analysis of directional wave fields using x band navigation radar the aim of this work is to present an approach to describe complex sea states including the ones consisting of superpositions of swell and wind sea components using a nautical radar in x band as a remote sensing technique in the present article the inversion method to obtain the spectral representation of the wave fields is described the method is applied to analyse data obtained from simulation techniques as well as from measurements obtained during oceanographic campaigns in the bay of biscay and north sea

meso scale transfer of sand during and after storms implications for prediction of shoreline movement abstract monitoring beach volume changes of the texas coast following a major hurricane reveals the impact of storms on sand dispersal and shoreline movement at spatial and temporal scales encompassing tens of kilometers and decades beach volume histories at profile sites show the interdependence of sand exchange among adjacent sites and the spatial autocorrelation of sand movement beach volume histories also indicate periods when either longshore or cross shore transport predominate and illustrate the long term effects of coastal structures on beach mobility this study confirms that net losses of sand from updrift barriers may not be directly linked with net gains of sand on adjacent downdrift barriers instead sand dispersal within a coastal compartment may depend partly on the dynamics of shoals and temporary sand storage at the intervening tidal inlet in our study sand eroded from the updrift barrier galveston island is deposited in a terminal sand flat of the barrier whereas sand accreted to the downdrift barrier follets island is derived from the intermediate ebb tidal delta san luis pass unlike continuous sand bypassing on some microtidal wave dominated coasts sand bypassing at san luis pass is episodic event driven and inefficient and sand is not transferred directly from one barrier to the next p because storms rapidly redistribute beach sediment they can be the most important factor controlling short term

morphological evolution of the dee estuary eastern irish sea uk a tidal asymmetry approach abstract asymmetry in the tide unequal ebb and flood duration is a dominant factor in causing residual sediment transport and morphological changes in estuaries the evolution of estuarine morphology is a process of dynamic equilibrium in the short term while these features are ephemeral in the long term in this study we investigate the spatial distribution of tidal distortion and asymmetry in the dee estuary uk by 3 dimensional numerical modelling methods high resolution lidar surveys are used to underpin and explain our numerical modelling results in terms of basin hypsometry and areas of recent erosion and deposition harmonic analysis of the numerical modelling results showed that the shallower intertidal areas sand and mud banks were the most tidally asymmetric showing flood dominance the main navigation channels showed some ebb dominance but the tides here were relatively undistorted this overall flood dominance is likely to induce net sediment import to the dee which explains known historical morphological changes large scale accretion over the last two centuries and also recent morphological changes as seen from the lidar surveys which show predominantly net accretion between 2003 and 2006 hypsometrical analysis suggests the dee may be approaching equilibrium and that the flood dominance and sedimentation rate may therefore decrease in the future in an infilling estuary an increase in the area and elevation of tidal flats can eventually shift an estuary towards ebb dominance as shown by previous research and by idealised estuary modelling results presented in this study the large tidal amplitude to hydraulic depth ratio of the dee however suggests that the tidal flats would have to be very extensive indeed for this to occur

intertidal beach profile estimation using video images abstract in this paper we present a technique suitable for measurement of intertidal bathymetry over a broad range of length scales 10 1 to 10 3 m and time scales days to decades a series of time averaged images of the swash zone are used to map contour lines of the beach surface in each image contours are identified using bands of maximum brightness associated with breaking waves at the shoreline by mapping the location of these bands in a sequence of images collected over one tidal cycle contour maps of the intertidal bathymetry are generated we expect this technique to work best smallest absolute error under waves which are nearly reflective at the shoreline but break enough to be observed visually this is typical of a barred beach since the wave height at the shoreline is limited by wave breaking over the bar crest the ability of the measurements made with this technique to resolve actual beach elevation variation depends on the ratio of the measurement error variance to the true beach elevation variance thus large measurement errors may be compensated by either large tidal ranges or large temporal changes of the beach itself in a comparison to bathymetry surveyed using a differential global positioning system dgps during the duck94 experiment in duck n c the image based elevation estimates were well correlated with the actual bathymetry the deviations imagebased vs dgps measurements may be partially attributed to effects scaled by wave height at the shoreline wave induced setup and wave height saturation over the sand bar in particular setup was important during dissipative conditions the rms deviation vertical between the dgps and image based bathymetry was reduced from 0 24 m to 0 06 m by correcting for the systematic deviations due to variations in setup and wave height saturation further improvement of the elevation estimates resulted from parameterizing the actual bathymetry with a simple plane beach surface which reduced random or unresolvable measurement errors this led to estimates of the beach slope that were accurate to within 10 of the actual slope and estimates of the cross shore location of the mean sea level line accurate to about 0 50 m

