magnetostratigraphy of the willwood formation bighorn basin wyoming new constraints on the location of paleocene eocene boundary abstract the lower eocene willwood formation in the bighorn basin of wyoming preserves a rich and diverse mammalian and floral record the paleomagnetic behavior of the sequence of floodplain paleosols of varying degrees of maturation ranges from excellent to poor we present a magnetostratigraphic section for a composite section near worland wyoming by using a set of strict criteria for interpreting the step wise alternating field and thermal demagnetization data of 266 samples from 90 sites throughout the composite section correlation to the geomagnetic reversal time scale was achieved by combining magnetostratigraphic and biostratigraphic data from this section from a section in the clark s fork basin in northern wyoming and from dsdp site 550 with the isotopic data determined on a tuff near the top of our section our correlation suggests that the bighorn basin composite section in the worland area spans from within chron c24r to near the top of chron c24n or from approximately 55 to 52 ma this correlation places the paleocene eocene boundary within the vicinity of the base of the section cryptochron c24r 6 of cande and kent is tentatively identified some 100 m above the base of the section the temporal framework provided here enables correlation of the mammalian biostratigraphy of the bighorn basin to other continental sequences as well as to marine records it also provides independent chronological information for the calculation of sediment accumulation rates to constrain soil maturation rates we exclude an age as young as 53 ma for the paleocene eocene boundary and support older ages as recommended in recent time scales the location of a tuff dated at 52 8 0 3 ma at the older boundary c24n 1 is consistent with the age of 52 5 ma estimated by cande and kent and inconsistent with that of 53 7 ma from harland et al

discriminating stacked distributary channel from palaeovalley fill sand bodies in foreland basin settings abstract stacked fluvial distributary channel deposits and palaeovalley fills can form major multi storey sand bodies with similar thicknesses and with lateral extents often greater than a single exposure consequently they can be difficult to tell apart from one another using outcrop data this study addresses this problem by quantitatively analysing the architecture of five stacked fluvial distributary channel deposits and two palaeovalley fills from the pennsylvanian pikeville and hyden formations of the central appalachian basin usa the a priori interpretation of the sand bodies as stacked distributary channels and palaeovalley fills is possible because a robust in place coal seam correlation framework allows for the recognition of different basin scale architectures for each type aspect ratios 1000 and a regional basinward facies shift at the bases of palaeovalley fills sand body thickness storey thickness position and length of storey contacts within the sand body are similar in both types however they can be distinguished by different up system to down system changes in their respective architectures stacked distributary channel sand bodies thin down system display a decrease in storey thickness an increase in the mean position of storey heights in the sand body and a decrease in the length of storey contacts these trends are the result of down system decrease in channel size and confinement associated with radially distributive fluvial systems palaeovalley fill sand bodies thicken down system display an increase in storey thickness a decrease in the mean position of storey heights and a decrease in the length of storey contacts the increase in sand body and storey thickness are the result of down system increases in original channel size consistent with trunk axial fluvial systems fed by tributaries that predominate during valley formation the down system increase in amalgamation reflects a down system decrease in accommodation from the higher subsidence rate active margin of the basin and is therefore not necessarily characteristic of palaeovalley fill architectures in all basin settings this study emphasises the requirement for detailed correlation work and quantitative analysis of external and internal architectures before the interpretation of sand bodies as stacked distributary channels or palaeovalley fills

evolution of mid channel bars in a braided river and complex response to reservoir construction an example from the middle hanjiang river china using the middle hanjiang river as an example this paper deals with the development of mid channel bars in a braided river as controlled by channel boundary conditions runoff and sediment load as well as reservoir construction relations have been established between indices describing the mid channel bars and the controlling variables such as the channel width the percentage silt clay content in the channel boundary and the energy expenditure of flowing water bank erosion provides space and material for mid channel bar formation so bank erosion rate can be closely related to mid channel bar indices the middle channel bars exhibit a complex evolutionary response to the reservoir regulated hydrological regime in the middle hanjiang river a descriptive model showing the complex response has been established 1997 john wiley sons ltd

coarse sediment storage and connectivity and off highway vehicle use board camp creek arkansas abstract upper board camp creek bcc in western arkansas drains the wolf pen gap wpg trail complex a designated off highway vehicle ohv area in use since the 1990s the mixed bedrock alluvial channel is quite active with extensive bars and eroding banks present within the higher order main valley channels this study was conducted to determine the relative magnitudes of sediment storage and production within the channel and whether geomorphic changes are synchronous with establishment and increasing ohv use levels on the trail system fourteen geomorphically active reaches within the main valley channels representing the range of conditions of bcc within the wpg complex were examined in detail all sites had significant alluvial storage in the form of point lateral or mid channel bars dominated by cobble and gravel sediment storage volumes ranged from 140 to nearly 10 000 m3 per kilometer of channel with a mean of about 3400 eleven of 14 reaches also had actively eroding banks ten reaches 71 exhibited net sediment storage two are possible net sources and two may be in approximate steady state storage erosion the imbalance between local bank erosion sources and in channel storage and the evidence of activity and mobility of most of the bars indicates a connected system with coarse sediment mobile during banktop flow events and no evidence of sediment starvation finer

