the role of feedback mechanisms in historic channel changes of the lower rio grande in the big bend region abstract over the last century large scale water development of the upper rio grande in the u s and mexico and of the rio conchos in mexico has resulted in progressive channel narrowing of the lower rio grande in the big bend region we used methods operating at multiple spatial and temporal scales to analyze the rate magnitude and processes responsible for channel narrowing these methods included hydrologic analysis of historic stream gage data analysis of notes of measured discharges historic oblique and aerial photograph analysis and stratigraphic and dendrogeomorphic analysis of inset floodplain deposits our analyses indicate that frequent large floods between 1900 and the mid 1940s acted as a negative feedback mechanism and maintained a wide sandy multi threaded river declines in mean and peak flow in the mid 1940s resulted in progressive channel narrowing channel narrowing has been temporarily interrupted by occasional large floods that widened the channel however channel narrowing has always resumed after large floods in 1990 and 1991 the active channel width of the lower rio grande has narrowed by 36 52 narrowing has occurred by the vertical accretion of fine grained deposits on top of sand and gravel bars inset within natural levees channel narrowing by vertical accretion occurred simultaneously with a rapid invasion of non native riparian vegetation tamarix spp arundo donax which created a positive feedback and exacerbated the processes of channel narrowing and vertical accretion in two floodplain trenches we measured 2 75 and 3 5 m of vertical accretion between 1993 and 2008 in some localities nearly 90 of bare active channel bars were converted to vegetated floodplain during the same period upward shifts of stage discharge relations occurred resulting in over bank flooding at lower discharges and continued vertical accretion despite a progressive reduction in stream flow thus although the magnitude of the average annual flood was reduced between 40 and 50 over bank flooding continued these changes reflect a shift in the geomorphic nature of the rio grande from a wide laterally unstable multi thread river to a laterally stable single thread channel with cohesive vertical banks and few active in channel bars

channel responses to declining flow on the rio grande between ft quitman and presidio texas abstract a profound decline in the discharge of the upper rio grande following upstream water development set in motion a chain of responses in channel geometry and sediment budget the case of the rio grande provides a well documented example of the evolution of channel geometry in response to change in a single external variable in a regime of declining flow channel change was driven by an excess of sediment relative to the energy available to do work in the stream channel several different responses can be identified which operated at different rates responses can be ranked according to reaction time to define 3 stages in channel evolution stage i is identified as the shrinking of the channel as excess sediment was deposited within it during stage ii channel capacity began to stabilize as overbank flow carried sediment onto natural levees and floodplain valley wide aggradation began and avulsive migration resumed especially at the mouths of tributaries where stage iii is occurring lag deposits of bedload at tributary mouths are locally regrading the valley initial shrinking of the channel produced positive feedback to the decrease in discharge and sediment transport capacity not until later stages did subordinate responses appear which tended to balance the sediment budget and these involved lateral migration the river approached a balanced sediment budget both by increasing its capacity by shortening and steepening and by decreasing sediment inout by migrating away from tributaries

japan sea a pull apart basin abstract recent field work in the hokkaido central belt and marine geology studies along the eastern margin of japan sea in addition to previously published data lead us to propose a new model of opening of the japan sea the synthesis of both on land and offshore structural data gives new constraints about the structural evolution of the system the rhombohedral shape of the japan basin and the particular tectonic behaviour of the margins on both east and west sides can be explained by an early eo oligocene rifting of a pull apart basin accommodated along two large right lateral shear zones east of korea and west of northeast japan and sakhalin it is followed during upper oligocene lower miocene by the main opening of the japan basin as a mega pull apart then a back arc spreading probably related to the subduction process induced the creation of the yamato and tsushima basins at the end of lower miocene and in middle miocene clockwise rotation of southwest japan larger than 20 or major bending of honshu mainland deduced from paleomagnetic studies is unlikely at this time since 1 or 2 my b p to present compression prevails along the eastern margin of the japan sea the generation of marginal basins as pull apart basins along intracontinental strike slip faults is a mechanism which has been proposed by other authors concerning the south china sea the question then is whether the fragmentation of the asiatic continent is an intracontinental deformation related process as proposed here or a subduction related one

regional strike slip in the eastern continental margin of korea and its tectonic implications for the evolution of ulleung basin east sea sea of japan air gun profiles delineate a large scale strike slip fault system along the eastern continental margin of korea this system comprises two right stepping curvilinear master faults hupo and yangsan faults that are closely associated with en echelon nominal faults and reverse faults and folds these structural features indicate two phases of regional deformation in the earlier phase late oligocene to early miocene the margin experienced extensional shear strain with dextral strike slip movements along the hupo and yangsan faults that guided a pull apart opening of the pohangyoungduk basin the later phase deformation late miocene to early pliocene was governed by shortening strain that induced a convergent strike slip reactivation of the hupo fault as well as widespread contractile faulting and folding the regional deformation in the eastern korean continental margin reflects three stages of tectonic evolution of the ulleung basin 1 pull apart opening stage from late oligocene to early miocene 2 rotational opening stage with a differential rotation of the japanese arc in middle miocene and 3 back arc closing stage from the end of middle miocene to present

spatial and temporal patterns in channel change on the snake river downstream from jackson lake dam wyoming abstract operations of jackson lake dam jld have altered the hydrology and sediment transport capacity of the snake river in grand teton national park prior research has provided conflicting assessments of whether the downstream river was perturbed into sediment surplus or sediment deficit in this paper we present the results of an aerial photo analysis designed to evaluate whether the history of channel change indicates either significant deficit or surplus of sediment that could be expressed as narrowing or expansion of the channel over time we analyze changes in braid index channel width channel activity and net channel change of the snake river based on four series of aerial photographs between 1945 and 1969 a period of relatively small main stem floods widespread deposition and up to 31 reduction in channel width occurred throughout the snake river between 1969 and 2002 a period of large main stem floods the style of channel change reversed with a decrease in braid index and an increase in channel width of up to 31 these substantial changes in the channel downstream from the dam primarily occurred in multithread reaches regardless of proximity to tributaries and no temporal progression of channel narrowing or widening was observed we demonstrate that channel change downstream from jld is more temporally and longitudinally complex than previously described

floodplain construction of the rio grande at el paso texas usa response to holocene climate change abstract the rio grande is one of the larger rivers in north america and the development of its floodplain is related to holocene climate and climate change the late pleistocene through early holocene channel is characterized by a meander or braided system with lateral cutting and backfilling resulting in the valley wide deposition of massive to cross bedded fine to medium textured sand the late pleistocene early holocene floodplain is also the sand source for the adjacent bolson sand sheet the sand sheet stopped accumulating new sand 5000 yrs ago an event directly related to the shutting off of the sand supply caused by the deposition of overbank muds that covered and sealed the floodplain surface during the middle holocene the river may have dried intermittently with the floodplain becoming deflated and local sand dunes forming on the floodplain after 5000 yrs the climate was less arid and the river shifted to a regime of increased flooding and overbank deposition of silt and clay by 2500 yrs a late holocene period of wet climate resulted in further overbank deposition and the formation of a cumulic mollisol across the floodplain the socorro paleosol the period of wet climate corresponds to the audubon neoglacial and active rock glaciers in the southern rocky mountains speleothem growth in nearby caves and other evidence for wet cool conditions in the region after 1000 yrs the climate became drier and the deposition and accumulation of overbank muds by the flooding rio grande came to a halt even though the river has flooded often in historic times and presumably during late prehistoric times as well there is little evidence for deposition of overbank sediments on the floodplain since a d 1000 accordingly the present day surface of the lower valley is ten centuries old three channels occur on the us side of the lower valley floodplain and during the past 2500 yrs stream flow has shifted from one to the other by the avulsion process of channel reoccupation although most flow has been in the rio grande channel the largest of the three

rapid rotation of southwest japan palaeomagnetism and k ar ages of miocene volcanic rocks of southwest japan summary miocene volcanic rocks have been sampled from the san in district in the central part of southwest japan reliable palaeomagnetic direction and k ar dating data have been obtained from 28 localities a clockwise deflection in declination d 38 5 is observed in the kawai formation having an age of 16 1 1 4 ma whereas a northerly declination is observed in formations younger than 14 2 0 6 ma these data indicate that southwest japan had ceased rotational motion by about 14 ma when compared with the amount of rotation estimated from cretaceous palaeomagnetic data it is apparent that more than 80 per cent of the overall clockwise rotation occurred between about 16 and 14 ma we conclude that the angular velocity of southwest japan about a rotation pole at 129 e 34 n reached 20 myr 1 at about 15 ma the corresponding rate of linear motion of the eastern part of southwest japan was 21 cm yr 1

