magnitude and variation in the contribution of bank erosion to the suspended sediment load of the river severn uk the wide range of studies describing the role of bank erosion in fluvial sediment supply have mostly lumped amounts of bank erosion into coarse temporal units such as years this paper investigates sediment yields from individual bank erosion events within the upper river severn uk basin area 380 km2 manual erosion pins and photo electronic erosion pins were used to estimate bank erosion and turbidity meters were used to determine suspended sediment transport at the annual time scale the silt clay fraction of bank derived sediment accounted for an equivalent of 17 per cent of the suspended load increasing to an average of 38 per cent at the monthly timescale and then to an average of 64 per cent at the event timescale this research highlighted that for an upland catchment bank erosion was an important supply of suspended sediment and that for some flood events bank erosion can supply more sediment than is transported 1997 john wiley sons ltd

bank collapse processes in a valley bottom gully western iowa widening and bank slope reduction of a valley bottom gully in western iowa was correlated to increasing subsurface flow over a 36 year period to study bank collapse at this gully we measured rainfall air temperature hydraulic head near the banks and bank movement nearly continuously over a 2 year period styles of movement ranged from imperceptible creep to rapid slab collapses preceded by the formation of tension cracks parallel to the gully walls bank movement was commonly correlated to rainfall or snowmelt and associated head increases in the banks if the banks are modelled as a two dimensional slab with an adjacent tension crack partly filled with water measured heads were sufficient to cause bank failures through reduction of frictional support at the base of the slab during winter months air temperature variations across 0 c were correlated with bank movement during mildly subfreezing periods banks expanded and most but usually not all of this movement was recovered during above freezing periods this motion is attributed to frost heave followed by thawing deformation of the banks by heaving and thawing during winter may weaken them and prime them for failure during spring rains and snowmelt when the frequency of mass wasting events is highest copyright 2008 john wiley and sons ltd

a sediment budget for a forested catchment in luxembourg and its implications for channel development in the forested catchments of the luxembourg keuper area deeply incised valleys have developed in which streambank erosion is a widespread phenomenon for one of the catchments in this area the schrondweilerbaach catchment a sediment budget was constructed in order to determine the relative contributions of the various channel and valley slope processes to sediment output streambanks contributed 53 percent of the output with bank scour and subsoil fall being the main processes while to a lesser extent bank material was supplied by bank failures splash erosion and soil creep the remaining 47 per cent of the sediment was derived from the valley slopes mainly through the combined action of rainsplash detachment and overland flow transport during the two years of investigations sediment output from the drainage basin almost equalled sediment input from streambanks and valley slopes the results of the measurements of the various streambank processes are integrated in a descriptive model for the present day widening of valley incisions in the study area and used to hypothesize the palaeohydrological development of the basin special attention is paid to the in direct effects of the forest vegetation on streambank erosion and sediment transport through the stream channel

stability of composite river banks the stability of a river bank depends on the balance of forces motive and resistive associated with the most critical mechanism of failure many mechanisms are possible and the likelihood of failure occurring by any particular one depends on the size geometry and structure of the bank the engineering properties of the bank material the hydraulics of flow in the adjacent channel and climatic conditions rivers flowing through alluvial deposits often have a composite structure of cohesionless sand and gravel overlain by cohesive silt clay bank erosion occurs by fluvial entrainment of material from the lower cohesionless bank at a much higher rate than material from the upper cohesive bank this leads to undermining that produces cantilevers of cohesive material upper bank retreat takes place predominantly by the failure of these cantilevers three mechanisms of failure have been identified shear beam and tensile failure the stability of a cantilever may be analysed using static equilibrium and beam theory and dimensionless charts for cantilever stability constructed application of the charts requires only a few simple measurements of cantilever geometry and soil properties in this analysis the effects of cracks and fissures in the soil must be taken into account these cracks seriously weaken the soil and can invalidate a stability analysis by affecting the shape of the failure surface following mechanical failure blocks of soil must be removed from the basal area by fluvial entrainment if rapid undermining and cantilever generation are to continue hence the rate of bank retreat is fluvially controlled even though the mechanism of failure of the upper bank is not directly fluvial in nature this cycle of bank erosion undermining cantilever failure and fluvial scour of the toe operates over several flood events and has important implications for river engineering channel changes and the movement of sediment through fluvial systems

