field experiments on erosion by overland flow and their implication for a digital terrain model of channel initiation dietrich et al 1992 1993 proposed a digital terrain model for predicting the location of channel heads on the basis of the assumption that they occur where saturation overland flow exerts a boundary shear stress in excess of a critical value flume experiments were conducted in the modeled field site to evaluate the threshold hypothesis and to constrain critical shear stress and flow resistance parameters under complete grass cover microtopography and grass stems were found to prevent significant sediment transport at all but the highest flows when the grass stems were cut close to the ground flow resistance and critical shear stress for significant sediment transport were reduced by up to an order of magnitude but the remaining dense root mat prevented deep scour these field experiments support the threshold assumption and the model estimations of the critical shear stress if local topographic convergence of flow is taken into account the experiments also support the interpretation that significant degradation of vegetation cover is required for channel incision

direct measurements of lift and drag on shallowly submerged cobbles in steep streams implications for flow resistance and sediment transport steep mountain streams have higher resistance to flow and lower sediment transport rates than expected by comparison with low gradient rivers and often these differences are attributed to reduced near bed flow velocities and stresses associated with form drag on channel forms and immobile boulders however few studies have directly measured drag and lift forces acting on bed sediment for shallow flows over coarse sediment which ultimately control sediment transport rates and grain scale flow resistance here we report on particle lift and drag force measurements in flume experiments using a planar fixed cobble bed over a wide range of channel slopes 0 004 s 0 3 and water discharges drag coefficients are similar to previous findings for submerged particles c d 0 7 but increase significantly for partially submerged particles in contrast lift coefficients decrease from near unity to zero as the flow shallows and are strongly negative for partially submerged particles indicating a downward force that pulls particles toward the bed fluctuating forces in lift and drag decrease with increasing relative roughness and they scale with the depth averaged velocity squared rather than the bed shear stress we find that even in the absence of complex bed topography shallow flows over coarse sediment are characterized by high flow resistance because of grain drag within a roughness layer that occupies a significant fraction of the total flow depth and by heightened critical shields numbers and reduced sediment fluxes because of reduced lift forces and reduced turbulent fluctuations

changes in physical properties of a reservoir sandstone as a function of burial depth the etive formation northern north sea abstract rock physical properties like velocity and bulk density change as a response to compaction processes in sedimentary basins in this study it is shown that the velocity and density in a well defined lithology the shallow marine etive formation from the northern north sea increase with depth as a function of mechanical compaction and quartz cementation physical properties from well logs combined with experimental compaction and petrographic analysis of core samples shows that mechanical compaction is the dominant process at shallow depth while quartz cementation dominates as temperatures are increased during burial at shallow depths

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

an estuarine facies model for the middle jurassic sleipner formation beryl embayment north sea the middle jurassic sleipner formation is sub divided into three units in the beryl embayment area of the north sea the lowermost two units the 9interbedded unit9 and 9lower coal marker9 overlie lower jurassic marine silts and were probably deposited in progressively shallowing coastal environments during a eustatic sea level fall an estuarine deposit overlies the 9lower coal marker9 and was deposited following sea level rise or tectonic subsidence of the area the 9estuarine succession9 forms the bulk of the formation and is composed of seven facies grouped into three facies associations representing sub tidal inter tidal and salt marsh sub environments the sub tidal facies association is dominated by sandstones deposited in tidal channels and sand flats the inter tidal association is characterized by alternations of sandstone and siltstone on a scale of millimetres to several metres and consists of tidal channel sandstones lenticular bedded siltstones and other tidally influenced facies the salt marsh association is dominated by coals and rooted siltstones with minor amounts of creek fill sandstones the estuary mouth probably lay towards the northern end of the embayment where a connection existed through the viking graben to the boreal ocean

