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

debris fan constrictions and flood hydraulics in river canyons some implications from two dimensional flow modelling rapids in river canyons are frequently found at sites where debris fans constrict flow along the channel whereas some fans may have persisted in the same location with unchanging geometry for centuries to millennia others have changed in response to flow conditions imposed by successive floods such a change in boundary conditions may alter local flow hydraulics this paper utilizes two dimensional flow modelling to compare flood hydraulics along two alternative versions of an idealized reach of a river canyon one with uniform width gradient and cross section and a second perturbed by a prominent debris fan along the valley wall the flow pattern along the reach with the fan is far more complex than the pattern along the uniform reach maximum velocity along the debris fan reach is up to 50 per cent higher than along the uniform reach maximum bed shear stress is up to three or four times higher and an area of supercritical flow is predicted extending from the nose of the fan into the zone of flow expansion immediately downstream comparison of model output along longitudinal profiles of the two reaches indicates that the backwater effect of the fan extends several valley widths upstream predicted flows based on the same stage are as much as 190 to 230 per cent greater along the uniform reach than along the debris fan reach reconstruction of palaeoflood discharge based on remnant flood marks in the vicinity of the fan would be sensitive to assumptions about boundary conditions that existed in the past this effect relaxes over a longitudinal distance of several hundred metres furthermore there are significant cross stream gradients that change slope and direction several times in the vicinity of the fan calling into question the utility of one dimensional step backwater hydraulic models for predicting high water marks in areas of complex valley morphology

tertiary uplift and shortening in the basin and range the echo hills southeastern nevada the echo hills is a distinctive area of tectonic uplift and shortening located at a right step in the left lateral bitter spring valley fault of the late tertiary lake mead fault system nevada the fundamental internal structure of the echo hills is an asymmetric anticline disrupted by reverse and oblique faulting an analysis of the stress distribution within the stepover indicates that the interaction between the two segments of the bitter spring valley fault is responsible for the compressive deformation and structural uplift in the echo hills given the number of strike slip faults in the basin and range similar examples of tertiary uplift and shortening probably occur elsewhere within the province

valley width variation influences riffle pool location and persistence on a rapidly incising gravel bed river abstract decades of research have demonstrated that gravel bed rivers exhibit multiple spatial scales of landform nonuniformity landform features such as valley wall oscillations alluvial fans terraces river meanders point bars boulder clusters and logjams contribute to river corridor heterogeneity further studies have shown that the locations of riffles and pools in gravel bed rivers are closely associated with the spatial pattern of river corridor morphological variability these studies imply but do not directly test that persistence of riffles and pools through time is also conditioned by landform variability mechanistically it may be hypothesized that overbank flows interact hydraulically with oscillating valley walls by way of a mechanism known as flow convergence routing in such circumstances can variation in valley width influence channel morphology forcing riffle pool location and persistence to address this question research was performed on a valley confined wandering gravel bed reach of the regulated lower yuba river california usa that is incising from reduced sediment supply and flow regulation after a historic period of mining related valley sedimentation this study quantified stream planform change 1984 2006 and elevation change 1999 2006 using eight aerial photo sets and two digital elevation models and it qualitatively assessed channel change in older aerial photos going back to 1937 analysis revealed that the river has undergone rapid incision 0 11 m year and planform change in response to frequent floods yet eight riffles persisted in the same locations which coincided with the locally wide areas of the valley longitudinal profiles revealed that deep pools were associated with long valley constrictions geomorphic analysis and design need to explicitly account for multiple scales of landform nonuniformity in order to rehabilitate natural fluvial processes

