surface based transport model for mixed size sediment we present a transport model for mixed sand gravel sediments fractional transport rates are referenced to the size distribution of the bed surface rather than subsurface making the model completely explicit and capable of predicting transient conditions the model is developed using a new data set of 48 coupled observations of flow transport and bed surface grain size using five different sediments the model incorporates a hiding function that resolves discrepancies observed among earlier hiding functions the model uses the full size distribution of the bed surface including sand and incorporates a nonlinear effect of sand content on gravel transport rate not included in previous models the model shares some common elements with two previous surface based transport models but differs in using the full surface size distribution and in that it is directly developed from a relatively comprehensive data set with unambiguous measurement of surface grain size over a range of flow transport rate and sediments

flood driven topographic changes in a gravel cobble river over segment reach and morphological unit scales regulated rivers generally incise below dams that cut off sediment supply but how that happens and what the consequences are at different spatial scales is poorly understood modern topographic mapping at meter scale resolution now enables investigation of the details of spatial processes in this study spatial segregation was applied to a meter scale raster map of topographic change from 1999 to 2008 on the gravel cobble regulated lower yuba river in california to answer specific scientific questions about how a decadal hydrograph that included a flood peak of 22 times bankfull discharge affected the river at segment reach and morphological unit scales the results show that the river preferentially eroded sediment from floodplains compared to the channel and this not only promoted valley wide sediment evacuation but also facilitated the renewal and differentiation of morphological units especially in the channel at the reach scale area of fill and mean net rate of elevational change were directly correlated with better connectivity between the channel and floodplain while the mean rate of scour in scour areas was influenced by the ratio of slope to bankfull froude number a ratio indicative of lateral migration versus vertical downcutting hierarchical segregation of topographic change rasters proved useful for understanding multiscalar geomorphic dynamics this article is protected by copyright all rights reserved

simple spatially distributed models for predicting flood inundation a review abstract in this paper we review recent progress in the use of reduced complexity models for predicting floodplain inundation we review the theoretical basis for modelling floodplain flow with simplified hydraulic treatments based on a dimensional analysis of the one dimensional shallow water equations we then review how such schemes can be applied in practice and consider issues of space discretization time discretization and model parameterisation before going on to consider model assessment procedures we show that a key advantage of reduced complexity codes is that they force modellers to think about the minimum process representation necessary to predict particular quantities and act as a check on any tendency to reductionism at the same time however the use compared to standard hydraulic codes of strong simplifying assumptions requires us to also address the question how simple can a model be and still be physically realistic we show that by making explicit this debate about acceptable levels of abstraction reduced complexity codes allow progress to be made in addressing a number of long standing debates in hydraulics

a conceptual model for determining soil erosion by water current estimates of rates of soil erosion by water derived from plots are incompatible with estimates of long term lowering of large drainage basins traditional arguments to reconcile these two disparate rates are awed the ux of sediment leaving a speci ed area cannot be converted to a yield simply by dividing by the area because there is no simple relationship between ux and area here we develop an approach to the determination of erosion rates that is based upon the entrainment rates and travel distances of individual particles the limited available empirical data is consistent with the predictions of this approach parameterization of the equations to take account of such factors as gradient and sediment supply is required to proceed from the conceptual framework to quantitative measurements of erosion however our conceptual model solves the apparent paradox of the sediment delivery ratio resolves recent discussion about the validity of erosion rates made using usle erosion plots and potentially can reconcile erosion rates with known lifespans of continents our results imply that previous estimates of soil erosion are fallacious copyright 2004 john wiley sons ltd

geomorphic mapping and taxonomy of fluvial landforms abstract fluvial geomorphologists use close to a 100 different terms to describe the landforms that make up riverscapes we identified 68 of these existing terms that describe truly distinctive landforms in which form is maintained under characteristic conditions and fluvial processes clear topographic definitions for these landforms to consistently identify and map them are lacking with the explosion of continuous high resolution topography and digital elevation models we have plenty of new basemaps in which these landforms are clearly visible but very few examples of manual or automated classification of fluvial landforms fluvial landforms are the building blocks of a river and are variously referred to as geomorphic units morphological units habitat units and channel units we present a tiered framework for describing geomorphic units with tier 1 differentiating units on the basis of their stage tier 2 separating shape e g concave convex or planar tier 3 using particular key attributes to narrow in on the likely specific geomorphic unit type and tier 4 differentiating those types on the basis of vegetative or roughness modifiers information on the assemblage and configuration of geomorphic units can be used to inform process based interpretations of the range of river behavior the accuracy and transferability of such analyses is fundamentally tied to the taxonomy we assign to these discrete building blocks in this paper we clarify the terminology and definitions relating to the identification and delineation of geomorphic units margins and structural elements we establish a set of procedures that can be used to manually map and identify these features the proposed framework provides a rigorous and repeatable approach to identification of topographically defined features of riverscapes we demonstrate the application of these systematic yet flexible procedures with a series of maps from rivers in differing valley settings

