incision due to gravel mining modeling a case study from the gallego river spain abstract historical information on river degradation was used in a case study on the gallego river a tributary of the ebro river in northeastern spain the gallego drains about 4000 km 2 of the southern slopes of the pyrenees good channel surveys since the 1940s allowed a comparison of longitudinal bed profiles over time over this period about 1 million m 3 of gravel was mined according to the archival records the volume of alluvium lost due to incision in the same period was 2 million m 3 this imbalance is tentatively explained by a budget model based on a bedload equation and an algorithm to determine whether the effective bedload transport is controlled by the transport capacity or by the supply of sediment it appears that the incision process has changed the magnitude of the shear stresses on channel bed as the river became deeper the channel could accommodate higher discharges without overbank flooding the results obtained from a second model based on diffusion equation for the bed elevation compared well with the field data this model is based on the hypotheses of steady uniform flow regarding water and sediment conservation

quantifying exhumation from apatite fission track analysis and vitrinite reflectance data precision accuracy and latest results from the atlantic margin of nw europe

source rock evaluation of middle jurassic coals northeast greenland by artificial maturation aspects of petroleum generation from coal paralic liptinite enriched coals and carbonaceous mudstones in northeast greenland constitute potential highly oil prone source rocks whereas the humic coals may be marginal source rocks the liptinite rich coals are dominated by resinite or fluorescing amorphous organic matter and alginite resulting in hydrogen index hi values generally above 300 and reaching up to 728 during artificial maturation up to 330 degreesc 72 hr the coals follow the maturation paths of kerogen types i and ii on an hi vs tmax diagram and calculations show that upon passage through the oil window roughly 85 of their generation potential is realized activation energy ea distributions with prominent principal ea values centered around 60 62 kcal mole and frequency factors from 5 855 x 1015 s 1 to 3 249 x 1016 s 1 strongly influence the generation characteristics from 300 to 330 degreesc 72 hr artificial maturation important changes include marked loss of liptinite fluorescence and increase in resinite reflectance small change in tmax significant decrease in hi pronounced increase in extract yields increased generation of saturates and generation of labile bitumen with low ea values these observations indicate significant bitumen petroleum formation from the coals during a relatively narrow temperature range which together with the petrographic composition may facilitate expulsion of a waxy crude oil the coals demonstrate that under certain depositional conditions highly prolific coal source rocks can form with the capacity not only to generate but also to expel liquid petroleum begin page 234

channel and floodplain response to recent abrupt climate change the tyne basin northern england this paper examines the timing nature and magnitude of river response in upland piedmont and lowland reaches of the tyne basin northern england to high frequency 20 30 year changes in climate and flood regime since 1700 ad over this period fluvial activity has been characterized by alternating phases of river bed incision and stability coinciding with non random decadal scale fluctuations in flood frequency and hydroclimate that appear to be linked to changes in large scale upper atmospheric circulation patterns episodes of widespread channel bed incision 1760 1799 1875 1894 1955 1969 result from a higher frequency of large floods 20 year return period and cool wet climate under meridional circulation regimes phases of more moderate floods 5 20 year return period corresponding to zonal circulation types 1820 1874 1920 1954 are characterized by enhanced lateral reworking and sediment transfer in upper reaches of the catchment and channel narrowing and infilling downstream rates of fluvial activity are reduced in intermediate periods 1800 1819 1895 1919 with no dominant circulation regime associated with lower flood frequency and magnitude the results of this study provide a valuable guide for forecasting probable drainage basin and channel response to future climate change

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

the mountains of north east greenland are not remnants of the caledonian topography a comment on pedersen et al 2012 tectonophysics vol 530 531 p 318 330 abstract pedersen et al 2012 suggest that the present day mountains in north east greenland represent remnants of the original caledonian topography modified during early rifting and that the area has undergone slow steady exhumation since 250 ma they base this hypothesis on inverse modelling calibrated by new apatite fission track data from samples of exposed caledonian basement however apatite fission track data on their own register only cooling and must be integrated with geological evidence to reveal episodes of reheating reflecting re burial the well documented geological record of north east greenland shows that the caledonian mountains were obliterated as topographic features during the late palaeozoic and provides clear evidence of a history involving episodic post caledonian exhumation and re burial the high grade metamorphic basement was at great depth during the devonian and was exhumed to the surface before being reburied by up to 2 km of upper carboniferous and younger sediments these sediments were then partially removed during renewed early middle jurassic exhumation that led to the formation of a low lying landscape which eventually subsided and was buried below a km thick cover of middle jurassic and younger sediments this cover was then partially removed during later phases of uplift and exhumation that eventually led to the formation of the present day relief in post jurassic times the geological record in east greenland is incompatible with the idea of slow steady exhumation since the caledonian orogeny