fluvial changes of the guadalquivir river during the holocene in cordoba southern spain this research was funded by a grant from proyectos de cordoba siglo xxi coordinated by prof r jose roldan canas universidad de cordoba

planform channel dynamics along the ningxia inner mongolia reaches of the yellow river from 1958 to 2008 analysis using landsat images and topographic maps channel planform dynamics were analyzed for the ningxia inner mongolia reaches of the yellow river map data were analyzed by means of gis and used to determine the planform characteristics and changes in width sinuosity and shoreline migration rates between 1958 and 2008 the study was based on topographic maps of 1958 and 1967 which had been derived from aerial photos and a field survey and from satellite imagery of 1977 1990 2000 and 2008 the channel planform dynamics were determined by comparing sequential changes in the position of the shorelines in these years sinuosity adjustments were small during the study range 1 34 1 45 the initial sinuosity 1 45 in 1958 gradually decreased to 1 34 in 1990 and then increased to 1 40 in 2008 channel contraction had been the dominant planform process but periodic floods resulted in channel expansion 1958 1990 the river s channel area expanded substantially from 1958 to 1990 by 42 1 then sharply contracted from 1990 to 2000 by 45 8 with no subsequent changes the bank erosion and accretion rates were severe the mean erosion rates ranged from 30 7 to 68 3 m year on the left side and 27 1 to 58 3 m year on the right side the mean accretion rates ranged from 44 4 to 68 3 m year on the left side and 30 5 to 60 4 m year on the right side the mean channel midline shifted by 57 8 m toward the right from 1958 to 2008 the mean channel midline moved 4 8 m to right from 1958 to 1967 54 3 m to the left from 1967 to 1977 44 2 m to the right from 1977 to 1990 64 3 m to the right from 1990 to 2000 and 2 8 m to the right from 2000 to 2008

the 1989 loma prieta earthquake imaged from inversion of geodetic data we invert geodetic measurements of coseismic deformation from the 1989 ms7 1 loma prieta earthquake to determine the geometry of the fault and the distribution of slip on the fault plane the data include electronic distance measurements global positioning system and very long baseline interferometry vectors and elevation changes derived from spirit leveling the fault is modeled as a rectangular dislocation surface in a homogeneous elastic half space first we assume that the slip on the fault is uniform and estimate the position orientation and size of the fault plane using a nonlinear quasi newton algorithm the best fitting dislocation strikes n48 4 w and dips 76 9 sw consistent with the trend of the aftershock zone and moment tensor solutions bootstrap resampling of the data is used to graphically illustrate the uncertainty in the location of the rupture plane the 95 confidence envelope overlaps the aftershock zone arguing that there is not a significant discrepancy between the geodetic data and the aftershock locations second we estimate the slip distribution using the best fitting uniform slip fault orientation but increase the fault length to 40 km and the downdip width to 18 km the fault is divided into 162 subfaults 18 along strike and 9 along dip each subfault is allowed to have constant right lateral and reverse components of slip we then solve for the slip on each subfault that minimizes a linear combination of the norm of the weighted data residual and the roughness of the slip distribution the smoothing parameter which determines the relative weight put on fitting the data versus smoothing the slip distribution is chosen by cross validation simulations indicate that cross validation estimates of the smoothing parameter are nearly optimal the preferred slip distribution is very heterogeneous with maximum strike slip and dip slip of about 5 and 8 m respectively located roughly 10 km north of the hypocenter there is insignificant dip slip in the southeastern most part of the fault causing the rake to vary from nearly pure right lateral in the southeast to oblique right reverse in the northwest the change in rake is consistent with a uniform stress field if the fault dip increases by about 10 toward the southeast as indicated by the aftershock locations there was little slip above 4 km depth consistent with the observation that there was little if any surface rupture

