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

field derived relationships for flow velocity and resistance in high gradient streams summary we measured velocity and channel geometry in 10 reaches bed gradient 0 08 0 21 of a predominantly step pool channel the rio cordon italy over a range of discharges 3 80 of the bankfull discharge the resulting data were used to compute flow resistance at a station hydraulic geometry relations indicate that in most reaches the exponent describing the rate of velocity increases with discharge was between 0 48 and 0 6 which is within the range of published values for pool riffle channels the rio cordon data are also combined with published hydraulics data from step pool streams to explore non dimensional relationships between velocity and flow resistance and factors including unit discharge channel gradient and step geometry multiple regression analysis of this combined field dataset indicated that dimensionless unit discharge q is the most important independent variable overall in explaining variations in velocity and flow resistance followed by channel slope and the ratio of step height to step length empirical equations are provided both for dimensionless velocity and flow resistance but prediction of the former variable appears more reliable

compression of oceanic lithosphere an analysis of intraplate deformation in the central indian basin intraplate compressional deformation in the central indian basin is expressed as linear e w trending topographic undulations and geoid anomlies with characteristic spacings of approximately 200 km to elucidate the nature of this deformation we develop models of an oceanic lithosphere in a state of horizontal compression the lithosphere is treated as a viscous or plastic layer of uniform strength which overlies a viscous half space in which strength decreases exponentially with depth we compare models in which deformation with a dominant wavelength develops in response to flexural buckling and the hydrodynamic growth of instabilities for the viscous flexural buckling model deformation is constrained to occur in the antisymmetric mode by flexural folding which is characterized by uniform bending of the layer in the hydrodynamic flow model a range of deformational styles are possible in a strong viscous lithosphere deformation of the layer occurs by flexural folding at a wavelength which agrees with that predicted from flexural buckling theory in a lithosphere of intermediate strength the layer deforms by folding characterized by thickening which localizes beneath topographic highs in a relatively weak lithosphere the layer incurs an even greater amount of localized thickening and deforms in the symmetric or pinch and swell mode by inverse boudinage if the layer has a plastic rheology deformation occurs by inverse boudinage independent of the yield stress results from models in which the layer folds either flexurally or with periodic thickening are consistent with the observed depth distribution of seismicity in the central indian basin and with experimental rock rheological data because of the trade off between buoyancy forces and layer strength in determining the dominant wavelength a lithosphere which was overlain by weak sediments when intraplate deformation initiated can be characterized by a compressive layer strength almost a factor of 3 less than a lithosphere which was initially sediment free for a range of plausible models which consider both a sediment covered and sediment free lithosphere the observed wavelength requires deviatoric stresses in the indian plate of several hundreds of mpa

the variability of critical shear stress friction angle and grain protrusion in water worked sediments the erodibility of a grain on a rough bed is controlled by among other factors its relative projection above the mean bed its exposure relative to upstream grains and its friction angle here we report direct measurements of friction angles grain projection and exposure and small scale topographic structure on a variety of water worked mixed grain sediment surfaces using a simple analytical model of the force balance on individual grains we calculate the distribution of critical shear stress for idealized spherical grains on the measured bed topography the friction angle projection and exposure of single grain sizes vary widely from point to point within a given bed surface the variability within a single surface often exceeds the difference between the mean values of disparate surfaces as a result the critical shear stress for a given grain size on a sediment surface is characterized by a probability distribution rather than a single value on a given bed the crtitical shear stress distributions of different grain sizes have similar lower bounds but above their lower tails they diverge rapidly with smaller grains having substantially higher median critical shear stresses large numbers of fines trapp ed within pockets on the bed or shielded by upstream grains are effectively lost to the flow our calculations suggest that critical shear stress as conventionally measured is defined by the most erodible grains entrained during transient shear stress excursions associated with the turbulent flow this implies a physical basis for the indeterminacy of initial motion these observations suggest that transport rate shear stress relationships may be controlled in part by the increasing numbers of grains that become available for entrainment as mean shear stress increases they also suggest that bed textures and grain size distributions may be controlled within the constraints of an imposed shear stress and sediment supply regime by the influence of each size fraction on the erodibility of other grain sizes present on the bed

a comparison between flume and field bed load transport data and consequences for surface based bed load transport prediction 1 the ability of simple equations to predict bed load transport with limited knowledge of the bed surface material was investigated this was done using a data set consisting of 7 636 bed load transport values from the flume 1 317 data and from 84 river reaches 6 319 field data it was possible to collapse field and flume data by correcting the ratio between the shields number and its critical value with a very simple hiding function proposed as a power law of the d84 d50 ratio in so doing a surface based bed load transport formula was proposed it was successfully tested on an independent data set comprising sand and gravel bed rivers with slope in the range 0 0002 0 08 with 86 of the values predicted within a precision of 1 order of magnitude moreover the formula reproduced the low transport rates well contrary to the usual surface based formulas also tested and is particularly well suited for estimating low transport rates associated with near bankfull flow discharge this new formula is neither time consuming no fractionwise calculation nor data consuming the required parameters are the flow discharge the active width the slope and the surface grain diameters d50 and d84

river channel slope flow resistance and gravel entrainment thresholds 1 river beds are traditionally assumed to become mobile at a fixed value of nondimensional shear stress but several flume and field studies have found that the critical value is higher in steep shallow flows explanations for this have been proposed in terms of the force balance on individual grains the trend can also be understood in bulk flow terms if total flow resistance has base and additional components the latter due to protruding immobile grains as well as any bedforms and the stress corresponding to additional resistance is not available for grain movement in threshold conditions a quantitative model based on these assumptions predicts that critical shields stress increases with slope critical stream power is near invariant with slope and each has a secondary dependence on bed sorting the proposed slope dependence is similar to what force balance models predict and consistent with flume data and most field data possible explanations are considered for the inability of this and other models to match the very low critical values of width averaged stress and power reported for some low gradient gravel bed rivers

