the downstream gradation of particle sizes in the squamish river british columbia the exponential downstream decline in particle size predicted by sternberg 1875 is examined within a highly active alpine fluvial environment the gravel bed squamish river in southwestern british columbia transect survey procedures for sampling within the coarse alluvial gravels are described in detail downstream trends for various particle size statistics plotted with distance from a major sediment source are considered according to two scenarios evaluation of overall trends indicates that the downstream expression derived by sternberg 1875 is not the most appropriate rather curves are better described by power functions this reflects a very rapid decline in particle size immediately downstream of the major sediment source secondly evaluation of downstream trends in relation to channel planform determines that exponential functions with different coefficients describe adequately relations within individual planform reaches there is insufficient evidence to suggest which of these two scenarios may be appropriate several lines of evidence suggest that the trends found are more the result of selective sediment transport phenomena than of abrasion a condition attributed to channel competence within a system dominated by sediment supply conditions

glacially conditioned specific stream powers in low relief river catchments of the southern laurentian great lakes abstract fluvial systems of the southern laurentian great lakes region are carved into a complex glacial landscape shaped by continental ice and meltwater of the late pleistocene these glacially conditioned river catchments are typically small with drainage areas 4 km 2 a 10 m digital elevation model dem is used to map the spatial distribution of stream gradient for 22 major river catchments of peninsular southern ontario which drain to base levels in the lower great lakes huron st clair erie and ontario raw data from the dem show stream gradients that exhibit multiscale variance from real and from artifact sources based on a vertical slice and multiple pass moving window averaging approach slope data are generalised to the river reach scale 1 2 km as a representative spatial scale for fluvial processes operating over holocene timescales models of specific stream power are then compared with glacial landform and surface geology mapping inherited glacial signatures in river slope appear as deviations in a stream length gradient index sl k index where river reaches are frequently oversteepened or understeepened based on a slope area analysis and complementary to theories of channel pattern discrimination constant stream power curves with power law exponent of 0 4 provide a first order approach to stratify river reaches in terms of glacial conditioning and expected planform morphologies however multiple channel planform types are rare and localised in southern ontario indicating that oversteepened reaches with high stream powers may often be moderated by 1 sediment calibre with cobble beds from inherited glacial sediments and or 2 relative bank strength with limited channel widening particularly in gravel and sand bed channels further discrimination of glacially conditioned fluvial process domains will ultimately require consideration of alluvial floodplain characteristics in addition to general observations of river morphology and channel pattern

systematic variations in the carbon and oxygen isotopic composition of pedogenic carbonate along elevation transects in the southern great basin united states stable carbon and oxygen isotope variations in holocene soil carbonates that formed in the unsaturated zone were examined along several elevation transects in the southern great basin united states a region with a semi arid climate our intent was to study the relationship between the stable isotopic composition of pedogenic carbonates and climate ecological variations differences in parent material and soil depth 13 c of pedogenic carbonate in three different soil profiles from different elevations decreases with soil depth indicating a decrease in the ratio of atmospheric to plantderived co 2 downprofile pedogenic carbonate at the soil air interface approaches a 13 c value in equilibrium with atmospheric co 2 in all three soils observed 13 c profiles for pedogenic carbonate can be described using a one dimensional model for 12 co 2 and 13 co 2 assuming isotopic equilibrium between soil co 2 and soil carbonate the modeled best fit to observed isotopic profiles suggests that the profile differences in part result from differing soil respiration rates at each site 13 c in deep pedogenic carbonate 50 cm varies by about 12 per mil over a 2 440 m elevation range being enriched in 13 c at the lowest elevations the slope of 13 c for these carbonates versus elevation is very similar for soils developed on carbonate and on noncarbonate parent materials depletion by 4 6 to 4 7 per mil per 1 000 m increase in altitude between 300 to 2 740 m above mean sea level for the localities studied this concordance makes it likely that there has been complete isotopic exchange between hco 3 in solution and soil co 2 prior to carbonate precipitation soil co 2 and soil respiration rates increase systematically with elevation the plantderived component of soil co 2 indicates that c 3 plants dominate the biomass at most measured sites in agreement with plant surveys calculated equilibrium fractionation factors between soil co 2 and soil carbonate are very similar to those observed again indicating complete isotopic exchange between carbon species in all the soil co 2 and soil carbonate data suggest that the 13 c variation with elevation observed in the soil carbonates results from differing soil respiration rates at each site as well as from variations in the proportion of c 3 to c 4 and cam plants in each site9s surface biomass 18 o values in pedogenic carbonates are higher at lower elevations due in part to the more positive 18 o values for meteoric waters at lower elevations the average 18 o value of deep 50 cm pedogenic carbonate at all sites however is enriched 2 4 to 3 7 per mil with respect to values we predict should be in equilibrium with the isotopic composition of local meteoric waters this suggests that evaporative isotopic enrichment of soil waters may have occurred at all elevations prior to precipitation of carbonate or that seasonal differences in the isotopic composition of meteoric waters coupled with differential infiltration may be taking place one or both of these processes also may explain the 18 o decrease in soil carbonate with depth observed in two of three soil profiles

