local scouring at grade control structures in alluvial mountain rivers 1 scour holes below 73 grade control structures check dams and bed sills in six mountain rivers located in the eastern italian alps have been surveyed the most likely formative water discharge is used to evaluate jet thickness at each structure which along with drop height appears to determine scour hole dimensions as shown by the consistent trends observed for nondimensional plots of both maximum scour depth and length versus the respective drop ratio sediment differences regarding size and lithology apparently play a minor role in determining scour hole dimension measured maximum scour depths are well predicted by a semiempirical equation developed through laboratory results showing an average relative error of 0 13 scour hole geometry is described by several ratios that are thought to represent approximately invariant characteristics a new energy based normalization for scour hole dimensions is proposed as the most suited to evaluate the role of jet geometry and aeration upon scouring efficiency it is noteworthy that the ratio between the maximum scour depth and the total energy available at a drop tends toward an asymptotic value around unity for increasing drop heights

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

comment on critical flow constrains flow hydraulics in mobile bed streams a new hypothesis by g e grant the writer discusses the challenging ideas proposed by grant 1997 on steep movable bed channel flows first the definition of critical flow are revisited then the calculation of bed shear stress in near critical flows are discussed new experimental data are presented and they highlight the three dimensional variations of boundary shear stress it is believed further that the applicability of grant s 1997 hypothesis is restricted because of the confusion between critical and near critical flows

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

purely erosional cyclic and solitary steps created by flow over a cohesive bed an erodible surface exposed to supercritical flow often devolves into a series of steps that migrate slowly upstream each step delineates a headcut with an associated hydraulic jump these steps can form in a bed of cohesive material which once eroded is carried downstream as washload without redeposition here the case of purely erosional one dimensional periodic or cyclic steps in cohesive material is considered the st venant shallow water equations combined with a formulation for sediment erosion are used to construct a complete theory of the erosional case the solution allows wavelength wave height migration speed and bed and water surface profiles to be determined as functions of imposed parameters the analysis also admits a solution for a solitary step or single headcut of self preserving form

channel bed steps along nahal yael negev desert israel abstract the height and spacing of channel bed steps formed in boulder and bedrock in the ephermeral channels of the nahal yael watershed show a strong correlation with the channel slope the distance between steps is inversely proportional to slope at slopes of 0 to 20 but then remains fairly constant at higher slopes step height increases proportionally with channel slope these bed steps are similar to those described on perennial channels elsewhere where step formation has been attributed to the effects of high flows which submerge the clasts forming the steps however the ephemeral flows in the tributary channels of the nahal yael system are not sufficient to submerge the clasts forming the boulder steps using rouse s criteria channel bed steps are creating maximum flow resistance at slopes of 12 to 50 along the channels of nahal yael using davies criteria bed steps are creating maximum flow resistance at slopes of 3 to 10 the bed steps also relate to sediment transport nahal yael has a low sediment yield by world standards and the increase in flow resistance due to step formation may serve to increase sediment movement both the boulder and bedrock steps at nahal yael are hypothesized to reflect the scales of flow turbulence along the channels we were unable to evaluate the role of flow volume or boundary roughness in controlling these scales but channel slope appears to exert some control on the scale of turbulence based on the correlation between slope and bed steps the hypotheses developed from field evidence at nahal yael should be testable in flume simulations

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

air water flows in the presence of staggered and row boulders under macroroughness conditions 1 free surface flow over a rough bed at steep slopes entrains large amounts of air bubbles due to the high interaction between the free surface and the bed materials the assessment of mixed air water flow features in the presence of a three dimensional bed configuration from macroroughness to intermediate roughness conditions can hardly be accomplished with aeration models developed for smooth or stepped bed configurations two phase flow properties were measured over rough bed materials in a setup assembled at the pitlab center at the university of pisa pisa italy coarser protruding materials were incorporated over the rough bed to intensify the aeration in the mixed air water flow flow discharges ranging between 0 02 and 0 09 m2 s and slopes between 0 18 and 0 44 were tested a detailed study of the air water inner layer and flow features over staggered and row coarser material arrangement over the base material was carried out results were compared with literature data on free surface flow over smooth and stepped beds