morphodynamics of a pseudomeandering gravel bar reach abstract a large number of rivers in tuscany have channel planforms which are neither straight nor what is usually understood as meandering in the typical case they consist of an almost straight slightly incised main channel fringed with large lateral bars and lunate shaped embayments eroded into the former flood plain in the past these rivers have not been recognised as an individual category and have often been considered to be either braided or meandering it is suggested here that this type of river planform be termed pseudomeandering a typical pseudomeandering river the cecina river is described and analysed to investigate the main factors responsible for producing this channel pattern a study reach 100 300 m was surveyed in detail and related to data on discharge channel changes after floods and grain size distribution of bed sediments during 18 months of topographic monitoring the inner lateral bar in the study reach expanded and migrated towards the concave outer bank which concurrently retreated by as much as 25 m a sediment balance was constructed to analyse bar growth and bank retreat in relation to sediment supply and channel morphology the conditions necessary to maintain the pseudomeandering morphology of these rivers by preventing them from developing a meandering planform are discussed and interpreted as a combination of a few main factors such as the flashy character of floods sediment supply influenced by both natural processes and human impact the morphological effects of discharges with contrasting return intervals and the short duration of flood events finally the channel response to floods with variable sediment transport capacity represented by bed shear stress is analysed using a simple model it is demonstrated that bend migration is associated with moderate floods while major floods are responsible for the development of chute channels which act to suppress bend growth and maintain the low sinuosity configuration of the river

channel adjustments to reservoir construction and gravel extraction along stony creek california stony creek drainage area 1920 km2 a tributary to the sacramento river 200 km north of san francisco has experienced channel adjustments to both dam construction and instream gravel extraction black butte dam constructed in 1963 reduced flood peaks and trapped the annual 100 000 m3 of bedload sediment formerly delivered from the upper watershed the reach below the dam changed from an active braided channel to an incised single thread channel shortly after dam construction about 25 km downstream of the dam large instream gravel mines annually extract 230 000 580 000 m su3 and have induced channel incision of over 5 m necessitating bridge repairs costing us 1 4 million

studying monogenetic volcanoes with a terrestrial laser scanner case study at croscat volcano garrotxa volcanic field spain erosional processes natural or anthropogenic may partly destroy the relatively small sized volcanic edifices characteristic of monogenetic volcanic zones leaving their internal structure well exposed nevertheless the study of these outcrops may be extremely challenging due to restricted accessibility or safety issues digital representations of the outcrop surface have been lately used to overcome such difficulties data acquired with terrestrial laser scanning instruments using light detection and ranging technology enables the construction of such digital outcrops the obtained high precision 3 d terrain models are of greater coverage and accuracy than conventional methods and when taken at different times allow description of geological processes in time and space despite its intrinsic advantages and the proven satisfactory results this technique has been little applied in volcanology related studies here we want to introduce it to the volcanological community together with a new and user friendly digital outcrop analysis methodology for inexperienced users this tool may be useful not only for volcano monitoring purposes but also to describe the internal structure of exposed volcanic edifices or to estimate outcrop erosion rates that may be helpful in terms of hazard assessment or preservation of volcanic landscapes we apply it to the croscat volcano a monogenetic cone in the la garrotxa volcanic field catalan volcanic zone ne spain quarrying of which leads to a perfect view of its interior but restricts access to its uppermost parts croscat is additionally one of the most emblematic symbols of the la garrotxa volcanic field natural park and its preservation is a main target of the park administration

channel adjustment of an unstable coarse grained stream opposing trends of boundary and critical shear stress and the applicability of extremal hypotheses channel adjustments in the north fork toutle river and the toutle river main stem were initiated by deposition of a 2 5 km3 debris avalanche and associated lahars that accompanied the catastrophic eruption of mount st helens washington on 18 may 1980 channel widening was the dominant process in combination adjustments caused average boundary shear stress to decrease non linearly with time and critical shear stress to increase non linearly with time at the discharge that is equalled or exceeded 1 per cent of the time these trends converged by 1991 1992 so that excess shear stress approached minimum values extremal hypotheses such as minimization of unit stream power and minimization of the rate of energy dissipation minimum stream power are shown to be applicable to dynamic adjustments of the toutle river system maximization of the darcy weisbach friction factor did not occur but increases in relative bed roughness caused by the concomitant reduction in hydraulic depths and bed material coarsening were documented predictions of stable channel geometries using the minimum stream power approach were unsuccessful when compared to the 1991 1992 geometries and bed material characteristics measured in the field it is concluded that the predictions are not applicable because the study reaches are not truly stable and cannot become so until a new floodplain has been formed by renewed channel incision retreat of stream side hummocks and establishment of riparian vegetation to limit the destabilizing effects of large floods further prediction of energy slope and consequently stream power by the sediment transport equations is inaccurate because of the inability of the equations to account for significant contributions of finer grained sand and gravel bank materials relative to the coarsened channel bed from bank retreat and from upstream terrace erosion

