connections between wintertime jet stream variability oceanic surface heating and transient eddy activity in the north pacific 1 a set of statistical analyses of the fields from the european center for medium range weather forecasts reanalysis era 40 are carried out to investigate the connections between three selected fields namely the wintertime western pacific jet stream wpjs as represented by the zonal wind at 200 hpa the oceanic surface heating represented by the latent and sensible heat fluxes and the synoptic scale transient eddy activity stea over the north pacific first empirical orthogonal function eof analysis is performed to characterize the wintertime wpjs variability further analyses yield the following conclusions 1 the most dominant relationship among the three selected fields is strongly linked to the el nino southern oscillation enso during enso events anomalous zonal wind at 200 hpa downstream of the wpjs main body shown in the first eof is accompanied by stea anomalies around the region of the anomalous midlatitude zonal wind 2 the strengthening weakening of the wintertime wpjs main body shown in the second eof is connected to the surface heating anomalies in the kuroshio and its extension region as well as to stea anomalies in the region downstream of the wpjs main body 3 the northward southward shift of the wintertime wpjs represented in the third eof is closely related to the south north dipolar structure of the surface heating anomalies in the western north pacific the stea spatial displacement is in conjunction with the shift of the jet stream in the same direction due to the dynamical connection between the winds and the eddies furthermore the stea anomalies in winter may cause the wpjs anomalies on the submonthly timescale as a consequence the northward southward shift of the stea is harmoniously in favor of the similar jet shift

methods for studying the response of flood flows to channel change abstract the effect of a change in channel morphology of a stream upon flood flows may be obliterated by simultaneous changes in meteorologic factors or in another physiographic factor and thus flood frequency analysis and statistical tests cannot be seen as definitely indicating the lack or existence of a genetic non stationarity of flow record related to the channel change in a study of two mountain rivers from the upper vistula drainage basin southern poland three alternative procedures are presented which analyse temporal trends in the relationship between inflow and outflow peak discharges of flood waves passing the modified reach while these techniques examine various aspects of the record of flood discharges all of them separate changes in flows accomplished in a reach under investigation from those born in the upstream part of the catchment annual maxima analysis allows direct comparison of the timing and relations between changes in channel morphology and their response in flood flows the high consistency of changes in vertical channel position of the analysed rivers and of variations in transformation of their flood flows shows the importance of channel incision for increasing flood hazard on channelized streams

a new look at deformation as a diagnostic for large scale flow abstractdeformation plays a key role in atmospheric dynamics because it provides a dynamical measure of the interaction between different scales such as in frontogenesis a climatology of deformation constructed from interim ecmwf re analysis era interim data 1979 2013 reveals four main processes associated with deformation 1 frontogenesis at lower levels 2 movement and evolution of jet streams in the upper troposphere 3 orographic blocking and 4 rossby wave breaking the merits of deformation as an additional perspective are discussed for these processes on the basis of case studies and composite analyses in conjunction with analytic solutions this study shows that deformation can be used to unambiguously detect orographic blocking through the local strength of the flow diversion around orography moreover the deformation signature for orographic blocking observed in case studies and composites closely resembles the analytic solution for two dimensional flow around an obstacle the climatolo

transient development in confluent and diffluent flow abstract explaining the growth of disturbances superimposed on mean flows is a central problem in meteorology most widely studied models of the development process involve perturbations to shear flows with shear restricted to the meridional direction recently the importance of zonal variation of the mean flow was recognized and the study of shear flows extended to include zonal variation in shear these studies found that the eigenfunctions associated with unstable modes in the simple shear problem are highly sensitive to zonal variation of the mean flow however there also exists another mechanism for development in a zonally inhomogeneous flow field transient growth not associated with exponential instability properly configured perturbations exhibit transient growth in deformation fields associated with regions of confluence and diffluence at rates comparable to development in shear flow in this work analytic solution of the linear initial value problem for the barotropic vorticity equation in de

assessment of the effectiveness of a constructed compound channel river restoration project on an incised stream compound channels are often constructed in restoration projects on rivers and streams that have been channelized or are deeply incised this design allows for flow over a wider cross sectional area during high flows and is expected to reduce both flow velocities and bed shear stresses in the channel during high flows using a compound channel restoration project on tassajara creek as a case study the effectiveness of a constructed compound channel in reducing channel velocities and bed shear stresses during high flow events was tested in two ways first since this is an a posteriori analysis postproject surveys and assessments of the project are used to demonstrate the geomorphic and ecological benefits of the constructed compound channel for reducing further channel incision improving channel stability and enhancing native riparian vegetation while still providing conveyance capacity for design flood flows second the effectiveness of a constructed compound channel in reducing channel velocities a

sampling techniques for gravel sized sediments the methods commonly used for sampling the coarser surface layers of gravel bed streams are reviewed it is found that while an areal sample is biased toward the coarser grains compared with a volumetric sample of the same material the conversion formula suggested by a voidless cube model overcompensates for this effect a modified version of the cube model that accounts for porosity is proposed the modified cube model and tests conducted with areal sampling using wax indicate that area by weight analyses can be converted successfully to the equivalent bulk sieve analyses the average depth of the wax samples ranged from d65 d91 increasing with median grain size the equivalence of the grid by number and bulk sieve analyses is reaffirmed

baroclinic development in observations and nasa gsfc general circulation models abstract comparative diagnostic analyses of developing synoptic scale baroclinic disturbances in ncep ncar reanalyses and the nasa ncar nascar and aries nasa s seasonal to interannual prediction project nsipp general circulation model simulations are performed in particular lag composite analyses of wintertime cyclonic and anticyclonic events occurring in the north pacific and north atlantic storm tracks are constructed to pursue a synoptic and dynamic characterization of eddy development the data are also seasonally stratified to study aspects of the north pacific midwinter suppression phenomenon winter averaged results indicate that the model simulated events are generally too weak in amplitude particularly in the upper troposphere for the north pacific storm track model simulated events are also anomalously distended in the meridional direction the existing model biases in eddy structure and magnitude lead to anomalously weak baroclinic energy conversions for both cyclonic and anticycloni

a model of channel response in disturbed alluvial channels dredging and straightening of alluvial channels between 1959 and 1978 in west tennessee caused a series of morphologic changes along modified reaches and tributary streams degradation occurred for 10 to 15 years at sites upstream of the area of maximum disturbance and lowered bed levels by as much as 6 1 m following degradation reaches upstream of the area of maximum disturbance experienced a secondary aggradation phase in response to excessive incision and gradient reduction aggradation downstream of the area of maximum disturbance reached 0 12 m per year with the greatest rates occurring near the stream mouths the adjustment of channel geometry and phases of channel evolution are characterized by six process oriented stages of morphologic development premodified constructed degradation threshold aggradation and restabilization down cutting and toe removal during the degradation stage causes bank failure by mass wasting when the critical height and angle of the bank material is exceeded threshold stage channel widening continues through the aggradation stage as the slough line develops as an initial site of lower bank stability the bank profile develops three dynamic elements 1 vertical face 70 to 90 2 upper bank 25 to 50 and 3 slough line 20 to 25 alternate channel bars form during the restabilization stage and represent incipient meandering of the channel

organization of storm tracks in zonally varying flows abstract a simple two layer quasigeostrophic model is employed to investigate the sensitivity of storm tracks to changes in an externally imposed zonally varying large scale flow zonally asymmetric temperature and horizontal deformation fields are varied systematically in order to compare the effects of baroclinicity and horizontal deformation on storm track dynamics the sensitivity of the storm tracks to uniform barotropic zonal flows is also examined the results show two competing processes for storm track organization one associated with a local maximum in baroclinicity and the other with a local minimum in horizontal deformation when the equilibrium state consists of a zonally symmetric temperature field and a barotropic stationary wave the maximum in synoptic scale transient eddy energy storm track is located in the entrance region of the upper jet just downstream of the point of minimum horizontal deformation as zonal variations in baroclinicity become large keeping the upper layer horizo

