quantitative remote sensing study indicates doubling of coastal erosion rate in past 50 yr along a segment of the arctic coast of alaska a new quantitative coastal land gained and lost method uses image analysis of topographic maps and landsat thematic mapper short wave infrared data to document accelerated coastal land loss and thermokarst lake expansion and drainage the data span 1955 2005 along the beaufort sea coast north of teshekpuk lake in the national petroleum reserve in alaska some areas have undergone as much as 0 9 km of coastal erosion in the past 50 yr land loss attributed to coastal erosion more than doubled from 0 48 km2 yr 1 during 1955 1985 to 1 08 km2 yr 1 during 1985 2005 coastal erosion has breached thermokarst lakes causing initial draining of the lakes followed by marine flooding although inland thermokarst lakes show some uniform expansion lakes breached by coastal erosion display lake expansion several orders of magnitude greater than inland lakes

on the potential for a bottom active layer below coastal permafrost the impact of seawater on permafrost degradation imaged by electrical resistivity tomography hornsund sw spitsbergen this paper presents the results of two dimensional electrical resistivity tomography ert of permafrost developed in coastal zone of hornsund sw spitsbergen the measurements were made using the wenner schlumberger electrode array with an electrode spacing 5 m for overview and 1 5 or 1 m spacing for detailed imaging using the ert inversion results we studied the sea influence on deeper parts of the frozen ground during the investigations we tested hypotheses that the operation of seawater on shoreface may cause changes in the shape of the coastal permafrost base and that the impact of seawater on more inland permafrost depends on the shape of the shoreline differently in the embayment and differently in a headland exposed to the open sea our study was inspired by previous ground temperature measurements conducted in several boreholes located in study area which captured the propagation of ground heat waves from the base of permafrost our resistivity models indicate a major differentiation in terms of resistivity of permafrost in the coastal zone the resistivity measures obtained in deeper layers of ground were so low 100 m that in the warm permafrost conditions they exclude a possibility of freezing the coastal sediments and bedrock from the side of the sea low values continue further inland going down under the surface layer of permafrost with higher resistivity we interpret this situation as an influence of seawater s temperature and salinity on deeper parts of permafrost based on the measurements conducted within two years we stated a change in the distribution of resistivity both in the active layer and in coastal front of permafrost in deeper parts of the ground as observed in the inverse models the geometric arrangement between the fields of extreme resistivity indicates the existence of a bottom active layer by the permafrost base depending on thermal and chemical characteristics of seawater the measurements conducted in the embayment as well as on the headland exposed to the operation of storm waves proved strong differences in the scale of the impact of seawater on permafrost

high frequency internal wave observations in the marginal ice zone three thermistor chains extending from 15 to 65 m were deployed from ice floes in the marginal ice zone north of svalbard in a triangle with sides of 500 800 m for a period of 7 days vertical displacement spectra indicate that the internal wave energy level is lower than the garrett and munk spectrum by a factor of 2 3 but higher than other observations in the arctic a group of internal waves a wave train with frequency of 2 3 cph was observed to propagate at 0 05 m s through the triangle in a west southwesterly direction during a 4 to 6 hour period a case study of this wave train where the horizontal phase differences between the three thermistor chains were analyzed showed wavelengths of 100 200 m and phase velocities of 0 10 0 15 m s observation of the density field and the velocity field indicated that stratification dominated over vertical shear consequently the dispersion relation was calculated by solving numerically the vertical mode equation for internal waves in a shearless ocean the estimated wavelengths and phase velocities agree with the dispersion relation for first mode internal waves the generating mechanisms may be tidal oscillations associated with a seamount located east of the triangle or ice keels moving in relation to the water creating lee waves in the pycnocline

improving understanding of near term barrier island evolution through multi decadal assessment of morphologic change abstract observed morphodynamic changes over multiple decades were coupled with storm driven run up characteristics at fire island new york to explore the influence of wave processes relative to the impacts of other coastal change drivers on the near term evolution of the barrier island historical topography was generated from digital stereo photogrammetry and compared with more recent lidar surveys to quantify near term decadal morphodynamic changes to the beach and primary dune system between the years 1969 1999 and 2009 notably increased profile volumes were observed along the entirety of the island in 1999 and likely provide the eolian source for the steady dune crest progradation observed over the relatively quiescent decade that followed persistent patterns of erosion and accretion over 10 30 and 40 year intervals are attributable to variations in island morphology human activity and variations in offshore bathymetry and island orientation that influence the wave energy reaching the coast areas of documented long term historical inlet formation and extensive bayside marsh development show substantial landward translation of the dune beach profile over the near term period of this study correlations among areas predicted to overwash observed elevation changes of the dune crestline and observed instances of overwash in undeveloped segments of the barrier island verify that overwash locations can be accurately predicted in undeveloped segments of coast in fact an assessment of 2012 aerial imagery collected after hurricane sandy confirms that overwash occurred at the majority of near term locations persistently predicted to overwash in addition to the storm wave climate factors related to variations within the geologic framework which in turn influence island orientation offshore slope and sediment supply impact island behavior on near term timescales