a global view of stratospheric gravity wave hotspots located with atmospheric infrared sounder observations 1 the main aim of this study is to find and classify hotspots of stratospheric gravity waves on a global scale the analysis is based on a 9 year record 2003 to 2011 of radiance measurements by the atmospheric infrared sounder airs aboard nasa s aqua satellite we detect gravity waves based on 4 3 m brightness temperature variances our method focuses on peak events i e strong gravity wave events for which the local variance considerably exceeds background levels we estimate the occurrence frequencies of these peak events for different seasons and time of day and use the results to find local maxima or hotspots in addition we use airs radiances at 8 1 m to simultaneously detect convective events including deep convection in the tropics and mesoscale convective systems at middle latitudes we classify the gravity wave sources based on seasonal occurrence frequencies for convection but also by means of time series analyses and topographic data our study reproduces well known hotspots of gravity waves e g the andes and the antarctic peninsula however the high horizontal resolution of the airs observations also allows us to locate numerous mesoscale hotspots which are partly unknown or poorly studied so far most of these mesoscale hotspots are found near orographic features like mountain ranges coasts lakes deserts or isolated islands this study will help to select promising regions and seasons for future case studies of gravity waves

episodic river flooding events revealed by palynological assemblages in jurassic deposits of the brent group north sea spore and pollen sporomorph assemblages from middle jurassic marine deposits of the brent group in the northern north sea are investigated to assess temporal and spatial variations in vegetation and depositional processes four wells were sampled for palynology from the penguins cluster and the don north east fields through the rannoch formation shoreface succession hyperpycnite deposits occur throughout but are concentrated within the lower part of the section these are expressed by sand prone beds displaying waxing and waning current motifs normally graded muddy beds and structureless mudstones hyperpycnal hypopycnal deposits resulting from episodic river flooding represent important sedimentary features as they may be preserved below fair weather wave base in more offshore settings and potentially be the only record of the former presence of a nearby river mouth the hyperpycnites typically contain abundant botryoccocus spp amorphous organic matter aom and hinterland sporomorph taxa with relatively few marine components compared to associated marine shoreface facies variations in palynofacies assemblages and botryococcus spp abundances indicate frequent river mouth avulsion ordination of samples using non metric multidimensional scaling nmds indicates that shoreface samples of the sampled wells are relatively distinct but hyperpycnite samples are highly similar regardless of their sampled well this suggests that depositional processes and spore pollen sources i e catchment zones were similar among hyperpycnite events across different wells abundant bisaccate pollen botryococcus spp and aom within interpreted hyperpycnites suggest sediment mixing along the fluvial drainage path during flooding events the terrestrial signature of hyperpycnite sporomorph assemblages demonstrates that underflows remained coherent as they descended the shoreface profile with little turbulent mixing with ambient marine waters sporomorph assemblages display few large changes through time suggesting vegetation on the adjacent coastal plain was relatively static through the studied interval

hydraulics of interrill overland flow on stone covered desert surfaces the hydraulics of interrill overland flow on stone covered desert surfaces depend on the resistance to flow which may be partitioned into grain resistance form resistance wave resistance and rain resistance efforts to model large scale roughness in open channels suggest that resistance to overland flow on such surfaces is a function of grain reynolds number froude number flow depth and the size shape spacing and pattern of the roughness elements the effect of flow depth on flow resistance f is often hidden in the flow reynolds number re in laboratory and field studies alike f re relations have been found to be convex upward and negatively sloping and these shapes have been explained in terms of the progressive inundation of the roughness elements where laboratory or field based models have been developed for predicting f they invariably contain percent stone cover the prominence of this variable reflects the strong influence of stone size and spacing on flow resistance a laboratory study shows that where the froude number f 0 50 wave resistance increases with stone cover and dominates resistance to flow on all surfaces with stone covers greater than 10 a field study indicates that where f 0 50 and wave resistance is inconsequential grain and form resistance typically account for about 5 and 95 of f respectively these findings have important implications for sediment transport modeling because percent grain resistance is equal to percent grain shear stress and it has recently been suggested that in overland flow as in river flow sediment transport capacity is determined by grain shear stress rather than total shear stress a laboratory study however demonstrates that this is not the case sediment transport capacity is in fact greater than predicted by grain shear stress because energy dissipated in the wakes of roughness elements in overland flow is transformed into turbulence sufficiently close to the bed to affect sediment transport

