a detached eddy simulation model for the study of lateral separation zones along a large canyon bound river lateral flow separation occurs in rivers where banks exhibit strong curvature in canyon bound rivers lateral recirculation zones are the principal storage of fine sediment deposits a parallelized three dimensional turbulence resolving model was developed to study the flow structures along lateral separation zones located in two pools along the colorado river in marble canyon the model employs the detached eddy simulation des technique which resolves turbulence structures larger than the grid spacing in the interior of the flow the des 3d model is validated using adcp flow measurements taken during the 2008 controlled flood release from glen canyon dam a point to point validation using a number of skill metrics often employed in hydrological research is proposed here for fluvial modeling the validation results show predictive capabilities of the des model the model reproduces the pattern and magnitude of the velocity in the lateral recirculation zone including the size and position of the primary and secondary eddy cells and return current the lateral recirculation zone is open having continuous import of fluid upstream of the point of reattachment and export by the recirculation return current downstream of the point of separation differences in magnitude and direction of near bed and near surface velocity vectors are found resulting in an inward vertical spiral interaction between the recirculation return current and the main flow is dynamic with large temporal changes in flow direction and magnitude turbulence structures with a predominately vertical axis of vorticity are observed in the shear layer becoming three dimensional without preferred orientation downstream

the 1983 hydraulic jump in crystal rapid implications for river running and geomorphic evolution in the grand canyon for the last 1 000 to 10 000 years dozens of large debris fans have severely constricted the path of the colorado river in the grand canyon arizona at most of these fans the narrowest part of the channel eroded by the river is 0 5 of the upstream width at crystal creek a debris fan was emplaced in 1966 constricting the channel of the colorado river to about 0 25 of its upstream width between 1967 and 1983 forming a major rapid in this paper the hydraulics of crystal creek rapid are described and an analysis is presented to support the hypothesis that the major wave in the rapid was a normal wave one type of hydraulic jump hydraulic jumps rarely occur in natural river channels with erodible beds but one was present at crystal rapid because of the unusually severe constriction of the colorado river by the 1966 debris fan observations on the hydraulics of the river during this time including mid 1983 when progressively higher discharges culminated in excess of 96 000 cubic feet per second h

hydraulic geometry river sediment and the definition of bedrock channels a growing literature deals with bedrock channels erosion processes within them and their role in landscape evolution formal definitions currently in use classify channels as bedrock when alluvial cover is discontinuous or thin this is equated with a physical property of the flow using up to date erosion laws and descriptions of channel dynamics we show that existing definitions are difficult to apply and may lead to conflicting classifications we propose the definition a bedrock channel cannot substantially widen lower or shift its bed without eroding bedrock applied to channels in taiwan this leads to a different classification than previous definitions by analysing at a station hydraulic geometry of these channels we show that the classification exposes different controls of sediment effects on dynamics of channels classified as alluvial and bedrock

channel bed steps and pool shapes along soda creek three sisters wilderness oregon abstract field study of bedrock step pool systems along the upper reaches of soda creek in the three sisters wilderness of oregon shows strong correlation between several form variables shape and channel slope although step height and step length showed no regular spacing and variable correlation with channel slope length to height ratios demonstrated strong negative correlations steep slopes 20 to 80 featured greater step height and shorter pool lengths than did flatter channel slopes correlations between step height to length ratios and channel slope varied between three lithologies explained variations ranged from 0 984 for the oldest channel steps developed in basalt to 0 982 for steps of intermediate age developed in andesite to 0 964 for the youngest steps developed in dacite sample size was 57 40 and 33 respectively the frequency of pool shape classes did not vary by lithology but specific shape classes developed under differing slope conditions by rock type all pool classes have adjusted developed their form to maximize resistance to flow h l s and they have done so in remarkably uniform fashion

bedform genesis in bedrock substrates insights into formative processes from a new experimental approach and the importance of suspension dominated abrasion bedrock channels are common in the natural environment and bedrock channel erosion sets the pace of denudation in many river catchments however in comparison to the large number of studies concerning the formation of alluvial bedforms relatively few investigations have concerned bedrock bedform genesis field based analysis of sculptured forms within bedrock channels has been restricted notably by the slow rate of bedform development in such environments furthermore only a limited number of flume scale experiments have been conducted that attempt to simulate the genesis of sculpted bedforms in bedrock channels this study demonstrates that optimisation of clay beds through analysis of clay strength enables the development of features analogous to bedrock river channel bedforms even at a scale that is orders of magnitude smaller than some natural examples three sets of suspended sediment laden experiments were carried out using hard medium and soft clay bed substrates a suite of erosive bedforms including potholes flutes and furrows developed on all experimental beds all observed erosional features have clear equivalents to those observed in natural bedrock rivers bed shear strength was found to be a significant factor for the genesis of different types of simulated bedrock bedforms in our experiments with other factors such as flow velocity bed slope and flow depth held approximately constant importantly in a subset of experiments performed with an absence of suspended sediment fluid flow did not result in the erosion and development of bedforms in the clay bed hence this work illustrates that abrasion by suspended sediments is the key process required for the formation of these simulated bedrock bedforms in our experiments in the absence of bedload abrasion other processes such as plucking cavitation and dissolution will have been negligible

application of an automated lspiv system in a mountainous stream for continuous flood flow measurements an imaging based automated large scale particle image velocimetry lspiv system for flash flood monitoring is developed and deployed in a mountainous stream in the longchi catchment chengdu china this system is built from a low cost raspberry pi board level computer with a camera module which can acquire continuous images videos automatically at programmed intervals the minimum quadratic difference algorithm tracks surface patterns as flow tracers to estimate the distribution of surface velocities meanwhile a stereo imaging based virtual pole method has been developed to reconstruct the three dimensional topography with a stereo digital camera and a cross sectional bathymetry has been generated without manual surveying the varying water stage and water surface gradient which are critical parameters that affect image rectification and surface velocity measurements can also be directly resolved by applying the two imaging modules together discharge can then be estimated with the velocity area method through selected cross sections a flash flood that occurred between 24 july 2014 and 25 july 2014 is selected for analysis the water surface level reconstructed from image processing was validated with marked water levels and a good agreement was found with a root mean square error of 3 7 cm the discharge recorded during the flood recession process ranged from approximately 3 5 to 27 m3 s the rating curve obtained can be well described by a power function and the linear regression suggested a manning s n roughness coefficient of 0 18 of one specific cross section some limitations of the presented large scale particle image velocimetry system are also put forward and possible solutions are provided for future improvements with these proposed upgrades the system can provide valuable datasets of flash floods in steep mountainous streams which are critically needed for improving our understanding and modelling of many hydrological processes associated with flood generation propagation and erosion as well as for real time forecasting copyright 2016 john wiley sons ltd

analytical approach to river regime rational regime relationships for the width depth and slope of a channel in equilibrium are developed using the ackers and white sediment transport formulae and the white paris and bettess friction relationships together with the principle of maximum sediment transporting capacity favorable comparisons are made with data from sand and gravel channels and with existing empirical regime relationships

calibration of floodplain roughness and estimation of flood discharge based on tree ring evidence and hydraulic modelling summary the roughness calibration of floodplain and channels represents an important issue for flood studies this paper discusses the genesis of scars on trees and their use as benchmarks in roughness calibration in addition it presents a methodology to reconstruct unrecorded flood discharge in the alberche basin of the spanish central system the study is based on the combined use of dendrogeomorphic evidence i e scars on trees data from the navaluenga flow gauge avila province as well as a 1d 2d coupled numerical hydraulic model a total of 49 scars have been analyzed with dendrogeomorphic techniques scar dates are in concert with seven flood events documented in the systematic record i e 1989 1993 1996 2000 2002 2003 and 2005 we were also able to identify an additional event dated to 1970 which is before the flow gauge was installed at navaluenga based on the rating curve obtained from the flow gauge cross sectional area and data from hydraulic modelling we cannot find a statistically significant difference between water depths registered at the flow gauge and scar heights on trees p value 0 05 indicating that scars would have been generated through the impact of floating wood and that scars on trees would represent a valuable and accurate proxy for water depth reconstruction under this premise we have estimated the peak discharge of the 1970 flood event to 1684 3 519 2 m 3 s 1 which renders this event the largest documented flood for the alberche river at navaluenga in a last analytical step we discuss the use of scars on trees as benchmark for roughness calibration in ungauged or shortly recorded basins and address the added value of dendrogeomorphic data in flood frequency analysis

alpine faunas from the white mountains california adaptive change in the late prehistoric great basin abstract high elevation archaeological sites in the white mountains of eastern california document the establishment of small villages at elevations above 3100 m at about ad 800 replacing occupations that lacked substantial structures storage facilities and abundant plant processing equipment previllage faunas are far more tightly focused on large artiodactyls than on smaller mammals but do not differ significantly from village faunas in richness or diversity these differences do not provide strong support for the bettinger baumhoff 1982 model of late prehistoric adaptive change in the great basin but adequate testing of more subtle versions of such hypotheses may require a massive research effort

gsett 3 evaluation of the detection and location capabilities of an experimental global seismic monitoring system this article presents the results of the seismological evaluation of the first 18 months january 1995 to june 1996 of the group of scientific experts third technical test gsett 3 performance measures such as completeness estimates of detection thresholds and equivalent circle areas as an estimate of location accuracies are obtained by comparing the reb reviewed event bulletin of gsett 3 to global and regional reference bulletins and also by intrinsic methods incremental detection thresholds are stated on the pde preliminary determination of epicenter m b scale magnitude conversion formulae are derived to convert reb m b and other reference bulletin magnitudes to this scale at the 90 confidence level an incremental detection threshold of about m b pde 3 5 or better is attained in northwest europe and parts of north america central asia and australia apart from these areas the threshold is generally around 4 0 in the northern hemisphere in the southern hemisphere it is 4 2 or better in most of south america and northern and equatorial africa and between 4 2 and 4 6 in other regions with the highest values being attained in some remote parts of the southern oceans still at the 90 confidence level equivalent circle areas for the m b pde 4 4 5 magnitude range come close to 1 000 km 2 in northern europe the global average is about 8 000 km 2 at the 50 level the median of all detected events most northern hemisphere regions have equivalent circle areas at or below 1 000 km 2 and even in the southern hemisphere 5 000 km 2 are not exceeded observed performance is used to calibrate network simulation codes which allow to interpolate system capabilities over aseismic regions and to extrapolate for the capabilities of the future international monitoring system ims seismic network it is concluded that at the 90 confidence level except in remote ocean areas a global incremental detection threshold of m b pde 4 and a location accuracy of the order of 1 000 km 2 are attainable with the ims seismic network however this will require a full calibration of the network and an optimized usage of the auxiliary station network new computational methods as well as calibration will help to improve the depth determination