intraplate extensional tectonics of the eastern basin range inferences on structural style from seismic reflection data regional tectonics and thermal mechanical models of brittle ductile deformation the general lack of a correlation between earthquakes and surface faulting in the interior of the western u s cordillera has motivated our efforts to evaluate the geometry structural style and mechanism of normal faulting characteristic of this region of intraplate extension to address the problem we have interpreted over 1500 km of seismic reflection data and constructed detailed cross sections of the upper crust rheological models of the continental crust were calculated to examine the possibility of shallow quasi plastic flow and its influence on faulting in the eastern basin range the western colorado plateau and the middle rocky mountains our data and interpretations have revealed the following styles of cenozoic deformation 1 steep to low angle dip normal faulting along the wasatch fault 2 low angle dip and listric normal faulting possibly associated with movement on preexisting thrusts 3 the occurrence of asymmetric mostly eastward tilted tertiary basins that are bounded by low to moderate dipping planar and listric faults and 4 at least three vertically stacked en echelon low angle reflections in the mid to upper crust that dip gently westward from 3 km beneath the wasatch plateau to over 15 km at the utah nevada border these reflections are interpreted as normal detachment faults the structural style of the pervasive low to moderate angle dipping faults cannot be easily reconciled with classic brittle failure theory but the interpreted termination of normal faults at or above the deeper low angle reflections suggests the presence of shallow zones of ductile deformation that may have accommodated slip an important observation based on interpretations of seismic reflection profiles is that normal fault zones dip more gently in the subsurface than their associated scarps in unconsolidated surficial deposits segment boundaries of the wasatch fault zone apparently coincide with the positions of east trending displacement transfer structures in thrust sheets and the position of the precambrian uinta aulacogen suggesting that preexisting crustal structure partly controls the geometry of extension to examine the influence of ductile deformation quasi plastic flow was modeled for appropriate geotherms of the basin range and colorado plateau crusts these models provide constraints on the depth to the frictional quasi plastic transition that occurs as shallow as 8 km in the eastern basin range this depth also corresponds to the approximate depth above which most accurately determined earthquake foci for small earthquakes m 5 5 appear to nucleate at 10 15 km in or near the brittle ductile transition the rheological modeling suggests that a thermally deforming continental lithosphere plays an important role in the evolution of this extending intraplate region large scale low angle reflections may represent decollements and normal faults at the top of upper crustal zones of reduced shearing strength and higher ductility

sampling techniques for gravel sized sediments the methods commonly used for sampling the coarser surface layers of gravel bed streams are reviewed it is found that while an areal sample is biased toward the coarser grains compared with a volumetric sample of the same material the conversion formula suggested by a voidless cube model overcompensates for this effect a modified version of the cube model that accounts for porosity is proposed the modified cube model and tests conducted with areal sampling using wax indicate that area by weight analyses can be converted successfully to the equivalent bulk sieve analyses the average depth of the wax samples ranged from d65 d91 increasing with median grain size the equivalence of the grid by number and bulk sieve analyses is reaffirmed

hydrodynamics of steep streams with planar coarse grained beds turbulence flow resistance and implications for sediment transport the hydraulics of steep mountain streams differ from lower gradient rivers due to shallow and rough flows energetic subsurface flow and macro scale form drag from immobile boulders and channel and bed forms heightened flow resistance and reduced sediment transport rates in steep streams are commonly attributed to macro scale form drag however little work has explored steep river hydrodynamics in the absence of complex bed geometries here we present theory for the vertical structure of flow velocity in steep streams with planar rough beds that couples surface and subsurface flow we test it against flume experiments using a bed of fixed cobbles over a wide range of bed slopes 0 4 30 experimental flows have a nearly logarithmic velocity profile far above the bed flow velocity decreases less than logarithmically towards the bed and is non zero at the bed surface velocity profiles match theory derived using a hybrid eddy viscosity model in which the mixing length is a function of height above the bed and bed roughness subsurface flow velocities are large 1 m s and follow a modified darcy brinkman forchheimer relation that accounts for channel slope and shear from overlying surface flow near bed turbulent fluctuations decrease for shallow rough flows and scale with the depth averaged flow velocity rather than bed shear velocity flow resistance for rough planar beds closely matches observations in natural steep streams despite the lack of bed or channel forms in the experiments suggesting that macro scale form drag is smaller than commonly assumed in stress partitioning models for sediment transport

three dimensional reconstruction of fluvial surface sedimentology and topography using personal mobile laser scanning high resolution quantification of fluvial topography has been enabled by a number of geomatics technologies hyperscale surveys with spatial extents of 1 km2 have been widely demonstrated by means of terrestrial laser scanning tls and structure from motion sfm photogrammetry recent advances in the development and integration of global navigation satellite system gnss inertial measurement unit imu and lightweight laser scanning technologies are now resulting in the emergence of personal mobile laser scanners mls that have the potential to increase data acquisition and processing rates by 1 2 orders of magnitude compared to tls sfm and thus challenge the recent dominance of these technologies this investigation compares a personal mls survey using a leica pegasus backpack that integrates velodyne puck vlp 16 sensors and a multi station static tls survey using a riegl vz 1000 scanner to produce digital elevation models dems and surface sedimentology maps the assessment is undertaken on a 500 m long reach of the braided river feshie comparison to 107 independent real time kinematic rtk gnss check points resulted in similar mean error me and standard deviation error sde for tls me 0 025 m sde 0 038 m and personal mls me 0 014 m sde 0 019 m direct cloud to cloud c2c comparison between a sample of tls and personal mls observations 2 8 million points revealed that c2c distances follows a sharply decreasing burr distribution a 2 35 b 3 19 rate parameter s 9 53 empirical relationships between sub metre topographic variability and median sediment grain size 10 100 mm demonstrate that surface roughness from personal mls can be used to map median grain size differences between tls and personal mls empirical relationships suggest such relationships are dependent on survey technique personal mls offers distinct logistical advantages over sfm photogrammetry and tls for particular survey situations and is likely to become a widely applied technique

flow resistance in steep mountain streams resistance to flow at low to moderate stream discharge was examined in five small 12 77 km2 drainage area tributaries of chilliwack river british columbia more than half of which exhibit planar bed morphology the resulting data set is composed of eight to 12 individual estimates of the total resistance to flow at 61 cross sections located in 13 separate reaches of five tributaries to the main river this new data set includes 625 individual estimates of resistance to flow at low to moderate river stage resistance to flow in these conditions is high highly variable and strongly dependent on stage the darcy weisbach resistance factor ff varies over six orders of magnitude 0 29 12 700 and manning s n varies over three orders of magnitude 0 047 7 95 despite this extreme range both power equations at the individual cross sections and keulegan equations for reach averaged values describe the hydraulic relations well roughness is divided into grain and form considered as all non grain sources components form roughness is the dominant component accounting for about 90 of the total roughness of the system i e form roughness is on average 8 6 times as great as grain roughness of the various quantitative and qualitative form roughness indicators observed only the sorting coefficient d84 d50 correlates well with form roughness copyright 2008 john wiley sons ltd

macroroughness and variations in reach averaged flow resistance in steep mountain streams 1 steep mountain streams typically feature macroroughness elements like large immobile boulders or channel spanning bedforms such as step pool sequences the effects of macroroughness on resistance and flow velocity are not well understood and appropriate field parameters for representing macroroughness in flow velocity equations have not been identified the prediction of flow velocity in rough and steep streams therefore remains challenging we measured flow velocity and several macroroughness parameters i e boulder concentration boulder diameter and protrusion and roughness of longitudinal channel profiles in six reaches of steep mountain streams with plane bed riffle step pool and cascade channel morphologies the between site variations in flow resistance can be explained to a large degree by nondimensionalization of discharge and flow velocity using channel slope and a characteristic roughness length using any of our roughness parameters as the characteristic roughness length this nondimensionalization leads to a similarity collapse of the entire data set the remaining differences in flow resistance among the streams are related to dimensionless measures of macroroughness that describe the concentration of boulders or step density in a reach boulder concentration represents the measure best describing the data and is used in a simple regression equation for flow velocity the predictions were better than predictions by the variable power law equation proposed by ferguson although the regression might not be statistically significant the observed trends suggest that boulder concentration partly explains the residual variance of between site variation of flow resistance