some characteristics of the stress field of the 1995 hyogo ken nanbu kobe earthquake we investigate the characteristics of the stress field associated with the 1995 hyogo ken nanbu kobe earthquake we use for the study a tomographic model of the fault slip inferred from the numerous near field recordings and we calculate the space and time evolution of shear stress on the fault during the earthquake we show that the spatial distribution of stress drop is very heterogeneous the apparent strength of the fault at the onset of the earthquake is low of the order of 1 mpa or less which indicates that the pre earthquake tectonic shear stress was close to the static friction over most of the fault at many locations the stress drop rotates significantly during sliding as was originally proposed by spudich 1992 we use the requirement of colinearity between the directions of maximum shear stress and instantaneous slip to determine the initial stress on the fault at the onset of the earthquake the pre earthquake tectonic stress varies greatly over the fault and ranges from about 1 to 10 mpa average values of the initial and final shear stresses over the fault are 3 3 and 1 6 mpa respectively indicating that about half of the pre earthquake tectonic stress was released during the earthquake there is a relatively strong correlation between the initial and final stress distributions which suggests that intrinsic fault properties not modified by the earthquake control the spatial distribution of tectonic stress over the fault we show that on average over the fault the dynamic friction coefficient is equal to about 40 of the static friction coefficient diagrams depicting the evolution of shear stress as a function of slip are consistent with slip weakening behavior but their interpretation is questionable because of the poor resolution of the data at high frequency and because of the constraints imposed on the model to perform the inversion

frictional constraints on crustal faulting we consider how variations in fault frictional properties affect the phenomenology of earthquake faulting in particular we propose that lateral variations in fault friction produce the marked heterogeneity of slip observed in large earthquakes we model these variations using a rate and state dependent friction law where we differentiate velocity weakening behavior into two fields the strong seismic field is very velocity weakening and the weak seismic field is slightly velocity weakening similarly we differentiate velocity strengthening behavior into two fields the compliant field is slightly velocity strengthening and the viscous field is very velocity strengthening the strong seismic field comprises the seismic slip concentrations or asperities the two intermediate fields weak seismic and compliant have frictional velocity dependences that are close to velocity neutral these fields modulate both the tectonic loading and the dynamic rupture process during the interseismic period the weak seismic and compliant regions slip aseismically while the strong seismic regions remain locked evolving into stress concentrations that fail only in main shocks the weak seismic areas exhibit most of the interseismic activity and aftershocks but can also creep seismically this mixed frictional behavior can be obtained from a sufficiently heterogeneous distribution of the critical slip distance the model also provides a mechanism for rupture arrest dynamic rupture fronts decelerate as they penetrate into unloaded complaint or weak seismic areas producing broad areas of accelerated afterslip aftershocks occur on both the weak seismic and compliant areas around a fault but most of the stress is diffused through aseismic slip rapid afterslip on these peripheral areas can also produce aftershocks within the main shock rupture area by reloading weak fault areas that slipped in the main shock and then healed we test this frictional model by comparing the seismicity and the coseismic slip for the 1966 parkfield 1979 coyote lake and 1984 morgan hill earthquakes the interevent seismicity and aftershocks appear to occur on fault areas outside the regions of significant slip these regions are interpreted as either weak seismic or compliant depending on whether or not they manifest interevent seismicity

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

a morphology independent methodology for quantifying planview river change and characteristics from remotely sensed imagery abstract remotely sensed imagery of rivers has long served as a means for characterizing channel properties and detection of planview change in the last decade the dramatic increase in the availability of satellite imagery and processing tools has created the potential to greatly expand the spatial and temporal scale of our understanding of river morphology and dynamics to date the majority of gis and automated analyses of planview changes in rivers from remotely sensed data has been developed for single threaded meandering river systems these methods have limited applicability to many of the earth s rivers with complex multi channel planforms here we present the methodologies of a set of analysis algorithms collectively called spatially continuous riverbank erosion and accretion measurements scream scream analyzes planview river metrics regardless of river morphology these algorithms quantify both the erosion and accretion rates of riverbanks from binary masks of channels generated from imagery acquired at two time periods additionally the program quantifies the area of change between river channels and the surrounding floodplain and area of islands lost or formed between these two time periods to examine variations in erosion rates in relation to local channel attributes and make rate comparisons between river systems of varying sizes the program determines channel widths and bank curvature at every bank pixel scream was developed and tested on rivers with diverse and complex planform morphologies in imagery acquired from a range of observational platforms with varying spatial resolutions validation and verification of scream generated metrics against manual measurements show no significant measurement errors in determination of channel width erosion and bank aspects scream has the potential to provide data for both the quantitative examination of the controls on erosion rates and for the comparison of these rates across river systems ranging broadly in size and planform morphology

the meandering braided river threshold a reappraisal abstract the concept of a threshold discharge slope q s combination that separates braided from meandering streams is critically re examined partly by review of previous data and partly by analysis of new data from south island new zealand it is argue d that discriminant functions that use mean annual discharge provide a poor physical basis for interpretations based on natural processes while bankfull discharge is also deficient because it is not a fully independent variable the common use of channel rather than valley slope adds a further misleading component because channel slope is partly dependent on channel pattern sinuosity most previous studies have inadequately treated the role of bed particle size in pattern discrimination failing to recognize that active gravel streams must plot higher on a q s chart than sand bed channels irrespective of pattern because of the greater power requirements for bed material movement within any one size class of bed material there is no evidence to indicate a clear discrimination between braiding and meandering only a weak statistical association between pattern and slope discharge values while this association may be explicable in terms of the high shear stress and stream power that accompany high qs values promoting braiding the real prerequisite for braiding appears to be high loads of bed calibre material producing wide shallow channels a factor that is only partly controlled by stream power accordingly the search for a pattern threshold based on discharge and slope seems to be a futile exercise an interpretation of existing pattern discriminant functions from the perspective of the threshold shear stress for particle movement is made it is concluded that in effect these functions merely state that gravel bed streams are more likely to be braided than channels in finer sediment statistically this appears to be valid and reasons for that difference are offered based on the balance between imposed bed material load and channel capacity

