the effect of lateral confinement on gravel bed river morphology in this paper we use a physical modeling approach to explore the effect of lateral confinement on gravel bed river planform style bed morphology and sediment transport processes a set of 27 runs was performed in a large flume 25 m long 2 9 m wide with constant longitudinal slope 0 01 and uniform grain size 1 mm changing the water discharge 1 5 2 5 l s and the channel width 0 15 1 5 m to model a wide range of channel configurations from narrow straight embanked channels to wide braided networks the outcomes of each run were characterized by a detailed digital elevation model describing channel morphology a map of dry areas and areas actively transporting sediment within the channel and continuous monitoring of the amount of sediment transported through the flume outlet analysis reveals strong relationships between unit stream power and parameters describing the channel morphology in particular a smooth transition is observed between narrow channels with an almost rectangular cross section profile with sediment transport occurring across the entire channel width and complex braided networks where only a limited proportion 30 of the bed is active this transition is captured by descriptors of the bed elevation frequency distribution e g standard deviation skewness and kurtosis these summary statistics represent potentially useful indicators of bed morphology that are compared with other commonly used summary indicators such as the braiding index and the type and number of bars

the evolution of el nino past and future abstract we review forecasts of the future of el nino and the southern oscillation enso a coupled instability of the ocean atmosphere system in the tropical pacific with global impacts enso in the modern world is briefly described and the physics of the enso cycle is discussed particular attention is given to the bjerknes feedback the instability mechanism which figures prominently in enso past and future our knowledge of enso in the paleoclimate record has expanded rapidly within the last 5 yr the enso cycle is present in all relevant records going back 130 kyr it was systematically weaker during the early and middle holocene and model studies indicate that this results from reduced amplification in the late summer and early fall a consequence of the altered mean climate in response to boreal summer perihelion data from corals shows substantial decadal and longer variations in the strength of the enso cycle within the past 1000 yr it is suggested that this may be due to solar and volcanic variations in solar insolation amplified by the bjerknes feedback there is some evidence that this feedback has operated in the 20th century and some model results indicate that it will hold sway in the greenhouse future but it is very far from conclusive the comprehensive general circulation models used for future climate projections leave us with an indeterminate picture of enso s future some predict more enso activity some less with the highly uncertain consensus forecast indicating little change

validation of the physical modeling approach for braided rivers 1 laboratory channels are often used to study the complexity of braiding mechanisms for the advantages with respect to field studies nevertheless the extensive use of experimental data raises the question of how representative laboratory braided channels are as compared to real braided rivers this study verifies to what extent laboratory braided patterns reproduce the main features of braided rivers experimental data display isotropic and anisotropic scaling of braided patterns state space plot of total widths anisotropic scaling of islands and statistical distribution of island areas that are similar to those observed in real rivers moreover the data reveals scaling in the perimeter area relation these results support both the reliability of experimental braided channels as physical models of braided rivers and also the possibility of investigating some aspects of braiding in the laboratory that are difficult to address in the field the lack of preferential scales in island characteristics suggests that other phenomena must play a key role in generating island shapes besides classical sediment transport based mechanisms which tend to select well defined length scales

interannual variability in a tropical atmosphere ocean model influence of the basic state ocean geometry and nonlinearity abstract the behavior of a tropical coupled atmosphere ocean model is analyzed for a range of different background states and ocean geometries the model is essentially that of cane and zebiak for the tropical pacific except only temporally constant background states are considered here for realistic background states and ocean geometry the model solutions feature oscillations of period of 3 5 yr by comparing the full model solution with a linearized version of the model it is shown that the basic mechanism of the oscillation is contained within linear theory a simple linear analog model is derived that describes the nature of the interannual variability in the coupled tropical atmosphere ocean system the analog model highlights the properties that produce coupled atmosphere ocean instability in the eastern ocean basin and the equatorial wave dynamics in the western ocean basin that are responsible for a delayed negative feedback into this instability growth the growth rate of the local instabil

