geomorphological significance of at many stations hydraulic geometry the critically important at a station hydraulic geometry ahg relationships relate hydraulic variables depth width or velocity to discharge in power law form the recently discovered at many stations hydraulic geometry amhg states that ahg exponents and coefficients are strongly correlated removing one parameter and lending amhgs to remote sensing discharge estimation despite the excitement there is an urgent need to clarify amhg s geomorphological significance for different hydraulic variables using data from 57 rivers in the u s and perturbation experiments we show that the width amhg is weak arising mainly from the mathematical construct involving the exponent in both the regressor and the regressand in contrast the depth amhgs result from geomorphological coevolution the similar time mean condition as argued for in the literature is sufficient but not necessary for rating curve convergence and in turn amhg for depth and velocity the predictive accuracy of amhgs whose coefficient of determination is unit dependent is similar to the flow percentile based downstream hydraulic geometry

effects of hydraulic roughness on surface textures of gravel bed rivers field studies of forest gravel bed rivers in northwestern washington and southeastern alaska demonstrate that bed surface grain size is responsive to hydraulic roughness caused by bank irregularities bars and wood debris we evaluate textural response by comparing reach average median grain size d50 to that predicted from the total bank full boundary shear stress t0 bf representing a hypothetical reference condition of low hydraulic roughness for a given t0 bf channels with progressively greater hydraulic roughness have systematically finer bed surfaces presumably due to reduced bed shear stress resulting in lower channel competence and diminished bed load transport capacity both of which promote textural fining in channels with significant hydraulic roughness observed values of d50 can be up to 90 smaller than those predicted from t 0 bf we find that wood debris plays an important role at our study sites not only providing hydraulic roughness but also influencing pool spacing frequency of textural patches and the amplitude and wavelength of bank and bar topography and their consequent roughness our observations also have biological implications we find that textural fining due to hydraulic roughness can create usable salmonid spawning gravels in channels that otherwise would be too coarse

glacially induced organization of channel reach morphology in mountain streams 1 we examine the spatial distribution of channel reach morphologies in formerly glaciated mountain drainage basins of coastal british columbia canada using field and geographic information systems derived data we show that the local channel slope and the degree of colluvial alluvial coupling imposed by the glacial valley morphology dictate the spatial organization of channel types in particular the complex glacially induced channel long profile produces characteristic sequences of channel reaches that depart from the downstream succession colluvial boulder cascade step pool rapids riffle pool distinctive of simple unglaciated mountain streams typically the presence of one hanging valley in the river long profile produces and separates two full successions of channel types a headmost one characterized by an ephemeral seasonal hydrologic regime and a downstream one where water runoff is perennial we document that channel types are well separated in plots of slope versus shear stress area versus shear stress and slope versus relative roughness in agreement with these outcomes multivariate discriminant analyses coupled with principal component analysis of 98 study reaches yield a highly successful channel type classification when slope shear stress and relative roughness are considered success rates depending on whether or not boulder cascade reaches are pooled together with step pools are 88 and 75 respectively previous work in unglaciated settings has suggested that mountain channels have distinct bed morphology states that vary primarily with slope our study reveals that even in formerly glaciated valleys where slope is largely inherited from glacial times these distinct bed states exist and vary mostly with slope adding considerable strength to this empirical knowledge

the hydrology and long term geomorphic significance of a flash flood in the cairngorm mountains scotland abstract on the 4th august 1978 a major flash flood occurred on the allt mor a mountain torrent within the cairngorm massif scotland this paper assesses the flood s immediate geomorphic impact as well as its longer term geomorphic significance in terms of slope and valley floor development the hydrometeorological characteristics of the flood are reconstructed and placed in the context of the catchment s flood hisotory in magnitudefrequency terms the dominant geomorphic processes in this environment are floods which occur several times a century the specific response of the allt mor to such floods varies spatially across the catchment the major impact being recorded in the entrenched and channel reaches also significant are the sequence and inter arrival times of floods of differing magnitudes the high thresholds for channel and slope adjustment and the nature of the coupling between slope and channel systems the results confirm and strengthen the findings reported from other sites in upland britain

freezing of ridges and water networks preserves the gamburtsev subglacial mountains for millions of years once an ice sheet grows beyond a critical thickness the basal thermal regime favors melting and development of subglacial water networks subglacial water is necessary for bedrock erosion but the exact mechanisms that lead to preservation of subglacial topography are unclear here we resolve the freezing mechanisms that lead to long term high altitude preservation across the gamburtsev subglacial mountains in east antarctica analyses of a comprehensive geophysical data set reveal a large scale water network along valley floors the ice sheet often drives subglacial water up steep topography where it freezes along high ridges beneath thinner ice statistical tests of hypsometry show the gamburtsevs resemble younger midlatitude mountains indicating exceptional preservation we conclude that the gamburtsevs have been shielded from erosion since the latest eocene 34 ma these freezing mechanisms likely account for the spatial and temporal patterns of erosion and preservation seen in other glaciated mountain ranges

pattern of deglaciation of the last late devensian scottish ice sheet evidence from ice marginal deposits in the dee valley northeast scotland the mode of deglaciation of the last scottish ice sheet is assessed from evidence provided by geomorphological mapping and sedimentology ice marginal deposits in the dee valley have a distinctive morphological expression and a characteristically varied sedimentology that strongly resembles those from subpolar glaciers the deposits tend to occur in certain topographic situations which can be accounted for by compression of ice near the margin and formation of an ice cored supraglacial land system a series of recessional stages of the ice front can be mapped demonstrating that active retreat occurred however additional evidence shows there was probably a thin marginal zone of stagnant ice recessional stages are inferred to be stillstands that are considered to be topographically controlled rather than related to climate development of the supraglacial land system during deglaciation suggests that the ice sheet had a polythermal basal regime with a cold based margin this implies that deglaciation took place in northeast scotland while the climate remained cold probably due to a precipitation deficit which agrees well with chronostratigraphic data

shallow shelf approximation as a sliding law in a thermomechanically coupled ice sheet model 1 the shallow shelf approximation a balance of membrane stresses for ice flow is an effective sliding law for ice sheet modeling our use of it as a sliding law becomes a standard model for ice stream flow when the sliding velocity is large 100 m a 1 and faster following schoof 2006a we describe the basal resistance as plastic till for which the yield stress is given by a mohr coulomb formula pore water pressure is related to basal melt rate the velocity field used in the mass continuity and conservation of energy equations is an average of velocities from the shallow shelf approximation and the nonsliding shallow ice approximation using this scheme our model has realistic time dependent ice streams which exhibit the range of surface velocities seen in actual ice streams we demonstrate the model at high spatial resolution 5 km grid over multiple millenia using its implementation in the parallel ice sheet model numerical experiments show that the entire scheme is stable with respect to many parameter changes some experiments reveal significant ice stream variability in a hypothetical steady climate with characteristic cycles on the order of 1000 years we believe this is the first practical whole ice sheet model with a unified treatment of vertical shear stresses and membrane stresses it is capable of high resolution thermomechanically coupled multimillenia simulations of ice sheets containing ice streams