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

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

a remote coal deposit revisited middle jurassic coals at kulhoj western germania land northeast greenland abstract in 1908 members of the danmark expedition discovered a coal deposit in a very remote area in western germania land close to the margin of the inland ice in northeast greenland the deposit was however neither sampled nor described and was revisited in 2009 for the first time since its discovery the outcrops found in 2009 amount to approximately 8 m of sediment including a coal seam of 2 m thickness more outcrops and additional coal deposits most certainly are to be found pending further fieldwork the deposits are middle jurassic callovian in age and were deposited in a floodplain environment related to meandering river channels spores and pollen in the lower fluvial deposits reflect abundant vegetation of ferns along the river banks in contrast a sparse spore and pollen flora in the coals show a mixed vegetation of ferns and gymnosperms based on proximate and petrographic analyses the coals are classified as medium rank high grade coal their composition is dominated by inertinite and vitrinite and they represent deposits laid down in a freshwater mire no evidence of marine incursion has been found the coal seam studied does not include liptinite rich coals such as those present in the same lithostratigraphic unit elsewhere in northeast greenland but loose blocks in the area suggest their presence in unknown parts of the succession

the role of vegetation and bed level fluctuations in the process of channel narrowing abstract a catastrophic flood ire 1965 on plum creek a perennial sandbed stream in the western great plains removed most of the bottomland vegetation and transformed the single thalweg stream into a wider braided channel following eight years of further widening associated with minor high flows a process of channel narrowing began in 1973 narrowing continues today the history of channel narrowing was reconstructed by counting the annual rings of 129 trees and shrubs along a 5 km reach of plum creek near louviers colorado sixty three of these plants were excavated in order to determine the age and elevation of the germination point the reconstructed record of channel change was verified from historical aerial photographs and then compared to sediment stratigraphy and records of discharge and bed elevation from a streamflow gaging station in the study reach channel narrowing at plum creel occurs in two ways first during periods of high flow sand and fine gravel are delivered to the channel temporarily raising the general bed level subsequently several years of uninterrupted low flows incise a narrower channel second during years of low flow vegetation becomes established on the subaerial part of the present channel bed in both cases surfaces stabilize as a result of vegetation growth and vertical accretion of sediment

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

causes of 20th century channel narrowing in mountain and piedmont rivers of southeastern france extensive channel narrowing in southeastern france provides an illustration of geomorphic response to land use changes the study region comprises a range of environments from large piedmont and intramountain gravel bed rivers to small mountain streams field measurements and analysis of historical data demonstrate two distinct periods of channel change from 1850 to 1950 channel narrowing is interpreted to be the result of a recovery process in response to widespread channel destabilization induced by major floods during the second half of the 19th century at the time the largely deforested basins were highly responsive to flooding whereas the recovery process was accelerated by floodplain and basin scale land use changes afforestation and torrential control works which in turn reduced sediment delivery and enabled vegetation development in channels from 1950 to 1970 channel narrowing accelerated in most of the studied rivers this recent phenomenon is considered as a human induced fluvial adjustment directly related to forest development on river margins and human abandonment of intensive floodplain land uses at the same time long profile degradation occurred as a result of long term bedload supply decrease in small mountain streams channel narrowing is mainly explained by channel incision which seems to progress from upstream where sediment sources are progressively stabilized by afforestation copyright 2002 john wiley sons ltd

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

sediment transfer and transformation of an alluvial valley floor the river south tyne northumbria u k the amounts of alluvial storage and the mechanisms responsible for the dispersal of sediment associated with historic metal mining are examined for a 115 year timespan on a 22 km reach of the river south tyne northern england analysis of lateral and vertical channel change over this period the extent of actively reworked gravels and identification of metals in alluvial units show five sedimentation zones separated by more stable reaches aggradation in the late nineteenth century was followed by a period of storage and local reworking and then incision some reaches show short term storage of sediment injected from tributaries which may be dispersed by floods there is some evidence of transfer of sediment bodies downvalley within sedimentation zones and of a sediment wave movement between zones in lower parts of the south tyne investigated present day incision the variation in the area of actively reworked gravel spreads and the widespread dispersal of fine grained toxic metal mining wastes all have practical implications the intricate response of the channel system to historic changes in sediment supply is not readily described by either a complex response model or a simple translatory wave

post breakup burial and exhumation of passive continental margins seven propositions to inform geodynamic models despite many years of study the processes involved in the post breakup development of passive margins remain poorly understood integration of apatite fission track analysis afta and stratigraph