researching the earth and a few of its neighbors during my career our knowledge of erupting geysers and volcanoes in the solar system has exploded in this prefatory i tell how i became fascinated with high speed processes through studying meteorite impact dynamics and then how my initial idea of studying old faithful geyser as a volcanic analog led me to work not only on the dynamics of eruption of mount st helens in 1980 but also on geysers erupting on io a fiery satellite of jupiter triton a frigid satellite of neptune and enceladus an active satellite of saturn unforeseeably the study of these events also led to work on mineral thermodynamics and the hydraulics and geomorphic evolution of rapids in the grand canyon this is a narrative not a formal review article but the reader can find references in the related resources section to explore topics in more detail

hyporheic flow path response to hydraulic jumps at river steps flume and hydrodynamic models 1 the conceptual model of hyporheic exchange below river steps may oversimplify exchange flow paths if it depicts a uniform pattern of downstream directed upwelling this research used nonmobile porous bed flume experiments and hydrodynamic simulation cfd to characterize hyporheic flow paths below a river step with a hydraulic jump bed slope was 1 step height was 4 cm downstream flow depth was 4 cm substrate was 1 cm median diameter gravel and hydraulic jump length was 25 cm in the flume and cfd experiments with the hydraulic jump flow paths changed to include downwelling beneath the water plunging into the pool and upstream directed upwelling at the base of the step and beneath the length of jump failure to represent the influence of static and dynamic pressures associated with hydraulic jumps leads to erroneous prediction of subsurface flow paths in 75 of the streambed beneath the jump a refined conceptual model for hyporheic flow paths below a step with a hydraulic jump includes reversed hyporheic circulation cells in which downwelling water moves upstream and then upwells and flow reversals in which the larger flow net of downstream directed upwelling encounters a nested flow path of upstream directed upwelling heterogeneity in hyporheic flow paths at hydraulic jumps has the potential to explain field observed mosaics in streambed redox patterns and expand structure function relationships used in river management and restoration

predicting head cut erosion and migration in concentrated flows typical of upland areas 1 soil erosion due to head cut development and migration can devastate agricultural lands yet current prediction technology does not address this important erosion process here an analytical model of this erosional phenomenon is presented realistic physically based approximations to the laws governing mass momentum and energy transfer in the neighborhood of the scour hole result in closed form predictive algorithms for the magnitude of the plunge pool erosion and the rate of head cut migration the model introduces a special treatment of nonventilated overfall conditions is limited to homogeneous unbounded soil layers and is validated by available experimental measurements

river incision into bedrock mechanics and relative efficacy of plucking abrasion and cavitation improved formulation of bedrock erosion laws requires knowledge of the actual processes operative at the bed we present qualitative field evidence from a wide range of settings that the relative efficacy of the various processes of fluvial erosion e g plucking abrasion cavitation solution is a strong function of substrate lithology and that joint spacing fractures and bedding planes exert the most direct control the relative importance of the various processes and the nature of the interplay between them are inferred from detailed observations of the morphology of erosional forms on channel bed and banks and their spatial distributions we find that plucking dominates wherever rocks are well jointed on a submeter scale hydraulic wedging of small clasts into cracks bashing and abrasion by bedload and chemical and physical weathering all contribute to the loosening and removal of joint blocks in more massive rocks abrasion by suspended sand appears to be rate limiting in the systems studied here concentration of erosion on downstream sides of obstacles and tight coupling between fluid flow patterns and fine scale morphology of erosion forms testify to the importance of abrasion by suspended load rather than bedload particles mechanical analyses indicate that erosion by suspended load abrasion is considerably more nonlinear in shear stress than erosion by plucking in addition a new analysis indicates that cavitation is more likely to occur in natural systems than previously argued cavitation must be considered a viable process in many actively incising bedrock channels and may contribute to the fluting and potholing of massive unjointed rocks that is otherwise attributed to suspended load abrasion direct field evidence of cavitation erosion is however lacking in terms of the well known shear stress or stream power erosion law erosion by plucking is consistent with a slope exponent n of 2 3 to 1 whereas erosion by suspended load abrasion is more consistent with a slope exponent of 5 3 given that substrate lithology appears to dictate the dominant erosion process this finding has important implications for long term landscape evolution and the models used to study it