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

field evidence for rapid downstream fining of river gravels through selective transport doubts have been expressed about the ability of either abrasion or sorting to explain strong downstream fining of river gravels we describe pronounced fining over a short distance in a scottish river that has no human disturbance or lateral input of water and sediment measured abrasion rates are far too small to explain observed downstream fining but bed load trap measurements and the dispersion of magnetic tracer pebbles in six subreaches both show sorting during transport the observed downstream fining is also simulated well by a numerical sediment routing model using hydraulic and transport laws consistent with our field measurements the geomorphological cause of the strong fining is slope reduction above a local base level control in this common situation the development of downstream fining is part of the river9s tendency to minimize downstream variation in bed load transport rates and can proceed far more rapidly than the major aggradation otherwise required for equilibration

stabilizing self organized structures in gravel bed stream channels field and experimental observations stable reticulate structures which we call stone cells have been observed in cobble gravel channel beds with low bed material transport rates experiments show that such structures develop simultaneously with the armor layer during an extended period when flows do not exceed the shields threshold by more than 2 times so that bed material transport is low they are constructed by particles moving from less stable positions into more stable configurations against each other intermediate developments include clusters and stone lines they reduce sediment transport by orders of magnitude and are evidently a major stability promoting mechanism in gravel channels the timescale for their development suggests that the boundaries of many gravel bed channels are not in equilibrium with recent competent flows but reflect the history of recent dominant flows

downstream changes in the channel geometry of a large gravel bed river 1 field data obtained on a nearly contiguous segment of the colorado river in western colorado and eastern utah are used to examine the mechanisms driving downstream changes in channel geometry measurements characterizing the bank full hydraulic geometry bed material grain size and average channel gradient were made at closely spaced intervals in 10 alluvial and quasi alluvial reaches covering 260 km of the river these data indicate that changes in surface and subsurface grain sizes are small in relation to the change in channel slope over the full length of the study area the median grain size of the surface sediment decreases by a factor of a little more than 2 whereas the average channel slope decreases by a factor of about 5 the decreases in slope and median grain size are offset by a large increase in bank full depth relative to width such that the bank full shields stress b is constant downstream for the reach as a whole b averages 0 049 which is roughly 50 higher than the threshold for bed load transport

fluvial clastic sediment yield in canada scaled analysis this report presents a set of maps of regional fluvial sediment yield in canada based mainly on the water survey of canada archive of riverine suspended sediment observations regional scaling rel

paired benthic foraminiferal cd ca and zn ca evidence for a greatly increased presence of southern ocean water in the glacial north atlantic benthic foraminiferal 13c and cd ca studies suggest that deep atlantic circulation during the last glacial maximum was very different from today with high nutrient low 13c high cd deep southern ocean water sow penetrating far into the north atlantic however if some glacial 13c values are biased by productivity artifacts and or air sea exchange processes then the existing 13c data may be consistent with the continual dominance of north atlantic deep water nadw cibicidoides wuellerstorfi cd ca results presented here indicate that the glacial north atlantic was strongly enriched in dissolved cd below 2500 m depth if nadw formation was still vigorous relative to sow formation these data could be explained by either increased preformed nutrient levels in the high latitude north atlantic or by increased organic matter remineralization within lower nadw high glacial zn ca values in the same samples however are best explained by a substantially increased mixing with zn rich sow the cause was most likely a partial replacement of nadw by less dense glacial north atlantic intermediate water this reorganization also lowered deep north atlantic co32 concentrations by perhaps 10 to 15 mol kg 1

