numerical model for sediment transport and bed degradation in the yangtze river channel downstream of three gorges reservoir this paper presents a two dimensional morphological model for unsteady flow and both suspended load and bed load transport of multiple grain size to simulate transport of graded sediments downstream from the three gorges reservoir the model system includes a hydrodynamic module and a sediment module the hydrodynamic module is based on the depth averaged shallow water equations in orthogonal curvilinear coordinates the sediment module describing nonuniform sediment transport is developed to include nonequilibrium transport processes bed deformation and bed material sorting the model was calibrated using field observations through application to a 63 km long alluvial river channel on the middle yangtze river in china a total of 16 size groups and a loose layer method of three sublayers were considered for the transport of the nonuniform bed materials in a long term simulation predictions are compared with preliminary results of field observations and factors affecting the reliability of the simulated results are discussed the results may be helpful to the development of more accurate simulation models in the future

three dimensional cfd modeling of self forming meandering channel a three dimensional cfd model was used to compute the formation of the meandering pattern in an initially straight alluvial channel the numerical model was based on the finite volume method using an unstructured grid with dominantly hexahedral cells the k e model was used to predict turbulence and the simple method was used to compute the pressure the sediment transport was computed as bed load in addition to solving the convection diffusion equation for suspended sediment transport the bed changes were calculated and the grid was altered during the computation as channel erosion and deposition caused wetting and drying the model was tested by comparing with results from physical model studies carried out at colorado state univ fort collins colo the results showed successfully the replication of many of the meander characteristics including secondary currents cross sectional profiles meander planform meander wavelength downstream meander migration and chute formation

numerical modeling of flow processes over gravelly surfaces using structured grids and a numerical porosity treatment this article describes the development and validation of a method for representing the complex surface topography of gravel bed rivers in high resolution three dimensional computational fluid dynamic models this is based on a regular structured grid and the application of a porosity modification to the mass conservation equation in which fully blocked cells are assigned a porosity of zero fully unblocked cells are assigned a porosity of one and partly blocked cells are assigned a porosity of between 0 and 1 according to the percentage of the cell volume that is blocked the model retains an equilibrium wall function and an rng type two equation turbulence model the model is combined with a 0 002 m resolution digital elevation model of a flume based water worked gravel bed surface acquired using two media digital photogrammetry and with surface elevations that are precise to 0 001 m the model is validated by comparison with velocity data measured using a three component acoustic doppler velocimeter adv model validation demonstrates a significantly improved level of agreement than in previous studies notably in relation to shear at the bed although the resolution of model predictions was significantly higher than the adv measurements making model assessment in the presence of strong shear especially difficult a series of simulations to assess model sensitivity to bed topographic and roughness representation were undertaken these demonstrated inherent limitations in the prediction of 3 d flow fields in gravel bed rivers without high resolution topographic representation they also showed that model predictions of downstream flux were more sensitive to topographic smoothing that to changes in the roughness parameterization reflecting the importance of both mass conservation i e blockage and momentum conservation effects at the grain and bed form scale model predictions allowed visualization of the structure of form flow interactions at high resolution in particular the most protruding bed particles exerted a critical control on the turbulent kinetic energy maxima typically observed at about 20 of the flow depth above the bed

computational fluid dynamics as a tool for investigating separated flow in river bends the detailed three dimensional structure of the flow patterns in river bends with separated flow and factors controlling the existence and characteristics of these flow patterns are unclear at present it is shown here firstly how a computational fluid dynamics cfd program may be used to reproduce the qualitative features of the mean flow in a real river bend to allow testing of the model s capabilities it is then shown how the cfd code may be used to construct hypothetical channel bends which allow the experimentation necessary to investigate the controls on the extent of the separated flow

embedding reach scale fluvial dynamics within the caesar cellular automaton landscape evolution model abstract we introduce a new computational model designed to simulate and investigate reach scale alluvial dynamics within a landscape evolution model the model is based on the cellular automaton concept whereby the continued iteration of a series of local process rules governs the behaviour of the entire system the model is a modified version of the caesar landscape evolution model which applies a suite of physically based rules to simulate the entrainment transport and deposition of sediments the caesar model has been altered to improve the representation of hydraulic and geomorphic processes in an alluvial environment in channel and overbank flow sediment entrainment and deposition suspended load and bed load transport lateral erosion and bank failure have all been represented as local cellular automaton rules although these rules are relatively simple and straightforward their combined and repeatedly iterated effect is such that complex non linear geomorphological response can be simulated within the model examples of such larger scale emergent responses include channel incision and aggradation terrace formation channel migration and river meandering formation of meander cutoffs and transitions between braided and single thread channel patterns in the current study the model is illustrated on a reach of the river teifi near lampeter wales uk

modelling differential catchment response to environmental change the caesar cellular automaton evolutionary slope and river model is used to demonstrate significant differences in coarse sediment transfer and alluviation in medium sized catchments when responding to identical holocene environmental changes simulations for four u k basins the rivers swale ure nidd and wharfe shows that catchment response driven by climate and conditioned by land cover changes is synchronous but varies in magnitude there are bursts of sediment transfer activity generally of rapid removal but with some sediment accumulation dspikest with longer periods of slow removal or accumulation of sediment in different valley reaches within catchments reach sensitivity to environmental change varies considerably some periods are only recorded in some reaches whilst higher potential sensitivity typically occurs in the piedmont areas of the catchments modelled here these differential responses appear to be highly non linear and may relate to the passage of sediment waves by variable local sediment storage and availability and by large and small scale thresholds for sediment transfer within each catchment differential response has major implications for modelling fluvial systems and the interpretation of field data model results are compared with the record of dated alluvial deposits in the modelled catchments d 2005 elsevier b v all rights reserved

cellular modelling of river catchments and reaches advantages limitations and prospects the last decade has witnessed the development of a series of cellular models that simulate the processes operating within river channels and drive their geomorphic evolution their proliferation can be partly attributed to the relative simplicity of cellular models and their ability to address some of the shortcomings of other numerical models by using relaxed interpretations of the equations determining fluid flow cellular models allow rapid solutions of water depths and velocities these can then be used to drive usually conventional sediment transport relations to determine erosion and deposition and alter the channel form the key advance of using these physically based yet simplified approaches is that they allow us to apply models to a range of spatial scales 1 100 km 2 and time periods 1 100 years that are especially relevant to contemporary management and fluvial studies however these approaches are not without their limitations and technical problems this paper reviews the findings of nearly 10 years of research into modelling fluvial systems with cellular techniques principally focusing on improvements in routing water and how fluvial erosion and deposition including lateral erosion are represented these ideas are illustrated using sample simulations of the river teifi wales a detailed case study is then presented demonstrating how cellular models can explore the interactions between vegetation and the morphological dynamics of the braided waitaki river new zealand finally difficulties associated with model validation and the problems prospects and future issues important to the further development and application of these cellular fluvial models are outlined 2007 elsevier b v all rights reserved