effects of dam operation and land use on stream channel morphology and riparian vegetation dams are well known for influencing channel and vegetation dynamics downstream but little work has focused on distinguishing effects of land use and channel responses to the impoundment in this paper we examined interacting effects of a dam and land use on downstream changes in channel morphology and riparian vegetation along an agricultural stream system in northern california measurements of planform channel morphology vegetation area and land use were mapped along multiple stream segments based on a chronological sequence of historical aerial photographs over a 34 yr period prior to operation of the dam in 1983 and over a 17 yr period after dam operation and compared to a nearby undammed reference stream a two factor analysis of covariance ancova was used to examine the effect of the dam on changes in bankfull area stream length and riparian vegetation area while accounting for the effect of land use and distance downstream the dammed stream s bankfull area contracted 94 after dam operation prior to dam operation bankfull area decreased when land use area increased but not after operation of the dam stream length varied 64 less after dam operation as a consequence of less frequent episodic channel migration and entrenchment the area of riparian vegetation was decreasing during the pre dam period but then increased 72 after operation of the dam across time periods decreases in the area of riparian vegetation were also associated with increases in land use area in both the dammed and reference stream after operation of the dam reduced peak discharges and sediment reduction likely lead to channel incision and constrained channel migration which allowed vegetation to increase 50 on less accessible abandoned banks rating curve and hydraulic exponent analyses based on stream gauge measurements corroborate statistical analyses of the mapped changes in conclusion we found that operation of the dam and land use patterns together influenced spatial and temporal changes in channel morphology and riparian vegetation use of a nearby undammed reference stream in conjunction with multivariable analysis of spatially and temporally replicated observations provided an effective framework for unraveling interacting effects of dams and land use activities on stream channel and vegetation dynamics

millennial scale climatic fluctuation in the fluvial record during mis3 very high resolution seismic images from ne hungary abstract alluvial architectures of a meandering river existing in mis3 were observed on very high resolution vhr single channel waterborne seismic profiles 20 30 m below the tisza river in the pannonian basin hungary the study investigated the spatial and temporal variations of two more than 2 km long continuous series of inclined reflections interpreted as laterally accreted point bar complexes the phases of natural meander migration were reconstructed in 3d based on the changes in the geometry and dip of the inclined reflections a channel forming discharge curve extending over approximately 2 5 ky was calculated by using paleo width and depth data derived from the lateral accretion surfaces systematic analysis of the geometrical variations coupled with the discharge curve evaluation on each point bar complexes indicates millennial scale discharge fluctuations 40 50 ky ago to that the river responded principally by incision and infilling the primary periodicity comparable to the sub milankovitch cycles is superimposed by shorter periods ca 500 year cycles reflect the phases of unidirectional meander development while the smallest ones reflect the recurrence interval 150 200 years of the highest floods river bed incisions happened step by step related to extreme floods when the meander development also changed the smaller scale and more rapid fluctuations within a development unit were represented in variations of the channel width although the poor geochronology of the sandy fluvial deposits cannot allow any direct correlation to the climatostratigraphic events the millennial scale climate variations of mis3 were pronouncedly characteristic in the discharge fluctuations

underlying gravel layers in a large sand bed river and their influence on downstream dam channel adjustment due to the changes in environmental factors during a river s historical development underlying gravel layers are found in many large plain rivers when the buried depth of this gravel layer is within the reach of down cutting by clear water scour after reservoir construction it may be exposed and exert a far reaching influence on channel adjustment in hanjiang river the longest tributary of the yangtze river in china down cutting has been greatly reduced and even stopped due to the total change of bed material composition the exposure of a gravel layer results in a dramatic increase in the bed s hydraulic roughness so the channel slope may increase after a decline during the period prior to the exposure of the gravel layer moreover the exposed gravel layer increases the erosion resistance of bed material making a lower relative erosion resistance of bank to bed material where the bank s erosional resistance is weak this may lead to a tendency towards channel widening