subaerial river bank erosion processes and their interaction with other bank erosion mechanisms on the river arrow warwickshire uk river bank erosion occurs primarily through a combination of three mechanisms mass failure fluvial entrainment and subaerial weakening and weathering subaerial processes are often viewed as preparatory processes weakening the bank face prior to fluvial erosion within a river basin downstream process domains occur with subaerial processes dominating the upper reaches fluvial erosion the middle and mass failure the lower reaches of a river the aim of this paper is to demonstrate that a subaerial processes may be underestimated as an erosive agent and b process dominance has a temporal as well as spatial aspect bank erosion on the river arrow warwickshire uk was monitored for 16 months december 1996 to march 1998 using erosion pins variations in the rate and aerial extent of erosion are considered with reference to meteorological data throughout the first 15 months all erosion recorded was subaerial resulting in up to 181 mm a 1 of bank retreat compared with 13 to 27 mm a 1 reported by previous researchers while the role of subaerial processes as preparatory is not contended it is suggested that such processes can also be erosive the three bank erosion mechanisms operate at different levels of magnitude and frequency and the river arrow data demonstrate this thus the concept of process dominance has a temporal as well as spatial aspect particularly over the short time periods often used for studying processes in the field perception of the relative efficacy of each erosive mechanism will therefore be influenced by the temporal scale at which the bank is considered with the advent of global climate change both these magnitude frequency characteristics and the consequent interaction of bank erosion mechanisms may alter it is therefore likely that recognition of this temporal aspect of process dominance will become increasingly important to studies of bank erosion processes copyright 2001 john wiley sons ltd

changes in streambank erodibility and critical shear stress due to subaerial processes along a headwater stream southwestern virginia usa despite more than 40 yr of research attributing temporal changes in streambank erosion rates to subaerial processes little quantitative information is available on the relationships between streambank erodibility kd and critical shear stress c and the environmental conditions and processes that enhance streambank erosion potential the study goal was to evaluate temporal changes in kd and c from soil desiccation and freeze thaw cycling soil erodibility and c were measured monthly in situ using a multiangle submerged jet test device soil moisture temperature and bulk density as well as precipitation air temperature and stream stage were measured continuously to determine changes in soil moisture content and state pairwise mann whitney tests indicted kd was 2 9 and 2 1 times higher p 0 0065 during the winter december march than in the spring fall april may october november and the summer june september respectively regression analysis showed 80 of the variability in kd was explained by freeze thaw cycling alone study results also indicated soil bulk density was highly influenced by winter weather conditions r2 0 86 bulk density was inversely related to both soil water content and freeze thaw cycling results showed that significant changes in the resistance of streambank soils to fluvial erosion can be attributed to subaerial processes water resource professionals should consider the implications of increased soil erodibility during the winter in the development of channel erosion models and stream restoration designs

the spatial and temporal patterns of aggradation in a temperate upland gravel bed river intensive field monitoring of a reach of upland gravel bed river illustrates the temporal and spatial variability of in channel sedimentation over the six year monitoring period the mean bed level in the channel has risen by 0 17 m with a maximum bed level rise of 0 5 m noted at one location over a five month winter period these rapid levels of aggradation have a profound impact on the number and duration of overbank flows with flood frequency increasing on average 2 6 times and overbank flow time increasing by 12 8 hours this work raises the profile of coarse sediment transfer in the design and operation of river management specifically engineering schemes it emphasizes the need for the implementation of strategic monitoring programmes before engineering work occurs to identify zones where aggradation is likely to be problematic exploration of the sediment supply and transfer system can explain patterns of channel sedimentation the complex spatial seasonal and annual variability in sediment supply and transfer raise uncertainties into the system s response to potential changes in climate and land use thus there is a demand for schemes that monitor coarse sediment transfer and channel response copyright 2009 john wiley sons ltd