understanding the influence of slope on the threshold of coarse grain motion revisiting critical stream power abstract this paper investigates the slope dependent variation in critical mean bed shear stress for coarse grain motion and evaluates stream power per unit bed area as an alternative threshold parameter explanations for observed slope dependency and existing approaches for predicting the critical stream power per unit bed area are reviewed an analysis of secondary bed load transport datasets is used to examine the strength of associations between stream power per unit bed area mean bed shear stress and mean velocity with bed load transport rate data from an original flume study are combined with secondary data from similar flume experiments to investigate the effect of slope on both critical stream power per unit bed area and critical mean bed shear stress results suggest that stream power per unit bed area is most closely correlated with bed load transport rate and also that critical stream power per unit bed area is less variable with slope than critical mean bed shear stress alternative solutions to approximating critical stream power are explored these include 1 modifying existing expressions for critical stream power to account for higher critical mean bed shear stresses at higher slopes and 2 applying a constant dimensionless critical stream power criterion

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

zenisu ridge mechanical model of formation abstract seabeam seismic and submersible surveys took place during the kaiko project and revealed significant compressive deformation at the northeastern end of the philippine sea plate related to the recent collision of the izu ogasawara arc against central japan intraoceanic thrusting at the base of the zenisu ridge a linear topographic high running a few tens of kilometers south of the nankai trough is supported by tectonic magnetic and gravimetric data we investigate the formation of the zenisu ridge in terms of compressive mechanical failure of a thin elastic perfectly plastic plate subducting at a trench and subject to a regional compressive axial force the rheological envelope concept is used throughout the numerical calculations based on a detailed study of flexure of the present day bending far from the deformation zone we evaluate the bending forces involved the bulge is 120 to 150 m high and the compressive stress all along the nankai trough is about 100 mpa in the zenisu ridge area an additional compressive stress is superimposed due to the nearby collision at izu peninsula we compute the vertical distribution of the deviatoric stress before failure and find that the deviatoric stress is maximum at a depth of 20 25 km in the trench area and again at the surface 60 to 100 km seaward in the vicinity of the bulge the development of a thrust joining these two maxima through the entire thickness of the lithosphere is discussed the model predicts that the formation of the zenisu ridge did not occur before 4 ma and is caused by progressive tectonic uplift due to the redistribution of bending stresses as the ridge approaches the nankai trough

applicability of bed load transport models for mixed size sediments in steep streams considering macro roughness in steep mountain streams macro roughness elements typically increase both flow energy dissipation and the threshold of motion compared to lower gradient channels reducing the part of the flow energy available for bed load transport bed load transport models typically take account of these effects either by reducing the acting bed shear stress or by increasing the critical parameters for particle entrainment here we evaluate bed load transport models for mixed size sediments and models based on a median grain size using a large field data set of fractional bed load transport rates we derive reference shear stresses and bed load transport relations based on both the total boundary shear stress and a reduced or effective shear stress that accounts for flow resistance due to macro roughness when reference shear stresses are derived from the total boundary shear stress they are closely related to channel slope but when they are derived from the effective shear stress they are almost invariant with channel slope the performance of bed load transport models is generally comparable when using the total shear stress and a channel slope related reference shear stress or when using the effective shear stress and a constant reference shear stress however dimensionless bed load transport relations are significantly steeper for the total stress approach whereas they are similar to the commonly used fractional wilcock and crowe wc transport model for the effective stress approach this similarity in the relations allows the wc model developed for lower gradient streams to be used in combination with an effective shear stress approach in steep mountain streams

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

flow resistance in steep streams an experimental study 1 frequently an assessment of the mean water velocity in a stream is necessary to estimate the discharge associated with a particular flow depth or conversely the mean depth associated with a particular discharge in the absence of a direct measurement of flow velocity a flow resistance approach which establishes the relation between depth and velocity can be applied two approaches have been used in the past traditional approaches based on the use of a resistance coefficient e g darcy weisbach or dimensionless hydraulic geometry approaches to examine if one approach is more appropriate for steep streams data from 31 flume experiments conducted to examine flow resistance in self formed cascade channels were analyzed a dimensionless hydraulic geometry approach developed using at a station data to characterize the q exponent and between site data to characterize the exponent on the channel slope term was more accurate than more traditional approaches the developed relation was similar to the established rational relation v g0 2q0 6s 0 4s0 2 suggesting that the rational relation has merit the approach does not utilize a flow partitioning approach since in steep streams with small relative depths the grains themselves generate form and spill resistance the observation that a single dimensionless hydraulic geometry flow resistance relation can describe measurements across a range of grain sizes and bed slopes 3 21 suggests that steep streams may follow a single scaling relation similar to the regime equations associated with lowland rivers

recent tectonics associated with the subduction collision of the d entrecasteaux zone in the central new hebrides abstract recent data from the new hebrides vanuatu subduction zone have enabled a morphological description and tectonic interpretation to be made of the complex plate contact between the d entrecasteaux zone and the west torres massif on the one hand and the old santo malekula block on the other between latitudes 14 30 and 17 s no trench occurs owing to the presence of the old rigid santo malekula block at the edge of the overriding plate the outer limit of plate contact describes a tortuous line westward of the projected line of the adjacent trenches this may be explained by local collision of the north d entrecasteaux ridge and the south d entrecasteaux chain with the west flank of santo this collision is compensated for by lateral plastic flow of the inner wall downward into the small basins which separate the d entrecasteaux zone ridges a process which may be explained by plastic plane strain theory the westward jump of the plate contact zone here may result from pieces of the north d entrecasteaux ridge being cut off and incorporated in the frontal arc a review of the geological evidence and the shallow seismicity of the central new hebrides shows that radiant horizontal stresses resulting from this collision have generated a specific compressive stress regime which influences the whole width of the arc the resultant deformation shows a close resemblance to a theoretical strain field produced by the indentation of a long narrow plastic body cf the arc by a rigid flat die cf the d entrecasteaux zone thus the central new hebrides block is both elastically bent under vertical stresses and plastically deformed and pushed eastwards by horizontal stresses recent uplift of the eastern chain can be explained by this model in contrast at the rear of both the northern and southern sections of the arc the tectonics are mainly controlled by a tensional stress regime the strong plate interaction due to the subduction of the d entrecasteaux zone is thought to be responsible for the compressive stress regime across the central new hebrides the same cause can be invoked to account for the tensional stress regime observed in north and south new hebrides rear arc regions

