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

alluvial channel geometry theory and applications the downstream hydraulic geometry of alluvial channels in terms of bank full width average flow depth mean flow velocity and friction slope is examined from a three dimensional stability analysis of noncohesive particles under two dimensional flows four governing equations flow rate resistance to flow secondary flow and particle mobility are solved to analytically define the downstream hydraulic geometry of noncohesive alluvial channels as a function of water discharge sediment size shields number and streamline deviation angle the exponents of hydraulic geometry relationships change with relative submergence four exponent diagrams illustrate the good agreement with several empirical regime equations found in the literature the analytical formulations were tested with a comprehensive data set consisting of 835 field channels and 45 laboratory channels the data set covers a wide range of flow conditions from meandering to braided sand bed and gravel bed rivers with flow depths and channe

stochastic variability of fluvial hydraulic geometry mississippi and red rivers major reasons for uncertainty in engineering predictions of river flows are the spatial variability and measurement error associated with depicting channel geometry this paper develops a descriptive spatial stochastic model of depth based hydraulic geometry in application to four dense data sets from the mississippi and red rivers to represent the irregularity in flow area and hydraulic radius as functions of flow depth at a station cross section geometry is defined using regressed power functions accompanied by random residuals more than 1600 surveyed cross sections are analyzed to describe trends in the spatial variance and gradual large scale and periodic medium scale trends in the spatial mean of cross sectional geometry parameters and channel bed slope also described are the probability distribution and correlation structure of each parameter s random component the relationships between spatial statistics of hydraulic geometry and bankfull width channel sinuosity meander patterns bed elevation and riffle pool spacing and bank composition are explored conclusions and implications are discussed regarding the variable nature of fluvial hydraulic geometry and regarding the incorporation of geometric parameter uncertainty into prescriptive models of river processes

refined hydraulic geometry data for british gravel bed rivers databases describing the dimensions of stable and adjusting river channels are necessary to calibrate and verify morphological models however existing databases do not provide quantitative descriptions of the strength and sedimentary properties of river bank materials they are therefore incompatible with the requirements of modern models which take into account river bank erosion processes this note describes the methods and results of a program of bank material sampling undertaken at 58 british gravel bed rivers bank material data have been merged with existing hydraulic geometry data for these sites to provide a resource for those who wish to calibrate and verify analytical and numerical models of channel morphology the merged dataset is available online from the url http www geog soton ac uk research 62rivers

assessing channel changes of the ganges padma river system in bangladesh using landsat and hydrological data abstract the ganga ganges 1 is an important river system in south asia which supports the life and livelihoods of millions of people both in india and bangladesh the system has a number of names throughout its length below its confluence with the brahmaputra at aricha it is known as the padma which in turn merges with the upper meghna at chandpur below which the channel is known as the lower meghna there is a growing concern about this large river system because its channels are subject to frequent migration threatening engineering structures and resulting in various environmental and social consequences which may be compounded by climatic variability land use change and agricultural intensification as the basin experiences rapid population growth concerns have been expressed that the construction of a barrage just upstream of the indo bangladesh border has adversely affected the ganges reach in bangladesh partly in order to investigate this the planform changes of the ganges and the padma within bangladesh was analysed over the period 1973 to 2011 using multitemporal landsat images and long term flow data in eight epochs with an average duration of 4 5 years the padma reach is less affected by the barrage and provides a useful control study areas of erosion and deposition were determined from sequential changes in the bankline positions mean channel width sinuosity and braiding index were analysed using a geographic information system gis flood frequency duration and magnitudes were studied using long term discharge records generally channel planform evaluation indicated that both the ganges and the padma experienced contraction expansion and readjustment in configuration over the last 38 years erosion and deposition statistics of the ganges indicate that 57 km2 of land was lost along the right bank whereas around 59 km2 has been gained along the left bank during the assessment period suggesting that the erosion and accretion of both banks is roughly balanced with a general movement towards the right bank the width of the ganges varied from a maximum of 5 36 to a minimum of 3 23 km during the observation period changes to sandbar area are in general much more radical than changes to the overall width and area of the channel measurement of areas of erosion and accretion showed that both banks of the padma experienced considerable loss of land the total net loss for left bank and right bank was 155 and 28 km2 respectively the padma is approximately twice the width of the ganges and the changes to its channel area are not as temporally dynamic as the ganges the relationship between bank curvature and erosion accretion of the river banks for both rivers was analysed and the results contradict established meander theory regression analysis between bank erosion rates annual average discharge and mean flood flow data showed that bank erosion was significantly correlated with annual average discharge for the padma r2 0 6283 and that the ganges bank erosion rate is influenced by mean flood flow r2 0 6738 the flood frequency shows generally good stability across the first eight of the nine epochs for the ganges but for the padma the frequency showed even greater stability we were unable to support the widely held belief that the upstream barrage has a deleterious effect on the ganges but note that there is a slight effect due to the periodic release of sediment through scour sluices