the natural magnetization of a 3 kilometer section of icelandic crust the magnetization and magnetic properties of samples from a 3 km vertical section of icelandic crust the iceland research drilling project section are described the section is located at the head of reydarfjordur eastern iceland at 65 01 n 14 21 w and extends vertically from about 0 5 km to 3 5 km depth beneath the original surface the section consists of 1 km of exposed flows with minor dikes and volcaniclastics underlain by a 2 km drill core component consisting of 60 flows and minor volcaniclastics and 40 dikes the section is largely normally magnetized corresponding in age and polarity to seafloor spreading anomaly 5 geomagnetic polarity epoch 9 flows which accumulated during anomaly 5 time extend vertically for 2145 m in contrast with 1000 m thick equivalent sections which are exposed updip this great increase in downdip thickening is consistent with observations elsewhere in eastern iceland and models for icelandic crustal formation involving the combination of volcanic activity subsidence and spreading a combination of paleomagnetic and structural evidence is used to provide an age calibration for the section and to predict the local presence of magnetic overprinting in the lower part of the section this overprinting is probably in part due to the production of secondary magnetite and is developed to a varying extent in epidote bearing flows at below 2 8 km crustal original depth where moderate secondary magnetite development has occurred flows frequently show both normal and reverse stable polarities with the latter being the original secondary magnetite development is high where dike density in the epidote bearing flows is also high here very strong well defined pervasive normal magnetization characterizes the flows this also being the dominant polarity of the dikes magnetic overprinting of this type imposed shortly after crustal formation could occur at 800 to 1200 m depth in typical ocean crust and may provide a contribution to the source for the linear magnetic anomaly patterns of the ocean basins the initial susceptibility of the flows shows the best defined depth trends over the section susceptibility increases with depth to about 2 km crustal depth and then decreases systematically to the bottom of the section the reason for the initial increase is not known but the decrease at depth can be explained by transfer of iron from primary oxides to secondary oxides and silicates the decrease is sufficiently linear to warrant extrapolation to a zero value at 4 3 km crustal depth or just below the estimated level of onset of greenschist facies metamorphic conditions in typical oceanic crust the equivalent level is estimated to be at 1 2 km depth the net magnetization of the section the combined remanent and induced contributions when expressed as average values for 500 m depth intervals is everywhere positive that is is in the sense of the present field variation in net magnetization is related to the proportions of the normal and reversely magnetized units in each interval

a cellular automata model of surface water flow previous cellular automata models of surface water flow have been constructed to reflect steady gradually varied flow conditions while these models are extremely important in showing the near equilibrium forms that result from the interactions of water and boundary material highly dynamic forms and processes require models that represent unsteady flow conditions in order to simulate unsteady flow in a cellular model of surface water flow the conservation of mass and the manning s equations are coupled with an algorithm to delay the movement of water from one pixel to the next until the correct timing is reached this approach yields highly realistic flood wave hydrographs when compared with flood observations in the walnut gulch experiment watershed coupling this unsteady flow model with simple laws of sediment erosion transport and deposition should allow event based simulations of watershed and river channel geomorphologic change copyright 2007 john wiley sons ltd

sedimentology and paleontology of a tsunami deposit accompanying the great chilean earthquake of february 2010 abstract at pichilemu in the northern third of the rupture area of the moment magnitude scale mw 8 8 2010 chile earthquake deposits of the tsunami accompanying the earthquake consist of a lower layer of medium to fine sand mean grain size of 200 m containing rock clasts overlain by a thin silty very fine sand mean grain size of 125 m layer based on a sedimentological model most 90 of the deposit is finer than 401 408 m suggesting tsunami flow velocities were between 7 m s and 13 5 m s ostracods were common in the upper layer along with a small number of broken benthic foraminifera and a single planktonic foraminifera diatoms were abundant throughout species assemblages represent a mixture of diatoms from differing environments life forms and substrate preferences we attribute the mixed assemblages to turbulence within the water column during tsunami inundation with erosion of beaches and salt marshes followed by redeposition of sand and mud inland breakage of fragile diatom valves in the lower layer may also support transport by turbulent flow a higher abundance of diatom species with mud substrate preferences in the upper layer implies a decrease in flow velocity from lower to upper layers

hydraulic validation of two dimensional simulations of braided river flow with spatially continuous adcp data 1 gravel bed braided rivers are characterized by shallow branching flow across low relief complex and mobile bed topography these conditions present a major challenge for the application of higher dimensional hydraulic models the predictions of which are nevertheless vital to inform flood risk and ecosystem management this paper demonstrates how high resolution topographic survey and hydraulic monitoring at a density commensurate with model discretization can be used to advance hydrodynamic simulations in braided rivers specifically we detail applications of the shallow water model delft3d to the rees river new zealand at two nested scales a 300 m braid bar unit and a 2 5 km reach in each case terrestrial laser scanning was used to parameterize the topographic boundary condition at hitherto unprecedented resolution and accuracy dense observations of depth and velocity acquired from a mobile acoustic doppler current profiler adcp along with low altitude aerial photography were then used to create a data rich framework for model calibration and testing at a range of discharges calibration focused on the estimation of spatially uniform roughness and horizontal eddy viscosity h through comparison of predictions with distributed hydraulic data results revealed strong sensitivity to h which influenced cross channel velocity and localization of high shear zones the high resolution bed topography partially accounts for form resistance and the recovered roughness was found to scale by 1 2 1 4 d84 grain diameter model performance was good for a range of flows with minimal bias and tight error distributions suggesting that acceptable predictions can be achieved with spatially uniform roughness and h

scales and causes of heterogeneity in bars in a large multi channel river rio parana argentina to date published studies of alluvial bar architecture in large rivers have been restricted mostly to case studies of individual bars and single locations relatively little is known on how the depositional processes and sedimentary architecture of km scale bars vary within a multi km reach or over several 100s km downstream this study presents ground penetrating radar gpr and core data from 11 km scale bars from the rio parana argentina the investigated bars are located between 30 km upstream and 540 km downstream of the rio parana rio paraguay confluence where a significant volume of fine grained suspended sediment is introduced into the network bar scale cross stratified sets with lengths and widths up to 600 m and thicknesses up to 12 m enable the distinction of large river deposits from stacked deposits of smaller rivers but are only present in half the surface area of the bars up to 90 of bar scale sets are found on top of finer grained ripple laminated bar trough deposits bar scale sets make up as much as 58 of the volume of the deposits in small incipient mid channel bars but this proportion decreases significantly with increasing age and size of the bars contrary to what might be expected a significant proportion of the sedimentary structures found in the rio parana is similar in scale to those found in much smaller rivers in other words large river deposits are not always characterised by big structures that allow a simple interpretation of river scale however the large scale of the depositional units in big rivers causes small scale structures such as ripple sets to be grouped in thicker co sets which indicate river scale even when no obvious large scale sets are present the results also show that the composition of bars differs between the studied reaches upstream and downstream of the confluence with the rio paraguay relative to other controls on downstream fining the tributary input of fine grained suspended material from the rio paraguay causes a marked change in the composition of the bar deposits compared to the upstream reaches the sedimentary architecture of the downstream reaches in the top 5 m of mid channel bars shows i an increase in the abundance and thickness up to m scale of laterally extensive 100s of metres fine grained layers ii an increase in the percentage of deposits comprised of ripple sets to 40 in the upper bar deposits and iii an increase in bar trough deposits and a corresponding decrease in bar scale cross strata

numerical simulation of three dimensional time averaged flow structure at river channel confluences current confluence research emphasizes three broad controls on flow structure generation 1 planform curvature 2 topographic steering and 3 anisotropic turbulence associated with flow separation and shear layer dynamics the relative importance of these processes in explaining observed flow structures is controversial a situation that may be related to the fact that different investigators have examined different confluence configurations this paper uses a three dimensional numerical model with a fully elliptic solution a free surface treatment and a turbulence model based on a renormalized group rng to help to provide a physically based explanation of the controls upon flow structure generation for both a laboratory rectangular and a field confluence the confluence of the kaskaskia river and copper slough and to identify the particular conditions under which particular flow structures are observed results suggest that an analogy with back to back meanders is possible for symmetrical configurations but that there will be progressive divergence from this state as confluence asymmetry increases in asymmetric situations a dual cell structure may be limited to the immediate vicinity of the junction because of the effects of streamline curvature and topographic steering these differences can be explained by consideration of the dynamic pressure field which may be specific to each confluence configuration as such this study partially reconciles differing views over what controls time averaged flow structures in river channel confluences although further research into the interaction of these processes with instantaneous velocity fluctuations is required