fluvially sculpted rock bedforms in twenty mile creek niagara peninsula ontario sculpted rock bedforms s forms on whirlpool sandstone are described from the bed of twenty mile creek the morphologies identified undulating surfaces rises furrows comma forms spindles potholes and transverse troughs are those described for sculpted bedrock forms p forms s forms developed in subglacial environments additional morphologies identified are undercut downsteps and quarried surfaces in the lee of bedrock rises morphological differences between the subglacial and fluvial forms are attributed to the difference between confined conduit flow in the subglacial case and open channel flow in the fluvial examples in fluvial systems the descending bedrock surface presents rock differently to oncoming flows and favours certain s forms quarried lee faces and undulating surfaces in a strong flow fluvial environment s forms develop by wear dominant sediment transport modes are large clasts up to metre dimensions and suspended silt clay with a small 7 hard or heavy mineral compone

effect of jet air content on plunge pool scour the effect of air discharge on plunge pool scour was investigated by using a simplified experimental configuration instead of considering the complete arrangement involving chute and deflector resulting in an air water jet impinging on a sediment surface the mixture flow was produced with a circular pipe for which the air concentration and the jet diameter close to impact on the free water surface are known the results of this study were primarily directed to the definition of a three phase froude number that accounts for the combined effects of an air water mixture jet on scour the analysis of data allows simple estimates of the scour geometry including a generalized scour profile the width of scour and the temporal advance of the extreme scour depths it was pointed out that for a certain water velocity and selected grain characteristics the addition of air to the jet results in an increase of scour depth however if the reference would be the air water mixture velocity scour depth decreases significantly by the addition of air to the jet

jet and hydraulic jump near bed stresses below a horseshoe waterfall 1 horseshoe waterfalls are a common but unexplained feature of bedrock rivers as a step toward understanding their geomorphology a six component force torque sensor was used to evaluate clear water scour mechanisms in a 0 91 m broad crested horseshoe waterfall built into a 2 75 m wide flume to measure longitudinal lateral and temporal profiles of the near bed spatially averaged stress vector jet impact caused moderate near bed stress downstream of the impact point the stress vector shifted into a much more forceful upthrust with peak stress beyond the boil crest instantaneous fluctuations in near bed lift exceeded drag by 5 10 times and occurred over a wider range of frequencies suggesting a larger role for particle entrainment predictions of bed stress significantly underestimated actual conditions these results show that horseshoe waterfalls have an extended region of high scour along their centerline corresponding with the three dimensional convergent dynamics associated with both jet impact and jump enhanced lift fluctuations

the influence of bedrock geology on knickpoint development and channel bed degradation along downcutting streams in south central indiana geologic controls on knickpoint development and the mechanics of channel bed degradation were eluci dated by comparison of downcutting streams in south central indiana developed in lithologically homoge neous carbonate units and layered siliciclastic strata knickpoints formed in a single lithologic unit are stepped each step consists of a knickpoint face and tread the height of each step is equal to and controlled by bed thickness spatially knickpoints in homogeneous terrain are limited to jointed strata that dip 1 upstream or 2 downstream at angles less than the channel gradient knickpoints observed in lithologically layered strata are characterized by a single step in which resistant jointed rocks overlie and protect weaker units total knickpoint relief is influenced by thickness of the weaker strata knickpoints in layered siliciclastic strata are spatially limited to bedrock reaches produced by differential rates of channel incision knickpoint distribution is also influenced by joint