progradational sequences in miocene shoreline deposits southeastern caliente range california abstract an exceptionally well exposed marine nonmarine transition in middle miocene strata exists in the southeastern caliente range california about 50 individual progradational sequences form a succession that ranges in thickness from approximately 1000 m where predominantly nonmarine to more than 2500 m where predominantly marine paleogeographic evidence in basalt flows near the top of the succession and in overlying fluvial deposits indicates that these middle miocene strata were deposited across a north northwest trending shoreline a complete progradational sequence typically is several meters to a few tens of meters thick and includes strata that represent three intertonguing stratigraphic units individual sequences generally rest on a thin gravel deposit interpreted as a transgressive lag on an erosional surface the gravel is overlain by structureless siltstone or fine grained sandstone deposited at water depths where the rate of faunal mixing exceeded that of production of structures by physical processes these rocks grade upward into bedded fine sandstone deposited closer to shore where physical processes exceeded bioturbation crossbedded lenses of coarse sand or fine gravel in the upper part of this facies suggest the presence of fairly long period surface waves the bedded fine sandstone is sharply ove lain by a cross bedded coarse sandstone facies that is interpreted as a combined offshore bar rip channel surf zone assemblage cross strata dip dominantly offshore suggesting substantial deposition from rip currents a secondary shoreparallel mode of cross strata direction suggests longshore currents produced by surface waves from the northwest the crossbedded coarse grained sandstone grades upward into planar bedded medium grained sandstone that is interpreted as a beach foreshore this facies grades upward through structureless medium grained sandstone into nonmarine or lagoonal red and green mudstone of the caliente formation the middle miocene succession was deposited in a subsiding basin that was otherwise remarkably stable tectonically the position of the strand line differed no more than a few kilometers through a period of 1 to 3 m y the average duration of the transgressive regressive cycles a few tens of thousands of years together with their distribution in groups of three or four in the lower two thirds of the succession is consistent with the pattern of long term climatic cycles produced by periodicity of the earth s solar orbit and may be related to eustatic sea level changes attendant to the development of the antarctic ice cap changes in the pattern of progradation in the upper part of the succession and nearby basaltic eruptions may have been precursors to the onset of movement along th san andreas fault in this area 12 14 m y ago

two dimensional idealized simulations of the impact of multiple windward ridges on orographic precipitation abstract this paper presents two dimensional 2d idealized simulations at 1 km grid spacing using the fifth generation pennsylvania state university national center for atmospheric research psu ncar mesoscale model mm5 in order to illustrate how a series of ridges along a broad windward slope can impact the precipitation distribution and simulated microphysics the number of windward ridges for a 2000 m mountain of 50 km half width is varied from 0 to 16 over a 150 km distance using different stratifications freezing levels uniform ambient flows and ridge amplitudes a few 200 400 m windward ridges can enhance the precipitation locally over each ridge crest by a factor of 2 3 meanwhile a series of 8 16 ridges that are 200 400 m in height can increase the net precipitation averaged over the windward slope by 10 35 this average precipitation enhancement is maximized when the ridge spacing is relatively small 20 km since there is less time for subsidence drying within the valleys and the m

incipient sediment motion at high slopes in uniform flow condition 1 this paper reviews the problem of the incipient motion of cohesionless particles in a high sloping water stream a theoretical analysis of the equilibrium of a gravel particle is developed by a deterministic approach with the introduction of the relative degree of exposure of the particle itself to the stream flow the parameter relative degree of exposure relates the positioning of a particle with the upstream one the problem of velocity distribution and the definition of drag coefficient is also revised to better account for low submergence the results of the theory are compared with a series of ad hoc experiments performed by c gregoretti