heartbeat of the southern oscillation explains enso climatic resonances the el ni no southern oscillation enso nonlinear oscillator phenomenon has a far reaching influence on the climate and human activities the up to 10 year quasi period cycle of the el ni no and subsequent la ni na is known to be dominated in the tropics by nonlinear physical interaction of wind with the equatorial waveguide in the pacific long term cyclic phenomena do not feature in the current theory of the enso process we update the theory by assessing low 10 years and high 10 years frequency coupling using evidence across tropical extratropical and pacific basin scales we analyze observations and model simulations with a highly accurate method called dominant frequency state analysis dfsa to provide evidence of stable enso features the observational data sets of the southern oscillation index soi north pacific index anomaly and enso sea surface temperature anomaly as well as a theoretical model all confirm the existence of long term and short term climatic cycles of the enso process with resonance frequencies of 2 5 3 8 5 12 14 61 75 180 years this fundamental result shows long term and short term signal coupling with mode locking across the dominant enso dynamics these dominant oscillation frequency dynamics defined as enso frequency states contain a stable attractor with three frequencies in resonance allowing us to coin the term heartbeat of the southern oscillation due to its characteristic shape we predict future enso states based on a stable hysteresis scenario of short term and long term enso oscillations over the next century

origin of upper ocean warming and el nino change on decadal scales in the tropical pacific ocean the cause of decadal scale variability in the tropical pacific ocean such as that marked by the 1976 77 shift in the el nino southern oscillation1 2 3 4 5 6 7 is poorly understood unravelling the mechanism of the recent decade long warming in the tropical upper ocean is a particularly important challenge given the link to el nino variability but establishing the hypothesized interannual decadal oceanic connections between middle latitudes and tropics has proved elusive8 here we present observational evidence that pacific upper ocean warming and decadal changes in the el nino southern oscillation after 1976 may originate from decadal mid latitude variability in the middle 1970s the north pacific ocean is observed to have undergone a clear phase transition a see saw subsurface temperature anomaly pattern that rotates clockwise around the subtropical gyre at middle latitudes a subsurface warm anomaly formed in the early 1970s from subducted surface waters and penetrated through the subtropics and into the tropics thus perturbing the tropical thermocline and driving the formation of a warm surface water anomaly that may have influenced el nino in the 1980s the identification of this teleconnection of extratropical thermal anomalies to the tropics through a subsurface ocean bridge may enable improved prediction of decadal scale climate variability

how do gravel bed rivers braid sedimentary processes and bed forms leading to the onset of braiding were observed in small scale hydraulic models of gravel bed streams the laboratory streams had a variety of combinations of constant discharge and slope but identical bed material particle size distributions from initially straight channels braiding occurred by four different processes deposition and accumulation of a central bar chute cutoff of point bars conversion of single transverse unit bars to mid channel braid bars and dissection of multiple bars in these experiments the chute cutoff mechanism was the most common but the predominant braiding mechanism depends upon sediment mobility excess bed shear stress and the bed form regime at very low excess bed shear stress the central bar process dominates but at higher excess bed shear stress slip face unit bars are more common bed scour at confluences is more pronounced and propogation of alternate convergence scour and divergence deposition is more likely thus chu

analysis of the effect of changing discharge on channel morphology and instream uses in a braided river ohau river new zealand constant discharges of 26 5 56 7 105 240 and 507 m3s 1 were released down the ohau river from ohau a power station and measurements of water depths and mean velocities made along cross sections in a braided section of the channel frequency distributions of water depth and velocity are presented both singly and jointly for each discharge the methods used provide much more information on the changing character of the river than is provided by conventional hydraulic geometry relations as discharge increases existing channels become wider deeper and faster and frequently merge to become a single larger channel however additional channels are generated with the same characteristics as those existing at lower discharges and the total number of channels at a cross section remains constant hence the increase of water surface area tends to be by addition of faster deeper water to a constant area of shallow slow water whose location in the river bed changes this process has the major implication for instream uses such as salmonid spawning in that the area suitable for these uses may remain constant over a wide range of flows in some respects then the braided river is morphologically more stable than a single thread river