geomorphological records of extreme floods and their relationship to decadal scale climate change extreme rainfall and flood events in steep upland catchments leave geomorphological traces of their occurrence in the form of boulder berms debris cones and alluvial fans constraining the age of these features is critical to understanding i landscape evolution in response to past present and future climate changes and ii the magnitude frequency of extreme ungauged floods in small upland catchments this research focuses on the cambrian mountains of wales uk where lichenometric dating of geomorphological features and palaeohydrological reconstructions is combined with climatological data and documentary flood records our new data from wales highlight a distinct flood rich period between 1900 and 1960 similar to many other uk lichen dated records however this study sheds new light on the underlying climatic controls on upland flooding in small catchments although floods can occur in any season their timing is best explained by the summer north atlantic oscillation snao and shifts between negative wetter than average conditions with regular cyclonic flow and flooding and positive phases drier than average conditions with less frequent cyclonic flow and flooding which vary from individual summers to decadal and multidecadal periods recent wet summer weather flooding and boulder berm deposition in the uk 2007 2012 are related to a pronounced negative phase shift of the snao there is also increasing evidence that recent summer weather extremes in the mid latitudes may be related to arctic amplification and rapid sea ice loss if this is the case continuing and future climate change is likely to mean that i unusual weather patterns become more frequent and ii upland uk catchments will experience heightened flood risk and significant geomorphological changes

an historical look at the binghamton geomorphology symposium abstract the binghamton geomorphology symposium bgs is an annual meeting held since 1970 usually in the u s a on timely topics in the field of geomorphology a special issue of this journal presents the papers from each meeting and provides an opportunity to disseminate to the international community research relevant to that year s theme written by key people in that field in this paper we review the history of the bgs examine the academic disciplines of each year s organizers compile a list of the researchers who have made multiple contributions to bgs note the citation impact of papers published in the annual proceedings map the spatial distribution of the meeting locations and categorize the gender distribution of the contributors to the symposium contributions from female authors to the bgs have steadily increased since the 1970s however from 2003 to 2013 females still only accounted for 23 6 of the proceeding s papers an increase of 16 4 from the 1970s these numbers are not surprising when compared to the gender distribution of the top positions in specialty groups in the u s between 1989 and 2010 over 7000 citations were from articles published in bgs special issues indicating their contributions to the geomorphology field when normalized by the number of years the articles have been available papers from bgs whose themes combined geomorphology with other fields i e natural hazards and geomorphology rated higher numbers of citations the dispersion of the location of bgs meetings illustrates how the series is maturing by moving away from its origin in the u s northeast

coupling fluvial hydraulic models to predict gravel transport in spatially variable flows this study investigated spatial temporal variations of shear stress and bed load transport at three gravel bed river reaches of the williams fork river colorado a two dimensional flow model was used to compute spatial distributions of shear stress for four discharge levels between one third of bankfull qbf and qbf results indicate that mean values are highly variable among sites however the properties of the mean normalized distributions of are similar across sites for all flows the distributions of are then used with a transport function to compute bed load transport rates of individual grain size fractions probability distributions of the instantaneous unit width transport rates qb indicate that most of the bed load is transported through small portions of the bed with high the mean normalized probability distributions of qb are different among sites for all flows except at qbf when the distributions overlap we also find that the grain size distribution gsd of the bed load adjusts with discharge to resemble the grain size distribution of the subsurface at qbf we extend these results to 13 locations in the basin using the mean normalized distributions of shear stress and measured subsurface grain sizes to compute bed load transport rates at qbf we found a remarkably similar shape of the qb distribution among sites highlighting the basin wide balance between flow forces and gsd at qbf and the potential to predict sediment flux at the watershed scale

