bed material transport estimated from the virtual velocity of sediment this study evaluates the possibility of determining bed material transport using the virtual rate of travel of individual particles dimensions of the active layer of the streambed and porosity and density of streambed material magnetically tagged stones and scour indicators were employed in carnation creek british columbia to quantify transport rates observations cover flows up to 36 m3 s 1 0 081 transport rates ranging from 0 090 to 9 7 kg s 1 0 12 13 2 m3 h 1 display a relatively sensitive trend with maximum stream power as expected error analysis indicates that uncertainty in virtual velocity covers the majority of sample variance an evaluation of the two measurement techniques used to delineate active layer dimensions magnetically tagged stones and scour indicators indicates that they yield comparable depths widths and transport rates over the range of flows observed issues for further study are discussed 1998 john wiley sons ltd

effects of hydraulic roughness on surface textures of gravel bed rivers field studies of forest gravel bed rivers in northwestern washington and southeastern alaska demonstrate that bed surface grain size is responsive to hydraulic roughness caused by bank irregularities bars and wood debris we evaluate textural response by comparing reach average median grain size d50 to that predicted from the total bank full boundary shear stress t0 bf representing a hypothetical reference condition of low hydraulic roughness for a given t0 bf channels with progressively greater hydraulic roughness have systematically finer bed surfaces presumably due to reduced bed shear stress resulting in lower channel competence and diminished bed load transport capacity both of which promote textural fining in channels with significant hydraulic roughness observed values of d50 can be up to 90 smaller than those predicted from t 0 bf we find that wood debris plays an important role at our study sites not only providing hydraulic roughness but also influencing pool spacing frequency of textural patches and the amplitude and wavelength of bank and bar topography and their consequent roughness our observations also have biological implications we find that textural fining due to hydraulic roughness can create usable salmonid spawning gravels in channels that otherwise would be too coarse

sedimentary characteristics of the gravel sand transition in the river rhine abstract a gravel bed river often changes abruptly into a sand bed river the causes of such so called gravel sand transitions have been elucidated in recent years but detailed observations of gravel sand transitions in large rivers are scarce the present study fills this knowledge gap by investigating the sedimentary characteristics of the gravel sand transition in the river rhine data on bed composition and flow characteristics are used in combination with a novel method for the evaluation of the bed structure the analysis shows that in contrast to common belief the bed structure in the gravel sand transition zone does not change from fully clast supported to fully matrix supported instead there is a strong cross stream variation in bed structure especially upstream of the transition zone the analysis also shows that the downstream decrease in gravel mobility in the gravel sand transition zone which is usually attributed to the change in bed structure and the so called patchiness effect is at least partly caused by the larger scale bend sorting process which concentrates gravel in outer bends where it is only infrequently mobile dune sorting which has been suggested to have an effect on the gravel mobility similar to that of bend sorting was found to be relatively unimportant in the rhine partly because it is strongly counteracted by armoring processes that affect an uncommonly thick sediment layer the gravel sand transition in the rhine with its length of 50 km is much less abrupt than the gravel sand transitions of smaller rivers reported on in the literature although the dependence of the transition length on river size intuitively is correct the exact causes remain unclear

particle path characteristics at the large gravel bed river danube results from a tracer study and numerical modelling a tracer study performed on a 3 km long reach of the danube river in austria is presented forty artificial stones of three different sizes intermediate b axis 25 mm 40 mm 70 mm were produced and a coded radio acoustic transmitter was implanted the measurement system had to be improved to be applicable to large rivers with water depths up to 12 m the positions of the stones were observed approximately once a week depending on hydrology over a period of at least one year by radio tracking from a boat including a 15 year flood event transport paths and velocities as well as the incipient motion of bedload transport could be monitored for the first time on a large gravel bed river the particle paths were found to be mostly bankline parallel even though the stones passed a 30 river bend the median of the transverse particle displacement was found to be 4 of the longitudinal displacement calculations considering both transverse slope and transverse flow velocities showed transverse transport to be 6 6 of the longitudinal transport indicating that marginal lateral transport is mainly influenced by morphology a three dimensional 3d numerical model using a stochastic particle tracing approach was validated with the data indicating that the observed positions are well reproduced by the model within the observation period 74 of all stones passed the reach with more than 1000 detections particle transport could be characterized by a mean travel velocity of about 10 m per day variable for the different grain sizes single tracer stones were transported up to 1000 m during a single flood event size selective behaviour could be shown and the incipient motion of the large 70 mm gravel was detected at lower discharges than predicted by commonly used uniform bedload transport formulae copyright 2012 john wiley sons ltd

effect of surface texture and structure on the development of stable fluvial armors abstract stable fluvial armors are found in river systems under conditions of partial sediment transport and limited sediment supply a common occurrence in nature stable armoring is also readily recreated in experimental flumes initially this bed stabilizing phenomenon was examined for different flow discharges and solely related to surface coarsening and bedload transport reduction the models developed suggest a specific armor composition i e texture dependent on the parent bed material and formative discharge following developments in topographic remote sensing recent research suggests that armor structure is an important control on bed stability and roughness in this paper replicated flume runs during which digital elevation models dems were collected from both exposed and flooded gravel beds are used to interpret armoring manifestations and to assess their replicability a range of methodologies was used for the analysis providing information on i surface grain size and orientation ii bed elevation distributions iii the spatial coherence of the elevations at the grain scale iv surface slope and aspect v grain imbrication and vi the spatial variability in dem properties the bed surface topography was found to be more responsive than bed material size to changes in flow strength our experimental results also provide convincing evidence that gravel beds response to water work during parallel degradation is unique i e replicable given the formative parameters based on this finding relationships between the armors properties and formative parameters are proposed and are supported by adding extensive data from previous research

assessment of bedload equations using data obtained with tracers in two coarse bed mountain streams narcea river basin nw spain abstract this paper evaluates the predictive power of nine bedload equations comparing the results provided by the equations with the bedload rates obtained in a previous field based tracer experiment accomplished in river piguena and river coto two coarse bed streams from nw spain rivers from nw spain draining the northern watershed of the cantabrian mountain range flow into the bay of biscay in a short path 50 60 km in this region they are developed forested catchments featured by fluvial networks with relatively steep slopes single thread sinuous channels and where bed sediment is typically coarse cobble and gravel tagged stones were used to trace bed sediment movement during flood events in river piguena and river coto the two main tributaries of the narcea river basin with the tracer results bedload transport rates between 0 2 and 4 0 kg s were estimated for six flood episodes the tracer based bedload discharges were compared with the bedload rates estimated with the bedload formulae duboys straub schoklitsch meyer peter muller bagbold einstein parker klingeman mclean parker klingeman parker and wilcock crowe our assessment shows that all of the bedload equations tend to overestimate when compared with the tracer based results with the wilcock and crowe 2003 equation the only exception in river piguena we linked these results to the particular geomorphology of coarse bed rivers in humid and forested mountain environments within these rivers armored textures and structural arrangements in the bed are ubiquitous these features together with a low sediment supply coming from upstream forested reaches define a supply limited condition for these channels limiting the potential use of bedload equations the wilcock and crowe 2003 equation introduces complex corrections into the hiding function and this could explain why it performs better

neomorphic spar versus cement in some jurassic grainstones significance for evaluation of porosity evolution and compaction thinly bedded upper bathonian grainstones with shales in wiltshire uk have intergranular spar of 2 kinds a primary calcite cement and a neomorphic spar that has replaced an earlier fibrous cement the earlier cemented grainstones have been less compacted than those cemented by a late calcite spar fewer broken grains fewer grain contacts more intergranular spar the crystals in the neomorphic intergranular spar are mostly subequant have irregular intercrystalline boundaries patchy extinction some dusty relics of earlier cement fringes and with cathodoluminescence show bright orange needle like relics of earlier cement fabric most of this subequant neomorphic spar is indistinguishable from the neomorphic spar that has replaced the aragonite of molluscan shells it is concluded that calcitization of an early cement and of the aragonite shells along with the precipitation of the true cement spar were delayed until after the carbonate sands had undergone some compactive fracture and grain grain pressure solution