bed slope effects on turbulent wave boundary layers 2 comparison with skewness asymmetry and other effects 1 a numerical model solving incompressible reynolds averaged navier stokes equations combined with a two equation k model for turbulence closure is used to systematically compare the relative strength of bed shear stress quantities and boundary layer streaming under wave motions from four contributions believed to play a prominent role in cross shore boundary layer and sediment transport processes 1 converging diverging effects from bed slope 2 wave skewness 3 wave asymmetry and 4 waves combined with superposed negative currents intended to loosely represent for example return currents or undertow the effects from each of the four components are isolated and quantified using a standard set of bed shear stress quantities allowing their easy comparison for conditions representing large shallow water waves on steep slopes the results suggest that converging diverging effects from beach slope may make a significant onshore bed load contribution generally however the results suggest wave skewness in addition to conventional steady streaming as the most important onshore contribution outside the surf zone streaming induced within the wave boundary layer is also investigated for each component and skewness and asymmetry are demonstrated to promote largely negative streaming velocities consistent with earlier work for hydraulically smooth cases however a thin region of positive streaming is revealed in the viscous sublayer which is effectively absent in hydraulically rough conditions cross shore boundary layer dynamics are generally acknowledged to be a complicated combination of numerous competing physical processes and this work is among few to systematically compare a number of these it is hoped that the results will be useful in assessing which of the contributions considered will be most prominent for a given set of local wave and beach slope conditions

vertical structure of surface gravity waves propagating over a sloping seabed theory and field measurements 1 theoretical predictions of the vertical structure of wave motion over a sloping seabed are compared with field observations close to the bed in the nearshore zone of particular interest is the effect of the local slope on the magnitude and phase of the vertical velocity field measurements of near bed velocity profiles on a 2 bed slope were obtained using a coherent doppler profiler the surface elevation was measured by a colocated upward looking acoustic sounder results are presented from two intervals of different wave energy levels during a storm event for wave height water depth ratios smaller than 0 3 and for ursell numbers smaller than 0 6 the local comparisons of magnitude and phase between the vertical velocity and surface elevation measurements are in good agreement with linear theory for a sloping bed but differ greatly from that for a horizontal bottom especially in the lower water column the sloping bottom however has little effect on the horizontal velocity linear theory appears to adequately describe the transfer function between the surface elevation and the near bed velocities not only at the peak frequencies but also at their harmonics however in relatively shallow water the local transformations of free and forced waves at the harmonic frequencies are indistinguishable in the lower water column therefore given surface elevation measurements at a particular location which reflect the integrated effects of nonlinearities associated with wave shoaling the vertical structure of the third moments of velocity fields estimated from linear theory is in reasonable agreement with the observations both theory and observations show that the skewness and asymmetry of the vertical velocity are subject to significant bottom slope effects whereas those of horizontal velocity are not index terms 4211 oceanography general benthic boundary layers 4203 oceanography general analytical modeling 4219 oceanography general continental shelf processes 4546 oceanography physical nearshore processes 4560 oceanography physical surface waves and tides 1255 keywords shoaling waves bottom slope vertical structure skewness asymmetry boundary layers citation zou q a e hay and a j bowen vertical structure of surface gravity waves propagating over a sloping seabed theory and field measurements j geophys res 108 c8 3265 doi 10 1029 2002jc001432 2003

seabed shear stress and bedload transport due to asymmetric and skewed waves abstract a simple conceptual formulation to compute seabed shear stress due to asymmetric and skewed waves is presented this formulation generalizes the sinusoidal wave case and uses a variable friction factor to describe the physics of the boundary layer and to parameterize the effects of wave shape predictions of bed shear stresses agree with numerical computations using a standard boundary layer model with a k e turbulence closure the bed shear stress formulation is combined with a meyer peter and muller type formula to predict sheet flow bedload transport under asymmetric and skewed waves for a horizontal or sloping bed the predictions agree with oscillatory water tunnel measurements from the literature