storm tracks and barotropic deformation in climate models abstract the relationship between the time mean planetary scale deformation field and the structure of midlatitude storm tracks is studied in wintertime simulations of the national center for atmospheric research ncar community climate model and the national aeronautics and space administration nasa goddard earth observing system model model biases are determined by contrasting model simulations forced by observed ssts with parallel analyses of ncep ncar reanalyses barotropic diagnostics are employed to identify potential dynamical linkages between regional biases in the midlatitude storm tracks and the horizontal deformation field initial observational analyses confirm that synoptic eddies are optimally configured to transfer kinetic energy to the mean flow in the jet exit regions where strong stretching deformation exists in these regions the major axes of the synoptic eddies are aligned along the dilatation axes of the mean flow consequently mean flow advection stretches synoptic eddies a

present day downcutting of the raba river channel western carpathians poland and its environmental effects abstract timing and causes of the present day channel downcutting of carpathian tributaries to the vistula river are exemplified by a case study of the raba river a gravel bed stream characterized by great variability of water stage and discharge up to 3 m of river incision has occurred since the beginning of the present century associated with an increase in stream power caused by river control works and reduction in bed material load linked to changes in basin management gravel extraction from the channel and modifications in flood flows have increased rates of incision over the last thirty years lowering of ground water levels on the valley floor increase in river bank susceptibility to erosion decrease or cessation of overbank sediment accretion and impoverishment of plant and animal communities of riverside biotopes are the principal environmental effects of channel downcutting

impact of channel incision on the hydraulics of flood flows examples from polish carpathian rivers abstract channel deepening may result from channel incision or river metamorphosis changing a wide and shallow channel to a narrow and deep one as only the first type of channel change leads to increased flow capacity of the channel a lowering of water stage associated with a given discharge rather than a lowering of river bed should be used to identify channel incision a lowering of minimum annual stage at gauging stations is typically used to assess the relative importance of channel incision along a river or within a particular region rivers of the polish carpathians incised by 0 5 3 8 m over the twentieth century with the amount of incision being greater in their lower and middle courses than in the upper ones variability in the hydraulic importance of channel incision with increasing river size is analysed by comparing changes in the frequency of valley floor inundation at gauging stations located along the seventh order dunajec river despite a lower absolute amount of channel incision in the upper river course here incision has increased channel conveyance and reduced the frequency of valley floor inundation considerably more than in the lower course hydraulic effects of channel incision depend also on lateral stability of an incising river low energy rivers from the eastern part of the polish carpathians remained laterally stable during channel incision this has resulted in substantial lowering of stages for low flood discharges and markedly smaller one for high magnitude floods whereas velocity of the flows conveyed over the highly elevated floodplains has decreased considerably in high energy rivers from the western part of the polish carpathians alternation of incision and lateral channel migration has led to the formation of incised meander belts with substantially lowered stages for all flood discharges and increased velocity of the flows conveyed over the newly formed low lying floodplains

a comparison of climatological subseasonal variations in the wintertime storm track activity between the north pacific and atlantic local energetics and moisture effect distinct differences of the storm track jet relationship over the north pacific and north atlantic are investigated in terms of barotropic and baroclinic energetics using ncep 2 reanalysis data for the period of 1979 2008 from fall to midwinter the pacific storm track pst activity weakens following the southward shift of the pacific jet whereas the atlantic storm track ast activity remains steady in position and intensifies regardless of the slight southward shift of the atlantic jet this study is devoted to seeking for the factors that can contribute to this conspicuous difference between the two storm tracks on climatological subseasonal variation by analyzing eddy properties and local energetics different eddy properties over the two oceans lead to different contribution of barotropic energy conversion to the initiation of storm tracks in the north atlantic meridionally elongated eddies gain kinetic energy efficiently from stretching deformation of the mean flow in the jet entrance on the other hand the term associated with shearing deformation is important for the initiation of pst analysis of baroclinic energetics reveals that the intensification of the ast activity in midwinter is mainly attributed to coincidence between location of maximum poleward and upward eddy heat fluxes and that of the largest meridional temperature gradient over slight upstream of the ast the relatively large amount of precipitable water and meridional eddy moisture flux along baroclinic energy conversion axis likely provides a more favorable environment for baroclinic eddy growth over the north atlantic than over the north pacific in the meantime the midwinter minimum of the pst activity is attributable to the southward shift of the pacific jet stream that leads to discrepancy between core region of poleward and upward heat fluxes and that of meridional thermal gradient weakening of eddy mean flow interaction due to eddy shape and reduction of moist effect are also responsible for the weakening of storm track activities in midwinter when the strongest baroclinicity exists over the north pacific

recent channel adjustments in alluvial rivers of tuscany central italy drastic channel adjustments have affected the main alluvial rivers of tuscany central italy during the 20th century bed level adjustments were identified both by comparing available topographic longitudinal profiles of different years and through field observations changes in channel width were investigated by comparing available aerial photographs 1954 and 1993 98 bed incision represents the dominant type of vertical adjustment and is generalized along all the fluvial systems investigated the arno river system is the most affected by bed level lowering up to 9 m whereas lower incision generally less than 2 m is observed along the rivers of the southern part of the region human disturbances appear to be the dominant factors of adjustments the main phase of vertical change occurred during the period 1945 80 in concomitance with the phase of maximum sediment mining activity at the regional scale the second dominant type of adjustment that involved most of the rivers in the region consists of a narrowing of the active channel based on measurements of channel width conducted on aerial photographs 38 of the reaches analysed experienced a narrowing greater than 50 of the initial channel width the largest values of channel narrowing were observed along initially braided or sinuous with alternate bars morphologies in the southern portion of the region a regional scheme of channel adjustments is derived based on initial channel morphology and on the amounts of incision and narrowing different styles of channel adjustments are described rivers that were originally sinuous with alternate bars to braided generally became adjusted by a moderate incision and a moderate to intense narrowing in contrast sinuous meandering channels mainly adjusted vertically with a minor amount of narrowing copyright 2003 john wiley sons ltd

northern hemisphere storm tracks during the last glacial maximum in the pmip2 ocean atmosphere coupled models energetic study seasonal cycle precipitation mid latitude eddies are an important component of the climatic system due to their role in transporting heat moisture and momentum from the tropics to the poles and also for the precipitation associated with their fronts especially in winter we study northern hemisphere storm tracks at the last glacial maximum lgm and their influence on precipitation using ocean atmosphere general circulation model oagcm simulations from the second phase of the paleoclimate modelling intercomparison project pmip2 the difference with pmip1 results in terms of sea surface temperature forcing fundamental for storm track dynamics is large especially in the eastern north atlantic where sea ice extends less to the south in oagcms compared to atmospheric only gcms our analyses of the physics of the eddies are based on the equations of eddy energetics all models simulate a consistent southeastward shift of the north pacific storm track in winter related to a similar displacement of the jet stream partly forced by the eddies themselves precipitation anomalies are consistent with storm track changes with a southeastward displacement of the north pacific precipitation pattern the common features of north atlantic changes in the lgm simulations consist of a thinning of the storm track in its western part and an amplification of synoptic activity to the southeast in the region between the azores islands and the iberian peninsula which reflects on precipitation this southeastward extension is related to a similar displacement of the jet partly forced by the eddies in the western north atlantic the synoptic activity anomalies are at first order related to baroclinic generation term anomalies but the mean flow baroclinicity increase due to the presence of the laurentide ice sheet is partly balanced by a loss of eddy efficiency to convert energy from the mean flow moisture availability in this region is greatly reduced due to more advection of dry polar air by stationary waves leading to less synoptic scale latent heat release and hence less precipitation also in terms of seasonality the stormy season is shifted later in the year by a few days to a month depending on the season and the model considered this shift does not directly reflect on the first order seasonal cycle of precipitation which also depends on other mechanisms especially in summer