estimation of discharge from three braided rivers using synthetic aperture radar satellite imagery potential application to ungaged basins analysis of 41 ers 1 synthetic aperture radar images and simultaneous ground measurements of discharge for three large braided rivers indicates that the area of active flow on braided river floodplains is primarily a function of discharge a power law correlation is found between satellite derived effective width we and discharge q where we is the water surface area within a braided reach divided by the reach length synthetic values of we and q generated from a cellular automata model of stream braiding display a similar power law correlation power functions that are fit through plots of we and q represent satellite derived rating curves that can subsequently be used to estimate instantaneous river discharge from space with errors ranging from tens to hundreds of cubic meters per second for ungaged rivers changes in relative discharge can be determined from satellite data alone to determine the shape and timing of annual flows in glacierized basins absolute discharge can probably be estimated within a factor of 2 more accurate estimates will require either 1 one or more ground measurements of discharge acquired simultaneously with a satellite image acquisition or 2 successful parameterization of known morphologic controls such as total sinuosity 5 p valley slope bank material and stability and braid channel hydraulic geometry values of total sinuosity 5 p derived from satellite imagery and field measurements from two rivers of braid channel width depth velocity water surface slope and bed material grain size indicate that while the shape of satellite derived we q rating curves may be influenced by all of these variables the sensitivity of flow area to changing discharge is most dependent upon the degree of braiding efforts to monitor river discharge from space will be most successful for intensely braided rivers with high values of total sinuosity subsampling of existing daily discharge records from the iskut river suggests that satellite return times of about 1 week are sufficient for approximating the shape and timing of the seasonal hydrograph in large glacierized basins although errors are large the presented technique represents the only currently available way to estimate discharge in ungauged braided rivers

an evaluation of stream characteristics in glacial versus fluvial process domains in the colorado front range abstract many of the conceptual models developed for river networks emphasize progressive downstream trends in morphology and processes such models can fall short in describing the longitudinal variability associated with low order streams a more thorough understanding of the influence of local variability of process and form in low order stream channels is required to remotely and accurately predict channel geometry characteristics for management purposes and in this context designating process domains is useful we define process domains with respect to glacial versus fluvial valleys and lateral confinement of valley segments we evaluated local variability of process domains in the colorado front range by systematically following streams categorizing them into stream morphologic type and process domain and evaluating a number of channel geometry characteristics we evaluated 111 stream reaches for significant differences in channel geometry among stream types and process domains location and clustering of stream types on a slope drainage area s a plot and downstream hydraulic geometry relationships although individual channel geometry variables differed significantly between individual stream types in glacial and fluvial process domains no single channel geometry variable consistently differentiated all stream types between process domains hypothetical s a boundaries between bedrock and alluvial bed channels proposed in previous studies did not reliably divide bedrock and alluvial reaches for our study sites although downstream hydraulic geometry relationships are well defined using all reaches in the study area reaches in glacial valleys display much more variability in channel geometry characteristics than reaches in fluvial valleys less pronounced downstream hydraulic geometry relationships and greater scatter of reaches on an s a plot local spatial variability associated with process domains at the reach scale 10 1 10 3 m overrides progressive downstream relationships in low order mountain streams of the colorado front range

reach scale channel geometry of mountain streams abstract the basic patterns and processes of steep channels remain poorly known relative to lower gradient channels in this analysis characteristics of step pool plane bed and pool riffle channels are examined using a data set of 335 channel reaches from the western united states nepal new zealand and panama we analyzed differences among the three channel types with respect to hydraulics channel geometry boundary roughness and bedforms step pool channels have significantly steeper gradients coarser substrate higher values of shear stress and stream power for a given discharge and larger ratios of bedform amplitude wavelength h l pool riffle channels have greater width depth ratios and relative grain submergence r d84 than the other channel types plane bed channels tend to have intermediate values for most variables examined relative form submergence r h is statistically similar for step pool and pool riffle channels despite the lesser relative grain submergence and greater bedform amplitude of step pool channels mean values of darcy weisbach friction factor do not change in response to changes in relative grain submergence these patterns suggest that adjustments along mountain streams effectively maximize resistance to flow and minimize downstream variability in resistance among the different channel types

the importance of pressurized subglacial water in separation and sliding at the glacier bed l effet de l eau sous glaciaire sous pression sur le processus de glissement est examine a partir d un parametre appele indice de decollement du lit qui exprime les contraintes perpendiculaires au lit et la pression d eau les donnees proviennent de trois glaciers de formes differentes une loi puissance du type de weertman avec un exposant voisin de 3 modifiee pour tenir compte de l effet de la pression des eaux sous glaciaires apparait comme etant la meilleure

quantifying subglacial bed roughness in antarctica implications for ice sheet dynamics and history abstract glaciated landscapes consist of complex assemblages of landforms resulting from ice flow dynamic regimes and ice sheet history superimposed over and in turn modifying preglacial topography lithology and geological structure insights into the formation of glaciated landscapes can in principle be obtained by analysing modern ice sheet beds but terrain analyses beneath modern ice sheets are restricted by the inaccessibility of the bed it is however possible to quantify roughness the vertical variation of the subglacial interface with horizontal distance along two dimensional images of the bed obtained from radio echo sounding res here we collate several case studies from antarctica where roughness calculations have been used as a glaciological tool to infer basal processes and ice sheet history over large 500 km 2 areas we present two examples from west antarctica which demonstrate the utility of bed roughness in determining the presence and extent of subglacial sediments glacial dynamics and former ice sheet size we also present two examples from east antarctica which illustrate how roughness provides knowledge of ice sheet dynamics in the interior and pre quaternary ice sheet histories in modern ice sheet settings characterising bed roughness along res tracks has the twin advantages of being relatively simple to calculate while producing informative subsurface data and is especially powerful at furthering understanding when coupled with knowledge of ice flow from field satellite and modelling investigations the technique also offers significant potential for the comparison of modern and former ice sheet terrains contributing to an improved understanding of the formation and evolution of glaciated landscapes

bankfull width and morphological units in an alpine stream of the dolomites northern italy abstract this research examines variations in bankfull cross sections along a steep stream of the dolomites cordevole stream belluno northern italy field measurements were conducted to determine variations in the channel top width at bankfull stage in relation to the drainage area and to the length of the flow path after grouping the bed morphologies according to the montgomery and buffington montgomery d r buffington j m 1997 channel reach morphology in mountain drainage basins geol soc of am bull 109 5 596 611 classification we analyzed the increase in bankfull width for the dominant stream units cascades step pools isolated pools and colluvial reaches at the head of the basin we observed that the morphologies more related to the drainage area are colluvial reaches and pools the less adaptable are steps and cascades these differences likely result from the absence of lateral constriction in the colluvial reaches and pools whereas the presence of coarser sediments in the bed can affect the transverse adjustments in steps and reaches dominated by cascades linkages between cross section geometry and parameters related to flow i e drainage area and stream power have been analyzed together with the distribution of surface grain sizes and its coarsening pattern the existence of distinctive bankfull widths between different morphological units points out the degree of susceptibility to be modeled according to the channel slope reference diameter d90 and contributing area

evidence of a hydrological connection between the ice divide and ice sheet margin in the aurora subglacial basin east antarctica subglacial hydrology in east antarctica is poorly understood yet may be critical to the manner in which ice flows data from a new regional airborne geophysical survey icecap have transformed our understanding of the topography and glaciology associated with the 287 000 km2 aurora subglacial basin in east antarctica using these data in conjunction with numerical ice sheet modeling we present a suite of analyses that demonstrate the potential of the 1000 km long basin as a route for subglacial water drainage from the ice sheet interior to the ice sheet margin we present results from our analysis of basal topography bed roughness and radar power reflectance and from our modeling of ice sheet flow and basal ice temperatures although no clear cut subglacial lakes are found within the aurora basin itself dozens of lake like reflectors are observed that in conjunction with other results reported here support the hypothesis that the basin acts as a pathway allowing discharge from subglacial lakes near the dome c ice divide to reach the coast via the totten glacier