climate and ephemeral stream processes twentieth century geomorphology and alluvial stratigraphy of the little colorado river arizona during the first 40 years of the twentieth century erosion was the dominant geomorphic process affecting the morphology of the little colorado river channel the discharge regimen was one of frequent large floods and high annual discharge that created a wide sandy channel free of vegetation in the 1940s and early 1950s average annual precipitation declined reducing annual discharge to about 57 of that of the preceding period as well as reducing the frequency of large floods the channel adjusted to the new hydrologic regimen by reducing its width parts of the channel were frequently dry and riparian vegetation primarily nonnative salt cedar became established on the higher channel surfaces precipitation and discharge thereafter increased and aggradation by overbank deposition was the primary geomorphic process as indicated by accretion of 2 to 5 m of flood plain alluvium between 1952 and 1978 events of 1980 however suggest that the flood plain has ceased to accrete although climate has not fluctuated the flood plain has probably reached a critical height above the channel beyond which further accretion is unlikely under the existing discharge regimen the recent history of the little colorado broadly suggests that flood plain development was initiated by climatically induced hydrologic fluctuations flood plain deposits in the stratigraphic column of such ephemeral streams may record repeated adjustments to altered hydrologic conditions

the hunghae formation se korea miocene debris aprons in a back arc intraslope basin during early to middle miocene times a sudden opening of the ulleung tsushima back arc basin in the east sea sea of japan led to the development of intraslope basins along the rifted southwestern margin southeast korea abrupt subsidence resulted in the deposition of the 200 m thick hunghae formation middle miocene a sand mudstone sequence that can be divided into five facies facies i sand and mudstone couplet and ii coarse sand are turbiditic in origin as evidenced by massive graded crudely layered and parallel laminated sand beds facies iii homogeneous mudstone is characterized by various lignite and plant fragments clastic and biogenic grains that are randomly oriented suggestive of hemipelagic deposition facies iv chaotic deposit is characterized by the disruption of beds the presence of isolated siltstone blocks or balls and large clasts in the muddy matrix indicative of retrogressive rockfall and slide slump facies v conglomerate is of debris flow origin as evidenced by clast and matrix supported features floating large clasts and absence of traction structures individual facies are organized into two types of facies association 1 homogeneous mudstone facies iii associated randomly with the rest facies i ii iv and v indicative of hemipelagic and episodic sediment gravity flow processes respectively 2 conglomerate facies v coarse sand facies ii and sand mudstone couplet facies i representing the flow transformation from debris flow to high and low concentration turbidity currents these facies associations are similar in many respects to modern and ancient debris or slope aprons found elsewhere numerous isolated slide slump blocks wedged conglomerates with armoured mudstone balls discontinuous lignite containing sand mudstone beds chaotic structure and growth faults suggest that the deposition occurred on a steep slope intraslope basin off coalescing fan deltas mainly by unchannellized sediment gravity flows ancient deposits with irregular facies sequences can be viewed as debris apron systems which provide alternatives to submarine fan models in many clastic basins with a line rather than point source

air photo based change in channel width in the minnesota river basin modes of adjustment and implications for sediment budget abstract the minnesota river and major tributaries have experienced large increases in discharge over the past century aerial photograph based measurements of channel width were made for the 1938 2015 period at 16 multibend subreaches by digitizing the area between vegetation lines and dividing by centerline length results show considerable increases in width for the main stem 0 62 0 10 y and major tributaries 0 31 0 08 y but are inconclusive for smaller channels width

the role of vegetation in the formation of anabranching channels in an ephemeral river northern plains arid central australia as the distribution and abundance of vegetation in drylands is often controlled by the greater availability of water along river channels riparian vegetation has the potential to influence significantly dryland river form process and behaviour this paper demonstrates how a small indigenous shrub the inland teatree melaleuca glomerata influences the formation and maintenance of anabranching channels in a reach of the ephemeral marshall river northern plains arid central australia here the marshall is characterized by ridge form anabranching where water and sediment are routed through subparallel multiple channels of variable size which occur within a typically straight channel train channels are separated by channel train ridges narrow flow aligned vegetated features or by wider islands by providing a substantial element of boundary roughness dense stands of teatrees growing on channel beds or atop the ridges and islands influence flow velocities flow depths and sediment transport resulting in flow diversion bank and floodplain erosion and especially sediment deposition ridges and islands represent a continuum of forms and their formation and development can be divided into a three stage sequence involving teatree growth and alluvial sedimentation 1 teatrees colonize a flat sandy channel bed initiating the formation of ridges by lee side accretion individual ridges grow laterally vertically and longitudinally and maintain a geometrically similar streamlined lemniscate form that presents minimum drag 2 individual ridges grow in size and interact with neighbouring ridges causing the lemniscate forms to become distorted ridges in the lee of other ridges tend to be protected from the erosive effects of floods and survive whereas individual teatrees or small ridges exposed to flow concentrated between larger ridges tend to be removed 3 ridges lengthen and coalesce with downstream ridges eventually subdividing the channel train into well defined anabranches this sequence turns a channel initially obstructed with dense and chaotic stands of teatrees into a well organized system of ridge form anabranches in the moderate to low gradient marshall river which is colonized by an abundance of within channel vegetation and subject to declining downstream discharges this helps to minimize flow resistance thereby maintaining an efficient water and sediment flux copyright 2000 john wiley sons ltd

flow velocity measurements in vegetated channels understanding of the hydraulics of flow over vegetation is very important to support the management of fluvial processes in this paper the flow over flexible bottom vegetation is experimentally studied a two dimensional acoustic doppler velocimeter is used to measure the local flow velocities for different vegetation concentrations discharges and flume slopes the influence of vegetation concentration and the depth vegetation height ratio on the measured velocity profiles is analyzed all measured velocity distributions are s shaped and exhibit a three zone profile the relationship between the velocity distribution and the turbulence intensity distribution is also analyzed the characteristics inflection point maximum value asymptotes of the measured velocity distributions and the results of the previous investigators are used to select an analytical expression for the shape of the velocity profile a theoretical velocity profile is deduced using the classical prandtl s mixing length approach with a new expression for the mixing length the deduced four coefficient profile allows description of the flow both inside and above the vegetation the physical and geometrical meaning of the four coefficients are also shown doi 10 1061 asce 0733 9429 2002 128 7 664 ce database keywords velocity profile vegetation channel flow

morphological and historical resilience to catastrophic flooding the case of lockyer creek se queensland australia this study aimed to determine the extent of geomorphic change resulting from the catastrophic flood of 2011 in the lockyer valley in southeast queensland and to place these impacts within a history of geomorphic adjustment aerial photographs dated from 1933 to 2011 and parish maps and historical on ground photographs dating from 1865 to 1966 were examined for evidence of geomorphic adjustment since european settlement in the first half of the nineteenth century eleven forms of geomorphic adjustment were identified in three categories erosional depositional and reorganisational only 26 of the lockyer creek channel length has been affected by some form of geomorphic adjustment since european settlement most of this adjustment was localised and dominated by reorganisation of geomorphic unit assemblages within the macrochannel and sediment deposition on floodplains no wholesale river change in the form of lateral migration or avulsion has occurred and the river s morphology has remained relatively characteristic over time i e morphology remains relatively uniform in a reach averaged sense geomorphic responses to extreme flooding have been minor and the geomorphic effectiveness of floods in this system including the 2011 flood has been limited over the last several hundred years the system is likely still adjusting to past flooding events that set the morphology of the current system i e the macrochannel a form of event resilience has resulted in this system such that it is less prone to geomorphic adjustment during events than would normally be considered geomorphically effective as a result antecedent controls on macrochannel presence and capacity are considered to be first order controls on contemporary forms and processes in this system work is required to test whether the resilience of this system will hold in the future with more extreme episodes of flooding predicted to occur in this region under future climate change