geological hazards in loess terrain with particular reference to the loess regions of china abstract the considerable morphodynamic energy provided by the continuing tectonic evolution of asia is expressed in high erosional potentials and very high rates of sediment production that make this continent unequalled as a terrestrial source of primary silt many of these environments are hazardous threatening human occupation health and livelihood especially in regions of dense population such as the loess lands of north china dry loess can sustain nearly vertical slopes being perennially under saturated however when locally saturated it disaggregates instantaneously such hydrocompaction is a key process in many slope failures made worse by an underlying mountainous terrain of low porosity rocks gully erosion of loess may yield very high sediment concentrations 60 by weight characteristic vertical jointing in loess influences the hydrology enlarged joints develop into natural sub surface piping systems which on collapse produce a loess karst terrain collapsible loess up to 20 m thick is common on the western loess plateau foundation collapse and cracked walls are common many rapid events following periods of unusually heavy monsoonal rain slope failure is a major engineering problem in thick loess terrain flow slide and spread types being common the results are often devastating in both urban and rural areas an associated hazard is the damming of streams by landslides the human population increases the landslide risk in china notably through imprudent land use practices including careless water management a number of environmentally related endemic diseases arise from the geochemistry of loess and its groundwaters including fluorosis cretinism kaschin beck disease keshan disease and goitre the chinese desert margins also have a major atmospheric dust problem the effect of such dust upon human health in these extensive regions including many large cities has yet to be evaluated but pneumoconiosis is thought to affect several million people in north and west china

new capabilities of the shoals airborne lidar bathymeter abstract the technology and methodology of airborne laser bathymetry are far from mature and new capabilities continue to be attained the shoals lidar system was recently augmented with the ability to utilize kinematic gps kgps with on the fly otf phase ambiguity resolution to permit the system to be used more extensively over land and for shoreline and other topographic mapping in addition to underwater bathymetry the seamless integration of these capabilities permits continuous surveying across the land water boundary importantly this also permits the production of sea bottom and topographic elevations without the need for concurrently measured water level data algorithms and procedures associated with the use of otf kgps are presented along with examples of performance

application of marine radar to monitoring seasonal and event based changes in intertidal morphology this paper demonstrates the application of marine radar and a newly developed waterline mapping technique to the continued surveillance and monitoring of inter and intra annual intertidal morphological change thus capturing new detail on coastal system behaviours marine radar data from 2006 to 2009 are used to create a sequence of waterline elevation surveys that show clear morphological evolution of two different sites in the dee estuary uk an estimate of volumetric change was made at two locations west hoyle sandbank and the nw wirral beach both sites exhibited a similar cyclic pattern of volumetric change with lowest volumes in autumn and winter respectively the average beach elevations above admiralty chart datum clearly reflect the observed change in sediment volume with reduced elevations in winter and increased elevations in summer suggesting a trend of high energy storm waves in autumn and winter that remove sediment and simultaneously moderate the vertical dimension of bedforms in the intertidal area data at this temporal and spatial scale are not easily obtainable by other current remote sensing techniques the use of marine radar as a tool for quantifying coastal change over seasonal and event timescales in complex hydrodynamic settings is illustrated specifically its unique application to monitoring areas with dynamic morphology or that is vulnerable to erosion and or degradation by storm events is exemplified

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

the loess of north central china geotechnical properties and their relation to slope stability abstract loess is an aeolian deposit consisting of predominantly silt sized quartz particles and containing variable amounts of clay sized minerals loess is generally classified as a water softening material because upon wetting the loess fabric rapidly weakens or collapses the strain hardening of malan loess and the brittle failure of lishi and wucheng loess are in strong contrast to the failure behaviour of these loess deposits in a remoulded state from tests carried out on samples with varying moisture contents using a modified bromhead ring shear apparatus it was found that the effective apparent cohesion gradually increases and the effective internal friction angle decreases with an increase in moisture content when the moisture content reaches a material specific threshold the effective cohesion decreases rapidly and the effective internal friction angle stabilises at a residual value the frequent failure of loess slopes in the western part of the chinese loess plateau is closely related to progressive weathering along zones in these slopes which causes a dramatic decrease in strength from the peak strength condition progressive weathering is common in the loess slopes in the western part of the chinese loess plateau during the process shear strength reduction along potential slip surfaces may be achieved by leaching of readily soluble salts destruction of cementation bonds and redistribution of particles localized collapse of the loess fabric causes internal deformation and consequently peak strength conditions are concentrated on a progressively smaller area of the failure plane therefore the mode of failure of loess slopes is generally determined by brittle failure of the undisturbed and unweathered central parts of the slopes it is important that both the weathered and unweathered strength of the loessmaterials in this area be established in order to analyze the stability of existing loessslopes many of which are steepand lie directly above domestic and industrial urban areas

