sediment dispersal and quantitative stratigraphic architecture across an ancient shelf two large 200 to 300 km near continuous outcrop transects and extensive well log data ca 2800 wells allow analysis of sedimentological characteristics and stratigraphic architecture across a large area ca 60 000 km2 of the latest santonian to middle campanian shelf along the western margin of the western interior seaway in eastern utah and western colorado usa genetically linked depositional systems are mapped at high chronostratigraphic resolution ca 0 1 to 0 5 ma within their sequence stratigraphic context in the lower part of the studied interval sediment was dispersed via wave dominated deltaic systems with a compound clinoform geomorphology in which an inner wave dominated shoreface clinoform was separated by a muddy subaqueous topset from an outer clinoform containing sand poor gravity flow deposits these strata are characterized by relatively steep net regressive shoreline trajectories 0 1 with concave landward geometries narrow nearshore belts of storm reworked sandstones 2 to 22 km wide offshore mudstone belts 250 km and relatively high sediment accumulation rates ca 0 27 mm year 1 the middle and upper parts of the studied interval also contain wave dominated shorefaces but coeval offshore mudstones enclose abundant isolated tide influenced sandstones that were transported sub parallel to the regional palaeoshoreline by basinal hydrodynamic tidal circulation these strata are characterized by relatively shallow net regressive shoreline trajectories 190 km and relatively low sediment accumulation rates ca 0 11 mm year 1 the change in shelfal sediment dispersal and stratigraphic architecture from i compound clinoform deltas characterized by across shelf sediment transport to ii wave dominated shorelines with isolated tide influenced sandbodies characterized by along shelf sediment transport is interpreted as reflecting increased interaction with the hydrodynamic regime in the seaway as successive shelfal depositional systems advanced out of a sheltered embayment utah bight this advance was driven by a decreasing tectonic subsidence rate which also suppressed autogenic controls on stratigraphic architecture

longitudinal changes in the size and shape of stream bed material evidence of variable transport conditions summary the pattern of downstream changes in particle size and shape is used to identify dominant transport conditions in a basin with two main lithologies having distinct spatial distributions grain size decreases exponentially and roundness increases geometrically in the sandstone group but shale particles show no such changes largely because shale is supplied discontinuously below headwater reaches where abrasion is no longer at its most effective particle flatness varies more consistently between the lithological groups an initial increase being followed by a geometric decrease discs and blades are the dominant zingg shapes reflecting the influence of bedrock structure and preferential transport three process regimes are identified in which different processes are dominant abrasion and size sorting in the headwater area shape and size sorting in the middle reaches sorting and breakage towards the downstream end of the stream underlying the general tendencies are discontinuities related to tributary inflow the main effects being to increase grain size and flatness below junctions

distinguishing depositional environments in shallow water mixed bio siliciclastic deposits on the basis of the degree of heterolithic segregation gelasian southern italy abstract a new sedimentological technique has been tested in gelasian cross stratified bio siliciclastic deposits cropping out in southern italy lucanian apennine to disentangle paleoenvironmental and model reconstructions for shallow water mixed sediments the proposed method suggests the use of the bioclastic siliciclastic ratio bls and the segregation index s i to evaluate the percentage of the dominant elastic component in a mixed deposit and in order to estimate the degree of the heterolithic segregation between bioclastic and siliciclastic particles the principle of this method is based on the experimental evidence that bioclasts and quartz grains reveal a different physical behavior if entrained by a hydraulic flow of a given energy thus a different internal texture of bioclastic and terrigenous particles in the same sedimentary deposit is regarded as the result of the variation in the energy of a number of hydrodynamic processes that characterize shallow marine settings including waves currents and tides the studied mixed sediments subdivided into facies associations exhibit stratigraphic shoaling upward successions recording repeated transitions from offshore to shoreface environments these trends are documented through the vertical variations in the degree of heterolithic segregation between mixed clastic particles quantified by using the s i introduced in the present study the assessment of the degree of heterolithic segregation is thus proposed as a proxy to distinguish depositional environments related to different water depths in shallow water mixed systems

progradational gravel beach sequences in a moderate to high energy microtidal marine environment the anatomy of progradational gravel beaches was analysed in two different tectonic settings the strongly subsiding messinian foreland basin of the eastern southern alps and the rising pleistocene marine terraces of the outer margin of the apenninic chain progradation took place near the mouths of fan delta or braid delta distributaries debouching in microtidal landlocked basins palaeo adriatic and palaeo ionian seas a wind wave climate comparable to that of the present day was characterized by periodic intense storm activity most of the beachface progradation is thought to have taken place during the post storm recovery and fair weather stages whereas the impact of storms is mostly recorded by the cutting of erosional surfaces on the beachface and by emplacement of poorly sorted and coarse grained gravels on the shoreface by storm intensified seaward trending flows and behind the highest berms by washover processes analysis of the sequences led to the identification of a number of typical divisions which are differently developed in the two settings compared here the characteristics of the apenninic sequences suggest a strongly variable wind wave climate with periodic changes from a relatively dissipative barred morphology during storms accompanied by strong longshore currents and rip development to a more reflective state typical of recovery and fair weather stages the southern alpine sequences on the other hand are characterized by poor evidence of barred morphology and of longshore currents and widespread effects of shear and gravity sorting in the lower beachface gravels these features indicate a comparatively more reflective average state due to location of beaches along the deeply embayed head of the palaeo adriatic and the very narrow directional width of the incoming wave spectrum which was almost shore normal most of the time in addition to well developed shape zonation of gravels the common presence of wave generated gravel megaripples in the southern alpine sequences indicates the greater influence of long period waves due to the greater available fetch distances in both settings the cyclicity is thought to be genetically related to minor changes of sea level

mixing of siliciclastic and carbonate sediments in shallow shelf environments the inhibiting effect that siliciclastic material has on carbonate secreting organisms has lead to the generalization that sediments composed of mixtures of carbonate and siliciclastic material should rarely form however many modern and ancient shelf deposits contain a spectrum of sediments that are of mixed composition the processes responsible for this mixing can be grouped into four categories 1 punctuated mixing where sporadic storms and other extreme periodic events transfer sediments from one depositional environment to another 2 facies mixing where sediments are mixed along the diffuse boundaries between contrasting facies 3 in situ mixing where the carbonate fraction consists of the autochthonous or parautochthonous death assemblages of calcareous organisms that accumulated on or within siliciclastic substrates and 4 source mixing where admixtures are formed by the uplift and erosion of nearby carbonate source terranes the allochemical constituents of mixed sediments are both coralgal and foram mollusc in composition the foram mollusc assemblage is the most common because of the effects of increased turbidity unstable substrates and the clogging of filter feeding mechanisms associated with a siliciclastic influx

a scaling approximation of equilibrium timescales for sand bed and gravel bed rivers responding to base level lowering the timescale required for a river channel to reach new equilibrium conditions following a disturbance presumably depends on channel substrate size and previous field studies have suggested that gravel bed channels should reach equilibrium more quickly than sand bed channels to estimate the relative timescale difference between sand bed and gravel bed rivers responding to base level lowering we developed a simple scaling approximation equilibrium timescales derived from these equations for sand bed rivers were found to be approximately half of those for gravel bed rivers while gravel bed channels do not need to transport as much sediment to reach equilibrium conditions as sand bed channels transport of sediment is more rapid in sand bed channels leading to quicker equilibration

impact of the atlantic meridional mode on gulf stream north wall position abstractthe path of the gulf stream as it leaves the continental shelf near cape hatteras is marked by a sharp gradient in ocean temperature known as the north wall previous work in the literature