the anthropogenic nature of present day low energy rivers in western france and implications for current restoration projects abstract as in other european countries western france has seen an increase in river restoration projects in this paper we examine the restoration goals methods and objectives with respect to the long term trajectory and understanding of the contemporary dynamics of the small low energy rivers typical of the lowlands of western europe the exhaustive geomorphological paleoenvironmental and historical research conducted in the seulles river basin normandy provides very accurate documentation of the nature and place of the different legacies in the fluvial systems we have inherited the sedimentation rate in the seulles valley bottom has multiplied by a factor of 20 since the end of the bronze age and has generated dramatic changes in fluvial forms hydraulic control of the rivers and valley bottoms drainage throughout the last millennium has channelized rivers within these deposits the single meandering channel which characterizes this river today is the legacy of the delayed and complex effects of long term exploitation of the river basin and the fluvial system bring to light that the naturalness of the restored rivers might be questioned our research emphasizes the gap between the poor knowledge of the functioning of these rivers and the concrete objectives of the restoration works undertaken including dam and weir removal account of the long term history of fluvial systems is required not only to produce a pedagogic history of the river degradation but more fundamentally i to situate the current functioning of the fluvial system in a trajectory to try to identify thresholds and anticipate the potential turning points in a context of climate and land use change ii to understand the role of morphosedimentary legacies on the current dynamics iii to open the discussion on reference functioning or expected states and iv to open discussion on the sustainability of ecological restoration to conclude we point out the necessity to take into account the hybrid nature of low energy rivers in rural environments and to develop specific evaluation protocols which would include both biophysical processes and usual human activities which could be a way to share the evaluation and overcome conflicts between socioeconomic needs and environmental issues

streambank erosion rates and loads within a single watershed bridging the gap between temporal and spatial scales abstract the importance of streambank erosion to watershed scale sediment export is being increasingly recognized however few studies have quantified bank erosion and watershed sediment flux at the basin scale across temporal and spatial scales in this study we evaluated the spatial distribution extent and temporal frequency of bank erosion in the 5218 ha walnut creek watershed in iowa across a seven year period we inventoried severely eroding streambanks along over 10 km of stream and monitored erosion pins at 20 sites within the watershed annual streambank recession rates ranged from 0 6 cm yr during years of hydrological inactivity to 28 2 cm yr during seasons with high discharge rates with an overall average of 18 8 cm yr the percentage of total basin export attributed to streambank erosion along the main stem of walnut creek ranged from 23 to 53 large variations in individual site annual rates and percentage of annual load suggested that developing direct relationships between streambank erosion rates and total sediment discharge may be confounded by the timing and magnitude of discharge events storage of sediments within channel system and the remobilization of eroded material

a comprehensive fluvial geomorphology study of riverbank erosion on the red river in winnipeg manitoba canada summary riverbank erosion on the red river in winnipeg manitoba has raised concerns over the last 20 years and more although several recent studies have shown that fluvial erosion can reduce riverbank stability and promote geotechnical slope failure there are too few that have focused on this phenomenon the present study includes field measurements experimental testing and numerical modelling to quantify fluvial erosion through a 10 km reach of the red river results have shown that seasonal freeze thaw processes can dramatically reduce the critical shear stress and increase erodibility of the riverbanks moreover a simple method has been employed using hydrodynamic numerical models to define the applied shear stresses on the river banks based on the river water level which will be useful for further research and design purposes the temp w numerical model was used to define seasonal frost depth to estimate freeze thaw effects finally all field measurements experimental and numerical models results were used to predict annual fluvial erosion through this reach of the river