infiltration of fine sediment into a coarse mobile bed a phenomenological study experiments were undertaken to study the nature of granular interaction in running water by examining the influence of fine grain inputs to a coarser sediment bed with a mobile surface video recordings of grain sorting by both kinetic sieving and spontaneous percolation are used to diagnose the critical processes controlling the overall bed response kinetic sieving takes place in the mobile bed surface with the finer sediment moving to the bottom of the bedload transport layer at the interface with the underlying quasi static coarse bed we show that the behavior at this interface dictates how a channel responds to a fine sediment input if by spontaneous percolation the fine sediment is able to infiltrate into the underlying quasi static bed the total transport increases and the channel degrades however if the fine sediment input rate exceeds the transport capacity or is geometrically unable to infiltrate into the underlying bed it forms a quasi static layer underneath the transport layer that inhibits entrainment from the underlying bed resulting in aggradation and an increase in bed slope this article is protected by copyright all rights reserved

grain size and topographical differences between static and mobile armour layers a series of laboratory flume experiments under conditions of sediment starvation zero sediment feeding and recirculation were conducted in order to identify the temporal evolution and surface properties of static and mobile armour layers the experiments were carried out in an 8 m long flume using a bimodal grain size mixture d50 6 2 mm and a range of shear stresses ranging from 4 0 to 8 6 n m 2 the results confirm that a static armour layer is coarser than a mobile one and that the grain size of a mobile armour layer is rather insensitive to changes in the imposed flow strength an analysis of laser scan bed surveys revealed the highly structured and imbricated nature of the static armour layer under these conditions the vertical roughness length scale of the bed diminished and it became topographically less complex at higher forming discharges the topography of mobile armour layers created by rising discharges differed they exhibited a greater roughness length scale and were less organized despite the fact that the grain size of the surface material maintained an approximately constant value during recirculation also the mobile armour tended to create larger cluster structures than static armour layers when formed by higher discharges these differences were mainly due to the transport of the coarser fraction of bed sediments which diminished to zero over the static armour because of being hidden within the bed whereas in the mobile armour the coarser particles protruded into the flow and were actively transported increasing the vertical roughness length scale overall the results show that an examination of the grain size characteristics of armour layers cannot be used to infer sediment mobility and bed roughness detailed elevation models of exposed surfaces of gravel bed rivers are required to provide critical insight on the sediment availability and sedimentation processes copyright 2011 john wiley sons ltd

channel adjustments to a succession of water pulses in gravel bed rivers gravel bed rivers commonly exhibit a coarse surface armor resulting from a complex history of interactions between flow and sediment supply the evolution of the surface texture under single storm events or under steady flow conditions has been studied by a number of researchers however the role of successive floods on the surface texture evolution is still poorly understood an experimental campaign in an 18 m long 1 m wide flume has been designed to study these issues eight consecutive runs each one consisting of a low flow period of variable duration followed by a sudden flood water pulse lasting 1 5 h have been conducted the total duration of the experiment was 46 h the initial bed surface was created during a 280 h long experiment focused on the influence of episodic sediment supply on channel adjustments our experiments represent a realistic armored and structured beds found in mountain gravel bed rivers the armor surface texture persists over the duration of the experiment the experiment exhibits downstream fining of the bed surface texture it was found that sorting processes were affected by the duration of low flow between flood pulses since bed load transport is influenced by sediment sorting the evolution of bed load transport is impacted by the frequency of the water pulses short interpulse durations reduce the time over which fine material transported as bed load can be winnowed this in turn contributes to declining reduction of the bed load transport over time while the sediment storage increases

thrust tectonics of the dibba zone and the structural evolution of the arabian continental margin along the musandam mountains oman and united arab emirates in the northern oman mountains several major thrust sheets of tethyan oceanic rocks dibba zone and a 12km thick complete ophiolite sequence have been thrust westward onto the depressed arabian continental margin musandam zone during the turonian to campanian late cretaceous early thrusting was dominantly a downward foreland propagating sequence as the higher earlier thrust sheets are folded around structurally lower and later culminations breached roof thrusts where imbricate thrusts do not always converge with a major roof thrust but in places actually penetrate up into the overlying duplex are common at outcrop scale affecting adjacent thrust sheets late stage breakback or leap frog thrusts cut through the whole pile of duplexes on to previously higher earlier dulexes late thrusting in the musandam zone affects the deeper previously autochthonous permian cenomanian shelf carbonate sequence and probably also the pre permian basement thrusting these rocks at least 15 km over previously allochthonous hawasina rocks late stage oblique dorsal culmination collapse along the se margin of the musandam mountains has downfaulted dibba zone rocks up to 2 5 km to the se along a hinged listric normal fault strain is transferred from the ne sw trending late cretaceous dibba zone to the n s striking mid tertiary musandam culmination at a major pivot point or transfer zone sw of the shelf carbonate culmination

rapid incision of a small coarse and steep fan delta in response to base level fall the case of nahal qedem the dead sea israel the dead sea has been continuously dropping 0 4 1 0 m yr 1 since the middle of the 20th century and thus provides a unique field laboratory for studying in real time the response of drainage systems to a non tectonic base level fall the aim of this work is to study the short term ongoing erosive response to a rapid base level drop in a small steep fronted erodible fan delta setting the work explores the controls of the steep qedem fan delta guided by its clinoform structure on its incision longitudinal profiles of the fan delta and of its entrenched channel were measured in the field sedimentary facies changes fluviatile shallow lacustrine and beach were followed along exposures the existence of large boulders provided an opportunity to examine the uncertain role of armouring and boulder flux on incision the field study was combined with digital elevation models dems that were extracted from pairs of overlapping aerial photos maps of erosion and deposition were prepared using a change detection algorithm the longitudinal profile of the entrenched channel was found to be steep and linear the outlet temporarily hangs elevated and ungraded above the retreating lake level indicating years without incision flow events which cause lags in response to the rapid lake level drop in spite of the large boulders the small drainage basin and precipitation volume over the basin of the qedem the recorded vertical incision rates in the unconsolidated sediments are as high as 0 8 m yr 1 i e similar to those of the largest wadis draining to the dead sea the steep front of the fan delta is suggested to be a main factor controlling the efficient incision a unique transport mechanism of rolling boulders following undercutting contributed to the entrenchment efficiency copyright 2010 john wiley sons ltd

structural properties of mobile armors formed at different flow strengths in gravel bed rivers differences in the structure of mobile armors formed at three different flow strengths have been investigated in a laboratory flume the temporal evolution of the bed surfaces and the properties of the final beds were compared using metrics of surface grain size microtopography and bed organization at both grain and mesoscales measurements of the bed condition were obtained on nine occasions during each experiment to describe the temporal evolution of the beds structured mobile armors formed quickly in each experiment at the grain scale 1 45 mm 9 ds50 17 mm where ds50 is the median surface particle size surface complexity decreased and bed roughness increased in response to surface coarsening and the development of the mobile armor particles comprising the armor also became flow aligned and developed imbrication at a larger scale 100 200 mm the surface developed a mesoscale topography through the development of bed patches with lower and higher elevations metrics of mobile armor structure showed remarkable consistency over prolonged periods of near constant transport demonstrating for the first time that actively transporting surfaces maintain an equilibrium bed structure bed structuring was least developed in the experiments conducted at the lowest flow strength however little difference was observed in the structural metrics of the mobile armors generated at higher flows although the range of transport rates studied was limited the results suggest that the structure of mobile armors is insensitive to the formative transport rate except when rates are low 0 03 where is the dimensionless shear stress

numerical simulation of downstream fining by selective transport in gravel bed rivers model development and illustration a numerical model has been developed for the routing of gravel sized sediment along a river channel which is free to adjust both its long profile and surface texture hydraulic calculations use a step backwater approach and sediment transport is predicted with the method of parker 1990a which uses a low degree of size selectivity exchange of sediment between the surface and subsurface is described using the modified exner equation of parker and sutherland 1990 the model is applied to an idealized channel based on the highly concave allt dubhaig scotland in which fining by particle wear is minor the rapid downstream fining observed in this river is closely matched by model predictions after a time equivalent to 102 years under the present flow regime of the river the evolution of the fining pattern during the model run and associated changes in sediment transport and bed aggradation are described it is concluded that strong profile concavity can force rapid downstream fining even though bed load transport is only slightly size selective this run of the model serves as a basis for testing of the sensitivity of downstream fining to alternative choices of parameter values and boundary conditions which are summarized here and will be described in a subsequent paper