regional clastic sediment yield in british columbia the data archive of the water survey of canada supplemented by data of the british columbia hydro and power authority is used to investigate the areal pattern of fluvial sediment yield in british columbia the data represent suspended sediment loads at 63 stations derived from observations within the period 1966 1985 in most of the province there is a single annual peak in sediment transport in spring corresponding to the dominant snowmelt freshet however on the coast winter rainfall induces the sediment peak and in the coast and cascade mountains there is a transitional regime with two peaks from 65 to 90 of annual sediment yield occurs in the spring three months sediment yield per unit area specific sediment yield increases with drainage area at all scales from 10 up to 30 000 km2 the pattern persists seasonally throughout the year this contradicts the conventional model in which sediment yield declines downstream because of deposition along channels of a portion of the load derived from e

measuring bluff erosion part 2 pairing aerial photographs and terrestrial laser scanning to create a watershed scale sediment budget effectively managing and reducing high suspended sediment loads in rivers requires an understanding of the magnitude of major sediment sources as well as erosion and transport processes that deliver excess fine sediments to the channel network the focus of this research is to determine the magnitude of erosion from tall bluffs a primary sediment source in the 2880 km2 le sueur watershed minnesota usa we coupled analyses of seven decades of aerial photographs with four years of repeat terrestrial laser scanning tls to determine erosion rates on bluffs together these datasets provide decadal scale retreat rates throughout the entire watershed and high resolution geomorphic change detection on a subset of bluffs to both constrain erosion rates and document how environmental conditions affect bluff retreat erosion rates from aerial photographs and tls were extrapolated from 243 and 15 measured bluffs respectively to all 480 bluffs in the le sueur watershed using multiple techniques to obtain estimates of sediment loading from these features at the watershed scale despite different spatial and temporal measurement scales the aerial photograph and tls estimates yielded similar results for bluff retreat rate and total mass of sediment derived from bluffs with bluffs in the le sueur watershed yielding 135 000 39 000 mg yr of fine sediment comparing this value to the average annual total suspended solids tss load determined from gauging from 2000 to 2010 we determined that bluffs comprise 57 16 of the total tss load making bluffs the single most abundant fine sediment source in the basin copyright 2012 john wiley sons ltd

channel stability in bed load dominated streams with nonerodible banks inferences from experiments in a sinuous flume 1 experimental and computational evidence shows that bed state adjustments can accommodate a twofold to fourfold change in sediment supply without otherwise affecting the morphology of a sinuous gravel bed stream channel with nonerodible banks in contrast previously published experiments of the same kind but with erodible channel banks suggest that changes in sediment supply are taken up almost exclusively by changes in channel sinuosity and hence the reach average water surface gradient it appears that stream channel response to changes in sediment supply is strongly conditioned by the nature of the stream boundary and that determines which of several potential adjustments are possible

on the origin of the oak ridges moraine landscape analysis mapping sedimentology shallow geophysics and borehole data are integrated to better understand the complex landform sediment geometries and event sequences of the oak ridges moraine southern ontario a model for the origin of the oak ridges moraine is based on the recognition that the moraine is built on a high relief erosional surface unconformity consisting of drumlin uplands and a network of deep steep walled interconnected valleys tunnel channels the development of the moraine is thought to have occurred in four stages i subglacial sedimentation ii subaqueous fan sedimentation iii fan to delta sedimentation iv ice marginal sedimentation the model traces the transition from subglacial to proglacial conditions during moraine formation and examines the order and timing of sedimentation it is thought that the early stages of moraine construction are better exposed in the east in the west these stages are buried by later stages resume les etudes de paysage cartographie sedimentologie geophysique de subsurface et des carottes de trous des sondages ont ete menees conjointement pour chercher a mieux comprendre les configurations complexes des formes de relief sediments et les sequences des evenements qui ont affecte la moraine d oak ridges dans le sud de l ontario un modele interpretant l origine de la moraine d oak ridges est fonde sur le fait que cette moraine fut edifiee sur une surface d erosion discordance en terrain a topographie accentuee comprenant des drumlins sur terres elevees et des vallees a parois subverticales interconnectees chenaux tunnels le modele propose un developpement de la moraine en quatre phases i sedimentation sous glaciaire ii sedimentation d un eventail sous aquatique iii sedimentation de l eventail evoluant vers un depot deltaique iv sedimentation en bordure d un glacier le modele retrace la transition de conditions sous glaciaires a proglaciaires durant la formation de la moraine et traite de l ordre et de la chronologie du sediment il apparait que c est dans le secteur oriental que les premieres phases de l edification de la moraine sont le mieux exposees tandis que dans le secteur partie occidental elles sont enfouies sous le sediment des phases plus tardives

