valley scale morphology drives differences in fluvial sediment budgets and incision rates during contrasting flow regimes abstract high resolution topographic surveys using lidar and multibeam sonar can be used to characterize and quantify fluvial change this study used repeat surveys to explore how topographic change fluvial processes sediment budgets and aggradation and incision rates vary across spatial scales and across two contrasting decadal flow regimes in a regulated gravel cobble river a novel method for quantifying digital elevation model uncertainty was developed and applied to a topographic change detection analysis from 2006 2008 to 2014 during this period which had four modest 3 5 year floods most sediment was laterally redistributed through bank erosion and channel migration erosion primarily occurred in the floodplain 97 000 m 3 terraces 80 000 m 3 and lateral bars 58 000 m 3 while deposition occurred in the adjacent pools 73 000 m 3 fast glides 48 000 m 3 and runs 36 000 m 3 in contrast significantly higher magnitude and longer duration floods from 1999 to 2006 2008 caused sediment to be displaced longitudinally with the upstream reaches exporting sediment and the downstream reaches aggrading the river maintained floodplain connectivity during both periods despite different processes dominating the type of connectivity larger floods promoted overbank scour and avulsion while smaller floods promoted bank erosion and lateral migration this study explores and illustrates how the geomorphic response to contrasting flood regimes in a nonuniform river is highly dependent on which landforms are controlling hydraulics

reenvisioning velocity reversal as a diversity of hydraulic patch behaviours past research investigated the surpassing of mean velocity at riffle cross sections by that at pool cross sections for flows up to bankfull termed velocity reversals to understand one mechanism by which riffle pool relief is maintained this study reenvisioned the classic velocity reversal by documenting stage dependent changes to the locations of peak velocity without cross sections instead the dynamics of peak velocity patches were considered for flows spanning 0 2 to 22 times bankfull discharge through the use of a high resolution dem and two dimensional hydrodynamic modelling a remarkable diversity in peak velocity patch behaviour was found across discharges including gradual expansion and shifting as well as abrupt disappearance and emergence relative to the low flow patch locations these behaviours blended together to varying degrees to produce many reversals in peak velocity across morphological units but it took substantially higher than bankfull discharge for peak velocities to move from riffles and chutes to fast glides and pools the discharges at which reversals occurred among morphological units were significantly higher for the valley confined reach than for the anastomosing reach copyright 2016 john wiley sons ltd

storm induced response of a nearshore bar system abstract a nearshore bar system was surveyed periodically through a storm and the following recovery period the data showed a very rapid response of morphology to changing wave conditions and allowed various models on bar formation to be tested under low energy conditions prior to the storm a small bar was surveyed 13 m offshore both the high reflectivity of the beach and the cross shore distance to the bar are consistent with a model of sediment convergence at the node or antinode of a standing wave of incident period such a small scale bar may be a common feature on beaches with steep foreshores and more gentle offshore slopes with the increase in wave height during the storm the bar became better developed and migrated offshore at rates up to 2 2 m h 1 the bar maintained its form in that the ratio of trough depth to crest depth h t h c remained roughly constant the bar was in no way related to processes which would cause the convergence of sediment in the breaker zone through most of the storm the bar crest distance offshore was typically only 10 of the surf zone width analysis of the bar distance offshore in terms of a standing wave motion showed that the causative wave period must have been much longer than that of incident waves probably on the order of a minute surf zone wave data showed significant energy in the infragravity band at these periods although no definite link has been made after the height of the storm the bar had a crescentic morphology the development of this morphology occurred very rapidly with parts of the bar migrating onshore at rates up to 1 2 m h 1 in contrast to the storm during the recovery period h t h c varied by nearly a factor of three analysis of the offshore and longshore length scales showed the bar to be similar to one which would be generated by a standing mode 1 edge wave of period on the order of one minute

reconstructing depositional processes and history from reservoir stratigraphy englebright lake yuba river northern california 1 reservoirs provide the opportunity to link watershed history with its stratigraphic record we analyze sediment cores from a northern california reservoir in the context of hydrologic history watershed management and depositional processes observations of recent depositional patterns sediment transport calculations and 137cs geochronology support a conceptual model in which the reservoir delta progrades during floods of short duration days and is modified during prolonged weeks to months drawdowns that rework topset beds and transport sand from topsets to foresets sediment coarser than 0 25 0 5 mm deposits in foresets and topsets and finer material falls out of suspension as bottomset beds simple hydraulic calculations indicate that fine sand 0 063 0 5 mm is transported into the distal bottomset area only during floods the overall stratigraphy suggests that two phases of delta building occurred in the reservoir the first from dam construction in 1940 to 1970 was heavily influenced by annual prolonged 20 m drawdowns of the water level the second built on top of the first reflects sedimentation from 1970 to 2002 when the influence of drawdowns was less sedimentation rates in the central part of the reservoir have declined 25 since 1970 likely reflecting a combination of fewer large floods changes in watershed management and winnowing of stored hydraulic mining sediment

sediment from hydraulic mining detained by englebright and small dams in the yuba basin recent initiatives to find ways to reintroduce anadromous fish to the central valley of california have identified the yuba river as one of the best potential watersheds for expanding spawning habitat of spring run chinook salmon and steelhead trout salmon spawning in the yuba river would require substantial modifications or removal of englebright dam a large dam 86 million m 3 capacity built by the u s army corps of engineers in 1941 an extensive on going feasibility study by local state and federal organizations therefore is examining aspects of various dam treatment scenarios that range from no action to complete dam removal this paper examines the extraordinary history of the watershed and resulting conditions pertinent to the feasibility of altering englebright dam it seeks to accomplish four goals first historical geomorphic changes in the watershed are outlined that influence the physical context of the feasibility study the yuba watershed is centered in the hydraulic gold mining region made

measuring floodplain spatial patterns using continuous surface metrics at multiple scales abstract interactions between fluvial processes and floodplain ecosystems occur upon a floodplain surface that is often physically complex spatial patterns in floodplain topography have only recently been quantified over multiple scales and discrepancies exist in how floodplain surfaces are perceived to be spatially organised we measured spatial patterns in floodplain topography for pool 9 of the upper mississippi river usa using moving window analyses of eight surface metrics applied to a 1 1 m 2 dem over multiple scales the metrics used were range sd skewness kurtosis cv sd curv rugosity and vol area and window sizes ranged from 10 to 1000 m in radius surface metric values were highly variable across the floodplain and revealed a high degree of spatial organisation in floodplain topography moran s i correlograms fit to the landscape of each metric at each window size revealed that patchiness existed at nearly all window sizes but the strength and scale of patchiness changed within window size suggesting that multiple scales of patchiness and patch structure exist in the topography of this floodplain scale thresholds in the spatial patterns were observed particularly between the 50 and 100 m window sizes for all surface metrics and between the 500 and 750 m window sizes for most metrics these threshold scales are 15 20 and 150 of the main channel width 1 2 and 10 15 of the floodplain width respectively these thresholds may be related to structuring processes operating across distinct scale ranges by coupling surface metrics multi scale analyses and correlograms quantifying floodplain topographic complexity is possible in ways that should assist in clarifying how floodplain ecosystems are structured

beach ridges and prograded beach deposits as palaeoenvironment records abstract beach ridges are landforms commonly developed on prograded coasts with beach shorelines a sequence of beach ridges coupled with their subsurface deposits can be regarded as a time series of coastal evolution methodological advances in field surveying and chronology applicable to beach ridges have led to detailed palaeoenvironmental reconstructions to be derived from such sequences this paper reconsiders the basic aspects of beach ridges and deposits which need to be properly understood for their comprehensive interpretation in a palaeo environmental context it also reviews case studies in which beach ridge sequences have been used to unveil past sea level history catastrophic events and climate changes proposed formative processes of beach ridges include 1 progradation of sandy beach and berm formations in relation to fairweather waves coupled with aeolian foredune accumulation 2 building of gravel ridges by storm waves 3 welding of longshore bars beach ridge formation through sea level oscillation is thought to be questionable and caution is suggested for this process when undertaking palaeoenvironmental reconstruction beach deposit stratification is known to dip either landwards or seawards but landward dips are uncommon seaward dipping stratification is formed in relation to beachface progradation and is usually dissected in places by erosion surfaces resulting from episodic beach retreat the boundary between the foreshore and the underlying shoreface is well defined only in the case that longshore bars lead to complex bedding structure relative to that of the foreshore reliable chronology of beach ridges can be determined by radiocarbon and optically stimulated luminescence osl dating radiocarbon dating of articulated shells which are considered not to be extensively reworked provides robust results but osl dating is more useful as it enables direct dating of sediment grains it is noted that there are restrictions in chronological resolution and continuity inherent to beach ridge and beach deposits the plan view geomorphic expression of beach ridges typically consists of ridge sets with multi decadal intervals whereas their internal sedimentary structures define shorter time scales records of beach sedimentation and erosion are likely to be reworked by episodic high magnitude beach retreat and the resultant record of the net progradation is likely to be sporadic and discontinuous the height of sandy beach ridges is often variable due to differing degrees of aeolian sand accumulation and they are thus not used as sea level indicators unless purely wave built gravel ridge height is a relatively reliable indicator of sea level but can vary in response to storminess fluctuations subsurface sediment facies boundaries are preferred as sea level indicators and those proposed include boundaries of aeolian beach foreshore shoreface and upper lower shorefaces catastrophic events are expressed in both erosional and depositional records erosion surfaces or scarp imprints revealed in a cross section of beach deposits indicate storm or tsunami events however erosional events are likely to rework previous records of sedimentation and even other erosional events and thus the apparent history decoded from the resultant deposits tends to be biased several attempts for estimating the frequency and intensity of prehistoric cyclones rely on assumed relationships between the level of coarse sand beach ridges and cyclone inundation the formative process of coarse sand ridges remains uncertain and needs to be clarified as it constitutes the fundamental basis of these attempts the growth rates of beach ridge systems are expected to reflect fluctuations in river sediment discharge to the coast and in aeolian sand flux due to onshore winds both of which are affected by climate change assessment of the growth rate is potentially improved by ground penetrating radar survey of subsurface structure and by detailed chronology orientation of beach ridges reflects long term trends in wave direction inferred relationships between beach ridges and cyclic fluctuations of sea level and climate rely on weak assumptions and are not substantiated by rigid chronological evidence and thus remain highly questionable correlation between the inherently decadal signal of beach ridge intervals and possible climate cycles such as sunspot activity is probably coincidental as it lacks causal explanations

intra shoreface erosion in response to rapid sea level fall depositional record of a tectonically uplifted strand plain pacific coast of japan this study documents lowering of the surf zone i e the upper shoreface leading to intra shoreface erosion following two rapid relative sea level falls along a tectonically uplifted coast during the holocene and the characteristics of the resultant prograding shoreface deposits these findings are based on high resolution analysis and radiocarbon dating of three new drill cores obtained from the kujukuri strand plain pacific coast of eastern japan combined with previously published borehole data and information on modern shoreline profile adjustments a shallowing upward sandy succession composed of lower and upper shoreface facies foreshore and backshore facies was recognized in the drill cores two rapid falls in relative sea level at 2ae 3t o 2ae6 and 1ae 8t o 2ae0 ka are recorded by downstepping of the base of the foreshore facies and farther seawards by the lowering of an erosional boundary between the upper and lower shoreface facies superimposed bed profiles of an adjacent modern beach define an envelope the base of which reflects shore normal migration of longshore bars and troughs the base of the envelope represents an erosional surface that divides the surface mobile layer above from preserved deposits beneath the surface is concave upwards and steeper than the mean beach profile and exhibits a flat platform approximately at the lower limit of the upper shoreface equating to the storm surf zone the seaward transition of this surface rather than the mean equilibrium profile controls the metre scale to decimetre scale internal structure of the kujukuri shoreface deposits depositional models for sea level fall based on an exponential equilibrium profile do not adequately account for the presence and migration of longshore bars and troughs