submarine lithification on windward reef slopes capricorn bunker group southern great barrier reef abstract windward reef slopes of the capricorn bunker group southern great barrier reef are the sites of extensive submarine lithification both crystalline aragonite and bladed mg calcite spar and microcrystalline micrite and peloids cements occur within skeletal pores and chambers whereas interskeletal cements are mainly microcrystalline these cements are considered to be contemporaneous with reef growth and have developed in an environment characterized by slow accretion rates continuous precipitation of aragonite cement has in some places been inhibited by the formation of mg calcite micrite apparent dissolution of some of the mg calcite cements was observed but the processes involved are unknown

applicability of bed load transport models for mixed size sediments in steep streams considering macro roughness in steep mountain streams macro roughness elements typically increase both flow energy dissipation and the threshold of motion compared to lower gradient channels reducing the part of the flow energy available for bed load transport bed load transport models typically take account of these effects either by reducing the acting bed shear stress or by increasing the critical parameters for particle entrainment here we evaluate bed load transport models for mixed size sediments and models based on a median grain size using a large field data set of fractional bed load transport rates we derive reference shear stresses and bed load transport relations based on both the total boundary shear stress and a reduced or effective shear stress that accounts for flow resistance due to macro roughness when reference shear stresses are derived from the total boundary shear stress they are closely related to channel slope but when they are derived from the effective shear stress they are almost invariant with channel slope the performance of bed load transport models is generally comparable when using the total shear stress and a channel slope related reference shear stress or when using the effective shear stress and a constant reference shear stress however dimensionless bed load transport relations are significantly steeper for the total stress approach whereas they are similar to the commonly used fractional wilcock and crowe wc transport model for the effective stress approach this similarity in the relations allows the wc model developed for lower gradient streams to be used in combination with an effective shear stress approach in steep mountain streams

size and distance of travel of unconstrained clasts on a streambed we have examined the relation between the mean distance of movement during individual flood events and the mean particle size of unconstrained clasts in gravel bed rivers distance of movement was scaled using the mean distance of movement of the median size group of the surface material size was scaled using the median b axis diameter of the subsurface material the scaled data are fitted with a nonlinear function clasts larger than the median of surface material exhibit a steep decline of mobility with an upper limit for mobility near di d50sub 10 smaller materials exhibit a less sensitive relation we suppose that trapping of small clasts affects their travel distance these results indicate that the movement of free surface stones is size preferred a subordinate analysis of free constrained and buried particles reveals that bed surface structure acts to reduce differential movement

grain size distributions of bed load inferences from flume experiments using heterogeneous sediment beds abstract the grain size fractions in the bedload transported over the five heterogeneous sediment beds of different values of bed roughness were computed from the flume experiments the existence of an entrapment factor associated with the sorting observed from the bed to active layer was modeled based on the modified critical shear stress to estimate the grain size fractions in the transport layer under given hydraulic conditions the efficiency of these models was tested with the observed data subsequently the patterns of observed grain size distributions in the transport layer were tested to identify the distributions developed in the active layer due to sorting using three probability density functions pdf such as log normal log hyperbolic and log skew laplace tests indicated that a log skew laplace distribution fitted best for 49 a log hyperbolic for 31 and a log normal for 20 out of forty five bedload samples collected under unidirectional flow with changes in flow discharge and bed roughness the results of this study would be useful to specify the grain size distributions in the bedload formed under different hydrodynamic conditions in various sedimentary environments

coarse bed material patch evolution in low order ephemeral channels abstract in river channel beds composed of a wide range of grain sizes the bed material is often arranged in discrete patches discernable by relative texture these bed material patches are the primary source of entrainable coarse sediment within the channel system and their composition and size have been found to influence the composition and rate of sediment transport twelve coarse gravel cobble sediment patches distributed throughout the channel network within a 4 53 ha watershed in southeastern arizona were monitored for 2 years changes in patch area and grain size were measured and painted patch grains were monitored to confirm that patch grains were mobilized during flow individual coarse bed material patches exhibited variable persistence during flows with return frequencies ranging from approximately 1 year to 4 6 years while no patch fully dispersed during the study period two new patches formed most coarse patches remained relatively stable in area and grain size distribution despite the entrainment of patch grains as lost grains were sufficiently replaced with sediment from upstream because of the grain replacement process and the effect of other sediment supply dynamics the changes in patch area and grain size distribution display a complex relationship with the magnitude of predicted grain mobilization within each patch results indicate that relative stability varies from patch to patch influenced by the balance of patch grains transported out of the patch and the deposition of new grains into the patch predictive models of coarse sediment transport and yield that assume the channel bed is a fixed source of sediment supply may not adequately capture the sediment dynamics within patchy channel beds and should be used with caution when applied to these environments due to the possibility of patch instability as documented in this study

time and the rivers flowing fluvial geomorphology since 1960 fluvial geomorphology has been the largest single subdiscipline within geomorphology for many decades fluvial geomorphic expertise is integral to understanding and managing rivers and to developing strategies for sustainable development this paper provides an overview of some of the significant advances in fluvial geomorphology between 1960 and 2010 with respect to conceptual models fluvial features and environments being studied tools used by fluvial geomorphologists geomorphic specialty groups within professional societies journals in which fluvial geomorphic research is published and textbooks of fluvial geomorphology during this half century fluvial geomorphology broadened considerably in scope from a focus primarily on physical principles underlying process and form in lower gradient channels with limited grain size range to a more integrative view of rivers as ecosystems with nonlinear behavior and great diversity of gradient substrate composition and grain size the array of tools for making basic observations analyzing data and disseminating research results also expanded considerably during this period as did the diversity of the fluvial geomorphic community

observations of bedload movement bar development and sediment supply in the braided ohau river relative bedload transport rate and hydraulic parameters were measured on two occasions in a reach of the braided gravel bedded ohau river each reach contained a deep fast flowing chute leading to an area of diverging shallow flow which contained a middle bar the measurements are self consistent and indicate that where flow is concentrated in a deep chute shear stress is high but where flow diverges depth slope and shear stress decrease in the first survey the bed was scoured in the chute and sediment transport rates were high but where flow diverged sediment transport rate decreased it appears that deposition leads to bar growth bar growth in turn reduces slope and depth deposition is encouraged and the bar continues to grow vertically laterally and upstream in the second survey no sediment transport was observed despite hydraulic conditions very similar to the first survey the absence of sediment transport is attributed to the cessation of sediment supply to the river channel

model experiments on mobile paved gravel bed streams laboratory experiments which model streams with poorly sorted gravel beds at reduced scale reveal that pavement is a mobile bed phenomenon it acts to decrease the inherent difference in mobility between large and small grains by overrepresenting the percentage of large grains exposed to the flow pavement can coexist with the motion of all available grain sizes because motion is sporadic so that at any given time only a small percentage of surface grains are actually in motion particles in the immediate subpavement are only occasionally moved and deeper particles are hardly ever moved the experiments were conducted at constant discharges they provide accurate quantitative models of two field streams in that they obey the same bedload law as field data both sediment feed and recirculating configurations were utilized the only systematic difference between the two is in the behavior of the finer grains

equal mobility of gravel in streams the remains of the day 1 the concept of equal mobility of gravel transport is 2 decades old the weak form of the hypothesis states that in order to transport the coarse half of the mean annual gravel load through a river reach at a rate equal to the fine half the coarser material must be overrepresented on the bed surface giving rise to a mobile bed armor the degree of mobile bed armoring necessary to accomplish this diminishes with increasing bed shear stress the strong form of the hypothesis states that the grain size distribution of the gravel portion of the bed load should be similar to that of the substrate and finer than that of the surface layer here the hypothesis is subjected to a rigorous test in the laboratory under controlled conditions which are nevertheless chosen to be as representative as possible of actual field conditions the grain size distributions used in the experiment included both model gravel and model sand at the end of the experiment the entire surface layer and a significant depth of substrate were removed from an entire reach of the channel and sieved the results of the experiment confirmed the weak form of equal mobility the surface layer was significantly coarsened compared with the bed load even when the sand was excluded from the size distributions the strong form of equal mobility was also supported by the experiment in that the size distribution of the gravel substrate was nearly identical to the size distribution of the gravel portion of the load the gravel substrate was however slightly but measurably coarser than the gravel load a tendency that has been observed in the field in cases for which the strong form is not satisfied