width adjustment in experimental gravel bed channels in response to overbank flows 1 we conducted a series of flume experiments to investigate the response of self formed gravel bed channels to floods of varying magnitude and duration floods were generated by increasing the discharge into a channel created in sand and gravel sized sediment with a median grain size of 2 mm flooding increased the shields stress along the channel perimeter causing bank erosion and rapid channel widening the sediment introduced to the channel by bank erosion was not necessarily deposited on the channel bed but was rather transported downstream a process likely facilitated by transient fining of the bed surface at the end of each experiment bank sediments were no longer in motion partial bed load transport characterized the flat bed portion of the channel and the shields stress approached a constant value of 0 056 about 1 2 times the critical shields stress for incipient motion furthermore the discharge was entirely accommodated by flow within the channel the creation of a stable channel entirely eliminated overbank flows we speculate that similar processes may occur in nature but only where bank sediments are non cohesive and where channel narrowing processes cannot counteract bank erosion during overbank flows we also demonstrate that a simple model of lateral bed load transport can reproduce observed channel widening rates suggesting that simple methods may be appropriate for predicting width increases in channels with non cohesive unvegetated banks even during overbank flows last we present a model for predicting the equilibrium width and depth of a stable gravel bed channel with a known channel forming shields stress

the response of braided planform configuration to flow variations bed reworking and vegetation the case of the tagliamento river italy morphological features of braided rivers bars channels and pools experience major changes in area shape and spatial distribution as a response to i the pulsation of discharge during a flood and ii the bed evolution induced by floods in this work at a station relationships between water level and planform configuration were investigated on the tagliamento river a large gravel bed braided river in northeast italy over a 2 year study period comprising three bankfull events and several small to medium floods the analysis was performed on two 1 km long reaches characterized by different riparian vegetation cover ground based images with an hourly temporal resolution were acquired using software controlled digital cameras bars channels pools and vegetated patches were manually digitized on more than 100 rectified images sequences of constant level images spanning the study period were used to quantify the impact of floods on the stability of at a station relationships and on the turnover rate of water bodies the analysis shows that wetted area increased almost linearly with water level in both reaches the average number of branches per cross section peaked at intermediate flow levels increasing from 2 at low flow up to 6 7 the number of branches displayed the largest fluctuations over time with significant changes produced also by moderate floods turnover rates were high in both reaches with more than 30 of wetted areas at low flow converting into bare gravel in less than 2 months vegetation colonization was found to limit the mobility of the low flow channels over time by concentrating the flow in fewer deeper anabranches the number of channels per cross section was 30 40 less in the vegetated reach and the proportion of low flow water bodies in the same position after 12 months increased from 3 to 14 copyright 2012 john wiley sons ltd

active width of gravel bed braided rivers previous analyses have identified the active width of braided rivers the bed area over which bed load flux and short term morphological change occurs as an important element of braiding dynamics and predictions of bed load flux here we compare theoretical predictions of active width in gravel bed braided rivers with observations from sunwapta river and from a generic physical model of gravel braided rivers to provide general observations of the variation in active width and to develop an understanding of the causes of variation bed topography was surveyed daily along a 150 m reach of the pro glacial sunwapta river for a total of four weeks during summer when flow was above threshold for morphological activity in the laboratory detailed digital elevation models dems were derived from photogrammetric survey at regular intervals during a constant discharge run from the field and flume observations there is considerable local and circumstantial variation in active width but also a general trend in average active width with increasing discharge there is also a clear relationship of active width with active braiding index number of active branches in the braided channel network and with dimensionless stream power which appears to be consistent across the range of data from field and physical models thus there is a link between active width and the river morphology and dynamics and the possibility of a general relationship for estimating active width from channel pattern properties or reach scale stream power values from which approximate bedload flux calculations may be made the analysis also raises questions about differences between hydraulically based numerical model computations of instantaneous active width and observation of time integrated morphological active width understanding these differences can give insight into the nature of bedload transport in braided rivers and the relationship to morphological processes of braiding copyright 2011 john wiley sons ltd