extracting dynamic topography from river profiles and cosmogenic nuclide geochronology in the middle atlas and the high plateaus of morocco abstract the moulouya river system has intensely eroded the arhbalou missour and guercif neogene foreland basins in northeastern morocco having changed from net aggradation during the miocene early pliocene to net incision punctuated by alluvial fan deposition at late pliocene or early quaternary time this region as a whole has experienced mantle driven surface uplift dynamic topography since the late cenozoic being locally affected by uplift due to crustal shortening and thickening of the middle atlas too knickpoints located along the major streams of the moulouya fluvial network appear on both the undeformed margins of the missour and guercif foreland basins high plateaus as well as along the thrust mountain front of the southern middle atlas where they reach heights of 800 1000 m 500 550 m of the knickpoint vertical incision might be explained by long wavelength mantle driven dynamic surface uplift whereas the remaining 450 500 m in the southern middle atlas front and 200 300 m in the northeastern middle atlas front seem to be thrust related uplift of the jebel bou naceur be 10 terrestrial cosmogenic nuclides have been used to date two quaternary river terraces in the chegg ard valley at 62 14 ka and 411 55 ka the dated terraces allow the incision rates associated with the frontal structures of the middle atlas to be estimated at 0 3 mm yr 1 furthermore these ages have served to evaluate mantle driven regional surface uplift since the middle pleistocene in the central missour basin yielding values of 0 1 0 2 mm yr 1

valley width variation influences riffle pool location and persistence on a rapidly incising gravel bed river abstract decades of research have demonstrated that gravel bed rivers exhibit multiple spatial scales of landform nonuniformity landform features such as valley wall oscillations alluvial fans terraces river meanders point bars boulder clusters and logjams contribute to river corridor heterogeneity further studies have shown that the locations of riffles and pools in gravel bed rivers are closely associated with the spatial pattern of river corridor morphological variability these studies imply but do not directly test that persistence of riffles and pools through time is also conditioned by landform variability mechanistically it may be hypothesized that overbank flows interact hydraulically with oscillating valley walls by way of a mechanism known as flow convergence routing in such circumstances can variation in valley width influence channel morphology forcing riffle pool location and persistence to address this question research was performed on a valley confined wandering gravel bed reach of the regulated lower yuba river california usa that is incising from reduced sediment supply and flow regulation after a historic period of mining related valley sedimentation this study quantified stream planform change 1984 2006 and elevation change 1999 2006 using eight aerial photo sets and two digital elevation models and it qualitatively assessed channel change in older aerial photos going back to 1937 analysis revealed that the river has undergone rapid incision 0 11 m year and planform change in response to frequent floods yet eight riffles persisted in the same locations which coincided with the locally wide areas of the valley longitudinal profiles revealed that deep pools were associated with long valley constrictions geomorphic analysis and design need to explicitly account for multiple scales of landform nonuniformity in order to rehabilitate natural fluvial processes

flood driven topographic changes in a gravel cobble river over segment reach and morphological unit scales regulated rivers generally incise below dams that cut off sediment supply but how that happens and what the consequences are at different spatial scales is poorly understood modern topographic mapping at meter scale resolution now enables investigation of the details of spatial processes in this study spatial segregation was applied to a meter scale raster map of topographic change from 1999 to 2008 on the gravel cobble regulated lower yuba river in california to answer specific scientific questions about how a decadal hydrograph that included a flood peak of 22 times bankfull discharge affected the river at segment reach and morphological unit scales the results show that the river preferentially eroded sediment from floodplains compared to the channel and this not only promoted valley wide sediment evacuation but also facilitated the renewal and differentiation of morphological units especially in the channel at the reach scale area of fill and mean net rate of elevational change were directly correlated with better connectivity between the channel and floodplain while the mean rate of scour in scour areas was influenced by the ratio of slope to bankfull froude number a ratio indicative of lateral migration versus vertical downcutting hierarchical segregation of topographic change rasters proved useful for understanding multiscalar geomorphic dynamics this article is protected by copyright all rights reserved

sediment budget for salmonid spawning habitat rehabilitation in a regulated river bed elevation feature adjustments and spawning use were monitored at three chinook salmon oncorhynchus tschawytscha spawning habitat rehabilitation sites to measure project longevity in a regulated river sites enhanced with 649 1323 m 3 of gravel lost from 3 20 of remaining gravel volume annually during controlled flows of 8 70 m 3 s and 2 6 4 6 of placed material during a short duration 19 days release of 57 m 3 s the oldest site lost 50 of enhancement volume over 4 years of the mechanisms monitored gravel deflation was the greatest contributor to volumetric reductions followed by hydraulic scour spawning local scour around placed features and oversteepened slopes contributed to volumetric changes as sites matured volumetric reductions decreased sites captured as much large woody debris as was lost while complexity is an extremely important aspect of ecological function artificial production of highly diverse and complex habitat features may lead to limited longevity without natural rejuvenation d 2005 elsevier b v all rights reserved

non linear principal component analysis of nearshore bathymetry spatially and temporally extensive nearshore bathymetric datasets have recently been analyzed with complex principal component analysis cpca to extract propagating spatial patterns that constitute most to the dominant lower dimensional structure in the datasets cpca assumes this structure to be linear which may be an oversimplification of the true structure as the nearshore is a strongly non linear system here we investigate whether a neural network based circular non linear principal component analysis nlpca cir provides a more representative approximation of the underlying lower dimensional structure of nearshore depth data than possible with cpca to that end nlpca cir was applied to three datasets characterized by interannual offshore directed sandbar behavior coming from egmond the netherlands hasaki coast japan and duck north carolina usa the main difference between these datasets is the temporal variation in sandbar amplitude which is smallest at egmond and largest at duck we find that the first nlpca cir mode 1 at egmond and hasaki leads to a more complete characterization of the lower dimensional data structure than possible with cpca i e the underlying low dimensional structure of bathymetric data at egmond and hasaki is indeed non linear this is not the case at duck where the temporal variations in sandbar amplitude are so large that the non linear lower dimensional structure in the data should it exist is no longer visually apparent and can no longer be detected by nlpca cir this suggests that a simple visual check of the data suffices to decide whether one should resort to nlpca cir or to the more simple and computationally quicker cpca

response of a gravel bed river to dam closure insights from sediment transport processes and channel morphodynamics this work deals with the impacts of dams on large gravel bed rivers in terms of altering coarse transport regimes and the relationship with river morphodynamics using data collected by a tracer based monitoring program carried out in a 4 km long study sector of the parma river italy located downstream from a relatively recently established dam we applied a virtual velocity approach to estimate the coarse bed material load at four river cross sections monitoring and calculation results provided new insights into the impacts of the dam on streambed material mobility and the sediment regime over the 17 month calculation period a longitudinal gradient of effects was observed along the study sector sections located closer to the dam are characterized by more evident impacts due to deficits in coarse sediment input from upstream sediment mobility here is strongly altered especially in the highly armored main channel and the overall bed material load is extremely low a partial recovery of sediment dynamics was observed at the sections located further from the dam where estimates indicate higher sediment yield the observed longitudinal trend in the coarse sediment transport regime matches the morphology as the river shifts downstream from a sinuous configuration with alternate bars to a wandering one the novel insights into alteration of coarse sediment dynamics and the relationship with river morphodynamics are potentially applicable to many other fluvial contexts affected by similar impoundments

influence of survey strategy and interpolation model on dem quality accurate characterisation of morphology is critical to many studies in the field of geomorphology particularly those dealing with changes over time digital elevation models dems are commonly used to represent morphology in three dimensions the quality of the dem is largely a function of the accuracy of individual survey points field survey strategy and the method of interpolation recommendations concerning field survey strategy and appropriate methods of interpolation are currently lacking furthermore the majority of studies to date consider error to be uniform across a surface this study quantifies survey strategy and interpolation error for a gravel bar on the river nent blagill cumbria uk five sampling strategies were compared i cross section ii bar outline only iii bar and chute outline iv bar and chute outline with spot heights and v aerial lidar equivalent derived from degraded terrestrial laser scan tls data digital elevation models were then produced using five different common interpolation algorithms each resultant dem was differentiated from a terrestrial laser scan of the gravel bar surface in order to define the spatial distribution of vertical and volumetric error overall triangulation with linear interpolation tin or point kriging appeared to provide the best interpolators for the bar surface lowest error on average was found for the simulated aerial lidar survey strategy regardless of interpolation technique however comparably low errors were also found for the bar chute spot sampling strategy when tins or point kriging was used as the interpolator the magnitude of the errors between survey strategy exceeded those found between interpolation technique for a specific survey strategy strong relationships between local surface topographic variation as defined by the standard deviation of vertical elevations in a 0 2 m diameter moving window and dem errors were also found with much greater errors found at slope breaks such as bank edges a series of curves are presented that demonstrate these relationships for each interpolation and survey strategy the simulated aerial lidar data set displayed the lowest errors across the flatter surfaces however sharp slope breaks are better modelled by the morphologically based survey strategy the curves presented have general application to spatially distributed data of river beds and may be applied to standard deviation grids to predict spatial error within a surface depending upon sampling strategy and interpolation algorithm

a simple model for interannual sandbar behavior time and length scales of beach variability have been quantified using 16 years of beach surveys sampled at the army corps of engineers field research facility located on the u s atlantic coast between 50 and 90 of the bathymetric variability at this site was explained by alongshore uniform response over the approximately 1 km alongshore span of the surveys although the incident wave height variance was dominated by frequencies at or higher than 1 cycle yr more than 80 of the bathymetric variance at all cross shore locations was explained by frequencies 1 cycle yr interannual cycles consisting of sandbar formation migration and decay contributed to the low frequency variability the observed behavior can be explained by a simple heuristic model the model assumes that bars migrate toward a wave height dependent equilibrium position this position was shown to coincide with the wave breakpoint additionally the rate of bar response is taken to be variable and was empirically determined to be proportional to the wave height cubed the net effect of a variable response rate is to shift the expected long term mean sandbar position offshore toward the equilibrium position associated with the largest waves the model explained up to 80 of the observed bar position time series variance and up to 70 of the variance of bar crest velocity time series which were extracted from three different sandbars characteristic bar response times related to the inverse of the response rate were found to be long relative to the characteristic timescale of the forcing 1 year in our case as a result transient response i e bar position far from equilibrium tended to persist for many cycles of the forcing transient bar behavior appears in the observations when bars formed near the shoreline or when outer bars decayed and inner bars faced a changed wave climate while the present model is able to explain the evolution of these transients it does not contain a mechanism for their introduction

process based one dimensional model for cyclic longshore bar evolution abstract a wave averaged process based one dimensional model for beach profile change was developed to predict the cyclic evolution of longshore bars the cross shore sediment transport was assumed to be composed of suspended load due to wave breaking and bed load due to velocity skewness acceleration skewness and beach slope the model s performance was investigated using the beach profile data obtained every weekday during a 12 year period from 1989 to 2000 along a 400 m long pier at the hazaki oceanographical research station located on the hasaki coast of japan where the mean duration of bar evolution is approximately 1 year the model was unable to reproduce bar development from a rather flat profile possibly because some sediment movement process was missing in the model however the model calibrated with a 1 year data set including the bar evolution cycle consisting of bar generation seaward migration decay and new bar generation can be used to predict the first cycles of bar evolution at hasaki