climate and surface properties hydrological response of small arid and semi arid watersheds abstract a positive relationship between annual rainfall and geomorphic processes runoff and erosion rates and environmental factors water regime soil and vegetation cover is often assumed for arid and semi arid areas with an annual rainfall in the range of 100 300 mm this assumption disregards the fact that changes along a climatic gradient at desert margins are not limited to purely climatic factors they are often accompanied by a parallel change in surface properties especially the relative extent of rocky or soil covered surfaces that differ greatly in their response to rainfall this raises the issue whether the change in surface properties along a climatic gradient enhances the assumed positive effects of rainfall increase or limits it the hypothesis advanced in this paper is that runoff generation and rate in arid and semi arid areas are primarily controlled by surface properties rather than by the absolute amounts of storm and annual rain amounts hydrological data collected at two instrumented watersheds located one in an arid rocky area and the second in a semi arid soil covered area support this hypothesis the implications of data obtained for runoff generation and flow continuity under changing climatic conditions are analyzed they point to the fact that the same regional climatic change may have different and even opposite effects on the hydrological response of different adjoining surface units this response is expected to be strongly controlled by the specific local surface conditions that prevailed in the area prior to the climatic change

sediment supply grain protrusion and bedload transport in mountain streams 1 steep streams occupy a large fraction of mountainous drainage basins and partially control the sediment supplied to downstream rivers in these channels sediment transport equations typically over predict bedload flux by several orders of magnitude because they do not account for sediment supply limited conditions thus accurate predictions of bedload flux require an estimate of the sediment available for transport in a given event we demonstrate through field measurements that boulder step protrusion is a proxy for sediment availability protrusion is also a function of the time elapsed since an extreme event and this simple relationship can be used to estimate the relative sediment availability at any given time in addition bedload transport predictions in a steep channel were only accurate if they included this variable protrusion predictions of sedimentation hazards water quality river restoration success long term channel network evolution and channel stability may therefore require estimates of sediment availability for transport

acfer 182 search for the location of15n enriched nitrogen in an unusual chondrite abstract acfer 182 an unusual chondrite recovered from the sahara in 1990 is highly enriched in 15 n bulk 15 n ca 600 15 n max 1584 at 900 c reinforcing conclusions that it is related to the very unusual chondrite alh 85085 stepped combustion of whole rock acfer 182 releases 15 n over a wide temperature range excluding a single carrier phase for the 15 n enriched nitrogen the highest relative abundance of 15 n is found in phase n c so far unidentified mineralogically with a c n of ca 8 which releases its nitrogen on combustion of the whole rock at 850 950 c attempts to isolate n c by physical means proved unsuccessful hence a chemical treatment was tried with preparation of an hf hcl resistant residue approximately two thirds of the original amount of nitrogen in the sample was lost on dissolution almost all of component n a the carbonaceous component was removed without significant change in 15 n 950 or c n ratio 75 n b originally thought to be nitrogen in metal was unchanged in abundance 15 n 500 and c n ratio ca 20 indicating that it could not be present in metal unless as an insoluble nitride it might even be an isotopically light entity mixing with residual n a and n c this last component now combusted at a lower temperature than in the whole rock and has a lower 15 n value 1274 a fourth minor component n d is revealed on combustion of the residue which burns above 675 c with 15 n ca 1000 and c n ratio ca 50 the 15 n enriched nitrogen in almost all constituents of acfer 182 is interpreted as emanating from a single source i e interstellar grains which were incorporated within the acfer 182 parent body during aggregation vaporisation condensation and mixing of components caused redistribution of 15 n enriched nitrogen throughout the parent with nitrogen either trapped or implanted into silicates and metal

sediment transport in a large impounded river the lower ebro ne iberian peninsula abstract the sediment transport of the highly regulated lower ebro river is estimated on the basis of a measuring programme carried out between 2002 and 2004 total sediment transport including both suspended load and bedload was measured upstream and downstream from the mequinenza and riba roja reservoirs with special attention to the transport during floods annual total load upstream from the dams is estimated at around 1 64 106 t of which at least 99 is transported in suspension annual total load downstream from the dams is estimated at around 0 45 106 t of which 60 is transported in suspension and the remaining 40 as bedload mean d50 bl in the range of 32 mm total load represents 3 of what was transported at the beginning of the 20th century in the delta plain sediment yield is three to four times lower below the dams a fact that is caused by the trapping of sediment within the reservoirs around 90 in the case of suspended sediment and 100 in the case of bedload as a consequence sediment that is transported downstream from the dams is all entrained from the riverbed and eroded from the banks the sediment deficit causes a mean riverbed incision of 30 mm per year as estimated from bedload measurements and by means of scour chains and painted pebbles located between the lowermost dam and the measuring section 28 km downstream since floods have been reduced on average by 25 but sediment supply from upstream has been reduced to almost nothing the river channel of the lower ebro river will continue exporting sediment both during floods 2000 m3 s mostly bedload and frequent high flows 1000 m3 s to 2000 m3 s making the incision progressive unless restoration steps are taken