patterns of sediment slug translation and dispersion following typhoon induced disturbance oyabu creek kyushu japan a six year monitoring programme characterized the migration dispersion patterns of sediment slugs generated following typhoon induced disturbances in 1993 and 1997 along a single thread gravel bed stream oyabu creek on kyushu island japan this laterally con ned creek comprises rif e pool sequences with intervening bedrock outcrops the passage of sediment pulses associated with sediment slug processes re ected and was controlled by the rif e pool structures which provided channel bed roughness the volume of sediment stored along valley oors and the distribution of bedrock outcrops changes to bed material size following major sediment inputs during the disturbance events also exerted an in uence on subsequent sediment slug processes the sequence of rainfall events together with changes to channel bed structure induced different phases in the sediment slug processes the capacity of a reach to store or trap sediment as recorded by the longitudinal structure of the channel varied during these differing phases copyright 2004 john wiley sons ltd

facies partitioning and sequence stratigraphy of cool water mixed carbonate siliciclastic sediments upper miocene guadalquivir domain southern spain during the late miocene the guadalquivir basin and its satellite basin the ronda basin were under atlantic cool water influence the aim of our study is to develop a sequence stratigraphic subdivision of the ronda basin fill and to provide models for the cool water carbonates the upper miocene of the ronda basin can be divided into three depositional sequences sequence 1 is early tortonian sequence 2 late tortonian to earliest messinian and sequence 3 messinian in age the sediments were deposited in a ramp depositional system sequence 1 is dominated by conglomerates and marls in sequence 2 and sequence 3 carbonate deposits dominate in the inner ramp whereas siliciclastics preferentially occur in the middle and outer ramp bryomol carbonate sediments occur in all sequences whereas rhodalgal carbonates are restricted to sequence 3 in bays protected from siliciclastic influx rhodalgal deposits formed under transgressive conditions a bryomol factory occurs in zones of continuous siliciclastic supply this distribution results from facies partitioning during the flooding of the ronda basin which has a rugged and irregular relief embayments were protected from siliciclastic influx and provided regions with less hydraulic energy

siliciclastic foundations of quaternary reefs in the southernmost belize lagoon british honduras analyses of a closely spaced lattice of seismic profiles from the southernmost belize lagoon combined with logs of nearby drill holes reveal that the quaternary late pleistocene plus holocene reefs and carbonate sediments are growing on siliciclastic sediments which have an alluvial and delta like morphology the residual relief of these coastal plain deposits localized initial coral growth or an accumulation of calcareous skeletal material favored sites for these were elevations such as levees and bars of remnant channels and deltaic lobes

response and recovery of a subalpine stream following a catastrophic flood the july 15 1982 lawn lake flood in rocky mountain national park colorado was caused by the failure of a 79 yr old earthen dam peak discharges of the flood far exceeded naturally occurring flows and it caused severe channel disturbance along most of roaring river and some parts of fall river this study documents the geomorphic response of a 5 km reach of fall river in the 5 yr following the flood in 1983 the first year after the lawn lake flood snowmelt flows were well above average these high flows together with very high sediment yields from roaring river resulted in significant geomorphic changes on reaches of fall river downstream during the 1983 snowmelt runoff 15 5 x 106 kg of bed load sediment was eroded from the upper part of the study area these loads were at least 1 000 times higher than before the lawn lake flood most of this sediment was then deposited in a highly sinuous reach of fall river in the lower part of the study area this reach had not been much affected by the lawn lake flood but sedimentation during the period of high flow in 1983 completely filled in the channel resulting in the formation of a continuous 2 3 km long depositional zone in 1984 sediment yield from roaring river declined dramatically and this trend continued for the next 3 yr by 1987 the bed load sediment yield in the upper reaches of fall river was only about 0 4 x 106 kg yr the decline in sediment loads resulted in progressive erosion and recovery of the original channel of fall river in the depositional zone reach recovery in the upstream part of the depositional zone was complete by 1985 recovery in the downstream part of the depositional zone took longer because of the continued supply of sediment and because the sediment was mobile less of the time as of 1987 about 80 of the material initially stored in the sedimentation zone had been eroded bed load sediment yields at a sampling site 1 km downstream of the terminus of the depositional zone ranged from 5 x 106 to 11 x 106 kg yr but showed no significant decline over the 5 yr study period the average rate of bed load transport through this reach was at least 100 times greater than before the lawn lake flood but few discernible channel changes resulted from the higher loads

classification of large scale subaqueous bedforms a new look at an old problem sepm bedforms and bedding structures abstract a symposium entitled classification of large scale flow transverse bedforms was convened at the 1987 mid year meeting of sepm in austin texas with the purpose of examining the problems involved in classifying large subaqueous flow transverse bedforms developed in fluvial intertidal and marine environments and recommending changes in nomenclature the consensus of the participants is that despite the wide spectrum of morphologies of large scale flow transverse bedforms excluding antidunes they all occupy a similar position in the lower flow regime sequence between ripples and upper plane bed the wide variety of forms is a reflection of secondary effects such as channelization fluctuating water levels and unsteady and reversing flows the bedforms appear not to fall into size classes with naturally occurring boundaries but rather form a continuum with spacing from just under 1 m to over 1 000 m the symposium panel proposes therefore that they should have only one name dune dune is preferred as it has historical precedence over other terms in use such as megaripple and sand wave the term dune should be modified by rimary descriptors of shape i e 2 d or 3 d and size based on spacing small 0 6 5 m medium 5 10 m large 10 100 m or very large 100 m and the adjective subaqueous when it is important to distinguish them from eolian dunes the panel recommends a morphologically based classification that is descriptive with an underlying genetic rationale second order descriptors such a sediment size and bedform superposition may be used to describe more thoroughly the variety of subaqueous dunes in nature

reaction and relaxation in a coarse grained fluvial system following catchment wide disturbance abstract the waiapu river catchment drainage area of 1734 km2 is one of the most prolific conveyors of sediment in the world annually delivering roughly 35 mt of fine material to the ocean from eroding gullies hillslopes and reworked sediment on valley floors tectonic and geologic influences in combination with a dynamic climate influenced by tropical cyclones and clearance of vegetation from steep hillslopes predisposes this region to high rates of erosion the bedload sediment regime of the river is strongly influenced by several exceptionally large gullies and gully complexes that produce a coarse grained poorly sorted sediment mixture rapid abrasion and breakdown leads to high rates of suspended sediment yield a wave of bedload material manifesting as elevated bed levels and significant widening of active alluvial fills has been triggered by large inputs of hillslope material from a few key tributary catchments following cyclone bola in 1988 we review the evidence for the relaxation process of the sedimentary system in the subsequent 29 years appraising some of the legacy effects that may endure as associated with reworking of the considerable alluvial stores within the waiapu system we use structure from motion sfm techniques and archival aerial photos to quantify changes in sediment storage at the base of two major gully systems in recent decades a record of over 850 cross section surveys at 62 sites on 10 rivers throughout the catchment 1958 2017 indicates recent transition from a trend of continuous accumulation to downcutting and remobilisation of valley bottom deposits the channel cross sections provide a minimum estimate of sediment flux from source areas to the lower reaches of the river giving a rudimentary but spatially extensive picture of the wave of material cascading through the drainage network the largest impacts occur in the upper steepland rivers closest to the landslide derived sediment supply transport rates here as inferred from cross section change are at a maximum during an aggradational phase following cyclone bola then taper off despite the large sediment accumulations remaining in the system as of 2017 the river is in the process of incising the upper extents of this deposit on a trajectory of recovery toward pre bola conditions the compilation of cross section data provides us with new insights into the sensitivity of particular sites in the landscape as well as the changing relationship between reach sediment storage and transport rates during the response and relaxation phase of a major disturbance in a large catchment