geomorphic and process domain controls on riparian zones in the colorado front range delineation of riparian zones along mountain streams is complicated by substantial longitudinal variability in gradient and valley geometry and the lack of a floodplain along many stream reaches we propose an approach to defining and delineating riparian zones based on site specific geomorphic features and process domains as well as the distribution of plant species we then 1 evaluate which basin scale elevation and drainage area and reach scale valley geometry gradient and channel width parameters correlate with riparian width along mountain streams in the colorado front range and 2 test a three parameter method for delineating the riparian edge using geomorphology hydrology and vegetation we identify four general process domains in the colorado front range based on valley geometry and elevation which reflect glacial history and hydroclimatology confined low elevation cl unconfined low elevation ul confined high elevation ch and unconfined high elevation uh we utilize process domains because we hypothesize that reach scale variables correlate more strongly than basin scale variables with riparian width the relationships between i connectedness a valley geometry metric describing the average absolute distance from the channel edge to the valley edge ii process domain and iii riparian width were evaluated using a multiple linear regression collectively these variables explained 86 of variability in field delineated riparian zone width reach scale processes exert a greater influence than longitudinally variable basin scale parameters on riparian width in the mountainous watersheds of the colorado front range with respect to the three parameter method hydrologic relationships are applicable when comparing by process domain allowing the stage associated with the riparian edge to be constrained between flow stages vegetation composition is significantly different for each of the four process domains and within each process domain vegetation is significantly similar within the geomorphically delineated riparian zone although vegetation composition commonly reflects geomorphic and hydrologic processes many plant species are relatively short lived and individual plants respond to local disturbances over short time scales consequently we recommend that the larger scale and longer duration riparian controllers hydrology and geomorphology be used to delineate riparian areas

channel geometry median grain size and stream power in small mountain streams abstract small mountain streams are typically affected by the same variables as larger counterparts but small headwater channels are also coupled with hillslopes the added degree of system complexity limits extension of existing conceptual and quantitative models of stream response to small mountain streams our objective is to determine how the presence of multiple lithologies on channel beds and coarse sediments affect relationships between channel geometry and driving and resisting variables in small mountain streams when the variables are examined at the landscape scale we test for systematic scaling of channel geometry stream power indices and median bed grain size d 50 in headwater streams draining 2 and overlying multiple strata on a passive continental margin field data were collected from 157 reaches in 32 watersheds local strata can be divided into a thick sequence of resistant sandstones and a thick sequence of low resistance calcareous siltstones and shales with interbedded limestones both stratigraphic units are present in every watershed and all streams carry abundant coarse bed load derived from the resistant unit mean widths and gradients of the channels are correlated with upstream drainage area unit stream power is not statistically different as a function of rock unit but channel gradients are lower atop the low resistance unit d 50 is not correlated with drainage area but is positively correlated with unit stream power the correlation between unit stream power and d 50 is evidence for mutual adjustments among gradients widths and d 50 as a function of the primary driving force in the drainage area discharge the small effect of bed lithology on stream processes and strong relationship between channel geometry unit stream power and d 50 implies that available driving forces and grain size are the primary controls on stream processes in the study area we conclude that future research into system response in this and similar settings should focus on sediment characteristics production and flux

the roughness of natural terrain a planetary and remote sensing perspective we examine the various methods and parameters in common use for quantifying and reporting surface topographic roughness it is shown that scale dependent roughness parameters are almost always required though not widely used we suggest a method of standardizing the parameters that are computed and reported so that topographic data gathered by different workers using different field techniques can be directly and easily intercompared we illustrate the proposed method by analyzing topographic data from 60 different surfaces gathered by five different groups and examine the information for common features we briefly discuss the implications of our analysis for studies of planetary surface roughness lander safety and radar remote sensing modeling and analysis

characterisation of channel reach morphology and associated controls in deglaciated montane catchments in the cairngorms scotland abstract the morphological characteristics of 50 channel reaches were surveyed in montane streams in the river dee catchment to test an existing process based typology included in the analysis were common reach types documented elsewhere e g cascade step pool and pool riffle in addition mixed bedrock alluvial alluvial transitional and wandering reach types that have received less attention were also investigated given their common occurrence in the study area differences in geometry substrate character and flow resistance are evident particularly between principal types although differentiation of mixed bedrock alluvial and transitional types was less marked wandering reaches occupy a slope range that overlaps with other types but are distinguished by a grain size distribution that is intermediate between plane bed and pool riffle reaches and a high channel width for a given discharge the quantitative differences observed support visually based differentiation of channel types based on their bedform assemblages morphological characteristics were also related to a suite of variables to determine first order controls on reach type channel cross sectional geometry is strongly correlated with discharge whilst grain size and indices of flow resistance are strongly correlated with slope and boundary shear stress in particular in addition the paraglacially conditioned geomorphic setting constitutes an important local control the morphological properties of common channel types bedrock cascade step pool plane bed and pool riffle broadly correspond with those observed elsewhere although channel slope ranges were markedly lower we hypothesise that channel types exist in a lower domain of slope because of a lower sediment supply rate that reflects the distinctive landscape evolution of the cairngorms area

widespread persistent thickening of the east antarctic ice sheet by freezing from the base an international polar year aerogeophysical investigation of the high interior of east antarctica reveals widespread freeze on that drives substantial mass redistribution at the bottom of the ice sheet although the surface accumulation of snow remains the primary mechanism for ice sheet growth beneath dome a 24 of the base by area is frozen on ice in some places up to half of the ice thickness has been added from below these ice packages result from the conductive cooling of water ponded near the gamburtsev subglacial mountain ridges and the supercooling of water forced up steep valley walls persistent freeze on thickens the ice column alters basal ice rheology and fabric and upwarps the overlying ice sheet including the oldest atmospheric climate archive and drives flow behavior not captured in present models

linking channel geomorphic characteristics to spatial patterns of spawning activity and discharge use by atlantic salmon salmo salar l this paper relates spatial patterns of spawning by atlantic salmon salmo salar l to channel geomorphic and hydrologic characteristics in two upland scottish streams the full length of each stream was surveyed and classified using a process based typology the precise locations of 845 spawning events were mapped over 3 successive years these locations were classified by reach type and a location specific discharge was calculated for each spawning event fish used response reach types pool riffle and transitional pool riffle plane bed preferentially avoiding transport reach types plane bed and step pool the spatial distribution of reach types contrasted markedly between the streams and as a consequence the distribution of spawning activity differed in each stream fish utilised relatively high flows for spawning with almost all spawning occurring at discharges greater than location specific median annual flows while optimum discharges defined as those where values of use most exceeded values of availability were as high as two to three times greater than reach median flows in each stream spawning occurred over a greater flow range in response than transport reach types primarily as a result of higher maximum utilised flows in the former because the channel classification procedure is process based and therefore transferable to other geographic areas the present study suggests that reach type may be used to predict the spatial distribution of atlantic salmon spawning activity within a catchment since the data indicate that discharge use by spawning fish is reach type specific the results also suggest that channel morphology should be considered when identifying environmental flow requirements

channel reach morphology in mountain drainage basins a classification of channel reach morphology in mountain drainage basins synthesizes stream morphologies into seven distinct reach types colluvial bedrock and five alluvial channel types cascade step pool plane bed pool rime and dune ripple coupling reach level channel processes with the spatial arrangement of reach morphologies their links to hillslope processes and external forcing by confinement ripar ian vegetation and woody debris defines a process based framework within which to assess channel condition and response potential in mountain drainage basins field investigations demonstrate character istic slope grain size shear stress and roughness ranges for different reach types observations consistent with our hypothesis that alluvial channel morphologies reflect specific roughness configurations ad justed to the relative magnitudes of sediment supply and transport ca pacity steep alluvial channels cascade and step pool have high ratios of transport capacity to sediment supply and are resilient to changes in discharge and sediment supply whereas low gradient alluvial channels pool rime and dune ripple have lower transport capacity to supply ra tios and thus exhibit significant and prolonged response to changes in sediment supply and discharge general differences in the ratio of transport capacity to supply between channel types allow aggregation of reaches into source transport and response segments the spatial distribution of which provides a watershed level conceptual model linking reach morphology and channel processes these two scales of channel network classification define a framework within which to in vestigate spatial and temporal patterns of channel response in moun tain drainage basins

