dune ramp indicates that losses to the water are mostly from the backshore, not the dune. The seaward slope gains sand from the landward slope and dune crest. Sand fences causing accretion on the dune ramp during onshore winds lower the seaward slope and reduce the likelihood of detached flows during offshore winds. Transport rates are higher in access gaps than on the dune crest despite lower wind speeds because of flatter slopes and absence of vegetation. Transport rates across dunes and through gaps can be reduced using vegetation and raised walkover structures. Copyright © 2017 John Wiley & Sons, Ltd.

Constraints on aeolian sediment transport to foredunes within an undeveloped backshore enclave on a developed coast

Landforms present in undeveloped beach enclaves located between properties developed with houses and infrastructure are often left to evolve naturally but are influenced by the human structures near them. This field study evaluates how buildings and sand-trapping fences change the direction of wind approach, reduce wind speed, and restrict fetch distances for sediment entrainment, thereby reducing the potential for aeolian transport and development of dunes in enclaves.Field data were gathered in an 80m long, 44m deep beach enclave on the ocean shoreline of New Jersey, USA. Comparison of wind characteristics in the enclave with a site unaffected by buildings revealed that offshore winds in the enclave are reduced in strength and altered in direction by landward houses, increasing the relative importance of longshore winds. Vertical arrays of anemometers on the foredune crest, foredune toe and berm crest in the enclave revealed increasing wind speed with distance offshore, with strongest winds on the berm crest. Vertical cylindrical traps on the foredune crest, foredune toe, mid-backshore, berm crest and upper foreshore revealed the greatest rate of sediment transport on the berm crest. Sediment samples from the beach and from traps revealed limited potential for aeolian transport because of coarse grain sizes.Strong oblique onshore winds are common in this region and are normally important for transporting sand to dunes. The length of an enclave and the setback distance on its landward side determine the degree to which sediment delivered by oblique winds contributes to dune growth. The landward edge of the enclave (defined by a sand fence near the dune toe) is sheltered along its entire length from winds blowing at an angle to the shoreline of 25° or less. A foredune set back this distance in an enclave the length of an individual lot (about 20m) would be sheltered at an angle of 57° or less, reducing the opportunity for dune building by onshore winds. Reduced potential for aeolian transport in enclaves implies that human actions may be required to build dunes artificially to protect buildings and roads from storm overwash.

Simulating cross-shore material exchange at decadal scale. Theory and model component validation

A model is developed to simulate the cross-shore (CS) exchange of sand and the resulting profile response at decadal scale to be used in regional coastal evolution models. The CS model consists of modules for calculating dune erosion and overwash, wind-blown sand transport, and bar-berm material exchange. The sand transport equations included in these modules are formulated based on relevant physics in combination with empirical observations and then validated towards laboratory and field data. In order to couple the transport equations to the evolution of key morphological features describing the profile a set of sand volume conservation equations are employed and solved together with the transport equations. The features that are modeled include dune height (from dune foot to crest), the locations of the landward dune foot, seaward dune foot, berm crest, and shoreline as well as the longshore bar volume. The CS model is employed and tested at three different field sites in a companion paper (Palalane et al., 2016), whereas in the present paper the properties of the model are demonstrated by simulating the evolution of the dune, berm, and shoreline in connection with accretion and erosion of sand in a groin compartment. This case derives from a study at Westhampton Beach that focused on shortening the length of a number of groins in order to release accumulated sand in the groin field to eroding downdrift beaches.