a froude scaled model of a bedrock alluvial channel reach 1 hydraulics the controls on hydraulics in bedrock alluvial rivers are relatively poorly understood despite the importance of the flow in determining rates and patterns of sediment transport and consequent erosion to measure hydraulics within a bedrock alluvial channel we developed a 1 10 froude scaled laboratory model of an 18 9 m bedrock alluvial river reach using terrestrial laser scanning and 3 d printing in the reported experiments water depth and velocity were recorded at 18 locations within the channel at each of five different discharges additional data from runs with sediment cover in the flume were used to evaluate the hydraulic impact of sediment cover the deposition and erosion of sediment patches in these runs are analyzed in the companion paper in our data 1 spatial variation in both flow velocity and froude number increases with discharge 2 bulk flow resistance and froude number become independent of discharge at higher discharges 3 local flow velocity and reynolds stress are correlated to the range of local bed topography at some but not most discharges 4 at lower discharges local topography induces vertical flow structures and slower velocities but these effects decrease at higher discharges and 5 there is a relationship between the linear combination of bed and sediment roughness and local flow velocity these results demonstrate the control that bedrock topography exerts over both local and reach scale flow conditions but spatially distributed hydraulic data from bedrock alluvial channels with different topographies are needed to generalize these findings

critical flow in rockbed streams with estimated values for manning s n the writer presented interesting experimental observations the discusser would like to comment on some aspects of the paper regarding critical flow or more accurately near critical flow critical slope calculations and boundary shear stress distributions in undular flows he hopes that the information will assist in refining the author s work

measuring foraging efficiency with archaeological faunas the relationship between relative abundance indices and foraging returns abstract in western north america models from foraging theory have been used to address subsistence change using archaeological faunas several studies have argued that return rates from foraging declined in a variety of late holocene contexts and support this position by applying a method involving the computation of a relative abundance index ai of large bodied animals to the sum of large and small ones we present the results of a series of computer simulations devised to identify the relationship between changes in such indices and changes in a forager s average return rate and discuss the implications of these simulations in light of our current work in the little boulder basin area of north central nevada these include 1 the importance of using knowledge of both post encounter return rates and changes in ai s to make inferences about changes in overall return rates 2 the fact that there are good reasons to expect ai values to be low and 3 what factors might contribute to the high ai values observed at archaeological sites

the educational value of the history of geomorphology abstract the history of geomorphology can be a valuable tool for educating students of geomorphology the largest and most available record of what geomorphologists thought and did in the past is their original published work also available are some fine papers on the history of geomorphology that review and analyze primary sources and past events in the discipline in order to generalize explain trends and reveal historical associations interest in the history of the discipline varies widely of course among geomorphologists nevertheless several educational benefits in addition to explaining the academic affiliation of geomorphology with two separate disciplines can be derived from incorporating the history of geomorphology into university level geomorphology courses history is a popular subject and presenting some geomorphic concepts using a historical approach can help to maintain or stimulate student interest because of the tendency for older literature to contain more qualitative description and methodological detail than more recent literature undergraduate students may comprehend some concepts better from older papers by reading the original literature students determine for themselves what previous practitioners accomplished rather than relying solely on the interpretations of others reading original literature also helps students realize that older does not mean less intelligent and that like the critical reading of recent geomorphic literature the critical reading of historic geomorphic papers can provide a wealth of new research ideas a thematic set of the historic literature can be used to demonstrate to students the scientific method the origin testing and evolution of hypotheses how explanations develop in this field and that science proceeds through individuals working in a sociological context including history of geomorphology in the curriculum helps to place contemporary research in the perspective of the past as well as the perspective of the future

unifying criterion for the velocity reversal hypothesis in gravel bed rivers it has been hypothesized that velocity reversals provide a mechanism for maintaining pool riffle morphology in gravel bed rivers an important habitat for salmonids which are at risk in many places worldwide and that are the focus of extensive environmental legislation in europe and north america however the occurrence of velocity reversals has been controversial for over 3 decades we present a simple one dimensional criterion that unifies and explains previous disparate findings regarding the occurrence of velocity reversals results show that reversal depends critically on the ratio of riffle to pool width residual pool depth difference between pool and riffle elevations and on the depth of flow over the riffle suggesting that land management activities which alter channel form or divert water from the channel can have negative impacts on the sustainability of pool riffle habitat in gravel bed rivers

characteristics of undular hydraulic jumps experimental apparatus and flow patterns in open channels the transition from supercritical to subcritical flows is called a hydraulic jump for low upstream froude numbers free surface undulations develop downstream of the jump and the hydraulic jump is called an undular jump new experiments on undular hydraulic jumps were performed in a rectangular channel in which the upstream flows were fully developed turbulent shear flows in this paper the main flow patterns are described visual and photographic observations indicate five types of undular jumps one of the main flow characteristics is the presence of lateral shock waves for froude numbers larger than 1 2 the results show that the disappearance of undular jump occurs for froude numbers ranging from 1 5 to 2 9 and that the wave length and amplitude of the free surface undulations are functions of the upstream froude number and the aspect ratio yc w

procedures for computing focal mechanisms from local sv p z data abstract a procedure for calculating the focal mechanism of an earthquake from the distribution of the ratio of the amplitudes of sv to p waves has been developed and tested the input consists of information taken from the hypocenter solution for the earthquake a factor for each station that corrects for the effect of the free surface on the observed wave amplitudes and the observed values of the ratio of the vertical component of p to the vertical component of sv the procedure starts with the selection of a slip direction the program then finds the best fault strike and dip corresponding to that slip direction with best measured by the smallest scatter of the dip for any strike all three fault parameters are then adjusted by an iterative least squares adjustment sv p z is a strongly nonlinear function of the fault parameters so the solution found by the procedure is inherently nonunique the acceptable solutions can be quite well constrained if the slip direction can be estimated initially on the basis of independent information a variety of tests of the procedure have been carried out on real and synthetic data given a set of amplitude data for an earthquake in bear valley california and told only that the mode of slip was predominantly strike slip the program found the san andreas fault i e converged to a fault with strike and dip close to the known values further work on a german earthquake served to bring out some of the ambiguities of the solutions analysis of data from a brief swarm of earthquakes in southwest germany showed that the method yields useful mechanisms for small events and revealed a rotation of the focal mechanisms during the swarm processing of amplitudes from synthetic seismograms gave a fault plane close to the known input but marked disagreement between the sv amplitudes on the synthetic seismograms and the amplitudes predicted by simple dislocation theory is unresolved

inversion for source parameters from sparse data sets test of the method and application to the 1951 m 6 9 kona hawaii earthquake we have tested a method originally developed by beisser et al 1990 to retrieve the source parameters strike dip rake and depth of sparsely recorded earthquakes from the inversion of teleseismic waveform data the complete wave train of all body waves is modeled using the reflectivity method the parameter space of strike dip and rake is searched to find the source orientation which leads to the minimum misfit between the observed and the synthetic seismogram the 1983 kaoiki hawaii earthquake ms 6 6 was chosen as a test case the inversion of the full data set 16 stations gave a fault plane solution similar to the best double couple moment tensor solution of harvard university and national earthquake information centre these three solutions were averaged to create a standard solution sparse data sets were simulated by decimating the full data set and the resulting fault plane solutions were compared with the standard we found that as few as one to three stations were sufficient to retrieve the focal mechanism of the 1983 kaoiki event we applied this technique to the 1951 kona hawaii earthquake ms 6 9 a total of four stations and nine components were used to model the source parameters of this earthquake the depth was estimated at 13 3 km the fault plane solution was a decollement type with a near horizontal plane dipping at about 15 to the southwest and a near vertical plane striking nw se this observation supports a tectonic model for the kona coast similar to that of kilauea s south flank the upper crust is pushed away from the center of hawaii slipping westward along a near horizontal plane of weakness

ungulate community richness grazer extinctions and human subsistence behavior in southern africa s cape floral region precipitation primary productivity and herbivore biomass are linked to ungulate richness the number of species in african ecosystems this study compares the richness of late middle to late pleistocene and holocene ungulate assemblages in southern africa s cape floral region cfr regression analysis demonstrates that pleistocene ungulate assemblages are significantly richer than their holocene counterparts elevated pleistocene ungulate richness is not explained by differential time averaging the presence of extinct taxa in pleistocene assemblages or by middle stone age msa to later stone age lsa technological change but instead by a greater number of grazing species in pleistocene faunal communities based on modern african analogs this implies that the pleistocene assemblages examined here sample time intervals characterized by elevated primary productivity particularly of grassland habitats greater ungulate biomass and altered rainfall regimes declining ungulate richness from the pleistocene to the holocene supports the hypothesis that the extinction of specialized grazers at the pleistocene holocene transition in the cfr was driven by declining productivity and availability of grassland habitats the contrast between rich pleistocene ungulate communities and impoverished holocene ungulate communities may also explain important differences in msa and lsa subsistence behavior it is proposed that intensified exploitation of fish shellfish tortoises and seabirds by lsa foragers during the holocene reflects an expansion of diet breadth in response to diminished ungulate biomass on the landscape rather than fundamental behavioral cognitive advances