a lagrangian framework for exploring complexities of mixed size sediment transport in gravel bedded river networks abstract the movement of sediment from source to sink in a watershed is a complex process with multiple interactions and feedbacks across scales at small scales the size characteristics of a sediment mixture affect the transport of that sediment through hiding and through the nonlinear effect of sand content on gravel transport at large scales the channel network itself through network geometry and the spatial pattern of transport capacity adds additional complexity in organizing sediment moving through the system such that aggradational hotspots can emerge the purpose of this paper is to present a lagrangian framework for exploring complexities of mixed size sediment transport in gravel bedded river networks the present model builds off of previous network based bed material sediment transport models but key advancements presented herein i allow for a mixture of sediment sizes in the river network ii incorporate a mixed size sediment transport equation and iii utilize a daily flow hydrograph to drive intermittent transport the model is applied to the roughly 4700 km2 methow river basin in washington state usa using simplified model inputs with the goal of illustrating the utility of the model for motivating future work

do deterministic sediment detachment and transport equations adequately represent the process interactions in eroding rills an experimental field study abstract this paper tackles two main questions by linking observations determination of hydraulic parameters and measurement of sediment transport with the formulae used in soil erosion models first do constant shear stress values in different rills with constant soil parameters result in the same soil detachment values secondly deterministic soil erosion models make the assumption that there is a relationship often further assumed to be linear between shear stress and soil detachment is this suitable for representing real erosion process combinations in natural rills following most process based deterministic soil erosion models derived hydraulic and erosion parameters should be similar however the results from the different experiments showed clear differences in sediment concentration transport rates and other measured as well as calculated values in contrast to our experimental results a model simulation would produce erosion parameters with low variations represented by the relative measurement error and the empirical variation coefficient this reveals the general problems of using process based deterministic models for erosion in shallow rills while soil erosion models simulate the processes resulting from the shear forces of flowing water on the soil surface other processes like side wall failure headcut retreat and plunge pool dynamics are not taken into account our results suggested that these other processes may contribute substantially to rill erosion processes the results of this study strongly suggested that the model concept of most physical based soil erosion models is inadequate for modeling rill erosion processes measured total rill erosion rates were the sum of erosion rates caused by a combination of different soil erosion processes with different spatial and temporal distribution this combination cannot be described by a single equation

grain growth in polar ice i theory many observations regarding grain growth in ice sheets are glaciologically interesting but imperfectly understood here we develop the theory of grain growth in ice that is not deforming rapidly and in the succeeding paper we use this theory to explain observations from glacial ice in the absence of significant strain energy the driving force for grain growth arises from grain boundary curvature grain growth is slowed by the interaction of grain boundaries with extrinsic materials microparticles bubbles and dissolved impurities if the driving force for growth is not large enough to cause boundaries to separate from an extrinsic material then the grain boundary velocity is determined by the velocity characteristic of the extrinsic material low velocity regime if the driving force is large enough to cause separation then boundaries migrate more rapidly than the extrinsic material high velocity regime but the net driving force is reduced through transient pinning by the extrinsic material polar ice is typically in the low velocity regime relative to dissolved impurities and the high velocity regime relative to microparticles and bubbles cross sectional area of grains is predicted to increase linearly with time under most but not all circumstances

holocene paleofloods related to climatic events in the upper reaches of the hanjiang river valley middle yangtze river basin china abstract holocene slackwater deposits along the river channels were used to study the magnitude and frequency of the paleofloods that occurred prior to gaged and historical data sets all over the world paleoflood hydrological investigations were carried out in the upper reaches of the hanjiang river china four bedsets of paleoflood slackwater deposits were found interbedded in the holocene loess soil sequence within the cliff riverbanks they were studied by field observations and laboratory analysis including magnetic susceptibility particle size distribution and optically stimulated luminescence osl dating these provide a complete catalog of holocene flood events at a watershed scale that is very important in understanding the regional hydrological response to monsoonal climatic change four episodes of holocene overbank flooding have been recorded over the basin these hydroclimatic events were dated to 8500 8400 4200 4000 3200 2800 and 1800 1700 ybp by using the osl method in combination with pedostratigraphic correlations with the previously studied holocene pedostratigraphy in the hanjiang river basin the peak discharges of these flood episodes vary in a range from 26 610 to 47 900 m 3 s 1 as estimated by using the slope area method of streamflow measurement these flood events are therefore considered a regional expression of known climatic events and demonstrate holocene climatic instability the study provides a solid reference that magnitudes and recurrence frequencies of floods are highly sensitive to climate change in the monsoonal zone in other parts of the world