coastal retreat and shoreface profile variations in the canadian beaufort sea the coastline of the southern canadian beaufort sea consists primarily of unconsolidated bluffs although the sea is ice free for 3 months of the year and wave energy is restricted by pack ice the coast is undergoing regional retreat with erosion rates as high as 10 m a 1 in some locations simple and multiple regression analyses were carried out to determine the degree of correlation between the mean retreat rate measured at various locations and the different parameters that may control shoreline recession sediment texture ground ice content cliff height wave energy and shoreface gradient revealed medium to poor correlation with erosion rates showing that the recessive evolution of the coastline can not be explained solely by wave induced and subaerial processes the comparison of nearshore echo sounding records from 1987 with bathymetry from 1971 showed substantial erosion up to 1 m of the submarine profile between 12 and 15 m of water there is strong evidence that this erosion has been caused by sea ice gouging on the seafloor from depths of 5 to 9 m accretion has taken place possibly induced by ice push processes and inshore of the 5 m isobath wave and current erosion of the shoreface has occurred these results suggest that the erosion of the inner shelf by ice gouging drives the erosion observed inshore on the coastal bluffs and nearshore zone as the shoreface profile strives for a state of dynamic equilibrium

effects of wave shape on sheet flow sediment transport 1 a two phase model is implemented to study the effects of wave shape on the transport of coarse grained sediment in the sheet flow regime the model is based on balance equations for the average mass momentum and fluctuation energy for both the fluid and sediment phases model simulations indicate that the responses of the sheet flow such as the velocity profiles the instantaneous bed shear stress the sediment flux and the total amount of the mobilized sediment cannot be fully parameterized by quasi steady free stream velocity and may be correlated with the magnitude of local horizontal pressure gradient or free stream acceleration a net sediment flux in the direction of wave advance is obtained for both skewed and saw tooth wave shapes typical of shoaled and breaking waves the model further suggests that at critical values of the horizontal pressure gradient there is a failure event within the bed that mobilizes more sediment into the mobile sheet and enhances the sediment flux preliminary attempts to parameterize the total bed shear stress and the total sediment flux appear promising

swell and sea in the emerging arctic ocean ocean surface waves sea and swell are generated by winds blowing over a distance fetch for a duration of time in the arctic ocean fetch varies seasonally from essentially zero in winter to hundreds of kilometers in recent summers using in situ observations of waves in the central beaufort sea combined with a numerical wave model and satellite sea ice observations we show that wave energy scales with fetch throughout the seasonal ice cycle furthermore we show that the increased open water of 2012 allowed waves to develop beyond pure wind seas and evolve into swells the swells remain tied to the available fetch however because fetch is a proxy for the basin size in which the wave evolution occurs thus both sea and swell depend on the open water fetch in the arctic because the swell is regionally driven this suggests that further reductions in seasonal ice cover in the future will result in larger waves which in turn provide a mechanism to break up sea ice and accelerate ice retreat

a 5000year record of intertidal peat stratigraphy and sea level change from northwest alaska abstract coastal environments of northwest alaska preserve a detailed record of sea level change during the past 5000 14 c yr rapid burial of intertidal marshes by storm overwash processes a short open water period and the arctic maritime climate contribute to the preservation of marine and eolian facies eustatic and storm controlled changes in sea level can be identified from interbedded sequences of marsh peat and coastal flood deposits on barrier islands and estuaries along northwest seward peninsula mean eustatic sea level has risen about 1 5 m during the last 5000 years at an average of ca 0 028 cm yr 1 based on the depth and age relationship of a suite of 23 peat horizons sampled from a 140 km long reach of coast nearshore erosion and sedimentation are controlled by secular variations in wave climate peaks in tidal amplitude and storminess correlate with transgressive sedimentary regimes and occurred during the periods 3300 1700 1200 900 and since about 400 14 c yr bp short term fluctuations in relative sea level are superimposed on the long term regional eustatic trend and record the coastal response to variable rates of sea level change during the late holocene