cross shore grain size and sorting patterns for the bed profile variation at a dissipative beach hasaki coast japan abstract three field observations were conducted in three consecutive years on a sandy beach on the east coast of japan sediment cores were collected from the shoreline to the end of the offshore bar region each core was subdivided into layers and the sorting and skewness were analyzed using predefined trask coefficients the correlations between sediment properties that is median diameter sorting and skewness with respect to the change in the bed profile are discussed in this paper the weekly bed profiles offshore wave conditions and wave energy along the bed profile during the observation periods are discussed two significant sediment types were observed finer well sorted sediment and coarser poorly sorted sediment both coarser skewed the latter sediment properties were observed near the shoreline and at deeper elevations of the cross shore bed profile finer well sorted sand was transported away from and toward the coast depending on the wave intensity which causes in depth materials of coarser poorly sorted sediments to reappear with time the offshore bar and trough region has a limited erosional depth due to the existence of poorly sorted coarser materials which has been confirmed using weekly bed profile measurements the sediment properties have a direct influence on the change of the bed profile

observations of sand bar evolution on a natural beach waves currents and the location of the seafloor were measured on a barred beach for about 2 months at nine locations along a cross shore transect extending 255 m from 1 to 4 m water depth the seafloor location was measured nearly continuously even in the surf zone during storms with sonar altimeters mounted on fixed frames the crest of a sand bar initially located about 60 m from the shoreline moved 130 m offshore primarily when the offshore significant wave height exceeded about 2 m with 1 5 m of erosion near the initial location and 1 m of accretion at the final location an energetics type sediment transport model driven by locally measured near bottom currents predicts the observed offshore bar migration but not the slow onshore migration observed during low energy wave conditions the predicted offshore bar migration is driven primarily by cross shore gradients in predicted suspended sediment transport associated with quasi steady near bottom offshore flows these strong 50 cm s currents intensified near the bar crest by wave breaking are predicted to cause erosion on the shoreward slope of the bar and deposition on the seaward side the feedback amoung morphology waves circulation and sediment transport thus forces offshore bar migration during storms

on bar growth and decay during interannual net offshore migration abstract multiple bar systems often show a cyclic net offshore directed migration with return periods on the order of years generally a bar is generated near the shoreline grows in height and width while migrating offshore before finally decaying at the seaward limit of the surf zone based on a three year hindcast of a bar cycle at noordwijk netherlands and on additional synthetic runs using a wave averaged cross shore process model this study identifies the dominant mechanisms that govern the bar amplitude growth and decay during net interannual offshore migration the bar amplitude response is particularly sensitive to the water depth above the bar crest h xb and the angle of wave incidence these variables largely control the amount of waves breaking on the bar and the strength and cross shore distribution of the associated longshore current the longshore current has its maximum landward of the bar crest inducing additional stirring of sediment on the landward bar slope and trough the enhanced sediment concentration in the trough region shifts the cross shore transports peak landward of the bar crest forcing bar amplitude growth during offshore migration for increased h xb values wave breaking becomes less frequent consequently reducing the influence of the longshore current on sediment stirring therefore the resulting dominance of the cross shore current results in a sediment transport peak at the bar crest causing bar amplitude decay all four types of bar response viz all combinations of onshore offshore migration and bar amplitude growth decay can occur for a single wave height and wave period combination depending on h xb and additional hindcast runs in which the wave direction was assumed time invariant confirmed that h xb and largely control the transient bar amplitude response

assessing the ability of airborne lidar to map river bathymetry airborne bathymetric lidar was collected for 220 river kilometers in the yakima and trinity river basins in the united states concomitant with the aerial data collection ground surveys of the river bed were performed in both basins we assess the quality of the bathymetric lidar survey from the perspective of its application toward creating accurate precise and complete streambed topography for numerical modeling and geomorphic assessment measurement error is evaluated with respect to ground surveys for magnitude and spatial variation analysis of variance statistics indicate that residuals from two independent ground surveys in similar locations do not come from the same population and that mean errors at different study locations also come from different populations systematic error indicates a consistent bias in the data and random error falls within values of expected precision

significant decadal channel change 58 67 years post dam accounting for uncertainty in topographic change detection between contour maps and point cloud models abstract construction of digital elevation models dems and the subtraction of dems between different points in time as a method to determine temporal patterns of scour and fill is a highly valuable procedure emerging in geomorphology these dems of differences dods must be assessed for error in order to distinguish actual topographic change from uncertainty and surface error current methods include 1 uniformly excluding all values that fall below a minimum threshold 2 using a spatially variable approach such as the construction of minimum level of detection lod grids or 3 the creation of a fuzzy inference system although spatially variable methods for determining error have been more accurate in excluding noise without discarding large amounts of meaningful data a challenge remains in performing dods against preexisting contour based maps for which no original point data are available the goals of this study were to 1 develop a method that overcomes the unknown point density of contour and other historical data sets and allows for some assessment of dod uncertainty on the basis of information on topographic variability 2 perform comprehensive uncertainty analysis testing to understand the opportunities and constraints associated with this new method and 3 report and interpret the overall pattern and volume of decadal topographic change for a regulated river 67 years post dam in light of alternate conjectured mechanisms of post dam longitudinal profile adjustment the key feature of the new approach is the introduction of a high density artificial point grid that samples the topographic variability evident in the available historical data set the testbed used to develop and assess this new dod method was the 37 5 km lower yuba river california historical data consisted of 0 6 m contours from a 1999 survey while a more detailed point cloud was available for the most recent survey in 2006 2008 to evaluate uncertainty in the method this study applied seven different uncertainty metrics of varying strictness t 1 t 1 96 uniform 0 3 m exclusion t 1 plus uniform 0 3 m exclusion t 1 with lod minimum at 0 3 t 1 96 plus uniform 0 3 m exclusion and t 1 96 with lod minimum at 0 3 and two different dod adjustment methods exclusion and subtraction a stringent approach involving joint use of the contour half interval and the spatially distributed lod grid at a 95 confidence limit excluded 44 3 of the study area from spatial assessment of channel change and volumetric change computation this preferred approach yielded an estimated 2 518 million m 3 of total scour and 2 455 million m 3 of total fill in 7 9 years after considering different mapping epochs the net annual average export was 17 000 m 3 32 500 tons to the feather river and a river valley sediment yield of 2205 tons km 2 year this amount is 36 of the post dam annual yield of gravel and cobble to the upstream reservoir that blocks sediment conveyance into the study domain suggesting that the lowland system is still highly dynamic 67 years after the dam was built the scientific significance of this is that the response of rivers to dams can be far more long lasting and complex depending on the suite of cumulative societal impacts to rivers the ability to account for spatially explicit dod uncertainty i e data retention when uncertainty is low and data removal when uncertainty is high when comparing historic contour based and modern point cloud based dems will allow for more detailed and reliable dods and sediment budgets in these cases

relationships between mesoscale morphological units stream hydraulics and chinook salmon oncorhynchus tshawytscha spawning habitat on the lower yuba river california an expert based approach was used to identify 10 morphological unit types within a reach of the gravel bed regulated yuba river california that is heavily utilized by spawning chinook salmon oncorhynchus tshawytscha analysis of these units was carried out using two dimensional hydrodynamic modeling field based geomorphic assessment and detailed spawning surveying differently classified morphological units tended to exhibit discrete hydraulic signatures in most cases the froude number adequately differentiated morphological units but joint depth velocity distributions proved the most effective hydraulic classification approach spawning activity was statistically differentiated at the mesoscale of the morphological unit salmon preferred lateral bar riffle and riffle entrance units these units had moderately high velocity unit median 0 45 m s 1 and low depth unit median 0 6 m but each exhibited a unique joint depth velocity distribution a large proportion of redds 79 were associated with conditions of convective flow acceleration at riffle and riffle entrance locations in addition to reflecting microhabitat requirements of fish it was proposed that the hydraulic segregation of preferred from avoided or tolerated morphological units was linked to the mutual association of specific hydraulic conditions with suitable caliber sediment that promotes the provision and maintenance of spawning habitat

nearshore bars and the break point hypothesis abstract the set of hypotheses calling for bar formation at the break point was tested with field data during two different experiments waves were measured across the surf zone coincident with the development of a nearshore bar we use a criterion based on the wave height to depth ratio to determine the offshore limit of the inner surf zone during the first experiment the bar became better developed and migrated offshore while remaining well within the inner surf zone during the second experiment the surf zone was narrower and we cannot rule out the possibility of break point processes contributing to bar development we conclude that bars are not necessarily coupled with the break point and can become better developed and migrate offshore while being in the inner surf zone landward from initial wave breaking in the outer surf zone

medium term bar behavior and associated sediment transport at hasaki japan 1 the medium term movement of a longshore bar and the associated cross shore sediment transport were investigated using beach profile data obtained nearly daily for 8 years from the seaward foot of a dune to a water depth of about 5 m at hazaki oceanographical research station hors bar crests were found to move seaward repeatedly with a period of a year the duration time of the seaward bar migration is shorter than those on the other coasts in the united states the netherlands and new zealand although bars migrated in one direction seaward the cross shore sediment transport rate associated with the bar migrations fluctuated seaward and shoreward seaward sediment transport occurred on and around bar crests whereas shoreward sediment transport occurred in trough regions the cross shore sediment transport was active when the offshore wave energy was large from winter to spring and in autumn however the direction of the sediment transport in a region where bars were most developed was different during the two periods it was seaward from winter to spring and shoreward in autumn a numerical model for beach profile change confirmed that the development and decay of a bar was caused by the spatial and temporal variations of the cross shore sediment transport rate

monitoring and modelling morphological change in a braided gravel bed river using high resolution gps based survey recent research in fluvial geomorphology has emphasized the direct monitoring of channel topography as a useful tool to better understand the interrelationship between river form and process and in particular to estimate bedload transport rates and reach scale sediment budgets until recently however this morphometric approach has been limited to comparison of repeatedly surveyed cross sections with the associated problems of low frequency sampling and an emphasis on cross stream as opposed to downstream morphological dynamics recent advances in analytical photogrammetry have however permitted the acquisition of data at sufficient resolutions to represent macroform 101 m and microform 10 m channel geometry in fully three dimensions while inherently spatially distributed the photogrammetric approach to land surveying is however restricted to observable areas of the channel and is thus of limited use in the subaqueous zone especially if flows are turbid or highly coloured this paper presents an alternative approach to the study of three dimensional morphological dynamics of a divided reach of the gravelly river feshie scotland in which topographic survey of both exposed and submerged areas of the reach was undertaken using the global positioning system gps survey results from two field programmes in 1998 and 1999 are presented in which a geotronics geotracer 2000 real time kinematic gps receiving unit was used to survey a 200 80 m reach rapid radial survey methods were employed permitting the collection of 2000 survey points per day giving a mean density over the 13 ha reach of 1 1 points per square metre a detailed assessment of survey errors and dem quality is presented and a limit of detection of c 10 cm proposed as an upper threshold for the identification of significant change between dems preliminary interpretation of channel dynamics in 1998 99 reveals relatively little change to the overall macroscale reach structure dem differencing techniques however highlight important local changes including the progradation of submerged bar fronts bar head aggradation and scour along major channel thalwegs and the erosion of fines from sloughs copyright 2000 john wiley sons ltd