channel adjustment and a test of rational regime theory in a proglacial braided stream the upstream reach of the sunwapta river alberta provides a useful quasi experimental field case of channel adjustment in a proglacial stream historically the formation of a proglacial lake deprived the river of its coarse sediment supply for several decades and lead to a dramatic decrease in braiding intensity close to the lake while braiding intensity increased further downstream this response to the reduction of gravel input is consistent with previous experimental results subsequent construction activity and channelization close to the lake have contributed to the continuation of these temporal and spatial trends in channel pattern the current state of adjustment of the river morphology can be explained in the context of these historical changes using rational regime equations the study reach has no tributaries and bed material size decreases twofold along the reach while width and braiding intensity increase yet channel slope decreases by only 10 the absence of any significant change in discharge downstream along the reach allows testing of regime equations under conditions in which discharge is held constant the current downstream trends in slope and fluctuations in width are predicted reliably from rational regime equations but not by the existing empirical hydraulic geometry relations the rational equations incorporate the effect of grain size and slope on channel width and the effect of width and grain size on channel slope the regime equations are successful even though they were devised for single channel gravel streams the small 10 decrease in slope along the reach despite a halving of median grain size is attributed to the counteracting positive effect on slope of the downstream increase in braiding intensity and width the downstream increase in braiding intensity must be largely the result of decreasing grain size this confirms the influence of grain size on channel pattern thresholds and demonstrates using spatial transitions in channel pattern that channel pattern predictions based on stream power alone are inadequate

geomorphic diversity in the braided wandering bela river slovak carpathians as a response to flood variability and environmental changes abstract changes in the morphological pattern of the gravel bed bela river slovak carpathians were investigated to infer about the impact of flood events and environmental changes on the evolutionary trend of the river since the mid twentieth century the post flood period serial geomorphic analysis popsega approach coupled with gis analysis was used to identify morphological changes that occurred during particular flood periods the study focused on assessing how six flood periods fp with differing flood characteristics have influenced the evolutionary trend of the river several sets of aerial photos 1949 1961 1973 1986 1992 2003 2009 taken after the periods with the occurrence or lack of major floods provided data about channel landform changes in 227 river segments of 100 m length a decreasing trend of the area of the river s active zone from 2 5 km2 in 1949 to 1 4 km2 in 2009 was identified the first fp 1949 1961 with a very high magnitude flood in 1958 ri50 was characterized by increasing total channel length island number area and the number density of confluence diffluence pairs nodes and by decreasing bar area during this fp the frequency of cores of channel dynamics as well as the shannon s index of landforms diversity reached the highest values the following fp 1962 1973 with four 5 to 10 year floods exhibited the inverse pattern of changes in channel form parameters although the core frequency of channel dynamics and shannon s diversity index were still high the river system seems to have been relatively stable between 1974 and 1986 third fp with some decrease in the area of channel forms and in pattern metrics values during the fourth fp 1987 1992 several 1 5 to 3 year floods occurred and were associated with a decrease in some channel forms and a further decrease of the pattern metrics values an increase in all analysed channel parameters especially bar area and pattern metrics values occurred in the years 1993 2002 fifth fp as a consequence of two floods of moderate magnitude in 1997 ri7 and 2001 ri3 5 the lowest values of bar area and pattern metrics during the whole study period were recorded during the last fp 2002 2008 whereas island area increased at that time the study shows that the occurrence of floods during the last six decades has not returned the bela to its former state because of the overall decrease in flood magnitudes changes in catchment sediment supply induced by the increasing forest cover in the catchment from 22 7 in 1957 to 34 8 in 2008 and changes in channel boundary conditions channelization channel incision small hydropower plant constructions

the simplest enso recharge oscillator 1 eastern pacific sea surface temperature sst and mean equatorial pacific thermocline depth are key variables in el nino southern oscillation enso a linear fit to observations leads to a remarkably simple picture enso can be represented by a classical damped oscillator with sst and thermocline depth playing the roles of momentum and position respectively an independent fit of observed relationships between western and eastern thermocline depth central wind stress and eastern pacific sst yields the same picture and supports a recharge oscillator interpretation the oscillation arises from the interaction between the recharge time of the warm pool and the time delay between east and west pacific both finite kelvin wave speed and sst dynamics contribute to the time delay including seasonality in the description we find two periods of relative instability boreal spring with a large phase progression and autumn with nearly stationary phase