an approach for assessing geomorphic river sensitivity across a catchment based on analysis of historical capacity for adjustment abstract contemporary river forms and processes can be heavily influenced by the legacies of anthropogenic disturbances to river systems knowledge of the historical range of river adjustment can be used to develop an understanding of a river s expected character and behaviour drawing upon the case study of richmond river catchment new south wales australia we track the history of geomorphic river adjustment from the time of european colonisation in the mid late nineteenth century we use this study to develop an approach called the behavioural sensitivity logical tree that can be applied to assess and quantify reach scale behavioural sensitivity defined as the ease with which geomorphic units and associated water sediment and vegetation interactions adjust within the expected behavioural regime we use the results to categorise rivers as fragile active sensitive passive sensitive insensitive and resistant fragile rivers have a behavioural sensitivity 75 and have the propensity to undergo wholesale river change such that a new river type and behavioural regime is created active sensitive rivers have a behavioural sensitivity ranging from 50 75 and have the ability to re configure within their contemporary behavioural regime the behavioural sensitivity of passive sensitive rivers lies between 20 50 these rivers have the ability to maintain their behavioural regime and withstand adjustment insensitive rivers have a behavioural sensitivity ranging from 5 20 they do not readily adjust and may contain significant antecedent elements that limit geomorphic adjustment resistant rivers have a behavioural sensitivity

sediment supply versus local hydraulic controls on sediment transport and storage in a river with large sediment loads the rio grande in the big bend region of texas usa and chihuahua and coahuila mexico undergoes rapid geomorphic changes as a result of its large sediment supply and variable hydrology thus it is a useful natural laboratory to investigate the relative importance of flow strength and sediment supply in controlling alluvial channel change we analyzed a suite of sediment transport and geomorphic data to determine the cumulative influence of different flood types on changing channel form in this study physically based analyses suggest that channel change in the rio grande is controlled by both changes in flow strength and sediment supply over different spatial and temporal scales channel narrowing is primarily caused by substantial deposition of sediment supplied to the rio grande during tributary sourced flash floods tributary floods have large suspended sediment concentrations occur for short durations and attenuate rapidly downstream in the rio grande depositing much of their sediment in downstream reaches long duration floods on the mainstem have the capacity to enlarge the rio grande and these floods released from upstream dams can either erode or deposit sediment in the rio grande depending upon the antecedent in channel sediment supply and the magnitude and duration of the flood geomorphic and sediment transport analyses show that the locations and rates of sand erosion and deposition during long duration floods are most strongly controlled by spatial changes in flow strength largely through changes in channel slope however spatial differences in the in channel sediment supply regulate sediment evacuation or accumulation over time in long reaches greater than a kilometer

multiscalar model for the determination of spatially explicit riparian vegetation roughness 1 improved understanding of the connection between riparian vegetation and channel change requires evaluating how fine scale interactions among stems water and sediment affect larger scale flow and sediment transport fields we propose a spatially explicit model that resolves patch scale submeter patterns of hydraulic roughness over the reach scale caused by stands of shrubby riparian vegetation we worked in tamarisk dominated stands on the yampa and green rivers in dinosaur national monument northwestern colorado usa where questions remain regarding the role of vegetation in inducing or exacerbating documented channel changes hydraulic roughness patterns were derived from patch scale measurements made with detailed terrestrial laser scan tls data that were extrapolated to reach scales based on correlation with light detection and ranging lidar als data two dimensional patch scale hydraulic models were used to parameterize the stage dependence of hydraulic roughness of typical patch types i e sparse moderate and dense patches we illustrate the value of using this approach to characterize vegetation roughness by applying our results to a two dimensional hydraulic model of flow for one of our study sites results from this work predict that the roughness of vegetated floodplains increases with flow depth and is dependent on patch scale stem organization geomorphically relevant patterns i e areas of low or high shear stress that are likely to scour or fill during high flows become apparent with the detail introduced by spatially explicit depth dependent roughness to our knowledge the multiscalar analysis presented here is the first to mechanistically account for shrubby riparian vegetation stand structure and associated hydraulic roughness of vegetation patches at the reach scale

impact of reach geometry on stream channel sensitivity to extreme floods predicting spatial and temporal variations in bank erosion due to extreme floods presents a long standing challenge in geomorphology we develop two methodologies for rapid regional scale assessments of stream reaches susceptible to channel widening the first proposes that channel widening occurs when unit stream power exceeds a critical threshold 300 w m2 the second is motivated by the observation that widening often occurs at channel bends we introduce a new metric the bend stress parameter which is proportional to the centripetal force exerted on a concave bank we propose that high centripetal forces generate locally high bank shear forces and enhance channel bank erosion we test both metrics using the geomorphic signature of tropical storm irene 2011 on the white and the saxtons rivers vermont specifically we test if reaches where significant channel widening occurred during irene required one or both metrics to exceed threshold values we observe two distinct styles of channel widening where unit stream power and bend stress parameter are high widening is usually due to bank retreat elsewhere widening is usually due to the stripping of the upstream end of mid channel islands excluding widening associated with the stripping of the heads of mid channel islands almost all the widening 98 occurred along reaches identified as susceptible to widening the combined metrics identify up to one quarter of the reaches lacking susceptibility to channel widening copyright 2014 john wiley sons ltd

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

arc deformation and marginal basin opening japan sea as a case study we discuss the opening mechanism of the japan sea in miocene time using 1 tectonic and published paleomagnetic data along the eastern margin from the north of hokkaido island to sado island 2 a mechanical model which is tested by small scale physical modeling and 3 crustal structure and bathymetric features in the japan sea which constrain our kinematic model and preopening reconstructions our main conclusions are the following the eastern margin of the japan sea was as a whole a dextral shear zone about 100 km wide this conclusion is supported by the existence of a ductile dextral shear zone in central hokkaido hidaka mountains and associated brittle deformation in western hokkaido and northeastern honshu the stress field during the opening which ended about 12 ma ago at the end of the middle miocene changes from right lateral transpression in the north to right lateral transtension in the south the western margin along the korean peninsula during the same period also was an active dextral shear zone paleomagnetic results indicate that clockwise rotations occurred in the south during the opening and counterclockwise rotations in the north we propose a model of right lateral pull apart deformation with clockwise rotations of rigid blocks in the southern transtensional domain and counterclockwise rotations in the transpressional one small scale physical models show that the clockwise rotation in transtension is possible provided that the eastern boundary pacific side is free of stress the opening stopped and compression subsequently began about 12 ma ago finally we show that the dextral shear which is distributed over the whole japan sea area is accommodated by n s trending right lateral faults and rotation of blocks located between these right lateral faults

japan sea opening history and mechanism a synthesis the respective tectonic effects of back arc spreading and continental collision in asia are considered either as two independent processes or as closely interrelated extrusion tectonics assumes that the opening of the south china sea and the left lateral motion along the red river fault are geometrically linked in a pull apart manner this model is not accepted by several workers because the structural link between the two processes is not clearly demonstrated in the case of the japan sea we can show without ambiguity that back arc opening was controlled by large intracontinental strike slip faults which can be easily understood as effects of the india asia collision far from the indenter the japan sea opened in the early miocene in a broad pull apart zone between two major dextral strike slip shear zones the first one extends from north sakhalin to central japan along 2000 km it has accommodated about 400 km of finite displacement deformation along it varies from dextral transpression in the north to dextral transtension in the south the second is between korea and sw japan and has accommodated a smaller displacement of about 200 km the extensional domain in between lies in the back arc region of japan distributed stretching of the arc crust resulted in the formation of most of the japan sea while localized oceanic spreading at the southern termination of the eastern transpressional shear zone shaped the japan basin the first oceanic crust was formed in a small triangle based on the eastern shear zone and spreading propagated westward inside the pull apart region timing of oceanic crust formation of formation of the dextral shear zones and of block rotation in between as well as the internal structure of the basins and the geometry of deformation along the master shear zones are used to reconstruct the opening history this evolution is discussed by comparison to other manifestations of the arc and back arc activity such as the history of sedimentation and volcanism the paper then suggests that the collision of india can have tectonic consequences as far north as japan and sakhalin and describes the geometrical relation of back arc opening there and diffuse extrusion