reconstructing the rise of recent coastal anoxia molybdenum in chesapeake bay sediments abstract sporadic direct observations over a 50 yr period inadequately characterize the history of seasonal hypoxia and anoxia in chesapeake bay a large estuary threatened by eutrophication here we undertake a reconstruction of 20th century oxygen depletion in this estuary using mo concentrations in 210pb dated sediments cu concentrations are used to control for anthropogenic influences cores from the central channel display mild mo enrichments above crustal backgrounds up to 5 g g and strong cu enrichments up to 35 g g temporally cu enrichment mostly anthropogenic began earlier and stabilized in the last two thirds of the 20th century in contrast mo enrichment has grown during the last two thirds of the century molybdenum enrichment is mostly hydrogenic except in a section of the channel that receives additional mo from erosion of early miocene shore deposits two geochemical mechanisms promote mo enrichment manganese refluxing concentrates dissolved moo42 at the sediment water interface and sulfide substitution into moo42 produces thiomolybdates which can be fixed by particles the mo enrichment mechanisms operate primarily during periods when bottom waters are anoxic and thiomolybdate formation can occur near the sediment water interface this implies a temporal coupling between water column anoxia and mo fixation even though fixation occurs only within sediments the mo enrichment profiles suggest that chesapeake bay has experienced growing o2 depletion since the first half of the 20th century but especially after 1960

geospatial organization of fluvial landforms in a gravel cobble river beyond the riffle pool couplet abstract morphological units mu are landforms with distinct local form process associations at 1 10 channel widths scale that may be the fundamental building blocks describing the geomorphic structure of a river past research has disproportionately focused on the two mus of pool and riffle conjecturing that they are the central linked couplet in the process form association the goal of this study was to delineate and map spatially explicit fluvial landforms in two dimensional planview within a gravel cobble bed river using two dimensional hydrodynamic delineation and then to statistically examine mu geospatial patterns for indicators of deterministic geomorphic control this procedure is not discharge dependent like mesohabitat methods but gets at the geometry of underlying landforms statistical testing confirmed that eight delineated in channel mu types comprise a complex and diverse channel morphology in which pools and riffles are not directly coupled specifically gravel cobble river channels 1 exhibit nonrandom spatial organization of their longitudinally and laterally variable landform morphology 2 consist of a variety of mu types not just pools and riffles and 3 show distinct mu collocations and avoidances with riffles linked to chutes and runs while pools are linked to slackwaters and glides planview mu delineation with two dimensional hydrodynamic modeling provides a bottom up approach to understanding and linking channel morphology with ecosystem services and geomorphic processes and is being used to guide river management and rehabilitation strategies

large scale experimental observations of sheet flow on a sandbar under skewed asymmetric waves a novel large wave flume experiment was conducted on a fixed barred beach with a sediment pit on the sandbar allowing for the isolation of small scale bed response to large scale forcing concurrent measurements of instantaneous sheet layer sediment concentration profiles and near bed velocity profiles were obtained on a sandbar for the first time two sediment distributions were used with median grain diameters d50 of 0 17 mm and 0 27 mm sheet flow occurred primarily under wave crests where sheet thickness increased with increasing wave height a proportionality constant was used to relate maximum shields parameter to maximum sheet thickness normalized by d50 with bed shear stress computed using the quadratic drag law an enhanced sheet layer thickness was apparent for the smaller sediment experiments 18 7 when directly compared to closed conduit oscillatory flow tunnel data 10 6 however varied significantly 5 31 depending on the procedure used to estimate grain roughness ds and wave friction factor fw three models for ks were compared keeping the model for fw fixed constant ks 2 5d50 and two expressions dependent on flow intensity derived from steady and oscillatory sheet flow experiments values of ks d50 varied by two orders of magnitude and exhibited an inverse relationship with where 30 for ks d50 of o 1 while 5 for ks d50 of o 100 two expressions for fw were also tested with the steady flow based model for ks yielding a difference of 69 13 versus 22

sediment transfer from beach to shoreface the sediment budget of an accreting beach on the danish north sea coast abstract the sediment budget along the southern part of the exposed danish north sea coast was assessed through a combination of cross shore profile analysis numerical modeling and field measurements of cross shore and longshore sediment transport at the boundary between the upper and the lower shorefaces the beaches along this coast are accreting but observed sediment storage is far smaller than sediment supplied by southerly directed wave driven currents the excess sediment volumes are transferred seaward across the shoreface by systematically offshore migrating nearshore bars that deliver sediment to the lower shoreface from where it is eventually removed by northward directed wind generated currents in the geological past sediment storage rates were much larger than at present and it is likely that the rate of storage along this coastline decreased as shoreface geometry adjusted towards equilibrium associated with shoreface steepening

bar trough generation on a natural beach mechanisms for bar trough generation are examined using velocities measured in the field applied to the bowen 1980 bailard 1981 energetics based sediment transport model measurements consist of a cross shore array of nine electromagnetic current meters spanning the surf zone and daily bathymetric surveys during a 10 day period during which two storms occurred when the bathymetry evolved from a three dimensional terrace to a well developed linear bar the model predicts bed and suspended load transport separately based on various velocity moments the velocities are partitioned into mean currents low frequency infragravity and shear instabilities 0 05 hz to determine the relative importance of various mechanisms to the total transport velocity moments are computed over 90 min intervals to resolve tidal fluctuations tidal signatures were apparent in all modes of transport predicted transport rates are integrated and compared with daily cross shore bathymetric profiles averaged over a 400 m length of beach the suspended load terms were an order of magnitude greater than bed load terms owing to the low fall velocity of the fine grain sand within the surf zone model results for this experiment indicate the dominant mechanism for bar development was sediments mobilized by the strong longshore current and incident short waves within the surf zone and transported offshore by the mean undertow and shoreward transport onshore due to short wave velocity skewness using standard coefficients the model correctly predicted the first order movement of the bar during storms but underpredicted trough development and did not always perform well during mild wave conditions

palaeoenvironmental and palaeogeographical implications of modern macaronichnus segregatis like traces in foreshore sediments on the pacific coast of central japan traces produced by modern animals provide useful information for our understanding of comparable trace fossils this paper reports on a polychaete worm euzonus producing traces which fall within the definition of the ichnotaxon macaronichnus segregatis observation on the wave dominated pacific sandy coast of central japan revealed that this animal and its trace occur exclusively in sediments of the mid foreshore portion of the beach owing to such a limited occurrence of the modern trace the ichnofossil m segregatis might be useful as an indicator of mid foreshore environment the longer axes of modern m segregatis like traces on a bedding plane are arranged perpendicular to the shoreline and accordingly its fossil counterpart can be utilized for reconstructions of the ancient shoreline orientation in support of this assumption a similar mode of m segregatis occurrence is reported from pleistocene shallow marine deposits in japan

hydrologic and topographic variability modulate channel change in mountain rivers summary the relationships between flow hydrology topography and channel change in mountain rivers is important to understanding landscape evolution the structure and persistence of aquatic habitat and also the physiochemical cycling of upstream derived organic and inorganic materials there is a paucity of detailed studies that analyze the joint roles of hydrology and topography in controlling multiple mechanisms of channel change in mountain rivers in this study gravel and cobble channel change in a bedrock river canyon were analyzed in light of a controlled yet natural experiment where 4491 metric tonnes of rounded gravel and cobble was augmented below a sediment barrier dam in a 1200 m long mountain river reach that had no prior sources of rounded gravel or cobble and still experiences floods above the bankfull discharge the overall study goal was to investigate how flow hydrology can modulate multiple channel change processes depending on the topographic features engaged by the flow channel change was assessed via differencing of high resolution repeat topographic and bathymetric surveys along with cm scale aerial photography post injection statistical tests used to implicate topographic feature specific mechanisms of channel change that vary with discharge included analyzing geomorphic covariance structures of flow dependent width bed elevation and channel change as well as autocorrelation of flow width spatial series stage dependent topographic steering was inferred from associations of erosion and deposition with changes in 2d model derived flow directions at multiple discharges a variety of mechanisms of channel change were qualitatively and quantitatively confirmed including particle hiding topographic steering eddying and flow convergence no single mechanism explained the observed patterns of channel change but rather it is thought that process blending occurs as modulated by the interactions of flow hydrology with complex topography results from this study suggest that both existing channel boundary variability and input hydrologic variability work together to create hydrodynamic spatial patterns that control the fate and transport of sediments in mountain rivers and ultimately their spatial structure

sediment transport storage relations for degrading gravel bed channels 1 in a drainage network sediment is transferred through a series of channel valley segments natural sediment storage reservoirs that are distinguished from their neighbors by their particular capacity to store and transport sediment we propose that the sediment transport capacity of each reservoir is a unique positive function of storage volume which influences sediment mobility and availability through variations in bed surface texture channel gradient and availability of valley floor sediments for erosion examinations of the form of transport storage relations of degrading alluvial reservoirs using published field studies flume experiments and simulations support a conceptual model that includes two phases in phase i filled channels respond to variations in supply primarily by changes in stored sediment volume with little change in transport rate in phase ii channel mobility is responsive to supply through armoring and form roughness although these phases could represent idealized transport limited phase 1 or supply limited phase ii states we propose that every alluvial reservoir responds to changes in sediment inputs by changing both storage and transport rate the propensity for either depending on reservoir characteristics and the sediment exchange processes in the channel transport storage relations for phase ii are approximately linear but examination of numerical simulations and flume experiments indicates that armoring imparts positive curvature simulations of degradation of an alluvial reservoir with channel and valley floor surfaces indicate that interactions between channel lowering and lateral erosion are critical in the manifestation of a transport storage relation better knowledge of transport storage relations could lead to improved sediment routing models for drainage basins wherein component sediment reservoirs dynamically adjust to varying sediment loads

riffle pool maintenance and flow convergence routing observed on a large gravel bed river abstract geomorphologists have studied and debated over the processes responsible for natural riffle pool maintenance for decades most studies have focused on small wadable rivers but they lack much description of overbank flood conditions or a spatially explicit characterization of morphodynamics in this study 1 m horizontal resolution digital elevation models were collected from a riffle pool run sequence before and after an overbank flood with a 7 7 year recurrence interval on the relatively large gravel bed lower yuba river california digital elevation model differencing was used to quantify the magnitude and pattern of flood induced morphodynamic change cross section based analysis and two dimensional hydrodynamic modeling of flows ranging from 0 147 to 7 63 times bankful discharge were completed to evaluate the hydraulic mechanisms responsible for the observed topographic changes one key finding was that riffle pool relief increased by 0 42 m confirming the occurrence of natural hydrogeomorphic maintenance spatially complex patterns of scour and deposition exceeding 0 15 m at the scale of subwidth morphological units were reasonably predicted by the two dimensional mechanistic model that accounts for convective acceleration the one dimensional cross section based method underperformed the two dimensional model significantly consequently multiple scales of channel non uniformity and a dynamic flow regime caused the observed maintenance of the pool riffle morphology through the mechanism of flow convergence routing proposed by macwilliams et al macwilliams m l wheaton j m pasternack g b kitanidis p k street r l 2006 the flow convergence routing hypothesis for riffle pool maintenance in alluvial rivers water resources research 42 w10427 doi 10 1029 2005wr004391

storm sequencing and beach profile variability at hasaki japan abstract beach profile evolution under storm sequence forcing presents an emerging research topic that has only been investigated at a limited number of sites the occurrence and effects of storm sequencing on beach profile evolution are studied at hasaki beach japan using weekly beach profile and two hourly offshore wave measurements during the 25 year study period the supratidal beach at hasaki is subjected to long term accretion and steepening while the shoreline shows a long term oscillation in addition oscillations of the supratidal beach volume and the shoreline at semi annual and annual intervals are identified which are largely controlled by the variability of the wave height hasaki beach is subjected to frequent storms that often cluster in sequences especially during the extra tropical cyclone season january to march the majority of storms and sequences generate erosion of the beach above the low water level but some also lead to recovery despite a tendency for storms and storm sequences with larger power to cause more erosion the present data does not demonstrate increased beach erosion by storm sequences following these findings the tendency of the beach to evolve towards equilibrium and the importance of the antecedent beach morphology are demonstrated