feedback between bed load transport and flow resistance in gravel and cobble bed rivers 1 to calculate bed load engineers often use flow resistance equations that provide estimates of bed shear stress in these equations on the basis of the estimate of the appropriate hydraulic radius associated with the bed only the bed roughness ks is commonly set as a constant whatever the bed load intensity however several studies have confirmed the existence of feedback mechanisms between flow resistance and bed load suggesting that a flow dependent bed roughness should be used therefore using a data set composed of 2282 flume and field experimental values this study investigated the importance of these feedback effects new flow resistance equations were proposed for three flow domains domain 1 corresponds to no bed load and a constant bed roughness ks d where d is a representative grain diameter whereas domain 3 corresponds to a high bed load transport rate over a flat bed with a constant bed roughness ks 2 6d between these two domains a transitional domain 2 was identified for which the bed roughness evolved from d to 2 6d with increasing flow conditions in this domain the darcy weisbach resistance coefficient f can be approximated using a constant for a given slope the results using this new flow resistance equation proved to be more accurate than those using equations obtained from simple fittings of logarithmic laws to mean values the data set indicates that distinguishing domains 2 and 3 is still relevant for bed load in particular the data indicate a slope dependence in domain 2 but not in domain 3 a bed load model based on the tractive force concept is proposed finally flow resistance and bed load equations were used together to calculate both shear stress and bed load from the flow discharge the slope and the grain diameter for each run of the data set efficiency tests indicate that new equations implicitly taking a feedback mechanism into account can reduce the error by a factor of 2 when compared to other equations currently in use showing that feedback between flow resistance and bed load can improve field bed load modeling

flow resistance estimation in mountain rivers examination of the flow resistance of high gradient gravel and boulder bed rivers using data collected in british mountain rivers with slopes of 0 4 4 shows that there are differences in resistance variation between mountain and lowland rivers and that between site variations do not necessarily reflect at a site variations comparison of data with the familiar resistance equation relating the dracy weisbach friction factor to the logarithm of relative submergence shows that the equation tends to overestimate the resistance in uniform flow the equation also tends to underestimate the rate of change of resistance at a site as discharge varies with high gradients the influences of nonuniform channel profile sediment size distribution channel slope and sediment transport are reviewed but the data do not allow any quantification of these effects instead an empirical approach based on the available data is presented allowing the friction factor to be calculated from the relative submergence with an error of up to n25 to n35 a summary of the field data is included

velocity prediction in high gradient channels summary in 15 mountain stream reaches containing instream wood we characterized velocity and flow resistance at bankfull through low flows these data were 1 used to assess the accuracy of previously published velocity prediction techniques for high gradient channels and 2 were combined with field data from other studies to develop general methodologies for predicting velocity and flow resistance in alluvial and mixed alluvial bedrock channels both with and without step forming instream wood velocity and flow resistance were poorly predicted by variables characterizing grain size and relative grain submergence conversely methods based on detrended standard deviation of bed elevations rz and relative bedform submergence h rz explained up to 84 of the variance in the measured flow resistance coefficients and 97 of the variance in dimensionless velocity with an average velocity of 0 44 m s for the collected measurements velocity was predicted with rms root mean square error as low as 0 071 m s 16 of average when discharge and bedform geometry is known and 0 10 m s 23 when only bedform geometry is known additionally an empirical relationship indicates v u h r z supporting previouslypublished laboratory findings using a field based dataset in complex high gradient channels interactions between instream wood and clasts result in substantially enhanced step heights and flow resistance this compound effect defies description by grain size and relative grain submergence however rz and h rz quantify variability due to both clasts in combination with wood and clasts alone providing relatively accurate predictions for the tested dataset and indicating substantial predictive capabilities in channels where bedforms are the primary source of flow resistance published by elsevier b v

incipient sediment motion across the river to debris flow transition sediment transport in mountain channels controls the evolution of mountainous terrain in response to climate and tectonics and presents major hazards to life and infrastructure worldwide despite its importance we lack data on when sediment moves in steep channels and whether movement occurs by rivers or debris flows we address this knowledge gap using laboratory experiments on initial sediment motion that cross the river to debris flow sediment transport transition results show that initial sediment motion by river processes requires heightened dimensionless bed shear stress or critical shields stress with increasing channel bed slope by as much as fivefold the conventional criterion established for lowland rivers beyond a threshold slope of 22 the channel bed fails initiating a debris flow prior to any fluvial transport and the critical shields stress within the debris flow regime decreases with increasing channel bed slope combining theories for both fluvial and debris flow incipient transport results in a new phase space for sediment stability with implications for predicting fluvial sediment transport rates mitigating debris flow hazards and modeling channel form and landscape evolution

characteristics of log and clast bed steps in step pool streams of northwestern montana usa the role of log and clast steps was studied in 53 step pool reaches in 32 streams in northwestern montana in each reach 20 consecutive steps were sampled drainage areas ranged from 0 5 to 11 5 km2 mean step spacing was found to be proportional to channel gradient width of the bankfull channel and drainage area mean step height was proportional to the width of the channel no significant difference exists between clast and log steps with regard to step spacing and step height this suggested either that 1 woody debris is mobile in even the smallest channels in the study area or 2 channel flows arrange clast steps around immobile woody debris calculations of theoretical entrainment and transport of sediment suggest that the coarse clasts forming steps are capable of being entrained at bankfull discharge in most channels the presence of immobile log steps composed of living roots in the upstream reaches an increase in the percentage of log steps with gradient and a decrease in this percentage with the width of the bankfull channel and drainage area imply that woody debris is mobile primarily in the downstream reaches calculations of flow resistance suggest that most steps serve to maximize flow resistance these results support the second hypothesis that the height and spacing of clast steps are adjusted around immobile log steps to maintain consistent step characteristics

bed load transport measurements with geophones and other passive acoustic methods abstractthis paper reviews the more widely used bed load surrogate acoustic measuring techniques that were tested both in flume experiments and field settings a fair number of these measuring tech

accelerating seismic moment release and outer rise compression possible precursors to the next great earthquake in the alaska peninsula region the moment release rate in the kodiak island ki segment increased prior to the great 1964 prince william sound earthquake mw 9 2 starting in 1983 the moment release rate in the shumagin island si segment shows a similar increase in july 1990 an outer rise reverse earthquake showed arc normal compression at a depth of 42 km seaward of the alaska peninsula ap segment because accelerating moment release and arc normal compression have both been proposed as precursors to large and great earthquakes we suggest this is evidence that the si ap region is nearing the end of the seismic cycle between large thrust earthquakes

evaluation of flow resistance in gravel bed rivers through a large field data set 1 a data set of 2890 field measurements was used to test the ability of several conventional flow resistance equations to predict mean flow velocity in gravel bed rivers when used with no calibration the tests were performed using both flow depth and discharge as input since discharge may be a more reliable measure of flow conditions in shallow flows generally better predictions are obtained when using flow discharge as input the results indicate that the manning strickler and the keulegan equations show considerable disagreement with observed flow velocities for flow depths smaller than 10 times the characteristic grain diameter most equations show some systematic deviation for small relative flow depth the use of new definitions for dimensionless variables in terms of nondimensional hydraulic geometry equations allows the development of a new flow resistance equation the best overall performance is obtained by the ferguson approach which combines two power law flow resistance equations that are different for deep and shallow flows to use this approach with flow discharge as input a logarithmic matching equation in terms of the new dimensionless variables is proposed for the domains of intermediate and large scale roughness the field data indicate a considerable increase in flow resistance as compared with the domain of small scale roughness the ferguson approach is used to discuss the importance of flow resistance partitioning for bed load transport calculations at flow conditions with intermediate and large scale roughness in natural gravel cobble and boulder bed streams