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

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

backward flow velocities of submerged hydraulic jumps this paper describes an experimental investigation of submerged hydraulic jumps forming downstream of overflow structures submergence happens when the hydrological tailwater depth in a channel exceeds the jump s subcritical sequent depth it is a common occurrence particularly with low overflow structures the jump may produce a vortex having significant countercurrent free surface velocities this phenomenon is held responsible for frequent personal injury accidents of unwary recreationists hence its appellation of drowning machine experimental results supported by analytical reasoning are presented that quantify these dangerously high velocities for all hydraulic situations

hydromorphological processes at submerged solitary boulder obstacles in streams abstract a series of 51 experiments was conducted in a laboratory flume to investigate hydromorphological processes at submerged solitary boulder like obstacles as part of a programme to validate the experimental results five sites with obstacle marks at large boulders were surveyed in two gravel bed ephemeral streams located in eastern spain three hydromorphological system states i iii were observed each exhibiting characteristic dynamic interactions between hydraulic and sedimentary processes i wake vortex domination and absent scouring ii wake vortex domination and downstream scouring iii horseshoe vortex domination frontal scouring and ridge like sediment accumulation at the lee side the latter system state iii comprises typical fluvial obstacle marks in mobile alluvial beds obstacles may tilt upstream into the scour hole when frontal scour depths exceed 0 6 times obstacle length favouring the rapid achievement of steady state conditions state iii field and experimentally modelled obstacle marks are related to each other when frontal scour depth width and length as well as ridge width are used as morphometric variables an analytical model was adapted and successfully applied for determination of these variables at the steady state condition the model was also used to assess the critical threshold for the formation of obstacle marks it integrates mean flow velocity water depth obstacle height and width obstacle shape median grain size relative to obstacle width and grain size distribution dynamic interactions between hydraulic processes and sediment exchange around obstacles together with well defined boundaries between evolutionary states critical thresholds suggest a self organised scale invariant mechanism driving the generation of obstacle marks

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

rockbed wear at a flow convergence zone in fifteen mile creek niagara peninsula ontario sculpted bedforms developed in rock channels must be considered within the context of temporally and spatially persistent flow dynamics a shallow meandering channel 14 m long 30 50 cm wide 3 4 cm deep with raised margins has been eroded into resistant irondequoit limestone forming the streambed of fifteen mile creek ontario potholes 18 cm deep 25 cm wide 35 cm long within the channel increase in size downstream subaerial solution of the limestone and fracture patterns within the irondequoit limestone are not responsible for this large dolostone blocks within the channel stabilize patterns of vorticity that form in the lee of the blocks during highflows when flow is about 1 3 m deep vortices migrating downstream along a major flow junction have eroded the distinctive channel small irregularities in the bed may enlarge to potholes by attracting vortices and undergoing erosional wear as they pass the feature may have developed within several hundred to several thousand years but likely d

using two dimensional hydrodynamic models at scales of ecological importance modeling of flow features that are important in assessing stream habitat conditions has been a long standing interest of stream biologists recently they have begun examining the usefulness of two dimensional 2 d hydrodynamic models in attaining this objective current modeling practices consider relatively long channel sections with their bathymetry represented in terms of large macro scale topographic features meso scale topographic features such as boulders root wads and other obstructions are typically not considered in the modeling process instead the overall effects of these flow obstructions are captured through increased values in the channel roughness parameters such an approach to 2 d modeling allows one to accurately predict average depth and velocity values however it is not capable of providing any information about the flow patterns in the vicinity of these obstructions biologists though have known that such meso scale features and the complex velocity patterns generated by their presence play an important role in the ecology of streams and thus cannot be ignored it is therefore evident that there is a need to develop better tools capable of modeling flow characteristics at scales of ecological importance the purpose of this study is to expand the utility of 2 d hydraulic models to capture these flow features that are critical for characterizing stream habitat conditions there exists a paucity of research addressing what types of topographic features should be included in 2 d model studies and to what extent a boulder or series of exposed boulders can influence predicted flow conditions and traditional useable habitat computations moreover little research has been performed to evaluate the impact mesh refinement has on model results in natural streams numerical simulations based on a natural river channel containing several large boulders indicate that explicitly modeling local obstructions boulders can significantly impact predicted flow parameters the presence of these obstructions create velocity gradients velocity shelters transverse flows and other ecologically important flow features that are not reproduced when their geometry is not incorporated into the hydraulic model sensitivity analyses show that reducing element sizes in the vicinity of obstructions and banks is crucial in modeling the spatial flow patterns created by meso scale topographic features this information combined with similar data obtained in future studies can provide guidelines for the placement of fishrocks and other structures often used in stream restoration projects as well as determining what types of mesoscale topographic features might need to be incorporated into habitat suitability studies such information may also ultimately allow new spatial habitat metrics to be developed q 2000 elsevier science b v all rights reserved