nature s complex flume using a diagnostic state and transition framework to understand post restoration channel adjustment of the clark fork river montana abstract there is an imperfect symmetry between the patterns of channel evolution observed during laboratory flume experiments and those which materialize in rivers exposed to ambient environmental conditions that produce hydrogeomorphic fluxes which are more complex contingent and unpredictable one strategy to improve our understanding of short to medium term channel evolution is to study landscapes that have undergone significant disturbance and have had their biogeomorphic templates reset to a known condition in effect creating a flume in nature this study adopts a diagnostic state and transition framework to narrate and document baseline hypotheses for the potential evolutionary trajectories clark fork river near milltown montana following dam removal and remediation a 5 km stretch of the clark fork river and its adjoining floodplain were reconstructed since flow was introduced to the newly constructed channel in december 2010 complex evolutionary trajectories have been observed on the clark fork s mainstem its secondary channels and floodplain focusing particularly on the river s secondary channels this paper develops a typology of channel states that have been observed and demonstrates that multiple adjustment trajectories have materialized sometimes within the same channel a diagnostic state and transition framework offers a parsimonious strategy to quantitatively or qualitatively anticipate the influence of water sediment and ecological fluxes on channel evolution at the basin reach or segment scale it provides environmental agencies with a robust method to devise spatially explicit scenario based management plans for rivers in a variety of geomorphic settings

a mid to late holocene history of floodplain and terrace reworking along the middle delaware river valley usa abstract this study tests and refines the traditional floodplain development model for the partly confined middle delaware river valley which has shown that the main channel was relatively stable and flanked by a 6000 8000 year old vertically accreting alluvial terrace the holocene alluvial processes and history presented here in 6 fluvial phases were reconstructed using morphostratigraphy 36 profile descriptions 332 grain size analyses and 82 14 c ages from soil trenches auger borings and archaeological excavations fluvial phases i iii largely validate previous reconstructions showing a late pleistocene i 10 7 ka braided stream transition into an early holocene wandering stream with prolonged floodplain stability ii 10 7 8 ka followed by early middle holocene erosion and then deposition iii 8 5 ka the early and middle holocene changes in alluvial stratigraphy and sedimentology broadly correlate with climatically derived holocene subdivisions suggesting climate change partly controls alluvial response along the middle delaware river valley this study documents for the first time a middle holocene episode of channel incision occurring sometime between 6 0 and 5 0 ka although the results reconfirm that the majority of alluvial landforms are composed of vertical accretion deposits we present here new evidence of oblique abandoned channel and lateral accretion deposits inset to similar landforms with different formation histories i e polycyclic terrace development depicting a river valley that has experienced floodplain and terrace reworking the majority of floodplain and terrace reworking occurs during the late middle and late holocene phases iv vi 5 5 0 ka following the middle holocene incision event these phases demonstrate floodplain reworking processes in the form of channel abandonment stripping flood channeling and convex bank erosion the subsequent space filled rapidly with evidence of multistory soil formation and eventually resulted in alluvial fill terraces with heights comparable to older surfaces the most recent fluvial phase vi 1 0 0 ka shows markedly faster sedimentation rates and coarser flood deposits associated with peak prehistoric population and the onset of euroamerican settlement the results presented here contribute newly documented evidence of erosion and depict a river valley that has undergone middle holocene incision and floodplain and terrace reworking since the late middle holocene stream modelers fluvial geomorphologists and geoarchaeologists working in the ne usa should consider floodplain reworking processes when examining alluvial history and predicting changes in stream dynamics

streamflow regulation and multi level flood plain formation channel narrowing on the aggrading green river in the eastern uinta mountains colorado and utah abstract the style and degree of channel narrowing in aggrading reaches downstream from large dams is dependent upon the dominant geomorphic processes of the affected river the magnitude of streamflow regulation and the post dam sediment transport regime we measured different magnitudes of channel adjustment on the green river downstream from flaming gorge dam ut usa that are related to these three factors bankfull channel width decreased by an average of about 20 in the study area in reaches with abundant debris fans and eddy deposited sand bars the amount of channel narrowing was proportional to the decrease in specific stream power the fan eddy dominated reach with the greatest decrease in stream power narrowed by 22 while the reach with the least decrease in stream power narrowed by 11 in reaches with the same magnitude of peak flow reduction meandering reaches narrowed by 15 to 22 and fan eddy dominated reaches narrowed by 11 to 12 specific stream power was not significantly affected by flow regulation in the meandering reaches in the diverse array of reach characteristics and deposit types found in the study area all pre and post dam deposits are part of a suite of topographic surfaces that includes a terrace that was inundated by rare pre dam floods an intermediate bench that was inundated by rare post dam floods and a post dam floodplain that was inundated by the post dam mean annual flood analysis of historical photographs and tree ring dating of tamarix sp shows that the intermediate bench and post dam floodplain are post dam landforms in each reach type although these two surfaces occur at different levels they are forming simultaneously during flows of different magnitude and while the relative elevation and sedimentologic characteristics of the deposits differ between meandering reaches and reaches with abundant debris fans and eddies both reach types contain deposits at all of these topographic levels the process of channel narrowing varied between fan eddy dominated and meandering reaches in the meandering reaches where stream power has not changed narrowing was accomplished by essentially the same depositional processes that operated prior to regulation in fan eddy dominated reaches where significant reductions in stream power have occurred channel narrowing has been accompanied by a change in dominant depositional processes mid channel sand deposits are aggrading on deposits that in the pre dam era were active gravel bars these deposits are creating new islands and decreasing the presence of open framework gravel bars in eddies bare sand bars are replaced with vegetated bars that have a simpler topography than the pre dam deposits

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

mechanisms of vegetation induced channel narrowing of an unregulated canyon river results from a natural field scale experiment abstract the lower yampa river in yampa canyon western colorado serves as a natural field scale experiment initiated when the invasive riparian plant tamarisk tamarix spp colonized an unregulated river in response to tamarisk s rapid invasion the channel narrowed by 6 in the widest reaches since 1961 taking advantage of this unique setting we reconstructed the geomorphic and vegetation history in order to identify the key mechanisms for which in the absence of other environmental perturbations vegetation alters fluvial processes that result in a narrower channel from our reconstruction we identified a distinct similarity in the timing and magnitude of tamarisk encroachment and channel change albeit with a lag in the channel response thus suggesting tamarisk as the driving force within a decade of establishment tamarisk effectively trapped sediment and as a result increased floodplain construction rates increasing tamarisk coverage over time also reduced the occurrence of floodplain stripping tamarisk recruitment was driven by both hydrologic and hydraulic variables and the majority of tamarisk plants 84 established below the stage of the 2 year flood thus upon establishment nearly all plants regularly interact with the flow and sediment transport field our analyses were predicated on the hypothesis that the flow regime of the yampa river was stationary and that only the riparian vegetation community had changed while not heavily impacted by water development we determined that some aspects of the flow regime have shifted however this shift which involved the clustering in time of extremely wet and dry years did not influence fluvial processes directly instead these changes directly impacted riparian vegetation and changes in vegetation cover in turn altered fluvial processes today the rate of channel change and new tamarisk recruitment is small we believe that the rapid expansion of tamarisk and related floodplain construction that led to a narrower channel pushed the yampa river into a new stable state characterized by a relatively static channel

destabilization of streambanks by removal of invasive species in canyon de chelly national monument arizona as part of a study to investigate the causes of channel narrowing and incision in canyon de chelly national monument the effects of tamarisk and russian olive on streambank stability were investigated in this study root tensile strengths and distributions in streambanks were measured and used in combination with a root reinforcement model riproot to estimate the additional cohesion provided to layers of each streambank the additional cohesion provided by the roots in each 0 1 m layer ranged from 0 to 6 9 kpa for tamarisk and from 0 to 14 2 kpa for russian olive average root reinforcement values over the entire bank profile were 2 5 and 3 2 kpa for tamarisk and russian olive respectively the implications of vegetation removal on bank stability and failure frequency were evaluated in two incised reaches by modeling bank toe erosion and bank stability with and without vegetation the effects of a series of 1 0 and 1 5 m deep flows on bank toe erosion pore pressure distributions and bank stability were evaluated first in addition bank stability model runs were conducted using iterative modeling of toe erosion and bank stability using a discretized flow and groundwater record for one year results showed that the effects of root reinforcement provided by tamarisk and russian olive have a significant impact on bank stability and bank failure frequency because the bank materials are dominated by sands cohesion provided by roots is significant to bank stability providing an average 2 8 kpa of cohesion to otherwise cohesionless bank materials bank retreat rates at one site following vegetation removal have approximately doubled when compared to the control reach from an approximate rate of 0 7 0 8 m y between 2003 and 2006 to 1 85 m y during the year modeled vegetation removal along the entire riparian corridor in canyon de chelly may lead to the introduction of significantly more sediment to the system through bank widening processes although it is not known whether this change alone would be sufficient to cause a shift in channel morphology to the wide braided channels that were once characteristic of this canyon