interpreting flash flood palaeoflow parameters from antidunes and gravel lenses an example from montserrat west indies the wavelength of stationary water surface waves and their associated antidune bedforms are related to the mean velocity and depth of formative flow in sand bed flume experiments alexander et al 2001 found that lens structures were preserved during antidune growth and change and the dimension of the lenses were empirically related to antidune wavelength and thus could be used to estimate flow velocity and depth this study is the first to compare observations of formative flow conditions and resulting sedimentary structures in a natural setting testing the alexander et al 2001 relationship at a field scale trains of stationary and upstream migrating water surface waves were prevalent during the flash flood in october 2012 in the belham valley montserrat west indies wave positions and wavelengths were assessed at 900 s intervals through the daylight hours of the event within a monitored reach the wave data indicate flow depths up to 1 3 m and velocity up to 3 6 m s 1 sedimentary structures formed by antidune growth and change were preserved in the event deposit these structures include lenses of clast supported gravel and massive sand with varying internal architecture the lenses and associated low angle strata are comparable to sand bed structures formed from stationary and upstream migrating waves in flume experiments confirming the diagnostic value of these structures using mean lens length in the event deposit underestimated peak flow conditions during the flood and implied that the lenses were preserved during waning flow

holocene paleoenvironmental change in the kenyan central rift as indicated by micromammals from enkapune ya muto rockshelter abstract an assemblage of micromammals recovered from the holocene levels of a rockshelter at 2400 m in the montane forest of the mau escarpment were examined with the goal of testing and contributing to prior reconstructions of paleoenvironments in the central rift valley of kenya species representation in the assemblage is consistent with a drying of the rift valley lakes in the middle holocene and suggests a decrease in forest accompanied by expanding grasslands near the site changes in the abundance of grassland species suggests an increase in the frequency of fires probably the result of pastoral burning the body size of the root rat tachyoryctes splendens decreases from the early holocene to the middle holocene and this may indicate increasing aridity or increasing temperature we compare measures of species diversity number of taxa species richness and the shannon diversity index for both micromammals and macromammals since species diversity may change with paleoenvironmental change the macromammals show no changes in species diversity that are assignable to paleoenvironmental change while the micromammals show a trend toward decreasing diversity from the early to middle holocene and then show an increase in diversity during the peak of the middle holocene dry phase though sample size effects may be confounding the patterning

dimensions of standing waves at steps in mountain rivers 1 oscillations of the water surface are common features of flows around critical conditions fr 1 and of both natural and structure induced undular hydraulic jumps the paper describes experimental tests and field data on the dimensions of standing waves created by artificial drops in steep gravel bed rivers the purpose of the research is to analyze what parameters affect the phenomenon to provide semiempirical formulations for wave dimensions and to assess whether previous models for undular hydraulic jumps and antidunes are reasonably predictive the dimensionless wavelength and wave amplitude were correlated to the froude number at the sill the first wavelength appears linearly related to the froude parameter whereas the amplitude of the first wave shows a less defined behavior possibly indicating that a maximum value occurs for sill froude numbers around 1 6 1 7 the corresponding wave steepness i e wave amplitude length results between 0 15 0 16 and this range also characterizes the point at which the dimensionless trough depth below the sill achieves a local maximum probably related to hydrodynamic conditions just before wave breaking the transition between roller and undular jumps at drops is then argued to likely represent a critical stage in step pool streams and the hydraulic and morphological implications of this finding are also discussed with particular emphasis on step stability and step wavelength

depth determination of north italian earthquakes using grafenberg data surface reflections such as pp and sp have long been used to determine the source depth of teleseismic events due to difficulties in identifying these phases at single narrow band stations they have rarely been used for regional events correlation over an array of stations and the possibility of applying different filters to broadband data allows such phases to be identified we describe a method to determine the source depth which uses such depth phases at regional distances complete theoretical seismograms are an important aid for the interpretation of these depth phases the method is demonstrated using small events from the lombardia region and large events from friuli northern italy good agreement is achieved with depth determinations by other authors for the friuli events relative source depths are determined very accurately since only time differences need to be compared

pleistocene cataclysmic flooding along the big lost river east central idaho relationships between cataclysmic flood generated landforms and flood hydraulics were investigated along box canyon an 11 km long bedrock gorge of the lower big lost river geomorphic mapping along box canyon indicates that a cataclysmic flood completely inundated the gorge resulting in large scale erosional and depositional features on the adjacent basalt upland step backwater hydraulic modeling indicates that a discharge of 60 000 m 3 s was required to produce the geologic paleostage evidence maximum stream power per unit area of bed locally attained values of 26 000 w m 2 during the peak ranking the big lost river flood third in terms of power behind the famous missoula and bonneville floods the spatial distribution of unit stream power indicates that bedrock erosion and boulder deposition on the basalt upland adjacent to box canyon were governed primarily by decreasing unit stream power and or fluctuating unit stream power gradients a preliminary depositional threshold for the largest flood boulders defines a lower limit of flood power required to sustain boulder transport along this bedrock fluvial system ultimately hydrodynamic controls on box canyon flood erosion and deposition derive from the irregular volcanic rift topography of the eastern snake river plain outburst floods from a glacial lake in headwater regions during the late pleistocene may have induced the torrential discharges within box canyon

critical flow constrains flow hydraulics in mobile bed streams a new hypothesis a new hypothesis predicts that in mobile bed river channels interactions between the channel hydraulics and bed configuration prevent the froude number fr from exceeding 1 for more than short distances or periods of time flow conditions in many steep competent streams appear to be close to critical froude numbers of steep slope 0 01 sand bed streams with considerable freedom to adjust boundaries oscillate between 0 7 and 1 3 over 20 to 30 s cycles with an average of 1 0 at the channel thalweg criticalflow in these streams is maintained by the interaction between the mobile bed and free water surface at highfr which results in a cyclical pattern of creation and destruction of bed forms field observations support that a similar mechanism offlow bed form interaction constrains fr 1 in active bed braided gravel rivers step pool streams laboratory rills lahar runout channels and even some bedrock channels empirical and analytical results show that as slope increases competentflows tend to asymptotically approach criticalflow an assumption of criticalflow would dramatically simplify paleohydraulicflow reconstructions and modeling offlow hydraulics in high gradient streams

minimum froude number and the equilibrium of alluvial sand rivers rivers adjust towards an equilibrium condition the stability of which depends upon a set of controlling factors expressed by the froude number as alluvial river channels approach stable conditions the froude number of the channel flow will tend to attain a minimum value which reflects minimum bed material motion and maximum channel stability under the constraints imposed by water discharge sediment load and particle size computer simulations for sand bed rivers show that the froude number of the flow tends to a minimum value when the equilibrium river tends to a certain hydraulic geometry evidence from 57 alluvial sand material rivers and stable canals shows that this simulated hydraulic geometry with minimum froude number corresponds to the natural equilibrium state

submerged and unsubmerged natural hydraulic jumps in a bedrock step pool mountain channel high resolution digital elevation models dems for natural submerged and unsubmerged jump regions were tested against the classical hydraulic jump chj and engineering analogues that have dominated previous geomorphic and engineering research dems were compared for two discharge conditions the data showed bed and water surface features of the natural jump regions differ significantly from chj conditions and engineering analogues with respect to boundary conditions roughness elements were highly irregular in frequency spacing size and orientation and were comprised of form obliquity and bed scour in boulder bed and pure bedrock conditions the data also showed bed and water surface features of natural jump regions have similarities and deviations from chj conditions and engineering analogues with respect to hydraulic characteristics several variations were observed in the hydraulic characteristics between the ballistic and sloping jets revised conceptual models based on idealized corollaries were developed for the natural jump regions based on upstream energy head relative to the downstream tailwater depth and step geometry the dems highlight the importance of recognizing the interrelationship between spatial transcritical flow structures and localized topographic heterogeneities in bedrock channels

effect of bank stability on geometry of gravel rivers a bank stability analysis is incorporated into an analytical procedure for modeling the hydraulic geometry of an alluvial gravel bed channel the new analysis includes a procedure that calculates the mean bed and bank shear stress as well as assessing the bank stability the bank stability criterion accounts for the increased stability of the channel banks due to consolidation of the bank sediment cementing by fines and binding of the sediment by root masses the two key parameters in the bank stability analysis are the median grain diameter of the bank sediment d50bank and the modified friction angle of the bank sediment a sensitivity analysis of the two parameters indicate that the bank stability can exert a large influence on the channel geometry this is supported by testing the theory on published field data the bank sediment size was assumed to equal the bed sediment size and the variation of the friction angle was investigated the estimated values are seen to increase systematically

field mapping and digital elevation modelling of submerged and unsubmerged hydraulic jump regions in a bedrock step pool channel high resolution tacheometric field surveying was integrated with computer assisted drafting to visualize and contrast three dimensional bed and water surface digital elevation models dems for submerged and unsubmerged hydraulic jump regions in a bedrock step pool channel measurements were conducted for two discharge conditions since previous applica tions of three dimensional field mapping and digital elevation modelling of stream channels have been limited to smoothly contiguous gravel bedded systems surveying was optimized by topographic setting and scaled to localized bed and water surface discontinuities traces and visualizations of the jump regions indicated that dichotomous decimetre shifts in water surface topography occurred for both jump regions from lower to higher discharges systematic removal of the survey points and dem differencing indicated that point densities of ten points per square metre in conjunction with a survey structure targeting grade breaks of 0 3 0 5 m were required to capture decimetre form variations of the natural jump regions the dems highlight the importance of recognizing the relationship between transcritical flow structures and localized topographic heterogeneities in bedrock channels copyright 2006 john wiley sons ltd

least action principle equilibrium states iterative adjustment and the stability of alluvial channels the energy based least action principle lap has proven to be very successful for explaining natural phenomena in both classical and modern physics this paper briefly reviews its historical development and details how in three ways it governs the behaviour and stability of alluvial rivers first the lap embodies the special stationary equilibrium state of motion and so its incorporation with the principle of energy conservation explains why so many optimizing hypotheses have been proposed in fluvial geomorphology second the variational approach underlying the lap provides a more straightforward and simpler fuzzy object orientated method for solving river regime problems than do the various complex newtonian formulations third it is shown that in fluvial systems with surplus energy the surplus can be expended with slope and or channel geometry adjustments with the degree of channel geometry adjustment quantified by the dimensionless numbers f for depth dominated adjustment and h for width depth dominated adjustment different planforms are preferred at different energy levels with h providing a quantitative measure of the flow s efficiency for moving sediment in rivers with insufficient energy the interactions of endogenous and exogenous factors are shown to be capable in certain circumstances of achieving a stationary equilibrium condition which acts as the attractor state importantly this study describes how iterative changes enable systems to achieve such a stable equilibrium copyright 2007 john wiley sons ltd