gradient irregularity in the herbert gorge of northeastern australia the seventy kilometre long herbert gorge of northeastern australia preserves a record of past floods in slackwater deposits and palaeostage indicators step backwater modelling of water surface profiles indicates that discharges ranging from 11000 to 17000 m3s 1 have occurred six times in the gorge during the last 900 years these flood reconstructions provide insight into the role of extreme flows in shaping bedrock channel morphology in particular the hydraulics of extreme flows can be related to boulder transport and to the location of large boulder bars large boulder bars occur throughout the herbert gorge being best developed at loci of stream power minima along the inside of bends at tributary junctions and at obstructions in the channel caused by bedrock highs only the flows exceeding approximately 8000 m3 s 1 are competent to transport the boulders which constitute the bars in the straight channel reaches the boulder accumulations and bedrock highs have a fairly regular spacing which appears to be independent of lithologic or structural controls the bars provide an efficient means of energy dissipation and they are interpreted as a result of the inherent high turbulence of flow in a steep channel the regular spacing of the bars and their correspondence with the hydraulics of large flows suggest that the bars and associated bedrock highs may represent a self regulating mechanism akin to the pool riffle sequence of alluvial channels it may therefore be appropriate to view bedrock channels as deformable on the timescale of extreme discharges

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

formation and maintenance of a forced pool riffle couplet following loading of large wood abstract pool riffle maintenance has been documented in numerous studies but it has been almost impossible to characterize detailed natural pool riffle formation mechanisms because of the lack of baseline data prior to pool establishment in 2013 a study was conducted on the blackledge river in connecticut to document the formation of a new pool riffle couplet on a section of river that had previously been studied from 1999 to 2001 in 2001 the study reach contained a scour hole with a residual depth of 0 08 0 09 m downstream of a 1930s paired deflector with no identifiable riffle immediately downstream at this time a large severely undercut hemlock tree was noted along the left bank sometime between fall 2001 and 2004 the tree fell perpendicular to flow across the channel and formed a large wood lw jam and new pool riffle couplet several meters downstream of the old scour hole pool spacing along the reach decreased from 4 47 bankfull widths bfw in 1999 to 3 83 bfw after the new pool riffle couplet formed the new pool has a residual depth the water depth of the streambed depression below the elevation of the immediate downstream hydraulic control of 1 36 0 075 to 1 59 0 075 m which resulted from a combination of 1 32 0 09 m or less of incision below the old scour hole 95 6 or less of the depth increase and up to 0 18 0 09 m of downstream deposition and associated backwater formation 13 2 or less of the depth increase to assess dynamic stability of the pool riffle couplet over several flood cycles surficial fine sediment and organic material along the reach were quantified the 23 m long pool stores 25 7 of the surficial fine grained sediments and 15 4 of organic material along a 214 m long reach that includes one additional artificially created pool an adjacent 50 m long secondary channel impacted by the lw jam stores 65 3 of the surficial fine grained sediments and 54 8 of organic material along the full reach

the linkage between velocity patterns and sediment entrainment in a forced pool and riffle unit a field based project was initiated in order to characterize velocities and sediment entrainment in a forced pool and riffle sequence three dimensional velocities and turbulence intensities were measured with an acoustic doppler velocimeter at 222 different points at three similar flows that averaged approximately 4 35 m 3 s 1 within a large pool riffle unit on north saint vrain creek colorado sediment sorting patterns were observed with the introduction of 500 tracer particles painted according to initial seeding location tracer particles moved sporadically during a 113 day period in response to the annual snowmelt peak flow which reached a maximum level of 14 8 m 3 s 1 velocity data indicate high instantaneous velocities and turbulence levels in the centre of pools patterns of sediment deposition support the notion that stream competence is higher in the pool than the downstream riffle flow convergence around a large channel constriction appears to play a major role in multiple processes that include helical flow development and sediment routing and backwater development with low velocities and turbulence levels above the constriction that may locally limit sediment supply jet flow flow separation vortex scour and turbulence generation enhance scour in the centre of pools ultimately multiple processes appear to play some role in maintenance of this forced pool and the associated riffle copyright 2008 john wiley and sons ltd

the characteristics of turbulence in a shear zone downstream of a channel constriction in a coarse grained forced pool a field based project was initiated to characterize the influence of varying discharge and bed topography along a pool exit slope on the strength of turbulence generated by vortex shedding velocities were measured with an adv downstream of a boulder constriction within a shear zone of a large pool measurements were repeated for four flows that varied from 20 to 50 of bankfull discharge an additional longitudinal profile was conducted along the pool thalweg plots of velocity demonstrate high near bed velocities and turbulence levels in the pools turbulence levels were highest closer to the constriction in the shear zone turbulent kinetic energy decayed in the downstream direction in response to the bed topography and at lower discharges instantaneous velocities are large enough to temporarily lift pebbles at this depth it appears that instantaneous forces created by vortex shedding may play an important role in scouring pools downstream of constrictions the turbulence may also respond to changes in bed topography in a manner that encourages feedbacks among bed topography characteristics of turbulence and sediment transport