variability of shore and shoreline evolution shore and shoreline evolution both due to natural and human induced causes or factors can be variable over a wide range of different temporal and or spatial scales our capability to understand and especially predict this variability is still limited this can lead to misinterpretation of coastal change information which hampers informed decision making and the subsequent design and implementation of soft engineering interventions collecting and describing example observations of shore and shoreline variability is one way to support and improve such human intervention this paper describes causes and factors for the variability and the resulting possible evolutions of wave dominated shores and shorelines which are illustrated by a number of case studies the new element of this work is that the variability is described in terms of a range of different time and space scales which helps to structure such analysis however it is difficult to generalise the results for arbitrary situations especially on decadal time scales scientific and engineering improvements require more quantitative insight into the physical mechanisms behind the free and forced shore behaviour responsible for the variability

bed slope effects on turbulent wave boundary layers 1 model validation and quantification of rough turbulent results 1 a numerical model solving incompressible reynolds averaged navier stokes equations combined with a two equation k turbulence closure is used to study converging diverging effects from a sloping bed on turbulent oscillatory wave boundary layers bed shear stresses from the numerical model are first validated against hydraulically smooth and rough data from flat bed experiments in the form of wave friction factor diagrams the results show that the model provides acceptable accuracy for wave orbital amplitude to roughness length ratios a kn 20 validation against experimental measurements for steady streaming induced by a skewed free stream velocity signal is also provided we then simulate a series of experiments involving oscillatory flow in a convergent divergent smooth tunnel and a good match with respect to bed shear stresses and streaming velocities is achieved the streaming is conceptually explained using analogies from steady converging and diffuser flows a parametric study is undertaken to assess both the peak and time averaged bed shear stresses in converging and diverging half periods under rough turbulent conditions the results are presented as friction factor diagrams a local similarity condition is derived for relating oscillatory flow in a convergent divergent tunnel as considered herein to shoaling shallow water waves by matching spatial gradients in the free stream orbital length

coastline responses to changing storm patterns 1 researchers and coastal managers are pondering how accelerated sea level rise and possibly intensified storms will affect shorelines these issues are most often investigated in a cross shore profile framework fostering the implicit assumption that coastline responses will be approximately uniform in the alongshore direction however experiments with a recently developed numerical model of coastline change on a large spatial domain suggest that the shoreline responses to climate change could be highly variable as storm and wave climates change large scale coastline shapes are likely to shift causing areas of greatly accelerated coastal erosion to alternate with areas of considerable shoreline accretion on complex shaped coastlines including cuspate cape and spit coastlines the alongshore variation in shoreline retreat rates could be an order of magnitude higher than the baseline retreat rate expected from sea level rise alone

modeling erosion of ice rich permafrost bluffs along the alaskan beaufort sea coast the arctic climate is changing inducing accelerating retreat of ice rich permafrost coastal bluffs along alaska s beaufort sea coast erosion rates have increased roughly threefold from 6 8 to 19 m yr 1 since 1955 while the sea ice free season has increased roughly twofold from 45 to 100 days since 1979 we develop a numerical model of bluff retreat to assess the relative roles of the length of sea ice free season sea level water temperature nearshore wavefield and permafrost temperature in controlling erosion rates in this setting the model captures the processes of erosion observed in short term monitoring experiments along the beaufort sea coast including evolution of melt notches topple of ice wedge bounded blocks and degradation of these blocks model results agree with time lapse imagery of bluff evolution and time series of ocean based instrumentation erosion is highly episodic with 40 of erosion is accomplished during less than 5 of the sea ice free season among the formulations of the submarine erosion rate we assessed we advocate those that employ both water temperature and nearshore wavefield as high water levels are a prerequisite for erosion any future changes that increase the frequency with which water levels exceed the base of the bluffs will increase rates of coastal erosion the certain increases in sea level and potential changes in storminess will both contribute to this effect as water temperature also influences erosion rates any further expansion of the sea ice free season into the midsummer period of greatest insolation is likely to result in an additional increase in coastal retreat rates