reach scale channel geometry of a mountain river mountain rivers can be subject to strong constraints imposed by changes in gradient and grain size supplied by processes such as glaciation and rockfall nonetheless adjustments in the channel geometry and hydraulics of mountain rivers at the reach scale can produce discernible patterns analogous to those in fully alluvial rivers mountain rivers can differ in that imposed reach scale gradient is an especially important control on reach scale channel characteristics as indicated by examination of north st vrain creek in colorado north st vrain creek drains 250 km2 of the rocky mountains we used 25 study reaches within the basin to examine controls on reach scale channel geometry variables measured included channel geometry large woody debris grain size and mean velocity drainage area at the study reaches ranged from 2 2 to 245 km2 and gradient from 0 013 to 0 147 m m 1 we examined correlations among 1 potential reach scale response variables describing channel bankfull dimension and shape hydraulics bedform wavelength and amplitude grain size ow resistance standard deviation of hydraulic radius and volume of large woody debris and 2 potential control variables that change progressively downstream drainage area discharge or that are likely to re ect a reach speci c control bed gradient we tested the hypothesis that response variables correlate most strongly with local bed gradient because of the segmented nature of mountain channels results from simple linear regression analyses indicate that most response variables correlate best with gradient although channel width and width depth ratio correlate best with discharge multiple regression analyses using mallow s cp selection criterion and log transformation of all variables produced similar results in that most response variables correlate strongly with gradient these results suggest that the hypothesis is partially supported channel bed gradient is likely to be a good predictor for many reach scale response variables along mountain rivers but discharge is also an important predictor for some response variables copyright 2004 john wiley sons ltd

ice flow in greenland for the international polar year 2008 2009 a digital representation of ice surface velocity is essential for a variety of glaciological geologic and geophysical analyses and modeling here we present a new reference comprehensive high resolution digital mosaic of ice motion in greenland assembled from satellite radar interferometry data acquired during the international polar year 2008 to 2009 by the envisat advanced synthetic aperture radar asar the advanced land observation system alos s phase array l band sar palsar and the radarsat 1 sar that covers 99 of the ice sheet in area the best mapping performance is obtained using alos palsar data due to higher levels of temporal coherence at the l band frequency but c band frequency sar data are less affected by the ionosphere the ice motion map reveals various flow regimes ranging from patterned enhanced flow into a few large glaciers in the cold low precipitation areas of north greenland to diffuse enhanced flow into numerous narrow fast moving glaciers in the warmer high precipitation sectors of northwest and southeast greenland we find that the 100 fastest glaciers v 800m yr drain 66 of the ice sheet in area marine terminating glaciers drain 88 of greenland and basal sliding motion dominates internal deformation over more than 50 of the ice sheet this view of ice sheet motion provides significant new constraints on ice flow modeling copyright 2012 by the american geophysical union

a morpho statistical classification of mountain stream reach types in southeastern australia abstract the concepts of sediment transport capacity q c and sediment supply q s have shown promise in broadly differentiating mountain streams the important role of lithology in determining reach characteristics is also noted but as yet not fully included in existing process domain frameworks this study uses topographic and grain size surveys undertaken over 42 channel reaches with slopes between 0 01 and 0 20 m m to describe mountain stream morphology in southeastern australia reaches with two different lithologies are surveyed to specifically address the role of lithology in resultant channel morphology spatial autocorrelation analysis based on moran s i is used to detect the frequency and occurrence of in stream features such as bars and pools these data are combined with the grain size data to describe eight dominant reach morphologies most channel morphologies display broad characteristics similar to previous accounts of mountain streams although a number of intermediate morphologies affecting subtle variations in form and process where evident there was no significant longitudinal arrangement of the observed morphologies particularly with respect to catchment area and slope this is related to the strongly segmented longitudinal profiles characteristic of these streams where increasing catchment area does not result in a commensurate decrease in slope five of the eight channel morphologies identified are lithology dependent with respect to grain size and shape regime diagrams applied to quantify the physical controls on the different reach morphologies identified different q c q s domains for most morphologies however some lithology dependent morphologies could not be differentiated supporting the need to incorporate the effects of dominant grain shape or sphericity in assigning dimensionless critical shear stress values in determining q s overall the differences in mountain stream reach morphologies described in this study reflect the characteristic segmentation of the longitudinal profiles of these streams and contrasts in the supply and breakdown of parent material

effects of sediment supply on surface textures of gravel bed rivers using previously published data from flume studies we test a new approach for quantifying the effects of sediment supply i e bed material supply on surface grain size of equilibrium gravel channels textural response to sediment supply is evaluated relative to a theoretical prediction of competent median grain size d9 50 we find that surface median grain size d50 varies inversely with sediment supply rate and systematically approaches the competent value d9 at low equilibrium transport rates furthermore equilibrium transport rate is a power function of the difference between applied and critical shear stresses and is therefore a power function of the difference between competent and observed median grain sizes d9 and d50 consequently we propose that the difference between predicted and observed median grain sizes can be used to determine sediment supply rate in equilibrium channels our analysis framework collapses data from different studies toward a single relationship between sediment supply rate and surface grain size while the approach appears promising we caution that it has been tested only on a limited set of laboratory data and a narrow range of channel conditions

theoretical basis for at many stations hydraulic geometry citation gleason c j wang j 2015 theoretical basis for at many stations hydraulic geometry geophysical research letters 42 17 7107 7114 doi 10 1002 2015gl064935

a catchment scale model of mountain stream channel morphologies in southeast australia the position of mountain streams high in the channel network and their proportional dominance mean that channel modifications and adjustments within these systems will have important implications for downstream processes and linkages this study develops an analysis framework for examining the catchment scale distribution of reach morphologies and the relationship among reach type catchment lithology and flow competence in southeast australian mountain streams the analysis framework is applied to three catchments which have contrasting proportions of the two dominant lithologies of the region devonian granites and ordovician metasediments the model successfully delineated 68 of reach types and the resultant spatial maps allowed the effects of stream network position and catchment specific controls on channel morphology to be evaluated maximum lengths of the majority of reach morphology types were in second order streams and the maximum number of morphology types six was present in third order streams with dramatic reductions in reach type variability as the network expands the position of catchment lithology within the channel network structure was recognized as more important than the aerial extent of a particular lithology on the distribution and abundance of reach morphologies the model provides an important tool in the management of channel networks for the protection or restoration of ecological diversity by identifying river segments and tributaries with high morphological diversity