coupled and decoupled numerical modeling of flow and morphological evolution in alluvial rivers existing numerical river models are mostly built upon asynchronous solution of simplified governing equations the strong coupling between water flow sediment transport and morphological evolution is thus ignored to a certain extent an earlier study led to the development of a fully coupled model and identified the impacts of simplifications in the water sediment mixture and global bed material continuity equations as well as of the asynchronous solution procedure for aggradation processes this paper presents the results of an extended study along this line highlighting the impacts on both aggradation and degradation processes simplifications in the continuity equations for the water sediment mixture and bed material are found to have negligible effects on degradation this is however in contrast to aggradation processes in which the errors purely due to simplified continuity equations can be significant transiently the asynchronous solution procedure is found to entail appreciable inaccuracy for both aggradation and degradation processes further the asynchronous solution procedure can render the physical problem mathematically ill posed by invoking an extra upstream boundary condition in the supercritical flow regime finally the impacts of simplified continuity equations and an asynchronous solution procedure are shown to be comparable with those of largely tuned friction factors indicating their significance in calibrating numerical river models it is concluded that the coupled system of complete governing equations needs to be synchronously solved for refined modeling of alluvial rivers

structure and palaeogeography of the external betic cordillera southern spain abstract a structural interpretation of the external betic cordillera in the granada jaen area of southern spain is proposed based on the interpretation of seismic reflection profiles subsurface well control and a balanced cross section restoration of this balanced cross section results in a new palaeogeographical interpretation for the area and a total estimated shortening of approximately 200 km traditionally the betic fold thrust belt has been described as a series of north vergent imbricate thrust sheets each having relatively little displacement 10 15 km restoration of this structural model to an undeformed state results in a mesozoic palaeogeographical scenario of three carbonate platforms separated by two deep basins an alternative interpretation is presented in this paper that the structural style of the granada jaen area is characterized by large displacement thrust faults restoration of the proposed cross section leads to the palaeogeographical interpretation of a single mesozoic basin along the transect of the cross section this palaeo basin is bounded to the north and south by platformal margins the major implication of this study is that the palaeogeographical interpretation of a fold thrust belt can be highly dependent on the structural interpretation

analysis of river lateral channel movement using quantitative geomorphometric indicators qara sou river iran qara sou river a permanent river in ardabil province iran has recently undergone changes by anthropogenic factors in this research through geomorphometric quantitative methods we have tried to carefully investigate lateral channel movement of qara sou river during the last 12 years so as to provide a comprehensive understanding of these changes and their calculation methods using gis techniques the study area is located 31 km away from qara sou river from the vicinities of qadilou village to the surroundings of la l ganj village the most important geomorphometric indices used in this paper include total bankline change e normalized lateral movement rate n width change dw true migration m and lateral stability index the results of river lateral movement indices show the high level of total bankline change e and low level of true migration m indices this is due to changes in the width change of qara sou river during the last 12 years in fact farming activities and encroachments in bed and riparian of qara sou river have caused channelization of the channel accelerating flooding around the river in addition the results revealed that high mobility in total bankline change e and normalized lateral movement rate n of qara sou river was not related to lateral migration of the river but it had a strong connection with width changes of the channel the calculated true migration rate in the study area for qara sou river was about 0 36 m per year during the last 12 years