inversion of source parameters for subcrustal earthquakes in the hellenic arc summary a one station method was developed to invert simultaneously for seismic moment focal depth and the orientations of the nodal planes this method was tested on seismograms recorded at the broadband grefenberg array grf for earthquakes in the central to eastern hellenic arc and southern turkey the complete p and s body wave responses including all near source surface reflections were synthesized using the reflectivity method the minimum misfit between the observed and theoretical seismograms in the wwssn lp band was determined by cross correlation searching the whole parameter space of strike dip and rake of a pair of orthogonal nodal planes and adjusting the source depth and seismic moment the initial searching step of 20 was reduced to 5 in the vicinity of the minimum misfit position for a final search the best fitting solution was then compared to the harvard hrvd moment tensor solution best double couple which was derived using long period data and to the p wave first motion polarities reported by the isc most solutions based on grf data agree well with those found by hrvd but in some cases some features of the observed grf signals cannot be matched by the hrvd solution or solutions similar to it the nine earthquakes we analysed in detail had magnitudes between 5 2 and 5 8 our depth determinations ranged from 35 to 155 km the deepest events 80 155 km were located near rhodes and to the east of it one earthquake located in southern turkey was confirmed to have a focus at about 125 km depth the focal mechanisms of the intermediate depth earthquakes in the eastern hellenic arc show p axes approximately parallel to the strike of the deep slab

possible hydraulic significance of two kinds of potholes examples from the paleo potomac river potholes preserved along abandoned sections of bedrock bounded rivers should provide significant paleohydraulic data if the conditions for pothole formation are understood in a prototype study we recognize two kinds of potholes along the paleo potomac river near great falls virginia vertical potholes drilled into the strath floor are circular in plan and are interpreted to form at sites of small stream depths and high flow velocity lateral potholes noncircular with overhanging roofs are found on flanks of rock obstacles they are interpreted to be eroded by sediment laden vertical flow near the air water interface the vortices circulate water in the horizontal plane and begin to form near the free surface in flow separation zones downstream of the obstacles the geometry of flow separation zones and thus the location of the lateral potholes are scaled by flow reynolds number therefore lateral potholes could be used to reconstruct paleoflow depths and velocities if parts of the channel bed adjacent to the flow obstruction are preserved

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

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

paleodischarge of the late pleistocene bonneville flood snake river idaho computed from new evidence the bonneville flood resulted from catastrophic outflow from pleistocene lake bonneville about 15 000 yr ago when the lake overtopped its rim at red rock pass in southeastern idaho and discharged a vast volume of water down the snake river this paper provides revised estimates of the paleodischarge volume and duration of the bonneville flood based on new evidence of its height and on current understanding of the amount of lowering of lake bonneville evidence for the revised height of the flood is derived from the altitude of erosional features and flood deposits at the head of a constricted reach of the snake river canyon at the mouth of sinker creek and from the altitudes of flood deposits at several places about 53 km upstream using the step backwater method we estimate that peak discharge for the bonneville flood through the constricted reach was from 793 000 to 1 020 000 m 3 s and most likely was 935 000 m 3 s this discharge is 2 2 times the discharge previously reported and is the second largest flood known to have occurred in the world at this rate of discharge the shear stress for the flood would have been 2 500 n m 2 and the unit stream power would have been 75 000 n m s as compared with values of 6 to 10 n m 2 and 12 n m s for recent floods on the mississippi and the amazon other recent studies of the history of lake bonneville show that the volume of water released was 4 700 km 3 or about 3 times greater than the volume previously inferred although this volume indicates a flood duration of 8 weeks at constant peak discharge an accurate estimate of the duration would require dam break modeling at red rock pass from a dam break model flood hydrographs at red rock pass and the hydraulics of the flood wave along the snake river could be computed

earthquake locations in the western hellenic arc relative to the plate boundary four vertical component seismograph stations were operated in western crete southeastern peloponnesus the island of milos and south of corinth on mount didimon from 1981 to 1984 combining arrival times from this network the greek national network and volnet we relocated hypocenters within greece and the surrounding area the difference between the relocations and the locations published in the national observatory of athens bulletin in most instances were minor except for earthquakes located in the vicinity of the western hellenic arc in this area we found that epicenters thought to lie south of the plate boundary within the african plate relocated an average of approximately 60 km to the n30 e which places them at or north of the plate boundary we suggest that this difference is a minimum estimate of the location error and the true locations may lie still further to the nne we propose that anomalously slow seismic velocities in the aegean back arc upper mantle cause travel time delays to the seismograph stations located to the ne of the source volumes resulting in location errors in a direction away from these stations extrapolating from our observations to other segments of the hellenic plate boundary and to periods not covered by our operation we hypothesize that most or all earthquakes thought to have originated on the african plate within about 100 km of the hellenic arc were actually located at the plate boundary or on the aegean plate

a new efficient method to solve the stream power law model taking into account sediment deposition a new efficient method to solve the stream power law key points we present an efficient o n and implicit method to solve a river erosion model taking into account sediment deposition we show how the foreland stratigraphy is controlled by the efficiency of river erosion and the efficiency of sediment transport by rivers we observe autogenic aggradation and incision cycles in the foreland once the system reaches a dynamic steady state the stream power law model has been widely used to represent erosion by rivers but does not take into account the role played by sediment in modulating erosion and deposition rates davy and lague 2009 provide an approach to address this issue but it is computationally demanding because the local balance between erosion and deposition depends on sediment flux resulting from net upstream erosion here we propose an efficient i e o n and implicit method to solve their equation this means that unlike other methods used to study the complete dynamics of fluvial systems including the transition from detachment limited to transport limited behavior for example our method is unconditionally stable even when large time steps are used we demonstrate its applicability by performing a range of simulations based on a simple setup composed of an uplifting region adjacent to a stable foreland basin as uplift and erosion progress the mean elevations of the uplifting relief and the foreland increase together with the average slope in the foreland sediments aggrade in the foreland and prograde to reach the base level where sediments are allowed to leave the system we show how the topography of the uplifting relief and the stratigraphy of the foreland basin are controlled by the efficiency of river erosion and the efficiency of sediment transport by rivers we observe the formation of a steady state geometry in the uplifting region and a dynamic steady state i e autocyclic aggradation and incision in the foreland with aggradation and incision thicknesses up to tens of meters

persistence of the surface texture of a gravel bed river during a large flood we present herein clear field evidence for the persistence of a coarse surface layer in a gravel bed river during flows capable of transporting all grain sizes present on the channel bed detailed field measurements of channel topography and bed surface grain size were made in a gravel bed reach of the colorado river prior to a flood in 2003 runoff produced during the 2003 snowmelt was far above average resulting in a sustained period of high flow with a peak discharge of 27 m3 s 170 of normal peak flow all available grain sizes within the study reach were mobilized in this period of time during the 2003 peak flow the river avulsed immediately upstream of the study reach thereby abandoning approximately one half kilometer of the former channel the abandonment was rapid probably within a few hours leaving the bed texture essentially frozen in place at the peak of the flood all locations sampled prior to the flood were resampled following the stream abandonment in response to the high flow the surface median grain size d50s coarsened slightly in the outer part of the bend while remaining nearly constant along the inner part of the bend resulting in an overall increase from 18 to 21 mm for the study reach thus the coarse bed surface texture persisted despite shear stresses throughout the bend that were well above the critical entrainment value this may be explained because the response of the bed texture to increases in flow strength depends primarily upon the continued availability of the various grain size percentiles in the supply which in this case was essentially unlimited for all sizes present in the channel copyright 2007 john wiley sons ltd

source parameters of the june 29 1992 little skull mountain earthquake from complete regional waveforms at a single station the june 29 1992 m sub b 5 5 little skull mountain earthquake occurred 20 km southeast of yucca mountain within the boundaries of the nevada test site this event was recorded at a very broadband station located about 310 km to the east at kanab utah both body and surface waves from this single station were used in a grid search technique for the best fitting double couple moment tensor the technique minimizes the misfit between reflectivity generated complete synthetic seismograms and the three component displacement data via a search over the strike dip and rake of the source in the passband of 50 15 s period the grid search results in a well defined nearly pure normal mechanism with a strike of 35 degrees a dip of 54 degrees a rake of minus 87 degrees and a seismic moment of 4 1 x 10 sup 17 n m applying the same technique to the large aftershock on july 5 1992 the authors obtain a somewhat less well defined minimum with a strike of 358 degrees a dip of 36 degrees a rake of minus 177 degrees and a moment of 4 3 x 10 sup 15 n m the minimum compression axes of these mechanisms are consistent with northwest southeast extension in the basin and range 14more refs 7 figs less

standing waves in high speed lava channels a tool for constraining lava dynamics and eruptive parameters abstract estimates of the rheological properties of lava flows are essential for understanding their emplacement and for hazard assessment despite being a well known phenomenon in water hydraulics the formation and presence of standing waves in lava channels is poorly understood standing waves generally located near the vent area have been frequently described at high speed channelized lava flows they are interpreted as hydraulic jumps indicating a flow under supercritical conditions identifying standing waves therefore offers an opportunity to apply open channel hydraulic theory for supercritical flows in order to determine important eruption parameters such as discharge rate and apparent viscosity we use the length and amplitude of standing waves to reconstruct flow dynamics from both observational data and video analysis the geometry of these standing waves allows us to extract the physical properties of the channelized lava velocity discharge rate apparent viscosity to estimate the channel depth and constrain the flow regime with the rapid advances in technology scientists can deploy equipment to enable low cost real time monitoring of these phenomena and constrain eruption discharge rate and apparent viscosity key parameters for volcanic hazard assessment and mitigation