conceptualization of runoff processes using a geographical information system and tracers in a nested mesoscale catchment tracer investigations were combined with a geographical information system gis analysis of the 31 km2 girnock catchment cairngorm mountains scotland in order to understand hydrological functioning by identifying dominant runoff sources and estimating mean residence times the catchment has a complex geology soil cover and topography gran alkalinity was used to demonstrate that catchment geology has a dominant influence on baseflow chemistry but flow paths originating in acidic horizons in the upper soil profiles controlled stormflow alkalinity chemically based hydrograph separations at the catchment scale indicated that 30 of annual runoff was derived from groundwater sources similar contributions 23 36 were estimated for virtually all major sub basins 18o of precipitation mean 9 4 range 16 1 to 5 0 and stream waters mean 9 1 range 11 6 to 7 4 were used to assess mean catchment and sub basin residence times which were in the order 4 6 months gis analysis showed that these tracer based diagnostic features of catchment functioning were consistent with the landscape organization of the catchment soil and host hydrology of soil type maps indicated that the catchment and individual sub basins were dominated by hydrologically responsive soils such as peats histosol peaty gleys histic gleysols and rankers umbric leptosols and histosols soil cover in combination with a topographic index predicted extensive areas of saturation that probably expand during hydrological events thus providing a high degree of hydrological connectivity between catchment hillslopes and stream channel network this was validated by aerial photographic interpretation and groundtruthing these characteristics of hydrological functioning i e dominance of responsive hydrological pathways and short residence times dictate that the catchment is sensitive to land use change impacts on the quality and quantity of streamflows it is suggested that such conceptualization of hydrological functioning using tracer validated gis analysis can play an important role in the sustainable management of river basins copyright 2006 john wiley sons ltd

channel morphology gradient profiles and bed stresses during flood in a step pool channel abstract the stability of a step pool channel is investigated on the basis of measurements during a median annual flood the study reaches range in gradient from 5 to 10 and the flow was 3 m3 s 1 in an 8 m wide channel the estimated shear stress based on the channel gradient was 102 pa which implies that the channel ought to move half meter class boulders calculations of the shear stress using flow resistance equations yield values of about 30 pa these figures imply that the largest boulders in the channel could be moved in fact the channel is stable the effective stress remains well below the threshold to move the large structure forming boulders the steps are stable structures that result from interlocking of the larger stones they are semi randomly located depending on the location of keystones that are deposited in the channel by debris flows or fall out of the banks the high variation in step pool wavelength step height residual pool depth and pool length is indicative of the random nature of step location and structure along a reach there is no convincing evidence that special conditions govern their formation

flood magnitude frequency and lithologic control on bedrock river incision in post orogenic terrain abstract mixed bedrock alluvial rivers bedrock channels lined with a discontinuous alluvial cover are key agents in the shaping of mountain belt topography by bedrock fluvial incision whereas much research focuses upon the erosional dynamics of such rivers in the context of rapidly uplifting orogenic landscapes the present study investigates river incision processes in a post orogenic cratonic landscape undergoing extremely low rates of incision the mobility of coarse bed materials up to 2 m diameter during late holocene palaeofloods of known magnitude and age is evaluated using step backwater flow modelling in conjunction with two selective entrainment equations a new approach for quantifying the formative flood magnitude in mixed bedrock alluvial rivers is described here based on the mobility of a key coarse fraction of the bed materials in this case the d84 size fraction a 350 m3 s formative flood fully mobilises the coarse alluvial cover with b 200 300 n m2 across the upper and lower gorge riffles peaking over 500 n m2 in the knickzone such floods have an annual exceedance probability much less than 10 2 and possibly as low as 10 3 the role of coarse alluvial cover in the gorge is discussed at two scales 1 modulation of bedrock exposure at the reach scale coupled with adjustment to channel width and gradient accommodates uniform incision across rocks of different erodibility in steady state fashion and 2 at the sub reach scale where coarse boulder deposits corresponding to b minima cap topographic convexities in the rock floor thereby restricting bedrock incision to rare large floods while recent studies postulate that decreasing uplift rates during post orogenic topographic decay might drive a shift to transport limited conditions in river networks observations here and elsewhere in post orogenic settings suggest to the contrary that extremely low erosion rates are maintained with substantial bedrock channel exposure although bed material mobility is known to be rate limiting for bedrock river incision under low sediment flux conditions exactly how a partial alluvial cover might be spatially distributed to either optimise or impede the rate of bedrock incision is open to speculation observations here suggest that the small volume of very stable bed materials lining sandy creek gorge is distributed so as to minimise the rate of bedrock fluvial incision over time

downstream channel adjustment in a low relief glacially conditioned watershed abstract river management practices are often informed by theoretical expectations of downstream channel adjustment which may not be valid in low relief glacially conditioned watersheds such as those in the lower north american great lakes region downstream trends in channel morphology and bed material size within a low relief glacially conditioned watershed are explored here and compared to a theoretical watershed model where slope and grain size are expected to decline exponentially the observed channel morphology is then tested against a theoretical concept of reach scale channel grade the downstream hydraulic geometry relations w bf q bf 0 51 s 0 02 and d bf q bf 0 32 s 0 21 were found to best describe downstream changes in channel morphology and are consistent with some prior studies bed material size varies irregularly down the channel slope controlled downstream fining trends are evident where inputs from glacial materials and tributaries are negligible but are masked by cobble boulder lag deposits where the channel is cut into these glacial deposits the asynchronous variability in slope and grain size produces downstream variations in graded and nongraded understeepened conditions separated at ex 0 graded reaches exist where ex 0 but an upper boundary with nongraded oversteepened reaches is less clear the results emphasize the geomorphic legacy of inherited slopes and sediment sources in dictating the modern downstream patterns of fluvial characteristics and morphologies in glacially conditioned and similarly complex watersheds

identification and control of subglacial water networks under dome a antarctica 1 subglacial water in continental antarctica forms by melting of basal ice due to geothermal or frictional heating subglacial networks transport the water from melting areas and can facilitate sliding by the ice sheet over its bed subglacial water flow is driven mainly by gradients in overburden pressure and bed elevation we identify small median 850 m water bodies within the gamburtsev subglacial mountains in east antarctica organized into long 20 103 km coherent drainage networks using a dense 5 km grid of airborne radar data the individual water bodies are smaller on average than the water bodies contained in existing inventories of antarctic subglacial water and most are smaller than the mean ice thickness of 2 5 km reflecting a focusing of basal water by rugged topography the water system in the gamburtsev subglacial mountains reoccupies a system of alpine overdeepenings created by valley glaciers in the early growth phase of the east antarctic ice sheet the networks follow valley floors either uphill or downhill depending on the gradient of the ice sheet surface in cases where the networks follow valley floors uphill they terminate in or near plumes of freeze on ice indicating source to sink transport within the basal hydrologic system because the ice surface determines drainage direction within the bed constrained network the system is bed routed but surface directed along flow variability in the structure of the freeze on plumes suggests variability in the networks on long 10s of ka timescales possibly indicating changes in the basal thermal state

a dynamic early east antarctic ice sheet suggested by ice covered fjord landscapes the east antarctic ice sheet has played a fundamental part in modulating climate and sea level during the past 30 million years understanding its history is crucial to evaluating its future behaviour and response to global warming airborne ice penetrating radar studies now reveal a fjord like landscape beneath several kilometres of ice in the east antarctic aurora subglacial basin the data confirm and provide a new constraint on the magnitude and dynamics of the oscillations of the east antarctic ice sheet during the late cenozoic which had previously been supported only by marine cores the first cenozoic ice sheets initiated in antarctica from the gamburtsev subglacial mountains1 and other highlands as a result of rapid global cooling 34 million years ago2 in the subsequent 20 million years at a time of declining atmospheric carbon dioxide concentrations2 and an evolving antarctic circumpolar current2 sedimentary sequence interpretation3 and numerical modelling4 suggest that cyclical periods of ice sheet expansion to the continental margin followed by retreat to the subglacial highlands occurred up to thirty times these fluctuations were paced by orbital changes and were a major influence on global sea levels5 ice sheet models show that the nature of such oscillations is critically dependent on the pattern and extent of antarctic topographic lowlands here we show that the basal topography of the aurora subglacial basin of east antarctica at present overlain by 2 4 5 km of ice is characterized by a series of well defined topographic channels within a mountain block landscape the identification of this fjord landscape based on new data from ice penetrating radar provides an improved understanding of the topography of the aurora subglacial basin and its surroundings and reveals a complex surface sculpted by a succession of ice sheet configurations substantially different from today s at different stages during its fluctuations the edge of the east antarctic ice sheet lay pinned along the margins of the aurora subglacial basin the upland boundaries of which are currently above sea level and the deepest parts of which are more than 1 km below sea level although the timing of the channel incision remains uncertain our results suggest that the fjord landscape was carved by at least two iceflow regimes of different scales and directions each of which would have over deepened existing topographic depressions reversing valley floor slopes