river width adjustment i processes and mechanisms in 1993 a task committee tc of the asce was established to study the hydraulics bank mechanics and modeling of width adjustment in alluvial channels the work of the tc in reviewing width adjustment processes and mechanisms is reported in this paper a companion paper presents the findings of the tc with regard to width adjustment modeling this paper first establishes the geomorphic context within which width adjustments occur and it demonstrates that width adjustment may take place over a wide range of scales in time and space in the past engineering analyses of channel width have tended to concentrate on prediction of the equilibrium width for stable channels most commonly the regime extremal hypothesis and rational mechanistic approaches are used and these are reviewed herein more recently attention has switched to channels that are adjusting their morphology either due to natural instability or in response to changes in watershed land use river regulation or channel engineering chara

evaluation of a linear bank erosion equation field surveys and aerial photographs were used to measure the rate of migration of a bend of the brandywine creek near chadds ford pennsylvania velocities near the bank were measured in the field during high flows and also estimated by solving a form of the st venant equations engineering properties of the bank soils and the spatial density of trees growing along the bank were also measured the data indicate that rates of bank migration are linearly related to the magnitude of the near bank velocity if the st venant equations are used to estimate the near bank velocity the data also suggest that erosion rates are proportional to ub u where ub is the near bank velocity and u is the reach averaged velocity in addition rates of bank migration are reduced where the density of silver maples acer saccharinum is high boxelder acer negundo and white ash fraxinus americana are also found along the bend but these species do not noticeably influence rates of bank migration

field and laboratory tests for recognition of ediacaran paleosols abstract not a single paleosol had been described from rocks of ediacaran age until 2011 but 354 ediacaran paleosols have been described by 20 different authors since then some of these newly recognized paleosols have proven controversial so this paper reviews 20 distinct tests to determine whether a particular ediacaran bed could be a paleosol or not one problem has been that ediacaran paleosols are not precisely like modern soils because they lack root traces a diagnostic feature of silurian and geologically younger paleosols the principal problem for recognition of some ediacaran paleosols is the occurrence in them of megafossils assumed to have been marine although most of these fossils remain problematic for both biological and ecological affinities not all the tests discussed here are diagnostic of paleosols some are ranked permissive or persuasive permissive conditions for paleosols include ripple marks hummocky bedding pyritic limestones acritarchs or thalloid fossils low strontium isotopic ratios high 26 mg ratios and red color persuasive tests include loessites tsunamites desert playa minerals low boron content high 10 b isotopic ratios high carbon sulfur ratios and very low total reactive iron ratios diagnostic tests include matrix supported lapilli or crystal tuff parent materials ice wedges and other cryoturbation sepic birefringence fabrics evaporitic sand crystals and negative geochemical strain and mass transfer and highly correlated 13 c and 18 o like other geological periods the ediacaran is known from a variety of marine and non marine paleoenvironments

disequilibrium of holocene sediment yield in glaciated british columbia it is generally supposed that specific sediment yield the quantity of sediment passing a monitored river cross section per unit area drained upstream of that section declines as the area drained increases1 3 part of the sediment mobilized from the land surface is supposed to go back into storage at field edges and on footslopes and floodplains in contrast we show here that data from british columbian rivers reveal a pattern of increasing specific sediment yield at all spatial scales up to 3 104 km2 this results from the dominance of secondary remobilization of quaternary sediments along river valleys over primary denudation of the land surface the result controverts the conventional model which has been derived from studies of small highly disturbed agricultural catch ments the rivers are still responding to the last glaciation giving a landscape relaxation time greater than 10 kyr this holds pro found implications for geomorphological theory and for studies of erosion