measurement of recent intertidal sediment transport in morecambe bay using the waterline method abstract an illustration of how sediment transport may be measured over a large dynamic intertidal area at reasonable cost and spatiotemporal resolution using the waterline method employing remote sensing and hydrodynamic modelling is presented areas and volumes of accretion and erosion were measured in the study area of morecambe bay in north west england over the period 1992 97 tidal asymmetry is considered to be the dominant agent of sediment movement in the bay with waves being of secondary importance waterlines i e land sea boundaries were extracted from 31 synthetic aperture radar images of the bay covering a substantial fraction of the tidal range heights were attached to the waterlines using water elevations from nested hydrodynamic tide surge models interpolation in space and time was carried out to produce a continuous spatiotemporal height map of the intertidal zone height maps with a spatial resolution of about 50 m and height accuracy of about 40 cm were constructed over an area of about 350 km 2 strong temporal decorrelation in the bay limited the height accuracy achievable differences between height maps for 1992 94 and 1995 97 allowed sediment volume changes to be extracted the intertidal region showed a loss of 16 1 4 5 10 6 m 3 over the period almost all the change being due to a significant decrease between mean sea level and the low water mark changes were also measured in three of the main river estuaries within the bay the leven kent and lune these included movement of the leven north east by about 2 km cutting into cartmel wharf accretion seaward of grange over sands and changes in the low water channels at the mouth of the lune these changes could be used to validate sediment transport models of the bay

laboratory studies of radar sea spikes at low grazing angles we report on measurements of low grazing angle radar sea spikes in a laboratory wave tank using an x band radar with 10 cm range resolution and multiple range bin capability the sea spikes were observed to have a horizontal vertical polarization ratio much larger than unity this is similar to observations in earlier field experiments but is in contrast to a ratio of unity recently observed for moderate grazing angles jessup et al 1990 our experiment was designed to validate the low grazing field results and to establish design criteria for spatial temporal measurement instrumentation single point measurements currently used as surface truth cannot provide water surface profiles needed for modeling of radar scatter from deterministic surface features surface scattering features were generated using a paddle generated wave combined with wind waves for a series of wind speeds the surface feature responsible for the sea spike echo was visually identified as a short wave crest occurring on the windward side of the paddle wave driven to extreme steepness by the passage of the faster paddle wave crest long decorrelation times observed in the field are also seen in these studies of the order of 500 ms for horizontal polarization and less than 5 ms for vertical we suggest that rather than bragg scatter the occurrence of similar ubiquitous features on the ocean are responsible for horizontally polarized low grazing angle sea scatter at the x band for low to moderate winds and perhaps at other frequencies as well

observations of morphological change and sediment transport on a steep gravel beach abstract observations of morphological change and swash sediment loads concurrent with measurements of water level waves and currents were obtained during a spring to spring tidal cycle on a steep macrotidal gravel beach in southwest england the wave conditions experienced during the field experiment were relatively calm and the significant inshore wave height and period averaged 0 4 m and 6 s respectively incident frequency water motions dominated the hydrodynamics and the phasing between water surface elevation and cross shore and alongshore currents was inconsistent with standing edge wave motion morphological change was directly related to maxima in shoreline elevation and four modes of berm adjustment identified regression and rollover in response to falling and rising water levels respectively and removal and reformation during and after storms respectively swash processes transported substantial amounts of sediment at rates comparable to sand beaches and the net transport under modal wave conditions was estimated to be 1 kg per swash onshore per unit metre beach width steep hydrodynamic gradients induced by the abrupt slope breaks of the step and berm are one of the main causes of the large morphological variability characteristic of gravel beaches

nearshore subtidal bathymetry from time exposure video images time averaged over many wave periods nearshore video observations show the process of wave breaking as one or more white alongshore bands of high intensity across a known depth profile similar bands of dissipation can be predicted with a model describing the time averaged cross shore evolution of organized wave and roller energy this close correspondence between observed and modeled dissipation proxies is used to develop a new remote sensing technique termed subtidal beach mapper sbm to estimate nearshore bathymetry sbm operates on a time series of cross shore intensity profiles to resolve the pattern in depth change on a morphological timescale including overall gain or loss of sediment rather than to focus on the particular change induced by a single intensity profile from each intensity profile the breaking induced component is isolated by removing the contribution of background illumination and persistent foam the depth profile is updated based on a comparison between this video derived dissipation proxy and a cross shore profile of the dissipation of the roller energy this updating is implemented through time dependent mass balance equations for the seabed and a buffer layer above the bed sbm was tested using 1 year of hourly video data collected at egmond aan zee netherlands the dominant morphological changes observed from ground truth data were reproduced reasonably well including the shoreward migration of the outer bar and the net sediment gain in the profile root mean square differences between surveyed and sbm derived depth after 1 year of video based depth updating with an average of about 70 intensity profiles per month were smallest 0 2 m on the inner bar and largest 0 6 m in the outer bar trough with a profile average value of about 0 4 m despite the many processes included in sbm the implementation of a heuristic scaling function in the mass balance equations to spatially adjust morphological growth rates was essential to these results in particular near the shoreline where otherwise the profile is prone to an unrealistic deepening