channel changes due to river regulation the case of the piave river italy this paper deals with the channel changes of the piave river in the eastern alps italy which have occurred during this century in response to human interventions in the fluvial system the flow regime and the sediment supply of the river have been considerably altered by hydroelectric dams flow diversions and gravel mining in addition river dynamics have been affected by the construction of streambank protection structures to document these changes a historical analysis was performed using maps and aerial photographs morphological features that were examined included planform configuration channel width braiding index and bed elevation the results indicate that as a consequence of decreases in the flows and sediment supply remarkable channel changes have occurred in the river during this century especially during recent decades the channel has undergone a general narrowing with a decrease in average width to 35 per cent of its initial value while the braiding index has decreased from about 3 to 1 5 in several reaches the planform pattern has changed from braided to wandering the observed trends of channel change suggest that the river has not yet reached a new equilibrium condition and it may therefore be predicted that reductions in width and braiding intensity are likely to continue in the immediate future copyright 1999 john wiley sons ltd

superimposed folding and oblique structures in the palaeomargin derived units of the central betics sw spain the subbetic units consist of a deformed wedge of sedimentary rocks deriving from the south iberian palaeomargin in the westernmost segment of the alpine mediterranean orogenic belt in the central betics shortening produced folding thrusting and nappe stacking the structural trend is ne sw to ene wsw and the internal structure of the thrust sheets which shows no preferred vergence is strongly controlled by the rheology of the decollement level a viscous layer of triassic evaporites and of the overlying carbonate rock sequence the relationships of piggyback basin miocene sediments with the main structures show that the latter developed during the aquitanian burdigalian transition superimposed folding is described for the first time in the study area the origin of the interference cannot be determined at present but may be related to initially oblique structures refolded during progressive deformation a revision of previously published palaeomagnetic data in the light of the data presented in this paper in conjunction with a model of the structural evolution of the subbetic units of the western betics permits us to establish milestones of the tectonic evolution of the external zones in the northern branch of the gibraltar arc

medium and short term channel planform changes on the rivers tay and tummel scotland abstract channel planform change was analysed using a variety of data sources for the medium term 25 years and

geomorphic response of the jingjiang reach to the three gorges project operation upstream damming often causes significant downstream geomorphic adjustments remarkable channel changes have occurred in the jingjiang reach of the middle yangtze river since the onset of the three gorges project tgp therefore it is important to investigate the variations in different fluvial variables for better understanding of the channel evolution characteristics as an example of the jingjiang reach recent geomorphic adjustments in the study reach have been investigated quantitatively including variations in sediment rating curve fluvial erosion intensity channel deformation volume and bankfull channel geometry these fluvial variables adjusted in varying degrees in response to the altered flow and sediment regime caused by the tgp operation a focus of this study has been especially paid on the variation in the bankfull channel geometry calculated bankfull dimensions at section and reach scale indicate that i there were significant bank erosion processes in local regions without bank protection engineering with empirical relations being developed to reproduce the variation in bankfull widths at four typical sections ii the variation in the reach scale channel geometry occurred mainly in the component of bankfull depth owing to the construction of large scale bank revetment works with the depth increasing from 13 7 m in 2002 to 15 0 m in 2014 and with an increase in the corresponding bankfull area of about 11 and iii the reach scale bankfull channel dimensions responded to the previous five year average fluvial erosion intensity during flood seasons at zhicheng with higher correlations for the depth and area being obtained when calibrated by the measurements in 2002 2012 furthermore these developed relations for the section and reach scale bankfull channel geometry were also verified by the observed data in 2013 2014 with encouraging results being obtained this article is protected by copyright all rights reserved

case study equivalent widths of the middle rio grande new mexico successive reaches of the rio grande have maintained equivalent channel widths of 50 and 250 m respectively over long periods of time it is hypothesized that alluvial channels adjust bed slope to match the long term changes in channel width analytical relationships show that wider river reaches develop steeper slopes a modeling approach using daily water and sediment discharges simulates the transient evolution of bed elevation changes the analytical and numerical models are in very good agreement with the longitudinal profile measurements of the bosque del apache reach of the rio grande nm from 1992 to 1999 the slope of the 50 m wide reach was 50 cm km and the slope of the 250 m wide reach of the same river increased to 80 cm km this unsteady daily transient model compares well with a steady transient solution at a constant discharge close to the mean annual flow the transient slope adjustments can also be approximated with an exponential model accordingly it takes about 20 25 years for the rio grande to achieve about 90 of its slope adjustment