alterations of channel parameters in response to river regulation works since 1840 on the lower tisza river hungary abstract in the last few years an increase in the frequency and magnitude of floods was detected on the tisza river endangering large areas of hungary the causes of these record floods were complex including both natural and human induced factors this paper focuses on river management works and their effect on planimetric and cross sectional parameters with special attention to the flood conductivity changes to the river channel during 19th century river regulation works half of the total length of the tisza river was altered by cut offs while in the 20th century mostly revetments and groynes were constructed subsequently horizontal and vertical channel parameters have changed considerably due to semi natural bed processes in order to reveal changes hydrological map series 1842 1890 1929 1957 1976 and 1999 and cross sectional surveys from the same dates were analysed prior to the intensive human interventions before 1890s the river s course was highly sinuous with some very sharp bends due to cut offs both the length and sinuosity of the tisza river decreased by 35 while the lengths of straight sections and the river s slope doubled as a consequence the river incised by up to 3 8 m until the 1929 survey resulting better flood conductivity which improved flood safety in the 1920s river management favoured bank stabilisation in order to stop the lateral migration of the channel despite these measures meander development has continued however in a distorted manner this is reflected by the opposing processes of lengthening centre line on the one hand and gradually decreasing radius of curvature on the other these processes can be explained by the continuous development of natural point bars on the convex bank and the lack of lateral retreat on the concave stabilised bank the width of the river decreased by 17 45 while its mean and maximum depth increased by 5 48 the area of cross sections influenced by revetments decreased by 6 19 resulting in a 6 15 decline in flood conductivity the non stabilised sections were influenced by upstream revetments therefore their parameters show similar changes but with a smaller rate at present the flood conductivity of the channel is worse than it was in its natural state in all it was found that the ongoing process of cross sectional distortion is a significant factor in increasing flood stage and hazard and high floods can be expected more frequently in the future partly due to this factor

geomorphic criteria for distinguishing and locating abandoned channels from upstream part of mun river khorat plateau northeastern thailand in order to develop geomorphic criteria for distinguishing and locating abandoned channels and meandered belts in this paper we examined geomorphologic characteristics from the mun river one of the main rivers in the khorat plateau northeastern thailand upstream of mun river originated at southwestern rim of the khorat plateau where the river now cuts through sandstone basement meandering process shaped meander from upstream ending at low lying plain about 30 km downstream from the mun bon dam reservoir and this process displays given values of geomorphic parameters including sinuosity index si channel width w and radius of curvature rc sinuosity index was calculated to express the sinuosity of the channel the relationship between w and rc helps to predict channel stability and also comprehend the possibility of cutoff process as a result paleo and recent flow directions of the mun river are similar from southwest to northeast geomorphic parameters from eight river reaches have changed through time since 1974 2015 two abandoned channel belts were identified and they own an average channel width of 35 and 16 m whereas the mun river nowadays is of 12 7 m si values of two abandoned channel belts are categorized as meandering river system relationship between meander migration rate and bend curvature suggests that the mun river possesses low erosion rate between 0 71 and 2 64 m year since 1974 to the present this rank of rc w ratio suggests stable state of river bank migration different migration indicates discontinuous meandering process from individual belt lateral migration rate was also decreased after mun bon dam was constructed upstream

spatial and temporal variations of channel lateral migration rates in the inner mongolian reach of the upper yellow river channel variations of the inner mongolian reach in the upper yellow river are very complicated because of diversity of channel patterns intense changes in water and sediment and enhanced human activities in the last decades it is important to examine the channel migration rates in this river reach based on channel planform changes at 236 digital channel cross sections the present study estimated the channel migration rates in terms of mid channel line shift at the digital channel cross sections during the periods 1975 1990 1990 2000 2000 2006 2006 2010 and 2010 2011 the results show that the average channel migration rate for the whole river reach is 5 0 7 9 5 9 8 6 and 1 0 m 1 in the five different periods respectively in both directions to the right and to the left the highest channel migration rate was always observed in the meandering channels while the lowest channel migration rate was in the whole inner mongolian reach except the sanhuhekou zhaojunfen s z sub reach the temporal variation of channel migration rate was mainly controlled by changing sediment concentration in river flow while the spatial variation along the straight braided and meandering channel reaches was largely affected by material differences of channel banks as reflected by different channel patterns with the highest average lateral migration rate to the left bank the meandering channel reach is extremely vulnerable to lateral migration and needs to be protected with engineering practices because a large population and wide farmland are located on its left floodplain

statistical analysis of lateral migration of the rio grande new mexico abstract the lateral migration rates of alluvial rivers are affected by changes in water and sediment regimes the rio grande downstream from cochiti dam exhibits spatial and temporal variability in lateral movement rates documented since 1918 a tremendous database exists that documents planform bed material size channel geometry and water and sediment regimes a statistical analysis reveals that migration rates primarily decreased with decreasing flow energy r2 0 50 p 60 the findings show that lateral movement increases with increasing flow energy and with degree of braiding