sedimentological and structural evolution of the arabian continental margin in the musandam mountains and dibba zone united arab emirates the northernmost extremity of the oman mountains the musandam peninsula is composed of an allochthonous sequence of permian to middle cretaceous shelf carbonates these are separated from ophiolitic rocks to the south by a northeast southwest trending belt known as the dibba zone this structurally complex belt is composed of allochthonous slope and basin facies sediments haybi volcanic rocks oman exotic limestones sub ophiolitic metamorphic rocks and ultra mafic slices lithofacies correlation confirms that fragmentation and rifting of a vast east facing carbonate platform occurred in middle to late triassic time resulting in the establishment of a shelf edge and small ocean basin this margin was typified from northwest to southeast by ooid skeletal lime sand shoals or small bioherms on the shelf edge a bypass foreslope of well laminated periplatform ooze and basin margin accumulations of carbonate turbidites or debris flows the shelf edge now coincides with the northern boundary of the dibba zone and appears to have remained stationary from middle triassic to late jurassic time periods of arrested carbonate sedimentation on the platform either because of exposure late triassic and middle cretaceous or because of drowning late jurassic are represented in the basin by starved sedimentation and deposition of radiolarian cherts a spectacular platform margin collapse occurred in the middle and late cretaceous as represented by massive conglomerates with clasts as young as albian above an unconformity that progressively removed all of the lower cretaceous the tethyan basinal and ophiolitic rocks of the dibba zone were emplaced from the east southeast during the turonian to lower maastrichtian after emplacement of these allochthonous units compressional deformation in the mid tertiary resulted in large scale open whaleback folds with wavelengths as much as 15 km generally with north south axes in places these folds which affect the complete shelf and allochthonous sequences are overturned toward the west and thrusting has caused previously lower tectonic units of the late cretaceous stacking order to be thrust over previously higher tectonic units thus reversing the late cretaceous tectonostratigraphy the maximum amount of translation on the later thrusts is in excess of 5 km on the hagab thrust where the complete shelf carbonate sequence of the musandam mountains has been thrust west northwest over the previously higher hawasina and haybi thrust sheets the tertiary folding and thrusting can be correlated in time and space with the zagros fold belt of southwestern iran

models for sediment yield in mountainous greek catchments abstract in this study we explore the controls over suspended sediment yield in 11 stations situated along six major rivers of western northern greece arachthos achelooos evinos aoos kalamas and aliakmon values of area specific sediment yield for these stations come from reanalysis of existing records by adaptation of the broken rating curve concept and range from 140 to 2300 t km 2 y 1 we investigate the correlations among suspended sediment yield values and many geomorphic topographic morphometric textural tectonic geological lithological and climatic precipitation runoff characteristics of the corresponding basins along with land cover variables and rusle factors ls r k and c rusle from maps of the european soil data center we find the principal controls to be slope and lithology followed by precipitation runoff and landslide frequency factors such as ground cover percentage of barren land within the basin and alluviation of the river have also some relevance with the use of stepwise multiple regression analysis we build a model that employs three variables slope in percent precipitation mean annual in mm and lithology as percentage of the easily erodible geological formations within the catchment where the contribution of lithology is an additive term to the slope precipitation power relationship the proposed model achieves good statistics nse 0 84 from the other models tested with our data set bqart performs well while rusle2015 of the esdc performs poorly

critical discharge for entrainment of poorly sorted gravel entrainment criteria for gravel sized particles on river beds are usually defined in terms of shear stress but some workers have proposed that critical discharge relationships are more reliable and more convenient the critical shear stress in poorly sorted gravels is known from recent work to depend much more on relative than absolute grain size it is shown that this effect can be included in a semi theoretical equation for the critical unit discharge to move individual grain sizes in a poorly sorted bed comparisons with published data on critical discharges in a variety of rivers show that both the sensitivity of critical discharge to grain size and the absolute levels of critical discharge are predicted quite well however any prediction of critical discharge is sensitive to the assumptions made first about flow resistance and secondly about the critical stress to move average sized particles

incipient motion of sand gravel sediment mixtures experiments on the incipient motion of gravel and sand mixtures of 0 100 10 90 25 75 45 55 and 100 0 percent ratios of gravel and sand respectively were made in a laboratory flume a series of transport experiments was made for each of the five sediment beds and the critical shear stress for motion was calculated for 12 size ranges by interpolating or extrapolating the bed shear stress for a very small transport rate the sand in each of the five bed mixtures began to move at nearly the same bed shear stress all gravel sizes began to move at nearly the same bed shear stress in the 100 gravel experiments but in the sand gravel experiments the gravel showed an increase in critical shear stress with increasing size reasons for this change in the initiation of motion of the gravel from the 100 gravel to the sand gravel mixtures may result from the abundant sand sized sediment inhibiting the formation of a coarse bed surface layer in the sand gravel experiments

frequency and magnitude of bedload transport in a mountain river magnitude and frequency of bedload transport was examined in the lainbach river bavaria using magnetically tagged particles during the study 18 small to moderate events and one major event occurred about 1 per cent of the flow period exceeded the entrainment threshold and at least once every year about 50 per cent of the tagged particles were mobile themajor event which occurred during the study period resulted in the deposition of a thick layer of sediment in parts of the channel and passive burial of most of the recovered particles the step pool pattern which characterized the study site prior to the large event was obliterated however the channel recovered quickly and has returned to a new step pool pattern the event changed the boundary conditions by increasing the availability of loose sediment and creating higher river bed slopes in reaches between breached check dams as a result movement of individual particles measured for events of both the same magnitude and duration occurring before and after the large event yielded different values for events which occurred after the large event the range and the mean distance of movement were about ten times higher

the maastrichtian transgression onto the northwestern flank of the proto oman mountains sequences of rudist bearing beach to open shelf facies

bed load transport of mixed size sediment fractional transport rates bed forms and the development of a coarse bed surface layer fractional transport rates bed surface texture and bed configuration were measured after a mixed size sediment had reached an equilibrium transport state for seven different flow strengths in a recirculating laboratory flume fractional transport rates were also measured at the beginning of each run when the bed was well mixed and planar the start up observations allow us to describe the variation of fractional transport rates with bed shear stress for a constant bed surface texture and bed configuration the start up and equilibrium observations together allow for the first time an unambiguous description of the mutual adjustment among the transport the bed configuration and the bed surface as the transport system moves toward equilibrium we find that a substantial interaction exists among the transport bed surface and bed configuration bed forms and a coarse surface layer coexist over a range of bed shear stress under some flow conditions the size and shape of the bed forms are controlled by the presence of the coarse surface layer at higher flows the coarse surface layer is eliminated by scour in the lee of the bed forms if the bed surface is defined as that over which the bed forms move a coherent relation between the bed surface texture and the transport grain size distribution may be defined at equilibrium the transport rates of all fractions were not equally mobile defined as identical transport and bed grain size distributions although equal mobility was approached for runs in which the bed shear stress was more than twice that for initial motion of the mixture under some flow conditions the transport was observed to adjust away from equal mobility as the bed adjusted from a well mixed start up condition to an equilibrium state development of a partial static armor wherein some individual grains become essentially immobile even though other grains in the same fraction remain in transport is suggested to explain these adjustments between the transport and bed surface grain size distributions constraints on equilibrium mixed size sediment transport are defined the special conditions for which equal mobility must hold and the relevance to natural conditions of flume results and the equal mobility concept are discussed