complexities in barrier island response to sea level rise insights from numerical model experiments north carolina outer banks using a morphological behavior model to conduct sensitivity experiments weinvestigate the sea level rise response of a complex coastal environment to changes ina variety of factors experiments reveal that substrate composition followed in rankorder by substrate slope sea level rise rate and sediment supply rate are the mostimportant factors in determining barrier island response to sea level rise we find thatgeomorphic threshold crossing defined as a change in state e g from landward migratingto drowning that is irreversible over decadal to millennial time scales is most likely tooccur in muddy coastal systems where the combination of substrate composition depth dependent limitations on shoreface response rates and substrate erodibility mayprevent sand from being liberated rapidly enough or in sufficient quantity to maintain asubaerial barrier analyses indicate that factors affecting sediment availability such aslow substrate sand proportions and high sediment loss rates cause a barrier to migratelandward along a trajectory having a lower slope than average barrier island slope therebydefining an effective barrier island slope other factors being equal such barrierswill tend to be smaller and associated with a more deeply incised shoreface therebyrequiring less migration per sea level rise increment to liberate sufficient sand to maintainsubaerial exposure than larger less incised barriers as a result the evolution of larger lessincised barriers is more likely to be limited by shoreface erosion rates or substrateerodibility making them more prone to disintegration related to increasing sea level riserates than smaller more incised barriers thus the small deeply incised north carolinabarriers are likely to persist in the near term although their long term fate is less certainbecause of the low substrate slopes that will soon be encountered in aggregate results point to the importance of system history e g previous slopes sediment budgets etc in determining migration trajectories and therefore how a barrier island will respondto sea level rise although simple analytical calculations may predict barrier responsein simplified coastal environments e g constant slope constant sea level rise rate etc our model experiments demonstrate that morphological behavior modeling is necessary toprovide critical insights regarding changes that may occur in environments havingcomplex geometries especially when multiple parameters change simultaneously

oblique flow over dredged channels ii sediment transport and morphology a three dimensional 3d investigation of sediment transport processes across long straight channels exposed to an oblique incoming current is presented for this purpose a detailed mathematical flow and sediment transport model is applied the governing flow and sediment transport equations are solved in a curvilinear coordinate system the sediment transport model is composed of bed and suspended load applying a convection diffusion equation for the latter as the flow crosses a channel obliquely it is refracted toward the channel alignment the effect of the current refraction on the sediment transport is studied using both 2d depth averaged and 3d models shortcomings of models based on depth averaged descriptions are underlined through comparison with the 3d model a reliable description of the backfilling process requires a flow and sediment transport model capable of capturing the following aspects the direction and magnitude of the bed shear stress and the adaptation of suspended sediment to local sediment transport capacities calculations of the morphological development of small scale excavations such as pipeline trenches exposed to an oblique incoming current are presented

delta progradation in greenland driven by increasing glacial mass loss climate change has the potential to erode coastlines but a rediscovered archive of aerial photographs from the second world war shows that in southern greenland deltas have recently extended seaward climate change has the potential to erode coastlines for example as a result of increased wave activity but the net effect depends on the balance between creative and destructive forces mette bendixen and colleagues show that deltas in southwestern greenland have grown over the past few decades following a period of stability in the mid twentieth century the delta expansions occurred during periods of reduced sea ice and increased melt from the greenland ice sheet although many coastlines remain under threat these findings reveal the intimate interactions that arise in a warming climate a loss of ice seems to lead to increased sediment delivery which has resulted in the expansion rather than degradation of greenland s deltas climate changes are pronounced in arctic regions and increase the vulnerability of the arctic coastal zone1 for example increases in melting of the greenland ice sheet and reductions in sea ice and permafrost distribution are likely to alter coastal morphodynamics the deltas of greenland are largely unaffected by human activity but increased freshwater runoff and sediment fluxes may increase the size of the deltas whereas increased wave activity in ice free periods could reduce their size with the net impact being unclear until now here we show that southwestern greenland deltas were largely stable from the 1940s to 1980s but prograded that is sediment deposition extended the delta into the sea in a warming arctic from the 1980s to 2010s our results are based on the areal changes of 121 deltas since the 1940s assessed using newly discovered aerial photographs and remotely sensed imagery we find that delta progradation was driven by high freshwater runoff from the greenland ice sheet coinciding with periods of open water progradation was controlled by the local initial environmental conditions that is accumulated air temperatures above 0 c per year freshwater runoff and sea ice in the 1980s rather than by local changes in these conditions from the 1980s to 2010s at each delta this is in contrast to a dominantly eroding trend of arctic sedimentary coasts along the coastal plains of alaska2 siberia3 and western canada4 and to the spatially variable patterns of erosion and accretion along the large deltas of the main rivers in the arctic5 6 7 our results improve the understanding of arctic coastal evolution in a changing climate and reveal the impacts on coastal areas of increasing ice mass loss and the associated freshwater runoff and lengthening of open water periods