advances in the continuous monitoring of erosion and deposition dynamics developments and applications of the new peep 3t system abstract in most episodic erosion and deposition systems knowledge of the timing of geomorphological change in relation to fluctuations in the driving forces is crucial to strong erosion process inference and model building validation and development a challenge for geomorphology however is that few studies have focused on geomorphological event structure timing magnitude frequency and duration of individual erosion and deposition events in relation to applied stresses because of the absence of key monitoring methodologies this paper therefore a presents full details of a new erosion and deposition measurement system peep 3t developed from the photo electronic erosion pin sensor in five key areas including the addition of nocturnal monitoring through the integration of the thermal consonance timing tct concept to produce a continuous sensing system b presents novel high resolution datasets from the redesigned peep 3t system for river bank system of the rivers nidd and wharfe northern england uk and c comments on their potential for wider application throughout geomorphology to address these key measurement challenges relative to manual methods of erosion and deposition quantification continuous peep 3t methodologies increase the temporal resolution of erosion deposition event detection by more than three orders of magnitude better than 1 second resolution if required and this facility can significantly enhance process inference results show that river banks are highly dynamic thermally and respond quickly to radiation inputs data on bank retreat timing fixed with peep 3t tct evidence confirmed that they were significantly delayed up to 55 h after flood peaks one event occurred 13 h after emergence from the flow this suggests that mass failure processes rather than fluid entrainment dominated the system it is also shown how by integrating turbidity instrumentation with tct ideas linkages between sediment supply and sediment flux can be forged at event timescales and a lack of sediment exhaustion was evident here five challenges for wider geomorphological process investigation are discussed this event based dynamics approach based on continuous monitoring methodologies appears to have considerable wider potential for stronger process inference and model testing and validation in many areas of geomorphology

the paleomagnetic record of late quaternary secular variation from anderson pond tennessee abstract a paleomagnetic record of the earth s secular variation between 12 500 and 21 000 years b p has been recovered from two replicate wet sediment cores of anderson pond tennessee 36 0 n 274 5 e error analysis indicates that the cores are correctly oriented in the vertical plane but that some azimuthal offsets of individual core segments did occur these offsets were corrected by cross correlation between the two replicate cores the final paleomagnetic data set is internally consistent and easily correlated with other high resolution late quaternary paleomagnetic records from the eastern united states there is no evidence for any regional excursion or global reversal between 12 500 and 21 000 years b p time series analysis indicates that both the field vector and vgp distributions are non fisherian and distinctly far sided compared to the axial dipole expectation the far sided effect is interpreted to be geomagnetic in source rather than an error in the drm pdrm mechanism spectral analysis suggests that the secular variation is due primarily to a single irregular waveform with a period of about 3200 years this is interpreted to result from zonal drift of the non dipole field past tennessee at the rate of about 0 11 year

hydraulic erosion of cohesive riverbanks abstract this study identifies and assesses the controls on hydraulic erosion of cohesive riverbanks on a 600 m reach of an urban ephemeral stream with active bank erosion we examined hydraulic bank erosion by separating estimated bank shear stress into four properties magnitude duration event peak and variability the values of these independent variables were used as a bank erosion context at three transects stepwise regression showed that the event peak maximum peak of excess shear stress best predicts cohesive bank erosion at the two transects with moderate critical shear stresses 1 93 4 08 n m 2 while the variability all peaks of excess shear stress best predicts erosion at the transect with low critical shear stress 0 95 n m 2 these results suggest that the amount of hydraulic erosion of cohesive riverbanks is dictated by flow peak intensities finally the results of this study were combined with results from previous bank erosion studies to produce a conceptual model for estimating bank erosion rates based on their silt clay content