Hydraulic stability of nominal and sacrificial toe berms for mound breakwaters on steep sea bottoms

When mound breakwaters are placed on steep sea bottoms in combination with very shallow waters, the design of the toe berm becomes a relevant issue. Toe berms built close to the water surface on a steep sea bottom must withstand such high wave loads that their design may not be feasible with available quarrystones. In this study, a new design method was developed to reduce the rock size by increasing the toe berm width. The analysis involved specific 2D small-scale tests with toe berms of different rock sizes and widths, placed on a m=1/10 bottom slope with the water surface close to the toe berm crest. Two new concepts were introduced to better characterize damage to wide toe berms: (1) the most shoreward toe berm area which effectively supports the armor layer, in this study referred to as the primary or “nominal” toe berm and (2) the most seaward toe berm area which serves to protect the nominal toe berm, in this study called the secondary or the “sacrificial” toe berm. Damage to the nominal toe berm was used to describe hydraulic stability of wider toe berms. Given a standard toe berm of three rocks wide (nominal toe berm), an equivalent toe berm with damage similar to the nominal toe berm was defined by increasing the berm width and decreasing the rock size. The reduction in rock size showed an inverse 0.4-power relation with the relative berm width.

Formation of Danube delta beach ridge plains and signatures in morphology

Danube delta, as most of the large deltas, favours complex interactions between river sediment supply and marine dispersing forces which create complex configurations with concurrent morphologies (i.e. river-versus wave-influenced) or processes (accretion versus erosion) and even distinct landscapes for the same accretionary features: strandplains with low monotonous beach ridges or covered by transgressive dunefields. Beach ridge plains (BRPs) are a common feature of the wave-influenced deltaic lobes, that are created by juxtaposition of succesive berms on the prograding sandy coasts with different shapes and sizes depending on the accretionary mechanisms and the accomodation space.This study reports the formation and dynamics of Danube delta BRPs based on numerical age determination (OSL and AMS) of the paleoshorelines, topographic and geophysical (GPR) surveys and stratigraphic records by cores. A chronological framework is established for all deltaic BRPs which points to the importance of formation timespan and growth rate (as a consequence of sediment supply) on the resultant morphology varying inter-site from small BRP (formation time < 300 years) to large quasi-equilateral triangle-shaped BRP (1400–3000 years) and intra-site from low ridgesets with subparallel beach ridges (progradation rates of 3.5–12 m/yr) to high ridgesets where the original configuration was replaced by massive parabolic dunes or transgressive dunefields (progradation rates ≤ 3.5 m/yr). A six-type morphogenetic classification of BRPs is discussed in respect with the various spatial patterns of progradation – from the large strandplains developed on the updrift side of asymmetric lobes to the small ones accommodating the prograding sectors of the river mouths spits – and with the progradation types encountered: i) beach face accretion during fair-weather, ii) nearshore bar welding, and iii) berm crest building during storms. Although the last is building ca. 1.5% from deltaic BRPs, this is the only case when the visible beach ridges are made by wave processes. For the other two, the aspect of “beach ridges” is the result of aeolian processes that create either unitary foredune or thin eolian sheets (incipient foredune) tens of centimeters higher than adjacent berms.

Storm flood impacts along the shores of micro-tidal inland seas: A morphological and sedimentological study of the Vesterlyng beach, the Belt Sea, Denmark

The morphological and sedimentological impacts of an extreme storm event (‘Bodil’ in December 2013) were investigated at a mixed sand and gravel beach (Vesterlyng) in a micro-tidal environment along the Belt Sea, Denmark. The storm response was characteristic for mixed sand and gravel beaches: gravelly storm berms with sandy to gravelly washover fans were formed at the upper beach where swash processes dominated during extreme water levels in combination with overtopping and overwash. In addition, storm scarps and gravel flats were formed. The elevation of the storm berm crest was identical to a summation of the still-water level (1.60m) in the Belt Sea during the storm flood and the wave run-up (0.75m) at the shore. The crest of 2.35m is therefore a precise measure of the storm flood level. This storm flood was classified as a large-scale extreme event. In a Holocene perspective it is suggested that storm berm (beach ridge) heights above contemporaneous sea level can be used as a proxy of past flood events along micro-tidal shores.