computational fluid dynamics modelling of boundary roughness in gravel bed rivers an investigation of the effects of random variability in bed elevation results from a series of numerical simulations of two dimensional open channel flow conducted using the computational fluid dynamics cfd code fluent are compared with data quantifying the mean and turbulent characteristics of open channel flow over two contrasting gravel beds boundary roughness effects are represented using both the conventional wall function approach and a random elevation model that simulates the effects of supra grid scale roughness elements e g particle clusters and small bedforms results obtained using the random elevation model are characterized by a peak in turbulent kinetic energy located well above the bed typically at y h 0 1 0 3 this is consistent with the field data and in contrast to the results obtained using the wall function approach for which maximum turbulent kinetic energy levels occur at the bed use of the random elevation model to represent supra grid scale roughness also allows a reduction in the height of the near bed mesh cell and therefore offers some potential to overcome problems experienced by the wall function approach in flows characterized by high relative roughness despite these benefits the results of simulations conducted using the random elevation model are sensitive to the horizontal and vertical mesh resolution increasing the horizontal mesh resolution results in an increase in the near bed velocity gradient and turbulent kinetic energy effectively roughening the bed varying the vertical resolution of the mesh has little effect on simulated mean velocity profiles but results in substantial changes to the shape of the turbulent kinetic energy profile these findings have significant implications for the application of cfd within natural gravel bed channels particularly with regard to issues of topographic data collection roughness parameterization and the derivation of mesh independent solutions copyright 2001 john wiley sons ltd

causes of rapid mixing at a junction of two large rivers rio parana and rio paraguay argentina 1 airborne and satellite observations show that when large rivers join they can take hundreds of kilometers to mix completely but on occasion may mix very rapidly application of established semitheoretical analyses shows that long mixing lengths should be expected the first measurements of mixing processes at a large river junction rio parana and rio paraguay argentina combined width 2 8 km are presented at two occasions first when they mix in 400 km and second when mixing is complete in only 8 km downstream of the junction for the case of slower mixing at a point surveys showed that mixing driven by turbulent shear associated with a near vertical shear layer was restricted to close to the junction to 0 272 multiples of the postconfluence width downstream transect surveys showed penetration of more turbid water from the rio paraguay underneath the rio parana but this was insufficient to promote more rapid mixing there was no clear channel scale circulation present and slow mixing was compounded by reverse topographic forcing on the mainstream rio parana side of the river this kept more turbid water on the rio paraguay side of the river close to the bed in the case of rapid mixing we found clear channel scale circulation the momentum ratio between the combining flows reinforced the effects of the discordance in bed height between the tributaries at the confluence and allowed penetration of more turbid rio paraguay water further across the channel width deeper within the flow the importance of the interaction between momentum ratio and bed morphology at channel junctions makes mixing rates at the confluence dependent upon basin scale hydrological response which is more likely to differ between large confluent rivers than small rivers as a result of the different climatic topographic zones that they may capture

numerical simulation of longitudinal and lateral channel deformations in the braided reach of the lower yellow river bank erosion frequently occurs in the lower yellow river lyr playing an important role in the evolution of this braided river a two dimensional 2d composite model is developed herein that consists of a depth averaged 2d flow and sediment transport submodel and a bank erosion submodel the model incorporates a new technique for updating bank geometry during either degradational or aggradational bed evolution allowing the two submodels to be closely combined using the model the fluvial processes in the braided reach of the lyr between huayuankou and laitongzhai are simulated and the calculated results generally agree with the field measurements including the water surface elevation variation of water surface width and variations of cross sectional profiles the calculated average water surface elevation in the study reach was 0 09 m greater than the observed initial value and the calculated mean bed elevation for six cross sections was 0 11 m lower than the observed value after 24 days these errors are attributed to the large variability of flow and sediment transport processes sensitivity tests of three groups of parameters are conducted and these groups of parameters are related to flow and sediment transport bank erosion and model application respectively analysis results of parameter sensitivity tests indicate that bank erodibility coefficient and critical shear stress for bank material are sensitive to the simulated bank erosion process the lateral erosion distance at huayuankou will increase by 19 as the value of bank erodibility coefficient changes from 0 1 to 0 3 and it will decrease by 57 as the value of critical shear stress for bank increases from 0 6 to 1 2 n m limited changes of other parameters have relatively small effects on the simulated results for this reach and the maximum change extent of calculated results is less than 5 because the process of sediment transport and bank erosion in the braided reach of the lyr is very complicated further study is needed to verify the model

investigation of spatially distributed braided river flows using a two dimensional hydraulic model this paper reports the application of a two dimensional hydraulic model to a braided reach of the avoca river new zealand field measurements of water surface elevation depth and velocity obtained at low flow were used to validate the model and to optimize the parameterization of bed friction the main systematic trends in the measured flow variables are reproduced by the model however field data are characterized by greater spatial variability than model output reflecting differences in the scale of processes measured in the field and represented by the model additional model runs were conducted to simulate flow patterns within the study reach at five higher discharges the purpose of these simulations was to evaluate the potential for using two dimensional hydraulic models to quantify the reach scale hydraulic characteristics of braided rivers and their dependence on discharge changes in flow depth and velocity with increasing discharge exhibit trends that are consistent with the results of previous field investigations although the tendency for the wetted area of the braidplain within particular depth and velocity categories to remain fixed as discharge rises as has been noted for several braided rivers in new zealand was not observed modelled shear stress frequency distributions fit gamma functions that incorporate a distribution shape parameter the value of which follows clear systematic trends with rising discharge these results illustrate both the problems of and potential for using two dimensional hydraulic models in braided river applications this leads to something of a paradox in that while such models provide a means of generating hydraulic information that would be difficult to obtain in the field at an equivalent spatial resolution they are due to the problems inherent to data collection difficult to validate conclusively despite this limitation the application of spatially distributed models to investigate relationships between discharge and reach scale form and process variables appears to have considerable potential copyright 2003 john wiley sons ltd

modelling hydrodynamics in the rio parana argentina an evaluation and inter comparison of reduced complexity and physics based models applied to a large sand bed river abstract depth averaged velocities and unit discharges within a 30 km reach of one of the world s largest rivers the rio parana argentina were simulated using three hydrodynamic models with different process representations a reduced complexity rc model that neglects most of the physics governing fluid flow a two dimensional model based on the shallow water equations and a three dimensional model based on the reynolds averaged navier stokes equations flow characteristics simulated using all three models were compared with data obtained by acoustic doppler current profiler surveys at four cross sections within the study reach this analysis demonstrates that surprisingly the performance of the rc model is generally equal to and in some instances better than that of the physics based models in terms of the statistical agreement between simulated and measured flow properties in addition in contrast to previous applications of rc models the present study demonstrates that the rc model can successfully predict measured flow velocities the strong performance of the rc model reflects in part the simplicity of the depth averaged mean flow patterns within the study reach and the dominant role of channel scale topographic features in controlling the flow dynamics moreover the very low water surface slopes that typify large sand bed rivers enable flow depths to be estimated reliably in the rc model using a simple fixed lid planar water surface approximation this approach overcomes a major problem encountered in the application of rc models in environments characterised by shallow flows and steep bed gradients the rc model is four orders of magnitude faster than the physics based models when performing steady state hydrodynamic calculations however the iterative nature of the rc model calculations implies a reduction in computational efficiency relative to some other rc models a further implication of this is that if used to simulate channel morphodynamics the present rc model may offer only a marginal advantage in terms of computational efficiency over approaches based on the shallow water equations these observations illustrate the trade off between model realism and efficiency that is a key consideration in rc modelling moreover this outcome highlights a need to rethink the use of rc morphodynamic models in fluvial geomorphology and to move away from existing grid based approaches such as the popular cellular automata ca models that remain essentially reductionist in nature in the case of the world s largest sand bed rivers this might be achieved by implementing the rc model outlined here as one element within a hierarchical modelling framework that would enable computationally efficient simulation of the morphodynamics of large rivers over millennial time scales

morphology and flow fields of three dimensional dunes rio parana argentina results from simultaneous multibeam echo sounding and acoustic doppler current profiling 1 most past studies of river dune dynamics have concentrated on two dimensional 2 d bed forms with constant heights and straight crest lines transverse to the flow and their associated turbulent flow structure this morphological simplification imposes inherent limitations on the interpretation and understanding of dune form and flow dynamics in natural channels where dune form is predominantly three dimensional for example studies over 2 d forms neglect the significant influence that lateral flows and secondary circulation may have on the flow structure and thus dune morphology this paper details a field study of a swath of 3 d dunes in the rio parana argentina a large 0 35 km wide 1 2 km long area of dunes was surveyed using a multibeam echo sounder mbes that provided high resolution 3 d detail of the river bed simultaneous with the mbes survey 3 d flow information was obtained with an acoustic doppler current profiler adcp revealing a complicated pattern of dune morphology and associated flow structure within the swath dune three dimensionality appears intimately connected to the morphology of the upstream dune with changes in crest line curvature and crest line bifurcations junctions significantly influencing the downstream dune form dunes with lobe or saddle shaped crest lines were found to have larger more structured regions of vertical velocity with smaller separation zones than more 2 d straight crested dunes these results represent the first integrated study of 3 d dune form and mean flow structure from the field and show several similarities to recent laboratory models of flow over 3 d dunes