wandering braided river channel pattern developed under quasi equilibrium an example from the hanjiang river china abstract this paper deals with the wandering braided channel pattern and its formative mechanism with the middle hanjiang river as an example the middle hanjiang river is characterized by a multi braided shallow and wide channel with a number of unstable mid channel bars and a frequently shifting thalweg however before the construction of the danjiangkou reservoir it basically exhibited an equilibrium of sediment transport the formation of the wandering braided channel pattern of the middle hanjiang river is not caused by strong sedimentation as in the lower yellow river but is controlled by strong erosion of the river bank large quantities of sediment are supplied to the channel by bank erosion after exchange with the sediment carried from the upstream the sediment from bank erosion is deposited in mid channel bars while some new mid channel bars are formed some old ones become attached to the bank in this way a wandering braided channel pattern with many unstable mid channel bars can develop under a condition of sediment transport equilibrium mineral analysis indicates that the material from bank erosion constitutes a major material source for mid channel bar building based on a plot of channel width against bankfull discharge a discriminant relation has been established to distinguish between wandering braided and the non wandering channel patterns

study of sedimentation zones in a large sand bed braided river an example from the hanjiang river of china abstract the concept of sedimentation zone is applied to the study of spatial and temporal variations of mid channel bars in the middle hanjiang river a large sand bed braided river in china the river channel can be divided into alternating sedimentation zones and transport zones the formation of which is basically controlled by local channel boundary conditions such as natural and artificial bank controls bedrock outcrops local hill spurs terraces artificial dikes and influence of tributaries a systematic comparison between sedimentation and transport zones is made in this study including the flow shear stress stream power mid channel bar features and channel stability the results obtained indicate that different channel boundary conditions in sedimentation and transport zones control channel width and width depth ratio which in turn control the reach s hydraulic and sediment transport characteristics the storage and removal of sediment in sedimentation zones correspond to the increase and decrease of the degree to which mid channel bars develop when the sediment input of the channel system is altered by reservoir construction the bed load sediment historically accumulated is released by clear water scour thus a macroscopic bed load wave forms and moves gradually downstream associated with this is the complex response phenomenon of mid channel bar evolution

lower miocene deformation in the hanging wall of the internal external zone boundary of the betic cordillera deformation at the edges of vertical axis rotation domains in oblique convergent margins

trace metal fluxes to the ocean the importance of high standing oceanic islands 1 trace metal analyses of river channel sediments from taiwan and new zealand provide new estimates for global budgets of trace metal inputs to the world s ocean mean trace metal values from high standing island river sediments are less chemically weathered than observed in sediments collected from large continental rivers and more similar to upper continental crust ucc values our mean values for cu mn co and pb are similar to the ucc zn ni and cr are more highly enriched compared to ucc values our new estimates of global trace metal budgets combining previous estimates with these new data show that geochemical fluxes of metals into the oceans are lower than previous estimates ranging from 9 lower for co to 24 lower for cu

stable channels with mobile gravel beds regime type equations for mobile gravel bed rivers are presented based on data obtained from 62 stable gravel bed river reaches in the united kingdom multiple regression techniques are applied to derive equations relating reach average and riffle values of width mean and maximum depth slope velocity sinuosity and riffle spacing to bankfull discharge bed and bank material characteristics valley slope bank vegetation type and an independent estimate of bankfull bed load transport rates although discharge has a dominant control on channel geometry these equations indicate that bed load discharge also has a significant influence particularly with regard to channel slope bank vegetation has a major control on width and velocity while depth velocity and slope are storngly affected by bed material size reasons for these results are considered in terms of the physical processes controlling channel adjustment the application of these regime equations is discussed and particular consideration is given to the design of sinuous channels with a pool riffle bed topograph

glycymeris shell accumulations as indicators of recent sea level changes and high energy events in cadiz bay sw spain abstract recent climatic and sea level changes have significantly modified coastal areas and caused the morphological evolution of littoral environments such is the case in cadiz bay sw spain where important changes have taken place from the late holocene to the present day and which have not yet been sufficiently established in this sense some sedimentary indicators such as the glycymeris shell deposits which can be found interstratified in recent coastal sand banks could shed new light on this issue three questions are addressed in this work firstly the age of these shell deposits secondly what is the depositional mechanism responsible for these shelly accumulations and finally what relationship can be established regarding recent sea level changes sample ages indicate that the shells are older than 1000 years bp while the facies indicate high energy flows as depositional mechanisms tides and waves seem insufficient in order to reach the upper shelly deposits for which a more energetic agent would be necessary such as tsunami waves which is feasible given that the zone is located in a tectonically active area where historical tsunamis have been recorded with respect to the relationship with a possible recent sea level rise this could be a better explanation since marine agents would be able to reach the necessary height