formation and evacuation of a large gravel bar deposited during a major flood in a mediterranean ephemeral stream nahal me arot nw israel abstract an unusual 240 mm rainstorm and a consequent major flood peak discharge 110 m 3 s 1 with an estimated recurrence interval of about 50 years occurred on dec 31 1998 in nahal me arot an ungauged 25 km 2 coastal ephemeral stream in mt carmel nw israel the flood caused morphological modifications along the channel including intensive stripping of the channel bed and floodplain along several segments and deposition of large gravel bars downstream of these segments one of such segments served as a study reach composed of a massive 1270 m 3 coarse 200 m long gravel bar formed downstream of a segment 150 m long that was deeply scoured the study reach was carefully mapped cross sections and driftwood lines allowed the calculation of the hydraulic parameters and peak flow using the slope area method the bar s sedimentological characteristics such as surface and substrate texture and stratigraphy were studied in detail using a survey of 15 pits the initial recovery of the channel started when dense low shrub vegetation re stabilized along the affected reaches a year later two smaller floods 3 and 4 years later evacuated and reworked the sediment until it lost most of its volume the study suggests that the flood s large impact and disturbance was local short lived and the channel almost returned to its pre flood state within about 4 years

effects of coarse woody debris and its removal on a channel affected by the 1980 eruption of mount st helens washington during the may 18 1980 eruption of mount st helens washington a pyroclastic surge introduced large volumes of coarse woody debris cwd and fine grained sediment to clearwater creek approximately 15 km northeast of the summit effects of controlled cwd removal on sediment storage substrate and pool frequency and volume were measured in four reaches each with three 200 m segments from 1982 to 1990 in each reach the upstream segment served as a control with no debris removal and cwd was totally and selectively removed from the other two segments unique among similar experiments are the large size and volume of cwd and the large inputs of fine grained sediment except for segments of two reaches that received debris torrents the clearwater channel thalweg scoured until 1985 in three reaches total debris removal caused additional scour and coarsening of the bed surface compared to segments with no or partial debris removal pools contracted from 1982 to 1985 and expanded afterward especially in control segments total debris removal apparently caused pools to become shallower and in segments of low sinuosity decreased the frequency of major pools habitat complexity decreased after total debris removal as indicated by a decrease in the standard deviation of residual depth and an increase in the size of substrate patches

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

development of channel organization and roughness following sediment pulses in single thread gravel bed rivers large episodic inputs of coarse sediment sediment pulses in forested mountain streams may result in changes in the size and arrangement of bed forms and in channel roughness a conceptual model of channel organization delineates trajectories of response to sediment pulses for many types of gravel bed channels channels exhibited self organizing behavior to various degrees based on channel gradient presence of large in channel wood or other forcing elements the size of the sediment pulse and the number of bed mobilizing flows since disturbance typical channel changes following a sediment pulse were initial decreases in water depth in variability of bed elevations and in the regularity of bed form spacing trajectories of change subsequently showed increased average water depth more variable and complex bed topography and increased uniformity of bed form spacing bed form spacing in streams with abundant forcing elements developed at a shorter spatial scale two to five channel widths than in streams without such forcing mechanisms five to 10 channel widths channel roughness increased as bed forms developed

translation and dispersion of sediment pulses in flume experiments simulating gravel augmentation below dams 1 the effectiveness of gravel augmentation as a river restoration strategy depends on the extent and duration of the topographic and bed texture changes created by the pulse of added sediment previous work has emphasized the strong tendency for natural sediment waves to propagate primarily by dispersion however pulse translation may occur for gravel additions to armored channels downstream of dams where added sediments are finer than the preexisting bed material here we report results of a laboratory investigation in which we created an immobile armored bed and documented the spatial and temporal evolution of the bed topography and bed texture in response to gravel pulses of various volumes and grain sizes the introduced sediment waves evolved by a combination of translation and dispersion with a significant translational component pulse translation and dispersion can be readily discerned on a graph of the time evolution of the downstream cumulative distribution of elevation differences from the preexisting bed topography translation was most evident for smaller volumes of added sediment pulses of finer grained gravel moved through the flume more rapidly resulting in a larger magnitude but shorter duration of bed fining more work is needed to understand the influence of bar pool topography and flow magnitude and duration before the grain size and volume of gravel additions can be selected to achieve optimal patterns of pulse propagation

lowstand carbonates highstand sandstones the sedimentary facies sediment dynamics and sequence architecture of modern high energy shelves in the mid and high latitudes are largely governed by wave abrasion processes cool water carbonates may form there if the influx and or net accretion of siliciclastics is kept at a minimum little dilution of the carbonate produced in situ is generally promoted by a wide epicontinental shelf subdued topography of the adjacent mainland the predominance of limestone outcrops and an arid climate the aforementioned requirements are rarely met and thus will automatically lead to the formation of mixed siliciclastic cool water carbonates such an example is found in the early to mid miocene lagos portimao formation algarve s portugal which formed on a narrow high energy shelf of the atlantic ocean that was bounded by a mountain range the sediments of the formation consist of fossiliferous sandstone fs shell beds and rhodolith blankets along strike the stratification of the formation is monotonous for tens of kilometres and well exposed in coastal cliffs whereas no outcrops of dip sections exist the bulk skeletal composition of the sediments is typical for the warm temperate climatic zone various endo and epibenthic bivalves bryozoans coralline algae echinoderms gastropods and large foraminifers heterostegina in some very rare beds a few isolated not framework forming specimens of zooxanthellate corals porites tarbellastrea indicate temporally elevated surface water temperatures close to the lower threshold of the coral reef ecosystem in sandstones the fauna is well preserved and burrowing bivalves are commonly found in life position in limestone beds the state of preservation of the grains ranges from intact to disintegrated and abraded specimens we infer an accumulation of the shell beds through winnowing of fine materials siliciclastic sand and carbonate mud at wave abrasion depth and concentration of calcareous skeletons associated with the subsequent attraction of new epibiota in a complex shell bed the vertical alternation of fossiliferous sandstone and shell beds and in phase variations of the photo index photic biota vs bryozoans and bryozoan index bivalves vs bryozoans is envisaged to document variations of water depth and sea level sandstone units built up when wave abrasion depth wad rose above the sea floor during tst and early hst whereas the shell beds formed during lst when the wad for sand intersected with the sea floor clastic sediments were probably brought on the outer shelf during early transgression and by longshore currents sea level signatures inferred in the mixed siliciclastic cool water carbonate shelf setting of s portugal therefore significantly deviate from conventional concepts of carbonate sequence stratigraphy which were developed for flat topped platforms successful interpretations of ancient mixed sequences must therefore take into consideration the processes of production concentration and accretion of the carbonate sediments