twentieth century channel change on the dunajec river southern poland patterns causes and controls abstract spatial and temporal patterns of the twentieth century channel changes of the dunajec the second largest river of the polish carpathians are analysed using data from six historical maps hand auger drillings in paleochannels and hydrometric data from 10 gauging stations in its lower course the river was considerably narrowed shortened and embanked between the 1880s and the 1920s here bed degradation commenced in the late 19th century and has so far resulted in 3 1 m of channel incision in the middle river course little change occurred in mountain reaches where the dunajec is confined by valley sides and where bedrock exposures prevent channel incision in the reaches within intramontane basins channelization works carried out in the 1950s 1970s considerably narrowed the river and transformed its multi thread channel into a single thread straight channel rapid bed degradation induced by the works resulted in up to 2 m of channel incision over the second half of the century upstream progression of bed degradation into the adjacent mountain reach was hindered by bedrock exposures at its downstream end in the upper river course reaches with the deeply incised channels up to 3 5 m prevail over a few past decades in response to gravel exploitation river channelization and a reduction in catchment sediment supply more scarce are vertically stable reaches which owe their stability to low unit stream power in wide unmanaged reaches and to fixing of the channel bed by drop structures in channelized reaches this study shows that despite the overall tendency to incision over the 20th century considerable differences in the timing and course of channel changes occurred between particular river reaches due to variable human impact and local geological and geomorphological conditions the main phase of channel incision took place progressively later in the upstream direction however upstream progression of bed degradation from the already incised downstream reaches was precluded by the roznow dam and bedrock controlled reaches where bed material flushed out from an incising upstream reach had been introduced into an artificially narrowed channel of high transport capacity it was easily transferred downstream and could not restore the downstream reach to its pre channelization vertical position

use of high water marks and effective discharge calculation to optimize the height of bank revetments in an incised river channel abstract in deeply incised rivers bankfull discharge i e the flow filling the channel to the top of the banks does not represent channel forming flow and increasingly large flows are associated with increasingly large boundary shear stress in such rivers solid bank revetments rip rap gabions retaining wall are usually constructed to the top of the banks similarly as in vertically stable rivers despite the fact that the upper parts of the banks may never be flooded to optimize the height of solid bank revetments in deeply incised channels it is thus important to determine whether a flood magnitude can be identified for which the combination of flow duration and bedload transport rate results in the highest river efficiency to transport bedload and perform geomorphic work this question was explored in the moravka river czech carpathians which deeply incised into non resistant flysch bedrock over the past few decades observations of high water marks e g trash lines wash lines after a flood in 2014 enabled reconstruction of the peak flood stage in the deeply incised reach and the adjacent vertically stable reach these observations together with post flood measurements of cross sectional channel geometry distances between consecutive cross sections and estimates of channel roughness were used in one dimensional hydraulic modelling aimed to determine a peak discharge of the flood in a number of cross sections in both reaches despite the close proximity of both reaches markedly higher discharge values were obtained for the incised reach and the discrepancy was used to calibrate roughness coefficients for the incised reach a flow duration curve determined on the basis of a 25 year series of daily discharges in the upstream gauging station together with data about channel geometry and roughness in the incised cross sections were used to simulate bedload transport at successive discharges with the bags sediment transport model the calculations indicated the effective discharge for bedload transport in the incised reach to have the recurrence interval of 7 12 years the upper limit of the reach average effective discharge is associated with the stage slightly higher than a half of the bankfull depth this highlights the disparity between effective and bankfull discharges and indicates that in incised channels channel forming flow should be linked with the former the vertical extent of the reach average effective discharge is proposed as an indicator of the optimal cost effective height of solid bank protection structures in the deeply incised channel and the suitability of this approach is discussed

impact of a large flood on mountain river habitats channel morphology and valley infrastructure abstract the biala river polish carpathians was considerably modified by channelization and channel incision in the twentieth century to restore the biala establishing an erodible corridor was proposed in two river sections located in its mountain and foothill course in these sections longer unmanaged channel reaches alternate with short channelized reaches and channel narrowing and incision increases in the downstream direction in june 2010 an 80 year flood occurred on the river and this study aims at determining its effects on physical habitat conditions for river biota channel morphology and valley floor infrastructure surveys of 10 pairs of closely located unmanaged and channelized cross sections performed in 2009 and in the late summer 2010 allowed us to assess the flood induced changes to physical habitat conditions a comparison of channel planforms determined before 2009 and after 2012 the flood provided information on the degree of channel widening as well as changes in the width of particular elements of the river s active zone in eight stretches of the biala the impact of the flood on valley floor infrastructure was confronted with the degree of river widening in unmanaged and channelized river reaches before the flood unmanaged cross sections were typified by finer bed material and greater lateral variability in depth averaged and near bed flow velocity than channelized cross sections the flood tended to equalize habitat conditions in both types of river cross sections obliterating differences in particular physical habitat parameters between channelized and unmanaged channel reaches river widening mostly reflected an increase in the area of channel bars whereas the widening of low flow channels was less pronounced a comparison of channel planform from 2009 and 2012 indicated that intense channel incision typical of downstream sections limited river widening by the flood active channel width increased by half in the unmanaged cross sections and by one third in the channelized cross sections however damage to the valley floor infrastructure was practically limited to the channelized river reaches with reinforced channel banks this indicates incompetent management of riparian areas rather than the degree of river widening as a principal reason for the economic losses during the flood

variability of the observed midlatitude storm tracks in relation to low frequency changes in the circulation pattern abstract the principal modes of month to month variability of the wintertime storm tracks over the north pacific and north atlantic are identified by empirical orthogonal function analysis of the root mean square statistics of bandpass 2 5 6 day filtered geopotential height data for 19 yr one of the two leading modes depicts fluctuations in the level of synoptic scale activity without any noticeable spatial displacement of the storm track axes whereas the other mode is associated with meridional shifts of the storm tracks from their time averaged positions higher order modes are indicative of diversion or truncation of cyclone tracks in particular geographical regions it is demonstrated that the leading storm track modes are linked to some of the best known monthly averaged teleconnection patterns the dipolar western pacific and western atlantic patterns for the monthly mean flow are seen to be accompanied by marked changes in the intensity of the storm tracks over the western oceans whereas the m

barotropic regeneration of upper level synoptic disturbances in different configurations of the zonal weather regime abstract barotropic dynamics of upper tropospheric midlatitude disturbances evolving in different configurations of the zonal weather regime i e in different zonal like large scale flows were studied using observational analyses and barotropic model experiments the contraction stage of upper level disturbances that follows their elongation stage leads to an increase of eddy kinetic energy that is called the barotropic regeneration process in this text this barotropic mechanism is studied through notions of barotropic critical regions btcrs and effective deformation that have been introduced in a previous paper the effective deformation field is equal to the difference between the square of the large scale deformation magnitude and the square of the large scale vorticity regions where the effective deformation is positive correspond to regions where the large scale flow tends to strongly stretch synoptic disturbances a btcr is an area separating two large scale regions of positive effective defo