postrift history of the eastern central atlantic passive margin insights from the saharan region of south morocco the passive margin of south morocco is a low elevated passive margin it constitutes one of the oldest margins of the atlantic ocean with an early jurassic breakup and little geological data are available concerning its postrift reactivation so far we investigated the postrift thermal history of the onshore part of the margin with low temperature thermochronology on apatite crystals fission track and u th sm he ages we obtained are significantly younger than the breakup 190 ma fission track ages range from 107 8 to 175 16 ma with mean track lengths from 10 7 0 3 to 12 5 0 2 m u th sm he ages range from 14 1 to 185 15 ma using inverse modeling of low temperature thermochronological data we demonstrate that the south moroccan continental margin underwent a complex postrift history with at least two burial and exhumation phases the first exhumation event occurred during late jurassic early cretaceous and we attribute this to mantle dynamics rather than to intrinsic rifting related processes such as flexural rebound the second event from late cretaceous to early paleogene might record the onset of africa europe convergence we show a remarkably common behavior of the whole moroccan passive margin during its early postrift evolution the present day differences result from a segmentation of the margin domains due to the africa europe convergence finally we propose that varying retained strengths during rifting and also the specific crustal lithospheric geometry of stretching explain the difference between the topographical expressions on the continental african margin compared to its american counterpart

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

hydromorphological parameters of natural channel behavior in conditions of the hercynian system and the flysch belt of the western carpathians on the territory of the czech republic abstract a fundamental prerequisite for assessing the current ecological status of streams is the establishment of reference conditions for each stream type that serve as a benchmark the hydromorphological reference conditions reflect the natural channel behavior which is extremely variable significant parameters of natural channel behavior were determined using a combination of four selected statistical methods principal component analysis agglomerative hierarchical clustering correlation and regression macroscale analyses of data about altitude stream order channel slope valley floor slope sinuosity and characteristics of the hydrological regime were conducted for 3197 reaches of major rivers in the czech republic with total length of 15 636 km on the basis of selected significant parameters and their threshold values channels were classified into groups of river characteristics based on shared behaviors the channel behavior within these groups was validated using hydromorphological characteristics of natural channels determined during field research at reference sites classification of channels into groups confirmed the fundamental differences between channel behavior under conditions of the hercynian system and the flysch belt of the western carpathians in the czech republic and determined a specific group in the flattened high areas of mountains in the bohemian massif validating confirmed the distinctions between groups of river characteristics and the uniqueness of each one it also emphasized the benefits of using qualitative data and riparian zone characteristics for describing channel behavior channel slope entrenchment ratio bed structure and d 50 were determined as quantitative characteristics of natural channel behavior

evolution of topography of post devonian scandinavia effects and rates of erosion abstract the mechanisms and timing of mountain growth in scandinavia remain enigmatic given that the region has not been involved in active orogenesis since the devonian and in any large scale tectonic activities after the ne atlantic breakup during the early cenozoic in this study we combine analysis of the vertical motions of the region caused by dominantly glacial erosion during the quaternary with apatite fission track aft analysis of rocks from the area using numerical models we first quantify how fluvial and glacial erosion carved out the fjords and valleys to a depth of 2 km below the paleosurfaces this erosional episode represents a major local weight loss and results in up to a 0 8 km uplift of rocks and up to a 0 5 km rise of local topography these estimates only marginally depend on the effective elastic thickness of the lithosphere and thus are robust we show then that no correlation exists between sample altitude and published aft data but that a correlation does exist between aft age and the depth below our constructed pre glacial summit surface this correlation demonstrates the robustness of the numerical erosional model quantifies average erosion rates during carboniferous cretaceous at

monogenetic volcanism personal views and discussion monogenetic volcanism produces small volume volcanoes with a wide range of eruptive styles lithological features and geomorphic architectures they are classified as spatter cones scoria or cinder cones tuff rings maars maar diatremes and tuff cones based on the magma water ratio dominant eruption styles and their typical surface morphotypes the common interplay between internal such as the physical chemical characteristics of magma and external parameters such as groundwater flow substrate characteristics or topography plays an important role in creating small volume volcanoes with diverse architectures which can give the impression of complexity and of similarities to large volume polygenetic volcanoes in spite of this volcanic facies complexity we defend the term monogenetic volcano and highlight the term s value especially to express volcano morphotypes this study defines a monogenetic volcano a volcanic edifice with a small cumulative volume typically 1 km3 that has been built up by one continuous or many discontinuous small eruptions fed from one or multiple magma batches this definition provides a reasonable explanation of the recently recognized chemical diversities of this type of volcanism