theoretical development on the effects of changing flow hydraulics on incipient bed load motion 1 several decades of flume and field measurements have indicated that in rough turbulent flows the critical shields stress increases with increasing slope and associated decreasing relative depth this result contradicts the usual consideration of a decreased critical shields value on very steep slopes because of increased gravitational effects however recent studies have demonstrated that these experimental results could be reproduced with a force balance model if the classical logarithmic velocity profile was replaced with a velocity profile that was more compatible with available velocity measurements over gravel beds these measurements indicate the existence of a roughness layer that is a zone of almost constant velocity close to the bed whose properties mean velocity and turbulence depended on the flow s relative depth unfortunately velocity profile measurements for low relative depth associated with steep slopes are scarce and it is still difficult to include such flow properties in a force balance model flow resistance data on the basis of depth average velocity measurements are very common and cover a wide range of slopes and relative depths in this paper these data are used to fit a velocity profile including a roughness layer when used in a force balance model for incipient motion it adequately reproduced a data set composed of 270 critical shields values measured in a flume with near uniform sediments the relevance of this research to field problems is discussed using a data set composed of 92 critical shields stresses obtained from field measurements finally a model is proposed for field applications taking into account the slope effect

geomorphological effectiveness of floods to rework gravel bars insight from hyperscale topography and hydraulic modelling bars are key morphological units in river systems fashioning the sediment regime and bedload transport processes within a reach reworking of these features underpins channel adjustment at larger scales thereby acting as a key determinant of channel stability despite their importance to channel evolution few investigations have acquired spatially continuous data on bar morphology and sediment size to investigate bar reworking to this end four bars along a 10 km reach of a wandering gravel bed river were surveyed with terrestrial laser scanning tls capturing downstream changes in slope bed material size and channel planform detrended standard deviations z were extracted from tls point clouds and correlated to underlying physically measured median grain size d50 across a greater range of z values than have hitherto been reported the resulting linear regression model was used to create a 1 m resolution median grain size map a fusion of airborne lidar and optical empirical bathymetric mapping was used to develop reach scale digital elevation models dems for rapid two dimensional hydraulic modelling using jflow software the ratio of dimensionless shear stress over critical shear stress was calculated for each raster cell to calculate the effectiveness of a range of flood events 2 33 100 year recurrence intervals to entrain sediment and rework bar units results show that multiple bar forming discharges exist whereby frequent flood flows rework tail and back channel areas whilst much larger less frequent floods are required to mobilise the coarser sediment fraction on bar heads valley confinement is shown to exert a primary influence on patterns of bar reworking historical aerial photography hyperscale dems and hydraulic modelling are used to explain channel adjustment at the reach scale the proportion of the bar comprised of more frequently entrained units tail back channel supra platform relative to more static units bar head exerts a direct influence upon geomorphic sensitivity

large woody debris and flow resistance in step pool channels cascade range washington abstract total flow resistance measured as darcy weisbach f in 20 step pool channels with large woody debris lwd in washington ranged from 5 to 380 during summer low flows step risers in the study streams consist of either 1 large and relatively immobile woody debris bedrock or roots that form fixed or forced steps or 2 smaller and relatively mobile wood or clasts or a mixture of both arranged across the channel by the stream flow resistance in step pool channels may be partitioned into grain form and spill resistance grain resistance is calculated as a function of particle size and form resistance is calculated as large woody debris drag combined grain and form resistance account for less than 10 of the total flow resistance we initially assumed that the substantial remaining portion is spill resistance attributable to steps however measured step characteristics could not explain between reach variations in flow resistance this suggests that other factors may be significant the coefficient of variation of the hydraulic radius explained 43 of the variation in friction factors between streams for example large woody debris generates form resistance on step treads and spill resistance at step risers because the form resistance of step pool channels is relatively minor compared to spill resistance and because wood in steps accentuates spill resistance by increasing step height we suggest that wood in step risers influences channel hydraulics more than wood elsewhere in the channel hence the distribution and function not just abundance of large woody debris is critical in steep step pool channels

mechanisms of the nyos carbon dioxide disaster and of so called phreatic steam eruptions abstract during the night of august 21 1986 a huge volume of concentrated co 2 was emitted by the crater maar of nyos cameroon it killed more than 1700 people and all animal life as far as 14 km away two hypotheses have been put forward to account for this disaster the chronologically first one imputes it to have been a phreatic eruption exceptionally co 2 rich as had been the case in february 1979 on the dieng plateau in central java indonesia where the erupting crater was lake less the second one claims a limnic origin for the co 2 release through an overturn of the 220 m deep lake nyos the hypolimnium of which was supposed to be oversaturated by dissolved gas of volcanic origin the present paper points to six observed facts for which the eruptive hypothesis easily accounts and which the authors of the limnic one do ignore

influence of particle shape and sorting upon sample size estimates for a coarse grained upland stream abstract present bulk sampling recommendations for the characterisation of fluvial sediments based upon ellipsoids of revolution do not take into account variations in particle shape and sorting disc shaped particles with equivalent b axes to spheres have lower relative masses and require more relaxed sampling criteria compared to existing recommendations whereas heavier cube and rod shaped particles require more stringent criteria empirical data from the river rede northumberland uk an upland gravel bed channel indicate that samples are dominated by discs however particle shape was not constant in every grain size fraction blocky material cubes and rods was more frequent in the 63 mm fraction in comparison to the other finer fractions data based on the weight of the d 99 9 particle indicate that a larger sample weight is required when the coarsest size category of that sample is dominated by blocky material sorting also affects the size of the sample required to characterise a deposit the more poorly sorted the deposit the larger the sample has to be or the finer should be the truncation grain size this is particularly evident in samples with a high matrix concentration two sample reference lines developed from these data using the 0 1 by mass criteria recommend larger minimum sample sizes or finer truncation in comparison to other published standards data from a second site support these results indicating that they may be applicable to other poorly sorted upland gravel bed streams analysis of the size category variance demonstrates that the new guidelines returned the lowest variance levels suggesting that they should be used where particularly accurate sampling procedures are required