relationship between beach profiles and waves at duck north carolina determined by canonical correlation analysis abstract an 11 year long measurement time series of waves and profiles from duck north carolina was analyzed using canonical correlation analysis cca in order to determine the covariability between waves and profile response the main objectives of this analysis were 1 to detect simultaneously occurring patterns in the wave and profile data and if possible give such patterns a physical interpretation to increase the insight into the governing processes and 2 to investigate the possibility to use cca in a predictive mode with the aim to calculate the profile response from the waves the profile shape itself and the change between consecutively surveyed profiles were correlated with both the offshore deep water and nearshore wave conditions in the offshore the waves were described by composite probability density functions pdf derived based on the measured wave conditions prior to a profile survey nearshore wave conditions were calculated using a random breaker decay model and averaged local wave properties were used as input to the cca the profile response displayed significantly higher correlation with the nearshore wave properties as compared to the offshore waves and the highest correlation was found between the profile shape and the mean ratio of breaking waves for the time period preceding the profile survey the cca using nearshore wave properties indicates a potential for predicting the profile response with an acceptable degree of accuracy once a regression matrix relating the profiles to the waves has been established that represents the typical variability at the site

dams and geomorphology research progress and future directions dams impose changes of flow and sediment transfer that drive changes of channel form along the downstream regulated river these changes have been described for more than 50 years but process form relationships have only been advanced with the establishment of a conceptual framework during the 1970s and then the extension of monitoring data and advancement of remote sensing technologies particularly over the past 20 years this paper reviews these developments and identifies three influential themes i channel dynamics ii the role of riparian vegetation and iii channel change as the driver of ecological change changes can be rapid in semi arid regions but elsewhere relaxation periods may extend to millenia in these latter cases regime or steady state models should be replaced by models of transient states applied to the reach scale in order to respond to the needs of river managers over decadal timescales

effects of lidar derived spatially distributed vegetation roughness on two dimensional hydraulics in a gravel cobble river at flows of 0 2 to 20 times bankfull abstract the spatially distributed effects of riparian vegetation on fluvial hydrodynamics during low flows to large floods are poorly documented drawing on a lidar derived meter scale resolution raster of vegetation canopy height as well as an existing algorithm to spatially distribute stage dependent channel roughness this study developed a meter scale two dimensional hydrodynamic model of 28 3 km of a gravel cobble bed river corridor for flows ranging from 0 2 to 20 times bankfull discharge with and without spatially distributed vegetation roughness results were analyzed to gain insight into stage dependent and scale dependent effects of vegetation on velocities depths and flow patterns at the floodplain filling flow of 597 49 m 3 s adding spatially distributed vegetation roughness parameters caused 8 0 and 7 4 increases in wetted area and mean depth respectively while mean velocity decreased 17 5 vegetation has a strong channelization effect on the flow increasing the difference between mid channel and bank velocities it also diverted flow away from densely vegetated areas on the floodplain vegetation stands caused high velocity preferential flow paths that were otherwise unaccounted for in the unvegetated model runs for the river as a whole as discharge increases overall roughness increases as well contrary to popular conception

floodplain inundation response to climate valley form and flow regulation on a gravel bed river in a mediterranean climate region abstract floodplain inundation regime defines hydrological connectivity between river channel and floodplain and thus strongly controls structure and function of these highly diverse and productive ecosystems we combined an extensive lidar data set on topography and vegetation long term hydrological records as well as the outputs of hydrological and two dimensional hydraulic models to examine how floodplain inundation regimes in a dynamic regulated gravel cobble river in a mediterranean climate region are controlled by reach scale valley morphology hydroclimatic conditions and flow regulation estimated relative differences in the extent duration and cumulative duration of inundation events were often as large as an order of magnitude and generally greatest for large and long duration events the relative impact of flow regulation was greatest under dry hydroclimatic conditions although the effects of hydroclimate and flow impairment are larger than that of valley floor topography the latter controls sensitivity of floodplain hydroperiod to flow regime changes and should not be ignored these quantitative estimates of the relative importance of factors that control floodplain processes in mediterranean semiarid rivers contributes to better understanding of hydrology and geomorphology of this important class of channels we also discuss implications of our findings for processes that shape floodplain habitat for riparian vegetation and salmonid fish especially in the context of ecological restoration

seasonal scale nearshore morphological evolution field observations and numerical modeling abstract a coupled waves currents bathymetric evolution model delft 3d is compared with field measurements to test hypotheses regarding the processes responsible for alongshore varying nearshore morphological changes at seasonal time scales a 2001 field experiment along the beaches adjacent to grays harbor washington usa captured the transition between the high energy erosive conditions of winter and the low energy beach building conditions typical of summer the experiment documented shoreline progradation on the order of 10 20 m and on average approximately 70 m of onshore sandbar migration during a four month period significant alongshore variability was observed in the morphological response of the sandbar over a 4 km reach of coast with sandbar movement ranging from 20 m of offshore migration to over 175 m of onshore bar migration the largest seasonal scale onshore migration event observed in a natural setting both observations and model results suggest that in the case investigated here alongshore variations in initial bathymetry are primarily responsible for the observed alongshore variable morphological changes alongshore varying incident hydrodynamic forcing occasionally significant in this region due to a tidal inlet and associated ebb tidal delta was relatively minor during the study period and appears to play an insignificant role in the observed alongshore variability in sandbar behavior at kilometer scale the role of fully three dimensional cell circulation patterns in explaining the observed morphological variability also appears to be minor at least in the case investigated here

revealing the natural complexity of topographic change processes through repeat surveys and decision tree classification title revealing the natural complexity of topographic change processes through repeat surveys and decision tree classification short title decision tree classification of topographic change processes authors joshua r wyrick a gregory b pasternack b a lafayette college 740 high street easton pa 18042 b university of california davis one shields drive davis ca 95616 corresponding author tel 1 610 330 5735 e mail wyrickj lafayette edu fax 1 keywords topographic change dem differencing river morphology regulated rivers geomorphic change abstract topographic change processes tcps are the mechanisms by which a landscape is interpreted to be experiencing landform deformation and are defined by the specific actions occurring within a contiguous localized region that cause sediment to be either deposited or eroded past topographic change studies have mostly been focused at the site scale the goal of this study was to identify and delineate spatially explicit tcp

numerical predictability experiments of cross shore sandbar migration 1 surf zone sandbars common features along the world s sandy coastlines continuously change their position in response to time variable offshore wave conditions process based predictions of cross shore sandbar migration relevant to the understanding of autonomous and artificially altered evolution of beaches are intrinsically imprecise because of uncertainty in the model equations and potentially the sensitive dependence on the initial bathymetry however the magnitude of the resulting predictability limit and its dominant source are unknown here we show that cross shore sandbar migration on the time scale of years is deterministically forced rather than deterministically chaotic and that the unpredictability of sandbar migration results primarily from model inadequacy during major wave events because the unpredictability of sandbar migration is related to the stochastic nature of the forcing the predictability limit is not a fixed value but depends on the timing of the wave event we anticipate that detailed experiments to understand nearshore evolution from the underlying first principles will eventually pay off by extending the range of plausible simulated behavior and consequently will increase our ability to understand and predict how coasts may respond to changing climate

methodological sensitivity of morphometric estimates of coarse fluvial sediment transport abstract the estimation of fluvial sediment transport rate from measurements of morphological change has received growing recent interest the revival of the morphological method reflects continuing concern over traditional methods of rate determination but also the availability of new survey methods capable of high precision high resolution topographic monitoring remote sensing of river channels through aerial digital photogrammetry is a potentially attractive alternative to labour intensive ground surveys however while photogrammetry presents the opportunity to acquire survey data over large areas data precision and accuracy particularly in the vertical dimension are lower than in traditional ground survey methods this paper presents results of recent research in which digital elevation models dems have been developed for a reach of a large braided gravel bed river in scotland using both digital photogrammetry and high resolution rtk gps ground surveys a statistical level of change detection is assessed by comparing surfaces with independent check points the methodological sensitivity of the annual channel sediment budget 1999 2000 to the threshold is presented results suggest that while the remote survey methods employed here can be used to develop qualitatively convincing moderate precision dems of channel topography rmse 0 21 m the remaining errors imply significant limits on reliable change detection which lead to important information losses tests at a 95 confidence interval for change detection show that over 60 of channel deposition and 40 of erosion may be obscured by the lower level of precision associated with photogrammetric monitoring when compared to ground survey measurements this bias reflects the difficulty of detecting the topographic signature of widespread but shallow deposition on bar tops

alongshore variability of cross shore bar behavior on a nontidal beach we report on a 6 year nearshore bathymetric dataset from the danube delta romanian black sea coast that comprises 16 km of erosive stable and accumulative low lying micro tidal beaches northward of sf gheorghe arm mouth two to three two dimensional longshore sandbars exhibit a net multi annual cyclic 2 8 5 5 years offshore migration 20 50 m yr1 in a similar way to other coasts worldwide bar morphology and behavior on the sediment rich accretionary dissipative sector differ substantially from that on the erosive intermediate sector shoreface slope is the most important factor controlling sandbar number and behavior it determines different wave breaking patterns in the surf zone translated into different offshore sediment transport and bar zone widths along the study site additionally sediment availability as a result of the distance from the arm mouth and of the long term evolution of the coast controls the sandbar volume variability these are all ultimately reflected in the variations of sandbar migration rates and cycle periods a non dimensional morpho sedimentary parameter is finally presented which expresses the bar system change potential as offshore sediment transport potential across the bar zone

the effects of survey frequency on estimates of scour and fill in a braided river model an erratum has been published for this article in earth surface processes and landforms 27 7 2002 795 estimates of scour and fill in rivers that are derived by differencing topographic surfaces are known to be negatively biased by local compensation of scour and fill between surveys but the magnitude of bias is not well known this study examines the effect of survey frequency on volumes of scour and fill over a period of active channel braiding in a small scale river model a 100 min high temporal resolution time series of digital elevation models is artificially coarsened by selectively removing models the resulting four overlapping time series have survey intervals of 10 min 20 min 50 min and 100 min cumulative scour and fill volumes for the 100 min period are compared between the four series it is concluded that the decay in measured volumes of scour and fill with increased survey interval can be described using inverse functions cumulative scour fill volumes are approximately 420 per cent greater over the study period for 10 min survey intervals than for a 100 min interval after the 100 min period of competent flow nearly 65 per cent of the channel area experienced significant compensation of scour and fill several compensation mechanisms were identified in association with braided channel kinetics including lateral channel migration the migration of bed forms and channel avulsion it is demonstrated that by negatively biasing scour fill and net estimates this error significantly affects morphological approaches to the estimation of bed load sediment transport copyright 2002 john wiley sons ltd

the behaviour of a multiple bar system in the nearshore zone of terschelling the netherlands 1965 1993 abstract the behaviour of a multiple bar system in the nearshore zone of the island of terschelling the netherlands is investigated on the time scale of years using a data set of soundings the data set covers the period from 1965 to 1993 the behaviour is analysed in terms of bar crest position and in terms of morphometric parameters such as bar crest depth height width and volume two or three breaker bars are permanently present in the study area each individual bar passes through three stages during its existence 1 generation close to the shore 2 seaward migration and 3 degeneration at the outer margin of the nearshore bar zone the key factor controlling the behaviour of the inner bars is the crest depth of the outer bar three different couplings between the behaviour of the individual bars have been observed 1 bar stage changes due to the degeneration of the outer bar 2 prevention of the transition of an inner bar from the first to the second stage caused by the appearance from alongshore of a new outer bar having a small crest depth and 3 difference in mean annual seaward migration rate caused by the possible presence of a more seaward positioned bar it is hypothesized that the crest depth of the outer bar governs the relative importance of processes inducing shoreward and seaward migration in the inner nearshore bar zone and therefore controls the behaviour of the nearshore bar zone on the time scale of years