a video based technique for mapping intertidal beach bathymetry abstract measuring the location of the shoreline and monitoring foreshore changes through time are core tasks carried out by coastal engineers for a wide range of research monitoring and design applications with the advent of digital imaging technology shore based video systems provide continuous and automated data collection encompassing a much greater range of time and spatial scales than were previously possible using field survey methods a new video based technique is presented that utilises full colour image information which overcomes problems associated with previous grey scale methods which work well at steep reflective sites but are less successful at flatter dissipative sites identification of the shoreline feature is achieved by the automated clustering of sub aqueous and sub aerial pixels in hue saturation value hsv colour space and applying an objective discriminator function to define their boundary i e shoreline within a time series of consecutive geo referenced images the elevation corresponding to the detected shoreline features is calculated on the basis of concurrent tide and wave information which is incorporated in a model that combines the effects of wave set up and swash at both incident and infragravity frequencies validation of the technique is achieved by comparison with dgps survey results to assess the accuracy of the detection and elevation methods both separately and together the uncertainties associated with the two sub components of the model tend to compensate for each other the mean difference between image based and surveyed shoreline elevations was less than 15 cm along 85 of the 2 km study region which corresponded to an horizontal offset of 6 m the application of the intertidal bathymetry mapping technique in support of czm objectives is briefly illustrated at two sites in the netherlands and australia

shallow water bathymetry derived from an analysis of x band marine radar images of waves image sequences of surface gravity waves are readily produced by standard marine x band radars these image sequences contain a great deal of information regarding wave parameters and their variation over an area by approaching the analysis of such data using image analysis techniques it is possible to map the variations in wave behaviour in a shallow water area wave celerity and direction can be mapped and inversion algorithms based on linear wave theory used to infer the underlying bathymetry knowledge of the period of the waves is necessary for the analysis and this can also be calculated from the radar data although there is some discrepancy between the figures derived from radar data and from an offshore s4dw instrument these discrepancies are investigated and the results presented three days of data from the holderness ii deployment during 1995 have been analysed and estimates of the bathymetry produced the calculated depths show a mean water level comparable to that read off an admiralty chart for the area and a tidal signal is also clearly superimposed on the data giving confidence in the water depths derived using this technique

extracting the intertidal extent and topography of the australian coastline from a 28 year time series of landsat observations abstract the physical environment of the intertidal zone presents a number of challenges which make traditional surveying methods difficult to implement whilst the acquisition cost of airborne elevation data can be prohibitive beyond localised applications remote sensing data from earth observation satellites has been well established as a method for mapping the extent and elevation profile of the intertidal zone however the majority of these applications are local in nature and based on analysis of a limited number of individual image observations in this paper we outline an automated methodology to model the intertidal extent and topography of the australian coastline that leverages a full time series of landsat observations from 1987 to 2015 managed in the australian geoscience data cube agdc our approach reframes the analysis from time of acquisition into the tidal domain through the use of a continental scale tidal model combined with a median pixel compositing of normalised difference water index ndwi stacks to robustly estimate the tidal extent and elevation profile across the observed tidal range we demonstrate the ability of a median based compositing approach to deal effectively with data quality modelling outliers and other issues that commonly affect single scene methodologies our new framework enables us to produce a continental scale intertidal model detailing intertidal zone topography at a 25 m spatial scale we then demonstrate the potential of the modelling framework to derive digital elevation data based on tidal model attribution validating our models against in situ gps observations before discussing issues that must be addressed to move this capability to a continental scale the ability of the model to examine coastal stability is introduced in the context of the conceptual reframing of the data into the tidal domain with a view to furthering this application in future versions of the model

morphodynamic modelling of intertidal sediment transport in morecambe bay abstract the construction of a morphodynamic model for the intertidal region of morecambe bay england and its calibration and validation using extensive sediment volume change data measured by remote sensing is described a properly validated sediment transport model of the bay would be of interest for coastal defence management and economic purposes the morphodynamic model consisted of a set of linked modules for predicting 2d depth averaged tidal currents waves sediment transport rates and sediment budgets the intertidal bathymetry was updated at regular intervals and the currents waves and sediment transport patterns recomputed using the new bathymetry tidal input filtering using representative spring and neap tidal cycles was used to reduce computational requirements sediment volume changes during the period 1992 1997 were measured over the intertidal zone at a resolution of 240 m using the waterline method employing remote sensing and hydrodynamic modelling the total volume of sediment eroded was 102 16 106 m3 and the total volume accreted was 107 15 106 m3 tidal asymmetry is shown to be the dominant agent of sediment transport in the intertidal zone with waves being of secondary importance a close correlation was found between the computed directions of tidal asymmetry and observed sediment transport paths it was necessary to use the remotely sensed data for calibration of the sediment transport model as well as for validation the model showed some limited capability for predicting gross changes in bathymetry but there were substantial differences between the predicted and observed patterns of sediment movement the possibility of improvement by a further incorporation of the spatially and temporally extensive field data into the modelling process is discussed