growth processes and melange formation in the southern apennines accretionary wedge abstract the southern apennines owe their present geometry to the subduction of an apulian continental lithospheric slab and are thus best interpreted as an accretionary wedge southward the apenninic thrust front branches on to the still active ionian wedge which is related to the present calabro sicilian subduction the interpretation of conventional seismic reflection profiles and exploration wells combined with geologic field studies biostratigraphy and structural geology provide constraints for a geodynamic model for the post messinian growth of the apenninic prism our model for the apennines is a good analogy for submerged oceanic accretionary prisms in both instances features such as out of sequence thrusts underplating and duplexes are viewed as processes to explain the thickening of accretionary wedges syntectonic terrigenous deposits have accumulated in the synclines developed above the flats of pliocene thrust faults these depocenters represent piggy back basins younger accretion at the eastern border of the accretionary wedge has led to a progressive uplifting and tilting of the already emplaced thrust sheets including a continous westward migration of the depocenters in the piggy back basins during pliocene and early quaternary times a contrary west to east migration of the depocenters locally occurred where preexisting flats of pliocene thrust faults have been refolded rather than only being rotated dewatering processes and effects of overpressures on undercompacted sediment deformations can also be studied in the southern apennines melanges and broken formations form an important component of the trench apparently restricted to the base of tectonic nappes listric normal faults are a major structural element which preserves in combination with the erosion of topographic highs and resedimentation in the piggy back basins a uniform geometric shape critical taper for the prism the age and location of these distensive or gravitational effects are also discussed

oceanic isopycnal mixing by coordinate rotation abstract current numerical models of oceanic circulation differentiate between the eddy diffusion and viscosity transport along the geopotential horizontal and vertical directions only in order to model the effect of anisotropic turbulence as diffusive transport along and across density surfaces the isopycnal mixing tensor has been transformed from a diagonal second rank tensor in the isopycnal coordinate system to a tensor containing off diagonal elements in the geopotential coordinate system

energy time and channel evolution in catastrophically disturbed fluvial systems abstract two diverse fluvial systems show that with time channels adjust such that the rate of energy dissipation is minimized one fluvial system characterized by high relief and coarse grained sediment was subjected to an explosive volcanic eruption the other system characterized by low relief and fine grained sediment was subjected to dredging and straightening study of the expenditure of kinetic and potential energy components of total mechanical energy provide an energy based rationale of the interdependency between processes and forms during channel evolution spatial and temporal trends of aggradation and degradation are similar although relative amounts of aggradation in the high energy system are greatly enhanced by the deposition of large amounts of eroded bank material from upstream reaches degradation accompanied by widening is the most efficient means of energy dissipation because all components of total mechanical energy decrease with time widening dominates energy dissipation in the coarse grained system to offset increases in hydraulic depth caused by incision in the low energy fine grained system channel adjustment and energy dissipation are dominated by vertical processes because of low relative values of kinetic energy and because eroded bank sediment is transported out of the drainage basin and does not aid in downstream aggradation energy dissipation or channel recovery specific energy is shown to decrease nonlinearly with time during channel evolution and provides a measure of reductions in available energy at the channel bed data from two sites show convergence towards a minimum specific energy with time time dependent reductions in specific energy at a point act in concert with minimization of the rate of energy dissipation over a reach during channel evolution as the fluvial systems adjust to a new equilibrium

management responses to pulses of bedload sediment in rivers abstract rivers can experience sudden pulses of sediment from human and natural erosion processes that can accumulate in the bed abundant studies have examined the sources and dynamics of sediment pulses and problems caused by these pulses particularly flooding avulsions and habitat simplification much less has been written about what managers can do about sediment pulses and that is the purpose of this review the first option for managers is to do nothing and this decision can be informed by many case studies and by theory on the propagation and character of sediment pulses their diffusion translation and celerity doing nothing should be informed by the secondary effects of sediment pulses on channels including widening avulsions and tributary interactions if managers decide that something needs to be done about the sediment they have four options 1 reducing the sediment supply at source 2 trapping sediment in the channel 3 accelerating sediment transport through a reach and 4 directly extracting sediment the most common of these actions is undoubtedly to reduce the supply at source but there are few examples of the consequences of this for sediment pulses there are even fewer examples of trapping accelerating and extracting sediment all of these options have great potential for managing sediment pulses however they also have the potential to trigger incision of tributaries and of the channel behind the passing sediment wave overall the literature equips managers to understand the dynamics of sediment pulses but it does not yet equip them to confidently manage these geomorphic events

equilibrium and time scales in geomorphology application to sand bed alluvial streams equilibrium is defined as a single valued temporally invariant functional relationship between the values of an output variable and the values of the input variable s in a geomorphic system disequilibrium occurs if the output deviates from the functional relationship by more than a consensual degree natural geomorphic variables are characterized by a relaxation time output variables are insensitive to cyclical inputs with frequencies much greater than the relaxation time but can respond completely for sufficiently low frequencies rapid trends recent step changes or pulse inputs and intermediate frequency inputs can cause disequilibrium the gradient of sand bed alluvial channels the output variable is determined by sediment and water delivery from slopes the input variables and changes in this hydraulic regime require regrading by erosion and deposition initial stages of adjustment to changed regime in a long unbranched channel with sediment and water delivery only at the upstream end propagate downstream but later stages of adjustment occur simultaneously throughout the reach in a dendritic channel network the gradient responds rather uniformly throughout the network to changes in regime during all stages of adjustment the time scale of adjustment to changed regime depends upon the size of the channel network or stream length the sediment and water discharges and to a lesser degree upon the magnitude of the change grade as defined by mackin 1948 is synonymous with equilibrium as used in this paper if a period of years is replaced by a time period commensurate with the relaxation time of the gradient the use of the term grade is best restricted to a single valued relationship between channel gradient and the hydraulic regime

objective identification of pools and riffles this paper presents a new technique for objectively identifying pools and riffles the technique is termed the bed form differencing technique and as its data base has bed elevations surveyed at a fixed interval along the channel these elevations are differenced and the difference or elevation change values are used to identify pools and riffles where the cumulative elevation change since the last bed form exceeds a certain tolerance value a new bed form is considered to exist the type of bed form being determined by the direction of the elevation change analysis of a small stream in western new york suggests that the most realistic pool riffle sequence is obtained where the tolerance value is 0 75 times the standard deviation of the difference values the bed form differencing technique can be used to identify bed forms other than pools and riffles such as ripples and dunes by simply modifying the surveying interval to reflect the scale of the bed forms

a centennial tribute to g k gilbert s hydraulic mining debris in the sierra nevada abstract g k gilbert s 1917 classic monograph hydraulic mining debris in the sierra nevada is described and put into the context of modern geomorphic knowledge the emphasis here is on large scale applied fluvial geomorphology but other key elements e g coastal geomorphology are also briefly covered a brief synopsis outlines key elements of the monograph followed by discussions of highly influential aspects including the integrated watershed perspective the extreme example of anthropogenic sedimentation computation of a quantitative semidistributed sediment budget and advent of sediment wave theory although gilbert did not address concepts of equilibrium and grade in much detail the rivers of the northwestern sierra nevada were highly disrupted and thrown into a condition of nonequilibrium therefore concepts of equilibrium and grade for which gilbert s early work is often cited are discussed gilbert s work is put into the context of complex nonlinear dynamics in geomorphic systems and how these concepts can be used to interpret the nonequilibrium systems described by gilbert broad basin scale studies were common in the period but few were as quantitative and empirically rigorous or employed such a range of methodologies as pp105 none demonstrated such an extreme case of anthropogeomorphic change