channel bed mobility response to extreme sediment loading at mount pinatubo since the 1991 eruption of mount pinatubo the specific sediment yields from watersheds draining its slopes have been the highest ever recorded in spite of this overwhelming sediment load rivers inundated by pyroclastic flow deposits delivered almost half of the initial deposits to downslope alluvial and or debris fans by 1996 although most of this transport occurred by hyperconcentrated flows and debris flows lahars very high sediment transport rates also characterize low flow measured flow velocities and depths channel properties and the size of both mobile and stable clasts in the sacobia and pasig potrero rivers indicate median bed surface grain sizes of 2 to 8 mm grain size independent dimensionless critical shear stresses c of 0 016 to 0 041 and manning s n values of 0 017 to 0 024 values well below those previously reported for steep mountain channels the dramatic bed surface fining bed mobility and selective transport in these extremely sediment rich channels indicate that changes in grain size c values and bed roughness can increase transport capacity in response to high sediment supply our observations also suggest viewing the apparently contradictory concepts of an equal threshold of bed mobility and grain size dependent selective transport as end member concepts that apply to channels with low or intermittent and high or continuous sediment supply respectively

fabrics in polar ice sheets development and prediction fabrics in polar ice sheets provide a record of deformational history and control the viscosity of ice during further deformation they affect geophysical sensing of ice sheets and provide an accessible analogue to fabric development during deformation of other geological and engineering materials a new synthesis of experimental and theoretical results shows that c axis fabrics are quantitatively related to cumulative strain and stress state in ice sheets for the full range of likely flow patterns basal shear divergent flow and parallel flow cause c axes to rotate toward the vertical axis whereas convergent flow causes c axes to rotate toward a vertical plane transverse to flow

the impact of humans on continental erosion and sedimentation rock uplift and erosional denudation of orogenic belts have long been the most impor tant geologic processes that serve to shape continental surfaces but the rate of geomor phic change resulting from these natural phe nomena has now been outstripped by human activities associated with agriculture con struction and mining although humans are now the most important geomorphic agent on the planet s surface natural and anthro pogenic processes serve to modify quite dif ferent parts of earth s landscape in order to better understand the impact of humans on continental erosion we have examined both long term and short term data on rates of sediment transfer in response to glacio fl u vial and anthropogenic processes phanerozoic rates of subaerial denuda tion inferred from preserved volumes of sedimentary rock require a mean conti nental erosion rate on the order of 16 m per million years m m y resulting in the accumulation of 5 gigatons of sediment per year gt yr erosion irregularly increased over the 542 m y span of phanerozoic time to a pliocene value of 53 m m y 16 gt yr current estimates of large river sediment loads are similar to this late neogene value and require net denudation of ice free land surfaces at a rate of 62 m m y 21 gt yr consideration of the variation in large river sediment loads and the geomorphology of respective river basin catchments suggests that natural erosion is primarily confi ned to drainage headwaters 83 of the global river sediment fl ux is derived from the high est 10 of earth s surface subaerial erosion as a result of human activity primarily through agricultural practices has resulted in a sharp increase in net rates of continental denudation although less well constrained than estimates based on surviving rock volumes or current river loads available data suggest that present farmland denudation is proceeding at a rate of 600 m m y 75 gt yr and is largely confi ned to the lower elevations of earth s land surface primarily along passive continental margins 83 of cropland erosion occurs over the lower 65 of earth s surface the conspicuous disparity between natu ral sediment fl uxes suggested by data on rock volumes and river loads 21 gt yr and anthropogenic fl uxes inferred from measured and modeled cropland soil losses 75 gt yr is readily resolved by data on thicknesses and ages of alluvial sediment that has been deposited immediately downslope from erod ing croplands over the history of human agriculture accumulation of postsettlement alluvium on higher order tributary channels and fl oodplains mean rate 12 600 m m y is the most important geomorphic process in terms of the erosion and deposition of sedi ment that is currently shaping the landscape of earth it far exceeds even the impact of pleistocene continental glaciers or the cur rent impact of alpine erosion by glacial and or fl uvial processes conversely available data suggest that since 1961 global cropland area has increased by 11 while the global population has approximately doubled the net effect of both changes is that per capita cropland area has decreased by 44 over this same time interval 1 per year this is 25 times the rate of soil area loss antici pated from human denudation of cropland surfaces in a context of per capita food pro duction soil loss through cropland erosion is largely insignifi cant when compared to the impact of population growth