ocean wave conditions in the chukchi sea from satellite and in situ observations 1 in situ observation of significant wave heights swhs conducted from three fixed bottom mounted recording doppler current profiler rdcp instruments in the south eastern chukchi sea in 2007 and 2009 were compared with corresponding satellite observations from envisat a strong correlation 0 96 was indicated between satellite andin situobservations for the off shore rdcp located approximately 82 km to the nearest coastline in the region with uniform topography however the corresponding cross correlations are much lower 0 79 and 0 58 for the rdcps located within 3 5 km and 10 8 km respectively of the nearest coastline probably due to a strong spatial topography gradient and an insufficient number of satellite data points for validation cross validated satellite observations were used for the analysis of wave conditions in the arctic during the years 1993 2011 we found approximately a 0 020 m year increase of swh for the se chukchi sea and a 0 025 m year increase for the pacific arctic which correlates well with gradual ice retreat observed in the arctic during the last two decades

sea ice loss enhances wave action at the arctic coast 1 erosion rates of permafrost coasts along the beaufort sea accelerated over the past 50 years synchronously with arctic wide declines in sea ice extent suggesting a causal relationship between the two a fetch limited wave model driven by sea ice position and local wind data from northern alaska indicates that the exposure of permafrost bluffs to seawater increased by a factor of 2 5 during 1979 2009 the duration of the open water season expanded from 45 days to 95 days open water expanded more rapidly toward the fall 0 92 day yr 1 when sea surface temperatures are cooler than into the mid summer 0 71 days yr 1 time lapse imagery demonstrates the relatively efficient erosive action of a single storm in august sea surface temperatures have already decreased significantly by fall reducing the potential impact of thermal erosion due to fall season storm waves

temporal and spatial variability in coastline response to declining sea ice in northwest alaska abstract arctic sea ice is declining in extent leaving coastlines exposed to more storm wave events there is an urgent need to understand how these changes affect geomorphic processes along arctic coasts here we describe spatial and temporal patterns of shoreline changes along two geomorphologically distinct storm wave dominated reaches of the chukchi sea coastline over the last 64 years one study area encompasses the west to southwest facing coarse clastic shoreline and ice rich bluffs of cape krusenstern cakr the other covers the north facing sandy shorelines on barrier islands ice rich bluffs and the cape espenberg spit in the bering land bridge national park bela both study areas lie within the zone of continuous permafrost which exists both on and offshore and outcrops as ice rich bluffs along the bela coast we mapped changes in coastal geomorphology over three observation periods 1950 1980 1980 2003 and 2003 2014 using aerial and satellite imagery we then compared these geomorphic changes to changes in sea ice coverage which declined 10 days per decade between 1979 and 2016 in the southern chukchi sea changes in coastal geomorphology in both bela and cakr exhibited high spatial variability over the study period between 2003 and 2014 shorelines of barrier islands in bela exhibited the highest mean rates of change 1 5 m yr 1 while coarse clastic barrier beaches in cakr showed only minimal change overall shorelines in both bela and cakr became more dynamic increasing erosion or increasing accumulation after ca 2003 with spatial variability in shoreline changes roughly doubling between the first period of observation 1950 1980 and the last 2003 2014 this increase in coastal dynamism may signal a transitional period leading to new state of geomorphic equilibria along these ice affected coastlines

calculation of dune morphology 1 the shape and dimensions of dunes formed in an erodible bed and exposed to flowing water are investigated by using a numerical model the flow is calculated using a curvilinear flow model where we combine a k turbulence closure scheme with a sediment transport description and the equation of continuity for the sand bed the complete flow description allows for a discussion about what determines the length of dunes from the equation of continuity for sediment it turns out that the sediment transport over dunes is proportional to the local height of the dune this means that the maximum height of the sand wave occurs at the location of maximum sediment transport we relate the dune length to the location of maximum sediment transport it is demonstrated that the effect of streamline curvature is essential for determining the location of maximum sediment transport at low bed shear stresses due to an overshoot in bed shear stress for large dimensionless bed shear stresses the downstream decay of turbulence from the former dune is demonstrated to play a major role