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

boundary shear in smooth and rough channels a series of flume experiments are reported in which the walls and bed were differentially roughened normal depth flow set and measurements made of the boundary shear stress distribution an empirically derived equation is presented giving the percentage of the shear force carried by the walls as a function of the breadth depth ratio and the ratio between the nikuradse equivalent roughness sizes for the bed and the walls the results are compared with other available data for the smooth channel case and some disagreements noted the systematic reduction in the shear force carried by the walls with increasing breadth depth ratio and bed roughness is illustrated further equations are presented giving the mean wall and bed shear stress variation with apsect ratio and roughness parameters although the experimental data is somewhat limited the equations are novel and thought to indicate the general behavior of such open channel flows with some success

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

glacial erosion evolution of river long profiles and the organization of process domains in mountain drainage basins of coastal british columbia 1 in glaciated british columbia canada quaternary climate changes are responsible for profound spatial reorganization of earth surface processes these changes have left a landscape characterized by topographic anisotropy associated with a hierarchy of glacial troughs the evolution of glaciated landscapes is examined by analyzing the structure of geomorphic process domains and channel long profiles to identify process domains we use channel surveys and gis analysis to construct slope area transects of the channel network this analysis reveals generalized process form disequilibrium with a mismatch between topographic signatures and currently active geomorphic process domains at the landscape scale of source colluvial channels contributing area 1 km2 the glacial paraglacial signature commonly overrides that produced by contemporary debris flows along the axis of former ice flows relict glacial cirques introduce a hanging fluvial domain at contributing areas as small as 8 10 2 km2 and produce complex channel long profiles similar to those observed for rivers responding to tectonic forcing slope area relations typical of unglaciated equilibrium environments do not apply here the concept of process domains appears to hold however some major glacially forced modifications in the alluvial colluvial transition are observed and the definition of a depositional colluvial subdomain is proposed comparison between field and gis measured slopes reveals that gis associated error is not uniform between process domains and that gis based plots do not successfully discriminate field based process domains the combination of glacial and post glacial fingerprints and the effects of ongoing earth surface processes generate a complex landscape whose glacial signatures may persist until the onset of the next ice age

bedload entrainment in low gradient paraglacial coastal rivers of maine u s a implications for habitat restoration abstract the rivers of coastal maine flow through mainstem lakes and long low gradient reaches that break the continuum of bedload transport expected in nonparaglacial landscapes stream erosion of glacial deposits supplies coarse sediment to these systems the land use history includes intensive timber harvest and associated dam construction which may have altered the frequency of substrate mobilizing events these watersheds are vital habitat for the last remaining wild anadromous atlantic salmon in the united states future adjustments in channel morphology and habitat quality via natural stream processes or restoration projects depend on erosion transport and deposition of coarse sediment these factors motivate our study of competence at four sites in the sheepscot and narraguagus watersheds three of the four sites behaved roughly similarly with particle entrainment during intervals that include winter ice and spring flood conditions and relatively minor bed mobilization during moderate floods in the summer and fall with a recurrence interval of 2 3 years the fourth site on the sheepscot river mainstem exhibits more vigorous entrainment of marked particles and more complex three dimensional channel morphology this contrast is partially due to local geomorphic conditions that favor high shear stresses particularly relatively steep gradient but also likely to nourishment of the bedload saltation system by recruitment from an eroding glacial deposit upstream our results suggest that the frequency and magnitude of bedload transport are reach specific depending on factors including local channel geometry upstream sediment supply and transport and formation of anchor ice this presents a challenge for stream practitioners in this region different reaches may require contrasting management strategies our results underscore the importance of understanding channel processes at a given site and assessing conditions upstream and downstream as a prerequisite for conducting habitat restoration projects