detailed river stage mapping and head gradient analysis during meander cutoff in a laboratory river analytical models of river evolution predict meander narrowing and elongation which creates sinuosity driven hyporheic exchange across the meander neck by decreasing flow distance and increasing head loss we used a laboratory river table and close range photogrammetry to map and analyze sinuosity as a driver of head gradients and hyporheic exchange during cutoff the river valley had relatively high slopes 1 8 and moderately cohesive sediment 10 talc 90 sand to facilitate cutoff and ratios of horizontal to vertical scaling were distorted to achieve dynamic similitude re 3200 incipient to cutoff the head gradient across the neck increased due to a narrowing neck upstream aggradation and downstream degradation longitudinal and transverse river surface slopes around the meander bend increased as the meander approached cutoff the steep head gradient across the moderately cohesive meander neck generated seepage erosion and scour that formed a low sinuosity avulsion sediment rich flow in the avulsed channel aggraded the downstream bed and separated the active channel and oxbow lake the limitation in geometric and dynamic similitude in the river table limits extrapolation to natural rivers yet river evolution may involve aggradation and degradation induced channel head loss and turnover hyporheic exchange as well as seepage induced meander neck erosion our submillimeter maps of meander morphology and water stage provide data to parameterize river evolution and hyporheic exchange models and may inform analysis and mapping of field sites

channel response to sediment wave propagation and movement redwood creek california usa redwood creek north coastal californa usa has experienced dramatic changes in channel confguation since the 1950s a series of large floods in 1955 1964 1972 and 1975 combined with the advent of widespread commercial timber harvest and road building resulted in extensive erosion in the basin and contributed high sediment loads to redwood creek since 1975 no peak flows have exceeded a 5 year recurrence interval twenty years of cross sectional survey data document the downstream movement of a sediment wave in the lower 26 km of this gravel bedded river at a rate of 800 to 1600 m a i durng this period of moderately low flows higher transit rates are associated with reaches of higher unit stream power the wave was initially deposited at a site with an abrupt decrease in channel gradient and increase in channel width the amplitude of the wave has attenuated more than i m as it moved downstream and the duration of the wave increased from eight years upstream to more than 20 years downstream channel aggradation and subsequent degradation have been accommodated across the entire channel bed channel width has not decreased significantly after initial channel widening from large 25 year recurrence interval floods three sets of longitudinal surveys of the streambed showed the highest increase in pool depths and frequency in a degrading reach but even the aggrading reach exhbited some pool development through time the aggraded channel bed switched from functioning as a sediment sink to a significant sediment source as the channel adjusted to high sediment loads from 1980 to 1990 sediment eroded from temporary channel storage represented about 25 per cent ofthe total sediment load and 95 per cent of the bedload exported from the basin

framing realistic river rehabilitation targets in light of altered sediment supply and transport relationships lessons from east gippsland australia since european settlement the cann river in east gippsland victoria has experienced a 700 increase in channel capacity a 150 fold increase in the rate of lateral channel migration a 45 fold increase in bankfull discharge and a 860 fold increase in annual sediment load over the last century and primarily the last 40 years channel incision has removed the equivalent of around 1500 years of floodplain deposition a numerical floodplain evolution model is presented which suggests that under a best case scenario infilling the incised channel trench will take 31 000 years and this is predicated on the full recovery of the immediate riparian vegetation and the in channel loading of woody debris the asymmetry in the recovery time following rapid channel change compared with the original deposition of the material is explained by a combination of the sediment starved character of the catchment and the altered hydraulic conditions within the channel principally associated with the role of woody debris these factors have major implications for geomorphic recovery potential constraining what can be realistically achieved in river rehabilitation

the internal generation of the atlantic ocean interdecadal variability abstractnumerical simulations of a realistic ocean general circulation model forced by prescribed surface fluxes are used to study the origin and structure of intrinsic interdecadal variability of

morphodynamic response of a variable width channel to changes in sediment supply river channels commonly exhibit downstream variations in channel width which can lead to the development of alternating shallow and deep areas known as riffle pool sequences the response of these channels to variations in sediment supply remains largely unexplored here we investigate the morphodynamic response of a variable width channel to changes in sediment supply through laboratory experiments conducted in a straight flume in which we imposed sinusoidal variations in width we first developed equilibrium conditions under a constant sediment supply and then eliminated the sediment feed to create a degraded armored bed this sediment starved bed was subjected to two types of sediment supply increases a return to the initial constant supply and the introduction of a well sorted sediment pulse analogous to gravel augmentation riffles and pools formed in wide and narrow areas respectively and the location of and relief between riffles and pools remained the same throughout all experimental runs regardless of the sediment supply the primary channel response to changes in supply was adjustment of the overall slope the sediment pulse evolved primarily through dispersion rather than translation which contrasts with prior gravel augmentation experiments conducted in constant width channels and suggests that width variation and resulting riffle pool topography enhances pulse dispersion our results indicate that width variation is a primary control on the location and relief of riffles and pools in straight channels and sediment supply changes are unlikely to affect riffle pool morphology when bank geometry is fixed and water discharge is steady

biocalcarenite and mixed cool water prograding bodies of the mediterranean pliocene and pleistocene architecture depositional setting and forcing factors

incision and morphologic evolution of an alluvial channel recovering from hydraulic mining sediment hydraulic gold mining in the sierra nevada california produced such a large volume of sediment from 1853 to 1884 that channels could not carry a substantial proportion of the delivered sediment the lower bear river aggraded as much as 5 m and underwent a major avulsion during the 1870s channel morphology continues to respond to these changes more than 100 years after the cessation of most hydraulic mining textures of mine tailings and older alluvium are contrasted and channel incision and channel shape changes from 1930 to 1985 are documented unlike the yuba and sacramento rivers the lower bear river had not returned to pre mining base levels by 1950 as sediment loads decreased nor were incision rates or morphological change governed by reduced sediment loads below dams built in 1928 and in the mid 1960s channel stability was due to resistance of a cohesive stratum on the channel bed an episode of channel down cutting was instigated by a moderately large flood in december 1955 that pierced the cohesive layer and was sustained through the 1970s by moderate magnitude floods the 1955 flood did not directly erode large volumes of sediment but it destabilized the channel allowing smaller floods to erode the channel at an accelerated rate episodic channel bed incision is contrasted to progressive morphologic changes cross section shape narrowed and deepened steadily from 1930 through the mid 1970s as the channel was superimposed onto cohesive older alluvium progressive deepening set up a positive feedback that ensured the ultimate penetration of the paved bed channel morphologic readjustment from the avulsion thus was both progressive and episodic

river adjustment to changes in sediment load the effects of tin mining on the ringarooma river tasmania 1875 1984 the mining of alluvial tin in the ringarooma basin began in 1875 reached a peak in 1900 20 and had virtually ceased by 1982 during that time 40 million m3 of mining waste were supplied to the main river quickly replacing the natural bed material and requiring major adjustments to the channel based on estimates of sediment supply from more than 50 widely scattered mines and the frequency of flows capable of transporting the introduced load the river s transport history is reconstructed using a mass conservation model because of the lengthy time period 110 years and river distance 75 km involved the model cannot predict detailed change but it does reproduce the main pattern of sediment movement in which successive phases of aggradation and degradation progress downstream peak storage is predicted in that part of the river where braiding and anastomosis are best developed aggradation was most rapid in the upper reaches close to major supply points becoming slower and later with distance downstream channel width increased by up to 300 per cent where the valley floor was broad and braiding became relatively common bridges had frequently to be replaced while bed levels were still rising in lower reaches degradation began in upper ones notably after 1950 and by 1984 had progressed downriver over 30 km rates of incision reached 0 5 m yr 1 especially in the early 1970s when record high flows occurred as a result of degradation the bed material became gravelly through either reexposure of the original bed or lag concentration of coarser fractions also a narrower unbraided channel has developed the river is beginning to heal itself and upper reaches now have reasonably stable beds but at least another 50 years will be required for the river to cleanse its channel of mining debris