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

modeling energy dissipation and hydraulic jump regime responses to channel nonuniformity at river steps 1 the river step is an important driver for geomorphic evolution in bedrock rivers but the effect that variations in channel geometry upstream and downstream of a river step have on hydraulic jump regime and energy dissipation has not previously been investigated the associated hydraulic jump is inherent to a river step and its regime is a primary control on step morphodynamics in turn the hydraulic jump regime is controlled by several variables as detailed in a new conceptual framework herein also in this study a parsimonious semianalytical numerical model of step hydraulics is developed to quantify energy dissipation and delineate hydraulic jump regimes accounting for discharge jump submergence and nonuniform channel geometry through a step despite remaining limitations in step theory the model simulates how natural steps respond to a wide range of conditions the model shows that hydraulic jump regime and energy dissipation exhibit greater sensitivity to channel nonuniformity as discharge increases and or step height decreases also channel conditions that create greater jump submergence lead to decreased energy dissipation regardless of the discharge regime the model also reinforces the common observation about gully erosion that downstream channel widening enhances upstream knickpoint migration the new algorithm may be used to aid river engineering involving steps and could be useful for landscape evolution modeling

geologically controlled waterfall types in the outer carpathians abstract more then fourty waterfalls occurring in the polish outer carpathians have been studied with regard to their geological settings they are small forms developed on faulted flysch rocks of different resistance on streams characterized by similar features of catchment basins and similar discharges the classification of these erosional landforms is based on criteria considering the bed sequence their position relative to the streamflow and morphological properties the course of the evolution of particular types of falls depends mainly on the degree of downcutting or headward erosion many types of carpathians falls may be considered as models of widely known great waterfalls

fluctuating uplift and lining design in spillway stilling basins the paper deals with the characterization and the control of transient uplift generated by turbulent pressure fluctuations in spillway stilling basins theoretical and experimental analyses are presented defining the maximum instantaneous uplift acting on the linings which lead to a design criterion for suitable floor slabs the thickness of concrete linings not accounting for the possible contribution of anchors required for stability is defined in this paper as a function of 1 the incoming kinetic head and or froude number 2 a dimensionless function of the longitudinal and transversal dimensions of the lining slabs the areal extent of extreme turbulent pressure fluctuations and the anisotropic integral scales of the instantaneous spatial correlation of pressure fluctuations 3 the ratio of specific weights of water and immersed concrete and 4 a dimensionless pressure coefficient qualifying the maximum difference of positive and negative pressure fluctuations about the stationary mean value it is concluded that safe design of protection works is significantly affected by the structure of instantaneous spatial distribution of pressures at the bottom of hydraulic jumps consideration of this factor leads to recommendations for the design of slabs in stilling basins

flow measurement in sloping channels with rectangular free overfall this technical note describes an experimental study of the free overfall from a rectangular channel with differing slopes and bed roughnesses the relationship between the upstream critical depth and brink depth is explored and found to be influenced by both slope and channel bed roughness with roughness having a greater effect at steeper slopes two empirical equations are proposed for calculating this relationship the first requiring only the channel slope to be known and the second requiring a knowledge of channel slope and roughness the accuracy of the two equations when used in a method for flow measurement are compared the first relationship in which the effects of slope and roughness are aggregated provides a useful estimate of channel discharge if only the channel slope is known if both bed roughness and slope are known then the second relationship can be used to calculate channel discharge with greater accuracy