the concept of transport capacity in geomorphology the notion of sediment transport capacity has been engrained in geomorphological and related literature for over 50 years although its earliest roots date back explicitly to gilbert in fluvial geomorphology in the 1870s and implicitly to eighteenth to nineteenth century developments in engineering despite cross fertilization between different process domains there seem to have been independent inventions of the idea in aeolian geomorphology by bagnold in the 1930s and in hillslope studies by ellison in the 1940s here we review the invention and development of the idea of transport capacity in the fluvial aeolian coastal hillslope debris flow and glacial process domains as these various developments have occurred different definitions have been used which makes it both a difficult concept to test and one that may lead to poor communications between those working in different domains of geomorphology we argue that the original relation between the power of a flow and its ability to transport sediment can be challenged for three reasons first as sediment becomes entrained in a flow the nature of the flow changes and so it is unreasonable to link the capacity of the water or wind only to the ability of the fluid to move sediment secondly environmental sediment transport is complicated and the range of processes involved in most movements means that simple relationships are unlikely to hold not least because the movement of sediment often changes the substrate which in turn affects the flow conditions thirdly the inherently stochastic nature of sediment transport means that any capacity relationships do not scale either in time or in space consequently new theories of sediment transport are needed to improve understanding and prediction and to guide measurement and management of all geomorphic systems

experimental study on the process of neck cutoff and channel adjustment in a highly sinuous meander under constant discharges abstract neck cutoff is an essential process limiting evolution of meandering rivers in particular the highly sinuous ones yet this process is extremely difficult to replicate in laboratory flumes here we reproduced this process in a laboratory flume by reducing at the 1 2500 scale the current planform of the qigongling bend centerline length 13 km channel width 1 2 km and neck width 0 55 km in the middle yangtze river with geometric similarity in five runs with different constant input discharges hydraulic parameters water depth surface velocity and slope bank line changes and riverbed topography were measured by flow meter and point gauges and bank line migration and a neck cutoff process were captured by six overhead cameras mounted atop the flume by analyzing the neck cutoff process development of the cutoff channel and adjustment of the old channel to cutoff we found that i bank erosion around the upstream and downstream channel segments of the neck reduced its distance subsequently increased water head gradient on both sides of the neck inducing the occurrence of neck cutoff in a short time period ii the width of the new cutoff channel increased quickly after neck cutoff because the increased local slope generated a higher unit stream power in the cutoff channel and iii neck cutoff significantly increased bank erosion and channel widening in upstream and downstream channels as it is a gradual process compared with chute cutoff these results suggest that bank revetment around the qigongling bend might be necessary to prevent the abrupt occurrence of natural neck cutoff in the future

large scale dam removal on the elwha river washington usa source to sink sediment budget and synthesis abstract understanding landscape responses to sediment supply changes constitutes a fundamental part of many problems in geomorphology but opportunities to study such processes at field scales are rare the phased removal of two large dams on the elwha river washington exposed 21 3 million m3 or 30 million tonnes t of sediment that had been deposited in the two former reservoirs allowing a comprehensive investigation of watershed and coastal responses to a substantial increase in sediment supply here we provide a source to sink sediment budget of this sediment release during the first two years of the project september 2011 september 2013 and synthesize the geomorphic changes that occurred to downstream fluvial and coastal landforms owing to the phased removal of each dam the release of sediment to the river was a function of the amount of dam structure removed the progradation of reservoir delta sediments exposure of more cohesive lakebed sediment and the hydrologic conditions of the river the greatest downstream geomorphic effects were observed after water bodies of both reservoirs were fully drained and fine silt and clay and coarse sand and gravel sediments were spilling past the former dam sites after both dams were spilling fine and coarse sediments river suspended sediment concentrations were commonly several thousand mg l with 50 sand during moderate and high river flow at the same time a sand and gravel sediment wave dispersed down the river channel filling channel pools and floodplain channels aggrading much of the river channel by 1 m reducing river channel sediment grain sizes by 16 fold and depositing 2 2 million m3 of sand and gravel on the seafloor offshore of the river mouth the total sediment budget during the first two years revealed that the vast majority 90 of the sediment released from the former reservoirs to the river passed through the fluvial system and was discharged to the coastal waters where slightly less than half of the sediment was deposited in the river mouth delta although most of the measured fluvial and coastal deposition was sand sized and coarser 0 063 mm significant mud deposition was observed in and around the mainstem river channel and on the seafloor woody debris ranging from millimeter size particles to old growth trees and stumps was also introduced to fluvial and coastal landforms during the dam removals at the end of our two year study elwha dam was completely removed glines canyon dam had been 75 removed full removal was completed 2014 and 65 of the combined reservoir sediment masses including 8 mt of fine grained and 12 mt of coarse grained sediment remained within the former reservoirs reservoir sediment will continue to be released to the elwha river following our two year study owing to a 16 m base level drop during the final removal of glines canyon dam and to erosion from floods with larger magnitudes than occurred during our study comparisons with a geomorphic synthesis of small dam removals suggest that the rate of sediment erosion as a percent of storage was greater in the elwha river during the first two years of the project than in the other systems comparisons with other pacific northwest dam removals suggest that these steep high energy rivers have enough stream power to export volumes of sediment deposited over several decades in only months to a few years these results should assist with predicting and characterizing landscape responses to future dam removals and other perturbations to fluvial and coastal sediment budgets