semi determinate hydraulic geometry of river channels south island new zealand data to describe the morphologic hydrologic and sedimentologic characteristics of 72 south island new zealand rivers were collected and analysed nearly 70 per cent of variation in channel morphology is accounted for by differences in cross sectional area slope and cross section shape only 53 per cent of the morphologic variability could be statistically explained by the hydrologic and sediment variables used the level of explanation varied for different morphologic variables nearly 90 per cent of the variability in cross sectional area could be explained but aspect ratio maximum depth divided by hydraulic radius was completely independent apart from the inadequacy of the measured variables as indices of the true underlying controlling factors and the imperfect measurement and sampling procedures the low level of explanation is probably due to the influence of factors such as floodplain vegetation high quasi random variability in bark sediment character boundary effects imposed by bedrock bluffs and the precise sequence of flood events none of which are easily quantified in addition observations indicate that there is a large random variation in channel form which cannot be related to any factor an attempt to relate channel morphology to flow variability using simple indices of the latter was unsuccessful

enso like interdecadal variability 1900 93 a number of recent studies have reported an enso like eof mode in the global sea surface temperature sst field whose time variability is marked by an abrupt change toward a warmer tropical eastern pacific and a colder extratropical central north pacific in 1976 77 the present study compares this pattern with the structure of the interannual variability associated with the enso cycle and documents its time history back to 1900 the analysis is primarily based on the leading eofs of the sst anomaly and anomaly deviation fields in various domains and the associated expansion coefficient or principal component time series which are used to construct global regression maps of sst sea level pressure slp and a number of related variables the use of anomaly deviations i e departures of local sst anomalies from the concurrent global mean sst anomaly reduces the influence of global mean sst trends upon the structure of the eofs and their expansion coefficient time series an important auxiliary time series used in this study is a southern oscillation index based on marine surface observations by means of several different analysis techniques the time variability of the leading eof of the global sst field is separated into two components one identified with the enso cycle related variability on the interannual timescale and the other a linearly independent residual comprising all the interdecadal variability in the record the two components exhibit rather similar spatial signatures in the global sst slp and wind stress fields the sst signature in the residual variability is less equatorially confined in the eastern pacific and it is relatively more prominent over the extratropical north pacific the corresponding slp signature is also stronger over the extratropical north pacific and its counterpart in the cold season 500 mb height field more closely resembles the pna pattern the amplitude time series of the enso like pattern in the residual variability reflects the above mentioned shift in 1976 77 as well as a number of other prominent features including a shift of opposite polarity during the 1940s

low amplitude obliquity changes during the early pliocene reflected in diatom fragmentation patterns in the andrill and 1b core abstract in the andrill antarctic geologic drilling project and 1b core an 80 m long interval of early pliocene diatomite was obtained 382 98 440 12 m below sea floor to better understand the role of fragmentation on diatom preservation within this unit data were collected from 154 samples on the size and number of fragments of specimens of the diatom genus rouxia the number of frustule fragments was classified into categories based on the amount of intact raphe and then evaluated using a formula created to characterize the nature and degree of fragmentation in each sample variations in fragmentation were compared with the age model and indicate a relationship between fragmentation and sediment accumulation rates for the lower 37 m with higher fragmentation related to lower accumulation rates of hemipelagic mud during warmer intervals this relationship is not as pronounced in the upper 20 m which can be related to the frequent occurrence of sandstone layers lenses and laminated intervals after evaluating a number of hypotheses the most plausible explanation is that the presence of greater proportions of hemipelagic mud produces a cushioning effect which prohibits the interaction of diatom frustules with sand grains or other diatoms thereby reducing fragmentation

a method for estimating the mean bed load flux in braided rivers prediction of bed load flux remains a significant problem in understanding braided river morphodynamics for geomorphic and engineering applications two sets of data from laboratory experiments on braided networks performed at the university of trento italy and at the university of alberta canada provide the basis for development of a dimensionless bed load function and for testing a simple predictive model measured total sediment transport rates time averaged at equilibrium channel configuration collapse to a single dimensionless relationship based on dimensionless stream power bed load fluxes predicted by the parker and bagnold functions and cross section average hydraulic parameters under predict the bed load flux particularly at low shear stress this is consistent with previous observation and theory demonstrating the significant influence of transverse variability of the hydraulic parameters in controlling and predicting bed load flux a simple method for adjusting for this lateral variation is proposed for computing the sediment transport rate using topographic cross sections of braided rivers results show good agreement with the measured values suggesting that simple assumptions combined with the mean morphology of the channel may be sufficient to estimate mean bed load flux model predictions also highlight the significance of active bed width rather than bed shear stress as a fundamental ingredient in the prediction of the bed load rate and therefore as an important morphological property to be modelled the model also predicts similar behaviour in the at a station variability of bed load and in the importance of variation of active width relative to bed shear stress in the transport process