application of a roughness length representation to parameterize energy loss in 3 d numerical simulations of large rivers 1 recent technological advances in remote sensing have enabled investigation of the morphodynamics and hydrodynamics of large rivers however measuring topography and flow in these very large rivers is time consuming and thus often constrains the spatial resolution and reach length scales that can be monitored similar constraints exist for computational fluid dynamics cfd studies of large rivers requiring maximization of mesh or grid cell dimensions and implying a reduction in the representation of bedform roughness elements that are of the order of a model grid cell or less even if they are represented in available topographic data these subgrid elements must be parameterized and this paper applies and considers the impact of roughness length treatments that include the effect of bed roughness due to unmeasured topography cfd predictions were found to be sensitive to the roughness length specification model optimization was based on acoustic doppler current profiler measurements and estimates of the water surface slope for a variety of roughness lengths this proved difficult as the metrics used to assess optimal model performance diverged due to the effects of large bedforms that are not well parameterized in roughness length treatments however the general spatial flow patterns are effectively predicted by the model changes in roughness length were shown to have a major impact upon flow routing at the channel scale the results also indicate an absence of secondary flow circulation cells in the reached studied and suggest simpler two dimensional models may have great utility in the investigation of flow within large rivers

on the relationship between flow and suspended sediment transport over the crest of a sand dune rio parana argentina the links between large scale turbulence and the suspension of sediment over alluvial bedforms have generated considerable interest in the last few decades with past studies illustrating the origin of such turbulence and its influence on flow resistance sediment transport and bedform morphology in this study of turbulence and sediment suspension over large sand dunes in the rio parana argentina time series of three dimensional velocity and at a point suspended sediment concentration and particle size were measured with an acoustic doppler current profiler and laser in situ scattering transmissometer respectively these time series were decomposed using wavelet analysis to investigate the scales of covariation of flow velocity and suspended sediment the analysis reveals an inverse relationship between streamwise and vertical velocities over the dune crest where streamwise flow deceleration is linked to the vertical flux of fluid towards the water surface in the form of large turbulent fluid ejections regions of high suspended sediment concentration are found to correlate well with such events the frequencies of these turbulent events have been assessed from wavelet analysis and found to concentrate in two zones that closely match predictions from empirical equations such a finding suggests that a combination and interaction of vortex shedding and wake flapping changing length of the lee side separation zone are the principal contributors to the turbulent flow field associated with such large alluvial sand dunes wavelet analysis provides insight upon the temporal and spatial evolution of these coherent flow structures including information on the topology of dune related turbulent flow structures at the flow stage investigated the turbulent flow events and their associated high suspended sediment concentrations are seen to grow with height above the bed until a threshold height ca 0 45 flow depth is reached above which they begin to decay and dissipate

diatom assemblages in tsunami deposits associated with the 2004 indian ocean tsunami at phra thong island thailand abstract diatom assemblages in sandy deposits of the 2004 tsunami at phra thong island thailand may provide clues to flow conditions during the tsunami the tsunami deposits contain one or more beds that fine upward commonly from medium sand to silty very fine sand diatom assemblages of the lowermost portion of the deposit predominantly comprise unbroken beach and subtidal species that live attached to sand grains the dominant taxa shift to marine plankton species in the middle of the bed and to a mix of freshwater brackish and marine species near the top these trends are consistent with expected changes in current velocities of tsunami through time during high current velocities medium sand is deposited only beach and subtidal benthic diatoms attached to sediment can be incorporated into the tsunami deposit high shear velocity keeps finer material including planktonic diatoms in suspension with decreasing current velocities finer material including marine plankton can be deposited finally during the lull between tsunami waves the entrained freshwater brackish and marine species settle out with mud and plant trash low numbers of broken diatoms in the lower medium sand implies rapid entrainment and deposition whilst selective breakage of marine plankton thalassionema nitzschioides and thalassiosira and coscinodiscus spp in the middle portion of the deposit probably results from abrasion in the turbulent current before deposition

numerical simulation of relatively wide shallow channels with erodible banks a two dimensional numerical model was developed to simulate relatively wide shallow rivers with an erodible bed and banks composed of well sorted sandy materials a moving boundary fitted coordinate system was used to calculate water flow bed change and bank erosion the cubic interpolated pseudoparticle method was used to calculate flow which introduced little numerical diffusion the sediment transport equation for the streamline and transverse transport was used to estimate bed and bank evolution over time while considering the secondary flow bank erosion was simulated when the gradient in the cross sectional direction of the banks was steeper than the submerged angle of repose because of bed erosion near the banks the numerical model reproduced the features of central bars well such as bar growth channel widening due to divergence of the flow around the bars scour holes at the lee of the bars and the increase of bar size with time these features were in accordance with the observations for laboratory experiments it also reproduced the features of braided rivers such as the generation of new channels and abandonment of old channels the bifurcation and confluence of channels and the lateral migration of the channels the model showed that the sediment discharge rate fluctuated with time one of the dynamic features observed in braided channels

statistical significance of the fold test in palaeomagnetism summary the significance of the change in direction dispersion on applying the fold test in palaeomagnetism is used as the criterion for deciding whether or not the fold test has statistical significance a set of tables is compiled which can be used for quick application of the test

high resolution finite volume method for shallow water flows a high resolution time marching method is presented for solving the two dimensional shallow water equations the method uses a cell centered formulation with collocated data rather than a space staggered approach spurious oscillations are avoided by employing monotonic upstream schemes for conservation laws muscl reconstruction with an approximate riemann solver in a two step runge kutta time stepping scheme a finite volume implementation on a boundary conforming mesh is chosen to more accurately map the complex geometries that will occur in practice these features enable the model to deal with dam break phenomena involving flow discontinuities subcritical and supercritical flows and other cases the method is applied to several bore wave propagation and dam break problems

the sedimentary record of the 2005 hurricane season from the mississippi and alabama coastlines abstract the instrumental record of hurricane activity is too short to fully capture the occurrence of the rare but most destructive hurricanes therefore obtaining a record of present and past landfalling hurricanes and their extent of geological and ecological impacts is one means to assess future risk reveal the spatial and temporal variability of hurricane activity and decipher its relationship with global climatic changes we rapidly dispatched survey teams to collect the readily available but perishable data of hurricanes katrina and rita storm surge from two salt marshes in mississippi and one salt marsh in alabama in mississippi we recorded hurricane katrina storm surge heights greater than 7 5 m north american vertical datum 88 navd88 with inland extents in excess of 700 m whereas in alabama the maximum recorded storm surge was 3 43 m navd88 at one salt marsh in mississippi we recorded the maximum inland extent and elevation of maximum penetration of hurricane rita as 370 m and 3 43 m navd88 respectively we observed a three dimensional distribution of hurricane induced storm surge deposits that tapered landward overlying salt marsh sediment there was a sharp or erosional boundary between the pre storm surge and storm surge sedimentary units which was accompanied by a change in color and lithology the overlying storm surge sediment unit was coarser than the pre storm surge unit with a lower organic content the thickness of the hurricanes katrina and rita storm surge sediments ranged from 9 to 13 cm and approximately 7 cm respectively foraminiferal analyses revealed a virtual absence of tests within the storm surge sediments whereas abundant agglutinated foraminifera were found in the underlying salt marsh deposits