spatial and temporal patterns of off slope sediment delivery for small catchments subject to shallow landslides within the waipaoa catchment new zealand abstract the waipaoa catchment in new zealand has one of the highest measured specific suspended sediment yields measured in new zealand compared to basins of comparable size a significant source of this sediment is from shallow landslides which are often triggered on a regional scale during large magnitude storm events defined as 200 mm rainfall within 72 h the first step of this sediment cascade is removal of landslide material from the slope and into the fluvial system when the debris tail is in physical contact and hence considered connected the difference between the volume of sediment liberated in the event and the volume remaining on the slope immediately following the event is termed the off slope sediment delivery ratio this value ranged from 0 12 to 0 28 for small sub catchments within the waipaoa catchment depending on catchment morphology landslide and triggering event characteristics in the waipaoa catchment a decrease in the catchment sediment delivery ratio is observed as the sub catchment size increased a human induced process which may affect off slope sediment delivery is regolith exhaustion as scars move further upslope in response to removal of preferred weathered material during previous events on the lower sections of slope however it appears that temporal scar migration away from the channels is not prevalent therefore the hypothesis that hillslope relaxation since deforestation is prevalent in this setting is considered null rather the temporal pattern to sediment delivery ratios supports the context of evolving catchment in response to deforestation in the terrain event resistance model

grain growth in polar ice ii application grain growth observed in polar ice that is not deforming rapidly can be accounted for if concentrations and distributions of extrinsic materials microparticles bubbles and dissolved impurities are characterized fully dissolved impurities segregate to grain boundaries and slow grain growth in all cold glacial ice the high concentration of soluble impurities in wisconsinan ice from the dome c antarctica ice core and perhaps other ice cores probably causes the small grain sizes observed in that ice microparticles have little effect on grain growth in ordinary ice in ice layers that appear dirty owing to concentrations of volcanic tephra such as in the byrd station antarctica ice core or of morainal material micro particles reduce grain growth rates significantly the relatively high vapor pressure of ice allows rapid growth and high mobility of intergranular necks so grain growth in firn is limited by boundary migration rather than by neck growth bubbles formed by pore close off at the firn ice transition are less mobile than grain boundaries causing bubble boundary separation whenever geometric constraints are satisfied however such separation reduces grain growth rates by only about 10 the observed linear increase of grain area with time is thus predicted by theory but the growth rate depends on soluble impurity concentrations as well as on temperature

can magic sand cause massive degradation of a gravel bed river at the decadal scale shi ting river china abstract massive bed degradation 20 m in 7 years has been observed in the shi ting river sichuan province china since the 2008 wenchuan ms 8 0 earthquake the reason for the massive bed degradation has not been well understood a hypothesis has been proposed that relates bed degradation to the augmentation of sand supply after the earthquake the effect of sand on gravel mobility magic sand effect has long been observed in laboratory experiments in this paper we study whether the augmentation of sand supply and its magic sand effect can lead to the observed massive degradation at decadal scales a one dimensional river morphodynamic model is implemented to study the problem in general at field scale and in context of the gravel bed shi ting river sediment transport is calculated with the wilcock and crowe 2003 relation in which the magic sand effect is explicitly embedded in terms of a function relating reference shields number to the surface sand fraction we find that the augmentation of gravel supply leads to bed aggradation whereas the augmentation of sand supply can indeed lead to bed degradation and surface fining the magnitude and timescale of bed degradation are not sensitive to the sand supply rate but are sensitive to the flood intermittency factor i e the fraction of time the river is in flood however an unrealistic flood intermittency factor 0 3 would be required in order to match the observed timescale of bed degradation thus indicating that the magic sand effect might not be the governing reason for massive bed degradation in the shi ting river and by implication in gravel bed rivers in general our simulation results also indicate that despite the fact that magic sand effects are not explicitly included in most sediment transport relations they are at least partly built in via the hiding function that is contained in most sediment transport relations for gravel sand mixtures while here we use the shi ting river as an example our results have applicability to gravel bed rivers subjected to augmentation in sand supply in general