grain size along two gravel bed rivers statistical variation spatial pattern and sedimentary links a new set of field data facilitates a detailed analysis of variations in bed material grain size within two confluent gravel bed rivers in northeastern british columbia canada a preliminary assessment of grain size variability establishes a basis for examination of the spatial pattern of grain size change standard anova techniques are inappropriate because individual samples have unequal variances and are not normally distributed alternative tests for homoscedasticity and comparison of means are therefore utilized within site between sample variability is not significant the grain size distributions that were obtained at individual sites are therefore representative of the depositional environments that were sampled in both rivers mean grain size does vary significantly between sites and there is therefore a basis for examining the data for spatial patterns such as downstream fining textural variations along the two rivers studied here are complex and show negligible overall fining in over 100 km this is the consequence of a large number of tributary inputs and non alluvial sediment sources which are the legacy of late pleistocene glaciation the identification of lateral sources like these is fundamental for understanding textural changes within rivers the sedimentary link a channel reach between significant lateral sediment inputs provides a means of isolating fluvial maturation processes abrasion and sorting from contingent lateral inputs strong fining trends are apparent in most links and classification of grain size measurements according to their location within particular links greatly improves the statistical explanation of textural variation identification of sedimentary links provides a means of applying models of fluvial fining processes so isolation of link networks will aid the development of basin scale models of textural variation 1998 john wiley sons ltd

similarity of organized patterns in driving and basal stresses of antarctic and greenland ice sheets beneath extensive areas of basal sliding the rate of ice transport from the interior of ice sheets to their margins and hence the rate with which it contributes to sea level is determined by the balance of driving stress basal resistance and ice internal deformation using recent high resolution observations of the antarctic and greenland ice sheets we compute driving stress and ice deformation velocities inferring basal traction by inverse techniques the results reveal broad scale organization in 5 20 km band like patterns in both the driving and basal shear stresses located in zones with substantial basal sliding both ice sheets experience basal sliding over areas substantially larger than previously recognized the likely cause of the spatial patterns is the development of a band like structure in the basal shear stress distribution that is the results of pattern forming instabilities related to subglacial water the similarity of patterns on the greenland and antarctic ice sheets suggests that the flow of ice sheets is controlled by the same fundamental processes operating at their base which control ice sheet sliding and are highly variable on relatively short spatial and temporal scales with poor predictability this has far reaching implications for understanding of the current and projection of the future ice sheets evolution

velocity and flow resistance in step pool streams flow resistance in steep streams with step pool morphology consists of form drag as well as skin friction it therefore alters rapidly as discharge increases and is not expected to show constant manning s n or simple log law behaviour but there is no widely accepted alternative representation we report measurements of at a station hydraulic geometry n and 1 f 0 5 for a range of discharges at each of six field sites and in flume experiments loosely froude scaled to the prototypes velocity and resistance vary strongly with discharge in all cases the flume data extend to formative flows and when rescaled extend the range of the field data but plot in line with them this suggests a single resistance law can describe the full range from trickle to formative flow equations based on the log law with ks step d84 perform unexpectedly well especially when allowance is made for flow blocking and or the ks d84 multiplier is optimised separately for each site the latter suggests step d84 is not a good summary representation of effective roughness but none of a variety of alternative grain size and microtopographic measures performed much better

stable channels with mobile gravel beds regime type equations for mobile gravel bed rivers are presented based on data obtained from 62 stable gravel bed river reaches in the united kingdom multiple regression techniques are applied to derive equations relating reach average and riffle values of width mean and maximum depth slope velocity sinuosity and riffle spacing to bankfull discharge bed and bank material characteristics valley slope bank vegetation type and an independent estimate of bankfull bed load transport rates although discharge has a dominant control on channel geometry these equations indicate that bed load discharge also has a significant influence particularly with regard to channel slope bank vegetation has a major control on width and velocity while depth velocity and slope are storngly affected by bed material size reasons for these results are considered in terms of the physical processes controlling channel adjustment the application of these regime equations is discussed and particular consideration is given to the design of sinuous channels with a pool riffle bed topograph

water slope and discharge in the amazon river estimated using the shuttle radar topography mission digital elevation model 1 we find that the standard deviation hence error of the water surface elevation data from the shuttle radar topography mission srtm is 5 51 m for basin wide regional and local amazon mainstem reaches this error implies a minimum reach length of 733km in order to calculate a reliable water surface slope resulting slopes are 1 92 0 19 cm km for manacapuru 2 86 0 24 cm km for itapeua and 3 20 0 34 cm km for tupe manning s equation is applied with these slopes and with channel width measurements from the global rain forest mapping project synthetic aperture radar mosaics grfm sar channel depths averaged from nautical charts and reasonable estimates of manning s n resulting discharge values are 84 800 m3 s at manacapuru 79 800 m3 s at itapeua and 62 900 m3 s at tupe averaged over the srtm mission period these values are within 6 2 at manacapuru 7 6 at itapeua and 0 3 at tupe of the in situ gage based estimates for the same or similar time period

spatial discontinuity and temporal evolution of channel morphology along a mixed bedrock alluvial river upper drome river southeast france contingent responses to external and internal controls abstract the rehabilitation of degraded river channels is often guided by assumptions of continuity yet in response to spatial and temporal variations in controlling conditions rivers typically display discontinuous response in space and time this study examines the development of a 5 km reach of the drome river s e france characterised by alternating alluvial and bedrock zones that are separated by abrupt downstream transitions this reach is representative of the drome river as a whole and other rivers in the european alps where braided channel planforms have been replaced by more complex discontinuous morphologies the primary aims are to understand how this spatial complexity has developed on the drome evaluate how temporal channel changes have been affected by local factors particularly bedrock exposures and by long term catchment scale changes in sediment supply and the flood activity and consider the implications of this discontinuous geomorphology for reach management the development of geomorphological zonation is examined by documenting sequential changes in channel planform between seven periods using aerial photography 1948 2006 and by analysing change in bed elevation from profiles surveyed in 1928 2003 and 2005 between 1948 and 2001 bedrock exposed in the channel bed and along the floodplain margins defined discontinuities in sediment connectivity that were largely responsible for the configuration of channel zones the impact of floods on this system was not proportional to flood magnitude a modest flood in 1978 was an important event that by incision and avulsion at key locations defined a pattern of zonation that persisted until the end of the study in 2006 during the final 5 years of the study alluvial zones that previously responded to large floods by widening underwent narrowing despite the occurrence of a large flood and led to an overall reduction in width variance this resulted from progressive incision beneath and disconnection from formerly active channel areas in response to long term catchment scale reductions in sediment supply and flood frequency in 2006 the pattern of zonation remains distinct disguising this recent change in channel response and underlining the need for long term and sequential perspectives of channel development to fully understand the processes in operation contemporary snapshots of channel form may be misleading understanding interactions between inherent channel complexity and prevailing flow and sediment conditions and how this shapes channel response to individual floods is essential when interpreting future trajectories of channel change and likely response to management intervention