source inversion of seismic waveforms the koyna india earthquakes of 13 september 1967 abstract the treatment of the seismic source inverse problem when diverse forms of waveform data are available is simple and elegant using a moment tensor formalism if earth structure is known and its effects predictable in terms of vertically inhomogeneous elastic layered models then all types of wave phenomena e g surface waves body waves leaky modes etc for a purely deviatoric moment tensor point source may be represented by at most a sum of three green9s functions for an arbitrary symmetric moment tensor point source one additional green9s function is needed for the p sv system however elegant this formalism may be for posing the linear inverse problem the major difficulties lie in earth structure unknowns and resultant nonlinearities in the green9s functions which can cause significant trade offs with source parameters a hybrid inversion procedure is set up to gain insight into the probable unknowns in particular problems by incorporating both a linearized least squares gradient method for the moment tensor or double couple and smoothed time function parameters and a nonlinear systematic trial and error search for moment tensor or double couple parameters for several assumptions of green9s function the inversion technique is applied to near regional waveform data from a small earthquake associated with the koyna reservoir which occurred 13 september 1967 as the second in a group of three events with very similar waveshapes but differing amplitudes the magnitudes of the second and third events are smaller by 0 2 and 0 8 units respectively compared to the first the absolute magnitude for the first event is poorly constrained but is estimated to be 4 0 to 4 5 rather than the previously published value of 5 5 to 6 0 from the similarity of waveshapes all three events are inferred to have the same mechanism and occurred within about 2 km of the same hypocenter the results from moment tensor and double couple inversions for event 2 data indicate that source depth was 5 km and that left lateral faulting occurred on a plane with a strike of n20 e 5 dip of 90 15 and a rake of 0 35 the inferred far field time function is approximately 3 sec in duration unusually long for the seismic moment of 9 10 22 dyne cm yielding a possible stress drop of about 0 05 bars a fault map was constructed from landsat image interpretation and shows a predominance of nnw to nne striking faults in the koyna area which is used to infer the appropriate nodal plane in the inversion results these faults tend to define a broad en echelon zone which parallels the western ghats in this area

three dimensional model of hellenic arc deformation and origin of the cretan uplift 1 the hellenic arc of greece is the most seismically active part of europe but little is know about its mechanics we modeled deformation along the arc using a finite element model the model was intended to capture large scale 3 d structure of nubian plate subduction beneath the aegean block and its deformational consequences the shape of the interface was developed using mapped traces at the surface and earthquake hypocenters at depth model block motions were constrained by recent compilations of gps velocity vectors we simulated a 10 ka period of convergence between nubia and the aegean and calculated the strain field in the overriding plate as well as the spatial distribution and orientation of differential stress 1 3 from these calculations we derived testable quantities such as the expected seismic moment rate on the interplate contact uplift pattern and distribution of strain modes our relatively simple model broadly reproduced observed uplift patterns earthquake activity and loci of extension and contraction the model showed a localization of uplift near the island of crete where the fastest aegean uplift rates are well documented comparison of calculated expected seismic moment and observed earthquake catalogs implies a nearly fully coupled interplate contact on the basis of our modeling results we suggest that south aegean deformation is driven primarily by the fast moving 33 mm a 1 aegean upper plate overriding a nearly stalled 5 mm a 1 nubian lower plate this tectonic setting thus more closely resembles a continental thrust than it does a typical oceanic subduction zone

floodplain persistence and dynamic equilibrium conditions in a canyon environment abstract canyon river systems are laterally constrained by steep walls strath terraces and bedrock intrusions however semialluvial reaches are nested within these environments as discontinuous floodplains along the river margins these semialluvial floodplains provide an example of dynamic equilibrium set within high energy fluvial systems marking areas where the river is free to alter its boundary conditions most research has focused on hydraulic conditions necessary for floodplain formation and persistence in unconfined systems whereas little is known about canyon streams this paper focuses on 1 characterizing dynamic equilibrium 2 describing the controls on floodplain formation and distribution and 3 evaluating the performance of extremal hypotheses to identify dynamic equilibrium and floodplain persistence in high energy semiconfined canyon environments these objectives were addressed with field and numerical data derived from a one dimensional hydraulic model for bankfull and 100 year return interval flood events supported by closely spaced cross sections for the lower 38 km canyon reach of the deadwood river idaho under bankfull conditions critical energy thresholds for equilibrium floodplain persistence at this study site present the upper limits of slope 0 018 shear stress 175 n m 2 and specific stream power 400 w m 2 channel and floodplains near equilibrium quantified with a near zero sediment transport divergence exner equation were successfully identified by the minimum unit stream power extremal hypothesis and to a lesser degree by the other extremal hypotheses that minimize energy expenditure minimum specific stream power minimum total stream power and minimum froude number provided backwater environments and major tributaries could be identified extremal results were compared to hydraulic geometry relations to evaluate how closely equilibrium floodplains approached values for unconfined alluvial river systems

can the discharge of a hyperconcentrated flow be estimated from paleoflood evidence 1 many ood events involving water and sediments have been characterized using classic hydraulics principles assuming the existence of critical ow and many other simplications in this paper hyperconcentrated ow discharge was evaluated by using paleo ood reconstructions based on paleostage indicators psi combined with a detailed hydraulic analysis of the critical ow assumption the exact location where this condition occurred was established by iteratively determining the corresponding cross section so that specic energy is at a minimum in addition all of the factors and parameters involved in the process were assessed especially those related to the momentum equation existing shear stresses in the wetted perimeter and nonhydrostatic and hydrostatic pressure distributions the superelevation of the hyperconcentrated ow due to the ow elevation curvature was also estimated and calibrated with the psi the estimated peak discharge was established once the iterative process was unable to improve thet between the simulated depth and the depth observed from the psi the methodological approach proposed here can be applied to other higher gradient mountainous torrents with a similar geomorphic conguration to the one studied in this paper likewise results have been derived with fewer uncertainties than those obtained from standard hydraulic approaches whose simplifying assumptions have not been considered

sediment supply and channel morphology in mountain river systems 2 single thread to braided transitions differences in sediment supply between single thread and braided channel types provide a long recognized though difficult to quantify pattern discrimination building on the results from our preceding paper we present a multiscale assessment of the sediment supply geomorphology and sediment transport characteristics of braided gravel bedded reaches in the northern rocky mountains usa first we present a quantitative theoretically based discriminant function that stratifies single thread and braided reaches on the basis of variations in bankfull sediment concentration and dimensionless discharge following the work of millar 2005 and eaton et al 2010 this function correctly classifies 50 of the 53 channel types where bed load concentrations are known second while channel pattern transitions are often linked to changes in slope field studies along sunlight creek wyoming show that downstream transitions between single thread and braided reaches are instead caused by valley constrictions and changes in the grain size of sediment from tributaries finally we demonstrate that the two dimensional variability in flow properties in braided reaches produces locally high values of shear stress and bed load transport yet bed load measurements and sediment transport calculations also show that sediment transport rates between adjoining braided and single thread reaches may be approximately equal where channels are near the pattern threshold and downstream variations in bank fortitude and channel constriction force pattern transitions taken together these results indicate that high bed load concentrations are fundamental to the braided channel planform and that braided channels likely reflect a quasi equilibrium state within watersheds with persistent high sediment supply

the missing dimension effects of lateral variation on 1 d calculations of fluvial bedload transport most calculations of bedload transport in rivers including those in numerical models of aggradation and degradation are 1 d all hydraulic and transport rate calculations are averaged over the channel width because bedload transport laws are nonlinear width averaged calculations will underestimate the true bedload flux if there is any local spatial variation in either the bed or the flow this paper analyses the effects on bedload transport capacity of spatial variation in applied and critical c shear stress separately and in combination a simple but versatile statistical model is used to represent variability in with allowance for differences between sand and gravel bed rivers and for below bankfull flow bedload flux is shown to increase greatly with the variance of especially in gravel bed rivers variability in c through bed patchiness may increase reduce or make little difference to bedload flux depending on the correlation between and c simple width averaging leads to severe underestimation of bedload transport in most conditions some alternatives are considered the findings have implications for sediment routing models srms but further research is needed to explore the issue fully

postglacial recession of niagara falls in relation to the great lakes abstract the recessional history of niagara falls in the present niagara gorge during the postglacial period has been a focus of study throughout this century radiocarbon ages of clam shells suggest that niagara falls migrated very slowly around the narrowed gorge section at niagara glen from 10 500 to 5500 yr b p when upper great lakes water bypassed lake erie and flowed to the ottawa river via the outlet at north bay ontario prior to that interval river discharge and recession rates were similar to those at present and similar rates resumed after 5200 yr b p by about 4500 yr b p the present gorge had intersected a buried gorge of the pre late wisconsinan niagara river st davids gorge the sediment derived from the excavated buried valley fill may be present as a distinct marker horizon in the sediments in southwestern lake ontario

morphodynamics of a 1000 year flood in the kamp river austria and impacts on floodplain morphology this paper investigates the impact of a 1000 year flood in august 2002 on floodplains and valley morphology of an austrian mixed alluvial bed rock river discharges with a recurrence interval between 500 and 2000 years caused distinctive overbank scouring and material deposition in the floodplains after the 1000 year flood those morphologically affected areas were at random intervals documented over the whole longitudinal profile in addition to overbank erosion in curved sections cut offs the river bed locally widened floodplain stripping occurred and local overbank scours were documented along straight parts of the river a hydrodynamic numerical model combined with field measurements was used to analyse the cause of these erosional landforms based on the modelled hydraulic conditions for a one year flood 30 78 m3 s 1 and the catastrophic 2002 event 700 800 m3 s 1 the numerical results allowed a cause effect study with 19 parameters deterministic and statistical analysis anova discriminant analysis showed that the morphodynamic effects of the 2002 flood were influenced by the variability of valley morphology of the kamp river which led partially to supercritical flow during flood constriction these processes were in some cases also anthropogenically influenced lateral constriction and expansion of the valley geometry over short distances led to scouring and aggradation within the inundated areas during the event these morphological features were therefore responsible for the elongated scour holes in the floodplains copyright 2009 john wiley sons ltd