river morphology and thresholds the regime geometry and channel patterns of alluvial rivers are analyzed wing an energy approach together with physical relationships of flow continuity flow resistance and sediment transport because of the discontinuity in flow resistance and thus in power expenditure between lower and upper flow regimes the adjustment in river regime consists of sudden changes in channel geometry channel pattern and sometimes silt clay content when such a discontinuity is crossed thresholds or discontinuities in river morphology are obtained in the analysis in accordance with such thresholds rivers of distinct morphological features are classified into four regions based upon the bankfull discharge channel slope and median size of bed sediment their respective features are described and certain regime relationships for channel width and depth are established the predicted channel geometries are compared with river data

mechanism diversity of the loma prieta aftershocks and the mechanics of mainshock aftershock interaction the diverse aftershock sequence of the 1989 loma prieta earthquake is inconsistent with conventional models of mainshock aftershock interaction because the aftershocks do not accommodate mainshock induced stress changes instead the sense of slip of the aftershocks is consistent with failure in response to a nearly uniaxial stress field in which the maximum principal stress acts almost normal to the mainshock fault plane this orientation implies that i stress drop in the mainshock was nearly complete ii mainshock induced decreases of fault strength helped were important in controlling the occurrence of after shocks and iii mainshock rupture was limited to those sections of the fault with preexisting shear stress available to drive fault slip

reconstruction of dynamic rupture process of an earthquake with constraints of kinematic parameters in this paper a simple approximate method that converts the distribution of kinematic rupture parameters on a fault into that of physical or dynamic parameters is proposed the method in which the static stress drop assumed to be equal to the dynamic stress drop is applied to investigate rupture dynamics of the 1979 imperial valley california earthquake m 6 5 the dynamic rupture process is reconstructed by using a propagating crack which is a process of expanding area of stress release if we know the amount of stress drop and rupture time at each point on the fault dynamic rupture process can be simulated we use the kinematic parameters previously obtained by using waveform inversion techniques with constraints of the kinematic parameters the dynamic rupture process of the event can be reconstructed and several dynamic parameters stress drop and strength excess the difference between strength and applied initial stress can be estimated at each point on the fault by applying this method to the 1979 imperial valley earthquake we found that the rupture initiated at the low strength excess part first and then expanded toward the north and ruptured a large size high stress drop region located in the north part of the fault and finally decelerated and stopped at the north edge where the strength is high and stress drop is low these features are well explained by barrier model das and aki 1977 and are quite similar to those obtained by quin in 1990 who investigated the dynamic rupture process by the monte carlo technique with a large number of trials since repeated calculation is unnecessary our method is very effective and practical compared with his method

volumetric measurement of river bank erosion from sequential historical aerial photography abstract understanding of the relative contribution of bank erosion to sediment budgets in new zealand is limited few measurements of bank erosion rates exist and this is a major limitation to the development of a locally calibrated model of bank erosion the new zealand sediment budget model sednetnz predicts bank erosion based on preliminary data and this study aims to underpin the development of an improved model for bank erosion photogrammetric techniques and lidar were used to collect data on bank erosion rates for five different river reaches ranging from 3 to 14 km in length in the kaipara catchment northland new zealand changing river channel planform between the 1950s and 2015 was assessed using four to five well spaced dates of historical aerial photographs changes in planform were combined with bank height to calculate erosion and accretion volumes which were compared with sednetnz modelled estimates erosion and accretion is relatively evenly balanced in the study sites the largest difference in terms of relative proportions of erosion and accretion are found along the tangowahine river 13 4 km reach length where 492 000 m3 of sediment eroded between 1956 and 2015 compared to 364 000 m3 of accretion lateral migration rates erosion for the five river reaches range between 0 14 m yr 1 and 0 21 m yr 1 and are comparable with those measured by previous assessments in new zealand the migration rates in channel widths per year for the three larger rivers stream order 5 6 range between 0 4 and 0 8 of channel width per year in contrast the smaller streams stream order 3 4 are retreating more rapidly with width averaged rates of 1 7 and 3 0 current sednetnz modelling tends to underestimate the bank height and greatly overestimates the migration rate

statistical models of fluvial systems abstract statistical methods have dominated quantitative analyses of fluvial systems over the last 40 years this paper assesses the utility of statistical models by examining methodological issues associated with empirical analysis of hydraulic and channel geometry relationships it also describes and presents examples of advanced statistical models that promise to enhance our understanding of the structure and dynamics of fluvial systems bivariate and multivariate power function models of fluvial systems provide objective numerical descriptions of the relationship between channel geometry and hydrologic hydraulic sedimentologic and biotic controls traditional regression models are limited in that they only describe simple input output relations between the states of dependent and independent variables advanced statistical models transcend these limitations simultaneous equation models continuously varying parameter models and distributed lag models are statistical tools for explicitly analyzing 1 mutual adjustments among fluvial variables 2 the factors controlling the spatial structure of channel geometry flow relations and 3 the equilibrium or disequilibrium dynamics of fluvial systems respectively these advanced statistical techniques can be used to empirically test conceptual models of fluvial systems at a variety of spatial and temporal scales