Morphological evolution of a submerged artificial nearshore berm along a low-wave microtidal coast, Fort Myers Beach, west-central Florida, USA

Nourishment in the nearshore is becoming an increasingly utilized method for regional sediment management, particularly for dredged material that contains more fine sediment than the native beach. A nearshore berm was constructed at Fort Myers Beach, Florida, USA using mixed-sized sediment dredged from a nearby channel. The nearshore berm, which is the shallowest of its kind, was placed in water depths between 1.2 and 2.4m with the berm crest just below the mean lower low water level. Based on time-series profiles surveyed from 2009 to 2013, the nearshore berm migrated onshore while the system was approaching a dynamic equilibrium. The distant passage of two tropical storms in the third year generated exceptionally high waves for the study area. Substantial profile change induced by the energetic conditions contributed to rapid evolution of the berm profiles toward equilibrium. Near the end of the fourth year, the berm profiles had returned to the equilibrium shape characteristic of the study area. Gaps in the berm allowed water circulation when the berm became emergent and watercraft access to the beach for recreational purposes. Gaps should be considered as a design parameter for future berm nourishments. Sediment samples collected and analyzed showed that the fine sediment content in the original placed material was selectively transported and deposited offshore, while the coarser component moved onshore. The dry beach maintained the same sediment properties throughout the study period and was not influenced by the fine sediment in the initial construction of the berm.

Shoreline dynamics and littoral transport around the tidal inlet at Pulicat, southeast coast of India

Pulicat is India׳s second largest brackish water lagoon with its mouth opening in the Bay of Bengal. The dynamics of the tidal inlet at Pulicat has been reported in this study on the basis of long term analysis using satellite remote sensing aided with Geographical Information System (GIS) and berm crest data. In addition, the short term analysis was carried out using monthly in situ Global Positioning System (GPS) profiling and sediment grain size analysis. The study of the shoreline dynamics along the inlet using the Linear Imaging Self – Scanning Sensor (LISS) – III along with the Survey of India toposheet of 1954 reveals that the inlet once with a single mouth is divided into two, over the period of time with the southern mouth migrating towards north with an inconsistent migration pattern of the northern mouth. The overall extent of migration is found to be within 3km. The outcome of the 25 year berm crest data starting from 1978 revealed the coastline around Pulicat is eroding upto 1990 and thereafter it is accreting with the net shoreline erosion rate of 20.34m/yr. The monthly in situ beach profiling studies from August 2004 to July 2005 revealed that the Pulicat inlet follows a variable migratory pattern with a shift of upto 914m North during August to December with a reversal migration of 600m thus leading to a net migration towards the north. The grain size analysis has unravelled the sediment transport around Pulicat inlet. The study of the inlet using satellite imagery during monsoon has clearly justified the dominant fresh water inflow regulatory force over the tidal forces and the positive influence of the Tsunami on opening the inlet during monsoon failure.

Determination of coastal border line: an integrated approach for a part of Antalya coast (Turkey)

Sustainable development in coastal areas requires mapping of geological and geomorphological features of the area and precise determination of coastal border line. Such a study was carried out in the city of Antalya, which is undergoing intense infrastructural development in order to accommodate touristic activities. In the field, high water level, which is determined from moist-dry sand border and current berm crest, was taken as the indicator for shoreline, while vegetation line and topographic rises were taken as indicators of coastal border line. The geographic coordinates of all of the features were determined using differential Global Positioning System with application of “real-time kinematic measurement” technique. Quickbird satellite images of 2002 and 2009 were used in order to observe natural state of the coastal area before the constructions, to complete geomorphological map, and to confirm the coastal border line determined in the field. In addition, the natural vegetation line before the infrastructural development was determined using normalized difference vegetation index approach. Using grain size parameters for identification of coastal border line, high and low water levels were tested. The results showed that from low water level to coastal border line, D 50 (median grain size) and coefficient of uniformity decrease while coefficient of curvature increases systematically. This study showed that use of only one approach to determine coastal border line is insufficient, and an integrated methodology is required.