effects of rock fragment size and cover on overland flow hydraulics local turbulence and sediment yield on an erodible soil surface the interactions between overland flow hydraulics and sediment yield were studied in flume experiments on erodible soil surfaces covered by rock fragments the high erodibility of a non cohesive fine sediment d50 0 09mm permitted the effects of local turbulence and scour on sediment yield to be examined overland flow hydraulics and sediment yield were compared for experiments with pebble d50 1 5cm and cobble d50 8 6cm rock fragment covers cover percentages range from 0 to 99 per cent rock fragment size strongly affects the relations between flow hydraulics and rock fragment cover for pebbles spatially averaged hydraulic parameters flow velocity flow depth effective flow width unit discharge total shear stress darcy weisbach friction factor percentage grain friction and grain shear stress vary most rapidly within cover percentages at low covers power functions in contrast for cobbles these parameters vary most rapidly within cover percentages at high covers exponential functions as the type of the function that describes the relation between flow hydraulics and cover percentage can be deduced from the ratio of rock fragment height to flow depth the continuity equation can be employed to determine the actual coefficients of the functions provided the regression of one hydraulic parameter e g flow velocity with cover percentage is known and a good estimate exists for two values of another hydraulic variable for a low and a high cover percentage the variation of sediment yield with cover percentage is also strongly dependent on rock fragment size but neither the convex upward relation for pebbles nor the positive relation for cobbles can be solely attributed to the spatially averaged hydraulics of sheet flow rock fragments induce local turbulence that leads to scour hole development on the stoss side of the rock fragments while deposition commonly occurs in the wake this local scour and deposition substantially affects sediment yield however scour dimensions cannot be predicted by spatially averaged flow hydraulics an adjustment of existing scour formulas that predict scour around bridge piers is suggested sediment yield from non cohesive soils might then be estimated by a combination of sediment transport and scour formulas

nonrigid nonsubmerged vegetative roughness on floodplains individual pine and cedar tree saplings and branches were used to model the resistance to flow in a water flume for nonsubmerged and nonrigid vegetation to determine the amount that streamlining decreases the drag coefficient and reduces the momentum absorbing area currently vegetation on floodplains is commonly assumed to behave as rigid roughness that can lead to large errors in the relationships between velocity and drag force this presents a basic fluid mechanics problem an extreme variation of roughness with depth of flow can result due to a large increase in the momentum absorbing area in nonsubmerged vegetation as depth is increased this deems all the available roughness equations which generally are based on relative roughness approach useless for this application in this paper a dimensional analysis supported by experimental results is developed to obtain a relationship between roughness conditions i e density and flexural rigidity and flow conditions i e velocity and depth for floodplains and vegetative zones of natural waterways

proximal distal ichnofabric changes in a siliciclastic shelf early pliocene guadalquivir basin southwest spain abstract the lower pliocene deposits cropping out along the atlantic coast of cadiz in the conil cabo roche area formed on a shelf gently deepening towards the w nw up to five types of facies can be recognized distributed in belts from proximal to distal parts of the shelf 1 coarse grained sandstone with trough cross stratification facies on the most proximal parts of the shelf inner shelf deposits 2 medium grained sandstone with low angle planar cross stratification facies deposited in a more distal position due to storm currents transporting sediment offshore this facies intercalates with the previous trough cross bedded sandstone 3 massive fine grained sandstone and siltstone facies laterally and vertically related with the previous facies type and representing sediments formed in the middle shelf close to the storm wave base 4 tabular sandstone bed facies corresponding to storm bed deposits intercalated within the two previous facies 5 greenish bluish shale facies accumulated on the outer shelf below storm wave base three ichnofabrics associated with these facies are recognized 1 the two cross bedded facies are dominated by a macaronichnus ichnofabric characterized by macaronichnus and bichordites traces that represent colonization of a shifting sandy substrate by polychaetes macaronichnus tracemakers and by sea urchins bichordites producers 2 a rosselia ichnofabric consisting of vertical traces of rosselia cross cutting macaronichnus characterizes the interval of massive fine grained sandstone and silt facies and interbedded tabular sandstones this ichnofabric formed under high sedimentation rates with rosselia traces exhibiting stacked patterns that indicate vertical readjustment following deposition 3 massive fine grained sandstone and silt facies are distinguished by a cylindrichnus ichnofabric this fabric was produced by the activity of a moderately diverse community dominated by sessile burrow dwelling probably superficial detritus feeding polychaetes rosselia and cylindrichnus tracemakers and vagile deposit feeding polychaetes planolites producers in addition infaunal deposit detritus feeders producing spreiten structures teichichnus are found in distal areas pervasive indistinct mottling of the sediment of this facies was probably due to the activity of very shallow burrowers in the uppermost sediment tiers this proximal distal replacement of ichnofabrics reflects the change of benthic communities across the shelf this distribution does not fit the traditional seilacherian ichnofacies model for soft ground shallow marine settings in which proximal vertical dwelling burrows of the skolithos ichnofacies dominate high energy environments in the pliocene of cadiz shallow tier burrows of deposit detritus feeders characterize the high energy facies instead which fit better with the cruziana ichnofacies this deviation can be related with the particular palaeoenvironmental conditions thus vagile opportunistic deposit feeders colonized the dune foreset when the dunes were stable and the progradation of the structure favored the preservation of the traces