communal hunting along the continental divide of northern colorado results from the olson game drive 5bl147 usa abstract the olson site 5bl147 is a multi component rock walled game drive located in the james peak wilderness area of northern colorado usa it is one part of a much larger game drive complex located at rollins pass situated above modern tree limit and along the continental divide at approximately 3600 m above sea level byron olson and james benedict conducted work at the site in the late 1960s we combined their efforts with our recent field and lab work to produce a synthetic overview of the site at least 45 blinds and 1307 m of rock walls are present to funnel game upslope to waiting hunters radiocarbon and lichenometric dates suggest occupations spanning the last 3200 years with diagnostic tools suggesting even older use lithic analysis of the debitage and tools from both excavated blinds and surface contexts intercept and processing areas provides possible scenarios for the use of the site large game drives of the colorado alpine zone represent accumulated landscapes of artifacts and features the byproduct of many years of construction use and re use and built for a variety of reasons

channel responses to varying sediment input a flume experiment modeled after redwood creek california article i nfo storage flume aggradation degradation at the reach scale a channel adjusts to sediment supply and flow through mutual interactions among channel form bed particle size and flow dynamics that govern river bed mobility sediment can impair the beneficial uses of a river but the timescales for studying recovery following high sediment loading in the field setting make flume experiments appealing we use a flume experiment coupled with field measurements in a gravel bed river to explore sediment transport storage and mobility relations under various sediment supply conditions our flume experiment modeled adjustments of channel morphology slope and armoring in a gravel bed channel under moderate sediment increases channel bed elevation increased and sediment output increased but channel planform remained similar to pre feed conditions during the following degradational cycle most of the excess sediment was evacuated from the flume and the bed became armored under high sediment feed channel bed elevation increased the bed became smoother mid channel bars and bedload sheets formed and water surface slope increased concurrently output increased and became more poorly sorted during the last degradational cycle the channel became armored and channel incision ceased before all excess sediment was removed selective transport of finer material was evident throughout the aggradational cycles and became more pronounced during degradational cycles as the bed became armored our flume results of changes in bed elevation sediment storage channel morphology and bed texture parallel those from field surveys of redwood creek northern california which has exhibited channel bed degradation for 30 years following a large aggradation event in the 1970s the flume experiment suggested that channel recovery in terms of reestablishing a specific morphology may not occur but the channel may return to a state of balancing sediment supply and transport capacity published by elsevier b v

expression of active tectonics in erosional landscapes understanding the manner and degree to which topography in active mountain ranges reflects deformation of the earth s surface remains a first order goal of tectonic geomorphology a substantial body of research in the past decade demonstrates that incising channel systems play a central role in setting relationships among topographic relief differential rock uplift rate and climatically modulated erosional efficiency this review provides an introduction to the analysis and interpretation of channel profiles in erosional mountain ranges we show that existing data support theoretical expectations of positive monotonic relationships between channel steepness index a measure of channel gradient normalized for downstream increases in drainage area and erosion rate at equilibrium and that the transient response to perturbations away from equilibrium engenders specific spatial patterns in channel profiles that can be used to infer aspects of the forcing these aspects of channel behavior lay the foundation for a series of case studies that we use to illustrate how focused quantitative analysis of channel morphology can provide insight into the spatial and temporal dynamics of active deformation although the complexities of river response to climate lithology and uplift patterns mean that multiple interpretations of topographic data alone will always possible we show that application of stream profile analysis can be a powerful reconnaissance tool with which to interrogate the rates and patterns of deformation in active mountain belts

tdr measurements of hydraulic jump aeration in the south fork of the american river california abstract turbulent pressure and velocity fluctuations associated with hydraulic jump air entrainment likely play an important role in local flow dynamics and morphologic changes of steep bedrock and alluvial rivers previous engineering research indicates that hydraulic jump air entrainment and energy dissipation locally intensify erosion of both bedrock and alluvial elements enhance hydraulic quarrying suppress cavitation and decrease the friction factor of a flow despite studies in artificial settings air content in natural hydraulic jumps remains largely unquantified in this study time domain reflectometry tdr a method commonly used to determine the volumetric water content of porous media for the last two decades was evaluated in the laboratory and then adapted to measure air contents of natural hydraulic jumps laboratory tests were conducted to determine the influence of turbulence temperature and sampling volume on the tdr signal over an air content range of 0 100 based on the results of the laboratory tests an empirical calibration was developed that converts the tdr signal into air content local air contents were then measured in hydraulic jumps occurring along a mixed alluvial and bedrock dominated 8 4 km section of the south fork american river two small jumps had a mean air content of 19 and 23 a coefficient of variation cv of 27 and 28 and a root mean square rms of 19 and 24 respectively a large jump had a mean air content of 42 a cv of 26 and a rms of 44 tdr provides fast accurate repeatable and nondestructive in situ measurements at one tenth the cost of traditional methods and is far more robust for field applications than traditional lab instruments future studies can now expand upon the hydrogeomorphic and ecological significance of jump aeration

the campo laborde site new evidence for the holocene survival of pleistocene megafauna in the argentine pampas abstract investigations have been carried out at the campo laborde archaeological site in the argentine pampas some issues related to pleistocene extinctions and the survivals of some species of megafauna into the early holocene are discussed at the site of campo laborde abundant bones of giant ground sloth megatherium americanum some from other pleistocene fauna doedicurus sp and neosclerocaliyptus sp and very few from extant fauna e g vizcacha lagostomus maximus patagonian hare dolichotis patagonum and peccary tayassu sp were found in association with two quartzite tools 128 microlithic debris from different raw material and two informal bone tools each of the species is represented by only one individual and only one bone of m americanum and one of d patagonum show cut marks different lines of evidence suggest that campo laborde is a giant ground sloth procurement site on the border of an ancient swamp where the prey was also initially butchered one of the recovered tools is the stem of a broken bifacial projectile point which would have been used as a hunting weapon based on the stratigraphic position this site could date to the early holocene six ams 14 c ages from m americanum bone collagen support this age although there is a wide chronological span between ca 9700 and 6700 bp the evidence obtained from campo laborde as well as from the la moderna site indicates that some pleistocene species such as giant ground sloth and some glyptodon d clavicaudatus and neosclerocaliyptus sp survived in the pampas until the early holocene therefore these megafauna coexisted with early hunter gatherers for several millennia and were exploited

channel adjustments to historical disturbances along the lower brazos and sabine rivers south central usa historical channel adjustments are documented and discussed in context with anthropogenic disturbances along two meandering coastal plain rivers the lower brazos and sabine rivers in the south central united states hard copy streamflow measurement notes of the u s geological survey were utilized to render historical cross sections 1925 2007 at nine gauging stations which were complemented with repeat photographs and flood frequency analysis to assess trajectories of channel change and interpret causative mechanisms downstream and upstream propagating disturbances caused episodes of channel bed incision and aggradation at different locations for distinct time periods along both rivers incision associated with upstream dams is detected but channels are compensated downstream with sediment inputs from lateral channel migration and tributaries in one case temporary aggradation along the brazos river at waco was likely caused by a combination of dam construction and regional soil erosion channel bed incision on the lowermost brazos river is unrelated to dams but is associated with instream aggregate extraction possibly in conjunction with downstream channelization on the sabine river extensive aggradation during the 1930s might be associated with logging activities 1880s 1930s but whether the cause is pervasive regional scale hillslope erosion or local scale mill site activities is indeterminate following passage of this sediment the river generally recovered to pre disturbance conditions and has exhibited stability despite a mainstem reservoir translation of this sediment slug is attenuated by a transition to a flood prone distributary dominated system downstream of the holocene pleistocene terrace onlap position additional findings include cross channel hingepoints separating thalweg incision from simultaneous point bar or bank accretion at meander bends which indicates channel adjustment occurs along non cohesive beds in preference to cohesive or artificially reinforced banks also flood reduction has resulted in bankfull stages that are higher than levels associated with the post regulation 2 year return period finally vegetation encroachment along banks since the 1970s coupled with reduced flooding along the lower brazos river has promoted bank accretion deposits that when fully developed serve as morphologic indicators of the post regulation 1 to 2 year return period stage

detection and location of earthquakes in the central aleutian subduction zone using island and ocean bottom seismograph stations a network of eight university of texas ocean bottom seismographs obs operated for 6 weeks in 1978 about 50 km offshore of adak island alaska and nearby islands in 1979 a similar network of nine instruments was deployed for 7 weeks farther offshore within and up to 100 km seaward of the aleutian trench for shallow earthquakes on the outer trench slope for shallow earthquakes in the thrust zone and for intermediate depth events we have analyzed the obs and island based network data and evaluated the island network s capabilities for earthquake detection and location and for focal mechanism determination our three major conclusions are presented the first concerns shallow earthquakes on the outer trench slope in 1979 about 30 earthquakes occurred within the aleutian trench and up to 60 km seaward of the trench axis the island network located none of these events and detected p phases for only three of them ray tracing shows that the islands lie in a geometric shadow zone for events on the outer trench slope the best located events are shallower than 20 km and exhibit first motions consistent with normal faulting several authors have suggested that these events are caused by bending of the oceanic lithosphere at the outer rise prior to subduction if so then the event locations reported here show that the bending stresses exceed the strength of lithosphere only in a narrow zone extending about 10 km landward and 60 km seaward of the trench axis the second conclusion concerns shallow earthquakes in the thrust zone epicenters determined by island stations alone are virtually identical to epicenters determined using data from both island and obs stations the locations are similar whether they are determined using flat layered velocity models or a more realistic model and a ray tracing scheme nearly all the earthquakes detected by the obs network are also recorded by island stations three composite focal mechanism solutions that use data from both island and obs stations have p axes parallel to the direction of plate convergence the thrust zone events are separated from events on the outer trench slope by a gap in seismicity about 50 km wide situated on the inner trench slope the third conclusion concerns earthquakes deeper than 70 km epicenters determined using island network stations alone lie 10 to 80 km south of those determined using obs and island stations with the differences between epicenters depending both on event depth and on the velocity model used ray tracing with a realistic velocity model shows that for events at 200 km depth locations are about 80 km north of locations determined from island data alone these results do not support the observed increase in the dip of the benioff zone beneath 100 km depth that is suggested by locations determined from island network data alone using a flat layered velocity model