enormous increase of stratospheric aerosols over fukuoka due to volcanic eruption of el chichon in 1982 large increases of stratospheric aerosol particles caused by the eruption of mexican volcano el chichon in early april 1982 were observed by a yag lidar system at two wavelengths 1 06 m and 0 53 m over fukuoka for three months since april 18 most of the observations show high concentrations of aerosols in the altitude regions from 15 to 33 km with highest concentrations between 21 and 30 km the aerosol optical thickness at 0 55 m is about 0 1 0 3 this is about 10 to 30 times the maximum monthly mean values that were observed after the mt st helens event in 1980 the mean radius of aerosols in the densest part of the el chichon cloud is estimated to be approximately 0 1 m this estimate is based on the slow settling velocity of the peak of the cloud and from information obtained by comparison of the two wavelength lidar returns a significant impact of the presence of the cloud on the climate through variations of atmospheric circulation is suggested

crater lake and post eruption hydrothermal activity el chichon volcano mexico abstract explosive eruptions of volcan el chichon in chiapas mexico on march 28 and april 3 4 1982 removed 0 2 km3 of rock to form a 1 km wide 300 m deep summit crater by late april 1982 a lake had begun to form on the crater floor and by november 1982 it attained a maximum surface area of 1 4 105 m2 and a volume of 5 106 m3 accumulation of 4 5 m of rainfall between july and october 1982 largely formed the lake in january 1983 temperatures of fumaroles on the crater floor and lower crater walls ranged from 98 to 115 c by october 1983 the maximum temperature of fumarole emissions was 99 c in january 1983 fumarole gas emissions were greater than 99 vol h2o with traces of co2 so2 and h2s the water of the lake was a hot t 52 58 c acidic ph 0 5 dilute solution 34 046 mg l 1 dissolved solids cl s 20 5 sediment from the lake contains the same silicate minerals as the rocks of the 1982 pyroclastic deposits together with less than 1 of elemental sulfur the composition and temperature of the lake water is attributed to 1 solution of fumarole emissions 2 reaction of lake water with hot rocks beneath the lake level 3 sediments washed into the lake from the crater walls 4 hydrothermal fluids leaching sediments and formational waters in sedimentary rocks of the basement 5 evaporation and 6 precipitation

longitudinal profile development into bedrock an analysis of hawaiian channels analysis of topographic maps of rivers incised into dated hawaiian lava flows shows that the long term average bedrock erosion rate along certain reaches is linearly related to stream power field observations suggest that two processes may control hawaiian channel downcutting 1 stream power dependent erosion including abrasion of the channel bed by transported particles and 2 step wise lowering caused by knickpoint propagation modeling results indicate that a simple stream power dependent erosion law predicts the straight to weakly convex longitudinal profiles characteristic of kauai channels but is insufficient to predict two other characteristic features the upslope propagation of knickpoints and the straight 5 8 channel slopes below the knickpoints thus more than this single transport law is apparently required to model bedrock channel incision field surveys also indicate that significant portions of the channel lengths below the knickpoints are mantled with large boulders we propose that

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

experiments on headcut growth and migration in concentrated flows typical of upland areas experiments were conducted to examine soil erosion by headcut development and migration in concentrated flows typical of upland areas in a laboratory channel packed sandy loam to sandy clay loam soil beds with preformed headcuts were subjected to simulated rain followed by overland flow the rainfall produced a well developed surface seal that minimized surface soil detachment during overland flow soil erosion occurred exclusively at the headcut and after a short period of time a steady state condition was reached where the headcut migrated at a constant rate the scour hole morphology remained unchanged and sediment yield remained constant a fourfold increase in flow discharge resulted in larger scour holes yet aspect ratio was conserved a sediment bed was deposited downstream of the migrating headcut and its slope depended weakly on flow discharge