needle ice processes and sediment mobilization on river banks the river ilston west glamorgan uk abstract this paper examines the role of needle ice processes in the bank erosion system of a site on the river ilston west glamorgan south wales uk bank retreat rates were monitored with erosion pins over a 2 25 year period concurrent detailed data were also obtained on river flow levels and ambient air and stream temperatures unique data on river bank thermal regimes are presented along with rare information on the morphological properties and sediment yield characteristics of needle ice growths needle ice occurred even with mild freezing temperatures if sufficient bank moisture was present with average growth rates of approximately 1 mm h 1 bank material incorporation and mobilization within needle ice was significant sediment yields of up to 4 02 kg m 2 of bank face were observed and represented between 32 and 43 of total bank erosion recorded most sediment was incorporated within needle ice when growth became stressed because of overrapid cooling and or limited moisture supplies which supports the models of outcalt and fukuda four mechanisms of direct needle ice sediment transport on river banks were identified direct particle fall sediment laden rivulets sliding failures and toppling failures however the indirect preparatory role of needle ice and frost disturbance of bank surfaces is also emphasized and the enhanced fluvial erosion which takes place when bank materials have first been conditioned by frost related processes is noted both indirect and direct effects are expressed in a simple conceptual model and a number of the important system linkages examined combinations of needle ice action and subsequent fluid entrainment of weakened bank material appear to be the dominant mechanism for bank erosion here pronounced and persistent erosional notches in the lower parts of the bank profile were observed showing that in winter even single low magnitude flow events can effect significant channel width adjustment here

post cranial remains of coelurosaurs dinosauria theropoda from the late jurassic of tanzania small theropod post cranial material from tendaguru tanzania the only known late jurassic theropod locality in the southern hemisphere is reviewed material originally described as coelurosaurs includes at least one taxon of basal tetanuran and one taxon of small abelisauroid together with the abelisauroid elaphrosaurus and the presence of a larger ceratosaur in tendaguru this material indicates that ceratosaurs were an important faunal element of late jurassic east african theropod faunas one bone furthermore shares derived characters with the holotype of the poorly known middle jurassic australian theropod ozraptor and allows the identification of the latter as the oldest known abelisauroid thus indicating an early divergence of ceratosaurids and abelisauroids within ceratosaurs abelisauroids might have originated in gondwana and represent important faunal elements of cretaceous gondwanan theropod faunas in general

the importance of high resolution monitoring in erosion and deposition dynamics studies examples from estuarine and fluvial systems abstract erosion and deposition processes lie at the centre of geomorphological explanation but progress in understanding has been limited by a lack of appropriate high resolution monitoring methodologies which permit detection of erosion and deposition dynamics this paper presents a case for monitoring erosion and deposition at high temporal resolutions and uses hypothetical approaches supported by example erosion and deposition events and analyses drawn from estuarine and fluvial systems the paper first presents testable hypotheses to demonstrate the complexity of possible event combinations sequences and juxtapositions for the erosion driving forces which underpin the need for high resolution monitoring second it summarises recent improvements to the photo electronic erosion pin peep automatic erosion and deposition monitoring system including the novel concept of thermal consonance timing tct which is particularly promising because it helps to define the timing of nocturnal events and through the entire hydrograph third example results are discussed from high resolution monitoring of bank erosion at a tidal site at burringham on the river trent in northern england tidal banks are revealed to be much more dynamic than previous conventional monitoring has indicated a key result is that because the high resolution approach allows erosional and depositional activity to be assigned to specific periods of tidal inundation it becomes possible for the first time routinely to produce event based erosion 36 mm h 1 and deposition rates 4 5 and 8 4 mm h 1 such rate determinations are potentially very useful in the field validation of sedimentological and geomorphological models including grain settling and resuspension theory fourth through a longer term of aggregated daily data a striking 2 week cycle of deposition and erosion emerges which correlates most strongly with spring neap tidal cycling but is moderated by wind stress effects sediment was deposited on the bank relatively quickly over 4 5 days but then removed by erosion rather slowly over 9 10 days fifth the dangers of low resolution monitoring are illustrated by comparing the daily peep data set with a series resampled at a lower 14 day frequency to simulate the information generated by conventional resurvey methodologies the low frequency series failed adequately to represent the cyclicity mean range variability and trend of bank elevation changes and without this dynamics information rate and process definition is very difficult largely because of self concealing activity sixth a useful advance is illustrated by the fluvial erosion sequence for the river wharfe n england this shows how tct can generate rare and important results with the definition of the precise time of an erosion event within the hydrograph bank retreat here occurred very quickly after initial inundation and within 4 h of the flow peak information which can be used to define thresholds for entrainment e g critical shear stresses such high resolution monitoring helps to unravel some of the erosional effects of complex sequences combinations and juxtapositions of similar or different forcing events finally high resolution approaches have been adopted worldwide for fluvial estuarine mudflat and canal systems but considerable potential exists for their development and use in these and other contexts e g gully hillslope beach and dune environments to improve understanding and modelling of geomorphological processes more widely