environmental geology in loess areas of china there are several unfavorable geological hazards in the loess area of china the major purposes of environmental geology studies in this region are to expound the causes of these hazards and to determine treatments geological hazards include endemic diseases depletion of groundwater land subsidence ground fissures soil erosion and collapsibility of loess this article is a summary of studies regarding these hazards keshan disease and kaschin beck disease for example can be prevented and cured by adding selenates to table salt ponds can be constructed on the loess plateau and dikes around farmlands to collect rainfall to recharge groundwater resources excess extraction of groundwater is the major cause of land subsidence ground fissures in xi an are primarily caused by tectonics but over extraction of ground water strengthens its activity observation stations should be established in order to forecast and prevent landslides planting trees in a regional shelterbelt is the primary measure necessary to prevent soil erosion as a result of these geological studies valuable experience in preventing collapse of loess in china has been gained

a temporal waterline approach to mapping intertidal areas using x band marine radar abstract mapping the morphology of intertidal areas is a logistically challenging time consuming and expensive task due to their large expanse and difficulties associated with access a technique is presented here that uses standard marine navigational radar operating at x band frequency the method uses a series of time exposure radar images over the course of a two week tidal cycle to identify the elevation of the wetting and drying transitions at each pixel in the radar images thereby building up a morphological map of the target intertidal area this temporal waterline method is applied to a dataset acquired from hilbre island at the mouth of the dee estuary uk spanning march 2006 to january 2007 the radar gathered data with a radial range of 4 km and the resulting elevation maps describe the intertidal regions of that area the results are compared with airborne lidar data surveyed over the same area and within the radar survey time period the residual differences show good agreement across large areas of beach and sandbanks with concentrations of poor estimations around points that are shadowed from the radar or likely to suffer from pooling water this paper presents the theoretical framework of the method and demonstrates its stability and accuracy the temporal waterline radar method is aimed at providing a useful tool for the monitoring and operational management of coastlines

an optimal waterline approach for studying tidal flat morphological changes using remote sensing data a case of the northern coast of vietnam abstract tidal flats on the north coast of vietnam suffer diurnal tide with a tide range varying between 0 3 m and 3 5 m along the 350 km long coastline the diversity of environmental conditions induces various tidal flats with different characteristics this study applies the waterline method for multi temporal satellite images to build digital elevation models dems of tidal flats during the last 25 years 117 landsat images acquired with tm etm and oli have been processed to construct tidal flat dems in 1989 2000 and 2014 waterlines extracted from single spectral bands near infrared nir short wave infrared swir or band ratios normalized difference water index ndwi normalized difference vegetation index ndvi green swir of the landsat data have been compared with waterlines digitalized on spot aster and worldview 2 images this experiment allows us to determine the best band or band ratio for extracting waterlines depending on local conditions consequently the study shows that the green swir ratio image is a good solution for extracting waterlines in the black coal tidal flats of cam pha however the ndwi index appears to be a better choice for the other parts of the study area the vertical accuracy of the tidal flat dems reaches 0 144 m the change analysis of the dems also emphasizes the tidal flat evolution in both vertical and horizontal dimensions i e erosion or accretion the erosion of the tidal flats along the northern coast of vietnam is particularly developed in the area extending from yen hung to mong cai especially in mong cai with an amount of about 50 106 m3 of sediments lost between 1989 and 2014 on the contrary the tidal flats in the south of the study area show a high rate of deposition due to the sediments fed by red and thai binh rivers about 35 106 m3 of sediments deposited in the tidal flat surrounding the red river mouth between 1989 and 2014 this study represents a development of the waterline extraction method to investigate the evolution of tidal flat at a large scale and a diversified coastal environment using optical satellite images and fieldwork