single station cmt application to the michoacan mexico earthquake of september 19 1985 observations of three dimensional ground motion at a single point on the surface of the earth following an earthquake can be sufficient to determine the zeroth order moment tensor of the event we adapt the centroid moment tensor cmt method dziewonski et al 1981 of analysis to single station data and apply it to the september 19 1985 michoacan earthquake the obtained mechanism indicates faulting on a shallow plane consistent with the ongoing subduction of the cocos plate the scalar moment is 1 3 1028 dyne cm a direct deconvolution of the observed p wave train indicates that the moment release occurred in two subevents each of 20 seconds duration with a peak to peak separation in time of 25 seconds

evaluation of supercritical subcritical flows in high gradient channel the quail creek dike failure flood near hurricane utah which occurred december 31 1988 and january 1 1989 affords the opportunity to evaluate the hydraulics of a high gradient channel for the first mile 1 6 km downstream from the dike this unnamed channel has an average slope of 0 032 until it enters the virgin river at a point where the average channel slope is 0 003 model computed depths and discharges are compared with field measured depths and indirect discharge measurements initially flows are modeled as supercritical in the 1 mi 1 6 km reach having a 0 032 channel slope however the field measured depths can be reconstructed only by modeling the complete reach as subcritical this paper questions whether supercritical flows occur in natural channels except for very short distances

single station fault plane solutions abstract fault plane solutions are derived from systematic trial and error grid testing of three component body waveform data from a single station modeling p and sh waveform data from five shallow events recorded teleseismically demonstrates that radiation pattern information contained within the interference of the direct wave and surface reflections and the overall relative amplitude between p and sh waveforms is sufficient to discriminate between fault type e g strike slip versus dip slip and often agrees with well constrained first motion studies events studied are the 9 april 1968 borrego mountain california 20 june 1978 thessaloniki greece 13 august 1978 santa barbara california 20 may 1979 alaska and 6 august 1979 coyote lake california earthquakes it is also shown using data from the 27 july 1980 sharpsburg kentucky earthquake that inclusion of pp p and sp p polarity and amplitude information to an otherwise unconstrained first motion study can significantly improve the quality of the fault plane solution although there are many potential problems source multiplicity directivity etc which can prohibit finding a good model with these techniques and inclusion of data from many stations is clearly desirable the results of this study suggest that sparse high quality waveform data sets may be as or more useful for obtaining source mechanisms than standard first motion studies at a minimum they should be performed together as a consistency check this procedure would be most useful in the common situation where only a few receivers are available for a particular event

moment and duration of shallow earthquakes from love wave modelling for regional distances abstract love waves from five earthquakes in southwest germany italy yugoslavia greece and algeria as recorded at the broadband grafenberg array in eastern bavaria are modelled in detail using an extended reflectivity method the focal mechanisms are taken from the literature or determined from long period wwnss data the theoretical double couple moment function used for modelling increases smoothly during the risetime t from zero to the seismic moment m0 t and m0 are determined by matching the observed and theoretical love wave seismograms in the long period wwnss frequency band t is approximately equal to the rupture duration values from 1 4 to 20 s are found seismic moments generally agree within a factor of about two with those found by other authors from larger data sets the earthquakes in southwest germany and greece were simple events and can be modelled very well by one double couple in the case of the other earthquakes the theoretical love wave seismograms are too short for these earthquakes there is some independent evidence for a multiple event nature this evidence is condensed into source models consisting of two or three double couples representing separate and complete sub earthquakes which then explain the observations quite well in the case of the algerian earthquake the long love wave duration may also be due to complications in structure along the wavepath across the mediterranean and the alps the present results show that accurate love wave modelling for a single station at regional distance from an epicentre is a reliable method for estimation of seismic moment and rupture duration use of a digitally recording station with large dynamic range allows events over a large magnitude interval to be studied the grafenberg array is well suited for such an investigation of european and north african earthquakes

boundary shear stress measurements in undular flows application to standing wave bed forms waters flowing in natural streams and rivers have the ability to scour and to deposit materials hence to change the bed topography it is recognized that undular flows have great potential for sediment transport in the present study a fixed bed model was used to investigate the spatial variations of boundary shear stress under standing waves i e undular flow the results figure 8 highlight the nonuniformity of the boundary shear stress distributions minimum boundary shear stress is observed under the wave crests and maximum shear stress is observed under the wave troughs the experimental findings suggest the formation of three dimensional standing waves bed forms overall the study highlights large variations of boundary shear stress in response to free surface undulations

bristlecone pine paleoclimatic model for archeological patterns in the white mountain of california abstract archeologists recognize that prehistoric human populations were a significant variable in the operation of past california ecosystem processes and that a changing environment created constraints and opportunities for prehistoric cultural adaptation the tie between paleoclimatology and archeology is an evolving interdisciplinary field of study that aims to facilitate a better understanding of prehistoric subsistence settlement patterns relative to climate variability a paleoclimatic model based on temperature inferences and precipitation reconstruction from tree ring widths of bristlecone pine in the white mountains of california is used to explain the distribution of prehistoric alpine villages in the white mountains the paleoclimatic model is visually and statistically compared with calendar ages converted from calibrated 14 c dates from the village sites results elucidate the role of water availability in the frequency and intensity of settlement as 88 of the calendar dates associated with 14 c dates fall within wet periods 0 05 p 0 005 the coincidence of the calendar dates around above average precipitation periods confirms that long term available resources are contingent on the availability of moisture the key to life in the desert environment

sediment supply and the development of the coarse surface layer in gravel bedded rivers the bed surface of most gravel rivers is considerably coarser than the sub surface or the gravel load transported over it a phenomenon affecting river dynamics morphology and ecology the coarse surface layer often called an armour or pavement has been attributed to an inherent tendency for small grains to settle between larger ones during active transport of all sizes1 2 and to selective erosion or trapping of finer particles when the coarse grains are relatively immobile3 4 where bedload supply is cut off below dams selective erosion causes coarsening5 6 using a simple quantitative model we propose that surface coarsening develops in gravel bedded rivers when local bedload supply from upstream is less than the ability of the flow to transport that load we present laboratory results which support this hypothesis and show that supply reduction causes changes in bedforms and progressive confinement of active bedload transport to a narrow band of finer bed surface bordered by a coarse less active bed it may therefore be possible to relate the degree of river bed surface coarsening to sediment supply resulting from land use

sediment transport part i bed load transport a method is presented which enables the computation of the bed load transport as the product of the saltation height the particle velocity and the bed load concentration the equations of motions for a solitary particle are solved numerically to determine the saltation height and particle velocity experiments with gravel particles transported as bed load are selected to calibrate the mathematical model using the lift coefficient as a free parameter the model is used to compute the saltation heights and lengths for a range of flow conditions the computational results are used to determine simple relationships for the saltation characteristics measured transport rates of the bed load are used to compute the sediment concentration in the bed load layer a simple expression specifying the bed load concentration as a function of the flow and sediment conditions is proposed a verification analysis using about 600 alternative data shows that about 77 of the predicted bed load transport rates are within 0 5 and 2 times the observed values

unified view of sediment transport by currents and waves i initiation of motion bed roughness and bed load transport attention is given to the properties of sediment beds over the full range of conditions silts to gravel in particular the effect of fine silt on the bed composition and on initiation of motion critical conditions is discussed high quality bed load transport data sets are identified and analyzed showing that the bed load transport in the sand range is related to velocity to power 2 5 the bed load transport is not much affected by particle size the prediction of bed roughness is addressed and the prediction of bed load transport in steady river flow is extended to coastal flow applying an intrawave approach simplified bed load transport formulas are presented which can be used to obtain a quick estimate of bed load transport in river and coastal flows it is shown that the sediment transport of fine silts to coarse sand can be described in a unified model framework using fairly simple expressions the proposed model is fully predictive in the sense that only the basic hydrodynamic parameters dep

the influence of pool length on local turbulence production and energy slope a flume experiment the in uence of pool length on the strength of turbulence generated by vortex shedding was investigated in a 6 m long recirculating ume the experiment utilized a 38 constriction of ow and an average channel bed slope of 0 007 the base geometry for the intermediate length pool experiment originated from a highly simpli ed 0 10 scale model of a forced pool from north saint vrain creek colorado discharge in the ume was 31 6 l s which corresponds to a discharge in the prototype channel of 10 m3 s three shorter and four longer pool lengths also were created with a xed bed to determine changes in turbulence intensities and energy slope with pool elongation three dimensional velocities were measured with an acoustic doppler velocimeter at 31 40 different 0 6 depth and near bed locations downstream of the rectangular constriction the average velocity and root mean square rms of the absolute magnitude of velocity at both depths are signi cantly related to the distance from the constriction in most pool locations downstream of the constriction in many locations pool elongation results in a non linear change in turbulence intensities and average velocity based on the overall ow pattern the strongest turbulence occurs in the center of the pool along the shear zone between the jet and recirculating eddy the lateral location of this shear zone is sensitive to changes in pool length energy slope also was sensitive to pool length due to a combination of greater length of the pool and greater head loss with shorter pools the results indicate some form of hydraulic optimization is possible with pools adjusting their length to adjust the location and strength of turbulent intensities in the center of pools and lower their rate of energy dissipation copyright 2004 john wiley sons ltd

identifying dynamic equilibrium of an undeveloped alluvial stream by extremal hypotheses abstract the indeterminate channel problem arises from uncertainty in finding a closure relation for alluvial channels created by self organizing erosional and depositional processes extremal hypotheses have been proposed as one potential approach to closing the system of governing equations for alluvial channels many different extremal hypotheses have been presented but no substantive evidence has been developed to select which hypothesis may be most appropriate for natural alluvial river systems this paper evaluates the ability of ten extremal hypotheses to identify dynamic equilibrium across a geomorphic gradient in the remote and undeveloped mid latitude watershed of rio murta chile this study a introduces extremal hypotheses b describes the field site and geomorphic conditions and c examines which extremal hypotheses are supported by the field data in identifying the evolutionary trend toward dynamic equilibrium the extremal hypotheses that identified dynamic equilibrium within the geomorphic gradient in the field are 1 minimum kinetic energy 2 minimum specific stream power 3 maximum friction factor and 4 maximum total friction factor which collectively support minimizing kinetic energy of the system