extracting decadal morphological behaviour from high resolution long term bathymetric surveys along the holland coast using eigenfunction analysis abstract the understanding and prediction of coastal behaviour over a time span of decades and alongshore stretches of tens of kilometres is important in coastal management the controlling variables for coastal behaviour on these scales are yet unknown it is hypothesised that regions exhibiting different large scale coastal behaviour lscb regions are controlled by different hydrodynamic forcings or by different sedimentological or morphological constraints or by some combination of these factors the objective of this study is to elaborate a method that effectively quantifies large scale morphological changes from a large bathymetric data set large temporal and spatial extent combined with a high resolution such to define lscb regions the method of analysis consists of a combination of the empirical eigenfunction technique and a moving window approach the method has been applied on a data set of over 14 000 nearshore profiles the data set consists of yearly soundings of the nearshore profile along a coastal stretch of 115 km length the holland coast the alongshore profile spacing is generally 250 m all profiles surveyed in the period 1963 1990 are included in the analysis application of the method on the dutch data set reveals that lscb regions indeed can be identified the sizes of the lscb regions are 5 km 15 km 20 km 32 km and 42 km differences in behaviour of the secondary morphology i e morphology other than the mean profile shape e g nearshore bars are most pronounced the change in behaviour between lscb regions generally occurs over distances as short as about 2 km the boundaries between the regions are therefore surprisingly sharp in general no clear long term trends in the development of the shape of the sub aqueous profile have been observed along the holland coast along certain stretches trends in cross shore shifting of the sub aqueous profile occurred the average shape of the sub aqueous profile seems to have no relation with the trend in cross shore shifting of the shoreline the 1 m contour the sub decadal shoreline fluctuations however are possibly related to the largescale dynamics of multiple bar systems

quantification of braided river channel change using archival digital image analysis historical archives of grey scale river channel imagery are extensive here we present and test a methodology to extract detailed quantitative topographic date from such imagery of sand bed rivers extracting elevation information from rivers is difficult as they are characterized by a low relative relief less than 4 m the area of interest may be spatially extensive e g active channel widths 500 m in large braided rivers the rate of change of surface elevation is generally low except in the vicinity of individual channel banks where the rate of change is very high there is the complication that comes from innundation and there may be an added complication caused by blockage of the field of view by vegetation here we couple archival photogrammetric techniques with image processing methods and test these for quantification of sand bed braided river dynamics illustrated for a 500 m wide 3 km long reach of the spouth sasketchewan river canada digitial photogrammetry was used to quantify dry areas and water edge elevations a methodology was then used to calibrate the special signature of inundated areas by combining established two media digital photogrammetric methods and image matching this allowed determination of detailed depth maps for inundated area and when combined with dry area data creation of depths detectable from sequential digital elevation models the result was a series of elevation models that demonstrate the potential for acquiring detailed and precise elevation data from any historical aerial imagery of rivers without needing associated calibration data provided that imagery is of the necessary scale to capture the features of interest we use these data to highlight several aspects of channel change on the south saskatchewan river including bar movement bank erosion and channel infilling

step by step error assessment in braided river sediment budget using airborne lidar data abstract sequential airborne lidar surveys were used to reconstruct the sediment budget of a 7 km long braided river channel in southeastern france following a 14 year return period flood and to improve its accuracy step by step data processing involved i surface matching of the sequential point clouds ii spatially distributed propagation of uncertainty based on surface conditions of the channel and iii water depth subtraction from the digital elevation models based on water depths measured in the field the respective influence of each processing step on sediment budget computation was systematically documented this showed that surface matching and water depth subtraction both have a considerable effect on the net sediment budget although dem of difference thresholding based on uncertainty analysis on absolute elevation values had a smaller effect on the sediment budget this step is crucial for the production of a comprehensive map of channel deformations a large independent data set of rtk gps checkpoints was used to control the quality of the lidar altimetry the results showed that high density 7 9 points m 2 airborne lidar surveys can provide a very high level of detection of elevation changes on the exposed surfaces of the channel with a 95 confidence interval level of detection between 19 and 30 cm change detection from lidar data revealed that 54 of the pre flood active channel was reworked by the flood the braided channel pattern was highly disturbed by the flood owing to the occurrence of several channel avulsions

designing forward with an eye to the past morphogenesis of the lower yuba river abstract the early geomorphic evolution of the lower yuba river lyr northern california up to 1906 is reconstructed using cartographic documentary topographic and stratigraphic evidence the importance of early river mining is identified along with rates and patterns of floodplain aggradation and channel incision at the turn of the 20th century the lyr is a classic example of anthropogeomorphic transformation of a river by episodic hydraulic mining sedimentation this was followed by channelization damming dredging and other engineering works to redirect contain and stabilize channels these geomorphic changes and engineering controls continue to govern channel and floodplain form and process control the trajectory of river responses and constrain flood control water quality and aquatic ecosystem management options returning a river system to a prior condition should not be the primary goal of river rehabilitation projects especially if hydrologic inputs have substantially changed reconstructing former conditions may be impractical and unsustainable under modern circumstances instead fluvial systems should be designed and managed for present inputs and processes while anticipating future conditions rapid changes in land use and climate that generate changes in runoff and sediment loadings are likely to generate morphological instability and these changes should be considered in the design and management of fluvial systems the past geomorphic evolution of fluvial systems should also be considered in design and management decisions to recognize trajectories and suppressed tendencies recognition of trends and system vulnerabilities may avoid potential blunders such as removing critical stabilizing works complex causalities may be difficult to reconstruct from geomorphic form alone however due to process form dynamics detailed research on the geomorphic and engineering history of a river is essential therefore if substantial changes and morphologic instabilities have occurred

nutrients trace metals and b vitamin composition of the moulouya river a major north african river discharging into the mediterranean sea abstract we analyzed dissolved nutrient trace metal and vitamin b vitamins and methionine concentrations in the lower course of the moulouya river mr morocco and its estuary the flow of this african river has changed drastically a reduction of almost 50 in the last 50 years due to the regulation of the river flow through dams and alterations of the course constructed to satisfy population necessities and growing agricultural requirements consequently it has produced a remarkable increase in nitrate concentrations up to 270 m and alteration of n p ratios within the river as well as a reduction of overall p and si efflux to nearby coastal waters despite the historical mining activities in the upper mr concentrations of pb zn and other metals in sediments and waters do not display significant contamination as compared with other mediterranean rivers mainly due to the retention by dams of upstream metal contamination mean concentrations of dissolved b vitamins in the river showed lower levels 13 55 lower than those in coastal waters and hence the river does not represent an important b vitamin source

classification of geomorphological effects downstream of dams abstract the effects of dams on downstream geomorphology are reviewed and a typology is devised consisting of nine cases the classification can be seen as a further development of lane s balance between water discharge sediment load grain size and river slope depending on changes in released water flow and changes in released sediment load relative to the transport capacity of the flow it is possible to estimate resulting cross sectional geomorphology the longitudinal extent of changes and their variability with time and the tributary response to altered mainstream cross section changes are also discussed

dynamics of longshore bars this paper presents empirical predictive expressions describing the cross shore movement of linear nearshore bars based on intensive analysis of survey data from duck north carolina the analysis centers on 300 beach profile surveys taken at approximately 2 week intervals for the continuous period from 1981 to 1989 together with accurate measurements of the wave conditions the geometry and dynamics of bars derived from the surveys are related to wave characteristics and criteria previously developed by the authors to predict beach erosion and accretion are found to be applicable to bar movement if a multiplicative empirical coefficient in each criterion is modified the results indicate that onshore movement of bars is more probable than previously estimated the implication is that linear bars formed of dredged material are more likely to move onshore to nourish the surf zone and beach than previously thought

using multiple bed load measurements toward the identification of bed dilation and contraction in gravel bed rivers 1 this study examines bed load transport processes in a small gravel bed river beard creek quebec using three complementary methods bed elevation changes between successive floods bed activity surveys using tags inserted into the bed and bed load transport rates from bed load traps the analysis of 20 flood events capable of mobilizing bed material led to the identification of divergent results among the methods in particular bed elevation changes were not consistent with the bed activity surveys in many cases bed elevation changes were significant 1 to 2 times the d50 even if the bed surface had not been activated during the flood leading to the identification of processes of bed dilation and contraction that occurred over 10 to 40 of the bed surface these dynamics of the river bed prevent accurate derivation of bed load transport rates from topographic changes especially for low magnitude floods this paper discusses the mechanisms that could explain the dilation and contraction of particles within the bed and their implications in fluvial dynamics bed contraction seems to be the result of the winnowing of the fine sediments under very low gravel transport bed dilation seems to occur on patches of the bed at the threshold of motion where various processes such as fine sediment infiltration lead to the maintenance of a larger sediment framework volume both processes are also influenced by flood history and the initial local bed state and in turn may have a significant impact on sediment transport and morphological changes in gravel bed rivers

the spatial and temporal variability of sand bar morphology the spatial and temporal variability of nearshore sand bar morphology is quantified using a unique data set spanning 2 years the data consist of daily time exposure images of incident wave breaking on an open coast sandy beach which may be used to infer bar morphology lippmann and holman 1989 the morphology in each image is classified into an eight state morphologic scheme in which bars are uniquely defined by four independent criteria the most frequently observed morphologies are the longshore periodic rhythmic bars observed in 68 of the data linear bars occur under highest wave conditions h s 1 78 m and are unstable mean residence time 2 days shore attached rhythmic bars are the most stable mean residence time 11 days and generally form 5 16 days following peak wave events non rhythmic three dimensional bars are very transient mean residence time 3 days eighty seven percent of transitions to lower bar types defined in text occurred one state at a time supporting our selection of the ordering of states and suggesting the suitability of a sequential morphology model transitions to higher states occurred under rising wave energy and were evenly spread among the possible higher states with more substantial changes in morphology resulting from larger wave increases this suggests that up state erosional transitions based on offshore bar migration are better described by an equilibrium model where response is better correlated with incident wave energy than with preceding morphological state time exposure images were also digitized to yield quantitative estimates of bar crest location as a function of longshore distance principal component analysis was used to decompose bar position into two dimensional linear and three dimensional longshore variable components cross shore linear bar position ranges 50 m about the 2 year mean 27 m standard deviation and dominates bar variability 74 6 three dimensional bar structure accounts for 14 of the variance 12 m standard deviation changes in incident wave height precede cross shore bar migration by less than 1 day changes in longshore variability are inversely correlated to changing wave conditions with bar morphology becoming linear rapidly during storms on time scales of less than 1 day evolution to significantly three dimensional structure typically occurs over 5 7 days following peak wave events

revealing the natural complexity of fluvial morphology through 2d hydrodynamic delineation of river landforms abstract fluvial landforms at the morphological unit scale 1 10 channel widths are typically delineated and mapped either by breaking up the one dimensional longitudinal profile with no accounting of lateral variations or by manually classifying surface water patterns and two dimensional areal extents in situ or with aerial imagery mapping errors arise from user subjectivity varying surface water patterns when the same area is observed at different discharges and viewpoints and difficulty in creating a complete map with no gaps or overlaps in delineated polygons this study presents a new theory for delineating and mapping channel landforms at the morphological unit scale that eliminates in field subjective decision making adds full transparency for map users and enables future systemic alterations without having to remap in the field delineation is accomplished through a few basic steps first near census topographic and bathymetric data are used in a two dimensional hydrodynamic model to create meter scale depth and velocity rasters for a representative base flow second expert judgment and local knowledge determine the number and nomenclature of landform types as well as the range of base flow depth and velocity over each type this step does require subjectivity but it is transparent and adjustable at any time third the hydraulic landform classification is applied to hydraulic rasters to quickly completely and objectively map the planform pattern of laterally explicit landforms application of this theory will reveal the true natural complexity yet systematic organization of channel morphology