episodic burial and exhumation in ne brazil after opening of the south atlantic it is a common assumption that elevated passive continental margins have remained high since rifting and breakup here we show that the atlantic margin of ne brazil has undergone a more complex history our synthesis of geological data landscape analysis and paleothermal and paleoburial data reveals a four stage history 1 after early cretaceous breakup the margin under went burial beneath a thick sedimentary cover 2 uplift episodes in the campanian and eocene led to almost complete removal of these deposits 3 the resulting large scale low relief erosion surface peneplain was deeply weathered and finally reburied at the oligocene miocene transition and 4 miocene uplift and erosion produced a new lower level peneplain by incision of the uplifted and re exposed paleogene peneplain previous studies have identified aspects of this interpretation but we have defined the absolute timing and magnitude of discrete events of burial and exhumation that followed early cretaceous rifting and eocene oligocene peneplanation we suggest that a late sedimentary cover protected paleogene weathering profiles until the present day the uplift phases in brazil are synchronous with uplift phases in africa and the andes the andean phases coincided with rapid convergence on the western margin of south america and the campanian uplift coincided with a decline in spreading rate at the mid atlantic ridge consequently we suggest that both vertical movements and lateral changes in the motion of the plates have a common cause which is lateral resistance to plate motion

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

colorado river sediment transport 1 natural sediment supply limitation and the influence of glen canyon dam analyses of flow sediment transport bed topographic and sedimentologic data suggest that before the closure of glen canyon dam in 1963 the colorado river in marble and grand canyons was annually supply limited with respect to fine sediment i e sand and finer material furthermore these analyses suggest that the predam river in glen canyon was not supply limited to the same degree and that the degree of annual supply limitation increased near the head of marble canyon the predam colorado river in grand canyon displays evidence of four effects of supply limitation 1 seasonal hysteresis in sediment concentration 2 seasonal hysteresis in sediment grain size coupled to the seasonal hysteresis in sediment concentration 3 production of inversely graded flood deposits and 4 development or modification of a lag between the time of a flood peak and the time of either maximum or minimum depending on reach geometry bed elevation analyses of sediment budgets provide additional support for the interpretation that the predam river was annually supply limited with respect to fine sediment but it was not supply limited with respect to fine sediment during all seasons in the average predam year sand would accumulate and be stored in marble canyon and upper grand canyon for 9 months of the year from july through march when flows were dominantly below 200 300 m3 s this stored sand was then eroded during april through june when flows were typically higher after closure of glen canyon dam because of the large magnitudes of the uncertainties in the sediment budget no season of substantial sand accumulation is evident because most flows in the postdam river exceed 200 300 m3 s substantial sand accumulation in the postdam river is unlikely

sediment supply and the development of the coarse surface layer in gravel bedded rivers the bed surface of most gravel rivers is considerably coarser than the sub surface or the gravel load transported over it a phenomenon affecting river dynamics morphology and ecology the coarse surface layer often called an armour or pavement has been attributed to an inherent tendency for small grains to settle between larger ones during active transport of all sizes1 2 and to selective erosion or trapping of finer particles when the coarse grains are relatively immobile3 4 where bedload supply is cut off below dams selective erosion causes coarsening5 6 using a simple quantitative model we propose that surface coarsening develops in gravel bedded rivers when local bedload supply from upstream is less than the ability of the flow to transport that load we present laboratory results which support this hypothesis and show that supply reduction causes changes in bedforms and progressive confinement of active bedload transport to a narrow band of finer bed surface bordered by a coarse less active bed it may therefore be possible to relate the degree of river bed surface coarsening to sediment supply resulting from land use

formation uplift and dissection of planation surfaces at passive continental margins a new approach the usefulness of large scale low relief high level landscapes as markers of uplift events has become a subject of disagreement among geomorphologists we argue that the formation of low relief surfaces over areas of large extent and cutting across bedrock of different age and resistance must have been guided by distinct base levels in the absence of other options the most likely base level is sea level we have analysed west greenland landscapes in a recent study by combining the cooling history from apatite fission track analysis afta data with the denudation history from landscape analysis and the stratigraphic record an important difference between our approach and that of classical geomorphology is that we now have the ability to document when thick sections of rocks have been deposited and then removed the present day high level plateau in west greenland is the remnant of a planation surface that was formed by denudation that lasted c 20 million years during which up to 1 km of cover was removed after maximum burial at the eocene oligocene transition here we present additional afta data to show that the planation surface is the end product of cenozoic denudation even in basement areas and argue that phanerozoic sediments most likely of cretaceous palaeogene age must have been present prior to denudation the planation surface was offset by reactivated faults and uplifted to present day altitudes of up to 2 km the uplift occurred in two late neogene phases that caused incision of valleys below the planation surface and their subsequent uplift we therefore find that the elevated and deeply dissected plateau is evidence of episodic post rift uplift that took place millions of years after cessation of sea floor spreading west of greenland we suggest that other margins with similar morphology may also be characterized by episodic post rift uplift unrelated to the processes of rifting and continental separation rather than being permanently uplifted since the time of rifting as is commonly assumed copyright 2009 john wiley sons ltd