Assessing aeolian beach‐surface dynamics using a remote sensing approach

ABSTRACTA remote sensing technique for assessing beach surface moisture was used to provide insight into beach‐surface evolution during an aeolian event. An experiment was carried out on 21 October 2007 at Greenwich Dunes, Prince Edward Island National Park, Canada, during which cameras were mounted on a mast on the foredune crest at a height of about 14 m above the beach. Maps of beach surface moisture were created based on a calibrated relationship between surface brightness from the photographs and surface moisture content measured in situ at points spaced every 2.5 m along a transect using a Delta‐T moisture probe. A time sequence of maps of surface moisture content captured beach surface evolution through the transport event at a spatial and temporal resolution that would be difficult to achieve with other sampling techniques such as impedance probes. Erosion of the foreshore and berm crest resulted in an increase in surface moisture content in these areas as the wetter underlying sediments were exposed. Flow expansion downwind of the berm crest led to sand deposition and a consequent decrease in surface moisture content. Remote sensing systems such as the one presented here allow observations of the combined evolution of beach surface moisture, shoreline position, and fetch distances during short‐term experiments and hence provide a comprehensive rendering of sediment erosion and transport processes. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Aeolian transport rates across raked and unraked beaches on a developed coast

AbstractWind characteristics and aeolian transport were measured on a naturally evolving beach and dune and a nearby site where the beach is raked and sand‐trapping fences are deployed. The beaches were composed of moderately well sorted to very well sorted fine to medium sand. The backshore at the raked site was wider and the foredune was more densely vegetated and about 1 m higher than at the unraked site. Wind speeds were monitored using anemometers placed at 1 m elevation and sand transport was monitored using vertical traps during oblique onshore, alongshore and offshore winds occurring in March and April 2009. Inundation of the low backshore through isolated swash channels prevented formation of a continuously decreasing cross‐shore moisture gradient. The surface of the berm crest was dryer than the backshore, making the berm crest the greatest source of offshore losses during offshore winds. The lack of storm wrack on the raked beach reduced the potential for sediment accumulation seaward of the dune crest during onshore winds, and the higher dune crest reduced wind speeds and sediment transport from the dune to the backshore during offshore winds. Accretion at wrack seaward of the dune toe on the unraked beach resulted in a wider dune field and higher, narrower backshore. Although fresh wrack is an effective local trap for aeolian transport, wrack that becomes buried appears to have little effect as a barrier and can supply dry sand for subsequent transport. Aeolian transport rates were greater on the narrower but dryer backshore of the unraked site. Vegetation growth may be necessary to trap sand within zones of buried wrack in order to allow new incipient foredunes to evolve. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Fecal indicator organism density in beach sands: Impact of sediment grain size, uniformity, and hydrologic factors on surface water loading

Fecal loading to beach sands and subsequent transport to surface water may result in the degradation of surface water quality. To better understand the relationship between Escherichia coli in sands, beach hydrology, and recreational water quality, we collected surface water, groundwater, and sand samples from three Lake Michigan beaches with varying substrates (fine sand to pebbles, July 2005–June 2006). Sediment cores collected within transects perpendicular to and at fixed distances from the shoreline (0m, 10m, 20m) and surface water samples collected at a depth of 1m were analyzed for E. coli. Grain size analysis was performed on duplicate core samples to assess the relationship between E. coli density and mean grain size and uniformity. Groundwater samples, collected from shallow drive-point piezometers within the test area, were also analyzed for E. coli. E. coli density in beach sands differed significantly with distance from shore with the highest density occurring at the berm crest (0m). Mean grain size and uniformity accounted for variation in E. coli density with fine sand of uniform distribution having the highest content. E. coli density in surface water was correlated to E. coli density in beach sand samples at the berm crest. E. coli in groundwater was <10 to 579MPN/100ml (2005); none was detected in 2006. Management interventions, including altered beach grooming practices and slope assessments, may be effective in reducing E. coli content at beaches comprised of fine sands of uniform grain size, hence reducing water quality advisories.