in situ measurements of erosion shear stress and geotechnical shear strength of the intertidal sediments of the experimental managed realignment scheme at tollesbury essex uk abstract managed realignment is one of several soft engineering options which may reduce the costs of coastal defence provide a more natural response to the problem of rising sea levels and at the same time deliver environmental specifically nature conservation benefits the success of this technique depends on the ability of the soils and sediments within the site to resist the erosive action of waves and tidal currents and allow sediment accretion to occur at least at a rate equal to mean sea level rise once a critical shear stress 0 crt exerted by the moving fluids over the bed is exceeded erosion will occur a cohesive strength meter csm and the fall cone method were used to gather data in situ on the strength and stability of sediments from an experimental managed realignment site and an adjacent established saltmarsh in south east england following six years of regular tidal cover the underlying agricultural soil appeared both very strong mean surface shear strength f 228 kpa and highly resistant to erosion 0 crt 6 23 n m 2 during this period much of the site had been covered by sediment and saltmarsh plants salicornia europaea had become established above the mean high water neap tide mhwn level above mhwn level tidal cover time f 11 6 kpa and resistance to erosion 0 crt 2 45 n m 2 below mhwn where sediment accretion rates were greatest poor consolidation resulted in very high water contents and low bulk densities these areas were at the highest potential risk of erosion 0 crt 1 5 n m 2 and had very low shear strengths f 0 33 kpa where sediment exceeded 25 cm depth gullies formed allowing their banks and adjacent margins to drain faster than the surrounding sediment this led to a significant increase in bed strength f 10 8 kpa and stability 0 crt 4 3 n m 2 these gullies were probably the early stages of the complex creek patterns characteristic of the adjacent established saltmarsh the established saltmarsh was rich in plants and had a well developed aggregated soil structure these soils had a moderate to high resistance to erosion 0 crt 2 45 n m 2 and shear strength f 25 6 kpa undrained sediment shear strength f obtained with the fall cone apparatus can also provide a useful indication of critical erosion shear stress 0 crt values of 0 crt measured across this site were all relatively large compared with computed bed stresses arising from locally generated waves thus this experimental managed realignment site was found to be primarily depositional and was thus successfully achieving the twin aims of protecting the coast from erosion and extending a rich ecosystem

hindcasting coastal sea levels in morecambe bay a method of variational data assimilation by means of an adjoint model is used to improve the boundary conditions for a high resolution depth averaged two dimensional non linear hydrodynamic model of morecambe bay the modelled region contains a large inter tidal area and has an unusually high tidal range the assimilation procedure is robust and effective in reducing model error this system performs considerably better than the previous simple method used for assimilating data into the same numerical model height errors as low as 10 cm root mean square can be achieved

coastal monitoring solutions of the geomorphological response of beach dune systems using multi temporal lidar datasets vendee coast france abstract three beach and dune systems located in the northeastern part of the bay of biscay in france were monitored over 5 years with a time series of three airborne lidar datasets the three study sites illustrate a variety of morphological beach types found in this region reproducible monitoring solutions adapted to basic and complex beach and dune morphologies using lidar time series were investigated over two periods bounded by the three surveys the first period between may 2008 and august 2010 is characterized by a higher prevalence of storm events and thus has a greater potential for eroding the coast than the second period between august 2010 and september 2013 during the first period the central and northeastern part of the bay of biscay was notably impacted by storm xynthia with water levels and wave heights exceeding the 10 year return period and 1 year return period respectively despite differences in dune morphology between the sites the dune crest dhigh and the dune base dlow are efficiently extracted from each dem based on the extracted dune base an original shoreline mobility indicator is built displaying a combination of the horizontal and vertical migrations of this geomorphic indicator between two lidar datasets a geomorphic change detection is also completed by computing dems of difference dod resulting in segregated maps of erosion and deposition and sediment budgets accounting for the accuracy of lidar datasets a probabilistic approach at a 95 confidence interval is used as a threshold for the geomorphic change detection showing more reliable results however caution should be taken when interpreting thresholded maps of changes and sediment budgets because some beach processes may be masked especially on wide tidal beaches by only keeping the most significant changes the results of the shoreline mobility and geomorphic change detection show a high variability in the beach responses between and within the three study sites explained mainly by beach orientation and local factors despite variable site specific mechanisms the recovery processes redistribute the available sand more on the upper parts of the beach producing significant deposition generally in the form of embryo dunes the monitoring of the beach and dune systems with airborne lidar datasets reveals that the three study sites show diverse behaviours during the first period likely associated with storms while the analysis show more homogenous beach responses during the second period likely associated with a recovery phase