assessing a numerical cellular braided stream model with a physical model a b murray and c paola 1994 nature vol 371 pp 54 57 1997 earth surface processes and landforms vol 22 pp 1001 1025 proposed a cellular model for braided river dynamics as an exploratory device for investigating the conditions necessary for the occurrence of braiding the model reproduces a number of the general morphological and dynamic features of braided rivers in a simplified form here we test the representation of braided channel morphodynamics in the murray paola model against the known characteristics mainly from a sequence of high resolution digital elevation models of a physical model of a braided stream the overall aim is to further the goals of the exploratory modelling approach by first investigating the capabilities and limitations of the existing model and then by proposing modifications and alternative approaches to modelling of the essential features of braiding the model confirms the general inferences of murray and paola 1997 about model performance however the modelled evolution shows little resemblance to the real evolution of the small scale laboratory river although this depends to some extent on the coarseness of the grid used in the model relative to the scale of the topography the model does not reproduce the bar scale topography and dynamics even when the grid scale and amplitude of topography are adapted to be equivalent to the original murray paola results strong dependence of the modelled processes on local bed slopes and the tendency for the model to adopt its own intrinsic scale rather than adapt to the scale of the pre existing topography appear to be the main causes of the differences between numerical model results and the physical model morphology and dynamics the model performance can be improved by modification of the model equations to more closely represent the water surface but as an exploratory approach hierarchical modelling promises greater success in overcoming the identified shortcomings copyright 2005 john wiley sons ltd

cellular modelling as a tool for interpreting historic braided river evolution abstract results are presented from a new cellular model of braided river dynamics that simulates flow sediment transport morphological change and the effects of braidplain vegetation this model is used to investigate the effect of changes in upstream sediment supply on braided river systems over simulation periods of 200 years modelled changes in channel morphology associated with both aggradation and degradation were seen to be consistent with those reported in the literature in addition simulation results allowed the identification of diagnostic characteristics of aggrading and degrading reaches in the form of relationships between the age extent and relative elevation of fluvial surfaces interpretation of spatial patterns of valley floor surface characteristics in the avoca river new zealand on the basis of these relationships allowed the identification of channel reaches that appear to be experiencing either aggradation or degradation these inferences are shown to be consistent with independent evidence of spatial patterns of sediment supply to the main valley floor derived from aerial photographs and an existing sediment source inventory these results illustrate the potential for using cellular models to develop an improved understanding of natural river behaviour

three dimensional modeling of sediment transport in a narrow 90 channel bend a three dimensional numerical model was used for calculating the velocity and bed level changes over time in a 90 bended channel the numerical model solved the reynolds averaged navier stokes equations in three dimensions to compute the water flow and used the finite volume method as the discretization scheme the k e model predicted the turbulence and the simple method computed the pressure the suspended sediment transport was calculated by solving the convection diffusion equation and the bed load transport quantity was determined with an empirical formula the model was enhanced with relations for the movement of sediment particles on steep side slopes in river bends located on a transversally sloping bed a sediment particle has a lower critical shear stress than on a flat bed also the direction of its movement deviates from the direction of the shear stress near the bed these phenomenona are considered to play an important role in the morphodynamic process in sharp channel bends the calculat

sensitivity of simulated flow fields and bathymetries in meandering channels to the choice of a morphodynamic model morphodynamic models are used by river practitioners and scientists to simulate geomorphic change in natural and artificial river channels it has long been recognized that these models are sensitive to the choice of parameter values and proper calibration is now common practice this paper investigates the less recognized impact of the choice of the model itself all morphodynamic models purport to simulate the same flow and sediment dynamics often relying on the same governing equations yet in solving these equations the models have different underlying assumptions for example regarding spatial discretization turbulence sediment inflow lateral friction and bed load transport these differences are not always considered by the average model user who might expect similar predictions from calibrated models here a series of numerical simulations in meandering channels was undertaken to test whether six morphodynamic codes basement cche 2d nays ssiim 1 telemac 2d and telemac 3d would yield significantly different equilibrium bathymetries if subjected to identical initial flow conditions we found that despite producing moderately similar velocity patterns on a fixed flat bed regression coefficient r of 0 77 0 20 the codes disagree substantially with respect to simulated bathymetries r 0 49 0 31 we relate these discrepancies to differences in the codes assumptions results were configuration specific i e codes that perform well for a given channel configuration do not necessarily perform well with higher or lower sinuosity configurations finally limited correlation is found between accuracy and code complexity the inclusion of algorithms that explicitly account for the effects of local bed slope and channel curvature effects on transport magnitude and direction does not guarantee accuracy the range of solutions obtained from the evaluated codes emphasizes the need for carefully considering the choice of code we recommend the creation of a central repository providing universal validation cases and documentation of recognized fluvial codes in commonly studied fluvial settings copyright 2015 john wiley sons ltd

crustal growth and late precambrian early palaeozoic plate tectonic evolution of england and wales comparison of the basement rocks of britain reveals major contrasts to the n and s of the iapetus suture solway shannon line north of the suture polymetamorphic high grade basement schists and gneisses and igneous rocks date from about 2900 ma to c 400 ma the latter age corresponding to closure of the iapetus ocean by contrast s of the suture in england and wales the basement is dominantly low grade metamorphic rock together with intrusive and extrusive igneous and sedimentary rocks there is little geological or geochemical evidence for the presence of basement older than c 900 ma below this area and the predominant expression of crustal growth in england and wales is indicated by radiometric ages between c 700 ma and 450 ma reflecting late precambrian palaeozoic magmatism and metamorphism palaeomagnetic data from scotland demonstrate that the crust in northern britain developed as an integral part of the laurentian shield during mid proterozoic times 1600 1000 ma the palaeomagnetic record from the pre ordovician rocks of england and wales shows that this area was unrelated to the laurentian shield prior to closure of the iapetus ocean the apparent polar wander a p w path is that of a distinct microplate involved in rapid growth of iapetus during early cambrian times and emplaced in its present configuration adjacent to northern britain as a result of subduction of the ocean basin between cambrian and silurian times we conclude that whereas the basement to the north of the iapetus suture formed an essentially continental unit from 2900 to 400 ma the basement of england and wales is a result of crustal growth from about 900 ma to 400 ma and formed by accretion of island arcs associated accretionary prisms and fore arc basin sediments within the iapetus ocean

comparison of fixed and moving vessel flow measurements with an adp in a large river a comparison of three dimensional flow velocity measurements made with an acoustic doppler profiler adp from fixed and moving vessels at cross sections of the parana river argentina was performed the purpose was to design a rapid and reliable procedure for quantifying the velocity field and related parameters such as bed shear velocity and the identification of secondary circulations in large rivers using an adp the fixed vessel measurements were performed over a period of 10 min at three vertical profiles along two of the sections these data were then compared with the results of ten moving vessel repeat transects made at each of the sections and which intersected the fixed vessel sampling locations using a number of different adp setup configurations from the velocity profiles obtained with both fixed and moving vessel measurements total bed shear velocity values were computed by applying the law of the wall the results indicate there can be significant differences between velocities obtained using the moving vessel method and fixed vessel measurements averaged over 10 min these differences in horizontal velocity can be significantly reduced by averaging five or more moving vessel transects with corresponding shear velocities calculated from five transect averages showing differences ranging between 10 and 15 dependent on the adp configuration location of the at a point vertical velocity profile in relation to large scale bed roughness may also be an influential factor and ideally the bed morphology should be quantified together with the adp derived velocities when using the adp to identify secondary flow cells it was found that although one cross section transect can provide a reasonable overall picture an average of five cross sections is necessary to resolve the finer details of flow the implications for applications that use moving vessel techniques for measurement and analysis of three dimensional flow structures including secondary flows are highlighted