channel dynamics and geomorphic resilience in an ephemeral mediterranean river affected by gravel mining abstract gravel mining has been a widespread activity in ephemeral rivers worldwide whose long lasting hydrogeomorphological impacts preclude effective implementation of water and environmental policies this paper presents a gis based method for temporal assessment of morphosedimentary changes in relation to in channel gravel mining in a typical ephemeral mediterranean stream namely the rambla de la viuda eastern spain the aims of this work were to identify morphosedimentary changes and responses to human activities and floods quantify river degradations and analyze factors favoring fluvial recovery for further applications in other rivers aerial photographs and lidar topography data were studied to analyze geomorphic evolution over the past 70 years along a 7 5 km reach of an ephemeral gravel stream that has been mined intensively since the 1970s to evaluate changes in the riverbed we mapped comparable units applying morphological hydraulic and stability based on vegetation density and elevation criteria to 13 sets of aerial photographs taken from 1946 to 2012 a detailed spatiotemporal analysis of comparable units revealed a 50 reduction in the active section and a 20 increase in stable areas compared to the conditions observed prior to gravel mining instream mining was first observed in 1976 aerial photograph covering already up to 50 of the 1956 riverbed area river degradation since then was quantified by means of a lidar dtm and rtk gps measurements which revealed a 3 5 m incision that had started simultaneously with gravel mining climate and land use changes were present but the effects were completely masked by changes produced by instream gravel mining therefore river incision degradation was triggered by scarcity of sediment and lack of longitudinal sedimentary connection creating an unbalanced river system that is still adjusting to the present hydrosedimentary conditions

channel adjustments bedload transport and sediment sources in a gravel bed river brenta river italy this paper deals with the brenta river the alps italy a gravel bed river strongly affected by human impact the aims of this work are a to reconstruct the channel adjustments that have occurred during the last decades and b to analyse the present condition of the river in terms of bedload transport and sediment sources the study reach which is 23 km long was investigated using historical maps aerial photographs 12 monumented cross sections laser altimetry data and field survey bedload transport rates were estimated by a morphological approach which allows the construction of a sediment budget dramatic channel adjustments have occurred in response to an alteration of sediment fluxes caused by different human interventions gravel mining dams torrent control works major channel adjustments specifically incision up to 8 9 m and narrowing took place between the 1950s and the 1980s on the other hand widening has become the most important process and incision has continued only in the upper part of the study reach in more recent times about the last 20 25 years the estimate of bedload transport rates for the period 1984 1997 was carried out starting from the erosion and deposition volumes of the single sub reaches such an estimate has shown that a a high spatial variability of gravel transport rates exists from 0 up to 73 200 85 400 m3 year and b most of the bedload is supplied by local sources bank erosion is the main source of sediments for bedload transport and its contribution can be estimated as from 9 up to 20 times higher than the upstream contribution finally from a practical point of view results from this study should be taken into account in addressing maintenance sediment management and restoration along a dynamic and unstable river such as the brenta copyright 2007 john wiley sons ltd

the ebro river in the 20th century or the ecomorphological transformation of a large and dynamic mediterranean channel in the first decades of the 20th century the ebro river was the iberian channel with the most active fluvial dynamics and the most remarkable spatial temporal evolution its meandering typology the dimensions of its floodplain and the singularities of its flow regime produced an especially interesting set of river functions the largest dynamics of the ebro river are concentrated along the meandering profile of the central sector during the 20th century this sector experienced a large alteration of its geomorphological structure we present here an analysis of this evolution through the cartographic study of a long segment of the river 250 km in 1927 1956 and 2003 the results show a large reduction in bank sinuosity a progressive loss of fluvial territory and a large decrease in channel width these changes are especially clear in the areas previously most ecologically connected with the active channel the fluvial territory of the river in 2003 was approximately half that found during the first decades of the 20th century forest plantations which were non existent in 1927 occupied more than 1500 ha of the study area in the last decade this intense geomorphological transformation becomes ecologically visible in i a 35 reduction of the area occupied by riparian vegetation ii a loss of the heterogeneity of riparian forest spots which were formerly structured in an irregular mosaic far from the river thalweg and iii a modification of the riparian forest structure which is currently linear uniform thin and very close to the river axis the ecomorphological alteration was intensified by the remarkable reduction in bank length 13 and the reduced dynamism of the present river system indicated by an increase in the percentage of fluvial territory occupied by riparian forests and a reduction in the area occupied by the active channel copyright 2002 john wiley sons ltd