indices of el nino evolution abstract to characterize the nature of el nino southern oscillation enso sea surface temperature sst anomalies in different regions of the pacific have been used an optimal characterization of both the distinct character and the evolution of each el nino or la nina event is suggested that requires at least two indices i sst anomalies in the nino 3 4 region referred to as n3 4 and ii a new index termed here the trans nino index tni which is given by the difference in normalized anomalies of sst between nino 1 2 and nino 4 regions the first index can be thought of as the mean sst throughout the equatorial pacific east of the date line and the second index is the gradient in sst across the same region consequently they are approximately orthogonal tni leads n3 4 by 3 to 12 months prior to the climate shift in 1976 77 and also follows n3 4 but with opposite sign 3 to 12 months later however after 1976 77 the sign of the tni leads and lags are reversed

fluvial geomorphology and river engineering future roles utilizing a fluvial hydrosystems framework abstract river engineering is coming under increasing public scrutiny given failures to prevent flood hazards and economic and environmental concerns this paper reviews the contribution that fluvial geomorphology can make in the future to river engineering in particular it highlights the need for fluvial geomorphology to be an integral part in engineering projects that is to be integral to the planning implementation and post project appraisal stages of engineering projects it should be proactive rather than reactive areas in which geomorphologists will increasingly be able to complement engineers in river management include risk and environmental impact assessment floodplain planning river audits determination of instream flow needs river restoration and design of ecologically acceptable channels and structures there are four key contributions that fluvial geomorphology can make to the engineering profession with regard to river and floodplain management 1 to promote recognition of lateral vertical and downstream connectivity in the fluvial system and the inter relationships between river planform profile and cross section 2 to stress the importance of understanding fluvial history and chronology over a range of time scales and recognizing the significance of both palaeo and active landforms and deposits as indicators of levels of landscape stability 3 to highlight the sensitivity of geomorphic systems to environmental disturbances and change especially when close to geomorphic thresholds and the dynamics of the natural systems and 4 to demonstrate the importance of landforms and processes in controlling and defining fluvial biotopes and to thus promote ecologically acceptable engineering challenges facing fluvial geomorphology include gaining full acceptance by the engineering profession widespread utilization of new technologies including gps gis image analysis of satellite and airborne remote sensing data computer based hydraulic modeling and geophysical techniques dovetailing engineering approaches to the study of river channels which emphasize reach scale flow resistance shear stresses and material strength with catchment scale geomorphic approaches empirical predictions bed and bank processes landform evolution and magnitude frequency concepts producing accepted river channel typologies fundamental research aimed at producing more reliable deterministic equations for prediction of bed and bank stability and bedload transport and collaboration with aquatic biologists to determine the role and importance of geomorphologically and hydraulically defined habitats

prediction of discharge from water surface width in a braided river with implications for at a station hydraulic geometry 1 the total discharge of small braided rivers can be monitored nearly continuously using ground based orthorectified oblique images and a locally derived relationship between mean water surface width in a reach and total discharge with accuracy of the order of 10 the width discharge relationship is nearly linear over the normal range of summer flows measured in this proglacial stream the width discharge relation for a given location and channel configuration is transferable to adjacent reaches with different morphology with little loss in accuracy however the prospect of a more universal relation for braided rivers is remote because of differences in channel geometry and hydraulics between rivers the classical at a station hydraulic geometry exponent for width in this case is approximately 1 05 which is unique well above that observed in the few other braided rivers for which this has been derived and implies almost no change in mean velocity and depth with changing stage