the fluid dynamics of river dunes a review and some future research directions 1 dunes are present in nearly all fluvial channels and are vital in predicting flow resistance sediment transport and deposition within many rivers progress in understanding the fluid dynamics associated with alluvial dunes has been significant in the last 15 years and has witnessed huge advances in field laboratory and numerical investigations progress has been made in detailing the principal features of mean and turbulent flow over asymmetric dunes that possess flow separation in their leesides and how these forms affect both downstream boundary layer structure and stress partitioning over the dune additionally the links between sediment transport over dunes and instantaneous coherent flow structures are being increasingly understood with the feedback of dune three dimensionality upon flow and sediment dynamics over these bed forms beginning to be recognized as vital such research now provides an outstanding background for beginning to address areas of greater complexity that will enable a fuller understanding of these important natural features this review paper summarizes the principal features of mean and turbulent flow over alluvial sand dunes five areas are then highlighted and discussed as a possible focus for future research 1 the influence of dune leeside angle upon flow processes in the dune wake and downstream flow field 2 the influence of three dimensionality in dune shape upon the generation of turbulence and distribution of bed shear stress 3 flow field modification resulting from bed form superimposition and amalgamation 4 the scale and topology of dune related turbulence and its interactions with sediment transport and the flow surface and 5 the influence of suspended sediment on the dune flow field and dune morphology

case study bed resistance of rhine river during 1998 flood detailed field measurements during the 1998 flood of the rhine river in the netherlands show that both manning in and darcy weisbach friction factor if increase with discharge the changes in bedform roughness height and friction factors are attributed to the increased dune height during floods there is a near peak hysteresis in the dune height measurements at a given discharge dunes are significantly larger after than before the peak discharge the trend is most apparent for the bovenrijn with weaker variations for the waal the methods of engelund and vanoni hwang provide similar estimates of form drag when combined with van rijn s method to estimate grain resistance both methods tend to overpredict the measured bed friction factor after the peak discharge these methods perform best when field bedform measurements are available to estimate form drag the composite effect of primary and secondary dunes should be considered in the analysis of resistance to flow

extreme inundation flows during the hokkaido nansei oki tsunami the tsunami generated by the july 12 1993 hokkaido nansei oki mw 7 8 earthquake produced in japan the worst local tsunami related death toll in fifty years with estimated 10 18m sec overland flow velocities and 30m runup these extreme values are the largest recorded in japan this century and are among the highest ever documented for non landslide generated tsunamis we model this event to confirm the estimated overland flow velocities and we find that given reasonable ground deformation data current state of the art shallow water wave models can predict tsunami inundation correctly including extreme runup current velocities and overland flow we find that even small local topographic structures affect the runup to first order and that the resolution of the bathymetric data is more important than the grid resolution our results qualitatively suggest that for this event coastal inundation is more correlated with inundation velocities than with inundation heights explaining also why threshold type modeling has substantially underpredicted coastal inundation for this and other recent events

a cellular model of holocene upland river basin and alluvial fan evolution coulthard t j macklin m g kirkby m j 2002 a cellular model of holocene upland river basin and alluvial fan evolution earth surface processes and landforms 27 3 269 288

sediment transport part iii bed forms and alluvial roughness a method is presented that makes the classification of bed forms the prediction of the bed form dimensions and the effective hydraulic roughness of the bed forms feasible the proposed relationships are based on the analysis of reliable flume and field data a verification analysis using about 1 500 alternative reliable flume and field data shows good results in predicting the hydraulic roughness friction factor for field conditions the proposed method yields considerably better results than previously proposed methods which are reviewed here the proposed method has also been used to predict the flow depth and the total bed material load

simulation of braided river flow using a new cellular routing scheme abstract results are presented from a numerical simulation of two dimensional flow patterns in a braided river using a simple cellular routing scheme the results of the routing scheme are compared with field measurements of discharge per unit width obtained within the study reach at low flow and for higher flows with the predictions of a more sophisticated hydraulic model that solves the two dimensional shallow water form of the navier stokes equations an assessment is made of the sensitivity of the routing scheme to variations in the values of its main parameters and appropriate values are determined based on the physical characteristics of the study site and available flow measurements it is shown that despite the simple approach adopted by the cellular routing scheme to simulate processes of water redistribution it is able to replicate accurately both the field data and the results of the more sophisticated hydraulic model these results indicate that the routing scheme outlined here is able to overcome some of the limitations of previous simple cellular automata models and may be suitable for use in modelling bedload transport and channel change in complex fluvial environments as such this research represents a small and ongoing contribution to the field of numerical simulation of braided river processes

crossing the divide representation of channels and processes in reduced complexity river models at reach and landscape scales abstract reduced complexity models have considerable potential as tools for elucidating river behaviour over periods of 10 0 10 4 years and consequently for addressing fundamental questions concerning the scale dependent nature of explanation in geomorphology this paper proposes a simple subdivision of reduced complexity models of river behaviour into two categories that mirror methodological developments in fluvial geomorphology over the past 50 years first high resolution cellular approaches that are implemented within a framework that resolves process form feedbacks at small time and space scales second models that incorporate section averaged representations of channel geometry and processes and that are typically underpinned by regime theory and equilibrium concepts examples of both model types are presented here in the form of a cellular representation of stream braiding and a combined lattice network model of alluvial fan evolution simulations conducted using these models demonstrate how small scale process form interactions determine the emergence of larger scale channel and fan morphology and in so doing regulate system response to external forcing in this sense both models demonstrate that internal feedbacks play a critical role in controlling river responses to environmental change over historic and holocene timescales however both classes of model are characterised by uncertainty in their parameterisation of geomorphic processes such that internal feedbacks and thresholds for channel response to external forcing may vary substantially between competing models methods of refining both approaches are considered and hybrid models based on lattice network structures and mechanistic representations of channel process form interactions are identified as a means of addressing the shortcomings of existing strategies

modelling three dimensional flow structures and patterns of boundary shear stress in a natural pool riffle sequence fluid sediment interactions control river channel forms and processes analysis of spatial hydraulic patterns and the resulting boundary shear stress are required to aid understanding of river system behaviour in this paper the hydraulic processes active in a natural pool riffle sequence are simulated using a three dimensional computational fluid dynamics cfd model methods employed for the prescription of model boundary conditions are outlined model calculations are assessed using comparisons with field observations acquired over a range of flows simulations are then used to illustrate flow structures and patterns of boundary shear stress for a near bankfull and an intermediate flow event results are used to assess existing theories that seek to explain the development and maintenance of pool riffle sequences simulated results suggest that near bed velocities and bed shear stresses decrease on riffles and increase in pools as discharge increases model simulations indicate that secondary flow acts to route near bed flow over the downstream side of riffles and into the pool head away from the centre of pools implications for sediment transport and pool maintenance are discussed

three dimensional cfd modeling of morphological bed changes in the danube river 1 the bed changes in a section of the river danube were computed using a 3 d computational fluid dynamics model a time series of discharges during the flood in 2002 was used the results compared reasonably well with regular bed level surveys before and after the flood the danube river section was 6 km long and located between vienna and the austrian slovakian border the fully three dimensional numerical model solved the navier stokes equations using the k epsilon turbulence closure nonuniform sediment transport was computed using the formulas of wu et al 2000b considering hiding exposure algorithms both bed deformation and sorting processes were calculated a number of parameter sensitivity tests were carried out on roughness values parameters in the sediment transport capacity formula parameters in the hiding exposure formulas critical shields number and variations in the formulas for the effect of a sloping bed additionally the sediment inflow to the section was varied together with investigations of physical parameters such as vegetation and groyne structures the results were most sensitive to the shields number for critical movement of the sediments an error analysis was performed to give a quantitative assessment of the parameter sensitivity tests

patterns of anabranching channels the ultimate end member adjustment of mega rivers abstract large fluvial systems adjust to a combination of controls to form distinctive channels which represent a dominant factor in the evolution of floodplain geomorphology and sedimentology fluvial geomorphology has commonly classified river channels into meandering straight and braiding patterns which are seen to represent a continuum of channel geometry anabranching patterns rivers with multiple channels however are characteristic of many rivers the identification of a combination of variables that discriminates specific channel patterns has been a significant focus of research in fluvial geomorphology the development of this body of knowledge however has been established from medium and small rivers and laboratory flume studies very few of these research ideas developed from analysis of large fluvial systems this paper assesses the pattern of channel adjustment of large fluvial systems by employing hydraulic geometry discharge w d slope grain size stream power specific stream power and froude number q mean 1000 m 3 s the study demonstrates that methods currently used to discriminate channel patterns are not useful when applied to very large rivers further with the exception of the lower mississippi alluvial rivers with mean annual discharges greater than 17 000 m 3 s here classified as mega rivers do not generate single thread meandering or typical braided patterns these mega rivers develop anabranching patterns