causes of planform stability of a low energy meandering gravel bed river cher river france abstract for at least two centuries the lateral mobility of the meandering reaches of the cher river france has been very low this article aims to identify the main causes of this behavior two not mutually exclusive explanatory hypotheses are proposed under the first hypothesis the natural mechanisms of loop migration would have been inhibited or blocked by the presence of bank protections under the second hypothesis a decrease in the frequency and or intensity of morphogenic hydrological events since the nineteenth century would have reduced the frequency of bedload mobilization and or reduced the capacity of the river to erode its banks to test these hypotheses the diachronic evolution of the planform was reconstituted at different time scales using a gis and field surveys morphological transformations were characterized and quantified eroded and vegetated areas length of eroded banks rates of bank retreat and the critical discharges of bedload mobilization and of lateral erosion were estimated engineering works in the riverbed were identified and when possible dated the results show that meander morphodynamics have been highly constrained and disrupted by engineering works probably for over a century however the meanders still have noticeable potential for bedload mobility and lateral erosion and hence for self restoration

logistic analysis of channel pattern thresholds meandering braiding and incising a large and geographically diverse data set consisting of meandering braiding incising and post incision equilibrium streams was used in conjunction with logistic regression analysis to develop a probabilistic approach to predicting thresholds of channel pattern and instability an energy based index was developed for estimating the risk of channel instability associated with specific stream power relative to sedimentary characteristics the strong significance of the 74 statistical models examined suggests that logistic regression analysis is an appropriate and effective technique for associating basic hydraulic data with various channel forms the probabilistic diagrams resulting from these analyses depict a more realistic assessment of the uncertainty associated with previously identified thresholds of channel form and instability and provide a means of gauging channel sensitivity to changes in controlling variables

vegetative impacts on hydraulics and sediment processes across the fluvial system summary vegetation creates a complicated system of feedbacks and linkages across the fluvial system that is realized through river planform shape interactions occur among flow hydraulics sediment deposition and erosion and plant morphology density and biomechanics interest in the interactions and feedback loops between vegetation and the fluvial system has grown extensively in the past few years this interest is partially driven by the popularity of stream restoration activities worldwide that include re vegetation of stream banks and formation of an ecosystem that is intended to encourage the growth of aquatic macrophytes we present a review of the research into the interactions and dependencies between vegetation and the fluvial system to identify hydraulic and sediment dynamics that are consistent around vegetation located in the channel on channel banks and over the floodplain we illustrate process commonalities operating across spatial locations within the fluvial system and highlight some of the current research opportunities and challenges to encourage research collaborations between those working in areas of the fluvial system traditionally viewed as disparate

anastomosis and the continuum of channel pattern anastomosing rivers are characterized by multiple channels separated by islands excised from the floodplain their status relative to the continuum concept of channel pattern is assessed with channel pattern defined in terms of three variables flow strength bank erodibility and relative sediment supply using an ordinal scaling l ow m oderate h igh the traditional forms of straight meandering and braided have respective representations of l l l m l m l m and h h m h in terms of those variables the anastomosing pattern is on average represented by l l m h but not so definitively as other forms specification of the third element sediment supply is particularly hampered by the paucity of data but aggradation a characteristic of many anastomosing rivers can be thought of as symptomatic of a moderately high rate of supply relative to the ability for onward transport a sufficiently high rate of supply to a channel with low flow strength and resistant banks would induce shoaling and or lateral constriction that locally forces flow out of the main channel and ultimately leads to the cutting of anabranches a flow regime characterized by concentrated floods of relatively large magnitude is also regarded as highly conducive to the formation of new channels where low bank erodibility constrains channel capacity anastomosis may in certain cases represent a transitional form of channel pattern but there is no denying the longevity of some anastomosing systems

planform channel dynamics and bank migration hazard assessment of a highly sinuous river in the north eastern zone of bangladesh rivers or watercourses in sylhet plain of bangladesh are very dynamic over time the aim of the present study is to investigate the channel planform dynamics the prediction of future lateral migration of the bankline and assessment of the hazards associated with manu river bangladesh the name manu river represents the river study reach from tripura india to moulvibazar bangladesh of 41 6 km channel contraction and expansion are very frequent in this river studies had shown that the sinuosity of the river varies from 1 36 to 2 48 also the meandering ratio of the river ranges from 0 32 to 1 67 satellite data were collected and analyzed to determine the planform characteristics meandering parameters and bankline migration rates between 1975 and 2013 the study is based on the landsat satellite imagery of 1975 1988 1999 2003 and 2005 and aerial photograph of 2009 and 2013 which were accumulated from united states geological survey specific critical bends have been elected where bank erosion and accretion rates were severe the purpose of this paper is to show the erosion rate behavior and pattern of upstream side of manu river bangladesh through the study period of 38 years from 1975 to 2013 by comparing its different geomorphological parameters this study has contributed to develop a model for bankline migration prediction of the forthcoming years and address the physical hazard to provide a risk surface present assessment has revealed that there are some critical regions where erosion would be up to 29 18 hectares in 2025