geomorphology and endangered fish habitats of the upper colorado river 2 linking sediment transport to habitat maintenance alluvial reaches of the colorado river near grand junction colorado provide important habitat for the endangered colorado squawfish this paper examines recent changes in the geomorphology of the colorado river and addresses the question of what can be done to improve existing fish habitats observations of channel change during periods of above average runoff from 1993 through 1995 indicate minor scour and fill of the main channel but more significant scour and enlargement of side channel and backwater habitats and flushing of fine sediment from the bed modeled relations between discharge and dimensionless shear stress indicate that the threshold of bed load transport 0 03 occurs at about half the bank full discharge these flows are exceeded about 26 days per year on average the bank full discharge produces an average of 0 047 and is exceeded about 8 days per year the width and depth of the channel thus appear to be set by a discharge that produces an average boundary shear stress of 1 5 times greater than the critical shear stress the effective discharge is slightly less than the bank full discharge and approximately 80 of the total sediment load is carried by the highest 10 of all discharges

micritic cement in microborings is not necessarily a shallow water indicator abstract intragranular micritic cement has been observed in microborings from deep sea sedimentary particles pteropod shells depths 528 m to 871 m it is particularly conspicuous in depositional environments such as the blake plateau such cementation may be concurrent and analogous to the formation of intergranular deep sea cement it can occur at such energy levels where particle to particle contacts do not persist for sufficient time to allow intergranular cementation

analysis of bedload transport characteristics of idaho streams and rivers field data are essential in evaluating the adequacy of predictive equations for sediment transport each dataset based on the sediment transport rates and other relevant information gives an increased understanding and improved quantification of different factors influencing the sediment transport regime in the specific environment data collected for 33 sites on 31 mountain streams and rivers in central idaho have enabled the analysis of sediment transport characteristics in streams and rivers with different geological topographic morphological hydrological hydraulic and sedimentological characteristics all of these streams and rivers have armored poorly sorted bed material with the median particle size of surface layer coarser than the subsurface layer the fact that the largest particles in the bedload samples did not exceed the median particle size of the bed surface material indicates that the armor layer is stable for the observed flow discharges generally bankfull or less and in some cases two times higher than bankfull discharge the bedload transport is size selective the transport rates are generally low since sediment supply is less than the ability of flow to move the sediment for one range of flow discharges or the hydraulic ability of the stream is insufficient for entrainment of the coarse bed material detailed analyses of bedload transport rates bedload and bed material characteristics were performed for each site the obtained results and conclusions are used to identify different influences on bedload transport rates in analyzed gravel bed rivers copyright 2008 john wiley sons ltd

experiments on bar formation in a straight flume 2 graded sediment laboratory experiments have been carried out in a large laboratory flume using a strongly bimodal sediment mixture in a range of flow conditions such that the initially flat bed of the flume became unstable enhancing the development of alternate bars in order to elucidate the effect of grain sorting the present experiments are compared with a previous set of experiments performed in the same flume under similar hydraulic conditions but using a nearly uniform sand with a mean geometric grain diameter equal to that characterizing present experiments the comparison suggests that sediment heterogeneity may appreciably affect bed form characteristics the development of smallscale ripples and mesoscale dunes sediment waves tended to be inhibited thus allowing a decrease in flow resistance owing to the bimodal character of the adopted mixture at low values of the bed shear stress a condition of partial transport was attained for which only the finer grained portion of the mixture was observed to move while the coarsergrained fractions remained essentially immobile throughout the experimental run however complete mobilization of all size fractions was observed to occur in runs carried out at higher slopes i e at higher bed shear stress in order to generate an alternate bar pattern selective transport of individual grain size fractions coupled with the characteristic bar topography pattern led to an intense longitudinal sorting which accreted the coarser particles on bar crests furthermore bar migration caused through scour and fill a significant vertical sorting as a consequence of these sorting processes and in accordance with previous experimental observations bar height turns out to be invariably damped with respect to uniform sediment experiments the trend exhibited by the wavelengths is less clear and suggests that in the present experiments sorting effects do not enhance the clear shortening of bar wavelengths typically observed in other series of flume experiments carried out with weakly bimodal mixtures

a model to predict the evolution of a gravel bed river under an imposed cyclic hydrograph and its application to the trinity river 1 major changes in the morphology of the trinity river in california such as narrowing of the cross section and sedimentation of fine sediment in pools occurred after the closure of a system of dams these changes caused a dramatic reduction in the salmonid population and a resulting decline of the fishery gravel augmentation regulated flood releases and mechanical channel rehabilitation are currently being implemented to help restore the aquatic habitat of the river the present paper describes a tool named the spawning gravel refresher for designing and predicting the effects of gravel augmentation in gravel bed rivers the tool assumes an imposed cycled hydrograph the model is calibrated and applied to the regulated reach of the trinity river in four steps 1 zeroing runs to reproduce conditions of mobile bed equilibrium as best can be estimated for the predam trinity river 2 runs to compare the predictions with the results of previous studies 3 runs at an engineering time scale to reproduce the effects of the dams and 4 runs to design gravel augmentation schemes in the fourth group of runs the combined effects of engineered flood flow releases and gravel augmentation are predicted at an engineering time scale the model indicates that the fraction of fine sediment in the surface layer and in the topmost part of the substrate should decrease when subjected to these two restoration measures with a consequent improvement of the quality of the spawning gravel

diagenetic aspects of tertiary carbonates west of the northern oman mountains united arab emirates abstract to the south of al ain united arab emirates uae lies the large mountain of jebel hafit it which consists of foredeep basin sediments which face the obducted allochthonous formations of neo tethys oceanic crust and associated deep marine sediments i e semail ophiolites and hawasina sediments the foredeep sediments formed during the early eocene miocene they are considered to be the main paleogene marine exposure in eastern arabia they are made up of limestones and marls and constitute four main rock units namely rus dammam asmari and fars formations respectively from base to top the rus late early eocene is made up of fossiliferous dolomitized limestone the dammam formation middle to late eocene conformably overlies the rus formation and comprises shale marl and limestone the asmari formation early to middle oligocene conformably overlies the dammam formation and is made up of nodular limestone this is the first in depth study of diagenesis within the dammam formation the petrographic investigation of this work reveals that the original textural and compositional characteristics of the dammam formation were modified by cementation micritization neomorphism dolomitization and to a lesser extent dissolution compaction dedolomitization and silicification cementation with calcite and less commonly dolomite and iron oxides in addition to dissolution effects are more evident in the upper part of the dammam formation silicification and dolomitization are also extensive in the upper part of the dammam formation shallow burial of the dammam formation sediments in a partially closed system resulted in their compaction and consequent cementation with calcite these carbonates display a wide spectra of diagenetic features reflecting different environments micritization and early phases of cementation with calcite isopachous calcite likely occurred in a marine phreatic environment dolomitization and silicification most likely took place in the marine meteoric mixing environment early phases of dissolution cementation neomorphism and dedolomitization also occurred within the phreatic environment

experiments on the effect of hydrograph characteristics on vertical grain sorting in gravel bed rivers 1 desert ephemeral gravel bed streams typically have bed surfaces that are relatively unarmored compared to the substrate below while gravel bed streams in humid and snowmelt areas typically have well armored surfaces the degree of armoring can be characterized in terms of an armor ratio defined as the ratio of the surface median size to the substrate median size a set of field data shows desert ephemeral gravel bed streams with armor ratios ranging from 0 5 to 2 4 and with an average value of 1 2 the armor ratio of snowmelt fed gravel bed streams in the same set ranges from 2 to 7 with an average value of 3 4 the reason for this difference is sought in terms of differing hydrological characteristics and sediment supply regimes thirteen experiments were conducted to study the formation of armoring under a range of hydrological conditions the experiments have two limiting cases a relatively flat hydrograph that represents conditions produced by continuous snowmelt and a sharply peaked hydrograph that represents conditions associated with flash floods all constant hydrograph experiments developed a well armored structured surface while short asymmetrical hydrographs did not result in substantial vertical sorting all symmetrical hydrographs show some degree of sorting and the sorting tended to become more pronounced with longer duration sediment supply appears to be a first order control on bed surface armoring while the shape of the hydrograph plays a secondary role