determining the mean depth of overland flow in field studies of flow hydraulics in field studies of interrill overland flow conducted on runoff plots the mean depth of flow is usually obtained by averaging measurements of flow depth at regularly spaced points across the plot including points where there is no flow although this procedure may be appropriate in studies aimed at runoff prediction it is not in studies concerned with flow hydraulics in the latter studies more realistic results can be obtained by excluding those points where the depth is zero and reducing the width of flow in proportion to the number of points excluded failure to do this results in the underestimation of the actual mean flow depth reynolds number and friction factor where discharges are small or microtopography is large this underestimation is likely to be significant

multiscale mountain waves influencing a major orographic precipitation event abstract this study combines high resolution mesoscale model simulations and comprehensive airborne doppler radar observations to identify kinematic structures influencing the production and mesoscale distribution of precipitation and microphysical processes during a period of heavy prefrontal orographic rainfall over the cascade mountains of oregon on 13 14 december 2001 during the second phase of the improvement of microphysical parameterization through observational verification experiment improve 2 field program airborne based radar detection of precipitation from well upstream of the cascades to the lee allows a depiction of terrain induced wave motions in unprecedented detail two distinct scales of mesoscale wave like air motions are identified 1 a vertically propagating mountain wave anchored to the cascade crest associated with strong midlevel zonal i e cross barrier flow and 2 smaller scale 20 km horizontal wavelength undulations over the windward foothills triggered by interaction

orographic precipitation and air mass transformation an alpine example a case of orographic precipitation in the alps on 20 september 1999 was studied using several models along with rain gauge and radar data the objective of the study is to describe the orographic transformation of an air mass including multi scale aspects several new and some conventional diagnostic quantities are estimated including drying ratio precipitation efficiency buoyancy work condensed water residence time parcel changes in heat moisture and altitude and dominant space and time scales for the case considered the drying ratio was about 35 precipitation efficiency values are ambiguous due to repeated ascent and descent over small scale terrain the sign of buoyancy work changed during the event indicating a shift from stratiform orographic to weak convective clouds cloud water residence times are different for the two mesoscale models 400 compared to 1000 s due to different cloud physical formulations the two mesoscale models agree that the dominant spatial scale of lifting and precipitation is about 10 km smaller than the scale of the main alpine massif trajectory analysis of air crossing the alps casts doubt on the classic model of fohn few parcels exhibit classic pattern of moist ascent followed by dry descent parcels that gain latent heat descend only briefly before rising into the middle troposphere parcels that descend along the lee slope originate in the middle troposphere and gain little or even lose latent heat during the transit as parcels seek their proper buoyancy level downstream a surprising scrambling of the air mass occurs radar data confirm the model prediction that the rainfall field is tightly controlled by local terrain on scales as small as 10 km rather than the full 100 km cross alpine scale a curious pulsing of the precipitation is seen indicating either drifting moisture anomalies or weak convection copyright 2003 royal meteorological society