transgressive surfaces of erosion as sequence boundary markers in cool water shelf carbonates abstract although sequence stratigraphy was first conceptualized in and applied to siliciclastic successions its methodology and concepts are applicable to the carbonate regimen provided that potential modifications to the existing models are appreciated that take into account the specificities of carbonate systems we demonstrate that some properties inherent to isolated i e continent detached shallow water temperate carbonate systems including their typical low diagenetic potential due to the prevalance of calcitic mineralogies the critical role exerted by storm waves and tidal currents on sediment dynamics e g shedding of sediments at wave abrasion depth during highstand and lowstand conditions and uneven sea bed topographies cause both the genesis and preservation of subaerial unconformities to be uncommon thereby rendering their use as sequence boundaries inappropriate instead transgressive surfaces of erosion tses that formed as wave base shifts upwards during early rise of relative sea level are readily identifiable in the field extensive and by their very nature are preserved in the rock record typically at the base of upward deepening stacked facies in pliocene cool water carbonate successions from new zealand the tses are characterized by starved sedimentation and burrowed network development and are overlain by coarse bioclastic shoreface sediments and shell beds in most cases the surfaces top truncate shoaling upward deposits but also deepening upward stacking facies in places emersive events rarely correspond to actual physical surfaces but diagenetic evidence preserved beneath tses indicates that occasionally subaerial surfaces had previously developed and were later modified into tses therefore we propose that tses are the most adequate unconformities to define high order depositional sequences 20 250 ka in the studied successions because by contrast with emersion surfaces their formation and preservation are not dependent upon cool water sedimentary facies and mineralogy and are favoured by the dynamics of the setting i e wave base shift and accommodation creation during relative sea level rise

sequence stratigraphy of sixth order 41 k y pliocene pleistocene cyclothems wanganui basin new zealand a case for the regressive systems tract this study is based on a late pliocene and early pleistocene approximately 2 6 1 7 ma succession about 1 km thick of 20 sixth order 41 k y duration cyclothems of shelf origin exposed in the rangitikei river valley in the eastern part of wanganui basin the cyclothems correlate with 18 o isotope stages 100 58 and each 41 k y glacialinterglacial stage couplet is represented by an individual depositional sequence comprising transgressive highstand and regressive systems tracts unlike most examples inferred from the stratigraphic record these systems tracts were deposited during phases of known sea level cycles indicated by the contemporary oxygen isotope ice volume curve because of the high rate of subsidence of wanganui basin glacioeustatic sea level falls during most cycles were not of sufficient magnitude to expose the outer shelf thus the rangitikei section provides an exceptional example of regressive strata deposited landward of the contemporary shelf break simple one dimensional modeling shows that moderate to high rates of basin subsidence 1 2 mm yr and low rates of sedimentation 0 2 mm yr during transgressions combined to produce an accommodation surplus at the relative highstand this surplus accommodation was infilled during the late highstand and ensuing fall partly by aggradational highstand systems tract shelf siltstone and chiefly by strongly progradational shoreface sediments of the regressive systems tract rangitikei regressive systems tracts are distinguished from forced regressive systems tracts sensu hunt and tucker 1992 by their different stratal geometry by definition forced regressive systems tracts display an erosional contact with the underlying highstand systems tracts and typically occur as a series of downstepped disjunct shoreline wedges stranded on the shelf and or slope in contrast regressive systems tracts exhibit a gradational lower contact above which parasequences are stacked in a strongly progradational pattern terminated by the superjacent sequence boundary cyclothems display two types of motif termed rangitikei dt depositional transgression and rangitikei nt nondepositional transgression which include the following architectural elements in ascending stratigraphic order 1 a basal sequence boundary that is coincident with either the transgressive surface of erosion which displays small scale up to 50 cm erosional relief and may be penetrated by the ichnofossil ophiomorpha or its deeper water correlative conformity 2 either a thick 5 30 m transgressive systems tract comprising a deepening upward nearshore to inner shelf mixed carbonate siliciclastic lithofacies succession depositional transgression or a thin 2 m transgressive systems tract comprising condensed fossiliferous facies deposited on the sediment starved offshore shelf nondepositional transgression 3 a sharp downlap surface separating condensed fossiliferous facies of the transgressive systems tract from terrigenous siltstone of the superjacent highstand systems tract 4 a highstand systems tract comprising a 10 20 m thick interval of aggradational shelf siltstone and 5 a thick up to 45 m progradational inner shelf to shoreface lithofacies assemblage ascribed to the regressive systems tract condensed shell beds are associated with intrasequence and sequence bounding discontinuities and together with the sedimentological and stratal characteristics of the sequences are important indicators of stratigraphic architecture four types of shell bed are associated with surfaces formed by four different types of stratal termination onlap backlap downlap and flooding surface shell beds cf kidwell 1991 are associated respectively with the transgressive surface of erosion apparent truncation at the top of the transgressive systems tract the downlap surface and local marine flooding surfaces a fifth shell bed type termed a compound shell bed forms in offshore environments where the downlap surface converges with the sequence boundary and elements of both the downlap and the backlap shell beds become mixed or superposed the shell beds mark zones of stratal attenuation and can be used as surrogates for seismic discontinuities when applying sequence stratigraphic concepts at outcrop scale

structural styles in the frontal zones of the southern apennines italy an example from the molise district structural interpretation of available geological and geophysical data from the molise area southern italy demonstrates that the frontal zones of this sector of the apennines are characterized by a threefold zoneography defined by distinct structural styles resolved geometry of both pellicular and deep seated structures and their relationships constrain possible reconstructions for the undeformed pre miocene southeastern margin of the afro adriatic continent and its neogene deformation history identification of peculiar structural associations in the foreland foredeep complex and reinterpretation of relevant stratigraphic data suggest that deformation in this sector of the apennines has already reached the most external apulian domains and is possibly migrating at present toward the currently active adriatic foredeep of the molisan thrust system

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

re evaluation of the wave model as a tool for quantifying the geomorphic recovery potential of streams disturbed by sediment slugs abstract a central principle of stream rehabilitation is that managers should accelerate the natural recovery of degraded streams in this paper we explore the recovery of channel morphology behind translating sediment waves using an observed expected space for time substitution sfts model channel recovery is defined by the variability of the thalweg cross sections and bed sediments of the three streams investigated in se australia one followed the general response described by gilbert s classic wave model with the stream bed returning to its pre disturbance geomorphic variability as the sediment wave passed in this case the recovery did not necessarily decline gradually with the distance away from the peak of the slug instead the geomorphic variability remained low within the slug and then increased dramatically once the slug evacuated by contrast the other two streams continued on their pre slug trajectory of channel incision which has not allowed geomorphic variability to establish once the sediment slug has passed the three study streams showed different recovery responses to a relatively simple pulse of sediment

the role of large woody debris in modulating the dispersal of a post fire sediment pulse abstract in 2001 a series of post fire debris flows brought 30 000 m3 of sediment deposited as fans to the narrow valley floor of sleeping child creek in western montana usa in 2005 pebble counts and surveys of the channel in proximity to six of the debris flow fans documented a regular sequence of fine grained aggradation upstream of the fans incision through the fans and coarse grained aggradation downstream of the fans these measurements were repeated in 2012 we found that the delivery of large woody debris lwd over the intervening 7 years has been a dominant factor in the disposition of the debris flow material the amount of lwd in the study reach has increased by as much as 50 in the areas with a high burn severity leading to the formation of large logjams that interrupt the flow of sediment along the streambed nearly all of the surveyed reaches have aggraded since 2005 including those that had initially begun incising through the debris flow deposits and the streambed has become generally finer we hypothesize that over the next few decades debris flow sediment not colonized and anchored by riparian vegetation will trickle out of the affected reaches as the logjams slowly degrade