morphological evolution of the maipo river in central chile influence of instream gravel mining abstract instream gravel mining is one of the most important causes of channel degradation in south america specifically in rivers located near large metropolitan areas with rapidly growing cities where no river management strategies exist in the western region of the continent many of these rivers belong to andean systems in which significant parts of the watersheds are located in mountain areas at high altitude with considerable seasonal rainfall variability and steep channel slopes in these rivers gravel mining has produced significant incision of the channels with serious physical and ecological consequences affecting habitats modifying the supply and transport of sediments and amplifying the risk to infrastructure in and around the channel during floods in spite of the degraded conditions of many channels no quantitative studies of the geomorphic impacts of gravel mining have been carried out in the region mostly because of the insufficient and sparse data available in this investigation we perform an analysis of the morphodynamic evolution in a section of the maipo river in the metropolitan region of santiago chile this river is economically the most important in the country as it provides drinking and irrigation water to urban and rural areas is utilized by the energy generation industry and runs along and below critical infrastructure we have collected and analyzed data from 1954 to 2015 during which the city population increased by more than 5 million inhabitants whose presence accelerated land use changes the analysis shows a rapid morphological evolution of the channel where in 31 years effects such as river sections showing incision of up to 20 m an increase of the area affected by gravel mining from 86 62 to 368 13 ha and a net erosion volume of 39 4 million m3 can be observed this work yields quantitative information on the consequences of gravel mining in the maipo river providing the necessary data to develop an integrated strategy to define management and restoration actions for this and other similar andean rivers

planetary and synoptic scale dynamic control of extreme cold wave patterns over the united states the roles of planetary and synoptic scale waves in extreme cold wave ecw events over the southeastern se and northwestern nw united states us are studied using a spherical harmonic decomposition in conjunction with piecewise tendency diagnosis ptd planetary waves and synoptic waves jointly work together to initiate ecw events notably the planetary waves not only provide a direct contribution to circulation field enacting ecw events but also alter the background circulation field in such a manner that promotes synoptic waves growth via increases in regional barotropic deformation the se ecw events concurrent with the northern hemisphere annular mode nam negative phase feature high latitude intensification and subsequent southeastward movement of cold surface air temperature sat anomalies the planetary scale pattern provides a sizable contribution to the total wave pattern on both sea level pressure slp and upper level moreover the negative nam planetary anomaly acts to displace the jet equatorward and thereby increases the barotropic deformation of the synoptic scale anomaly over southeastern us ptd confirms that the planetary scale barotropic deformation plays a key role in deepening the negative height anomaly with a secondary contribution from baroclinic growth in contrast nw ecw events feature a regional sat cold anomaly that intensified in situ in association with a quasi stationary positive slp anomaly with a substantial planetary scale wave component the upper level circulation is characterized by a pronounced anomalous ridge over the gulf of alaska and a northeast southwest tilted negative height anomaly to its east the negative height anomaly axis is orthogonal to the planetary scale dilatation result in a stronger planetary barotropic deformation of the incipient negative height anomaly

estimating mean flow velocity in channel and floodplain areas and its use for explaining the pattern of overbank deposition and floodplain retention abstract stage discharge curves for out of bank flows are derived from direct discharge measurements and theoretical calculations of channel and floodplain conveyance at a station and comparisons of volumes of flood waves at successive stations a method was developed which permits estimation of the mean flow velocity in the channel and floodplain zones at a given total discharge taken from a rating curve out of bank channel flows are estimated under the assumption that the interface planes between the channel zone and the floodplain are included in the wetted perimeter for the channel subarea the floodplain flows are then calculated as the residual values after subtracting the flow in the channel zone from the total discharge results obtained using the method are presented for three cross sections located on mountain foothill and piedmont rivers within the upper vistula drainage basin southern poland and are considered in relation with the pattern of floodplain sedimentation caused by a major flood of july 1997 high rates of lateral thinning and fining of overbank deposits were observed for the piedmont vistula river which is characterized by a marked contrast in mean velocity between the channel and floodplain flows on the mountain skawa river and the foothill skawinka river mean velocity of the floodplain flow was high both in absolute values and when compared with that of the channel flow overbank deposits were generally thin there and showed minor changes in thickness mean size and sorting across the floodplains this study shows that the proposed method of estimating mean flow velocity in channel and floodplain areas may yield valuable information about hydraulics of out of bank flows which may be used for explaining the observed pattern of floodplain deposition the results also demonstrate that the floodplain of the vistula acts mainly as a storage reservoir at low out of bank flows but its efficiency in carrying flood water grows when flow exceeds that of 12 year frequency on the other hand retention potential of the skawa floodplain is very low but flow becomes increasingly stored after water starts to spread rapidly onto the higher terrace at a discharge of 14 year recurrence interval

earthquake risk and fracture statistics abstract on the basis of fracture statistics which establishes a relation between the cumulative probability of fracture in a brittle body and the stress field to which it is subjected it is possible to describe some seismological statistics the cumulative probability of time intervals between two consecutive strong earthquakes and the cumulative probability of the strong earthquakes magnitude appears as weibullian comparison with chilean set data gives evidence to the theory

nature of the differences in the intraseasonal variability of the pacific and atlantic storm tracks a diagnostic study abstract on the basis of an intraseasonal variability index of storm track evaluated for 40 winters 1963 64 through 2003 04 of ncep ncar reanalysis data it is found that well defined midwinter minimum mwmin midwinter maximum mwmax occurs in 21 8 winters over the north pacific in contrast mwmin mwmax occurs in 4 25 of the 40 winters over the north atlantic the power spectrum of such an index for the pacific has a broad peak between 5 and 10 yr whereas the spectrum of the index for the atlantic has comparable power in two spectral bands 2 2 8 and 3 5 8 yr over the north pacific the increase in the zonal asymmetry of the background baroclinicity as well as in the corresponding horizontal deformation of the time mean jet from early late winter to midwinter is distinctly larger in an mwmin winter associated with these changes there is a distinctly stronger barotropic damping rate in the january of an mwmin winter the increase in the net conversion rate of eddy kinetic energy from early

bankfull discharge in mountain streams theory and practice the results are presented of an investigation of bankfull discharge in two polish carpathian streams skawica and krzyworzeka existing definitions of river bankfull were reviewed and applied in tests carried out on selected cross sections of the streams the woodyer method was given special attention with a correspondingly detailed survey of plants characterizing river benches riley s bench index method and the methods of williams wolman schumm and brown and woloszyn were tested the report concludes that bankfull discharge value for a mountain stream should not be reported as a single number but rather as a range of discharges within which one could expect the bankfull value to lie copyright 2002 john wiley sons ltd

thresholds and the spatial variability of flood power during extreme floods abstract analysis of the effects of extreme events on overall landscape form has shifted geomorphic attention away from a focus on the magnitude and frequency relationship of discharge to a focus on flood power this paper analyzes the variation in flood power both at a station and downstream in a basin of differing lithologies and discusses the geologic and geomorphic controls on flood power design floods ranging from the 2 year discharge tothe 500 year discharge are routed trough a drainage basin and channel boundary shear stress and unit stream power are calculated using hec 2 along 21 cross valley transects because of the strong lithologic control on valley width and channel slope an irregular downstream pattern of flood power emerges which reflects primarily the pattern in valley width narrow valleys correspond to a greater percent of channel conveyance during large magnitude floods and increasing rates of depth increases thus maximizing flood power in these zones the opposite occurs in anomalously wide valleys where flood power is minimized a downstream spatial pattern emerges reflecting both local and general controls for a given probability event flood power varies at least threefold within the basin with a maximum occuring in a specific downstream section holding flood power constant produces an extremely wide range in flow probabilities in order to establish a link between critical flood power magnitude and flow frequency minimum flood powers are developed from an analysis of previous work on catastrophic flooding for humid alluvial channels these minimum thresholds tentatively correspond to 100 n m2 or 300 w m2 for shear stress and unit stream power respectively discharges required to attain these critical flood powers vary from events roughly twice the 100 year flood to a maximum of roughly 18 times the discharge of the 100 year flood