cross shore distribution of long term average longshore sediment transport rate on a sandy beach exposed to waves with various directionalities abstract the cross shore distribution of long term average longshore sediment transport rate on a sandy beach exposed to waves with various directionalities was investigated using a process based one dimensional model the cross shore distributions of longshore sediment transport rate were simulated at 2 hour intervals for 15 years at the hasaki coast of japan the simulation results showed that although the direction of average total longshore sediment transport rate was southward the direction of predominant longshore sediment transport near the shore was northward this was caused by the cross shore distribution of average longshore sediment transport rate that was northward near the shore but southward away from the shore the cross shore distribution was formed because when the longshore sediment transport developed only near the shore owing to relatively small waves northward transport was dominant however when the transport developed both near and away from the shore owing to relatively large waves southward sediment transport developed these results indicate that examination of the cross shore distribution of longshore sediment transport rate is crucial for gaining a better understanding of longshore sediment transport on a sandy beach exposed to waves with various directionalities

filtering spatial error from dems implications for morphological change estimation abstract scour and fill estimation from digital elevation model dem subtraction or differencing is an increasingly common technique in morphological and sediment transport investigations the technique is commonly used to estimate scour and fill volumes and to produce scour and fill maps that provide process based information to geomorphologists accounting for sources of uncertainty within the dem is of critical importance dem error is spatially variable and has a tendency to be greater at breaks of slope such as bar and bank edges in the past however this has been achieved using a uniform error metric across the dem resulting in over conservative estimates of error in turn this has led to over conservative scour and fill volumes and incorrect process interpretation this paper applies a new approach that permits assessment of spatially distributed error across a dem the method is tested on a sequence of field surveys of the gravel bed river nent cumbria uk the results demonstrate some dramatic differences application of conventional techniques that account for mean error across a dem led to a 15 and 31 underestimation in scour and fill volumes respectively between july and october 1998 whilst for the october 1998 june 1999 subtraction 31 and 13 of scour and fill were underestimated respectively use of a uniform error across a surface captures less change in comparison to a spatially distributed approach furthermore the changes captured using a uniform error are biased toward areas of the channel that have more local topographic variability such as bar and bank edges in contrast the use of a spatially distributed approach provides information on change from flatter surfaces such as bar tops that would otherwise be missed this study also demonstrates that estimates of morphological change can be misleading in the absence of an error filter where the raw survey data is available it is recommended that sediment budgeting studies take account of the spatial variability of error in each dem involved in the subtraction

the impact of the streamflow hydrograph on sediment supply from terrace erosion abstract sediment supply from banks and terraces has important implications for grain size distributions in alluvial rivers and by extension for aquatic habitat as well as for the delivery of floodplain stored nutrients and contaminants to the aquatic environment the interactions between streamflow hydrographs and lateral channel boundary failure control the sediment supply from banks and terraces however the relationships between variable flow and discrete sediment supply from catastrophic erosion of lateral boundaries and subsequent mass sediment flux in rivers are not well characterised by existing methods and models that focus only on one of several relevant interrelated processes in order to improve predictive capability of catastrophic sediment supply from lateral boundaries we adopt a new approach to modelling the process interactions between stream hydrology erosion of banks terraces and the corresponding discrete supply of sediment to channels we develop a modelling framework for terrace channel coupling that combines existing theories of flow through porous media bank stability and fractional sediment flux we demonstrate the utility of this modelling approach by assessing hydrologically driven erosion evolution of grain size in the channel and fine sediment flux from a study site along the yuba river in california over individual flood hydrographs and over decadal historical flow series we quantify the supply of sediment eroded from a contaminated nineteenth century fan terrace of hydraulic gold mining tailings intersecting the yuba and find that a threshold for erosion exists at a stage in the channel in excess of 8 m producing episodic sediment concentrations in excess of 300 mg l 1 the modelling produced erosion and fine sediment pulses from each of three major floods in the past several decades until the flow drops below 500 m3 s 1 and a bed armor layer forms while no sediment was generated from the terrace during smaller floods we further assess the impact on terrace erosion of various river management scenarios with distinct hydrograph shapes and find increased erosion potential when the terrace contains antecedent moisture or the flood time series is run over an extended duration sensitivity analysis demonstrated that elevated antecedent moisture within the lateral boundary and increased hydrograph rising time each reduce bank stability and thus increase volumes of failed material we also show that fluctuations in the hydrograph typically associated with hydroelectricity generation result in a more stable terrace than those of a longer duration because there is less time for hyporheic stream water to infiltrate the lateral boundary this study demonstrates that changes in hydrograph shape as a consequence of climatic forcing or anthropogenic dam releases may have considerable impacts upon sediment delivery and associated contaminants from banks and terraces to the downstream environment

meandering anabranching river channel change in response to flow sediment regulation data analysis and model validation abstract anabranching river has been recognized as an independent river pattern a variety of investigations have attempted to disclose the formation of anabranching rivers however most previous studies mainly focused on the controls of anabranching channels formation the mechanism of transition among sub channels with varying flow sediment regime in anabranching rivers has been poorly understood in this study we used multi source data sets to investigate the changes in river channels and island wugui island about 7 km2 along the 27 km long jianli reach tashiyi tianziyihao in the middle yangtze river nine landsat images 1987 1990 1994 1996 2000 2003 2006 2010 and 2014 with 30 m spatial resolution were used to map the channel planform dynamics obvious changes in channel width and morphology of the island were observed during 1987 2014 the width of the left branch had reduced from 1041 m to 340 m while the width of the right branch had increased from 632 m to 1531 m during 1994 1996 the main river channel shifted from the left branch to the right during the period of 1987 2014 the total width of the compound cross section increased and the mean length width ratio of the island increased from 3 59 to 4 32 the mean annual flow discharge increased about 9 and mean annual suspended sediment concentration and sediment transport coefficient the ratio of mean annual suspended sediment concentration to mean annul flow discharge decreased about 75 and 76 respectively from 1951 to 2009 in response to the operation of gezhouba dam and three gorges dam the meandering anabranching channel planform adjusted by narrowing the island width and enlarging compound cross section in response to upstream water sediment regime the shift of the main river channel from left branch to the right may resulted from the increase in flow discharge and decrease in sediment transport coefficient since 1980s the adjustment has been intensified by the changes in the sediment transport rate after 1995 after the main channel was switched from left branch to right branch the flow sediment diversion capacity was kept stable with a diversion percentage of 90 in right branch due to the persistent influence of the three gorges dam the right branch will function as the main channel for a long time before the meandering anabranching system achieves equilibrium the shift and stability of main channel was closely related with the relative magnitude of flow sediment partition in each branch the significance of this study is that we successfully manifested the main channel shift process of anabranching river with the support of direct hydromorphological observation and theoretical verification

dynamics of single barred embayed beaches abstract the dynamics of single submerged sandbars of two artificial embayed beaches la barceloneta and bogatell barcelona nw mediterranean has been studied with a video recorded data set of 4 3 years the alongshore averaged cross shore migration the orientation with respect the shoreline and the sinuosity of the barlines have been analyzed and related to wave conditions alongshore sediment transport and shoreline variability in general the submerged bars follow the general cyclic morphological behaviour observed in natural beaches switching among the four intermediate morphodynamic states but the studied beaches can be arrested during long periods of low wave conditions the dominant up state transition in barcelona beaches during storms is the transition toward the rhythmic bar and beach state the complete morphodynamic reset longshore bar and trough state only occurring during extreme wave events the cross shore migration of bars is dominated by the weekly and interannual components the interannual component shows an onshore bar migration trend at both beaches in contrast with the net offshore migration observed in multibarred open beaches bar disposition is located progressively seaward in the dominant alongshore transport direction i e oblique with respect to the shoreline at la barceloneta beach shoreline and barline orientations change consistently and a significant correlation between the accumulated alongshore sediment transport and the associated change in bar orientation has been found suggesting that alongshore transport can play a significant role in barline orientation finally bar sinuosity increases during eastern storms in both beaches this indicates that the formation of crescentic bars occurs for approximately shore normal waves some of the differences observed in bar morphology and mobility in the two studied beaches are related to their different level of protection with respect to the incident waves beach indentation

application of a diffusion erosion model to alluvial channels which degrade due to base level lowering the applicability of a diffusion erosion model that predicts transient longitudinal profiles of degrading alluvial channels has already been demonstrated in laboratory experiments and is here applied to some field examples by fitting simulated longitudinal profiles to measured ones for several streams with discharge 0 04 q5 680 m3s 1 diffusion erosion coefficients k were determined which are well correlated to discharge and drainage area headward knickpoint migration which results from base level lowering was also treated through the diffusion erosion model theoretically the distance of a knickpoint from the mouth of a tributary should be proportional to the square root of the time that elapsed since the base level was lowered field observations are in accordance with these theoretical considerations use of the model is discussed for prediction of erosion and for assessment of the age of alluvial fault scarps crossed by streams

estimating accumulation rates and physical properties of sediment behind a dam englebright lake yuba river northern california 1 studies of reservoir sedimentation are vital to understanding scientific and management issues related to watershed sediment budgets depositional processes reservoir operations and dam decommissioning here we quantify the mass organic content and grain size distribution of a reservoir deposit in northern california by two methods of extrapolating measurements of sediment physical properties from cores to the entire volume of impounded material englebright dam completed in 1940 is located on the yuba river in the sierra nevada foothills a research program is underway to assess the feasibility of introducing wild anadromous fish species to the river upstream of the dam possible management scenarios include removing or lowering the dam which could cause downstream transport of stored sediment in 2001 the volume of sediments deposited behind englebright dam occupied 25 5 of the original reservoir capacity the physical properties of this deposit were calculated using data from a coring campaign that sampled the entire reservoir sediment thickness 6 32 m at six locations in the downstream 3 4 of the reservoir as a result the sediment in the downstream part of the reservoir is well characterized but in the coarse upstream part of the reservoir only surficial sediments were sampled so calculations there are more uncertain extrapolation from one dimensional vertical sections of sediment sampled in cores to entire three dimensional volumes of the reservoir deposit is accomplished via two methods using assumptions of variable and constant layer thickness overall the two extrapolation methods yield nearly identical estimates of the mass of the reservoir deposit of 26 106 metric tons t of material of which 64 7 68 5 is sand and gravel over the 61 year reservoir history this corresponds to a maximum basin wide sediment yield of 340 t km2 yr assuming no contribution from upstream parts of the watershed impounded by other dams the uncertainties and limitations of the estimates of overall sediment quantities are discussed implications for watershed management and future reservoir sedimentation studies are also presented