long term riverbed response of lower tedori river japan to sediment extraction and dam construction effects of sediment extraction and dam construction on changes of riverbed characteristics over yearly to decadal scales in the lower tedori river of japan are clarified over 1950 1991 the riverbed degraded in excess of 0 5 3 5 m concurrently riverbed sediment volume of the 0 16 km reach decreased by 12 7 106 m3 intensive sediment extraction was the dominant cause of riverbed degradation during the period during 1991 2007 an increase in riverbed sediment volume of 0 6 106 m3 resulted in accretion of the riverbed by average depth 0 04 m the cessation of sand and gravel mining sgm coupled with tedorigawa dam operation since 1980 was responsible for that accretion temporal change in riverbed elevation during 1950 2007 indicates that there were five phases of vertical adjustment combination of nonlinear regression models described four of these phases well during 1950 1979 the first four modes of empirical orthogonal function analysis successfully captured temporal and spatial responses of the riverbed to natural and anthropogenic impacts that is the first mode explained the mean riverbed profile and temporal variation in riverbed sediment volume the second through fourth spatial eigenfunctions reflected spatial variation in vertical adjustment rate for phases ii iii and i respectively the corresponding temporal eigenfunctions explained the respective effects on the riverbed of sgm of imbalance between sediment transport capacity and sediment supply and of dredging activity

composition and organic maturity of middle jurassic coals north east greenland evidence for liptinite induced suppression of huminite reflectance abstract middle jurassic coals from kuhn o north east greenland may contain up to 85 vol liptinite principally resinite up to 68 6 vol the coals are thus petrographically comparable to the middle jurassic muslingebjerg formation coals at hochstetter forland approximately 40 50 km to the north and they are inherently excellent petroleum source rocks liptinite poor 6 0 vol coal samples from both kuhn o and hochstetter forland yield mean random huminite reflectance values of 0 49 0 53 ro implying a rank of sub bituminous a above a threshold value somewhere between 3 and 24 vol resinite and 6 and 35 vol total liptinite significant reflectance suppression is induced and between 24 and 69 vol resinite and 35 and 85 vol total liptinite a nearly linear inverse relationship exists between the content of liptinite resinite and the mean random reflectance values at the highest liptinite resinite contents reflectance suppression may be up to 0 23 ro the reflectance suppression is related to bitumen adsorption caused by bitumen expulsion from resinite and total reflectance distributions of the huminite fractions suggest that the reflectance of all huminite macerals is lowered with increasing liptinite resinite content

estimating the probability of river channel adjustment river channels respond not only to natural external controls and natural controls internal to individual drainage basins but also to the influence of human activity although many site specific instances of change have been documented the complexity of the process interactions means that very little is known about the general nature of different styles of adjustment or their relative sensitivity to drainage basin controls data obtained from the thames basin southeast england are used in a probabilistic approach to differentiate between four styles of river channel adjustment and a variety of drainage basin characteristics adopting a probabilistic approach quantifies the degree of confidence attributable to any prediction of river channel adjustment while acknowledging that certainties are difficult to obtain in studies of the natural environment this approach could thus allow environmental planning decisions to be made with a quantified degree of uncertainty four multivariate logistic regression models are described which use a combination of continuous and categorical variables to associate drainage basin characteristics with four styles of river channel adjustment derived from a reconnaissance evaluation survey in comparison it is shown that laterally migrating river channels are the most common natural channel type in the thames basin and their probability of occurrence rises to 71 per cent in sand gravel environments in channels regulated by low weirs deposition is the most likely channel activity where gradients are lower than 0 0040 whilst above this threshold the majority of channels are morphologically inactive in urban channels many of which are also lined by concrete the likelihood of obtaining a stable channel is mostly in excess of 80 per cent in channels straightened during this century deposition is most likely in gradients below 0 0050 whereas erosional enlargement is most probable above this value in channels which were initially channelized prior to this century deposition gives way to stability at a threshold gradient of 0 0080