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

errors in daily ablation measurements in northern greenland 1993 94 and their implications for glacier climate studies ablation climate studies were made at two locations in northern green land in the summers of 1993 and 1994 respec tively daily ablation ii as measured at ten stakes within a small area and the data were compared with each other to detect gross errors for example high deviations for data taken on the same day or low cor rela tions between data series at differ ent stakes indicate erroneous data a fter cl iscard i ng data for one stake in 1993 and t wo stakes in 1994 random errors in daily ablation data for individ ual stakes arc 5 kg m 2 d i which is further reduced to only about 2 kg m 2 d 1 by averag ing over eight or nine stakes random errors in cal culated energy bala nces using the pres ent abla tion data are much imover than found in earlier studies in vest greenland where ablation was only measured on three stakes without any attem pt to detect gross errors aside from day to day errors there arc 10 diffe rences in mca n ablation at different sta kes which are probably caused by small s cal e variations in surface albedo such inters take diffe rences gi e 10 uncertainty in positive degree day faetors which arc 9 8 0 9 and 5 9 0 6 kg m 2 d 1 deg 1 for the two sites

influence of coarse lag formation on the mechanics of sediment pulse dispersion in a mountain stream squire creek north cascades washington united states 1 mountain channels closely coupled to landslide prone hillslopes often exhibit bed surface grain sizes coarser than transportable by annual high flows coarse particles within poorly sorted sediment delivered to channels by mass wasting processes may not be readily transported as bed load and can consequently form lag deposits that influence the morphology hydraulic roughness and sediment storage within mountain channel networks a tracer study and comparison of supply and bed grain size distributions from a valley spanning landslide in the north cascades of washington state were used to derive relations between shear stress and the probability of particle entrainment and erosion from the sediment pulse rapid bed surface armoring formed a relatively immobile lag deposit within 2 years covering of 20 of the bed by lag boulders with 5 probability of entrainment was sufficient to retard vertical incision and force considerable channel widening during a flood with an 8 to 152 year recurrence discharge on locally gauged streams our results imply that numerical models of sediment pulse evolution that do not explicitly incorporate the influence of lag formation may substantially overestimate long term dispersion rates the grain size distribution and lithology of a sediment input relative to the flow competence of the receiving channel are important factors influencing the rates and mechanisms of sediment pulse dispersion and the sediment capacitance provided by coarse grained sediment pulses in mountain drainage basins

water velocity and the nature of critical flow in large rapids on the colorado river utah 1 rapids are an integral part of bedrock controlled rivers influencing aquatic ecology geomorphology and recreational value flow measurements in rapids and high gradient rivers are uncommon because of technical difficulties associated with positioning and operating sufficiently robust instruments in the current study detailed velocity water surface and bathymetric data were collected within rapids on the colorado river in eastern utah with the water surface survey it was found that shoreline based water surface surveys may misrepresent the water surface slope along the centerline of a rapid flow velocities were measured with an adcp and an electronic pitot static tube integrating multiple measurements the adcp returned velocity data from the entire water column even in sections of high water velocity the maximum mean velocity measured with the adcp was 3 7 m s the pitot static tube while capable of only point measurements quantified velocity 0 39 m below the surface the maximum mean velocity measured with the pitot tube was 5 2 m s with instantaneous velocities up to 6 5 m s analysis of the data showed that flow was subcritical throughout all measured rapids with a maximum measured froude number of 0 7 in the largest measured rapids froude numbers were highest at the entrance of a given rapid then decreased below the first breaking waves in the absence of detailed bathymetric and velocity data the froude number in the fastest flowing section of a rapid was estimated from near surface velocity and depth soundings alone