sediment transport in oscillatory boundary layers in cases of rippled beds and sheet flow an experimental study was focused on the process of sediment transport in unsteady flow conditions due to wave action wave induced oscillatory flow conditions near the seabed were simulated at full scale 1 1 in a new large oscillating water tunnel two sets of experiments series a and b were carried out during series a bed forms and wave cycle averaged suspended sediment concentrations were measured under sinusoidal waves series b focused on measurement of the wave cycle averaged sediment transport rates under regular and random asymmetric oscillatory flows upper shoreface conditions and was aimed at the verification of quasi steady formulas for the description of cross shore sediment transport bedform dimensions appeared to decrease considerably under the influence of wave asymmetry and wave randomness only the measured ripple dimensions under asymmetric waves series b showed good agreement with nielsen s 1979 relations for most of the series b experiments the bed was plane sheet flow the net sediment transport was directed onshore and the measured transport rates showed a strong correlation with the velocity moment an empirical quasi steady transport model is proposed which is based on the new tunnel data and other existing data sets the limitations of the quasi steady model approach became clear in the rippled bed regime and through the presence of a consistent influence of the wave period in plane bed conditions in rippled bed conditions the suspended concentration profiles followed a negative exponential distribution for most of the experiments the measured concentration decay length showed a linear relation with the ripple height in plane bed sheet flow conditions the measured suspended concentration profiles followed a negative power function the power or concentration decay parameter was constant 2 1 for a wide range of velocity conditions it is suggested that the mobile bed sheet flow layer has a strong damping effect on the mixing of suspended sediments turbulence damping

reconstructing ice conditions in the southern chukchi sea during the last millennium based on chemical composition of sediments and diatom assemblages abstract using transfer functions this study reconstructed the ice free period ifp that occurred 4 7 kya in the southern chukchi sea based on the comparison between the observed data and the chemical composition of sediments accumulated during the observation period during the analysis a double normalization of the chemical element contenton rubidium and minimax was implemented for the first time it was established that the duration of the ifp varied between 90 and 140 days year the highest values are observed in the 21st century and 4 5 kya coinciding with pacific water inflow through the bering strait the reconstruction of water masses based on diatom thanatocoenosis has revealed the considerable impact of the alaskan coastal current on the duration of the ifp the penetration of its waters to the west during the following time periods 2750 2550 1450 800 350 0 cal yr bp led to an increase in the duration of the ifp in the central part of the sea by 10 15 days relative to background values as a result the identified variations in the duration of the ifp in the southern chukchi sea do not coincide with global climate events of the last millennium but are clearly demonstrated by an increase in the ifp during the little ice age currently the influence of the alaskan coastal water is summed up by the effect of increasing global temperatures and pacific water inflow which has led to a sharp increase in the ifp in the last few decades

facies analysis of yedoma thermokarst lakes on the northern seward peninsula alaska thermokarst lakes develop as a result of the thaw and collapse of ice rich permanently frozen ground permafrost of particular sedimentological importance are thermokarst lakes forming in late pleistocene icy silt yedoma which dramatically alter the land surface by lowering surface elevation and redistributing upland sediment into lower basins our study provides the first description of yedoma thermokarst lake sedimentology based on the cross basin sampling of an existing lake we present lake sediment facies descriptions based on data from sediment cores from two thermokarst lakes of medium depth claudi and jaeger informal names which formed in previously non thermokarst affected upland yedoma on the northern seward peninsula alaska we identify four prominent facies using sedimentological biogeochemical and macrofossil indicators a massive silt lacking aquatic macrofossils and other aquatic indicators situated below a sub lacustrine unconformity facies 1 two basal deposits interbedded organic silt and chaotic silt facies 2 3 and a silt rich mud facies 4 facies 1 is interpreted as yedoma that has thawed during lake formation facies 3 formed adjacent to the margin due to thaw and collapse events from the lake shore material from facies 3 was reworked by wave action to form facies 2 in a medium energy margin environment facies 4 formed in a lower energy environment toward the lake basin center this facies classification and description should enhance our ability i to interpret the spatial and temporal development of lakes and ii to reconstruct long term patterns of landscape change

extreme wave activity during 2013 2014 winter and morphological impacts along the atlantic coast of europe studies of coastal vulnerability due to climate change tend to focus on the consequences of sea level rise rather than the complex coastal responses resulting from changes to the extreme wave climate here we investigate the 2013 2014 winter wave conditions that severely impacted the atlantic coast of europe and demonstrate that this winter was the most energetic along most of the atlantic coast of europe since at least 1948 along exposed open coast sites extensive beach and dune erosion occurred due to offshore sediment transport more sheltered sites experienced less erosion and one of the sites even experienced accretion due to beach rotation induced by alongshore sediment transport storm wave conditions such as were encountered during the 2013 2014 winter have the potential to dramatically change the equilibrium state beach gradient coastal alignment and nearshore bar position of beaches along the atlantic coast of europe