episodes of vertical accretion and catastrophic stripping a model of disequilibrium flood plain development this paper describes flood plains formed episodically by vertical accretion along high energy laterally stable channels in southeastern australia overbank deposition gradually builds a flood plain of fine textured alluvium over a period of hundreds or thousands of years following which catastrophic erosion by a single large flood or a series of more moderate floods strips the flood plain to a basal lag deposit from which it slowly reforms this periodic destruction appears due to the progressive development of large levee banks and flood plain surfaces of highly variable relief as the levees and flood plain grow overbank flow is gradually displaced from the broad flood plain into the main channel and flood plain backchannels with a resulting concentration of erosional energy eventually high flows greatly exceed erosional thresholds and wholesale scour of the channel boundary and flood plain occurs vertical accretion flood plains at different stages of development result in a wide range of bankfull recurrence intervals even along the same river some of these flood plains are so infrequently flooded that they can be mistaken for terraces formed under a prior flow regime the almost random but catastrophic nature of this flood plain erosion means that sediment supply and transport are highly variable and probably impossible to predict this model of flood plain formation is seen as only part of a continuum of alluvial environments ranging from vestigial coarsegrained traction load flood plains along high energy rivers in narrow gorges to extensive low gradient flood plains in which alluvial stratigraphy is dominated by fine grained overbank deposition

preface multiscale feedbacks in ecogeomorphology 1 introductiongeomorphic systems are known to exhibit nonlinear responses tophysical biological feedbacks thornes 1985 baas 2002 reinhardtet al 2010 these responses make understanding and or predictingsystem response to change highly challenging with growingconcerns over ecosystem health a pressing need exists for researchthat tries to elucidate these feedbacks jerolmack 2008 darby 2010 national research council 2010 a session was convened at the fall2008 meeting of the american geophysical union agu to providean outlet for some of this truly interdisciplinary and original research which is central to understanding geomorphic and ecologicaldynamics the session attracted over 39 contributions which weredivided into two well attended oral sessions and a very busy postersession this special issue presents new research from the agu session which highlights clear physical biological feedbacks the aim is tobring together contrasting perspectives on biological and geomorphicfeedbacks in a diversity of physiographic settings ranging fromwetlands and estuaries through rivers to uplands these papershighlight biological and physical feedbacks which involve themodulation or ampli cation of geomorphic processes these paperswill be of interest to a core geomorphology audience and should alsodraw attention from the elds of ecohydraulics hydroecology ecohydrology ecomorphology biogeochemistry and biogeography and biogeomorphology as well as the more traditional elds ofhydrology ecology and biology in this preface to the special issue we a review past contributionsto the emerging eld of ecogeomorphology and related disciplines b provide some context for how this topical special issue came tofruition and c summarize the contributions to this special issue 2 what is ecogeomorphology examples of studies explicitly integrating ecology and geomor phology date back to at least the late 1800s e g cowles 1899 withmore examples appearing in the 1950s e g olson 1958 and 1960s e g hack and goodlet 1960 terms such as ecogeomorphology andbiogeomorphologyonlybecamepopularinthe1990s osterkampandhupp 2010 the 1990 british geomorphology research groupannual meeting thornes 1990 and the 1995 binghamton sympo sium on biogeomorphology hupp et al 1995b were two of the rstsymposiums to emphasize the theme of biogeomorphology ecogeo morphology and biogeomorphology are generally considered syno nyms hupp et al 1995a but they do sprout from slightly differentresearch interests both are part of a larger family of terms thatresearchers have used somewhat inconsistently to describe researchat the interface between some combination of hydrology geomor phologyand orecology biology fig 1 unlikesomeoftheothereco geo hydro combinations in fig 1 the eco or bio root is an adjectivemodifying the noun geomorphology based on the types of researchpublished under these two banners the biogeomorphology commu nity has generally focused more on how chemical and physicalweathering are ampli ed and modulated with biological feedbacks ecogeomorphology is commonly used to describe studies that focusmore on the ampli cation and modulation of erosion and depositionprocesses both are fundamentally concerned with the bidirectionalin uences of biota and landscapes on each other biogeomorphologyis concerned with both the in uence of landforms on plants animalsand micro organisms distribution and development as well as thein uence of those plants animals and micro organisms on earthsurfaceprocessesandthelandformsshapedbythoseprocesses viles 1988 naylor et al 2002 p 4 loosely de ne biogeomorphology asinvolving the cooperation between ecology and geomorphology tostudy two way linkages between ecological and geomorphologicalprocesses murray et al 2008 argue that biomorphodynamics is amore restrictive term than biogeomorphology or ecogeomorphology and that it highlights landscape dynamics in which an explicit twoway coupling i e feedback occurs between biotic and physicalprocesses therelatedzoogeomorphology e g butler 1995 termhasreceived less play but it is worth mentioning that research under thisbanner focuses on examples of animals in uencing geomorphicprocesses and landforms e g beaver salmon burrowing animals etc the term biogeomorphology has been more widely used sinceviles 1988 rst attempted to provide a comprehensive overview ofwhat was at that time an emerging discipline a review of web of

paleomagnetism of tertiary rocks on the korean peninsula tectonic implications for the opening of the east sea sea of japan abstract two different distributions of declinations with dual polarities are found in the tertiary rocks of the yeonil basin and yangnam basin along the yangsan fault in the southeastern part of the korean peninsula these are northward declinations in the middle miocene yeonil group and strong eastward declinations in the early miocene yangbuk group and in the eocene volcanic rocks this is interpreted by invoking 1 the yangsan fault as a dextral wrench fault system by spreading in the uleung basin of the east sea sea of japan and 2 a clockwise vertical rotation caused by the movement of the fault at around 17 3 ma just prior to the sedimentation of the yeonil group the timing of the deflection found in korea is distinguished from that in southeastern and northwestern japan at around 15 ma two stages of spreading are thus constrained in the east sea area parallel at 23 15 ma and pivotal at around 15 ma crustal thinning also occurred a reliable pole position 84 9 n 292 6 e d p d m 3 3 4 8 for the miocene about 15 ma in korea is obtained from the yeonil group

early neogene biochemostratigraphy of pohang basin a paleoceanographic response to the early opening of the sea of japan east sea abstract the location of the pohang basin near the korea strait in the southwest of the sea of japan east sea makes this area appropriate for providing a record of paleoenvironmental biotic changes associated with the early neogene 16 5 ma opening of this gateway to the pacific ocean stable isotopic and planktonic foraminiferal records are presented that assist with the understanding of paleoenvironmental changes in the sea of japan resulting from the opening of the korea strait the oldest sediments of early neogene age of the pohang basin overlie cretaceous basement and are early miocene 16 5 ma shallow estuarine facies containing a benthic foraminiferal assemblage dominated by ammonia beccarii l the oldest early neogene planktonic foraminiferal assemblages in the basin are 16 5 ma in age latest early miocene foraminiferal zone n8 the migration of these planktonic assemblages to the sea of japan at that time appears to have resulted from the initial opening of the korea strait the overlying early neogene marine sequence of the pohang basin extends from 16 5 ma zone n8 through 14 ma zone n10 change in the oxygen isotopic record of the pohang basin sequence suggests strong local paleoenvironmental control related to the early opening of the korea strait early middle miocene isotopic temperatures of planktonic foraminifera are relatively cool at 15 ma at a time when global temperatures were high in the middle low latitude regions it was not until 14 8 ma that isotopic temperatures of planktonic foraminifera increased markedly this distinct warming is inferred to reflect the major intrusion of the kuroshio current into the sea of japan probably as a result of further critical opening and deepening of the korea strait at this time planktonic foraminifera increased in abundance reflecting expanding oceanic influence a cooling that followed at 14 5 ma when the strait was well open is unlikely to reflect local tectonic control on the paleoceanography but global cooling during the early middle miocene associated with the expansion of the east antarctic ice sheet