flow law hypotheses for ice sheet modeling ice flow modeling requires a flow law relating strain rates to stresses in situ but a flow law cannot be measured directly in ice sheets microscopic processes such as dislocation glide and boundary diffusion control both the flow law for ice and the development of physical properties such as grain size and c axis fabric these microscopic processes can be inferred from observations of the physical properties and the flow law can then be estimated from the microscopic processes a review of available literature shows that this approach can be imperfectly successful interior regions of large ice sheets probably have depth varying flow law constants with the stress exponent n for power law creep less than 3 in upper regions and equal to 3 only in deep ice n probably equals 3 through most of the thickness of ice shelves and ice streams

effective timescales of coupling within fluvial systems this paper presents a review of the coupling concept in fluvial geomorphology based mainly on previously published work coupling mechanisms link the components of the fluvial system controlling sediment transport down the system and the propagation of the effects of base level change up the system they can be viewed at several scales at the local scale involving within hillslope coupling hillslope to channel coupling and within channels tributary junction and reach to reach coupling at larger scales coupling can be considered as zonal coupling between major zones of the system or as regional coupling relating to complete drainage basins these trends are illustrated particularly by the examples of hillslope to channel coupling in the howgill fells northwest england badland systems in southeast spain alluvial fans in spain usa and uae and base level induced dissection of neogene sedimentary basins in southeast spain as the spatial scales increase so do the timescales involved effective temporal scales relate to magnitude and frequency characteristics recovery time and propagation time the relative importance changing with the spatial scale for downsystem coupling at the local scale the first two are important with propagation time increasing in importance in larger systems especially in those involving upsystem coupling related to base level change the effective timescales range from the individual event with a return period of decades through decadal to century timescales for downsystem coupling to tens to hundreds of thousands of years for the basinwide response to base level change the effective timescales influence the relative importance of factors controlling landform development

superplasticity owing to grain growth in polar ices on considere le grossissement des grains de la glace depuis la surface jusqu a plusieurs centaines de metres de profondeur l augmentation de la taille avec leur ge est due a l energie libre des joints de grains cette migration continue des joints de grains semble etre un processus d accommodation beaucoup plus efficace que les processus de diffusion pour le glissement au joints de grains de faibles viscosites devraient resulter de cette deformation superplastique localement heterogene

sediment connectivity a framework for understanding sediment transfer at multiple scales a major challenge for geomorphologists is to scale up small magnitude processes to produce landscape form yet existing approaches have been found to be severely limited new ways to scale erosion and transfer of sediment are thus needed this paper evaluates the concept of sediment connectivity as a framework for understanding processes involved in sediment transfer across multiple scales we propose that the concept of sediment connectivity can be used to explain the connected transfer of sediment from a source to a sink in a catchment and movement of sediment between different zones within a catchment over hillslopes between hillslopes and channels and within channels using fluvial systems as an example we explore four scenarios of sediment connectivity which represent end members of behaviour from fully linked to fully unlinked hydrological and sediment connectivity sediment travel distance when combined with an entrainment parameter reflecting the frequency magnitude response of the system maps onto these end members providing a coherent conceptual model for the upscaling of erosion predictions this conceptual model could be readily expanded to other process domains to provide a more comprehensive underpinning of landscape evolution models thus further research on the controls and dynamics of travel distances under different modes of transport is fundamental copyright 2014 john wiley sons ltd

crystalline texture of the 2083 m ice core at vostok station antarctica crystalline texture and c axis orien tation of the 2083 m ice core at vostok station covering more than 150 kyear reveal the existence of strong anisotropies changes in crystal size with depth are compatible with the growth of grains driven by the free energy of grain boundaries a smaller growth rate appears to be associated with cold periods a gradual increase in the horizontal elongation of grains was observed between 350 and 680 m but the mean value of the coefficient of the linear dimensional orientation of grains does not cha nge below 700 m the e axis orientation of ice grains tends to orientate perpendicular to the direction of the elongation of grains forming a vertical girdle patt ern this charac teristic fabric has been interpreted as resulting from the gradual rotation of grains by basal glide under uniaxial longit udi nal tension the rotation of grains was calcu lated with respect to the total strain simulating the form ation of the girdle fabric pattern the fabric enhance ment factor was calculated at various depths it appears that vostok ice hardens gradua lly