response of the water level in a well to earth tides and atmospheric loading under unconfined conditions the response of the water level in a well to earth tides and atmospheric loading under unconfined conditions can be explained if the water level is controlled by the aquifer response averaged over the saturated depth of the well because vertical averaging tends to diminish the influence of the water table the response is qualitatively similar to the response of a well under partially confined conditions when the influence of well bore storage can be ignored the response to earth tides is strongly governed by a dimensionless aquifer frequency q u the response to atmospheric loading is strongly governed by two dimensionless vertical fluid flow parameters a dimensionless unsaturated zone frequency r and a dimensionless aquifer frequency qu the differences between q u and qu are generally small for aquifers which are highly sensitive to earth tides when q u and qu are large the response of the well to earth tides and atmospheric loading approaches the static response of the aquifer under confined conditions at small values of q u and qu well response to earth tides and atmospheric loading is strongly influenced by water table drainage when r is large relative to qu the response to atmospheric loading is strongly influenced by attenuation and phase shift of the pneumatic pressure signal in the unsaturated zone the presence of partial penetration retards phase advance in well response to earth tides and atmospheric loading when the theoretical response of a phreatic well to earth tides and atmospheric loading is fit to the well response inferred from cross spectral estimation it is possible to obtain estimates of the pneumatic diffusivity of the unsaturated zone and the vertical hydraulic conductivity of the aquifer

effects of bed forms and large protruding grains on near bed flow hydraulics in low relative submergence conditions in mountain rivers bedforms large relatively immobile grains and bed texture and topographic variability can significantly alter local and reach averaged flow characteristics the low relative submergence of large immobile grains causes highly three dimensional flow fields that may not be represented by traditional shear stress flow velocity and turbulence intensity equations to explore the influence of large protruding grains and bedforms on flow properties we conducted a set of experiments in which we varied the relative submergence while holding the sediment transport capacity and upstream sediment supply constant flow and bed measurements were conducted at the beginning and end of each experiment to account for the absence or presence of bedforms respectively detailed information on the flow was obtained by combining our measurements with a 3d numerical model commonly used velocity profile equations only performed well at the reach scale when shallow flow effects and the roughness length of the relatively mobile sediment were considered however at the local scale large deviations from these profiles were observed and simple methods to estimate the spatial distribution of near bed shear stresses are likely to be inaccurate zones of high turbulent kinetic energy occurred near the water surface and were largely controlled by the immobile grains and plunging flow the reach averaged shear stress did not correlate to depth or slope as commonly assumed but instead was controlled by the relative boulder submergence and degree of plunging flow for accurate flow predictions in mountain rivers the effects of bedforms and large boulders must be considered

air concentrations of submerged and unsubmerged hydraulic jumps in a bedrock step pool channel 1 the classical hydraulic jump which is a hydraulic jump formed in a horizontal smooth and prismatic laboratory flume has often been used for estimating hydraulic and morphologic characteristics of mountain river channels however most studies utilizing classical hydraulic jump relationships have neglected the role of aerated flows and jump types prevalent in natural systems by developing a methodology to survey digitize and visualize air concentrations for jumps in bedrock rivers we present new data for submerged jumps and sloping jumps in a bedrock step pool channel as with laboratory research our results indicated peak mean and local air concentrations of natural jumps were skewed by submergence of the jump roller beneath the free surface however unlike laboratory research cross stream variations were significant for both jumps varying up to 20 across the jump width traces through each jump thalweg also indicated the classical hydraulic jump was a poor analogue for estimating surficial air concentrations

geometric scaling of step pools in mountain streams observations and implications understanding the geometric structuring of alluvial step pools is an enduring problem in mountain stream geomorphology many previous studies propose that the key control parameter governing the step pool form is mean bed slope as explored through several examples however we find that slope control formulations are inconsistently demonstrated for broad data sets on this basis we reexamine the bed form architecture of step pools with a new descriptive parameter termed the aspect ratio active stream width divided by step drop height we test with data collected from three different mountain settings for step pools observed over mean bed slopes ranging from 2 to 22 we find that step wavelength and height are well described by when these dimensions are normalized by the step drop height furthermore we observe that varies inversely with mean bed slope context for our findings is provided by recent field and laboratory work which highlights that the cross stream component to the overall flow structure in step pools and scour pools is significant this is important because it expands upon and relates our work to formative models which are based on jet scour and the associated three dimensional flow structure of step pools our work has practical implications for the design of step pool channels because existing approaches are based in large part on structuring artificial systems according to a narrowly defined geometry we observe however that under certain conditions this approach may yield constructed step pools that are unstable as an alternative approach we propose that the geometric relationships developed here can be applied to identify artificial step pool geometries that will be more fully reflective of natural analogs and thus possibly more stable