rivers in the anthropocene the u s perspective abstract during the past 50 yr the number and variety of papers written by u s fluvial geomorphologists that examine human alterations of rivers has accelerated substantially from an initial focus primarily on how human induced changes in land cover influence sediment yield and river dynamics the literature has expanded to emphasize the effects of flow regulation channel engineering removal of large wood and beavers and changing climate these multiple human influences are now widely recognized to have resulted in global scale cumulative effects including significantly altered fluxes of water sediment nitrogen and carbon and complete transformation of river networks across much of the planet one outgrowth of this recognition is the increasing involvement of geomorphologists in diverse forms of river restoration a form of river management that thus far has largely been dominated by engineers acknowledging the ubiquity of human alteration of rivers implies that i investigators cannot assume that even the most remote and seemingly pristine river segment has not been affected at least indirectly by people ii the use of reference conditions requires careful consideration with respect to what reference sites indicate about past conditions as well as their relevance for the future iii detailed geomorphic understanding of the nature and timing of past human alterations of rivers is likely to be critical to effective restoration and iv each scientist must decide how to engage within the context of research and advocacy with the issues of ecosystem degradation and loss of river form and function

timing and structure of termination ii in north china constrained by a precisely dated stalagmite record abstract the timing and structure of termination ii t ii is still debatable as the number of high quality records is insufficient this study presents precisely dated stalagmite 18 o data between 133 4 0 3 to 126 6 0 3 ka bp covering most of t ii from north china near the northern limit of the east asian summer monsoon easm an area sensitive to climate change the onset of the last interglacial is constrained at 129 4 0 3 ka bp consistent with south chinese speleothem records further supporting the idea that northern hemisphere summer insolation plays an important role in initiating glacial terminations an extended interval of heavy 18 o is observed immediately prior to this abrupt transition named as the weak monsoon interval wmi in south chinese cave records which was associated with the heinrich stadial 11 h11 in the north atlantic a significant millennial scale interstadial peaking at 132 7 0 3 ka bp is identified preceding the weakest phase of the wmi a synchronous counterpart is also found in some south chinese speleothem and north atlantic alkenone mg ca sst records it is inferred that the main h11 freshwater penetration possibly occurred after 131 5 ka bp leaving some aspects of ocean and atmospheric circulation still in interstadial mode from 134 to 131 5 ka bp following the onset of the last interglacial there was a millennial scale pause in our 18 o record synchronized with a slowdown in the rate of decrease in 18 o in south chinese cave records this is possibly a large regional climate oscillation as it is also identified in some north atlantic records but one which is too weak to be a younger dryas yd type event in summary compared to south chinese cave records significant millennial scale climate oscillations before and after the synchronous onset of the last interglacial is the main feature of our record nevertheless the sequence of these climate events remains very different from termination i t i which is possibly ascribed to the stronger insolation higher atmosphere co2 and the resultant faster and greater meltwater pulse to the north atlantic during t ii than during t i

modeling effects of bank friction and woody bank vegetation on channel flow and boundary shear stress in the rio puerco new mexico 1 we have applied a physically based model for steady horizontally uniform flow to calculate reach averaged velocity and boundary shear stress distributions in a natural stream with woody vegetation on the channel banks the model calculates explicitly the form drag on woody plant stems and includes the effects of vegetation on the boundary shear stress velocity and turbulence fields average channel shapes bed gradients and shrub characteristics were determined for four long internally similar reaches covering an 81 km segment of the lower rio puerco in north central new mexico hydraulic geometries for each of three flow events were determined from reach average channel shapes slopes and measured silt line heights above the bed model results show that friction on the lateral boundaries reduced the boundary shear stress in the center of the rio puerco channel by as much as 20 in reaches with moderate to dense bank shrubs perimeter averaged boundary shear stresses were reduced by almost 40 during near bankfull flows model calculated discharges for all three flow events indicate there was a loss of about 40 of the upstream discharge through the 81 km river segment infiltration rates estimated from discharge losses during the quasi steady peak flows and areas of the bed and banks suggest rates of flow loss into the silty sand of the upper banks are about 8 times greater than rates of loss into the clayey silt covered bed and lower banks

revised stratigraphy and reinterpretation of the miocene pohang basinfill se korea sequence development in response to tectonism and eustasy in a back arc basin margin abstract the miocene pohang basin is a pull apart basin formed along the eastern continental margin of korea ecmk during the back arc opening of the east sea sea of japan the basin is filled by more than 1 km thick nonmarine to deep marine strata these strata show extreme vertical and lateral lithofacies changes and have caused decades long controversies on their nature and stratigraphy previous sedimentological studies suggest that the basinfill was deposited by a series of contemporaneously developed depositional systems including fan delta prodelta slope apron and basin plain detailed mapping and magnetotelluric surveying show however that the basinfill is composed of several packages of strata sequences that are bounded by distinct and laterally persistent stratigraphic discontinuities sequence boundaries this suggests that the depositional systems in the pohang basin developed sequentially rather than contemporaneously six packages of strata are identified in the basin a nonmarine to shallow marine transgressive sequence sequence 1 a gilbert type delta conglomerate sequence 2 and alternations of submarine conglomerates and hemipelagic mudstones sequences 3 6 the conglomerates and hemipelagic mudstones of the latter four sequences are interpreted to represent lowstand depositional systems slope apron submarine fan and high gradient delta and condensed intervals respectively compilation of geochronologic paleomagnetic and biostratigraphic data suggests that sequence 1 formed during the gradual subsidence of the ecmk prior to 17 ma whereas sequence 2 formed in response to abrupt downfaulting of the pohang basin at about 17 ma both sequences are interpreted to have developed in response to the early miocene back arc opening tectonism of the east sea on the other hand sequences 3 6 formed between 17 and about 10 5 ma the pohang basin was subject to only minor tectonism during this period and could record global sea level fluctuations we suggest that the four alternations of conglomerates lowstand systems and hemipelagic mudstones condensed intervals resulted most probably from the 3rd order glacioeustatic cycles during the middle miocene this finding implies that the signatures of global sea level fluctuations can be deciphered from a tectonically active sedimentary basin if the timing of regional tectonic development is well constrained and the global sea level chart of haq et al haq b w hardenbol j vail p r 1987 chronology of fluctuating sea levels since the triassic science 235 1156 1167 haq b u hardenbol j vail p r 1988 mesozoic and cenozoic chronostratigraphy and eustatic cycles in wilgus c k hastings b s posamentier h van wagoner j ross c a kendall c g s c eds sea level changes an integrated approach soc econ paleont mineral spec publ 42 pp 71 108 may serve as a guide to basinfill interpretation even in tectonically active sedimentary basins

controls and evolution of fan delta systems in the miocene pohang basin se korea abstract the miocene pohang basin southeastern korea occurs in the eastern part of the ne sw trending yangsan fault which has experienced right lateral strike slip deformation since the eocene during the miocene however the strike slip movement was negligible and instead was under extensional regime large scale drainage systems were developed at the junction between the strike slip zone and the oblique transfer faults acting as major sources for coarse grained sediments high rate of sediment supply and rapid subsidence of the hanging wall resulted in the progradation of large scale gilbert type fan deltas doumsan duksung and gohyun systems which all show a radial distributional pattern along the steeply inclined footwall scarps created by ne sw trending faults the drainage systems were relatively small here low rate of sediment supply formed scree apron type malgol and yugye systems and steep faced slope type maesan system fan deltas based on variations in sedimentary facies and distribution architecture and overlapping patterns the fan delta systems in the pohang basin can be divided into four stages of evolution during the early stage early miocene alluvial fans prograded into shallow marine setting in the doumsan and duksung systems high rate of sediment supply and rapid rise of relative sea level resulted in the transformation of shoal water type to gilbert type foresets in the malgol and maesan systems rapid sea level rise accompanied with low rate of sediment supply caused transformation of alluvial fans to scree apron type and steep faced slope type fan deltas respectively in the second stage subsidence of the hanging wall formed large scale truncation surfaces in the doumsan and duksung fan deltas coarse grained sediments were continuously supplied in the doumsan system whereas only fine grained sediments were deposited in the duksung system in the malgol system sediment supply was almost terminated in this stage in the third stage middle miocene sediment supply rate of the doumsan fan delta decreased abruptly and the system was overlain by fine grained gilbert type deposits the duksung fan delta was overlain by the maesan and gohyun systems the maesan system prograded further basinward during the last stage late miocene sediment supply of the doumsan and maesan systems was also terminated and the entire basin was draped by fine grained biogenic materials mainly diatoms