stream geomorphology in a mountain lake district hydraulic geometry sediment sources and sinks and downstream lake effects lakes are common in glaciated mountain regions and geomorphic principles suggest that lake modifications to water and sediment fluxes should affect downstream channels lakes in the sawtooth mountains idaho usa were created during glaciation and we sought to understand how and to what extent glacial morphology and lake disruption of fluxes control stream physical form and functions first we described downstream patterns in channel form including analyses of sediment entrainment and hydraulic geometry in one catchment with a lake to expand on these observations and understand the role of glacial legacy we collected data from 33 stream reaches throughout the region to compare channel form and functions among catchments with lakes meadows filled lakes and no past or present lakes downstream hydraulic geometry relationships were weak for both the single catchment and regionally our data show that downstream patterns in sediment size channel shape sediment entrainment and channel hydraulic adjustment are explained by locations of sediment sources hillslopes and tributaries and sediment sinks lakes stream reaches throughout the region are best differentiated by landscape position relative to lakes and meadows according to channel shape and sediment size where outlets are wide and shallow with coarse sediment and inlets are narrow and deep with finer sediment meadow outlets and lake outlets show similarities in the coarse sediment fraction and channel capacity but meadow outlets have a smaller fine sediment fraction and nearly mobile sediment estimates of downstream recovery from lake effects on streams suggest 50 per cent recovery within 2 4 km downstream but full recovery may not be reached within 20 km downstream these results suggest that sediment sinks such as lakes in addition to sources such as tributaries are important local controls on mountain drainage networks copyright 2006 john wiley sons ltd

slope induced changes in channel character along a gravel bed stream the allt dubhaig scotland changes in channel character along a small river in the scottish highlands are described using measurements in seven reaches over a 3 km length with no significant tributaries but a decline in slope from 0 02 to o ooo15 because of local baselevel control this decline in slope is associated with rapid downstream fining of the gravel bed followed by an abrupt transition to a sand bed the channel pattern alters progressively rather than abruptly in the sequence 1 near braided 2 meandering with active point bar chutes 3 meandering with active outer bank talweg 4 stable equiwidth sinuous the changes in channel pattern and hydraulic geometry are predicted better by rational approaches based on critical shear stress or other physical cdncepts than by purely empirical discriminant or trend equations measurements in five reaches confirm a downstream decrease in shear stress and the amount and calibre of bedload it is argued that the downstream changes in channel character in this stream are induced by profile concavity inherited from deglacial conditions are typical of many streams in mountainous areas and can be understood in terms of slope induced changes in hydraulic properties

the multivariate controls of hydraulic geometry a causal investigation in terms of boundary shear distribution most downstream hydraulic geometry exponents have been found to be very close to the classic values reported by leopold and maddock 1953 these have been viewed as the simplified cases to general trends because the hydraulic geometry of alluvial channels is actually the product of multivariate controls richards 1982 this paper is an attempt to develop a soundly based foundation for the explanation of the physical mechanisms of these controls a quantitative relationship between channel shape and boundary shear distribution developed from experimental flume results is found to be applicable in some instances to alluvial channels particularly to stable canals on the basis of this relationship it is shown that downstream hydraulic geometry is determined not only by flow discharge but also by channel slope channel average roughness and sediment composition of the channel boundary this is strongly supported by our analysis of 529 observations from both stable canals and natural rivers in the u s a and the u k the difference between regime relations in canals and the hydraulic geometry of rivers appears to be caused mainly by channel slope and average roughness which can be regarded as constants only in stable canals the close relationship between discharge and channel average roughness observed in canals is not repeated in natural channels partly because of the variety of flow values used to define the channel forming discharge furthermore it is indicated that the effects of the sediment composition of the channel boundary on hydraulic geometry are significant and need further investigation

the nature and controls on downstream fining within sedimentary links abstract at scales of 100 to 102 km grain size change in gravelly alluvial systems is characterized by punctuated downstream fining significant lateral sediment inputs define a sequence of sedimentary links within which fluvial processes produce fining trends using a new set of surface grain size data eighteen such links along two canadian gravel bed rivers are examined negative exponential functions are found to be most appropriate for describing within link grain size changes development of a pragmatic means of predicting grain size is then pursued by searching for a means to relate model diminution coefficients to link attributes consideration of lithologically differentiated fining trends indicates that lithology plays an insignificant role in controlling fining rate examination of within link longitudinal profiles indicates a reasonable relation between fining rate and the rate of change of channel slope the predictive value of this relation is limited by the regional nature of the data upon which it is based and the relative difficulty of obtaining accurate gradient information however as previously noted for alluvial fans although for different reasons channel gradient is correlated with link length and a reasonable predictive tool is apparent in a relation between link length and diminution rate the validity of the derived relation cannot be tested for want of a suitable data set several lines of evidence indicate that abrasion is unimportant as a fining mechanism on these rivers and it is argued that this may be typical of sedimentary links fining rate must then be a function of the efficiency with which sorting processes operate and it is suggested that this efficiency is dependent on aggradation rates associated with the lateral sediment influxes at the head and terminus of individual links