numerical simulation of bar and island morphodynamics in anabranching megarivers 1 bar and island morphodynamics in the world s largest anabranching rivers are investigated using a new numerical model of hydrodynamics sediment transport bank erosion and floodplain development operating over periods of several hundred years simulated channel morphology is compared to that of natural rivers and shown to be realistic both in terms of the statistical characteristics of channel width depth and bar shape distributions and mechanisms of unit bar compound bar and island evolution results demonstrate that bar and island stability may be sensitive to hydrologic regime because greater variability in flood magnitude encourages the formation of emergent bars that can be stabilized by vegetation colonization simulations illustrate a range of mechanisms of unit bar generation that are linked to local bed or bank instabilities this link may explain the reduced frequency of unit bars observed in some large anabranching rivers that are characterized by stable vegetated islands and slow rates of channel change model results suggest that the degree to which sand sized bed material is carried in suspension likely represents an important control on bar morphodynamics and channel network evolution because of its influence on sand transport direction consequently differences in the partitioning of the total sand load between bed load and suspension may provide a partial explanation for contrasting styles of anabranching in the world s largest sand bed rivers these results highlight a need for spatially distributed flow and sediment transport data sets from large rivers in order to support improved parameterizations of sand transport mechanics in morphodynamic models

palaeomagnetism of late ordovician igneous intrusions from the northern welsh borderlands implications to motion of eastern avalonia and regional rotations the palaeomagnetism of a late ordovician dolerite suite widely distributed in the northern welsh borderlands has been investigated to evaluate i regional rotations associated with later deformations and ii lower palaeozoic latitudes of eastern avalonia only local effects of acadian and variscan overprinting are observed in this region and most bodies appear to preserve a primary cooling related magnetization magnetic properties in the breidden dolerite are related to primary igneous differentiation and a dual polarity characteristic remanence d i 333 1 71 6 6 sites 95 10 4 predates late ordovician folding dolerites elsewhere in the breidden hills inlier record the same reversal of remanence and the combined mean d i 314 3 72 8 is rotated clockwise from the mean remanence d i 291 5 59 5 21 sites 95 6 0 in a similar dolerite suite within the adjoining shelve inlier which is also of dual polarity and predates late ordovician folding the difference in magnetic declinations is similar to the rotation of late ordovician fold axes and fracture systems between the two inliers and is probably the resultant effect of local rotation possibly about a constraining bend in the severn valley fault system the moel y golfa andesite of caradocian soudleyan age has a remanence d i 294 3 50 4 13 samples 95 2 8 which study of an adjoining volcanic conglomerate shows to be of primary cooling related origin the equivalent palaeolatitude is 31 s in early caradocian times a similar estimate is derived from a probable diagenetic overprint in the contemporaneous castle hill conglomerate at montgomery the mynydd bryn andesite in the berwyn inlier of probable similar origin and age to moel y golfa has a magnetization of opposite polarity but similar inclination d i 239 1 47 4 14 samples 86 5 5 declination differences between these volcanic outcrops are a possible signature of later block rotations between the lower palaeozoic inliers and identify the importance of terrane definition in analysis of lower palaeozoic palaeomagnetic results from the caledonides a dolerite sheet complex at hendre in the berwyn hills has a younger remanence d i 182 3 3 0 20 samples 95 7 8 probably of mid carboniferous age the collective upper ordovician results define a rapid movement of the avalonian plate probably spanning no more than 10 ma from 30 s in early caradocian times to 57 s prior to folding of the dolerites in late caradocian to early ashgill times this motion into higher southerly palaeolatitudes marks a reversal of the motion of avalonia into more shallow southerly palaeolatitudes between arenig and llanvirn times and shows that ordovician closure of the iapetus ocean was more complex than recognized hitherto

case study two dimensional model simulation of channel migration processes in west jordan river utah the paper presents the application of a two dimensional depth averaged numerical model to simulate the lateral migration processes of a meandering reach in the west jordan river in the state of utah a new bank erosion model was developed and then integrated with a depth averaged two dimensional hydrodynamic model the rate of bank erosion is determined by bed degradation lateral erosion and bank failure because bank material in the west jordan river is stratified with layers of cohesive and noncohesive materials a specific bank erosion model was developed to consider stratified layers in the bank surface this bank erosion model distinguishes itself from other models by relating bank erosion rate with not only flow but also sediment transport near the bank additionally bank height slope and thickness of two layers in the bank surface were considered when calculating the rate of bank erosion the developed model was then applied to simulate the processes of meandering migration in the study reach

a cellular model of braided rivers a broad sheet of water flowing over non cohesive sediment typically breaks up into a network of interconnected channels called a braided stream fig 1 the dynamics of such networks are complex channels migrate laterally split rejoin and develop bars with the flow shifting unpredictably from one part of the network to another many processes are known to operate in a braided river1 3 but it is unclear which of these are essential to explain the observed dynamics we describe here a simple deterministic numerical model of water flow over a cohesionless bed that captures the main spatial and temporal features of real braided rivers the patterns arise from local scour and deposition caused by a nonlinear dependence of bedload sediment flux on water discharge although the morphology of the resulting network depends in detail on the sediment transport rule used in the model our results suggest that the only factors essential for braiding are bedload sediment transport and laterally unconstrained free surface flow

measuring velocity and shear stress over dunes with acoustic doppler profiler this study evaluates the use of an acoustic doppler profiler adp for measurement of velocity profiles over dunes in an estuary the adp can be deployed from a moving launch and provides three dimensional velocity profiles that can be used to describe flow structure and to provide rough estimates of shear stress quadratic stress models are recommended for shear stress because they estimate skin friction and form stress whereas the law of the wall only reliably estimates total stress over dunes the most serious limitation of the adp is a beam geometry that results in a large sampling diameter close to the bed that does not adequately measure velocity in dune troughs

tsunami sediments and their foraminiferal assemblages abstract tsunami hazard assessment begins with a compilation of past events that have affected a specific location given the inherent limitations of historical archives the geological record has the potential to provide an independent dataset useful for establishing a richer chronologically deeper time series of past events recent geological studies of tsunami are helping to improve our understanding of the nature and character of tsunami sediments wherever possible geologists should be working to improve the research tool kit available to identify past tsunami events marine foraminifera single celled heterotrophic protists have often been reported as present within tsunami deposited sediments but in reality little information about environmental conditions and by analogy the tsunami that deposited them has been reported even though foraminifera have an enormous capacity to provide meaningful palaeo environmental data here we review what foraminifera are describe their basic form and significance summarise where they have been reported in tsunami sediments and identify what can be learnt from them we review the gaps in our understanding and make recommendations to assist researchers who examine foraminiferal assemblages in order to enhance their use within tsunami geology