inelastic models of lithospheric stress 11 implications for outer rise seismicity and dynamics summary outer rise seismicity and dynamics are examined using inelastic models of lithospheric deformation which allow a more realistic characterization of stress distributions and failure behaviour we conclude that thrust and normal faulting outer rise earthquakes represent substantially different states of stress within the oceanic lithosphere specifically the normal faulting events occur in response to downward plate bending which establishes the standard bending dominated state of outer rise stress and the thrust faulting events occur in response to an elevated level of in plane compression which develops only in response to exceptional circumstances this interpretation accounts for the observation that normal faulting outer rise earthquakes occur more frequently and are more widely distributed than their thrust faulting counterparts an observation for which the simple bending model offers no explanation in addition attributing both thrust and normal faulting outer rise earthquakes to plate bending implies that both classes of events should occur within relatively close lateral proximity to one another because both are allegedly a manifestation of the same bendingdominated stress distribution whereas in reality this is not observed we propose that the tendency for thrust faulting outer rise earthquakes to exhibit greater source depths than their normal faulting counterparts an observation that is frequently cited in support of the bending interpretation of the former is merely a consequence of the fact that bending induced tension is confined to the upper lithosphere our model predicts that outer rise in plane force variations may promote thrust faulting outerrise activity prior to an underthrusting interplate subduction earthquake and normalfaulting outer rise activity following such an earthquake but that both forms of outerrise activity are unlikely to be associated with the same subduction earthquake a corollary implication of our model is that subduction earthquakes are likely to be either preceded by or followed by an absence of large outer rise earthquakes levels of in plane compression necessary to generate thrust faulting outer rise earthquakes are attributed to stress concentrations within the subducting plate that are induced by relatively localized resistance to regionally distributed plate driving forces resistance of this nature may result from either the attempted subduction of relatively buoyant i e isostatically compensated bathymetric features or the existence of strong interplate

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

is the critical shields stress for incipient sediment motion dependent on channel bed slope data from laboratory flumes and natural streams show that the critical shields stress for initial sediment motion increases with channel slope which indicates that particles of the same size are more stable on steeper slopes this observation is contrary to standard models that predict reduced stability with increasing slope due to the added downstream gravitational force processes that might explain this discrepancy are explored using a simple force balance model including increased drag from channel walls and bed morphology variable friction angles grain emergence flow aeration and changes to the local flow velocity and turbulent fluctuations surprisingly increased drag due to changes in bed morphology does not appear to be the cause of the slope dependency because both the magnitude and trend of the critical shields stress are similar for flume experiments and natural streams and significant variations in bed morphology in flumes is unlikely instead grain emergence and changes in local flow velocity and turbulent fluctuations seem to be responsible for the slope dependency due to the coincident increase in the ratio of bed roughness scale to flow depth i e relative roughness a model for the local velocity within the grain roughness layer is proposed based on a 1 d eddy viscosity with wake mixing in addition the magnitude of near bed turbulent fluctuations is shown to depend on the depth averaged flow velocity and the relative roughness extension of the model to mixed grain sizes indicates that the coarser fraction becomes increasingly difficult to transport on steeper slopes

self adjustment of stream bed roughness and flow velocity in a steep mountain channel understanding how channel bed morphology affects flow conditions and vice versa is important for a wide range of fluvial processes and practical applications we investigated interactions between bed roughness and flow velocity in a steep glacier fed mountain stream riedbach ct valais switzerland with almost flume like boundary conditions bed gradient increases along the 1 km study reach by roughly 1 order of magnitude s 3 41 with a corresponding increase in streambed roughness while flow discharge and width remain approximately constant due to the glacial runoff regime streambed roughness was characterized by semivariograms and standard deviations of point clouds derived from terrestrial laser scanning reach averaged flow velocity was derived from dye tracer breakthrough curves measured by 10 fluorometers installed along the channel commonly used flow resistance approaches darcy weisbach equation and dimensionless hydraulic geometry were used to relate the measured bulk velocity to bed characteristics as a roughness measure d84 yielded comparable results to more laborious measures derived from point clouds flow resistance behavior across this large range of steep slopes agreed with patterns established in previous studies for both lower gradient and steep reaches regardless of which roughness measures were used we linked empirical critical shear stress approaches to the variable power equation for flow resistance to investigate the change of bed roughness with channel slope the predicted increase in d84 with increasing channel slope was in good agreement with field observations

stress in the indo australian plate cloetingh s and wortel r 1986 stress in the ind austr ian plate in b johnson and a w bally editors intraplate deformation characteristics processes and causes tectonophysics 132 49 67 we modelled the state of stress in the indo australian plate in order to investigate quantitatively variations observed in tectonic style the numerical procedure incorporates the dependence of slab pull and ridge push on the age of the oceanic lithosphere estimates are presented for the average net resistive forces at the himalayan collision zone the suction force acting on the overriding indo australian plate segment at the tonga kermadec trench and the drag at the base of the lithosphere our modelhng shows a concen ation of compressive stresses of the order of 3 5 lcbar in the ninetyeast ridge area the effects of the compressive resistance associated with himalayan collision and subduction of young lithosphere off the northern part of the sunda arc are focused in this region the stress field as calculated gives a consistent explanation for the observed concentration of seismic activity stein and okal 1978 and significant deformation in the oceanic crust weissel et al 1980 mcadoo and sandwell 1985 in the area the calculated stress field in the area adjacent to the southeast and central india ridges is characterized by tension parallel to the spreading axis this explains the concentration of near ridge normal faulting seismicity with t axes subparaile1 to the spreading ridge in the indian ocean as recently observed by bergman et al 1984 and wiens and stein 1984 the regional stress field along the strike of the sunda arc varies from compression seaward of and parallel to the sumatra trench segment to tension perpendicular to the java flores segment this explains the selective occurrence of well developed grabens seaward off the java flores segment of the trench observed by hilde 1983 our modelling shows that the observed rotation of the stress field denham et al 1979 in the australian continent is mainly the consequence of its geographic position relative to the surrounding trench segments and the variations of the forces acting on the down going slab in each of these the state of compression in west and central australia is induced by the action of resistive forces at the himalayan and banda arc collision zones the joint occurrence of high levels of compression in the plate s interior and normal faulting seismicity in the near ridge areas is a transient feature unique to the present dynamic situation of the indo australian plate

discussion of understanding the influence of slope on the threshold of coarse grain motion revisiting critical stream power by c parker n j clifford and c r thorne geomorphology volume 126 march 2011 pages 51 65 abstract this paper presents a discussion of parker et al 2011 in particular some theoretical developments are presented that give additional material to apprehend the effects of grain size water depth and slope on the critical shields parameter and critical stream power

constraints on yield strength in the oceanic lithosphere derived from observations of flexure summary the wavelength and amplitude of outer rises seaward of sub duction zones and arches surrounding islands and seamounts are used to parameterize flexure profiles in terms of the moment and curvature at the first zero crossing the data show the clear age dependence in the mechanical thickness of the lithosphere up to 60 100myr saturation of moment at large curvature is interpreted in terms of a depth dependent yield strength for the lithosphere using relations adopted from laboratory experiments of rock deformation a comparison of theoretical curves with observed moments indicates that old oceanic lithosphere has no long term strength below about 40 km depth with no difference between 100 and 165 myr old crust moderate axial loading forces 200 mpa can explain most variations in the moment curvature observations except in the case of the kuril trench which appears anomalous given the age of the crust regional tension causes greater variability in moment as compared to regional compression because of the greater slope in the brittle failure envelope under tension the observations point to a lithosphere weaker than the prediction from experimental deformation of rocks of the possible weakening mechanisms elevated pore fluid pressure on faults does not predict the correct age dependence and is incompatible with earthquake focal mechanisms our favoured explanation is that the activation energy q appropriate for ductile flow at geological strain rates is lower than the values derived from laboratory extrapolations of dry olivine data taken at high temperatures if recent oceanic geotherms are reliable q in the lower lithosphere must be lower than 100kcal mol 1 the method used here is most appropriate for trench profiles with curvatures greater than 10 7m 1 for lower curvatures such as along seamount profiles small errors in the curvature estimate cause large changes in rheological parameters