on why gravel bed streams are paved bedload transport in poorly sorted gravel bed streams downstream of dams is considered bedload and typical bed material subpavement size distributions are observed to be similar it follows that the coarse half of the subpavement moves through a reach at a rate near that of the fine half since coarser grains are intrinsically less mobile than fine grains it follows that some mechanism must act to nearly equalize mobility it is hypothesized that the pavement seen in gravel bed streams at low flow is in fact in place during typical transport events capable of moving all available sizes this pavement can provide the equalizing mechanism by exposing proportionally more coarse grains to the flow field data are used to quantify this concept and to develop a predictive relation for river pavement the model indicates that pavement should be absent in most sand bed streams in agreement with observation

variation in the reference shields stress for bed load transport in gravel bed streams and rivers 1 the present study examines variations in the reference shear stress for bed load transport r using coupled measurements of flow and bed load transport in 45 gravel bed streams and rivers the study streams encompass a wide range in bank full discharge 1 2600 m3 s average channel gradient 0 0003 0 05 and median surface grain size 0 027 0 21 m a bed load transport relation was formed for each site by plotting individual values of the dimensionless transport rate w versus the reach average dimensionless shear stress the reference dimensionless shear stress r was then estimated by selecting the value of corresponding to a reference transport rate of w 0 002 the results indicate that the discharge corresponding to r averages 67 of the bank full discharge with the variation independent of reach scale morphologic and sediment properties however values of r increase systematically with average channel gradient ranging from 0 025 0 035 at sites with slopes of 0 001 0 006 to values greater than 0 10 at sites with slopes greater than 0 02 a corresponding relation for the bank full dimensionless shear stress bf formulated with data from 159 sites in north america and england mirrors the relation between r and channel gradient suggesting that the bank full channel geometry of gravel and cobble bedded streams is adjusted to a relatively constant excess shear stress bf r across a wide range of slopes

scale variation of post glacial sediment yield in chilliwack valley british columbia the holocene volumetric sediment budget is estimated for coarse textured sediments sand and gravel in a large formerly glaciated valley in southwest british columbia erosion is estimated by compiling volumetric loss estimated in digital elevation models dems of gullied topography and by applying a non linear diffusion model on planar undissected hillslopes estimates of steepland yield are based on estimates of post glacial deposition volumes in fans cones and deltas at the outlets of low order tributary catchments erosion of post glacial fans and tributary valley fills is estimated by reconstructing formerly continuous surfaces results are classed by catchment order and compared across scales of contributing area revealing declining specific sediment yield in m3 km 2 a 1 with catchment area for the smaller tributaries 10 km2 and increasing specific sediment yield for larger tributaries and chilliwack valley itself approximately 60 of mobilized sediment is redeposited in first to third order catchments with lesser proportions stored at the outlets of higher order catchments a simple network routing model emphasizes the significant sediment flux contributions from colluvium drift blankets and gullies in steeper terrain as this material is deposited at junctions within the lower drainage network an increasing proportion of material is derived from remnant valley fills and para glacial fans in the major valleys yield from lower order steepland catchments tends to remain in storage indefinitely sequestered on footslopes these observations have implications for modelling the post glacial sediment balance amongst catchments of varying size after 104 years the system remains in disequilibrium the critical linkage lies between low order hillslope catchments fourth order and the larger valleys with more complex fluvial systems copyright 2010 john wiley sons ltd

disequilibrium of holocene sediment yield in glaciated british columbia it is generally supposed that specific sediment yield the quantity of sediment passing a monitored river cross section per unit area drained upstream of that section declines as the area drained increases1 3 part of the sediment mobilized from the land surface is supposed to go back into storage at field edges and on footslopes and floodplains in contrast we show here that data from british columbian rivers reveal a pattern of increasing specific sediment yield at all spatial scales up to 3 104 km2 this results from the dominance of secondary remobilization of quaternary sediments along river valleys over primary denudation of the land surface the result controverts the conventional model which has been derived from studies of small highly disturbed agricultural catch ments the rivers are still responding to the last glaciation giving a landscape relaxation time greater than 10 kyr this holds pro found implications for geomorphological theory and for studies of erosion