debris flow deposition and reworking by the colorado river in grand canyon arizona 1 flow regulation by large dams affects downstream flow competence and channel maintenance debris flows from 740 tributaries in grand canyon arizona transport coarse grained sediment onto debris fans adjacent to the colorado river these debris fans constrict the river to form rapids and are reworked during river flows that entrain particles and transport them downstream beginning in 1963 flood control operations of glen canyon dam limited the potential for reworking of aggraded debris fans we analyzed change in debris fans at the mouths of 75 mile and monument creeks using photogrammetry of aerial photography taken from 1965 to 2000 and supplemented with ground surveys performed from 1987 to 2005 our results quantify the debris fan aggradation that resulted from debris flows from 1984 to 2003 volume area and river constriction increased at both debris fans profiles of the two debris fans show that net aggradation occurred in the middle of debris fans at stages above maximum dam releases and surface shape shifted from concave to convex dam releases above power plant capacity partially reworked both debris fans although reworking removed much less sediment than what was added by debris flow deposition large dam releases would be required to create additional reworking to limit the rate of debris fan aggradation in grand canyon

flow convergence routing hypothesis for pool riffle maintenance in alluvial rivers 1 the velocity reversal hypothesis is commonly cited as a mechanism for the maintenance of pool riffle morphology although this hypothesis is based on the magnitude of mean flow parameters recent studies have suggested that mean parameters are not sufficient to explain the dominant processes in many pool riffle sequences in this study two and three dimensional models are applied to simulate flow in the pool riffle sequence on dry creek california where the velocity reversal hypothesis was first proposed these simulations provide an opportunity to evaluate the hydrodynamics underlying the observed reversals in near bed and section averaged velocity and are used to investigate the influence of secondary currents the advection of momentum and cross stream flow variability the simulation results support the occurrence of a reversal in mean velocity and mean shear stress with increasing discharge however the results indicate that the effects of flow convergence due to an upstream constriction and the routing of flow through the system are more significant in influencing pool riffle morphology than the occurrence of a mean velocity reversal the hypothesis of flow convergence routing is introduced as a more meaningful explanation of the mechanisms acting to maintain pool riffle morphology

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

debris fan reworking during low magnitude floods in the green river canyons of the eastern uinta mountains colorado and utah comment the recent paper by larsen et al 2004 1 provides interesting new data that extend concepts developed for the grand canyon s colorado river to the green river utah however previous work is misrepresented and an internal inconsistency causes confusion about the conclusions in larsen et al

controls on pool characteristics along a resistant boundary channel abstract the north fork poudre river in phantom canyon has a pool riffle sequence formed in granitic bedrock we address two questions what controls downstream pool spacing within a pool what factors control pool dimensions we hypothesize that both pool spacing and pool geometry could be governed by available flow energy or by substrate characteristics these hypotheses were addressed using channel bed and water surface gradients surveyed under moderate flow selby rock mass strength at vertical outcrops forming lateral pool constrictions and at other vertical outcrops and joint density measured from high resolution digital images of the bedrock outcrop along each of 10 pools the downstream length between pools is quite variable documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fonten

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

changes in the water surface profile of the colorado river in grand canyon arizona between 1923 and 2000 1 in 1923 a u s geological survey expedition surveyed the water surface profile of the colorado river through grand canyon with theodolite and stadia rod in 2000 lidar overflights collected topographic data centered on the river corridor allowing construction of a new water surface profile and detection of change in the profile since 1923 by registering the surveys with respect to each other on the basis of 11 locations that were independently determined to have been unchanged between 1923 and 2000 80 rapids were directly compared for change between 1923 and 2000 the average change for all measured rapids was 0 26 m indicating net aggradation of the coarse grained alluvium forming the rapids throughout grand canyon in addition comparison of the two water surface profiles showed enhanced pool and rapid morphology while 50 of the total drop of the river occurred in just 9 of the river distance in 1923 that value increased to 66 by 2000