stream curvature and bank erosion a model based on the momentum equation based on the momentum equation of flow the force per unit area which the flow exerts radially on the outer bank of a stream bend is expressed by an equation in which the force is explicitly related to the curvature ratio r w curve radius channel width a dimensionless curvature coefficient c alpha is defined which is dependent on r w and the coefficient of dynamic bedload friction tan alpha exploring the changes of c alpha with r w reveals a functional relationship which for the known values of tan alpha shows maximal values of c alpha for r w values between 2 and 4 the theoretical results agree with field measurements of the relationship between r w and the rate of channel migration

geological controls on the geometry of incised valley fills insights from a global dataset of late quaternary examples incised valleys that develop due to relative sea level change are common features of continental shelves and coastal plains assessment of the factors that control the geometry of incised valley fills has hitherto largely relied on conceptual experimental or numerical models else has been grounded on case studies of individual depositional systems here a database driven statistical analysis of 151 late quaternary incised valley fills has been performed the aim being to investigate the geological controls on their geometry results of this analysis have been interpreted with consideration of the role of different processes in determining the geometry of incised valley fills through their effect on the degree and rate of river incision and on river size and mobility the studied incised valley fills developed along active margins are thicker and wider on average than those along passive margins suggesting that tectonic setting exerts a control on the geometry of incised valley fills likely through effects on relative sea level change and river behaviour and in relation to distinct characteristics of basin physiography water discharge and modes of sediment delivery valley fill geometry is positively correlated with the associated drainage basin size confirming the dominant role of water discharge climate is also inferred to exert a potential control on valley fill dimensions possibly through modulations of temperature peak precipitation vegetation and permafrost which would in turn affect water discharge rates of sediment supply and valley margin stability shelves with slope breaks that are currently deeper than 120 m contain incised valley fills that are thicker and wider on average than those hosted on shelves with breaks shallower than 120 m no correlation exists between valley fill thickness and present day coastal prism convexity which is measured as the difference in gradient between lower coastal plains and inner shelves these findings challenge some concepts embedded in sequence stratigraphic thinking and have significant implications for analysis and improved understanding of source to sink sediment route ways and for attempting predictions of the occurrence and characteristics of hydrocarbon reservoirs

hydrological controls on the morphogenesis of low energy meanders cher river france summary river restoration is a key issue for european hydrosystems that were modified over centuries by human activities this is particularly true for numerous low energy rivers flowing in the plateaus of western europe because of this limited energy their potential in terms of autogenic restoration a priori appears strongly restricted this study examines the conditions under which the morphogenesis on one of these systems occurs in relation to various hydrologic conditions two complementary approaches are combined on three reaches of the meandering cher river france firstly we examine at a pluri decadal scale the control of duration frequency and intensity of floods on the planimetric erosion bank retreat mainly secondly we estimate the range of effective discharge for bedload transport the results show that the morphogenesis is controlled by low magnitude hydrological events two major controlling factors are suggested low differential of energy between small and large floods peculiar to low energy rivers of mid latitude and low critical discharges for lateral erosion and bedload mobilization for these reasons the ability of the alluvial cher river to self restore its fluvial dynamics seems to be relatively high

reconstruction of a pleistocene meandering river in east hungary by vhr seismic images and its climatic implications abstract the upper 20 30 m of the pleistocene alluvial sequence on the tisza river hungary is investigated by 200 km of vhr single channel seismic sections frequent internal configurations such as 1 bundles of inclined reflections 2 trough shaped converging and 3 horizontal parallel reflections are interpreted respectively as lateral accretion of point bars abandoned channel fills and floodplain deposits the series of 5 8 m thick inclined strata sets occurring at the same depth throughout the area suggest the presence of a meandering river dated to about 43 47 ka in the late pleistocene according to osl data newly recorded quasi 3d seismic profiles reveal that each 1 3 km long inclined series correlates with an individual point bar continuously migrating in the same direction small deviations in the direction of migration are caused by natural wandering of the meander bend morphometric parameters of point bars are used to calculate ancient channel parameters width and depth of 200 500 m and 5 8 m respectively values imply a channel forming discharge of q 400 900 m 3 s these results imply a greater amount of runoff and supply in the basin during mis3 compared to the present day long lasting meandering indicates the role of local factors and a different fluvial environment compared to the commonly anastomosing systems in nw europe our data support the thesis of the three axis drainage system for the basin new evidence is provided for the antecedent existence of a temporally active third trunk river in addition to the ancestors of danube and tisza rivers contrary to the present day two axis drainage pattern