role of the low frequency deformation field on the explosive growth of extratropical cyclones at the jet exit part i barotropic critical region abstract by using new theoretical results on perturbation growth in spatially and temporally complex quasigeostrophic flows this paper investigates the role of the large scale deformation field on extratropical cyclones and especially on their explosive growth in the jet exit region theoretical ideas are tested by decomposing the atmospheric flow into a high and a low frequency part and by analyzing four dimensional variational data assimilation 4dvar reanalysis data of the fronts and atlantic storm track experiment fastex during february 1997 as well as reanalysis data for the end of december 1999 regions where the low frequency deformation magnitude is greater than the absolute value of the low frequency vorticity are shown to correspond to regions where synoptic disturbances at the same level tend to be located these regions in the upper troposphere are intrinsically related to the horizontal inhomogeneities of the low frequency large scale upper tropospheric jet but cannot be detected by look

stochastic slip predictable model for earthquake occurrences recent geophysical studies have indicated that an earthquake recurrence interval and the size of the preceding event are positively correlated this observation is the basis for the deterministic time predictable recurrence model of shimazaki and nakata using the basic assumptions of the time predictable recurrence model we develop a stochastic model of earthquake occurrence that incorporates temporal dependence this paper discusses the formulation of the model and the effect of including temporal dependence hazard estimates for a section of the san andreas fault near parkfield where data has suggested time predictable behavior are obtained for illustrative purposes comparisons are made with the poisson model results indicate that currently used poisson models may give lower estimates of the seismic hazard when there has been a seismic gap of the various sensitivity analyses performed it is observed that slip rate has the largest effect on exceedence probabilites computed from the stochastic time predictable model therefore accurate determinations of slip rates both seismic and aseismic can substantially reduce the uncertainty in seismic hazard estimates

monitoring co and pre seismic motion by geodetic techniques a recently built extensometer which is based on a highly stable capacitance transducer as well as a liquid bubble hughes tiltmeter are discussed in view of monitoring strain and deformations at the earth s surface these instruments are being used to control local variations whereas regional and global changes including gravity variations are monitored using repeated gps and very precise relative gravimetry with sufficient exterior control such as absolute gravimetry for calibration tidal measurements for separating tidal from other effects we will acquire a more or less complete system in combination with local leveling etc as used by several other authors as well for determination of time dependent phenomena

persistent anomalies of the extratropical northern hemisphere wintertime circulation structure abstract in a previous study of the extratropical northern hemisphere wintertime circulation significant variations were described in the occurrence of anomalies that persist beyond the durations associated with synoptic scale variability persistent anomalies the present study extends that work by identifying the typical structures of persistent anomalies focusing on whether persistent occur in certain key regions the central north pacific pac the eastern north atlantic atl and the northern soviet union nsu are related to recurrent large scale flow patterns for each region detailed comparisons are provided of the flow patterns associated with persistent positive and negative anomaly cases and with the patterns obtained in other observations and theoretical studies of persistent phenomena the results provide evidence for the recurrence of certain preferred anomaly patterns to a first approximation the composite anomaly patterns of the positive and negative cases for a region can be de

barotropic wave propagation and instability and atmospheric teleconnection patterns abstract a global barotropic model linearized about the 300 mb climatological mean january flow is perturbed by applying a series of localized forcings distributed throughout the tropics and subtropics structures which resemble the observed pacific north american and east atlantic teleconnection patterns noted by wallace and gutzler 1981 tend to recur in the responses similar patterns are found to result from the dispersion of isolated initial perturbations placed at a variety of locations in the tropics and midlatitudes it is shown that these structures are related to the most rapidly growing mode associated with barotropic instability of the zonally varying climatological basic state in the absence of damping this mode has an e folding time of about a week and a period close to 50 days in localized regions the instantaneous growth rates can be competitive with those of baroclinic instability these episodes of rapid local barotropic growth are interspersed with intervals in which the local

hydraulic controls on the entrapment of heavy metal polluted sediments on a floodplain of variable width the upper vistula river southern poland distribution of heavy metal polluted overbank sediments deposited by a major flood in july 2001 in three gauging sections of different width on the vistula river southern poland was investigated and related to reconstructed pattern of flow velocity during the event the mean velocity of the flow over the floodplain was low and showed a marked contrast with mean velocity in the channel zone in the smolice and the sieroslawice cross sections 4 5 and 9 times wider than the respective channel widths high rates of lateral thinning and fining of overbank deposits were observed at sieroslawice the heavy metal concentrations first rapidly increased with distance from the channel and then remained high over most of the floodplain at smolice concentrations were relatively low within the levee deposits and high over the rest of the floodplain in both cross sections the loads of heavy metals were highest close to the channel margins and decreased exponentially with increasing distance from the channel due to the rapid lateral thinning of the flood deposits the mean velocity of the flow over the floodplain was high in the bielany cross section only 2 6 times wider than the channel width sediments deposited on the narrow floodplain were mostly sand slowly thinning laterally while the concentrations of various heavy metals increased gradually with increasing distance from the channel their loads varied across the floodplain the highest load of some metals occurred near the channel margin and that of others away from the channel this study indicates that floodplain width and the resultant flow hydraulics exert a significant influence on the lateral distribution of floodplain sediments and entrapped heavy metals in wider floodplain sections the largest amounts of heavy metals accumulate near the channel margin and may be remobilized in the future due to bank erosion

assessment of channel changes due to long term bedload supply decrease roubion river france this paper presents the observations made in the watershed of the upper roubion river which drains a submediterranean mountainous environment and in two of its main tributaries the soubrion and bine creeks our aim was to analyze contemporary morphological and sedimentary changes in response to a progressive decrease in bedload supply this decrease is linked to an increase of forest cover in the watershed during the 20th century following rural depopulation and to a correlated decrease in peak flows several variables were systematically measured width slope bed level change sediment size along 23 km of river whereas dendrochronological data floodplain cross sections and estimated recurrence intervals of sediment entrainment based on critical shear stress calculations were also produced for specific sites to complete our analysis evidence of three major phenomena was obtained on both the roubion and its tributaries i bed degradation ii development of stable pavement in incised reaches and iii channel narrowing associated with the development of alluvial forest on recently abandoned portions of the pre existing active channel forest development began in the 1950s these three phenomena show positively covariant relationships that lead us to propose a descriptive model of mountain fluvial system adjustments to progressive decrease of bedload

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

modelling the flooding capacity of a polish carpathian river a comparison of constrained and free channel conditions abstract the gravel bed biala river polish carpathians was heavily affected by channelization and channel incision in the twentieth century not only were these impacts detrimental to the ecological state of the river but they also adversely modified the conditions of floodwater retention and flood wave passage therefore a few years ago an erodible corridor was delimited in two sections of the biala to enable restoration of the river in these sections short channelized reaches located in the vicinity of bridges alternate with longer unmanaged channel reaches which either avoided channelization or in which the channel has widened after the channelization scheme ceased to be maintained effects of these alternating channel morphologies on the conditions for flood flows were investigated in a study of 10 pairs of neighbouring river cross sections with constrained and freely developed morphology discharges of particular recurrence intervals were determined for each cross section using an empirical formula the morphology of the cross sections together with data about channel slope and roughness of particular parts of the cross sections were used as input data to the hydraulic modelling performed with the one dimensional steady flow hec ras software the results indicated that freely developed cross sections usually with multithread morphology are typified by significantly lower water depth but larger width and cross sectional flow area at particular discharges than single thread channelized cross sections they also exhibit significantly lower average flow velocity unit stream power and bed shear stress the pattern of differences in the hydraulic parameters of flood flows apparent between the two types of river cross sections varies with the discharges of different frequency and the contrasts in hydraulic parameters between unmanaged and channelized cross sections are most pronounced at low frequency high magnitude floods however because of the deep incision of the river both cross section types are typified by a similar low potential for the retention of floodwater in floodplain areas the study indicated that even though river restoration has only begun here it already brings beneficial effects for flood risk management reducing flow energy and shear forces exerted on the bed and banks of the channel in unmanaged river reaches only within wide unmanaged channel reaches can the flows of low frequency high magnitude floods be conveyed with relatively low shear forces exerted on the channel boundary in contrast in channelized reaches flow velocity and shear forces are substantially higher inevitably causing bank erosion and channel incision