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

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

random controls on semi rhythmic spacing of pools and riffles in constriction dominated rivers average pool spacing between five and seven bankfull widths has been documented in environments throughout the world but has limited theoretical justification in coarse bedded and bedrock environments pool formation in coarse bedded and bedrock channels has been attributed to bedrock and boulder constrictions because the spacing of these constrictions may be irregular in nature it is difficult to reconcile pool formation processes with the supposedly rhythmic spacing of pools and riffles to address these issues a simulation model for pool and riffle formation is used to demonstrate that semi rhythmic spacing of pools with an approximate spacing of five to seven bankfull widths can be recreated from a random distribution of obstructions and minimum pool and riffle length criteria it is assumed that a pool riffle couplet will achieve a minimum length based on dominant discharge conditions values for the minimum length assumption are based on field data collected in new england and california while the theoretical basis relies on the demonstrated hydraulic response of individual pools to elongation results from the simulations show that the location of pools can be primarily random in character but still assume an average spacing between four and eight bankfull widths for a variety of conditions field verification data generally support the model but highlight a highly skewed distribution of pool forming elements and pool spacing the relation between pool spacing and bankfull widths is attributed to the common geometric response of these features to dominant discharge conditions copyright 2001 john wiley sons ltd

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

tributary debris fans and the late holocene alluvial chronology of the colorado river eastern grand canyon arizona bouldery debris fans and sandy alluvial terraces of the colorado river developed contemporaneously during the late holocene at the mouths of nine major tributaries in eastern grand canyon the age of the debris fans and alluvial terraces contributes to understanding river hydraulics and to the history of human activity along the river which has been concentrated on these surfaces for at least two to three millennia poorly sorted coarse grained debris flow deposits of several ages are interbedded with overlie or are overlapped by three terrace forming alluviums the alluvial deposits are of three age groups the striped alluvium deposited from before 770 b c to about a d 300 the alluvium of pueblo ii age deposited from about a d 700 to december 1900 and the alluvium of the upper mesquite terrace deposited from about a d 1400 to 1880 two elements define the geomorphology of a typical debris fan the large inactive surface of the fan and a smaller entrenched active debris flow channel and fan that is about one sixth the area of the inactive fan the inactive fan is segmented into at least three surfaces with distinctive weathering characteristics these surfaces are conformable with underlying debris flow deposits that date from before 770 b c to around a d 660 a d 660 to before a d 1200 and from a d 1200 to slightly before 1890 respectively based on late 19th century photographs radiocarbon and archaeologic dating of the three stratigraphically related alluviums and radiocarbon dating of fine grained debris flow deposits these debris flows aggraded the fans in at least three stages beginning about 2 8 ka if not earlier in the late holocene several main stem floods eroded the margin of the segmented fans reducing fan symmetry the entrenched active debris flow channels contain deposits 100 yr old which form debris fans at the mouth of the channel adjacent to the river early and middle holocene debris flow and alluvial deposits have not been recognized as they were evidently not preserved adjacent to the river or are buried by younger deposits

geomorphology of the colorado river in the grand canyon sediment supplied to the colorado river within the grand canyon has been sorted into distinct deposits of three grain size ranges the major rapids are formed by boulder deposits from side canyon tributaries as a result of a fourfold reduction in peak discharge when glen canyon dam was closed in 1963 new fan debris may increase the gradient through some of the rapids by a factor of 1 8 cobbles and gravel transported only during flood stages are preferentially deposited in the wider sections of the river as bars and riffles and are for the most part inactive during post dam discharges fine grain largely sandy terraces occur throughout the canyon especially along the banks of the large reverse eddies above and below the rapids the lower terraces are being reworked into beach like shores by diurnally varying post dam discharges a slight net lateral erosion of the terraces has resulted prior to construction of the dam sandy bed deposits underwent scour averaging about 1 m during spring floods