validation of a three dimensional numerical code in the simulation of pseudo natural meandering flows validation of a three dimensional finite volume code solving the navier stokes equations with the standard k epsilon turbulence model is conducted using a high quality and high spatial resolution data set the data set was collected from a large scale meandering channel with a self formed fixed bed and comprises detailed bed profiling and laser doppler anemometer velocity measurements comparisons of the computed primary and secondary velocities are made with those observed and it is found that the lateral momentum transfer is generally under predicted at the apices this results in the predicted position of the primary velocity maximum having a bias towards the channel center compared to the position where it has been measured using a simplified two zone roughness distribution whereby a separate roughness height was prescribed for the channel center and channel sides relative to a single distributed roughness height generally led to a slightly improved longitudinal velocity distribution the higher velocities were located nearer to the outside of the bend improving both the free surface calculation and scheme for discretization of the convection terms led to no appreciable difference in the computed velocity distributions a more detailed study involving turbulence measurements and bed form height distribution should discriminate whether using distributed roughness height is a precursor to using an anisotropic turbulence representation for the accurate prediction of three dimensional river flows

case study modeling the lateral mobility of the rio grande below cochiti dam new mexico the cochiti reach of the rio grande served as a case study to test the hypothesis that the lateral mobility of an alluvial river decreases as the river approaches equilibrium the lateral mobility of the river was measured using a geographic information system from digitized aerial photographs of the nonvegetated active channel between 1918 and 2001 reach averaged lateral mobility was quantified in terms of width change lateral migration and total lateral movement by 2001 the width of the cochiti reach was close to the expected equilibrium width indicating that the river had adjusted to the incoming water and sediment load an exponential equation based on deviation from equilibrium width described 95 96 of the variance in channel width 78 90 of variance in migration rates and 92 of the variance in total lateral movement between 1918 and 1992 for validation of the model the 2001 width and migration rates were predicted with errors as low as 19 and 8 respectively the exponential width model

case study river training and its effects on fluvial processes in the lower yellow river china more than 50 years river training practices in the lower yellow river provide valuable experience in river management for flood control in rivers having rapid flow changes silting beds and active channel migrations and are of importance in understanding the fluvial processes in regulated rivers with high sediment loads planned channel alignments for river training in the lower yellow river usually consist of a series of consecutive moderate bends representing the natural tendency of flows flow guide works namely spur dikes were constructed on the concave banks of the planned bends to protect the channel against scouring and migration by deflecting the current away from bends and further guiding the main flow from one bend to the next one as a result well planned flow guide works can play a crucial role in limiting channel shifting and migration and in establishing a relatively stable channel enough flow guide works on both sides together reaching about 80 of the channel length may change the transitional and braided channel patterns to a confined meandering pattern

meandering channel response to altered flow regime milk river alberta and montana mean and peak flows channel width and rates of meander migration are examined for two sandy meandering reaches of the milk river in south alberta and north montana one reach upstream of the international boundary near onefour alberta is affected by the st mary diversion the other reach near havre montana is below the fresno dam and reservoir comparisons are possible because of the ample and long term availability of maps air photos and hydrometric records preceding and succeeding the two altered flows for both reaches understanding the natural river regime and effects of diversion and dam storage are critical for predicting channel responses to a proposed additional dam on the milk river results indicate that increased discharge due to a diversion has increased channel width 5 5 m and increased the rate of meander migration by 0 85 m year downriver reservoir storage has decreased channel width 16 8 m and the rate of meander migration by 1 3 m year and caused channel bed degradation up to 1 5 m near the dam

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

modeling for width adjustment in alluvial rivers the width adjustment models in current use for application to alluvial rivers are based on the extremal hypotheses in these models the increase in slope required to sustain higher sediment concentration is provided by aggradation of the river bed an alternative approach was presented by the writer chitale 2001 which showed that on a long term basis the increase in slope required for higher sediment concentration is accompanied by a reduction of the meander sinuosity associated with a bigger width to depth ratio in width adjustment aggradation is thus a transient phenomenon of temporary duration until the final stable width is achieved the physical sequence of the adjustment process according to this hypothesis is presented and supporting evidence is given it is also concluded that the predictive models for stable width on a long term basis need necessarily to include the meander sinuosity as an essential parameter