steady nonuniform shallow flow within emergent vegetation surface flow redistribution on flat ground from crusted bare soil to vegetated patches following intense rainfall events elevates plant available water above that provided by rainfall the significance of this surface water redistribution to sustaining vegetation in arid and semiarid regions is undisputed what is disputed is the quantity and spatial distribution of the redistributed water in ecohydrological models such nonuniform flows are described using the saint venant equation sve subject to a manning roughness coefficient closure to explore these assumptions in the most idealized setting flume experiments were conducted using rigid cylinders representing rigid vegetation with varying density flow was induced along the streamwise x direction by adjusting the free water surface height h x between the upstream and downstream boundaries mimicking the nonuniformity encountered in nature in natural settings such h x variations arise due to contrasts in infiltration capacity and ponded depths during storms the measured h x values in the flume were interpreted using the sve augmented with progressively elaborate approximations to the roughness representation the simplest approximation employs a friction factor derived from a drag coefficient cd for isolated cylinders in a locally but not globally uniform flow and upscaled using the rod density that was varied across experiments comparison between measured and modeled h x suggested that such a naive approach overpredicts h x blockage was then incorporated into the sve model calculations but resulted in underestimation of h x biases in modeled h x suggest that cd must be varying in x beyond what a local or bulk reynolds number predicts inferred cd x from the flume experiments exhibited a near parabolic shape most peaked in the densest canopy cases the outcome of such cd x variations is then summarized in a bulk resistance formulation that may be beneficial to modeling runon runoff processes on shallow slopes using sve

paleogeography of monterey formation cuyama basin california the cuyama basin is one of several discrete middle cenozoic basins that formed a continental borderland in the coastal california province during the miocene the monterey formation is lithologically and stratigraphically complex it varies widely in thickness up to 4 500 ft 1 400 m reflecting variable subsidence within the basin thinning over anticlines and the cox fault zone suggests structural movement occurred contemporaneously with sedimentation beginning in the late saucesian early miocene the age of the monterey formation also varies becoming younger to the northwest areas of maximum subsidence migrated from southeast cuyama valley to northwest northern la panza range schematic paleogeographic maps constructed on 4 time slices illustrate that the depositional history of the basin reflects these subsidence patterns and various depositional controls late saucesian relizian early miocene time is characterized by relatively low sea level maximum subsidence in the southeast and basinal sedimentation varying from calcareous biogenous sediments to sandy submarine fan deposits luisian early mohnian middle miocene patterns reflect high sea level maximum subsidence in the northwest and basinal sediments of a calcareous or siliceous biogenous nature finally the entire southern salinian block shoaled to shallow marine or nonmarine conditions by the end of mohnian late miocene time modified journal abstract

cyclic deposits and hummocky cross stratification of probable storm origin in upper cretaceous rocks of the cape sebastian area southwestern oregon abstract cyclic deposits containing hummocky cross stratification occur in the upper part of the cape sebastian sandstone of bourgeois 1980 a shallow marine transgressive sandstone of late cetaceous age on the southern oregon coast the cycles average 1 6 m in thickness and consist where complete of a lower hummocky cross stratified sandstone a middle planar and ripple bedded sandstone with a shale bed in its middle part and an upper bioturbated sandstone noteworthy features of the hummocky cross stratification include the presence of depositional domes in addition to scoured depressions the absence of significant bedform migration and the presence of a small proportion of dip angles greater than the angle of repose 34 in addition to the large proportion of low 15 deg dip angles the lower stratified fining upward part of the cycle up to the top of the shale bed is interpreted as having accumulated under conditions of initially great but gradually decreasing current velocity and deposition rate the currents probably had a strong oscillatory component and the depositional event is inferred to have been a storm the part of the planar and ripple bedded sandstone above the shale bed was probably deposited during relatively fair weather after the storm but before re establishment of a normal benthic fauna the bioturbated sandstone is interpreted to have been deposited during fair weather or during minor storms separated by long intervals of fair weather