planform dynamics of braided streams the high dynamism and complexity of braided networks poses a series of open questions significant for river restoration and management the present work is aimed at the characterization of the morphology of braided streams in order to assess whether the system reaches a steady state under constant flow conditions and in that case to determine how it can be described and on which parameters it depends a series of 14 experimental runs were performed in a laboratory physical model with uniform sand varying the discharge and the longitudinal slope planimetric and altimetric configurations were monitored in order to assess the occurrence of a steady state a set of parameters was considered such as the braid plain width and the number and typology of branches and nodes results point out that a relationship exists between braiding morphology and two dimensionless parameters related to total water discharge and stream power we found that network complexity increases at higher values of water discharge and a larger portion of branches exhibits morphological activity results are then compared to the outputs of a simple one dimensional model that allows to easily predict the average network complexity once the bed topography is known model computations permit also the investigation of the effect of water discharge variations and to compare different width definitions the at a station variability of planimetric parameters shows a peculiar behaviour both regarding number of branches and wetted width in particular the analysis of the relationship between width and discharge highlighted relevant differences in comparison to single thread channel copyright 2009 john wiley sons ltd

evolutionary trajectory of channel morphology and controlling factors in a large gravel bed river abstract interpretation of channel changes is not always straightforward since it requires a detailed reconstruction of the evolutionary trajectory of channel morphology a quantitative analysis of controlling factors and finally identification of links between evolutionary trajectories and controlling factors the aim of this paper is to explain channel adjustments and controlling factors in the tagliamento river a large gravel bed river in northeastern italy traditional methods for studying historical channel changes i e use of aerial photos topographic data were employed but numerical modelling turned out to be very useful for the quantification of bedload transport and for supporting interpretation of past changes and likely future channel evolution river channel underwent three main phases of adjustment over the last 200 years the first two phases from the end of the nineteenth century to the early 1990s were characterized by narrowing channel width decreased from 1250 to 540 m and incision about 1 m and the third phase from the 1990s to present day by widening from 540 to 600 m and slight aggradation about 0 2 m combining evolutionary trajectories of channel morphology and analysis of controlling factors we argue that the long term channel evolution of the tagliamento river was driven mainly by human intervention at the reach scale i e sediment mining and channelization changes in sediment supply in the catchment area had no or minor effects in the study reach the most recent changes i e widening and slight aggradation are explained as a response to past disturbances that have produced a remarkable change of channel geometry and an increase of unit stream power in the reach magnitude and frequency of formative discharges are a key driving factor of the intensity of recent changes while this was not the case during the previous phases of adjustment

a theory of interdecadal climate variability of the north pacific ocean atmosphere system abstract a linear coupled model for the atmosphere upper ocean system is proposed to highlight the mechanisms of decadal to interdecadal climate variability in the north pacific in this model wind stress anomalies over the north pacific are related to anomalies in the meridional temperature gradient of the upper ocean the latter depends upon air sea thermodynamical feedbacks and meridional heat transport by upper ocean currents slow adjustment of the oceanic gyre circulation to the change in wind stress is accomplished by the forced baroclinic oceanic rossby waves which carry out the meridional heat transport uncoupled ocean dynamic adjustment can produce a weak decadal to interdecadal peak in the power spectrum of the meridional transport under temporal white noise wind stress forcing with organized spatial structure coupled dynamics produce a basin scale interdecadal oscillatory mode this mode arises from the dynamic coupling and the memory of the system residing in the slow gyre circulation ad

capturing the spatiotemporal variability of bedload transport a time lapse imagery technique monitoring sediment transport in morphologically complex and labile channels remains a difficult task even at the laboratory scale to address this challenge a fully automated imagery technique for continuously mapping the spatial and temporal variability of bedload transport is proposed this method uses differentiated time lapse imagery taken from a fixed camera to detect bed variations induced by grain displacement the technique is not based on tracking the individual particles rather it evaluates macroscopic colour changes within a region that contains several grains which depend on the occurrence and intensity of the bedload transport image derived data were compared with the sediment flux measured during four flume experiments and produced good correspondence the method provides continuous tracking of the location of the transporting channels and enables estimation of local variations in the magnitude of the bedload flux moreover the spatial extent of the monitoring area offers an unprecedented opportunity to aggregate spatially dense and continuous data at the reach scale as needed to properly capture the full range of variability of morphologically complex and rapidly evolving gravel bed rivers despite being limited to laboratory scale physical experiments the method provides useful data to investigate fundamental morphodynamic processes such as bar migration bank erosion anabranches opening closure and the associate spatial and temporal scales further the data obtained have the potential to enhance numerical model calibration and improve our understanding of the complex dynamics of real world settings copyright 2017 john wiley sons ltd