characterization of subglacial landscapes by a two parameter roughness index previous studies using fourier transformation ft methods to analyze subglacial roughness have shown promise for distinguishing between different types of subglacial landscape from raw subglacial elevation data we derive a two parameter ft roughness index whereis based on the ft of elevation as previously considered in isolation andis based on both the ft of elevation and the ft of bed slope profile in this way we take account of both vertical and horizontal irregularities in subglacial surfaces we demonstrate the statistical veracity of using to consider roughness in terms of obstacle amplitudes and spacing and consider the use of in studies of ice dynamics and subglacial geomorphological interpretation we show that can be linked to basal sliding rates on the metre scale and can be used to differentiate further than single parameter roughness indices between different classes of subglacial landscape in particular between erosional and depositional settings

estimation of bathymetric depth and slope from data assimilation of swath altimetry into a hydrodynamic model 1 the proposed surface water and ocean topography swot mission would provide measurements of water surface elevation wse for characterization of storage change and discharge river channel bathymetry is a significant source of uncertainty in estimating discharge from wse measurements however in this paper we demonstrate an ensemble based data assimilation da methodology for estimating bathymetric depth and slope from wse measurements and the lisflood fp hydrodynamic model we performed two proof of concept experiments using synthetically generated swot measurements the experiments demonstrated that bathymetric depth and slope can be estimated to within 3 0 microradians or 50 cm respectively using swot wse measurements within the context of our da and modeling framework we found that channel bathymetry estimation accuracy is relatively insensitive to swot measurement error because uncertainty in lisflood fp inputs such as channel roughness and upstream boundary conditions is likely to be of greater magnitude than measurement error

basal roughness of the east antarctic ice sheet in relation to flow speed and basal thermal state basal motion of ice sheets depends in part on the roughness and material properties of the subglacial bed and the occurrence of water to date basal motion represents one of the largest uncertainties in ice flow models it is that component of the total flow velocity that can change most rapidly and can therefore facilitate rapid variations in dynamic behaviour in this study we investigate the subglacial properties of the east antarctic ice sheet by statistically analysing the roughness of the bed topography inferred from radio echo sounding measurements we analyse two sets of roughness parameters one derived in the spatial and the other in the spectral domain with two roughness parameters each this enables us to compare the suitability of the four roughness parameters to classify the subglacial landscapes below the ice sheet we further investigate the relationship of the roughness parameters with observed surface flow velocity and modelled basal temperatures of the ice sheet we find that one of the roughness parameters the hurst exponent derived in the spatial domain coincides with the thermal condition at the base of the ice sheet for slow flow velocities and varies with flow velocity

subglacial geology in coats land east antarctica revealed by airborne magnetics and radar sounding during the austral summer of 2001 02 five thousand line kilometres of airborne radio echo sounding and aeromagnetic data were collected in the region of three tributaries of slessor glacier east antarctica which drains into the filchner ice shelf basal topography and roughness estimates were obtained from the echo sounding data which have been combined here with the subglacial geological units inferred from an analysis of the aeromagnetic data this analysis included euler and werner deconvolution to determine the location and depth of sills dykes and faults in addition we high pass filtered the magnetic anomaly profiles to obtain information about the near surface subglacial geology this revealed a prominent area of low magnetic susceptibility lying in a deep topographic basin underneath the northern tributary of slessor glacier forward and inverse magnetic models indicate that this area is likely underlain by a 3 km thick sedimentary basin ice flow modelling suggests that this sedimentary basin influences the ice dynamics in the tributary these results have important implications for understanding the dynamics of this and other east antarctic flow features that may be underlain by a weak sedimentary bed

calculating quaternary glacial erosion rates in northeast scotland northeast scotland is an area exhibiting selective erosion by quatemary ice sheets in this area both glacial and preglacial landforms exist in close proximity the depths of erosion which this modification represents are calculated on the assumption of various depths of preglacial weathering a depth of erosion of between 34 and 62 m per unit area is indicated calculated rates of erosion are 0 021 nun a for the entire 2 3 m y of the quaternary and between 0 1 and 0 5 mm aa1 on the assumption that glacial conditions existed in this area for 500 000 years and 100 000 years respectively these figures are compared to the offshore sedimentary record in the adjacent west central north sea the volume of sediment deposited offshore is equivalent to a depth of erosion of 195 m per unit area yielding an average erosion rate of 0 085 mm a i over the entire quatemary rates of erosion were low in the preglacial pliocene 0 049 mm a 1 and early quatemary 0 063 mm a the expansion of ice sheets across the area in the middle quatematy was associated with a sharp increase in the rates of erosion 0 13 mm a but the last late devensian ice sheet in the area was less erosive 0 095 mm a the estimated rates of erosion represented by the offshore sedimentary record therefore exceed the estimated rates of glacial erosion from the onsho re geomorphological reconstruction

estimating reach averaged discharge for the river severn from measurements of river water surface elevation and slope summary an algorithm is presented that calculates a best estimate of river bathymetry roughness coefficient and discharge based on input measurements of river water surface elevation h and slope s using the metropolis algorithm in a bayesian markov chain monte carlo scheme providing an inverse solution to the diffusive approximation to the shallow water equations this algorithm has potential application to river h and s measurements from the forthcoming surface water and ocean topography swot satellite mission the algorithm was tested using in situ data as a proxy for satellite measurements along a 22 4 km reach of the river severn uk first the algorithm was run with gage measurements of h and s during a small in bank event in june 2007 second the algorithm was run with measurements of h and s estimated from four remote sensing images during a major out of bank flood event in july 2007 river width was assumed to be known for both events algorithm derived estimates of river bathymetry were validated using in situ measurements and estimates of roughness coefficient were compared to those used in an operational hydraulic model algorithm derived estimates of river discharge were evaluated using gaged discharge for the in bank event when lateral inflows from smaller tributaries were assumed to be known the method provided an accurate discharge estimate 10 rmse when lateral inflows were assumed unknown discharge rmse increased to 36 finally if just one of the three river reaches was assumed to be have known bathymetry solutions for bathymetry roughness and discharge for all three reaches were accurately retrieved with a corresponding discharge rmse of 15 6 for the out of bank flood event the lateral inflows were unknown and the final discharge rmse was 19 these results suggest that it should be possible to estimate river discharge via swot observations of river water surface elevation slope and width

the sensitivity of scottish rivers and upland valley floors to recent environmental change abstract rivers in humid zones are delicately adjusted within narrow limits to evacuate the water and sediment supplied from upstream without significant changes in channel type and the morphology of the valley floor prevailing climate and land use are the major controls determining the nature of that adjustment significant environmental change either climate and or land use has the potential to change radically the channel type and destabilise the adjacent valley floor channel metamorphosis in which a river shifts from an aggrading to a degrading regime or from a single thread to multiple thread channel often provides the clearest evidence that environmental change has occurred this paper examines the stability of river channels and their associated valley floors in the uplands of scotland since 1750 changes in global scale atmospheric circulation patterns during this period have resulted in regionally distinct flood rich and flood poor periods with potential geomorphic impacts changes in the planform of nine active rivers in the piedmont zone of upland scotland are examined from series of rectified maps and aerial photographs at scales close to 1 10 000 at none of the sites other than one affected by an artificial increase in base level is there evidence of abrupt changes in river behaviour or channel metamorphosis however rates of lateral channel shift and extents of bare gravels do vary and these are clearly driven by changes in the incidence of floods since the mid 19th century the scale of valley floor reworking is less dramatic than that recently reported for comparable sites in northern england differences in geomorphic history land use and degree of slope channel coupling are identified as the likely causes of marked differences in the behaviour of active rivers in scotland and northern england over the last 250 years