a new technique for the automatic monitoring of erosion and deposition rates the rates and processes of erosion and deposition of soils and sediments are subjects of widespread and increasing concern in the earth and environmental sciences process inference from field studies however has been hampered by a lack of information on the precise magnitude frequency and timing of erosional and depositional activity because no automatic monitoring technique has hitherto been available i describe here an automatic photo electronic erosion pin peep system which apparently for the first time allows quasi continuous time series of erosion and deposition data to be collected example results from a river bank site show how the peep system helps to define the true temporal distribution of geomorphological change quantify the erosional impact of individual forcing events and discriminate between competing hypotheses of process control in erosional and depositional contexts the system should thus allow more effective testing of erosion models of high temporal resolution and facilitate a more rigorous linking of catchment sediment output to supply dynamics

the measurement of river bank erosion and lateral channel change a review a detailed review and chronological survey is presented of the various techniques which have been used for the measurement of river bank erosion and channel change the techniques are classified according to the time scales involved long intermediate and short and each is discussed with respect to accuracy and repeatability the methods covered include sedimentological evidence botanical evidence historical sources planimetric resurvey repeated cross profiling erosion pins and terrestrial photogrammetry prospects for future developments are also discussed

geomorphology in context dispatches from the field abstract field research enables a researcher to view geomorphic systems in broader contexts than those envisioned while at a desk and can yield unanticipated insights that change the course of an investigation or affect the interpretation of results geomorphological field research often produces aha moments epiphanies that enhance understanding and lead toward more complete explanation of the processes and landforms under study this paper uses examples from aha moments in the field to demonstrate the importance of field observation as a way of gaining information about the broader contexts of research sites especially in process geomorphology spatial contexts include the scales of processes and features linkages between a study site and its surroundings and information observed in the field about other processes anthropogenic activities or unexpected factors that might affect a study temporal contexts not as evident in the field place a research site in a longer term history of changes and adjustments finally exploring an abstract set of mental contexts reveals reasons that expectations differ from the realities encountered in the field constraints and biases that a researcher may not have noted and the possibility that the unexpected can potentially advance geomorphic research time spent in the field complements scientific reductionism and provides opportunities to appreciate the richness and complexity of earth surface systems

dynamics of erosion and deposition events on an intertidal mudbank at burringham river trent uk measurements using an automatic bank level monitoring technique the photoelectronic erosion pin peep system over a 70 day period between 16 march and 27 may 1997 have revealed a complex pattern of erosion and deposition on an intertidal mudbank on the river trent at burringham comparison of mean daily changes in bank elevation at upper and lower bank positions suggest that wave activity induced by high wind speeds causes erosion while high tidal range leads to deposition as a result of higher suspended solids concentrations a greater variability in mean daily erosion and deposition events at the lower bank compared with the upper bank appears to indicate that higher bed shear stresses as well as a greater availability of sediment for settling owing to higher concentrations and a greater depth of water lead to a more dynamic exchange of material at this position the peep data also show longer term trends in sedimentation with the mean deposition for the period exceeding mean erosion manual erosion pin measurements at a lower frequency over a longer seven month period confirm this and also highlight the advantage of the peep system in monitoring events at a finer temporal resolution copyright 1999 john wiley sons ltd