a sedimentological approach to refining reservoir architecture in a mature hydrocarbon province the brent province uk north sea improved reservoir characterisation in the mature brent province of the north sea aimed at maximising both in field and near field hydrocarbon potential requires a clearer understanding of sub seismic stratigraphy and facies distributions in this context we present a regional high resolution sequence stratigraphic framework for the brent group uk north sea based on extensive sedimentological re interpretation of core and wireline log data combined with palynostratigraphy and published literature this framework is used to place individual reservoirs in an appropriate regional context thus resulting in the identification of subtle sedimentological and tectono stratigraphic features of reservoir architecture that have been previously overlooked we emphasise the following insights gained from our regional high resolution sequence stratigraphic synthesis 1 improved definition of temporal and spatial trends in deposition both within and between individual reservoirs 2 development of regionally consistent predictive sedimentological models for two enigmatic reservoir intervals the broom and tarbert formations and 3 recognition of subtle local tectono stratigraphic controls on reservoir architecture and their links to the regional middle jurassic structural evolution of the northern north sea we discuss the potential applications of these insights to the identification of additional exploration potential and to improved ultimate recovery

a new palaeogeographic reconstruction for the middle jurassic of the northern north sea an estuarine sequence equivalent in age to the brent group deltaic deposits further north is recognized in the central viking graben it indicates a persistent marine connection southwards from the boreal ocean during deltaic accumulation and suggests that the brent delta did not prograde from the south along the graben as previously suggested evidence from the uk north viking graben indicates the brent delta was probably derived transversely rather than axially as were the other jurassic clastic systems infilling the graben

hydraulic modeling of runoff over a rough surface under partial inundation 1 this study presents a numerical method to derive the darcy weisbach friction coefficient for overland flow under partial inundation of surface roughness to better account for the variable influence of roughness with varying levels of emergence we model the flow over a network which evolves as the free surface rises this network is constructed using a height numerical map based on surface roughness data and a discrete geometry skeletonization algorithm by applying a hydraulic model to the flows through this network local heads velocities and froude and reynolds numbers over the surface can be estimated these quantities enable us to analyze the flow and ultimately to derive a bulk friction factor for flow over the entire surface which takes into account local variations in flow quantities results demonstrate that although the flow is laminar head losses are chiefly inertial because of local flow disturbances the results also emphasize that for conditions of partial inundation flow resistance varies nonmonotonically but does generally increase with progressive roughness inundation

sedimentary geology and evolution of an outcropping shelf margin delta late proterozoic wonoka formation south australia discrete sand units or accumulations crop out within the late proterozoic wonoka formation northern flinders ranges south australia these sand wedges are unique in their size contacts facies and associations to other sands in the formation and are interpreted as shelf margin deltas the wedges can be divided into a main body and a series of discrete feeder channels the main body consists of basal slump masses a sandstone dominated succession and an overlying shale dominated facies lithofacies grossly define a deepening upward succession from a lower shoreface to outer shelf setting the formation and deposition of the feeder channels and sand wedges was controlled largely by relative sea level changes initial exposure of the shelf and subaerial erosion produced a regional erosional surface and incised valleys across the paleoshelf prior to deposition of the wedges slope instabilities and minor uplift occurred sediment was then transported across the shelf and deposited near or at the shelf break and reworked in a shallow marine environment deposition of the shelf margin deltas continued during relative sea level rise but ended with shelf drowning

the climatology of small scale orographic precipitation over the olympic mountains patterns and processes the climatology of small scale patterns of mountain precipitation is poorly constrained yet important for applications ranging from natural hazard assessment to understanding the geologic evolution of mountain ranges synthesizing four rainy seasons of high resolution precipitation observations and mesoscale model output from the penn state ncar mm5 reveals a persistent small scale pattern of precipitation over the 10 km wide 800 m high ridges and valleys of the western olympic mountains washington state usa this pattern is characterized by a 50 70 excess accumulation over the ridge crests relative to the adjacent valleys in the annual mean while the model shows excellent skill in simulating these patterns at seasonal time scales major errors exist for individual storms investigation of a range of storm events has revealed the following mechanism for the climatological pattern regions of enhanced condensation of cloud water are produced by ascent in stable flow over the windward slopes of major ridges synoptically generated precipitation grows by collection within these clouds leading to enhanced precipitation which is advected by the prevailing winds instances of atypical patterns of precipitation suggest that under certain conditions during periods with a low freezing level or convective cells fundamental changes in small scale patterns may occur however case studies and composite analysis suggest that departures from the pattern of ridge top enhancement are rare the basic patterns and processes appear robust to changes in temperature winds and background rainfall rates copyright 2008 royal meteorological society