paleomagnetism of the early miocene kani group in southwest japan and its implication for the opening of the japan sea paleomagnetic directions of a volcanic and sedimentary sequence of the kani basin ranging from 22 to 15 ma show a clockwise declination shift of about 50 degree this result implies that detectable rotation of southwest japan did not occur in this period but after 15 ma the initial opening of the japan sea before 15 ma might have caused a southeastward translation of southwest japan which was then followed by clockwise rotation between 16 and 14 ma

channel narrowing by vertical accretion along the green river near green river utah the green river is the longest tributary of the colorado river near the town of green river utah the green river narrowed in two discrete phases during the twentieth century the first phase of narrowing decreased average width by about 5 and occurred between about 1930 and 1940 when the magnitude of 2 yr flood mean annual discharge and effective discharge decreased by about 30 28 and 37 respectively during this first phase of narrowing saltcedar tamarisk spp an invading non native tree began to establish itself in the study area but botanists of that time did not describe the tree as abundant channel width was stable in the 1940s and 1950s even though saltcedar were becoming already abundant on the river9s banks further narrowing of an additional 14 occurred after 1959 this latest period of narrowing began following three successive years when the magnitude of floods was less than the present 1 5 yr recurrence flood and when saltcedar were already abundant along the river the deposits that comprise the banks of the narrowing green river are composed of the suspended load of the river and these alluvial deposits are characterized by horizontal layers which indicate that they formed by vertical accretion a mechanism is proposed to explain the coarsening upward sequence of beds found in these vertically accreted deposits these changes in the channel of the green river are based on analysis of more than 2600 discharge measurements made by the u s geological survey resurvey of an abandoned measurement site matches of historical ground level photography and analysis of historical aerial photography within a geographic information system we have developed analytical techniques that permit analysis of width data from u s geological survey discharge measurements where gaging cross sections have adjustable beds and banks these techniques allow the spatially rich but temporally poor data from aerial photographs to be supplemented with gaging station data which add great detail about the timing and actual processes of channel narrowing that cannot be determined from aerial photographs alone such an analytical strategy provides a more complete record of historical channel adjustment than can be obtained by other means

dating floodplain sediments using tree ring response to burial floodplain sediments can be dated precisely based on the change in anatomy of tree rings upon burial when a stem of tamarisk tamarix ramosissima or sandbar willow salix exigua is buried subsequent annual rings in the buried section resemble the rings of roots rings become narrower vessels within the rings become larger and transitions between rings become less distinct we combined observations of these changes with tree ring counts to determine the year of deposition of sedimentary beds exposed in a 150 m long trench across the floodplain of the rio puerco a rapidly filling arroyo in new mexico this method reliably dated most beds thicker than about 30 cm to within a year of deposition floodplain aggradation rates varied dramatically through time and space sediment deposition was mostly limited to brief overbank flows occurring every few years the most rapid deposition occurred on channel margin levees which migrated laterally during channel narrowing at the decadal timescale the cross section average sediment deposition rate was steady but there was a shift in the spatial pattern of deposition in the 1980s from 1936 to 1986 sediment deposition occurred by channel narrowing with little change in elevation of the thalweg after 1986 sediment deposition occurred by vertical aggradation from 1936 to 2000 about 27 per cent of the arroyo cross section filled with sediment the rate of filling from 1962 to 2000 was 0 8 vertical m decade or 85 m2 decade published in 2005 by john wiley sons ltd

channel adjustments to changing discharges powder river montana sixteen years of annual surveys reveal how powder river responds to varying discharges during 1978 the second largest recorded daily mean discharge occurred cutbank migration bed degradation net bank erosion and overbank deposition all contributed to increase the channel area at 12 cross sections by an average of 62 during the ensuing years the channel area decreased as sediment was stored in low lying benches adjacent to the active bed of the channel the survey data indicate that the balance between bank erosion and deposition varies with discharge in years when the annual maximum daily mean discharge is 3 s a flow of 60 m 3 s has a recurrence interval of 1 1 yr bank erosion and deposition are approximately equal in years when the annual maximum daily mean discharge is between 60 and 150 m 3 s a discharge of 150 m 3 s has a recurrence interval of 2 7 yr bank deposition exceeds bank erosion and the channel contracts often by developing benches in years with higher discharges the channel expands through net bank erosion these results demonstrate that the channel of powder river is influenced by a wide variety of formative discharges powder river9s recent history of expansion and contraction and the development of prominent benches cannot be explained by equilibrium models based on a single channel forming discharge

a gravel lobe deposit in the prodelta of the doumsan fan delta miocene se korea abstract the doumsan fan delta system in the pohang basin miocene se korea comprises tripartite components of gilbert type topset foreset and bottomset environments with an extended prodelta in the deeper part a few hundred metres deep the present study documents sedimentologic features and origin of a gravel body here interpreted as a gravel lobe formed in the prodelta region of the doumsan fan delta the gravel lobe lies on sandy mud deposits and is capped by a thick massive sand bed it extends for more than 1 5 km with a height of up to 30 m and shows a narrow tongue like geometry eight sedimentary facies have been distinguished to describe characteristic features of the gravel lobe and the associated deposits of these three types of gravelly sedimentary facies are important with regard to volumetric contribution and depositional processes 1 crudely stratified pebble grade conglomerate 2 disorganized clast rich pebble to cobble grade conglomerate and 3 matrix rich bimodal cobble grade conglomerate the former two types dominate the central part of the lobe where they are not accompanied by sand beds whereas the latter as subordinate units is prevalent in the fringe which otherwise is dominated by thick sandy mud deposits the stacked successions of crudely stratified pebble grade conglomerate are representative of the active aggradational phases of the gravel lobe whereas the occurrence of channels within the lobe reflects that the gravel lobe prograded under the influence of subaqueous channel systems the gravel lobe resulted from catastrophic disturbance slumping on the foreset region that further caused the development of channel systems promoting efficient transport of gravelly sediments this type of deposit may represent an important additional category of low efficiency subaqueous fans

paleoceanographic evolution of the japan sea abstract multidisciplinary studies on nearly continuous hemipelagic sequences recovered from the deeper parts of the japan sea during odp leg 127 128 in 1989 yielded new information on the paleoceanographic conditions of the sea since its establishment as a deep marginal basin of significant size approximately at 20 ma by synthesizing these new information on surface and bottom water conditions ccd biogenic silica accumulation and paleogeog raphy it is possible to reconstruct changes in paleo ocean circulation within the sea it is also possible to specify the ultimate cause of such changes by comparing their timing and nature with those of global paleoceanographic as well as local tectonic events the result of our synthesis suggests that the japan sea has been responding to the high frequency changes of global surface conditions in very sensitive manner throughout its history however the mode of its response changed from time to time the changes in response mode have been strongly influenced by such factors as sill depth position of channels and the degree of closure of the sea which were controlled either by local tectonism or global eustatic sea level changes

vegetation induced sedimentary structures from fossil forests in the pennsylvanian joggins formation nova scotia vegetation induced sedimentary structures viss are primary structures formed by the interaction of detrital sediment with in situ plants viss provide physical evidence of vegetation s fundamental role in mediating sediment accumulation and erosion in clastic depositional systems despite the abundance of modern viss descriptions from the ancient record are surprisingly rare analysis of fossil forests in floodplain strata of the pennsylvanian joggins formation has identified seven types of viss five hydrodynamic types comprise simple forms developed around a single plant centroclinal cross strata scratch circles upturned beds and complex forms where structures have amalgamated between several plants coalesced scour fills scour and mound beds two types mudstone filled hollows downturned beds form by the decay of an entombed plant and represent infilling of an empty hollow and or soft sediment deformation hydrodynamic types are present in both dryland and wetland settings whereas decay related types occur only in dryland settings where the water table was perennially or periodically low viss represent significant accumulations of sediment and are present in a high proportion of joggins formation strata the paucity of descriptions from the ancient record suggests that these structures have been overlooked or misinterpreted as strictly hydrodynamic recognition of viss in early to middle palaeozoic strata may provide an important insight into the distribution of early land plants in oxidizing environments where organic material was not preserved