a determination of source properties of large intraplate earthquakes in alaska historically large and potentially hazardous earthquakes have occurred within the interior of alaska however most have not been adequately studied using modern methods of waveform modeling the 22 july 1937 16 october 1947 and 7 april 1958 earthquakes are three of the largest events known to have occurred within central alaska ms 7 3 ms 7 2 andms 7 3 respectively we analyzed teleseismic body waves to gain information about the focal parameters of these events in order to deconvolve the source time functions from teleseismic records we first attempted to improve upon the published focal mechanisms for each event synthetic seismograms were computed for different source parameters using the reflectivity method a search was completed which compared the hand digitized data with a suite of synthetic traces covering the complete parameter space of strike dip and slip direction in this way the focal mechanism showing the maximum correlation between the observed and calculated traces was found source time functions i e the moment release as a function of time were then deconvolved from teleseismic records for the three historical earthquakes using the focal mechanisms which best fit the data from these deconvolutions we also recovered the depth of the events and their seismic moments the earthquakes were all found to have a shallow foci with depths of less than 10 km

river channel adjustments downstream from channelization works in england and wales relatively little attention has been given to river channel adjustments that occur downstream from channelization works this study is concerned with the nature of channel adjustments downstream from a total of 46 channelization works located in low and high energy environments in england and wales channel changes are identified principally by the method of field survey and by reconstructing the original positions of eroded beds and banks use is also made of maps aerial photographs and engineering drawings of different dates and the technique of space for time substitution is applied enlargement of channel cross sections through erosion had occurred downstream from a variety of types sizes and dates of channelization works the maximum increase of channel size was 153 per cent out of a total of 14 sites with enlarged channel cross sections seven had undergone a change of width only at a further three width increased rather than depth and at the remaining four sites depth increases were dominant these sites all have relatively high stream powers factors causing spatial variation of erosion included tree roots locally binding bank sediments and the occurrence of bends planform change had taken place at only one site a further three high stream power sites had downstream reaches incised into bedrock and therefore did not exhibit adjustment channel enlargement is explained in terms of increased flood flows downstream from channelization works causing higher stream velocities which in turn cause erosion thereby increasing channel width and or depth examination of flow records for 35 stations revealed flood events which would formerly have spread overbank but are now confined by the channelization works and are therefore likely to alter downstream flows at sites with downstream change it is proposed that the energy of increased flows was sufficient to exceed a threshold required for erosion of perimeter sediments by contrast the absence of change at a majority of sites in low energy lowland areas could be a reflection of both the incompetence of increased flows to erode and resistance provided by perimeter sediments sites with erosion features appear not to have yet attained new equilibrium conditions

effects of aggradation and degradation on riffle pool morphology in natural gravel channels northwestern california after the flood of december 1964 12 gaging sections in northern california widened as much as 100 and aggraded as much as 4 m and then degraded to stable levels during a period of 5 years or more as channels aggraded bed material became finer and low to moderate flow through gaging sections in pools became shallower faster and steeper comparisons of longitudinal profiles also show the diminishment of pools as well as a decrease in bar relief accompanying the excessive sediment load as gaging sections degraded hydraulic geometries recovered to a limited degree full recovery probably depends on channel narrowing and further depletion of sediment supply the hydraulic changes with aggradation indicate an increase in the effectiveness of moderate discharges less than i to 2 year recurrence interval annual flood series to transport bed load and shape the bed bars become smaller pools preferentially fill and rimes armored with relatively small gravel tend to erode headward during falling stages and form a gentler gradient excess sediment can thus be more readily transported out of channels when additional contributions from watersheds are usuall slight

greek tectonics and seismicity abstract the validity of existing tectonic models for the area of greece is examined in the light of the new recalculated parameters for earthquakes of the region makropoulos and burton 1981 relocated hypocentral positions are extracted from the catalogue to form radial and vertical distance depth cross sections centred on a reference point near the mid point of the aegean volcanic arc and these are used to form a three dimensional topography of the base of earthquake occurrence below 60 km isodepth maps are extracted from this topography as both three and two dimensional map presentations these maps reveal several significant features of deep seated tectonic processes in the region isodepths exceeding 150 km are seen in the northwest aegean and these are more closely linked to the sporadhes and gulf of thermaicos rather than the north aegean trough the 150 km isodepths are also seen in the northeast aegean straddling the dardanelles in the northeastern part of the peloponnesus gulf of saronikos and eastern gulf of corinth in the southern peloponnesus towards crete and extending from north of kos to south of rodos the largest extent of deepest activity is seen south of rodos and this continues towards southwest of turkey the subduction zone of the hellenic arc is clear but smooth benioff zones are not the norm and these data show that structural complexity is more readily observed it is concluded that none of the proposed tectonic models completely explain the observed activity over the whole area and rather than propose yet another model places where further work is still particularly necessary are identified

a stability criterion inherent in laws governing alluvial channel flow the stability criterion of maximum flow efficiency mfe has previously been found inherent in typical alluvial channel flow relationships and this study investigates the general nature of this criterion using a wider range of flow resistance and bedload transport formulae for straight alluvial channels in which the effect of sediment sorting is insignificant our detailed mathematical analysis demonstrates that a flow efficiency factor e occurs generally as the ratio of sediment bedload discharge qs to stream power qs in the form of when e is maximized i e qs is maximized or is minimized maximally efficient straight channel geometries derived from most flow resistance and bedload transport formulae are found compatible with observed bankfull hydraulic geometry relations this study provides support for the use of the criteria of mfe maximum sediment transporting capacity and minimum stream power for understanding the operation of alluvial rivers and also addresses limitations to the direct application of its findings copyright 2002 john wiley sons ltd

human subsistence and environmental stability during the last 2200 years in epullan chica cave northwestern patagonia argentina a perspective from the zooarchaeological record abstract the faunal content from epullan chica archaeological site ech thereafter a small cave located in northwestern patagonia argentina was studied from taphonomic and paleoenvironmental points of view this cave is placed in the ecotone between monte desert and the patagonian steppe in the middle limay river basin was occupied since the end of the late holocene zooarchaeological evidence retrieved from ech is diverse including fresh water mollusk shells diplodon chilensis eggshell and bone fragments of rheidae bones and teeth of large lama guanicoe medium e g chaetophractus villosus conepatus chinga and micro sized several species of sigmodontine and caviomorph rodents mammals most of the recorded taxa were the result of human exploitation however owl pellets preserved in the sediments and other taphonomic signatures clearly indicate that avian predators are responsible for part of the micromammal record micromammal abundances during the last 2 2 ka bp are suggestive of a relative environmental stability around ech at least until the beginning of the last century in this sense late holocene landscapes were dominated by open steppe areas and large rocky outcrops with minor changes in humidity and temperature during this period

peak discharge estimates of glacial lake outburst floods and normal climatic floods in the mount everest region nepal abstract glacial lake outburst floods glofs in the mount everest region of nepal on 3 september 1977 and 4 august 1985 dramatically modified channels and valleys in the region by eroding transporting and depositing large quantities of sediment for tens of kilometers along their flood routes prior to this research the glof discharges had not been determined and the hydrology of normal climatic floods shffs seasonal high flow floods was not known a one dimensional step backwater flow model was utilized in conjunction with paleostage indicators to estimate the peak discharges of the glofs and shffs and to reconstruct the hydrology and hydraulic conditions of the glofs at 10 reaches and shffs at 18 reaches the most reliable glof and shff peak discharge estimates were upstream from constrictions where there was critical depth control the peak discharge of the 1977 glof at 8 6 km from the breached moraine was approximately 1900 m3 s at 7 1 km downstream from the breached moraine the 1985 glof discharge was estimated at 2350 m3 s at 27 km downstream from the breached moraine the 1985 glof attenuated to an estimated discharge of 1375 m3 s the peak discharges of shffs ranged from 7 to 205 m3 s and were positively correlated with increasing drainage area the glof discharges were 7 to 60 times greater than the shff discharges with the greatest ratios occurring near the breached moraines the downstream decline in the ratio between the glof discharge and shff discharge is the result of the downstream attenuation of the glof and the increased discharge of the shff because of increased contributing drainage area and the increased effects of monsoonal precipitation at lower elevations

morphological effects of local scouring in step pool streams step pool morphology characterizes many high gradient streams in a variety of natural settings but formative processes and evolutionary dynamics are still poorly understood in this paper natural step pool geometry is compared with steep alluvial channels where grade control structures such as check dams and bed sills make the stream profile resemble a natural stepped stream along these channels local scouring due to falling jets forms plunge pools under each structure analogous to natural steps determining the formation of pools in order to test the hypothesis that natural pools are analogous to pools formed below grade control works with respect to their dimensions shape and formative dynamics 37 natural pools and 73 artificial pools were surveyed in 10 mountain streams of the eastern italian alps pools below grade control works featured a transitional zone between the scour hole and the downstream sloping bed marked by a depositional berm when geometric parameters such as maximum pool depth length and step berm distances are normalized to the jet virtual energy no statistically significant differences were detected between natural and artificial systems these results lend support to an upstream forced cascade model for step pool formation where the energy of falling jets controls the geometry of the pools and is therefore regarded as the most important scaling independent variable copyright 2005 john wiley sons ltd

moisture history and small mammal community richness during the latest pleistocene and holocene northern bonneville basin utah abstract precipitation and net primary productivity are positively correlated in arid environments both variables are in turn correlated with mammal species richness but this relationship is not necessarily positive with increasing precipitation in arid areas of low to moderate productivity mammal richness increases linearly as rainfall and productivity increase beyond this point mammal richness is known to decline in some areas producing a relationship that has been termed unimodal or humped in the great basin of the arid western united states studies of the relationship between rodent species richness and precipitation have revealed only a positive relationship between these two variables it has however been argued that if areas of higher precipitation were to be sampled within this region the decline phase would become evident when latest pleistocene and holocene small mammal assemblages from the northern bonneville basin central utah are examined across a temporal moisture gradient species richness declines as moisture declines since the great basin was significantly moister during the latest pleistocene and early holocene than it has been since that time the unimodal response model does not appear to apply to this region