palaeomagnetic dating of sub torridon group weathering profiles nw scotland verification of neoproterozoic palaeosols a palaeoplain that cuts across lewisian gneiss in the cape wrath area northwest scotland is weathered to depths of 1 6 m beneath fluvial red conglomerates and sandstones of the applecross formation of the early neoproterozoic torridon group weathered lewisian rocks are enriched in k 2 o and fe 2 o 3 and contain hematite as an alteration product of biotite and magnetite palaeomagnetic analysis of the weathering profiles has been carried out to constrain the age of alteration thermal step demagnetization of 87 oriented core specimens of biotite gneiss and amphibolite spanning four profiles at poll a mhurain and sheigra reveal a stable high temperature component with a mean direction of remanence of d 149 1 i 57 2 95 5 0 corrected for dip of the overlying applecross strata that gives a pole at 9 8 s 199 2 e dp 5 3 dm 7 3 this direction differs significantly from that for little weathered lewisian at those two localities and also from directions for the late mesoproterozoic stoer group the remanence direction for the weathered rocks is however near the dip corrected high temperature remanence direction d 122 3 i 50 5 95 10 8 obtained by us from the thermal step demagnetization of 39 sandstone specimens of the applecross formation in the cape wrath area furthermore the direction for the weathered rocks agrees closely with other dip corrected results for the torridon group such as the detrital remanent magnetization drm mean direction d 148 3 i 59 9 95 13 8 for the applecross formation on rum and that for the main outcrop of the aultbea formation d 139 7 i 52 6 95 14 5 the concordance of palaeomagnetic results for the sediments and weathered rocks implies that the weathering profiles in the cape wrath area acquired their remanence penecontemporaneously with deposition of the applecross and aultbea formations the palaeomagnetic results therefore argue strongly that the weathering profiles are palaeosols of applecross age c 980 ma that formed at a palaeolatitude of 38 and constitute the oldest known palaeosols in the british isles views that the weathering is substantially older or younger than applecross deposition cannot be sustained our findings carry implications for applecross palaeoclimate and source and strengthen the conclusion that atmospheric oxygen was a substantial fraction of its present abundance by early neoproterozoic time

the effects of spatial resolution and dimensionality on modeling regional scale hydraulics in a multichannel river as modeling capabilities at regional and global scales improve questions remain regarding the appropriate process representation required to accurately simulate multichannel river hydraulics this study uses the hydrodynamic model lisflood fp to simulate patterns of water surface elevation wse depth and inundation extent across a 90 km anabranching reach of the tanana river alaska to provide boundary conditions we collected field observations of bathymetry and wse during a 2 week field campaign in summer 2013 for the first time at this scale we test a simple raster based model s capabilities to simulate 2 d in channel patterns of wse and inundation extent additionally we compare finer resolution 25 m 2 d models to four other models of lower dimensionality and coarser resolution 100 500 m to determine the effects of simplifying process representation results indicate that simple raster based models can accurately simulate 2 d in channel hydraulics in the tanana also the fine resolution 2 d models produce lower errors in spatiotemporal outputs of wse and inundation extent compared to coarse resolution 1 d models 22 6 cm versus 56 4 cm rmse for wse and 90 versus 41 critical success index values for simulating inundation extent incorporating the anabranching channel network using subgrid representations for smaller channels is important for simulating accurate hydraulics and lowers rmse in spatially distributed wse by at least 16 as a result better representation of the converging and diverging multichannel network by using subgrid solvers or downscaling techniques in multichannel rivers is needed to improve errors in regional to global scale models

land level changes produced by the mw 8 8 2010 chilean earthquake we observed vertically displaced coastal and river markers after the 27 february 2010 chilean earthquake moment magnitude mw 8 8 land level changes range between 2 5 and 1 meters evident along an approximately 500 kilometers long segment identified here as the maximum length of coseismic rupture a hinge line located 120 kilometers from the trench separates uplifted areas to the west from subsided regions a simple elastic dislocation model fits these observations well model parameters give a similar seismic moment to seismological estimates and suggest that most of the plate convergence since the 1835 great earthquake was elastically stored and then released during this event

finite volume model for shallow water flooding of arbitrary topography a model based on the finite volume method is developed for unsteady two dimensional shallow water flow over arbitrary topography with moving lateral boundaries caused by flooding or recession the model uses roe s approximate riemann solver to compute fluxes while the monotone upstream scheme for conservation laws and predictor corrector time stepping are used to provide a second order accurate solution that is free from spurious oscillations a robust novel procedure is presented to efficiently and accurately simulate the movement of a wet dry boundary without diffusing it in addition a new technique is introduced to prevent numerical truncation errors due to the pressure and bed slope terms from artificially accelerating quiescent water over an arbitrary bed model predictions compare favorably with analytical solutions experimental data and other numerical solutions for one and two dimensional problems

the application of computational fluid dynamics to natural river channels three dimensional versus two dimensional approaches this paper addresses the recent trend in fluvial geomorphology towards using computational fluid dynamics to explore the adjustment between flow processes sediment transport and river channel morphology it aims to evaluate the extent to which three dimensional 3d models improve predictive ability and prediction utility compared to two dimensional 2d applications this is achieved through comparing the predictions of both 3d and 2d models with high quality field data identical boundary conditions obtained from a confluence within a gravel bed river system with high relative roughness are defined for each model evaluation of the 3d model suggests that there is a fundamental limitation upon model predictive ability due to problems of specifying topographic complexity however comparison with the 2d model shows that the 3d model has a higher predictive ability particularly if the 2d model is not corrected for the effects on flow structure of secondary circulation further the 3d model provides more reliable estimates of bed shear stress and other more useful information such as the three dimensional flow field important for mixing processes this suggests that there is significant merit in the move towards 3d models but that research is required to incorporate methods developed in other fields for dealing with boundary condition uncertainties

palaeomagnetic study of the lower cambrian longmyndian sediments and tuffs welsh borderlands summary this study covers detailed thermal chemical and alternating field demagnetization from 50 sites distributed through all units of the longmyndian sedimentary succession with the exception of the stretton shales and eight sites in the tuff bands comprising the batch volcanics the resultant effect of treatment is to remove a low blocking temperature steep component and isolate a coherent remanence direction d 116 i 76 the total nrm is composite and not an adequate indicator of the palaeofield chemical demagnetization indicates that both hematite and magnetite grains contribute to this component and these two phases are magnetized in the same direction a negative fold test shows that this remanence was acquired during or after the longmyndian folding formation of the major magnetic constituent authigenic magnetite is linked to dewatering during rapid uplift following the folding which is dated by both the rb sr and fission track methods at c 525 ma the study defines a palaeopole of this age remote from the later apw path for britain and links the late precambrian lower cambrian path defmed from basement rocks of england and wales with the ordovician and younger results palaeomagnetic results from tuff bands within the sediments and lower silurian age intrusions cutting the outcrop are also reported

defining large river channel patterns alluvial exchange and plurality abstract large rivers have anabranching channels with components that may be defined as braided meandering or straight this paper shows that application of such holistic terminologies is complicated by recognition of within type and transitional type variety a confusingly varied use of terms and a coverage of pattern characteristics that for many large rivers is incomplete in natural states big rivers can be plural systems in which main accessory tributary and floodplain channels and lakes differ functionally and vary in terms of morphological dynamics a distinction is drawn between the hydrological and geomorphological connectivity of components in big river plural systems at any one time even at flood stage only some channels are geomorphologically active six types of geomorphological connectivity are described that range from coupled through to partially coupled and decoupled the interplay between geomorphological and hydrological connectivity in large rivers is shown to determine habitat status and therefore ecological diversity for improved understanding of the dynamics as well as the forms of these large composite systems it is helpful to 1 adopt element level specification not only for sediment bodies but also for functioning channels 2 track the sediment transfer processes and exchanges that produce channel forms over the highly varied timescales operating within large rivers and 3 recognise the ways in which partially coupled and connected geomorphological systems produce naturally a composite set of forms at different rates such augmenting information will provide an improved platform for both river management and ecological understanding

diatom biostratigraphy of tsunami deposits examples from the 1998 papua new guinea tsunami abstract distinctive diatom assemblages may be associated with tsunami sediments and may often contrast with the assemblages found within sediments underlying the tsunami deposit as well as those associated with the modern coastal environment sediments associated with the 1998 tsunami that destroyed much of the sissano lagoon area in northern papua new guinea have been investigated surface sediments from three transects across the sediment spit near warapu have been examined for diatom content and preservation the preservation is variable and the data show an often chaotic assemblage that can be attributed to the tsunami waves incorporating and depositing diatoms from distinctive habitat zones during their runup and subsequent backwash the diatoms identified within the warapu sediments indicate an origin from within the inter tidal and offshore area rather than from the beach sand spit complex the sand deposits disclose a high percentage in excess of 75 of broken diatom valves and a predominance of centric circular species due to preferential preservation the study demonstrates that the application of diatom biostratigraphy to modern tsunami deposits can be used in conjunction with other stratigraphical lines of evidence to interpret the source and provenance of historical and palaeo tsunami deposits