cross shore sediment transport on natural beaches and its relation to sandbar migration patterns 1 field observations and derivation of a transport parameterization 1 cross shore sediment transport processes are investigated with measurements of horizontal velocity and sediment suspension obtained with electromagnetic current meters and optical backscatter sensors on five different beaches across europe data were gathered under a wide variety of hydrodynamic and morphological conditions spanning the swash surf and shoaling zones results show that the near bed velocity moments normalized by the local energy level ut2 n have consistent shapes shape functions when plotted against normalized cross shore depth h hb according to the energetics approach near bed velocity moments are good descriptors of sediment transport processes consequently the shape functions describe and quantify the cross shore distribution of the most relevant cross shore sediment transport processes the pattern consists of net onshore transport in the swash zone offshore transport in the surf zone and onshore transport in the shoaling zone thereby producing divergence of sediment in the inner surf swash zone and convergence in the breaker zone in consequence the shape function supports the breakpoint hypothesis for sandbar generation this behavior is a product of the balance between multiple opposing mechanisms including undertow coupling between mean flows and short long wave stirring short long wave skewness and long wave coupling with short wave variance the cross shore structure of the measured and normalized cross shore sediment fluxes is consistent with the velocity moment shape functions showing the robustness of the approach apart from the shortcomings bound to the energetics approach the present parameterization is also limited due to the difficulty of defining with confidence a breaker depth hb in bar trough systems

virtual manipulation of topography to test potential pool riffle maintenance mechanisms in this study numerical experimentation with two dimensional hydraulic modeling of pool riffle river topography drawing on the testbed data from the classic keller 1971 study was used to investigate the effect of synthetically manipulating topography on the occurrence and magnitude of velocity and shields stress reversals in a pool riffle sequence reversals in velocity and shear stress have been used to explore mechanisms of pool riffle maintenance while shields stress a combined measure of transport capacity and substrate erodibility is emerging in importance the original site topography was modeled alongside six altered ones to evaluate the sensitivity of hydraulic reversals to subtle morphology five incrementally wider pools and a filled pool the caamano 2009 criterion a simplified geometric threshold for predicting velocity reversals was applied to each terrain to evaluate its utility the original pool riffle topography was just over the threshold for a velocity reversal and well over the threshold for a strong shields stress reversal overall pool widening caused a predominantly local response with change to pool hydraulics and no change in section averaged velocity in the riffle beyond the initial widening of 10 filling in the pool significantly increased the magnitude of reversals whereas expanding it eliminated the occurrence of a reversal in mean velocity though the shields stress reversal persisted because of strong differentiation in bed material texture using shields stress as a reversal parameter enabled the quantification of pool modification effects on pool riffle resiliency the caamano 2009 criterion accurately predicted reversal occurrence for the altered terrains with exaggerated effects but failed to predict the weak reversal for the original topography two dimensional modeling coupled with previously accepted hydrologic geomorphic and engineering analyses is vital in project design and evaluation prior to construction

equilibrium slopes and cross shore velocity asymmetries in a storm dominated barred nearshore system abstract the near bed 0 10 m elevation horizontal velocities were measured across a two barred lacustrine shoreface during a storm and reveal a spatially coherent but temporally variable pattern in the low order moments of the velocity field large cross shore velocity asymmetries indicated 1 1 spatially extensive and temporally persistent offshore mean flows up to 0 18 m s 1 across the landward slope of the linear outer bar reflecting an undertow driven by a wave induced setup 2 2 an onshore directed skewness opposing the mean flow of wind wave origin and persistent under propagating bores in the inner bar system long after this asymmetry had disappeared from the outer bar extensive sediment reactivation with near zero net sediment flux over the whole of the upper shoreface indicated a sediment prism in a steady state volumetrically over the storm cycle uniform depths of sediment reactivation with zero bed elevation change over the storm cycle revealed local slopes in a steady state in the outer linear bar however time integration of the near bed velocity field at this location indicated an offshore net flux of water while sedimentary structures indicated bedform migration and thus at least bedload almost uniformly onshore when ripples and megaripples were present the sediment transport giving rise to the local equilibrium cannot be explained therefore on the basis of the mean properties of the near bed velocity vector but requires knowledge of the time varying instantaneous sediment transport vector onshore migration of the inner bar correlated well with the large and persistent onshore skewness of the velocity distribution in the inner surf zone associated with translatory surf bores throughout the storm decay period low frequency oscillations were only significant close to the shoreline but may have influenced the development of a sinuous three dimensional inner bar form as it migrated onshore

sandbar dynamics in microtidal environments migration patterns in unprotected and bounded beaches abstract novel observations of bar features and migration patterns at three italian sandy beaches in senigallia central adriatic sea and terracina central tyrrhenian sea are presented while two of these beaches are unprotected one is artificially embayed through the presence of a concrete jetty bar locations and motions are analysed with video imagery data sets from coastal monitoring stations wave climate from the copernicus oceanographic model is used to correlate hydrodynamics and beach morphology clear net offshore migration nom patterns are identified at all beaches although exhibiting different response scales at the low slope beach of senigallia mean surf zone slope of 0 009 bars are more sensitive to seasonal changes in wave climate with offshore shifts in winter and inactivity in summer mean annual migration rates of up to 0 26 m day and 0 09 m day are observed for outer and inner bars respectively no significant response to single storms is observed except during a single nne storm no distinct erosive or accretive trend for the shoreline is evidenced at the steep beach of terracina mean surf zone slope of 0 018 conversely bars are strongly responsive to single storm events with displacements of up to 25 50 m across a single storm the mean inter annual migration rate is 0 08 m day for the single outer bar whereas a slight onshore trend 0 02 m day for the newborn inner bar is established the presence of an artificial jetty at the misa river mouth in senigallia finally leaves the bar system typically oscillating around an equilibrium position susceptible to larger seasonal oscillations and strong offshore migration due to two ese storm events numerical simulations of nearshore circulation for two storms from different directions predict the birth of longshore currents higher ratios of significant wave height to water depth and stronger bottom orbital velocities over bars in case of the ese storm suggesting a greater tendency for offshore directed sediment transport

enhanced trapping of molybdenum by sulfurized marine organic matter of marine origin in mesozoic limestones and shales there have been many studies devoted to trace metals and their value in assessing the paleoredox conditions of ancient marine deposition among them molybdenum mo is frequently cited as an effective proxy for sediments and sedimentary rocks recently helz et al helz g r miller c v charnock j m mosselmans j l w pattrick r a d garner c d vaughan d j 1996 mechanisms of molybdenum removal from the sea and its concentration in black shales exafs evidences geochim cosmochim acta 60 3631 3642 and adelson et al adelson j m helz g r miller c v 2001 reconstructing the rise of recent coastal anoxia molybdenum in chesapeake bay sediments geochim cosmochim acta 65 237 252 suggested that mo does not behave conservatively in the water column when h2s reaches a threshold concentration above this concentration a switch operates and mo is scavenged by forming bonds with metal rich notably iron particles sulfur rich organic molecules and pyrite in this paper mo trapping by sulfur rich organic matter om in ancient marine deposits is emphasized the following mesozoic geological formations were selected for study because of their relatively high concentration of sulfurized om the akkuyu formation turkey the calcaires d orbagnoux france and kimmeridge clay uk and its timeequivalent in boulonnais france the kashpir oil shales russia and the la luna formation venezuela the sulfur rich om is identified by either measured organic s abundance or kerogen microscope observation our results show that mo is systematically more enriched relative to the other redox sensitive sulfide forming elements studied u v ni cu zn cr and mo enrichment is positively correlated with the amount of sulfurized om but not with pyrite abundance these results illuminate the role played by sulfurized om in geologic scale mo capture and retention but they also underline the role played by reactive iron significant om sulfurization is only possible when reactive iron is limited nevertheless pyrite formation though limited could act as an initial mo trap prior to mo uptake by om that is sulfurized after the pyritization step in future paleoenvironmental reconstructions attention must be paid to this enhanced mo enrichment in the presence of sulfurized organic matter in such cases the use of mo could lead to overestimation of the reducing conditions of the depositional environment

the behaviour of nearshore bars on the time scale of years a conceptual model abstract soundings of the sandy dutch coast have demonstrated the presence of a multiple bar system that exhibits cyclic offshore directed migration on the time scale of years medium term a cycle comprises bar generation interannual offshore migration and decay in this paper we propose a conceptual model in which we qualitatively outline the relationships between short term hourly process knowledge waves currents sediment transport based on a 15 week data set of near bed hydrodynamics obtained in the multiple bar system of terschelling the netherlands and medium term bar behaviour the short term process knowledge is aggregated to the medium term by combining probabilistic characterisations of medium term wave conditions and sediment transports estimated from the short term field measurements essential to the conceptual model is the observed cross shore change in short term conditions that dominate medium term onshore and offshore sediment transport q on and q off respectively in the cross shore direction the conditions contributing most to q on change from predominantly breaking situations outside the bar zone to mainly non breaking conditions on the beach in contrast q off remains restricted to breaking conditions over the entire profile in the model we qualitatively describe how this cross shore change in the forcing conditions results in interannual offshore bar migration bar decay and the onset of the next cycle as such our model may serve as a first step towards a more coherent quantitative model on medium term periodic bar behaviour

medium term variations of bar properties and their linkages with environmental factors at hasaki japan beach profile data obtained every weekday for 15 years along a 427 meter long pier were analysed by complex empirical orthogonal function analysis the seaward bar migration was represented by the first mode and the migration frequency and the temporal variation of the bar amplitude were estimated with the complex time coefficient of the first mode although the seaward bar migration frequency which is the reciprocal of the duration time of the bar migration cycle was relatively constant before 1993 and ranged between 1 3 to 0 8 cycles year 0 7 to 1 25 years cycle it gradually decreased after 1994 and reached 0 1 cycle year 10 years cycle at the end of 1996 subsequently it gradually recovered to the frequency before 1993 the bar amplitude had a similar long period fluctuation it was large before 1993 but small from 1995 to 1997 and then returned to the pre 1993 value the bar migration frequency was weakly correlated with the bar amplitude and the offshore wave energy flux

leveling rod base required for surveying gravel river bed surface elevations consistent surveying of bed elevations in natural channels containing gravel and cobble substrates is subject to measurement error if a leveling rod is placed indiscriminately between or on top of individual particles the influence of surface microtopography decreases with increasing leveling rod base diameter while the influence of bed form topography increases field tests were performed to identify a rod base diameter that minimizes these survey errors a leveling rod base diameter of 127 mm 5 inches is suggested to be most appropriate for consistent bed surveys

forecasts of seasonal to inter annual beach change using a reduced physics beach profile model abstract the observed seasonal to inter annual variability of beach profiles has been investigated using a one dimensional beach profile model the model used here is developed on the reduced physics modelling approach the model uses a diffusion formulation as the governing equation and adopts an inverse modelling technique for solving the equation the model is calibrated and validated against historic measurements of beach profiles at hasaki coast located in the east coast of japan the beach is longshore uniform and characterised by a highly dynamic longshore bar trough system the model is then used to forecast seasonal to inter annual scale beach change the results are compared with beach change determined from measured beach profiles at hasaki between 2007 and 2011 the simple modelling approach used yields encouraging results of seasonal to inter annual scale beach change at hasaki coast

formulas for sediment porosity and settling velocity several existing formulas for the initial porosity and settling velocity of sediment have been tested by using extensive data collected from different countries and regions and modified to achieve better reliability or convenience in use

investigation of medium term barred beach behavior using 28 year beach profile data and rotated empirical orthogonal function analysis abstract a 28 year beach profile dataset for a stretch of the hasaki coast in japan was examined using rotated empirical orthogonal function reof analysis to investigate the cross shore variation in the characteristics of beach profile change the data were obtained weekly on a micro tidal wave dominated intermediate beach along a survey line extending from the backshore to a water depth of approximately 5 m reof analysis using the first eight empirical orthogonal functions led to the study area being divided into five unique zones based on beach profile change patterns namely the backshore the foreshore the inner and outer transition zones and the bar trough zone although these zones were notably distinct from one another the profiles in foreshore and the shoreward part of the inner transition zone changed in the same way over periods of 6 and 12 months