modelling cross shore intensive sand transport and changes of bed grain size distribution versus field data abstract the study is focused on the cross shore transport of size graded sediment under combined wave current flow in the intensive flow regime the mathematical method for the description of hydrodynamic processes and sediment transport is adapted from the approach of kaczmarek and ostrowski coast eng 45 2002 1 for non graded sediment the theoretical model of vertical structure of sediment concentration as well as vertical mixing and sorting is presented the model of transport of graded sediment accounts for two directional cross shore sand flux the first component of this flux is directed onshore and results from wave asymmetry effects while the second one is directed seawards and is caused by undertow the vertical structure of this two directional sediment flux and its variability along a cross shore profile is a reason for segregation of grains in a horizontal direction this horizontal sorting of sand is theoretically modelled using the present approach a concept of the carpet of sorted sediments is implemented to reproduce the segregation of sediment in time and to assess the influence of grain size changes on short term evolution of the cross shore profile the results of computations are compared with the large scale laboratory data from the literature and with field measurements carried out by the authors the agreement between the model results and the experimental data is found to be very good particularly it has been theoretically shown that the observed in situ bimodal grain size distributions result from two directional sediment fluxes on the cross shore profile

bed load texture in an alpine gravel bed river the spatial and temporal variations in bed load texture measured in a gravel bed river with a helley smith sampler are compared with its bed material texture most measurements were undertaken at low excess shear stress with low bed load discharge over an armored bed cross sectionally averaged fractional bed load discharge increases with water discharge but the explanation of the variance in fractional discharge is low 20 40 cross sectional distribution of shear velocity explains in part the spatial variation in bed load texture because local hydraulic parameters are weak predictors of fractional bed load discharge for the granule pebble range at nonequilibrium conditions it reinforces the hypothesis that this size range which comprises the bulk of bed load derives from upstream sources temporal variations in the cross sectional distribution of bed load texture are shown to depend on variations in bed topography and local shear stress we demonstrate that the dominance of granule pebble fractions is in part related to the hiding behavior of smaller fractions

the concept of transport capacity in geomorphology the notion of sediment transport capacity has been engrained in geomorphological and related literature for over 50 years although its earliest roots date back explicitly to gilbert in fluvial geomorphology in the 1870s and implicitly to eighteenth to nineteenth century developments in engineering despite cross fertilization between different process domains there seem to have been independent inventions of the idea in aeolian geomorphology by bagnold in the 1930s and in hillslope studies by ellison in the 1940s here we review the invention and development of the idea of transport capacity in the fluvial aeolian coastal hillslope debris flow and glacial process domains as these various developments have occurred different definitions have been used which makes it both a difficult concept to test and one that may lead to poor communications between those working in different domains of geomorphology we argue that the original relation between the power of a flow and its ability to transport sediment can be challenged for three reasons first as sediment becomes entrained in a flow the nature of the flow changes and so it is unreasonable to link the capacity of the water or wind only to the ability of the fluid to move sediment secondly environmental sediment transport is complicated and the range of processes involved in most movements means that simple relationships are unlikely to hold not least because the movement of sediment often changes the substrate which in turn affects the flow conditions thirdly the inherently stochastic nature of sediment transport means that any capacity relationships do not scale either in time or in space consequently new theories of sediment transport are needed to improve understanding and prediction and to guide measurement and management of all geomorphic systems

a conceptual model for meander initiation in bedload dominated streams a simple analytic model is presented relating local sediment transport capacity to variance in the transverse shear stress distribution in a stream channel the model is used to develop a physically based conceptual model for the initiation of meandering in straight bedload dominated streams as a result of a feedback mechanism the feedback maximizes the cross sectional shear stress variance and in order to achieve stability ultimately minimizes the energy slope at repeated locations along the channel subject to steady state mass flux and the stability of the channel boundary these locations develop into pools in a fully developed meandering channel they represent attractor states wherein sediment continuity is satisfied using the least possible energy expenditure per unit length of channel however since the cross sectional geometry of a pool and the adjacent bar is asymmetric these attractor states are only conditionally stable requiring strong curvature induced secondary circulation to maintain their asymmetry between two successive pools a stream occupies a metastable higher energy state corresponding to a riffle that requires greater energy expenditure per unit length of channel to transport the same volume of sediment the model we present links processes at the scale of a channel width to adjustments of the channel sinuosity and slope at the scale of a channel reach we argue that the reach scale extremal hypotheses employed by rational regime models are mathematical formalisms that permit a one dimensional theory to describe the three dimensional dynamics producing stream morphology our model is consistent with the results from stream table experiments with respect to both the rate of development of meandering and the characteristics of the equilibrium channel morphology copyright 2006 john wiley sons ltd

friction angle measurements on a naturally formed gravel streambed implications for critical boundary shear stress we report the first measurements of friction angles for a naturally formed gravel streambed for a given test grain size placed on a bed surface friction angles varied from 10o to over 100o friction angle distributions can be expressed as a function of test grain size median bed grain size and bed sorting parameter friction angles decrease with increasing grain size relative to the median bed grain size and are a systematic function of sorting with lower friction angles associated with poorer sorting the probability distributions of critical shear stress for different grain sizes on a given bed surface as calculated from our friction angle data show a common origin but otherwise diverge with larger grains having narrower and lower ranges of critical shear stresses the potential mobility of a grain as defined by its probability distribution of critical shear stress may be overestimated for larger grains in this analysis because our calculations do not take into account the effects of grain burial and altered near bed flow fields

dolomitization and chertification of the early eocene rus formation in abu dhabi united arab emirates abstract the early eocene carbonates of the rus formation in the jabal hafit area near al ain united arab emirates were sampled to study their diagenetic history these carbonates were cyclically deposited in a shallow water environment alternating with marls or marly limestones and are characterized by extensive dolomitization and chertification with associated glauconitization the cyclic nature of sedimentation suggests that deposition was eustatically driven the diagenetic history of the limestones proceeded through the following path 1 marine cementation of allochems concomitant with formation of micrite envelopes 2 micritization of peloids ooids and skeletal grains 3 neomorphism of formerly high mg calcite and aragonite grains to low mg calcite 4 partial to complete dolomitization 5 partial chertification of both calcite and dolomite 6 glauconitization of chert 7 fracturing during shallow burial and 8 precipitation of late coarse calcite spar or mosaic and saddle baroque dolomite spar filling voids and fractures porosity is virtually nil in these rocks except for infrequent unfilled fractures vugs and oomolds due primarily to cementation and chertification biogenic grains are abundant in the limestones with nummulites sp alveolinid and miliolid foraminifera and crinoid ossicles and other echinoderm fragments being most common the tests of nummulites sp are commonly replaced by length fast chalcedony fibers which are occasionally later replaced by glauconite spherulitic and zebraic chalcedony and more rarely megaquartz occur as void filling cements and fringing chalcedonic fibers frequently rim the tests of skeletal grains all except the fringing chalcedonic fibers were subject to glauconitization prior to the chertification process is an extensive dolomitization period rhombic and sucrosic dolomite partially to completely replaced calcite at a relatively early diagenetic stage silicification caused the replacement of calcite by chert at a much more rapid rate than that of dolomite which was found floating within a chertified matrix fractures occurred both early and late in the rus and are usually filled by a late coarse mosaic calcite spar or coarse mosaic and saddle dolomite spar in completely dolomitized samples

on why gravel bed streams are paved bedload transport in poorly sorted gravel bed streams downstream of dams is considered bedload and typical bed material subpavement size distributions are observed to be similar it follows that the coarse half of the subpavement moves through a reach at a rate near that of the fine half since coarser grains are intrinsically less mobile than fine grains it follows that some mechanism must act to nearly equalize mobility it is hypothesized that the pavement seen in gravel bed streams at low flow is in fact in place during typical transport events capable of moving all available sizes this pavement can provide the equalizing mechanism by exposing proportionally more coarse grains to the flow field data are used to quantify this concept and to develop a predictive relation for river pavement the model indicates that pavement should be absent in most sand bed streams in agreement with observation