river response to channel regulation case study of the raba river carpathians poland processes induced by the channelization of the raba river in the present century are examined to illustrate the response of a gravel bed stream following narrowing and straightening of its channel up to 3 m of incision has occurred the change from a slow and relatively steady degradation in the lower reaches to separate degradation events in the higher reaches is attributed to the differential rate of headcut retreat and to the control exerted by mid channel bars upon the rate of river energy dissipation progressive outwashing of finer grains from bed material has followed the diminishing sediment yield of the basin and the increase in stream power the ensuing growth in mean grain size and changes in sediment fabric have increased boundary resistance to flow and reduced particle susceptibility to entrainment downstream magnification of peak discharges has become increasingly pronounced with the advancing incision the decrease in flood plain storage and self acceleration of flows passing the relatively deep and straight channel has caused flood waves to become progressively more flashy in nature an increase in channel depth and reduction in gradient caused by downward and backward erosion as well as bed material coarsening has promoted the re establishment of an equilibrium conversely flow velocity increases due to flow concentration in the deepened channel reduction in grain mobility allows the river to attain a new equilibrium at flow velocity and stream power levels higher than before the channelization numerous disadvantages of the applied regulation scheme and its failure to reduce flood hazard raise the question of its maintenance to be successful any regulation design must take into account changes in sediment supply and flood hydrographs resulting from the simultaneous alterations in basin management

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

channel incision on the lower american river california from streamflow gage records channel incision along the lower american river from 1905 to 1995 is investigated using channel cross section plots and statistical analysis of stage discharge data from two streamflow gages located at three sites channel incision lowered thalweg elevations at rates of up to 8 2 cm yr 1 and flow stages decreased at rates of up to 4 3 cm yr 1 for periods lasting several decades at a critical flood risk location in sacramento flow stages lowered 2 m from 1924 to 1970 channel incision was the result of channel recovery from aggradation due to hydraulic gold mining sediment and was exacerbated by sediment storage behind dams prolonged erosion and transport of historical alluvium in this river suggest that g k gilbert s symmetrical sediment wave model is inappropriate for the lower american river and may not adequately allow for the importance of sediment storage and remobilization in fluvial systems

channel floodplain connectivity during an extreme flood event implications for sediment erosion deposition and delivery the term connectivity has emerged as a powerful concept in hydrology and geomorphology and is emerging as an innovative component of catchment erosion modeling studies however considerable confusion remains regarding its definition and quantification especially as it relates to fluvial systems this confusion is exacerbated by a lack of detailed case studies and by the tendency to treat water and sediment separately extreme flood events provide a useful framework to assess variability in connectivity particularly the connection between channels and floodplains the catastrophic flood of january 2011 in the lockyer valley southeast queensland australia provides an opportunity to examine this dimension in some detail and to determine how these dynamics operate under high flow regimes high resolution aerial photographs and multi temporal lidar digital elevation models dems coupled with hydrological modeling are used to assess both the nature of hydrologic and sedimentological connectivity and their dominant controls longitudinal variations in flood inundation extent led to the identification of nine reaches which displayed varying channel floodplain connectivity the major control on connectivity was significant non linear changes in channel capacity due to the presence of notable macrochannels which contained a 3000 average recurrence interval ari event at mid catchment locations the spatial pattern of hydrological connectivity was not straight forward in spite of bankfull discharges for selected reaches exceeding 5600m 3 s 1 data indicate that the main channel boundary was the dominant source of sediment while the floodplains where inundated were the dominant sinks spatial variability in channel floodplain hydrological connectivity leads to dis connectivity in the downstream transfer of sediments between reaches and affected sediment storage on adjacent floodplains consideration of such variability for even the most extreme flood events highlights the need to carefully consider non linear changes in key variables such as channel capacity and flood conveyance in the development of a quantitative connectivity index copyright c 2013 john wiley sons ltd

nature rehabilitation by floodplain excavation the hydraulic effect of 16 years of sedimentation and vegetation succession along the waal river nl abstract the ewijkse plaat is a floodplain along the waal river nl in 1988 the floodplain was excavated as part of a program for enlargement of the discharge capacity and was assigned as a nature rehabilitation area this paper describes the combined geomorphological and vegetation evolution of the floodplain until 16 years after the initial excavation using elevation data and data on vegetation structure derived from detailed aerial stereographic imagery the impact of these processes on flow velocity and water surface elevation was evaluated by using a hydraulic model within 16 years the excavated amount of sediment was redeposited in the area the dominant geomorphological process after excavation was vertical accretion of the floodplain which resulted in the formation of natural levees the amount of sedimentation was correlated to the across floodplain flow r 2 0 89 in the research period 41 of the sedimentation took place during two single major flood events the creation of pioneer stages by excavation promoted softwood forest establishment which influenced the sedimentation pattern significantly the landscape evolved toward structure rich vegetation nine years after excavation the initial hydraulic gain was lost by the combined effect of sedimentation and vegetation succession implications for river and nature management are discussed

patterns of alluvial rivers the pattern planform of a river can be considered at vastly different scales depending upon both the size of the river and the part of the fluvial system that is under consideration figure 1 for example in the broadest sense river patterns comprise a drainage network dendritic parallel trellis etc figure la the type of pattern is of interest to geomorphologists and geologists who interpret geologic conditions from aerial photographs at another scale a river reach which in figure lb is meandering is of interest to the geomorphologist who is interested in what that pattern reveals about river history and behavior and to the engineer who is charged with maintaining navigation and preventing major instability when a single meander is examined figure 1 c the hydraulics offtow the sediment transport and the potential for bank erosion are of concern in addition the sedimentologist is interested in the distribution of sediment within the bend bed forms within the channel figure ld and sedimentary structures figure ie which also establish a component of roughness for the hydraulic engineer finally the individual grains figure if provide geologic information on the sediment sources the nature of sediment loads and the feasibility of dredging for gravel there is an interaction of hydrology hydraulics geology and geomorphology at all scales which emphasizes the point that the fluvial system as a whole cannot be ignored even though only a component of the system is to be studied in this review only the patterns or planforms of alluvial rivers are discussed although it is apparent that the hydrologic and sediment yield characteristics of the drainage basin figure la as well as its geologic history cannot be ignored in the explanation of the pattern of any river

evolution of the morphology of the river dragonja sw slovenia due to land use changes the effects of increasing agricultural land use on fluvial morphology have received much attention in fluvial research however in several regions in europe a reversing trend of decreasing agricultural activity and land abandonment followed by reforestation is observed the response of fluvial morphology deserves attention because of its large impacts on landscape and riverine habitats with the help of geomorphological mapping multi date aerial photography and a range of dating techniques we reconstructed the evolution of the morphology of the riverbed and the floodplain of the dragonja river in southwestern slovenia the results of this study show that the fluvial morphology in this mediterranean catchment has changed considerably as a result of shifts in agricultural land use in particular large scale land abandonment in the second half of the 20th century until the first half of the 19th century floodplain aggradation prevailed probably around 1870 a large erosion event occurred from which the floodplain did not fully recover a terrace standing 2 5 m above the present floodplain was formed natural reforestation due to depopulation since world war ii caused a reduction in discharge and sediment supply to the river the decreased intensity and frequency of floods allowed invasion of the riverbed by vegetation causing narrowing and incision of the riverbed this resulted in the formation of a terrace which now stands 1 5 m above the present day river this terrace is about 60 years old however the largest increase in forest area occurred since 1975 which intensified this process of riverbed narrowing and incision creating a local terrace at 0 5 m at 0 5 m above the presently meandering river