calculating bed load transport in steep boulder bed channels 1 steep rough channels occupy a large fraction of the total channel length in mountainous regions most sediment mobilized on hillslopes must pass through these streams before reaching lower gradient channels steep channels have wide grain size distributions that are composed of finer more mobile sediment and large rarely mobile grains the large grains can bear a significant portion of the total shear stress and thereby reduce the stress available to move the finer sediment conventional bed load transport equations often overpredict the sediment flux in steep channels by several orders of magnitude we hypothesize that sediment transport equations overpredict the sediment flux because they do not 1 account for the stress borne by rarely mobile grains 2 differentiate between highly and rarely mobile sediment and 3 account for the limited availability of mobile sediment here we modify a conventional bed load transport equation to include these three effects we use measurements of the flow bed properties and sediment flux in a small steep flume to test this equation we supply gravel at a constant rate through fields of regularly spaced immobile spheres and measure the bed coverage by gravel and sphere protrusion the percent of the sphere that protrudes above the gravel deposit for a given sphere spacing the proportion of the bed covered by gravel increases and the sphere protrusion decreases with greater sediment supply thus bed coverage and immobile grain protrusion may serve as proxies for sediment availability in steep rough streams unlike most transport equations that we tested our modified bed load equation predicts sediment fluxes to within an order of magnitude of the measured values our results demonstrate that accurately predicting bed load transport in steep rough streams may require accounting for the effects of local sediment availability coverage by mobile sediment and drag due to rarely mobile particles

flow resistance and hydraulic geometry in bedrock rivers with multiple roughness length scales many models of incision by bedrock rivers predict water depth and shear stress from discharge conversely palaeoflood discharge is sometimes reconstructed from flow depth markers in rock gorges in both cases assumptions are made about flow resistance the depth discharge relation in a bedrock river must depend on at least two roughness length scales exposed rock and sediment cover and possibly a third sidewalls a conceptually attractive way to model the depth discharge relation in such situations is to partition the total shear stress and friction factor but it is not obvious how to quantify the friction factor for rough walls in a way that can be used in incision process models we show that a single flow resistance calculation using a spatially averaged roughness length scale closely approximates the partitioning of stress between sediment and rock and between bed and walls in idealised scenarios both approaches give closer fits to the measured depth discharge relations in two small bedrock reaches than can be achieved using a fixed value of manning s n or the chezy friction factor sidewalls that are substantially rougher or smoother than the bed have a significant effect on the partitioning of shear stress between bed and sidewalls more research is needed on how best to estimate roughness length scales from observable or measurable channel characteristics

critical shear stress for incipient motion of sand gravel streambeds results of an experimental study of the incipient motion of streambeds composed of sand gravel sediment mixtures are reported and compared with the earlier findings for uniform sediments the experiments were conducted in an 8 m long by 0 30 m wide glass walled tilting flume and an 18 m long by 0 80 1 10 m wide trapezoidal concrete channel a reference transport method is used to define the beginning of bed material movement the experiments demonstrate that the incipient motion of individual size fractions within a mixture is controlled by their relative size with respect to median size intergranular effects mixture standard deviation effect of the shape of grain size distribution absolute value of median size absolute size effect and bed slope effect of relative depth on overall flow resistance the shear stress at incipient motion of median sized grains in mixtures is found to be the same as for uniform sediment of this size the present findings are consistent with available flume and field data a technique for calculating the critical shear stress of different grain sizes in coarse uniform sediments and unimodal weakly bimodal sediment mixtures is proposed

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

thermal mechanical controls on seismicity depth distributions in the san andreas fault zone earthquake depth distributions in continental crust can be related to factors which determine the depth of the transition from brittle to ductile failure these factors include temperature strain rate and lithology the san andreas fault zone of northern and central california is an ideal place to test the relative importance of these factors since there is abundant earthquake data and our understanding of the tectonic interaction of the pacific and north american plates provides constraints for several parameters in the san andreas fault zone we have found an approximately 3 km increase from northern to central california of the median depth of events and the depth above which 90 of events occur in addition depth distributions of earthquakes vary systematically from northern to central california both the maximum depth of earthquakes and the depth of the peak of seismic activity are shallower in northern california utilizing critical strength envelopes we have found that unlike the oceanic case this variation is not thermally controlled rather a combination of low strain rate and low stress level cause the seismicity in northern california to be shallow relative to central california

flow resistance of rock chutes with protruding boulders steep and short rough channels such as rock chutes are used in river restoration as grade stabilization structures the stability of these channels can be increased using boulders placed over the base material the boulders can be placed with different configurations such as randomly or in rows in each case their presence affects the geometry of the channel and modifies the hydraulic resistance this paper shows the results of tests conducted on rough channels with or without the insertion of protruding boulders the parameters that influence the flow resistance such as slope relative submergence and blocks disposition were systematically investigated to describe the hydraulic behavior of the structure the aim is to define a relationship useful for practical design which relates the flow resistance in terms of both darcy weisbach friction factor and manning coefficient the results were combined with available data for loose rock riprap to determine new experimental relationships

bedload transport measurements with impact plate geophones comparison of sensor calibration in different gravel bed streams indirect bedload transport measurements have been made with the swiss plate geophone system in five gravel bed mountain streams these geophone sensors record the motion of bedload particles transported over a steel plate mounted flush with the channel bed to calibrate the geophone system direct bedload transport measurements were undertaken simultaneously at the erlenbach in switzerland a moving basket sampler was used at the fischbach and ruetz streams in austria a helley smith type bedload sampler provided the calibration measurements a bunte type bedload trap was used at the rofenache stream in austria at the nahal eshtemoa in israel reid type slot bedload samplers were used to characterize the response of the geophone signal to bedload particles impacting on the plate geophone summary values were calculated from the raw signal and stored at one second intervals the number of impulses i e the number of peaks above a pre defined threshold value of the geophone output signal correlated well with field measured gravel transport loads and was found to be a robust parameter the relations of impulses to gravel transport loads were generally near linear but the steepness of the calibration relations differed from site to site by comparing the calibration measurements from the different field sites and utilizing insights gained during preliminary flume experiments it has been possible to identify the main factors that are responsible for site specific differences in the calibration coefficient the analysis of these calibration measurements indicates that the geophone signal also contains some information about the grain size distribution of bedload copyright 2013 john wiley sons ltd