maastrichtian to early tertiary stratigraphy and palaeogeography of the central and northern oman mountains abstract maastrichtian to tertiary sedimentary rocks outcrop extensively around the periphery of the oman mountains they form part of a geologically distinct suite of strata deposited after obduction of the semail ophiolite and thrusting of the hawasina and sumeini imbricates onto the eastern edge of the arabian plate the lithostratigraphy of maastrichtian and early tertiary rocks of the central and northern oman mountains is revised and a number of new formations are erected the proto oman mountains were emergent in the early maastrichtian and were subject to subaerial erosion and weathering nw and w of the mountains gradual subsidence followed during the maastrichtian allowing for formation of a transgressive onlapping sequence represented by the qahlah fluviatile to shallow marine terrigenous clastics and simsima shallow shelf carbonate formations more rapid subsidence ne of the mountains produced fan delta and submarine debris flow turbidite apron sequences comprising the al khawd and thaqab formations respectively a low angle unconformity separates tertiary strata from older units during the palaeogene basinal and slope facies with debris flows and turbidite sequences were deposited directly upon the unconformity surface in rapidly subsiding basins nw muthaymimah formation and nne ruwaydah formation of the oman mountains elsewhere shallow carbonate shelf facies were extensively developed in less rapidly subsiding areas during the palaeogene the palaeocene and early eocene is represented by the jafnayn limestone formation this is succeeded and overlapped by a variety of later eocene units ene and e of the mountains early eocene regression is marked by restricted facies of the rusayl formation overlying the rusayl formation are shallow open shelf limestones of the seeb formation which is rich in alveolinid and nummulitic foraminifera on the arabian side of the mountains the rusayl formation is not developed and the jafnayn formation is succeeded either by the seeb formation or fine grained faunally restricted limestones and marls of the fahud beds which represent intra shelf facies

input and output mass flux correlations in an experimental braided stream implications on the dynamics of bed load transport through the development of a model experiment it is shown that there exists a correlation between input and output sediment fluxes in a micro scale braided stream that remains valid regardless of the stability of the braided river this correlation has some important consequences on the mechanics of bed load transport by braided rivers it enables the definition of both a dimensionless stream power and a dimensionless transport efficiency these dimensionless variables in turn permit the definition of a braided river stability criterion with regard to bed load transport the existence of such a correlation also suggests that the average critical shear stress or slope of motion may depend on the flux of mass input to the system using these findings together with a one dimensional exner equation for the conservation of mass a kinematic wave equation for the average evolution of the riverbed is eventually derived and its significance analyzed

fluvial transport of sand and gravel mixtures with bimodal size distributions abstract initiation of motion and fractional transport rates of sediments with bimodal size distributions were measured in a laboratory channel and in a natural channel transport experiments were conducted with unimodal 100 sand and 100 gravel bed sediments and three bimodal mixtures of the two sediments 10 gravel 90 sand 25 gravel 75 sand and 45 gravel 55 sand in the bimodal sediment beds the critical shear stress for the initiation of motion showed very little change with grain size for the sand sizes but increased with grain size for the gravel sizes for low flow strengths only the sand sizes were in transport while for the highest flow strengths the bed load sediment size distribution approached that of the bed material

influence of the sediment supply texture on morphological adjustments in gravel bed rivers the role played by the texture of the sediment supply on channel bed adjustments in gravel bed rivers is poorly understood to address this issue an experimental campaign has been designed flume experiments lasting 96 h in a 9 m long 0 60 m wide have been performed with different sand gravel mixtures as feed textures the response of the surface texture has been found to be highly dependent on the grain size distribution of the feed when the feed texture included gravel the finest fractions of the sediment supply infiltrate beneath the surface conversely sand remains on the surface when the feed texture lacks gravel this different textural response becomes obscured when water discharge increases further the sediment transport rate approaches the feed rate differently depending on the content of gravel in the feed texture when a small proportion of gravel is part of the feed texture bed load transport rate asymptotically approaches the feed rate however when a significant fraction of gravel is part of the feed grain size distribution bed load transport rate approaches the feed rate by following an oscillatory path these findings have been verified in terms of a one dimensional numerical model this modeling reveals that the higher the differences in mobility among the grain sizes contained in the feed texture the more evident is the nonasymptotic transient trend toward equilibrium

frequency distribution of river bed materials the size distribution of river bed material plays an important role in the study of fluvial hydraulic processes it is not always easy to sample the river bed material for the determination of its size distribution but knowledge of the frequency distribution and of bed material sizes can be used to predict its size distribution therefore data on bed material size distributions of 63 streams from 10 different countries have been analysed to determine the frequency distribution which can be best fitted to them the log normal distribution cannot be fitted to the bed material mixtures when the entire range of sizes is considered the method of power transformation is found to normalize these mixtures relationships have been proposed between the parameters of the normalization and the stream slope these relations can be used to predict the size distribution of the river bed material

nearly pure sorting waves and formation of bedload sheets bedload sheets are coherent migrating patterns of bed material recently observed both in flume studies and in field streams with beds of coarse sand and fine gravel this newly recognized feature is inherently associated with the heterogeneous character of the sediment and consists of sorting waves with distinct coarse fronts only one or two coarse grains high the question of the formation of bedload sheets poses an interesting and peculiar stability problem for the grain size distribution sorting waves are essentially two dimensional migrating perturbations associated with variations of this distribution we show that their growth is strictly associated with grain sorting in fact the latter gives rise to perturbations of bedload transport which drive small perturbations of bottom elevation the amplitude of which scales with grain size the sorting wave also induces spatial variations of bottom roughness and consequently alters the fluid motion which conversely exerts a spatially varying stress on the bed the feature of bedload sheets which allows them to be distinguished from dunes over beds with coarse sand or fine gravel is then the fact that sorting is the dominant effect controlling their growth rather than being a relatively small perturbation of the mechanism which gives rise to dunes in the case of uniform sediment the requirement that perturbations should not alter the sediment budget leads to an integral condition which gives rise to an integro differential mathematical problem with the help of recently developed bedload relationships suitable for mixtures as well as appropriate modelling of turbulent channel flow over a bed with spatially periodic perturbations of bottom elevation and roughness we are able to derive a general dispersion relation which can be readily solved in terms of undisturbed size densities in the form of sums of dirac distributions perturbations are found to be unstable within a range of wavenumbers depending on the relative roughness and froude number we show that when the effects of perturbations of bottom elevation are neglected the unstable region corresponds to the range of conditions where the bottom stress leads bottom roughness a range distinct from that which characterizes the formation of dunes this result is given a physical explanation which depends crucially on the deviation from equal mobility of different grain sizes in the surface layer the effect of perturbations of bottom elevation is however not negligible when the bottom roughness is fairly large compared to depth in the latter case perturbations of bottom elevation and of bottom roughness are equally important and gravel sheets are not easily distinguished from small amplitude dunes comparison with the field observations of whiting et al 1985 1988 is satisfactory insofar as the bedload sheet mode is unstable under the conditions of the experiments and the predicted wavelengths fall within the experimental range the laboratory observations of kuhnle southard 1988 on the other hand appear to fall within a range of bottom roughness where the observed bedforms do not exhibit features unambiguously distinct from those of small amplitude dunes

mobilization of coarse surface layers in gravel bedded rivers by finer gravel bed load 1 additions of sand to gravel beds greatly increase the mobility and flux of gravel however it is not known how additions of finer gravel to coarser gravel beds will affect the mobility of bed material here we examine the effect of fine gravel pulses on gravel bed material transport and near bed flow dynamics in a series of flume experiments bed material refers exclusively to sediment in the channel prior to the pulse introduction the observations indicate that fine sediment pulses tend to migrate downstream in low amplitude waves as the waves pass over the gravel bed the interstitial pockets in the bed material surface fill and coarse gravel particles are entrained this increases bed material transport rates and causes a distinct shift from a selective mobility transport regime where particles coarser than the bed material median 8 mm make up 30 of the load to an equal mobility transport regime where bed materials coarser than 8 mm and finer than 8 mm are transported in equal proportions the only possible source for this coarser bed load material is the sediment bed suggesting that portions of the coarse surface layer are being mobilized observations of near bed velocity and turbulence suggest that fine gravel pulses cause fluid acceleration in the near bed region associated with a reduction in the level of turbulence produced at the sediment boundary this accelerated fluid at the bed increases drag exerted on coarse surface layer particles promoting their mobilization our findings suggest that in general finer bed sediment not just sand can mobilize coarser sediment and that expressions for the influence of sand on bed mobility need to be generalized on the basis of grain ratios