a simple identification scheme for upper level troughs and its application to winter precipitation variability in northwest africa abstract a simple algorithm for the identification of upper level trough axes is introduced in contrast to the assumption of a basically circular geometry in many comparable routines found in the literature the presented identification scheme is based on the east west gradient in the 500 hpa geopotential height field accounting for the meridionally elongated troughs often found in the subtropics on the basis of the ncep ncar reanalysis data from 1958 to 1998 climatological aspects are discussed for the area 22 5 47 5 n 38 5 w 18 5 e for the period from 1977 to 1998 12 hourly precipitation reports from 37 stations in northwestern africa are used to investigate the influence of the identified troughs on winter precipitation it is demonstrated that more than 90 of the precipitation in this region can be assigned to nearby trough axes a comparison of rainy periods with the climatology reveals a significant enhancement of the occurrence of trough axes in a range of 10 15 longitude close to the re

structure of a warm front helsinki testbed observations and model simulation abstractthe purpose of this study is to document the structure of a warm front in northeast europe identify the effects that the finnish coastline has on the evolution of the front and investigate factors that influence the speed that the warm front moves at within and above the boundary layer the warm front formed over estonia traveled northward across the gulf of finland and then crossed the southern coastline of finland surface based measurements from the helsinki testbed are analyzed together with output from a high resolution numerical weather prediction model application of research to operations at mesoscale arome during the early stages of development the warm front interacted with a stationary baroclinic zone and consequently evolved into an s shape as the front approached the southern coast of finland the temperature gradient at 1000 hpa increased as it merged with a diabatically generated temperature gradient at 1000 hpa the front stalled at the coastline due to friction enh

the influence of river training on mountain channel changes polish carpathian mountains the purpose of this paper is to explain the influence of river training on channel changes in mountain rivers also considered are the causes of failure of different training schemes the research was conducted on the regulated mszanka and porebianka rivers belonging to the raba river drainage basin in the polish flysh carpathian mountains channel mapping carried out in 2004 drew attention to the contemporary morphology of the channels and the development of their dynamic typology general changes in channel morphometry and land cover were identified by comparing cartographic sources from various years archive material from cracow s regional water management authority rzgw was used to analyse the detailed channel changes caused by each regulation structure the material consisted of technical designs of individual training works as well as plans longitudinal profiles and cross sections of trained channel reaches a series of minimum annual water stages at the mszana dolna gauging station was used to determine the tendency of channel bed degradation over 53 years during the first half of the 20th century the middle and lower courses of the mszanka and porebianka rivers had braided patterns the slopes mostly covered with crops were an important source of sediment delivery to the river channels today both channels are single threaded narrow and sinuous downcutting is the leading process transforming the channels they cut down to bedrock along about 60 of their lengths the main type of channel is an erosion channel which occurs also in the middle and lower courses of the rivers the channel sediment deficit is an important cause for river incision sediment supply to the channels was reduced after a replacement of crops on the slopes by meadows or forests gravel mining has also caused channel downcutting the rapid channel changes began after 1959 as systematic training was introduced channel regulation seems therefore to be a major factor determining channel adjustment debris dams and groynes were built before 1980 and these caused the greatest change of channel pattern increase of channel gradient and magnitude of river incision after that date the measures mostly involved drop structures from then on the rate of downcutting decreased considerably but has not ceased the rivers continued to incise until bedrock was exposed or training structures were destroyed after that a tendency to lateral migration and local braiding were observed in the deepened channel the channels displayed a tendency to return to their morphology and dynamic from before the training the results demonstrate that river training distorts the equilibrium of channel systems a channel becomes divided into artificial reaches which later follow different evolutionary patterns most training schemes on mountain channels are ineffective in the long term as river managers seem to consider a channel at a reach scale only individual channel reaches however are not independent but rather form a system that must be managed at the entire channel scale

the continuum and dynamics of northern hemisphere teleconnection patterns this study presents an alternative interpretation for northern hemisphere teleconnection patterns rather than comprising several different recurrent regimes this study suggests that there is a continuum of teleconnection patterns this interpretation indicates either that 1 all members of the continuum can be expressed in terms of a linear combination of a small number of real physical modes that correspond to basis functions or 2 that most low frequency patterns within the continuum are real physical patterns each having its own spatial structure and frequency of occurrence daily ncep ncar reanalysis data are used that cover the boreal winters of 1958 97 a set of nonorthogonal basis functions that span the continuum is derived the leading basis functions correspond to well known patterns such as the pacific north american teleconnection and north atlantic oscillation evidence for the continuum perspective is based on the finding that 1 most members of the continuum tend to have similar variance and autocorrelation time scales and 2 that members of the continuum show dynamical characteristics that are intermediate between those of the surrounding basis functions the latter finding is obtained by examining the streamfunction tendency equation both for the basis functions and some members of the continuum the streamfunction tendency equation analysis suggests that north pacific patterns basis functions and continuum are primarily driven by their interaction with the climatological stationary eddies and that north atlantic patterns are primarily driven by transient eddy vorticity fluxes the decay mechanism for all patterns is similar being due to the impact of low frequency period greater than 10 days transient eddies and horizontal divergence analysis with outgoing longwave radiation shows that tropical convection is found to play a much greater role in exciting north pacific patterns a plausible explanation for these differences between the north atlantic and north pacific patterns is presented

causes of river bed degradation river bed degradation can proceed downstream as well as upstream depending upon the cause of degradation the causes of downstream progressing degradation are primarily related to changes in independent river channel variables such as increase in water discharge decrease in size of bed material and decrease in bed material discharge the causes of upstream progressing degradation are all related to an imposed increase in river slope which can occur as a result of natural river behavior or by man made changes study of various case histories indicates that river slopes are increased by lowering a base level by decreasing the length of a river or by removal of a control point case histories also show that downstream and upstream progressing degradation can act in combination along a river system downstream progressing degradation along the main stream of a river system can initiate upstream progressing degradation on a tributary

floods in mountain environments a synthesis floods are a crucial agent of geomorphic change in the channels and valley floors of mountains watercourses at the same time they can be highly damaging to property infrastructure and life because of their high energy mountain watercourses are highly vulnerable to environmental changes affecting their catchments and channels many factors have modified and frequently still tend to modify the environmental conditions in mountain areas with impacts on geomorphic processes and the frequency magnitude and timing of floods in mountain watercourses the ongoing climate changes vary between regions but may affect floods in mountain areas in many ways in many mountain regions of europe widespread afforestation took place over the twentieth century considerably increasing the amounts of large wood delivered to the channels and the likelihood of jamming bridges at the same time deforestation continues in other mountain areas accelerating runoff and amplifying the magnitude and frequency of floods in foreland areas in many countries in channel gravel mining has been a common practice during recent decades the resultant deficit of bed material in the affected channels may suddenly manifest during flood events resulting in the failure of scoured bridges or catastrophic channel widening during the past century many rivers in mountain and foreland areas incised deeply the resultant loss of floodplain water storage has decreased attenuation of flood waves hence increasing flood hazard to downstream river reaches on the other hand a large amount of recent river restoration activities worldwide may provide examples of beneficial changes to flood risk attained as a result of increased channel storage or reestablished floodplain water storage relations between geomorphic processes and floods operate in both directions which means that changes in flood probability or the character of floods e g increased wood load may significantly modify the morphology of mountain rivers but morphological changes of rivers can also affect hydrological properties of floods and the associated risk for societies this paper provides a review of research in the field of floods in mountain environments and puts the papers of this special issue dedicated to the same topic into context it also provides insight into innovative studies methods or emerging aspects of the relations between environmental changes geomorphic processes and the occurrence of floods in mountain rivers