sediment transport and channel adjustments associated with dam removal field observations 1 this study documents changes in channel geometry bed level profile and bed grain size distribution and their relations with the sediment transport at the reach scale following the removal of a low head dam after the removal net sediment deposition occurred downstream of the dam and net erosion occurred in the reservoir but approximately less than 1 of the sediment stored in the reservoir was transported downstream no bank erosion was evident either upstream or downstream of the dam bed deposition and scouring in the reservoir accounted for a decrease in the bed slope of 30 the stations downstream of the dam had surface bed material sizes at least 40 finer than preremoval conditions however the sediment transport rates downstream of the dam were not significantly different from predam to postdam removal or from an upstream control overall the removal of the dam had only minor effects on the channel adjustment downstream of the dam a simple analysis linking transport to channel geometry explains this effect

sediment pulse evolution and the role of network structure abstract sediment pulses are triggered through a variety of mechanisms from landslides to land use change how do these pulses move through the fluvial system and how do they evolve in a system with perfect sediment connectivity the erosional response to a perturbation and the resulting signal at the river mouth would match however this rarely occurs many studies have addressed reach scale dynamics of sediment pulses and how they translate or disperse downstream at the watershed scale network structure and storage become more important in modulating the sediment signal here we review the current literature on sediment pulse behavior and then address the role of network structure on maintaining dispersing or transforming sediment pulses in a fluvial system we use a reduced complexity network routing model that simulates the movement of bed material through a river basin this model is run in the greater blue earth river gber basin in minnesota usa first with spatially uniform inputs and then with inputs constrained by a detailed sediment budget once the system reaches equilibrium a sediment pulse is introduced first at a single location and then throughout the system and tracked as it evolves downstream results indicate that pulses able to translate downstream disperse in place upon arriving at over capacity reaches as sediment goes into storage in the gber basin these zones occur just upstream of a knickpoint that is propagating upstream through all mainstem channels as the pulses get caught in these sediment bottlenecks there is a decoupling of the original pulse of sediment and the resulting bed material wave these results show that the network structure both in terms of network geometry and the spatial pattern of transport capacity can play a dominant role in sediment connectivity and should be considered when predicting sediment pulse behavior at the watershed scale

an intrinsic mode of interannual variability in the indian ocean abstractan intrinsic mode of self sustained interannual variability is identified in a coarse resolution ocean model forced by an annually repeating atmospheric state the variability has maximum loading in the indian ocean with a significant projection into the south atlantic ocean it is argued that this intrinsic mode is caused by baroclinic instability of the model s leeuwin current which radiates out to the tropical indian and south atlantic oceans as long rossby waves at a period of 4 yr this previously undescribed mode has a remarkably narrowband time series however the variability is not synchronized with the annual cycle the phase of the oscillation varies chaotically on decadal time scales the presence of this internal mode reduces the predictability of the ocean circulation by obscuring the response to forcing or initial condition perturbations the signature of this mode can be seen in higher resolution global ocean models driven by high frequency atmospheric forcing but altimeter and

the record of tidal cycles in mixed silici bioclastic deposits examples from small plio pleistocene peripheral basins of the microtidal central mediterranean sea the pliocene pleistocene peripheral marine basins of the mediterranean sea in southern italy from basilicata and western calabria to northern and eastern sicily represent tectonically formed coastal embayments and narrow straits here units of cross stratified mixed silici bioclastic sand 25 to 80 m thick record strong tidal currents the central mediterranean sea has had a microtidal range of ca 35 cm and the local amplification of the tidal wave is attributed to tides enhanced in some of the bays and to the out of phase reversal of the tidal prism in narrow straits linking the tyrrhenian and ionian basins the siliciclastic sediment was generated by local bedrock erosion whereas the bioclastic sediment was derived from the contemporaneous foramol type cool water carbonate factories the cross strata sets represent small to medium sized 10 to 60 cm thick two dimensional dunes with mainly unidirectional foreset dip directions these tidalites differ from the classical tidal rhythmites deposited in mud bearing siliciclastic environments firstly the foreset strata lack mud drapes and instead show segregation of siliciclastic and bioclastic sand into alternating strata secondly the thickness variation of the successive silici bioclastic strata couplets measured over accretion intervals of 2 to 3 m and analysed statistically reveal only the shortest term diurnal and semi diurnal tidal cycles thirdly the record of diurnal and semi diurnal tidal cycles is included within the pattern of neap spring cycles differences between these sediments and classical tidal rhythmites are attributed to the specific palaeogeographic setting of a microtidal sea with the tidal currents locally enhanced in peripheral basins it is suggested that this particular facies of mud free silici bioclastic arenite rhythmites in the stratigraphic record might indicate a specific type of depositional sub tidal environment of straits and embayments and the shortest term tidal cycles

modelling sediment transport as a moving wave the transfer and deposition of mining waste abstract the movement of slugs of bedload from a discrete input point down a river has proved difficult to model using conventional finite difference formulations of equations of motion a model is proposed which makes explicit allowance for the mean sediment velocity and through a dispersion coefficient the distribution of sediment velocity about the mean a second comparative model uses the normal mass conservation or sediment transport continuity approach the models have been tested over a 43 month period using data from seven monitored cross sections of the kawerong river on bougainville island papua new guinea a system which receives waste from a large copper mine the dispersion model performs considerably better than the mass conservation model

the gravel sand transition in a disturbed catchment abstract more than 40 million cubic metres of mining waste were supplied to the ringarooma river between 1875 and 1984 leading to successive phases of aggradation and degradation the natural bed material is gravel but given the volume of introduced load and the fact that much of the input was less than 5 mm in diameter the size composition of the bed changed from gravel to sand during the phase of downstream progressive aggradation a very sharp gravel sand transition developed in which median grain size decreased from over 30 mm to under 3 mm in less than 500 m with upstream supplies of mining debris becoming depleted first degradation followed the same downstream progressive pattern as aggradation causing the transition to migrate downstream by 1984 the river could be regarded as a series of zones each characterized by a particular bed condition a natural cobble gravel bed unaffected by mining inputs 0 32 km pre disturbance bed re exposed by degradation over 35 40 years 32 53 km sandy substrate with a gravel armour produced by differential transport during degradation 53 65 km sand dominated but with developing surface patches of coarser material 65 75 km sandy bed reflecting the size composition of the original mining input 75 118 km although the gravel sand transition itself is sharp the transitional zone is lengthy 53 75 km as degradation continues the gravel sand transition is expected to progress downstream but it has remained in a stable position for 12 years indeed two major floods during the period released large quantities of sand from the sub armour layer and newly formed banks of mine tailings causing fining both above and below the transition surface grain size is an adjustable component in the transitional zone as the river strives to recover from a major anthropogenic disturbance

radiating instability of a meridional boundary current a linear stability analysis of a meridional boundary current on the beta plane is presented the boundary current is idealized as a constant speed meridional jet adjacent to a semi infinite motionless far field the far field region can be situated either on the eastern or the western side of the jet representing a western or an eastern boundary current respectively it is found that when unstable the meridional boundary current generates temporally growing propagating waves that transport energy away from the locally unstable region toward the neutral far field this is the so called radiating instability and is found in both barotropic and two layer baroclinic configurations a second but important conclusion concerns the differences in the stability properties of eastern and western boundary currents an eastern boundary current supports a greater number of radiating modes over a wider range of meridional wavenumbers it generates waves with amplitude envelopes that decay slowly with distance from the current the radiating waves tend to have an asymmetrical horizontal structure they are much longer in the zonal direction than in the meridional a consequence of which is that unstable eastern boundary currents unlike western boundary currents have the potential to act as a source of zonal jets for the interior of the ocean