jabal hafit anticline uae and oman formed by decollement folding followed by trishear fault propagation folding abstract creating three dimensional 3d models to replicate geological structures is crucial in discerning the geometry and kinematics of an orogen the jabal hafit anticline in the foreland of the al hajar mountains extends through oman and the united arab emirates and is a relatively simple and well exposed structure surprisingly previous studies of this anticline have presented conflicting interpretations regarding the strain field and the timing of deformation in this study a structural 3d geological model of the jabal hafit anticline is constructed and demonstrates that the anticlines geometry can be reproduced by a two phase model 1 flexural slip folding followed by 2 trishear fault propagation folding the trishear mode occurred due to a west dipping backthrust that propagated from the decollement to accommodate wsw directed shortening the different geometries of the various biostratigraphic layers indicate that anticline growth occurred during the late oligocene to early middle miocene this timing supports the recently established age for uplift of the al hajar mountains

stochastic prediction of sediment transport in sand gravel bed rivers classical deterministic bedload transport predictors are applied to sand gravel bed rivers the turbulent bed shear stress is modeled according to a probability distribution to obtain realistic bedload transport rates at incipient motion in extending the predictors to stochastic predictors for nonuniform sediment many parameters that represent near bed turbulence and the particle size distribution must be chosen the parameters that give realistic results are chosen by analyzing the results of a new experimental flume dataset with relatively large water depths choosing other combinations of parameters may give equal total bedload transport rates but at the cost of large errors in fractional transport rates attention is given to the hiding exposure phenomenon and a hindrance effect related to nonuni form sediment validation based on two independent field datasets shows that successful predictions of particle sizes near the threshold for motion are feasible using the stochastic approach while the deterministic approach gives successful predictions well above incipient motion

laboratory simulation of the salt weathering of schist 1 weathering of schist blocks in a seasonally wet tropical environment data describing sediment generation focusing on the temporal evolution of size gradation are required for the prediction of long term landform evolution this paper presents such data for the salt weathering of a quartz chlorite schist obtained from the ranger uranium mine in northern australia rock fragment samples are subjected to three different climate regimes 1 a dry season climate 2 a wet season climate both based on observations at the ranger site and 3 an oven drying sequence designed to test the sensitivity of the weathering process by exposing the rocks to more extreme temperatures two mgso4 salt solutions are applied one being typical of wet season runoff and the other a more concentrated solution salt solution is applied daily in the wet season experiments and once only at the beginning of the dry season experiments results of the experiments reveal four stages of weathering the kinetics of each stage are described and related to the formation of sediment of different sizes wet season climate conditions are shown to produce greater moisture variability and lead to faster weathering rates however salt concentrations in the wet season are typically lower and so when climate is combined with observed salt concentrations the dry and wet season experiments weather at approximately equal rates finally small variations in rock properties were shown to have a large impact on weathering rates leading to the conclusion that rock weathering experiments need to be carefully designed if results are to be used to help predict weathering behaviour at the landscape scale copyright 2006 john wiley sons ltd

virtual velocity of tracers in a gravel bed river using size based competence duration virtual velocity vi of river gravels is commonly used to determine sediment transport rates and gravel dispersion dynamics virtual velocity is calculated from tracer gravel step length data as the distance travelled divided by the duration of competence however no allowance is usually made for differences in competence duration according to grain size in this investigation vi of gravel tracer clasts for the river rede northumberland uk is calculated using a method that takes into consideration an approximation of size based competence duration although scaled transport distance data compared favourably to past studies it was the comparatively smaller clasts that tended to have lower vi in comparison to coarser clasts because of their longer competence duration contrasting with previously published research the key findings of the study serve as proof of concept and should be adopted in future studies that focus upon vi estimation

breakup and reestablishment of the armour layer in a large gravel bed river below dams the lower ebro changes in armour layer during floods under supply limited conditions are little known this paper describes the breakup and the reestablishment of the bed armour layer in the regulated gravel bed ebro river during a flooding period the study was conducted over a 28 km study reach from 2002 to 2004 the surface subsurface and bed load grain size distribution constitute the bases for the analysis of bed armouring dynamics the results indicate that the magnitude of floods controlled the degree of armouring of the river bed the initial mean armouring ratio was 2 3 with maximum values reaching 4 4 floods in the winter of 2002 2003 q8 caused the breakup of the armour layer in several sections this resulted in the erratic bed load pattern observed during the december 2002 flushing flow and in the increase in bed load transport during successive events most grain size classes were entrained and transported causing river bed incision the mean armouring ratio decreased to 1 9 in contrast during low magnitude floods in 2003 2004 q2 the coarsest fractions 64 mm did not take part in the bed load while finer particles were winnowed thus surface deposits coarsened as a result the armour layer was reestablished i e the mean armouring ratio increased to 2 3 and the supply of subsurface sediment decreased the supply and transport of bed material appear to be in balance in the river reach immediately below the dam in contrast the transport of medium and finer size classes in the downstream reaches was higher than their supply from upstream a phenomenon that progressively reduced their availability in the river bed surface hence the armour layer reworking

tectonic sedimentology sediment systems deciphering global to local tectonics tectonic sedimentology has broad appeal because it can be applied at many time and length scales such as sedimentary consequences of changing rates of plate creation at mid ocean ridges continent continent collisions plateaux uplift active plate margins extensional rift tectonics and the birth growth and death of individual folds and faults tectonic sedimentology deals with the direct influence of neotectonics on sedimentation and basin development and with the inverse problem of reconstructing the order and development of palaeotectonic structures this review attempts to show how the scope and importance of the subject has developed over the last decade and is divided into five themes i at the largest tectonic scale constraints on mid ocean ridge activity and continent continent collisions come from a precise chemical analyses of fluid inclusions in marine halite deposits dating back to ca 550 ma b sr isotopic ratios of marine phanerozoic calcitic fossils and c chemical composition of archaean and proterozoic banded iron formations ii at regional scales constraints on the timing and extent of continental plateau uplift incision and cratonic tilting are given by a palaeoaltimetry estimates from oxygen isotope depletion in carbonate palaeosols b radiometric dating of palaeowater table speleothems and c preferential river migration iii at basin scales catchment processes are emphasized as key controls on sediment flux from tectonic uplands to sedimentary basins the inadequacy of sediment transport algorithms based on tractive stress and flow power to describe erosion incision and sediment transport during the most formative catchment hydrological events is emphasized iv rates of basin scale fault and fold growth displacement death and basement uplift are provided by application of facies analysis and sequence stratigraphy to accurately dated sediments in sedimentary basins v the effects of changing climate and varying basin base level in modifying tectonic influences on erosion and sedimentation are examined in such cases experimental and numerical modelling using multi variate parameters of subsidence rate sediment supply and sea level change can shed light on the problem future developments will undoubtedly improve such models hopefully establishing full linkage and feedback between sediment water supply and changing climate within an overall tectonic framework that may itself be changing

sediment storage partial transport and the evolution of an experimental gravel bed under changing sediment supply regimes abstract the adjustment of a gravel bed during cycles of sediment storage was analyzed for a flume experiment designed to study the effects of episodic sediment supply regimes as the bed aggraded and degraded due to changes in sediment feed it developed a complex topography with bedforms at different scales e g pebble clusters bars sediment inputs increased bedload rates and promoted large changes in bed morphology without an external supply the bed armored which increased bed stability counteracted bed degradation and decreased bedload rates fully mobile gravel 2 8 mm was the only fraction that exhibited a deficit over the experiment preferential storage of coarse grains caused the development of a sediment wedge upstream and downstream fining on the bed surface the storage of sand was also significant 60 of feed probably because of infiltration e g in the upstream wedge and hiding effects promoted by bed armor and structures size selective transport caused a cumulative increase in bed slope which was likely to affect sediment transport capacity the large variability in bedload rates for same levels of bed storage indicated that sediment availability and bed state were the main controls on sediment transport regime we provide empirical evidence that cycles of aggradation and degradation caused by changes in sediment feed upstream condition bed composition and topography and the rate and texture of sediment output