historical geomorphic analysis 1932 2011 of a by passed river reach in process based restoration perspectives the old rhine downstream of the kembs diversion dam france germany the old rhine downstream of the kembs diversion dam is one of the largest by passed river reaches in the world 50 km it offers a unique opportunity to study the morphological effects of by passing and address physical and ecological restoration approaches in regulated rivers we conduct a space time analysis of channel adjustment over a period of 80 years 1932 to 2011 we examine planform changes from aerial photographs erosional and depositional patterns from vertical profiles sediment sizes within the active channel and the new established floodplain and we date riparian vegetation encroachment results show that the old rhine exhibited rapid response to the completion of the by passing scheme in the 1950s with a 26 narrowing in median active channel width between 1956 and 2008 from vegetation encroachment on dewatered channel margins mostly groyne fields the narrowing was accompanied by overbank fine sediment deposition 1 5 cm y 1 aggradation since 1950 as well as slight bed degradation 0 7 cm y 1 since 1950 we found no downstream propagation of active channel narrowing over time nor propagation of bed degradation the channel was already significantly adjusted prior to the diversion scheme following the nineteenth century river straightening and groyne construction by passing dewatering mainly provided new pioneer habitat for synchronous vegetation establishment and promoted channel stability by decreasing sediment transport owing to peak flow reduction the morphological budget calculated over the past 20 years estimated a downstream output for coarse sediments at 16 000 m3 y 1 with 80 originating from bed degradation and 20 from bank erosion without significant inputs from upstream the present day morphodynamics remain sensitive to changes because of dynamic bed armouring 2 1 this retrospective analysis permits us to discuss management strategies for altered rivers recommended activities are gravel reintroduction with particle sizes finer than the armoured river bed to enhance sediment transport and promote form dynamism under current flood magnitudes this should be coupled with river widening to allow for complex depositional patterns that benefit ecological habitats these actions should not be implemented without prior analysis of local sediment transfer processes based on in situ experiments and modelling

the geomorphic effectiveness of a large flood on the rio grande in the big bend region insights on geomorphic controls and post flood geomorphic response abstract since the 1940s the rio grande in the big bend region has undergone long periods of channel narrowing which have been occasionally interrupted by rare large floods that widen the channel termed a channel reset the most recent channel reset occurred in 2008 following a 17 year period of extremely low stream flow and rapid channel narrowing flooding was caused by precipitation associated with the remnants of tropical depression lowell in the rio conchos watershed the largest tributary to the rio grande floodwaters approached 1500 m 3 s between a 13 and 15 year recurrence interval and breached levees inundated communities and flooded the alluvial valley of the rio grande the wetted width exceeding 2 5 km in some locations the 2008 flood had the 7th largest magnitude of record however conveyed the largest volume of water than any other flood because of the narrow pre flood channel conditions record flood stages occurred we used pre and post flood aerial photographs channel and floodplain surveys and 1 dimensional hydraulic models to quantify the magnitude of channel change investigate the controls of flood induced geomorphic changes and measure the post flood response of the widened channel these analyses show that geomorphic changes included channel widening meander migration avulsions extensive bar formation and vertical floodplain accretion reach averaged channel widening between 26 and 52 occurred but in some localities exceeded 500 the degree and style of channel response was related but not limited to three factors 1 bed load supply and transport 2 pre flood channel plan form and 3 rapid declines in specific stream power downstream of constrictions and areas of high channel bed slope the post flood channel response has consisted of channel contraction through the aggradation of the channel bed and the formation of fine grained benches inset within the widened channel margins the most significant post flood geomorphic changes have occurred at and downstream from ephemeral tributaries that contribute large volumes of sediment

topographic hydraulic and vegetative controls on bar and island development in mixed bedrock alluvial multi channeled dryland rivers we investigate processes of bedrock core bar and island development in a bedrock influenced anastomosed reach of the sabie river kruger national park knp eastern south africa for sites subject to alluvial stripping during an extreme flood event 4470 5630 m3 s 1 in 2012 pre and post flood aerial photographs and lidar data 2d morphodynamic simulations and field observations reveal that the thickest surviving alluvial deposits tend to be located over bedrock topographic lows at a simulated peak discharge 4500 m3 s 1 most sediment sand fine gravel is mobile but localized deposition on bedrock topographic highs is possible at lower simulated discharges 1 000 m3 s 1 topographic highs are not submerged and deposition occurs in lower elevation areas particularly in areas disconnected from the main channels during falling stage field observations suggest that in addition to discharge rainwash between floods may redistribute sediments from bedrock topographic highs to lower elevation areas and also highlight the critical role of vegetation colonization in bar stability and in trapping of additional sediment and organics these findings challenge the assumptions of preferential deposition on topographic highs that underpin previous analyses of kruger national park river dynamics and are synthesized in a new conceptual model that demonstrates how initial bedrock topographic lows become topographic highs bedrock core bars and islands in the latter stages of sediment accumulation the model provides particular insight into the development of mixed bedrock alluvial anastomosing along the kruger national park rivers but similar processes of bar island development likely occur along numerous other bedrock influenced rivers across dryland southern africa and farther afield

the nahal oz reservoir dam break flood geomorphic impact on a small ephemeral loess channel in the semi arid negev desert israel abstract the nahal oz reservoir in the coastal semi arid southwestern israel was designed to enhance local irrigation of crops using reclaimed sewage water during the dry summer months on march 2001 part of the western dike of the reservoir was breached and generated a flow release of 3 5 106 m3 of secondary irrigation water that was channeled down the 1st order ephemeral loess stream nahal yare akh the consequent 12 hour flood surge with an estimated peak discharge of 1000 m3s 1 inflicted severe loess erosion agricultural property and infrastructural damage downstream 6 million post flood mapping documented the geomorphic response to the flood which included channel scour and widening along the initial 2 km downstream of the reservoir where a spillway channel was formed the increase in the cross sectional area was about 60 and had an estimated 170 000 m3 of sediment bed bank and floodplain erosion calculated maximum shear stress and stream power along this section are estimated at 300 nm 2 and 900 wm 2 respectively the peak discharge at the end of this segment was estimated at 800 m3s 1 indicating only minor attenuation along this segment two km downstream of the breach a wide braided fan indicated deposition of the eroded sediments at the end of this segment the floodwater diverged into several watercourses and inundated tilled agricultural fields and neighborhoods downstream 9 km from the reservoir the discharge attenuated to 100 m3s 1 slightly above bankfull further downstream and upon reaching the large shikma stream the flow was already very low this reduction in discharge is attributed to the anthropogenic infrastructure roads neighborhoods and agricultural fields and the large transmission losses typical of sandy ephemeral streams the study shows that channels within erodible materials respond to high peak discharges very locally erosional thresholds that severely incised the channel are only maintained for 2 km below the breached reservoir and as distance from the source area increases available energy is substantially reduced due to high transmission losses gentler valley gradients very wide shallow flow and the ability of the drainage network to accommodate large discharges consequently the geomorphic impact was limited to the first 2 6 km with only minor erosional or depositional evidence downstream the current natural flow regime has only minor impact on the newly formed channel geometry below the breached dam accordingly the channel geometry may be preserved for a relatively long time however channel recovery in this segment was rapid and within a few years all bare loess surfaces exposed during the flood have been covered by dense vegetation the analysis also shows that nahal oz reservoir s dam break flood transmission losses and flood attenuation rates were extreme in comparison to other case studies this artificial flood event in a desert environment offers a rare opportunity to quantify channel and bank erosion evolution processes during an extremely high magnitude flood within highly erodible fine sediment as well as to detect the recovery processes a few years later

dynamic single thread channels maintained by the interaction of flow and vegetation most rivers on earth today flow as a single channel in some cases with occasional islands and follow a more or less sinuous course however single thread channels have proven difficult to reproduce and study experimentally experimental self formed channels tend to widen and subdivide leading to a braided pattern cohesive sediment has been the main mechanism studied for stabilizing banks and producing a single thread channel we show how laboratory experiments using vegetation to stabilize banks can organize the flow and convert the planform morphology from braided to single thread our experimental strategy a repeated cycle of short periods of high water discharge alternating with longer periods of low discharge accompanied by plant seeding and growth leads to the evolution of a dynamic self maintaining single thread channel with well defined banks and floodplain by eliminating weak flow paths the vegetation corrals the water into a single dominant channel until the reduction in total wetted width leads to a new self organized state in which the flow removes vegetated area as fast as it is produced the new channel is deeper and has a broader distribution of depths than the braided one with channel size adjusted to carry almost all the flood flow the resulting system maintains a dynamic steady state via similar mechanisms to those that operate in meandering channels in the field specifically erosion at the outside of bends bend growth and bar development our methodology provides a basis for experimental development of self sustaining high amplitude meanders and has applications for river management and basic research purposes