the shape propagation and mean flow interaction of large scale weather systems abstract for a zonal average operator the eliassen palm flux provides a diagnostic of both eddy behavior and the feedback of the eddies onto the mean flow this paper addresses the diagnosis problem for other averaging operators and in particular for time averaging which has proved in recent years such a powerful means of viewing the three dimensional tropospheric flow the horizontal velocity correlation tensor gives a measure of the characteristic horizontal eddy shape at a point it also implies the direction of the group velocity relative to the mean flow in cases where such a concept is valid however the major emphasis here is on the mean flow feedback of eddies in this respect the eddy vorticity flux is determined by derivatives of the components of the anisotropic part of the tensor making a reasonable approximation allows the eddy vorticity flux convergence to be written in terms of e v 2 u 2 u v a simple interpretation of the mean flow feedback of eddies is then possible a sligh

river channel adjustments downstream from channelization works in england and wales relatively little attention has been given to river channel adjustments that occur downstream from channelization works this study is concerned with the nature of channel adjustments downstream from a total of 46 channelization works located in low and high energy environments in england and wales channel changes are identified principally by the method of field survey and by reconstructing the original positions of eroded beds and banks use is also made of maps aerial photographs and engineering drawings of different dates and the technique of space for time substitution is applied enlargement of channel cross sections through erosion had occurred downstream from a variety of types sizes and dates of channelization works the maximum increase of channel size was 153 per cent out of a total of 14 sites with enlarged channel cross sections seven had undergone a change of width only at a further three width increased rather than depth and at the remaining four sites depth increases were dominant these sites all have relatively high stream powers factors causing spatial variation of erosion included tree roots locally binding bank sediments and the occurrence of bends planform change had taken place at only one site a further three high stream power sites had downstream reaches incised into bedrock and therefore did not exhibit adjustment channel enlargement is explained in terms of increased flood flows downstream from channelization works causing higher stream velocities which in turn cause erosion thereby increasing channel width and or depth examination of flow records for 35 stations revealed flood events which would formerly have spread overbank but are now confined by the channelization works and are therefore likely to alter downstream flows at sites with downstream change it is proposed that the energy of increased flows was sufficient to exceed a threshold required for erosion of perimeter sediments by contrast the absence of change at a majority of sites in low energy lowland areas could be a reflection of both the incompetence of increased flows to erode and resistance provided by perimeter sediments sites with erosion features appear not to have yet attained new equilibrium conditions

disturbance stream incision and channel evolution the roles of excess transport capacity and boundary materials in controlling channel response abstract channel incision is part of denudation drainage network development and landscape evolution rejuvenation of fluvial networks by channel incision often leads to further network development and an increase in drainage density as gullies migrate into previously non incised surfaces large anthropogenic disturbances similar to large or catastrophic natural events greatly compress time scales for incision and related processes by creating enormous imbalances between upstream sediment delivery and available transporting power field examples of channel responses to antrhopogenic and natural disturbances are presented for fluvial systems in the mid continent and pacific northwest usa and central italy responses to different types of disturbances are shown to result in similar spatial and temporal trends of incision for vastly different fluvial systems similar disturbances are shown to result in varying relative magnitudes of vertical and lateral widening processes and different channel morphologies as a function of the type of boundary sediments comprising the bed and banks this apparent contradiction is explained through an analysis of temporal adjustments to flow energy shear stress and stream power with time numerical simulations of sand bed channels of varying bank resistance and disturbed by reducing the upstream sediment supply by half show identical adjustments in flow energy and the rate of energy dissipation the processes that dominate adjustment and the ultimate stable geometries however are vastly different depending on the cohesion of the channel banks and the supply of hydraulically controlled sediment sand provided by bank erosion the non linear asymptotic nature of fluvial adjustment to incision caused by channelization or other causes is borne out in similar temporal trends of sediment loads from disturbed systems the sediments emanating from incised channels can represent a large proportion of the total sediment yield from a landscape with erosion from the channel banks generally the dominant source disturbances that effect available force stream power or flow energy or change erosional resistance such that an excess of flow energy occurs can result in incision channel incision therefore can be considered a quintessential feature of dis equilibrated fluvial systems

the statistics and horizontal structure of anomalous weather regimes in the community climate model abstract the statistics horizontal structure and linear barotropic dynamics of anomalous weather regimes are evaluated in a 15 winter integration of the ncar community climate model ccm2 statistical and ensemble analyses of simulated regimes are contrasted with parallel analyses derived from ncep ncar reanalyses the ccm2 replicates much of the structure of observed frequency distributions for anomalous weather regimes over the north pacific and north atlantic regions the main differences are a northward shift and longitudinal broadening of the north pacific frequency maximum and a weakening and southward shift of the north atlantic maximum ensemble analyses reveal that simulated north pacific regimes attain a more isotropic horizontal anomaly structure than observed cases which are zonally elongated the e vector diagnoses indicate that north pacific cases in the ccm2 are also associated with much weaker local barotropic energy conversions from the climatological mean flow this is partly due to

seasonal variations of the synoptic scale transient eddy activity and polar front jet over east asia abstract seasonal variations of the synoptic scale transient eddy activity stea and the jet streams over east asia are examined through analysis of the 40 yr european centre for medium range weather forecasts ecmwf re analysis era 40 data extracted from the 6 hourly upper level wind fields the distribution of the jet core numbers exhibits a distinct geographical border for the east asian subtropical jet easj and the east asian polar front jet eapj at the latitudes of the northern tibetan plateau tp in the cool seasons two branches of the stea and low level baroclinicity exist over the east asian landmass accompanied by the two jet state of the easj and eapj in the warm seasons a single jet pattern of the easj along the north flank of the tp is accompanied by the weakened stea over the mid to high latitudes of east asia further analysis shows two distinct features of the seasonal variations of the stea over east asia compared with that over the north pacific first during the transit

changes in the magnitude and transformation of flood waves subsequent to the channelization of the raba river polish carpathians alterations in flood flows of the raba river are examined to determine the influence exerted on flood waves by changing morphological conditions with stable vertical channel position the river increased its sinuosity during the 1920s to 1940s and the change was accompanied by a growing tendency to flood wave attenuation the temporal change in flood wave transformation is typical of a developing low flow system subsequently streambed degradation has been induced due to channnelization works which straightened and narrowed the river flood waves became progressively more flashy as channel incision progressed the increase in magnitude of flood waves passing the deepened reach was greatest for bankfull flows and diminished for lower in bank flows and higher overbank flows the tendency to magnification of peak discharges has been also found in other carpathian rivers which were considerably degraded in the 20th century in response to channelization introducing an empirically found correcting factor into the analysis of the ratio of outflow to inflow peak discharges shows how the conditions of peak flow transformation in a reach have changed since the beginning of the study period a marked coincidence between changes in vertical channel location and variations in the corrected peak discharge ratio proves channel changes to be a very important reason for the growing flood hazard in southern poland gradient oversteepening and channel narrowing caused by channelization lead to formation of a river system having a steep straight narrow and deep channel such a morphology distinguishes the system from natural low flow and high flow systems reduced floodplain water storage and self acceleration of flow concentrated in a channel zone make flood waves progressively more flashy on their way down the channelization formed system

bed level adjustments in the arno river central italy abstract two distinct phases of bed level adjustment over the last 150 years are identified for the principal alluvial reaches of the arno river upper valdarno and lower valdarno the planimetric configuration of the river in these reaches is the result of a series of hydraulic works canalization rectification artificial cut offs etc carried out particularly between the 18th and the 19th centuries subsequently a series of interventions at basin level construction of weirs variations in land use intense instream gravel mining after world war ii and the construction of two dams on the arno river caused widespread degradation of the streambed since about 1900 total lowering of the channel bed is typically between 2 and 4 m in the upper valdarno reach and between 5 and 8 m in some areas of the lower valdarno reach bed level adjustments with time are analyzed for a large number of cross sections and described by an exponential decay function this analysis identified the existence of two main phases of lowering the first triggered at the end of the past century the second triggered in the interval 1945 1960 and characterized by more intense degradation of the streambed the first phase derived from changes in land use and land management practices the second phase is the result of the superimposition of two factors intense instream mining of gravel and the construction of the levane and la penna dams