heightened north pacific storminess during synchronous late holocene erosion of northwest alaska beach ridges a progradational regime of falling sea level and or high sediment input has produced extensive beach ridge plains in northwest alaska during the last 4000 yr eleven chukchi sea beach ridge complexes oriented at various angles to wind fetch provide a cumulative history of longshore transport and erosion archaeological and geological upper limiting radiocarbon ages n 59 allow correlations between depositional units on seven beach ridge complexes progradation started 4000 yr b p at nearly all complexes as eustatic sea level stabilized two disconformities or truncations are found on most of the complexes providing time parallel storm horizons dated at 3300 1700 and 1200 900 14c yr b p between 1700 and 1200 14c yr b p most of the complexes prograded indicating the predominance of less stormy conditions modern synoptic patterns that produce chukchi beach ridge erosion are linked to northerly shifts in north pacific storm tracks the regionwide beach ridge erosional truncations correlate with records of glacier expansion heightened precipitation evident in tree rings stream flooding and shelf deposits reworked by storm surges

morphology of the canadian beaufort sea coast a study of the canadian beaufort sea coast alaskan yukon border to baillie island was conducted to provide a regional summary of a coastal morphology b coastal stability and c coastal processes a total of 2077 km of coastline was mapped using aerial photographs low altitude and oblique aerial video imagery and information from previous field studies the coast can be adequately characterized by six repetitive coastal types four of which are erosional landforms and comprise 60 of the coast ice rich cliffs ice poor cliffs low tundra cliffs and inundated tundra two repetitive coastal types are accretional landforms and comprise 40 of the coast barrier islands and spits and deltas the deltas in the study area are retreating rapidly and therefore over 80 of the coast is considered erosional and less than 20 accretional over 1000 measurements of coastal stability indicate wide scale coastal retreat most sections of the coast show mean coastal retreat rates in excess of 1 m yr 1 despite very low annual wave exposure levels near active areas of the mackenzie river delta mean retreat rates are in excess of 2 m yr 1 and a maximum retreat rate of 18 m yr 1 was documented near shallow bay the presence of significant quantities of ice in the coastal sediments both in the form of pore ice and massive ice beds appears to be the primary cause of the wide scale regional retreat of the coast although a relative sea level rise in the region may also be important

fifty years of coastal erosion and retrogressive thaw slump activity on herschel island southern beaufort sea yukon territory canada abstract patterns of coastal erosion in the arctic differ dramatically from those coasts in more temperate environments thick sea ice and shore fast ice limit wave based erosional processes to a brief open water season however despite this permafrost coasts containing massive ice ice wedges and ice bonded sediments tend to experience high rates of erosion these high rates of erosion reflect the combined thermal mechanical processes of thawing permafrost melting ground ice and wave action climate change in the arctic is expected to result in increased rates of coastal erosion due to warming permafrost increasing active layer depths and thermokarst rising sea levels reduction in sea ice extent and duration and increasing storm impacts with the most ice rich permafrost in the canadian arctic the southern beaufort sea coast between the tuktoyaktuk peninsula and the alaskan border is subject to high rates of erosion and retrogressive thaw slump activity under many climate change scenarios this area is also predicted to experience the greatest warming in the canadian arctic this paper presents results of a remote sensing study on the long term patterns of coastal erosion and retrogressive thaw slump activity for herschel island in the northern yukon territory using orthorectified airphotos from 1952 and 1970 and an ikonos image from 2000 corrected with control points collected by kinematic differential global positioning system and processed using softcopy photogrammetric tools mean coastal retreat rates of 0 61 m yr and 0 45 m yr were calculated for the periods 1952 1970 and 1970 2000 respectively the highest coastal retreat rates are on north west facing shorelines which correspond to the main direction of storm related wave attack during the period 1970 2000 coastal retreat rates for south to south east facing shorelines displayed a distinct increase even though these are the most sheltered orientations however south to south east facing shorelines correspond to the orientations where the highest densities of retrogressive thaw slumps are observed differences in rates of headwall retreat of retrogressive thaw slumps and coastal erosion results in the formation of larger thermokarst scars and the development of polycyclic thaw slumps on south to south east exposures the number and the total area of retrogressive thaw slumps increased by 125 and 160 respectively between 1952 and 2000 as well the proportion of active retrogressive thaw slumps increased dramatically polycyclic retrogressive thaw slumps appear to develop in a periodic fashion related to retrogressive thaw slump stage and maximum inland extent

oblique flow over dredged channels i flow description a 3d investigation of flow across long straight channels aligned obliquely to the flow direction has been conducted the applied mathematical model solves the reynolds averaged navier stokes equat