between the tides modelling the elevation of australia s exposed intertidal zone at continental scale abstract the intertidal zone represents a critical transition between marine and terrestrial ecosystems supporting a complex mosaic of highly productive and biologically diverse habitats however our understanding of these important coastal environments is limited by a lack of spatially consistent topographic data which can be extremely challenging and costly to obtain at continental scale satellite remote sensing represents an important resource for monitoring extensive coastal zones previous approaches to modelling the elevation of the intertidal zone using earth observation eo data have been restricted to small study regions or have relied on manual image interpretation thus limiting their ability to be applied consistently over large geographic extents in this study we present an automated open source approach to generate satellite derived elevation data for over 15 387 km2 of intertidal terrain across the entire australian coastline our approach combines global tidal modelling with a 30 year time series archive of spatially and spectrally calibrated landsat satellite data managed within the digital earth australia dea platform the resulting national intertidal digital elevation model nidem dataset provides an unprecedented three dimensional representation of australia s vast exposed intertidal zone at 25 m spatial resolution we validate our model against lidar rtk gps and multibeam bathymetry datasets finding that modelled elevations are highly accurate across sandy beach 0 41 m rmse and tidal flat environments 0 39 m rmse model performance was least accurate 2 98 m rmse within rocky shores and reefs and other complex coastal environments with extreme and variable tidal regimes we discuss key challenges associated with modelling intertidal elevation including tidal model performance and biased observations from sun synchronous satellites and suggest future directions to improve the accuracy and utility of continental scale intertidal elevation modelling our model can be applied to tidally influenced coastal environments globally addressing a key gap between the availability of sub tidal bathymetry and terrestrial elevation data

detecting the intertidal morphologic change using satellite data abstract the objectives of this study were a to generate an intertidal digital elevation model dem using waterlines extracted from landsat tm and in situ ground levelling data b to quantitatively estimate morphologic change from the generated dems for the years 1991 and 2000 and c to evaluate the chenier migration in the tidal flats of gomso bay korea on extracting the waterlines we considered the tidal flat environments such as tidal conditions remnant surface water suspended sediment and exposure time ground levelling was carried out along one line in 1991 and two lines in 2000 from the extracted waterlines and ground levelling data we succeeded in generating intertidal dems with an accuracy of 10 9 cm r m s overall and 7 3 cm r m s in the lower tidal flats the morphologic changes estimated by subtracting the two dems showed an erosion rate of 9 0 cm over 9 yr that corresponds to an annual mean morphologic change budget of 309 865 m 3 yr overall the gomso tidal flats can be defined as an erosion dominant environment the changes with respect to the sedimentary facies were also evaluated as a the sandy silt flat had a sedimentation rate of 3 4 cm over 9 yr that corresponds to an annual mean budget of 52 552 m 3 yr b the silty sand flat had a sedimentation rate of 14 3 cm over 9 yr that corresponds to a mean erosion of 197 927 m 3 yr and c the sand flat had a sedimentation rate of 11 8 cm over 9 yr that corresponds to a mean change of 58 808 m 3 yr the results comply with the general rules of sedimentology we also investigated the chenier migration which is the most dynamic geomorphologic change in the tidal flats chenier is usually composed by sand and shell as a result of coastal progradation in sand and it is dominantly fed by sediments transported by long shore currents the chenier was found to have migrated about 148 m landward over 6 yr the results demonstrate that satellite remote sensing is an efficient and effective tool for a long term morphologic change estimation in tidal flats

determination of bathymetric and current maps by the method disc based on the analysis of nautical x band radar image sequences of the sea surface november 2007 morphodynamic processes in coastal areas are affected by tidal currents and sea state the continuous observation of near coastal areas is important in order to monitor dangerous current regime and bathymetry changes therefore there is an urgent need for remote sensing techniques delivering the important hydrographic parameters with a high spatial resolution dispersive surface classificator disc is a newly developed method based on the analysis of nautical x band radar image sequences of sea surface waves to determine spatial maps of hydrographic parameters e g spatial maps of the bathymetry and the ocean current field the method disc is described and is illustrated by the presentation of results based on a dataset acquired with a ground based x band radar installation mounted on the island of sylt in the german bight the calculated bathymetric maps are verified by multibeam echo sounder observations

construction of an inter tidal digital elevation model by the water line method progress in the development of a method for constructing a digital elevation model dem of an inter tidal zone using remote sensing and hydrodynamic modelling is described the method allows the construction of an inter tidal dem over large areas relatively quickly as well as frequent subsequent monitoring of the dem to detect changes and is particularly suited to sar satellite data because of the all weather day night capability of sar the resulting dem may be used for the development of improved hydrodynamic models and for studying sediment mass transport in the inter tidal zone