flow regimes bed morphology and flow resistance in self formed step pool channels received 3 july 2008 revised 28 december 2008 accepted 13 january 2009 published 25 april 2009 1 we used a mobile bed flume with scaled grain size distribution channel geometry and flow to examine morphology and hydraulics of stepped channels we hypothesized that 1 step geometry and flow resistance differs significantly as a function of the range of grain sizes present 2 a transition from nappe to skimming flow occurs in stepped channels with mobile beds for conditions similar to stepped spillways and 3 the partitioning of flow resistance changes significantly when flow passes from nappe to skimming conditions results support each of these hypotheses and help to illuminate the complexity of v q relationships in stepped channels in which a dramatic decrease in flow resistance and increase in velocity accompany the transition from nappe to skimming flow near step forming events therefore a single flow resistance equation applicable to both ordinary and large floods may not be ideal in stepped channels nonetheless models based on dimensionless velocity and unit discharge appear more robust compared to those based on the darcy weisbach friction factor

controls of channel morphology and sediment concentration on flow resistance in a large sand bed river a case study of the lower yellow river abstract accurate estimation of flow resistance is crucial for flood routing flow discharge and velocity estimation and engineering design various empirical and semiempirical flow resistance models have been developed during the past century however a universal flow resistance model for varying types of rivers has remained difficult to be achieved to date in this study hydrometric data sets from six stations in the lower yellow river during 1958 1959 are used to calibrate three empirical flow resistance models eqs 5 7 and evaluate their predictability a group of statistical measures have been used to evaluate the goodness of fit of these models including root mean square error rmse coefficient of determination cd the nash coefficient na mean relative error mre mean symmetry error mse percentage of data with a relative error 50 and 25 p 50 p 25 and percentage of data with overestimated error poe three model selection criterions are also employed to assess the model predictability akaike information criterion aic bayesian information criterion bic and a modified model selection criterion msc the results show that mean flow depth d and water surface slope s can only explain a small proportion of variance in flow resistance when channel width w and suspended sediment concentration ssc are involved the new model 7 achieves a better performance than the previous ones the mre of model 7 is generally

can high resolution 3d topographic surveys provide reliable grain size estimates in gravel bed rivers high resolution topographic surveys such as those provided by structure from motion sfm contain a wealth of information that is not always exploited in the generation of digital elevation models dems in particular several authors have related sub metre scale topographic variability or surface roughness to sediment grain size by deriving empirical relationships between the two in fluvial applications such relationships permit rapid analysis of the spatial distribution of grain size over entire river reaches providing improved data to drive three dimensional hydraulic models allowing rapid geomorphic monitoring of sub reach river restoration projects and enabling more robust characterisation of riverbed habitats however comparison of previously published roughness grain size relationships shows substantial variability between field sites using a combination of over 300 laboratory and field based sfm surveys we demonstrate the influence of inherent survey error irregularity of natural gravels particle shape grain packing structure sorting and form roughness on roughness grain size relationships roughness analysis from sfm datasets can accurately predict the diameter of smooth hemispheres though natural irregular gravels result in a higher roughness value for a given diameter and different grain shapes yield different relationships a suite of empirical relationships is presented as a decision tree which improves predictions of grain size by accounting for differences in patch facies large improvements in d50 prediction are possible sfm is capable of providing accurate grain size estimates although further refinement is needed for poorly sorted gravel patches for which c axis percentiles are better predicted than b axis percentiles

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

controls on at a station hydraulic geometry in steep headwater streams colorado usa detailed hydraulic measurements were made in nine step pool five cascade and one plane bed reach in fraser experimental forest colorado to better understand at a station hydraulic geometry ahg relations in these channel types average values for ahg exponents m 0 49 f 0 39 and b 0 16 were well within the range found by other researchers working in steep gradient channels a principal component analysis pca was used to compare the combined variations in all three exponents against five potential control variables wood d84 grain size distribution coefficient of variation of pool volume average roughness area projected wetted area and bed gradient the gradient and average roughness area were found to be significantly related to the pca axis scores indicating that both driving and resisting forces influence the rates of change of velocity depth and width with discharge further analysis of the exponents showed that reaches with m b f are most likely dominated by grain resistance and reaches below this value m b f are dominated by form resistance copyright 2010 john wiley sons ltd

the role of water in the deformation of dunite specimens of two natural dunites anita bay of 100 m grain size and aheirn of 900 m grain size have been deformed in experiments at temperatures between 1200 and 1400 c and constant strain rates between 10 4 and 10 6 s 1 in a gas medium deformation apparatus at 300 mpa confining pressure prior to these experiments the specimens were given a heat treatment in a controlled oxygen fugacity furnace at 1200 c for 60 hours to dehydrate the trace layer silicate minerals present and drive off adsorbed water the predried specimens are much stronger than specimens tested under wet conditions in an earlier study the predried specimens also do not show the apparent grain size dependence seen under wet conditions infrared absorption measurements on the present specimens and those of the earlier study indicate that for a given rock flow stress can be correlated with the intensity of a residual water related broad absorption the addition of water to a predried specimen results in both a mechanical reweakening and an intensifying of the broadband infrared component the weakening of the dunites under wet conditions is probably strongly influenced by the presence of small amounts of a water related species in the grain boundaries but intragranular weakening may also be contributing it is suggested that the concentration of the water related species in the grain boundaries is governed by its concentration in the small melt fraction present the amounts of water that have been found to be of importance for the strength of these dunites are of the order of 0 01 wt amounts much less than most estimates of the water content of the earth s undepleted upper mantle such water may have an important role in determining upper mantle flow behavior stress strain curves for all experiments are available with entire manuscript on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b84 008 2 50 payment must accompany order

modeling river bed morphology roughness and surface sedimentology using high resolution terrestrial laser scanning 1 recent advances in technology have revolutionized the acquisition of topographic data offering new perspectives on the structure and morphology of the earth s surface these developments have had a profound impact on the practice of river science creating a step change in the dimensionality resolution and precision of fluvial terrain models the emergence of hyperscale survey methods including structure from motion photogrammetry and terrestrial laser scanning tls now presents the opportunity to acquire 3 d point cloud data that capture grain scale detail over reach scale extents translating these data into geomorphologically relevant products is however not straightforward unlike traditional survey methods tls acquires observations rapidly and automatically but unselectively this results in considerable noise associated with backscatter from vegetation and other artifacts moreover the large data volumes are difficult to visualize require very high capacity storage and are not incorporated readily into gis and simulation models in this paper we analyze the geomorphological integrity of multiscale terrain models rendered from a tls survey of the braided river feshie scotland these raster terrain models are generated using a new computationally efficient geospatial toolkit the topographic point cloud analysis toolkit topcat this performs an intelligent decimation of point cloud data into a set of 2 5 d terrain models that retain information on the high frequency subgrid topography as the moments of the locally detrended elevation distribution the results quantify the degree of terrain generalization inherent in conventional fluvial dems and illustrate how subgrid topographic statistics can be used to map the spatial pattern of particle size grain roughness and sedimentary facies at the reach scale