controls on the distribution of channel reach morphology in selectively glaciated catchments abstract to assess the controls on the distribution of channel reach morphology in a selectively glaciated landscape we used field mapping and a geographical information system gis in the river dee catchment northeast scotland controls on channel morphology were investigated using 1 continuous longitudinal assessment of channel morphology distribution in relation to geology glacial history topography and total stream power in two subcatchments and 2 slope s and a slope drainage area s a framework to understand the occurrence of 173 widely distributed bedrock mixed bedrock alluvial and alluvial three different types reaches the s a framework used indicators of transport capacity qc and sediment supply qs to differentiate channel types the study highlights the disjointed nature of channel reach distribution at the river scale that reflects variable lithology and glacial modification because of the subdued topography in contrast to other regions colluvial forcing of channel morphology in the headwaters was lacking however in common with other glaciated landscapes repeated sequences of channel reach type progression determined by valley steps were evident the s a analysis successfully discriminated 87 2 of alluvial and 91 4 of bedrock reaches despite the variable land use and glacial modification discrimination of the full range of channel types using s or the s a framework was poor however notably a third of the transport alluvial reaches were located in the bedrock s a domain and the majority of mixed reaches were widely distributed mostly within the bedrock domain and not close to the critical slope sc in comparison to other regions the sc above which qc qs and bedrock reaches dominate was notably higher we hypothesise that a drier climate and the higher entrainment threshold of coarse granite dominated bed materials create a higher sc

alluvial architecture in headwater streams with special emphasis on step pool topography alluvial mountain streams exhibit a range of channel forms pool riffle plane bed step pool and cascades previous work suggested that these forms exist within discrete and progressively steeper slope classes measurements conducted at over 100 sites in west central and central idaho confirm that slope steepens progressively as one moves from pool riffle to plane bed to step pool and finally to cascades median slope for pool riffle topography is 0 0060 for plane beds 0 013 for step pools 0 044 and for cascades 0 068 there is substantial overlap in the slopes associated with these channel forms pool riffle topography was found at slopes between 0 0010 and 0 015 plane beds between 0 0010 and 0 035 step pools between 0 015 and 0 134 and cascades between 0 050 and 0 12 step pools are particularly striking features in headwater streams they are characterized by alternating steep and gentle channel segments the steep segments step risers are transverse accumulations of boulder and cobbles while the gentle segments pools contain finer material step wavelength is best correlated to step height which is in turn best correlated to the median particle size found on step risers this result differs from past studies that have reported channel slope to be the dominant control on step wavelength the presumed geometry and froude number associated with the features under formative conditions are consistent with the existence field for antidunes and by extension with the hypothesis that step pools are formed by antidunes copyright 2000 john wiley sons ltd

bam bayesian amhg manning inference of discharge using remotely sensed stream width slope and height the forthcoming surface water and ocean topography swot nasa satellite mission will measure water surface width height and slope of major rivers worldwide the resulting data could provide an unprecedented account of river discharge at continental scales but reliable methods need to be identified prior to launch here we present a novel algorithm for discharge estimation from only remotely sensed stream width slope and height at multiple locations along a mass conserved river segment the algorithm termed the bayesian amhg manning bam algorithm implements a bayesian formulation of streamflow uncertainty using a combination of manning s equation and at many stations hydraulic geometry amhg bayesian methods provide a statistically defensible approach to generating discharge estimates in a physically underconstrained system but rely on prior distributions that quantify the a priori uncertainty of unknown quantities including discharge and hydraulic equation parameters these were obtained from literature reported values and from a usgs dataset of acoustic doppler current profiler adcp measurements at usgs stream gauges a dataset of simulated widths slopes and heights from 19 rivers was used to evaluate the algorithms using a set of performance metrics results across the 19 rivers indicate an improvement in performance of bam over previously tested methods and highlight a path forward in solving discharge estimation using solely satellite remote sensing

calving fluxes and basal melt rates of antarctic ice shelves iceberg calving has been assumed to be the dominant cause of mass loss for the antarctic ice sheet with previous estimates of the calving flux exceeding 2 000 gigatonnes per year1 2 more recently the importance of melting by the ocean has been demonstrated close to the grounding line and near the calving front3 4 5 so far however no study has reliably quantified the calving flux and the basal mass balance the balance between accretion and ablation at the ice shelf base for the whole of antarctica the distribution of fresh water in the southern ocean and its partitioning between the liquid and solid phases is therefore poorly constrained here we estimate the mass balance components for all ice shelves in antarctica using satellite measurements of calving flux and grounding line flux modelled ice shelf snow accumulation rates6 and a regional scaling that accounts for unsurveyed areas we obtain a total calving flux of 1 321 144 gigatonnes per year and a total basal mass balance of 1 454 174 gigatonnes per year this means that about half of the ice sheet surface mass gain is lost through oceanic erosion before reaching the ice front and the calving flux is about 34 per cent less than previous estimates derived from iceberg tracking1 2 7 in addition the fraction of mass loss due to basal processes varies from about 10 to 90 per cent between ice shelves we find a significant positive correlation between basal mass loss and surface elevation change for ice shelves experiencing surface lowering8 and enhanced discharge9 we suggest that basal mass loss is a valuable metric for predicting future ice shelf vulnerability to oceanic forcing

channel geometry of mountain streams in new zealand abstract a dataset of 21 study reaches in the porter and kowai rivers eastern side of the south island and 13 study reaches in camp creek and adjacent catchments western side of the south island was used to examine downstream hydraulic geometry of mountain streams in new zealand streams in the eastern and western regions both exhibit well developed downstream hydraulic geometry as indicated by strong correlations between channel top width bankfull depth mean velocity and bankfull discharge exponents for the hydraulic geometry relations are similar to average values for rivers worldwide factors such as colluvial sediment input to the channels colluvial processes along the channels tectonic uplift and discontinuous bedrock exposure along the channels might be expected to complicate adjustment of channel geometry to downstream increases in discharge the presence of well developed downstream hydraulic geometry relations despite these complicating factors is interpreted to indicate that the ratio of hydraulic driving forces to substrate resisting forces is sufficiently large to permit channel adjustment to relatively frequent discharges

what controls the location of ice streams ice streams influence ice sheet mass balance and stability but key aspects of their behaviour remain poorly understood this paper reviews and discusses one very important aspect what controls their location in an ice sheet seven potential controls on ice stream location are identified from the literature topographic focusing topographic steps macro scale bed roughness calving margins subglacial geology geothermal heat flux and subglacial meltwater routing for each control the theoretical basis for its link to rapid ice flow is introduced followed by discussion of the evidence of its influence on the location of both contemporary and palaeo ice streams based on this new synthesis topographic focusing subglacial geology meltwater routing and calving margins appear to be most commonly associated with fast ice flow it is clear that rather than a single control however there exist a number of potential controls of varying influence we propose a hierarchy of factors with those occurring at the top of the hierarchy exerting a stronger influence on ice stream location and where present beneath an ice sheet are very likely to be associated with fast flow those factors occurring lower down the hierarchy are less commonly associated with ice streaming but appear to be influential in the absence of more common controls in such a hierarchy topographic focusing in the presence of a calving margin is the primary control in the absence of this ice streams will preferentially occur in areas with favourable subglacial meltwater routing and subglacial geology in the absence of these bed roughness geothermal heat flux and topographic steps may promote ice streaming significantly the primary controls on a given ice stream location are likely to influence its spatial and temporal dynamics ice streams governed by the presence of meltwater routing and or calving processes might exhibit more variable behaviour because these controls can vary over relatively short time scales compared to controls that vary over longer time scales e g geothermal heat flux subglacial roughness geology and topography identifying the controls on ice stream location is therefore of paramount importance when understanding ice stream longevity and their past and future activity