the influence of controlled floods on fine sediment storage in debris fan affected canyons of the colorado river basin abstract prior to the construction of large dams on the green and colorado rivers annual floods aggraded sandbars in lateral flow recirculation eddies with fine sediment scoured from the bed and delivered from upstream flows greater than normal dam operations may be used to mimic this process in an attempt to increase time averaged sandbar size these controlled floods may rebuild sandbars but sediment deficit conditions downstream from the dams restrict the frequency that controlled floods produce beneficial results here we integrate complimentary long term monitoring data sets from the colorado river in marble and grand canyons downstream from glen canyon dam and the green river in the canyon of lodore downstream from flaming gorge dam since the mid 1990s several controlled floods have occurred in these canyon rivers these controlled floods scour fine sediment from the bed and build sandbars in eddies thus increasing channel relief these changes are short lived however as interflood dam operations erode sandbars within several months to years controlled flood response and interflood changes in bed elevation are more variable in marble canyon and grand canyon likely reflecting more variable fine sediment supply and stronger transience in channel bed sediment storage despite these differences neither system shows a trend in fine sediment storage during the period in which controlled floods were monitored these results demonstrate that controlled floods build eddy sandbars and increase channel relief for short interflood periods and this response may be typical in other dam influenced canyon rivers the degree to which these features persist depends on the frequency of controlled floods but careful consideration of sediment supply is necessary to avoid increasing the long term sediment deficit

variability in eddy sandbar dynamics during two decades of controlled flooding of the colorado river in the grand canyon abstract sandbars are iconic features of the colorado river in the grand canyon arizona u s a following completion of glen canyon dam in 1963 sediment deficit conditions caused erosion of eddy sandbars throughout much of the 360 km study reach downstream from the dam controlled floods in 1996 2004 and 2008 demonstrated that sand on the channel bed could be redistributed to higher elevations and that floods timed to follow tributary sediment inputs would increase suspended sand concentrations during floods since 2012 a new management protocol has resulted in four controlled floods timed to follow large inputs of sand from a major tributary monitoring of 44 downstream eddy sandbars initiated in 1990 shows that each controlled flood deposited significant amounts of sand and increased the size of subaerial sandbars however the magnitude of sandbar deposition varied from eddy to eddy even over relatively short distances where main stem suspended sediment concentrations were similar here we characterize spatial and temporal trends in sandbar volume and site scale i e individual eddy sediment storage as a function of flow channel and vegetation characteristics that reflect the reach scale i e kilometer scale hydraulic environment we grouped the long term monitoring sites based on geomorphic setting and used a principal component analysis pca to correlate differences in sandbar behavior to changes in reach scale geomorphic metrics sites in narrow reaches are less vegetated stage changes markedly with discharge sandbars tend to remain dynamic and sand storage change dominantly occurs in the eddy compared to the main channel in wider reaches where stage change during floods may be half that of narrow sites sandbars are more likely to be stabilized by vegetation and floods tend to aggrade the vegetated sandbar surfaces in these locations deposition during controlled floods is more akin to floodplain sedimentation and the elevation of sandbar surfaces increases with successive floods because many sandbars are intermediate to the end members described above high elevation bar surfaces stabilized by vegetation often have a more dynamic unvegetated sandbar on the channel ward margin that aggrades and erodes in response to controlled flood cycles ultimately controlled floods have been effective at increasing averaged sandbar volumes and while bar deposition during floods decreases through time where vegetation has stabilized sandbars future controlled floods are likely to continue to result in deposition in a majority of the river corridor

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

effects of tributary debris on the longitudinal profile of the colorado river in grand canyon 1 the colorado river in grand canyon has long been known as a rapids and pools river with the rapids owing their existence primarily to tributary debris flows the debris flows deposit subaerial debris fans that constrict the channel laterally and when they enter the river raise the bed elevation the rapids are short wavelength 0 1 to 1 km small amplitude 5 m convexities in the river s longitudinal profile arising from the shallow gradient in the upstream pool and the steep gradient through the rapid itself analysis of the entire longitudinal profile through grand canyon reveals two long wavelength 100 km large amplitude 15 30 m river profile convexities the eastern canyon convexity between river mile rm 30 and rm 80 and the western canyon convexity between rm 150 and rm 250 convexities of intermediate scale are also identified in the longitudinal profile these longer wavelength larger amplitude convexities have strong spatial correlations with high rates of debris flow occurrence high densities of holocene debris fans the largest debris fans along the river and alluvial thicknesses of 10 m or more river profile convexities are unstable and require an active and powerful geologic process to maintain them in this case the abundant frequent and voluminous holocene debris flow activity in grand canyon at all wavelengths the most likely cause for these river profile convexities is holocene aggradation of the riverbed beneath them driven by the coarse particles of tributary debris flows large enough debris flows will slow river flow for kilometers upstream causing it to drop much of its suspended load integrated over time and all of the tributary point source contributions this process will build short wavelength convexities into long wavelength convexities for most if not all of the holocene the colorado river has been dissipating most of its energy in the rapids and expending the remainder in transporting fine sediment through grand canyon with little or no regional incision of bedrock