indirect velocity measurement from standing waves in rockbed rivers direct measurement of velocities and discharge in turbulent rockbed rivers is dangerous and often impracticable float measurements of surface velocity in sediment free rockbed reaches of rivers are used to test the equation due to kennedy that the mean velocity of a critical wave train is given by v 1 2495 where is the wavelength of the standing waves field data collected for wavelengths between 0 5 m and 7 m estimates surface velocity as about 2 significantly higher than the predicted mean velocity it is concluded that the kennedy equation successfully represents the mean velocity in rockbed rivers which are essentially free from sediment and that measuring the wavelengths of standing wave trains is an accurate and economical method of measuring mean velocity in the field from estimated wave train width and computed critical depth minimum discharge can be estimated for the section

convergent hydraulics at horseshoe steps in bedrock rivers abstract horseshoe waterfalls are a common feature of steep bedrock rivers as a first step toward understanding their geomorphology a detailed study of the fluid mechanics at a 0 91 m vertical drop horseshoe waterfall was performed in a 2 75 m wide flume five non dimensional upstream energy levels each with 3 5 non dimensional downstream tailwater depths 21 runs total were assessed for water surface topography via digital elevation modeling flow dynamics via digital videography and overall energy dissipation via an energy and momentum conservation model regardless of tail depth the horseshoe waterfall was found to have three distinct zones beyond the step brink 1 a nappe whose degree of convergence depends on upstream energy and brink configuration 2 a convergence zone whose features vary strongly with upstream energy brink configuration and tail depth and 3 a downstream tailwater region whose dynamics primarily depend on tail depth the centerline nappe profile and brink velocity were reasonably predicted using rouse s jet trajectory equations when h p h 2 peripheral profiles were not predictable using existing equations for any arbitrary broad crested step brink configuration maximum energy dissipation was found to occur when no jump was present and downstream tail depth was exactly critical rather than providing maximal energy dissipation hydraulic jumps below steps provide efficient conversion of kinetic energy to potential energy

flow separation berms downstream of a hydraulic jump in a bedrock channel abstract the first direct observation of the development of lateral gravel berms associated with hydraulic jumps in bedrock channels is reported cobbles and pebbles were observed being swept through jumps and deposited in the tranquil flow immediately downstream and either side of the v shaped shock waves field measurements of jumps and geometry current speed and water depth are found to be consistent both with laboratory data and theoretical considerations the deposits have significance in constraining flood palaeoflow reconstructions as the presence of berms determines the former location of hydraulic jumps whilst the angle subtended by the berm crestline with respect to a regular bankline may be used to estimate the froude number of the flow

modulation of headcut soil erosion in rills due to upstream sediment loads 1 headcut erosion can severely accelerate soil loss in upland concentrated flows and lead to significant soil degradation in agricultural areas previous experimental work has demonstrated that actively migrating headcuts display systematic morphodynamic behavior and that impinging jet theory can provide an excellent analytic foundation for predicting these erosional phenomena this research sought to examine systematically the effect of an upstream sediment load on the morphodynamics of actively migrating headcuts in upland concentrated flows using a specially designed experimental facility actively migrating headcuts in packed soil beds were allowed to develop freely when subjected to concentrated clear water flows similar to rills crop furrows and ephemeral gullies after such headcut development and without altering the boundary conditions of the experiment a sediment load composed of relatively coarser grained sand was introduced into the flow well upstream of the erosional feature at relatively low upstream sediment loadings the morphodynamics and sediment discharge of the actively migrating headcuts remained unchanged in time and space as upstream sediment loadings increased the size and migration rate of the headcuts decreased markedly yet sediment discharge was not strongly affected as its sediment texture shifted from headcut controlled flux to sediment feed flux the headcut erosion process was completely arrested when the upstream sediment feed rate exceeded a specific magnitude analytic arguments are used to explain the reaction time and morphodynamic response of an actively migrating headcut to this upstream sediment loading this research shows that headcut erosion can be strongly modulated by an upstream sediment load further complicating the prediction of soil erosion on upland areas dissected by sediment laden concentrated flows