high resolution bathymetry estimates via x band marine radar 1 beaches abstract in this paired study we apply a recently developed high resolution bathymetry estimation algorithm cbathy to x band marine radar observations at two nearshore field sites the algorithm exploits observations of the spatial structure of wave phase to attain wavenumber estimates inverts the linear water wave dispersion relation for depth and then applies a kalman filter to objectively update the bathymetry estimates previously performance has only been tested using optical video observations in this first of two papers performance of the algorithm using x band radar image time series is tested at two disparate barred beach environments duck nc usa and benson beach wa usa each of the test beaches is either co located with duck nc or geographically close to benson beach wa those utilized in the original algorithm verification concurrent echosounder surveys are used as ground truth the bulk performance of the radar derived bathymetry estimate at duck nc achieves 0 49 m root mean square error rmse with 0 26 m bias deep this compares well with the bulk performance of the concurrent estimate derived using optical video 0 44 m rmse and 0 23 m bias deep the radar derived bathymetry estimate performance at benson beach is similar 0 35 m rmse and 0 11 m bias shallow and is comparable to that of an optical video derived estimate at a similar pacific northwest beach 0 56 m rmse and 0 41 m bias shallow at both beaches significantly higher performance is achieved at locations deeper than 2 m offshore of the surfzone than at locations shallower than 2 m surfzone where errors are often a large fraction of the total depth lastly several weeks of observations are utilized to assess the sensitivity of algorithm quality control to environmental conditions thresholds based on the shoreward component of wind stress and offshore wave steepness are identified and shown to impact the areal coverage of radar derived bathymetric estimates overall these results demonstrate the viability of marine radar observations as input to the cbathy algorithm and delineate some environmental constraints on algorithm performance in the companion paper the algorithm is extended to areas where tidal currents are important including an ebb tidal shoal and an estuary mouth

waterline extraction from landsat tm data in a tidal flat a case study in gomso bay korea waterline extraction is potentially one of the most effective satellite remote sensing tools for studying changes in tidal flat environment and coastlines however its application to the study of tidal flats has not been investigated in detail the waterline in a tidal flat in gomso bay korea is characterized and evaluated using 27 sets of landsat thematic mapper tm and earth observing system terra eos terra advanced spaceborne thermal emission and radiometer aster data ground truth data including grain size soil moisture content ground levelling and waterline tracking have been obtained the choice of spectral bands in terms of tidal conditions turned out to play a key role in locating the waterline while the waterlines extracted from near infrared nir short wavelength infrared swir and thermal infrared tir data are commonly reliable on the flood tide the discrepancies between different bands become large on the ebb tide the bands tir nir and swir are in that order decreasingly effective in extracting the waterline while ebb tides are in progress the effect of turbid water on nir can be reduced by a ratioing of nir and the visible band the location of the waterline is also an important factor to consider the discrepancy is largest on the middle tidal flat selection of the proper band for waterline extraction under various conditions is suggested however no single band can accommodate all aspects of the tidal flat environment a schematic model associated with the spectral reflectance of the tidal flat is proposed in which the remnant water scattered on the surface after exposure is emphasized as an additional factor

engineering properties and zoning of loess and loess like soils in china the widely distributed loessic soils of china are described concentrating on the collapsible soils of the upper strata of the loessic series a general trend of gradual steady reduction in the tendency to collapse on wetting is found going in the direction from northwest to southeast cases of damage and flooding tests of pits are cited for illustration results of electron microscope studies of structural features of loess specimens from different locations are compared with the engineering behavior especially the susceptibility to self subsidence and degree of collapsibility in view of this trend and the differences between loessic soils of different regions a preliminary zoning of the loessic soils was made resulting in seven zones as shown on a schematic map

automated mapping of the intertidal beach bathymetry from video images this paper presents a fully automated procedure to derive the intertidal beach bathymetry on a daily basis from video images of low sloping beaches that are characterised by the intermittent emergence of intertidal bars bathymetry data are obtained by automated and repeated mapping of shorelines from video time exposure images for different tidal water levels aarninkhof s g j turner i l dronkers t d t caljouw m nipius l 2003 a video based technique for mapping intertidal beach bathymetry coastal engineering 49 275 289 plant n g and holman r a 1997 intertidal beach profile estimation using video images marine geology 140 1 24 the developed procedure handles intelligent selection of a shoreline search area and unsupervised quality control of the obtained bathymetry data the automatically retrieved beach bathymetries compare very well to bathymetries derived from the original manual mapping procedure and to ground truth data points dgps

topographic mapping of the german tidal flats analyzing sar images with the waterline method the waterline method is used to derive the topography of the tidal flats along the german coast by evaluation of synthetic aperture radar sar images a series of about 70 european remote sensing satellites sar images of the german bight taken at different water levels within four years is analyzed to detect the borderline between tidal flats and adjacent water areas using a wavelet based edge detection algorithm after geocoding the waterlines are combined with the corresponding water levels to represent the topography on an irregularly spaced grid the water levels are taken from a numerical tide model and corrected with the measured gauge data interpolation of these data into a regular grid yields a topographic map of the intertidal zone while the general practicability of this method has been demonstrated in previous studies for smaller test areas this paper is the first attempt to generate maps of a large area on a yearly basis