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

residence time of buoyant objects in drowning machines hydraulic jumps are a common feature of rivers and waterways where they can be found close to spillways weirs rocky ledges and boulders people adrift upstream of a hydraulic jump are liable to become trapped in the turbulent roller of the hydraulic jump for this reason hydraulic jumps have been termed drowning machines and are recognized as a public hazard we use experiments and theory to show that on average a buoyant object spends a time p trapped in a jump where is the period of a harmonic process inherent in the jump and p is the probability that the object will escape in any time interval the probability p is governed by the statistical theory of extreme values and depends primarily on the ratio between the density of the object and the density of the fluid we use our results to draw conclusions that might prove to be useful to public safety agencies intent on carrying out tests in drowning machines our results can also be used to predict the amount of flotsam that accumulates at the toe of a hydraulic jump

debris fan reworking during low magnitude floods in the green river canyons of the eastern uinta mountains colorado and utah the magnitude and frequency of tributary debris flows and the historical range of main stem river discharges are the main factors that create and modify rapids in the colorado river system monitoring of two recently aggraded debris fans in the green river canyons of the eastern uinta mountains shows that main stem floods with magnitudes between 40 and 75 of the predam 2 yr flood cause significant reworking of fan deposits cutbanks formed at fan margins during both small and large flows indicating that lateral bank erosion is an important reworking mechanism armoring of the debris fan surface limited the degree of reworking by successive floods even when subsequent flood magnitudes were similar to those that caused significant reworking peak discharges increased the width of the reworked zone decreased fan constrictions and lowered the water surface elevation of the ponded backwater contrary to predam geomorphic evidence monitoring indicated that eroded material from recently aggraded debris fans was deposited in bars adjacent to the downstream parts of both fans this change in the organization of the fan eddy complex has the potential to alter the location of recirculating eddies and associated areas of fine grained sediment deposition and storage

pool fills a window to palaeoflood history and response in bedrock confined rivers channel scale sedimentary units associated with bedrock controlled riffle pool morphology are examined in detail along sandy creek gorge an ephemeral stream in arid south eastern central australia pool fills comprise cut and fill assemblages of poorly sorted sediments ranging in texture from muds to boulders five unit types are defined based on particle size sedimentary structures geometry and bounding surface character 1 coarse grained bar platform 2 fine grained bar supraplatform 3 fine grained pool fill 4 fine grained bench and 5 modern pool fill the last coarse grained unit currently lining the pools suggests an altered sedimentation style over the post settlement period post ad 1860s situated at bedrock valley constrictions pool fills are compared with other sedimentary units associated with recirculating currents eddy bars and slackwater deposits but only the fine grained bench units reflect eddy recirculation the pool fills are principally forced bars associated with bedrock controlled or forced riffle pool morphology a late holocene palaeoflood history is proposed based on radiocarbon ages from the pool fills multiple phases of cut and fill activity were preceded by a superflood 3400 1900 years ago that eroded the pool fills to bedrock the resilience of the pool fills was illustrated by the passage of a 1 in 100 year flood in 1992 which caused only minor erosion the presence of pool fills may provide a window to past phases of river activity that cannot be extracted from either historical records observations or palaeoflood slackwater sediment analyses the formation and sedimentary preservation potential of these landforms reflect a combination of hydraulic and structural influences but the occurrence of high magnitude floods exerts the dominant control