morphology of riffle pool sequences in the river severn england despite the occurrence of pool riffle sequences in many rivers there are few data concerning pool riffle unit morphology of many criteria proposed to identify pool riffle units only two methods can be regarded as objective and robust these are the zero crossing and the control point methods in this paper statistics are developed from the zero crossing method to describe the streamwise morphology of 275 riffles and 285 pools which form a near continuous 32 1km of the bed of the river severn in shropshire england yalin s theoretical relationship between pool riffle unit length i p and channel width w i p 3w applies to the river severn reach average riffle height h is a constant proportion of bankfull depth h typically h i 0 16h riffle height is a positive function of riffle length pool depth is a positive function of pool length however both riffle length and pool length increase more rapidly than the bed level amplitude such that long riffles or pools are relatively flat as channel gradient reduces bedforms flatten and become more asymmetric as riffle stoss sides and the proximal slope of pools lengthen at the expense of riffle lee sides and pool distal slopes the statistical relationships between riffle height length and water depth are similar to those for equilibrium subaqueous dunes the severn data are partially consistent with yalin s theoretical analysis relating riffle bedform length lr to water depth i e lr i i2i h wherein i i i 1 for steep near equilibrium bedforms but i i i 2 to 3 as the relative depth decreases and riffles become long low features a consideration of turbulence data indicates that the frequency of coherent turbulent flow structures associated with the riffle pool mixing length is of the order of 60 seconds the morphological and dynamic similarity of the river severn riffles with dunes raises intriguing questions with respect to self similar convergent organization of periodic alluvial bedforms and to bedform dynamic classification particularly

pliocene pleistocene sequences bounded by subaerial unconformities within foramol ramp calcarenites and mixed deposits salento se italy nine discrete metre scale sequences of early pliocene to middle pleistocene age were deposited in the small novoli graben salento peninsula puglia s italy they consist of carbonate and mixed carbonate siliciclastic sediments deposited on a slowly subsiding foreland ramp skeletal concentrations and intervening less fossiliferous intervals have been examined to provide information on major environmental parameters and infer the dynamics of their changes taphonomic and palaeoecological analyses indicate that storm induced waves and currents reduced sediment input and settling behaviour of components were the main factors controlling the features of the various shellbed types the concentrations were formed below fair weather wave base in low stress inner to outer shelf environments and are often associated with surfaces or intervals that are characterized by sedimentary condensation vertical change in the fossil content within individual cycles indicates water depth changes that were parallel to climatic fluctuations hence may result from glacio eustatic sea level changes most sequences are bounded by subaerial karstic unconformities because of the regional setting of low subsidence rate the record of the relative sea level fluctuations is incomplete episodes of subaerial exposure and concomitant effects of vadose diagenesis are documented by i diagenetic changes leading to hardening of unconformity horizons ii local subvertical solution pits developed in the vadose zone below unconformity surfaces iii networks of polygonal cracks below unconformities and iv infilling of solution pits and polygonal cracks with vadose silt and marine sediment inwashed during transgressions following the subaerial stages lower sequences are characterized by tighter cementation and significant increase in moldic and vuggy porosity due to superimposition of the diagenetic effects of repeated high amplitude sea level fluctuations

effects of sediment pulses on channel morphology in a gravel bed river sediment delivery to stream channels in mountainous basins is strongly episodic with large pulses of sediment typically delivered by infrequent landslides and debris flows identifying the role of large but rare sediment delivery events in the evolution of channel morphology and fluvial sediment transport is crucial to an understanding of the development of mountain basins in july 2001 intense rainfall triggered numerous debris flows in a severely burnt watershed in the sapphire mountains of montana ten large debris flow fans were deposited on the valley floor and investigations focused on the channel response to these sediment pulses the channel has aggraded immediately upstream of each fan and braided in reaches immediately downstream channel incision through the fans has created sets of coarse grained terraces the deposition upstream of the pulses consists almost exclusively of fine material resulting in a median bed material size d 50 1 2 orders of magnitude lower than the ambient channel material the volume of sand being transported is so great that these aggrading reaches can extend hundreds of meters upstream of the fans with 1 2 m of sand deposited across the entire valley floor along a 10 km study reach cross section surveys longitudinal profiles and pebble counts chronicle channel response to a punctuated increase in sediment supply and provide insight on the processes of sediment wave dispersal

experimental evidence for the effect of hydrographs on sediment pulse dynamics in gravel bedded rivers 1 gravel augmentation is a river restoration technique applied to channels downstream of dams where size selective transport and lack of gravel resupply have created armored relatively immobile channel beds augmentation sediment pulses rely on flow releases to move the material downstream and create conditions conducive to salmon spawning and rearing yet how sediment pulses respond to flow releases is often unknown here we explore how three types of dam releases constant flow small hydrograph and large hydrograph impact sediment transport and pulse behavior translation and dispersion in a channel with forced bar pool morphology we use the term sediment pulse generically to refer to the sediment introduced to the channel the zone of pronounced bed material transport that it causes and the sediment wave that may form in the channel from the additional sediment supply which can include input sediment and bed material in our experiments we held the volume of water released constant which is equivalent to holding the cost of purchasing a water volume constant in a stream restoration project the sediment pulses had the same grain size as the bed material in the channel we found that a constant flow 60 greater than the discharge required to initiate sediment motion caused a mixture of translation and dispersion of the sediment pulse a broad crested hydrograph with a peak flow 2 5 times the discharge required for entrainment caused pulse dispersion while a more peaked hydrograph 3 times the entrainment threshold discharge caused pulse dispersion with some translation the hydrographs produced a well defined clockwise hysteresis effecting sediment transport as is often observed for fine sediment transport and transportlimited gravel bed rivers the results imply a rational basis for design of water releases associated with gravel augmentation that is directly linked to the desired sediment behavior

palinspastic restoration and paleogeographic reconstruction of the peri tyrrhenian area during the neogene abstract this paper presents the results of research carried out on the paleogeographic and geodynamic post collisional evolution of the peri tyrrhenian area from the southern alps to sicily during this post collisional evolution a back arc area thrust belt foredeep system developed in which the following tectono sedimentary zones can be distinguished from the external to the internal ones the foreland zone connected to the foredeep through a slope generally controlled by normal faults the foredeep an assymmetric depression with strong subsidence related to the compressional activity of the thrust zone the chain whose outward migration from the late oligocene onward was discontinuus with important stages of crisis partially connected to the mechanical response of different crustal thicknesses existing in the foreland the discontinuous satellite basins developed within the thrust belt the back arc basins developed in the inner part of the chain where the superposition of the extensional tectonics over previous compressional domains causes the fragmentation of the thrust belt leading to its destruction according to this model seven palinspatic maps are discussed regarding the following time intervals late oligocene 25 24 m y burdigalian 22 20 m y langhian 17 16 m y serravallin 15 13 m y tortonian 10 9 m y late messinian 5 5 5 3 m y and early pliocene 5 3 4 6 m y during five of these time intervals significant geodynamic modifications occurred in the whole peri tyrrhenian area leading to paleogeographic changes in any case the geodynamic evolution of the whole area seems clearly controlled by the activity of important bundles of tectonic lines transversal to the chain which in the same time interval in the outermost part of the thrust belt separated areas with different values of shortening and in tthe most internal zones separated segments having different amount of extension these tectonic lines certainly have a crustal significance and have probably acted along previous formed discontinuities