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

conodont geothermometry and tectonic overburden in the northernmost east greenland caledonides kronprins christian land lies at the northernmost limit of the east greenland caledonides and may be divided into four main tracts foreland parautochthon thin skinned thrust sheets containing neoproterozoic sediments and thick skinned thrust sheets of crystalline basement the eastern part of the foreland and the parautochthon are composed of ordovician silurian shelf carbonates overlain by llandovery lower wenlock turbidites deposited at the southern margin of the franklinian basin deformation of the parautochthon occurred beneath a major detachment the vandredalen thrust with neoproterozoic sediments of the rivieradal group lying in the hanging wall the rivieradal group was deposited in an e facing half graben and was displaced westwards across its rift shoulders during caledonian thrusting extensive sampling for conodonts has been carried out within the lower palaeozoic rocks of the foreland and parautochthon in order to increase the precision of structural interpretations and to provide data on maximum burial temperature and in turn the thickness of overburden in contrast to earlier studies conodont colour alteration indices cai show a gradual and continuous increase from cai 3 in the eastern part of the foreland to cai 5 in the easternmost parts of the parautochthon the isopleths are not disrupted or truncated by thrusting as previously suspected indicating that the heating is not attributable to pre thrusting stratigraphic overburden furthermore considerations of the regional geology indicate that there was no significant accumulation of sedimentary overburden in post caledonian time the predominant component is thus considered to be loading by thrust sheets modelling of the overburden thickness suggests that prior to erosion it increased from 3 9 km cai 3 in the easternmost foreland to a maximum of 12 5 km beneath the vandredalen thrust sheet in the easternmost part of the area providing constraints for restoring cross sections across the orogen

channel metamorphosis floodplain disturbance and vegetation development ain river france abstract the purpose of this paper is to describe and explain channel metamorphosis of the ain river in east central france and the effects of this metamorphosis on floodplain disturbance and vegetation development the ain river is a 195 km long stream originating in the jura mountains which flows into the rhone river between lyon france and geneva switzerland the lower 40 km of the ain river beyond the mountain front are situated in a valley of outwash deposits where the floodplain is 0 2 to 1 2 km wide a complex mosaic of floodplain landscape units has developed maps dating back to 1766 and six sets of aerial photographs dated between 1945 and 1991 were used to document changes in channel pattern aerial photos and field surveys were used to compile maps of landscape units based on dominant vegetation life forms species and substrate six maps dated between 1945 and 1991 were digitized in arc info and an overlay was generated to determine the changes in landscape units as related to channel disturbance change from a braided to a single thread meandering channel probably took place in the period 1930 1950 the process of river entrenchment has occurred throughout the holocene but has accelerated in the present century due to shortening of the river course construction of lateral embankments and vegetation encroachment following reservoir construction and cessation of wood cutting and grazing the increase in horizontal channel stability coupled with channel entrenchment have decreased floodplain disturbance and lowered the water table by approximately one meter pioneer and disturbance dependent landscape units have experienced a more terrestrial like succession to an alluvial forest abandoned channels have also been replaced by alluvial forests on poorly drained soils shrub swamp communities of willow and hydrophytic herbaceous plants have been replaced by mixed forests of ash alder black poplar and oak on well drained alluvial soils ash and oak dominated hardwood forests have declined in favor of mesophytic stands of black poplar all types of vegetation but particularly dry grasslands shrublands have been cleared for mines campgrounds agriculture and other types of development using several measures landscape diversity decreased between 1945 and 1991

types of river channel patterns and their natural controls river channel patterns are thought to form a morphological continuum this continuum is two dimensional defined by plan features of which there are three straight meandering branching and structural levels of fluvial relief of which there are also three floodplain flood channel low water channel combinations of these three categories define the diversity of patterns one of the most important factors in channel development is stream power defined by water discharge and river slope the greater the stream power the stronger the branching tendency but threshold values of stream power are different for the three different hierarchical levels of channel relief the critical stream power values and hydrological regime together define the channel pattern and analysis of the pattern type can be undertaken using effective discharge curves 1998 john wiley sons ltd

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

geomorphology and topography of relict surfaces the influence of inherited crustal structure in the northern scandinavian mountains low relief surfaces in northern norway are mapped and analysed to explore 1 whether surfaces were once continuous and possibly correlative recording an ancient relict landscape 2 whether the distribution of now disrupted surfaces reveals a tectonic history related to rifting of the north atlantic and 3 how topography changes across the transition between the north atlantic and barents sea margins elevation contours on surfaces a smoothed fit to mean elevations and histograms of elevation show three distinct coast parallel zones onshore northern norway and a different pattern in coastal lofoten vesteralen a sharp transition from continuous surfaces to lower discretely stepped discontinuous surfaces is located where the crust thins rapidly to the nw from 39 to 100 km north of the senja fracture zone and then decrease gradually further ne the spatial pattern suggests that a continuous low relief relatively low elevation surface formed in late mesozoic time and was preserved despite modification by cenozoic faulting uplift and slow erosion scandinavia9s present day topographic envelope reflects a crustal strength profile set up during earlier hyperextension and maintained by slow neogene erosion rather than resulting from opening of the north atlantic or caused by glacial erosion supplementary material a map of polygons of all surface heights within the study area and data on the location of median centres of polygons assigned attributes and selected zonal statistics are available at https doi org 10 6084 m9 figshare c 3312960