storm and tide dominated shorelines in cretaceous moosebar lower gates interval outcrop equivalents of deep basin gas trap in western canada the moosebar and gates formations crop out in the deformed foothills belt south of fort st john british columbia they permit examination of the depositional environments of sandstones and conglomerates that are gas bearing in the equivalent wilrich falher interval of the deep basin of alberta and british columbia the moosebar gates interval consists of several upward coarsening and marine to nonmarine sequences moosebar bioturbated shales pass upward into turbidites and offshore storm deposits flow directions indicate a north dipping paleoslope a second coarsening upward sequence at the top of the moosebar and base of the gates terminates in a lenticular fluvial conglomerate up to 30 m thick which is overlain by coals carbonaceous mudstones and sandstones above the carbonaceous zone a major lateral facies change is observed fluvial conglomerates in the south grade into beach conglomerates northward the upper part of the beach conglomerate consists of exposed three dimensional storm berms at least 500 m long up to 1 5 m high with wavelengths of 12 to 24 m the berms trend east west seaward of the conglomerate beach are herringbone cross bedded tidal sandstones with a marine trace fauna graded sharp based conglomerates also are present probably washed out to sea by storms farther north at the same stratigraphic level is a series of partly overlapping conglomerate bars up to 5 m thick and 40 to 50 m across the tops of these bars are covered with storm formed symmetric conglomeratic dunes details of the orientation and geometry of these conglomerate bodies along with their internal structure and pebble fabrics suggest that four major environments fluvial beach offshore conglomerate bars and offshore graded storm conglomerates should be identifiable and predictable in the subsurface

slope shelf nearshore depositional sequences with transgressive conglomerate in a miocene backarc and arc junction setting central japan abstract several third order slope shelf nearshore depositional sequences are found in the middle to late miocene aoki and ogawa formations in the southern part of the northern fossa magna region central japan each depositional sequence consists of a transgressive systems tract varying in thickness from several tens of centimetres to about 10 m a falling stage systems tract several tens of metres in thickness and a highstand systems tract 20 80 m thick the highstand systems tract and falling stage systems tract are bounded by the regressive surface of marine erosion each depositional sequence mainly consists of coarse grained sediments the materials of the transgressive conglomerate beds were derived from the gravelly foreshore and upper shoreface by transgressive shoreface erosion the thin and conglomeratic transgressive systems tract indicates that these slope shelf nearshore sequences were deposited on the steep slope area under a rapid transgression therefore these sequences were formed in response to excess sediment supply and a rapid rise in relative sea level at an active margin of the backarc side of the arc trench system

effects of surface roughness and rainfall impact on overland flow bed roughness and rainfall impact affect hydraulic friction in overland flow the relationship between friction velocity discharge and channel slope was examined for the case of shallow spatially varied flow on rough surfaces rainfall was simulated on artificially roughened surfaces in a laboratory measured flow velocities were compared to theoretical velocities computed from a dynamic equation for spatially varied flow and from the darcy weisbach uniform flow equation the measurements showed that the constant that relates the darcy weisbach friction coefficient to reynolds number can become larger than the theoretical value for smooth laminar flow an analysis of the dynamic equation showed that frictional forces were much larger than forces resulting from changes in hydrostatic pressure and momentum water surface profiles based on the darcy weisbach friction equation nearly matched those from the dynamic equation for spatially varied flow a regression was developed from the darcy weisbach equation the regression accurately predicted flow velocity when absolute roughness rainfall rate channel discharge slope slope length and viscosity were known

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

orographic modification of convection and flow kinematics by the oregon coast range and cascades during improve 2 abstract this paper describes the kinematic and precipitation evolution accompanying the passage of a cold baroclinic trough over the central oregon coast range and cascades during 4 5 december 2001 of the second improvement of microphysical parameterization through observational verification experiment improve 2 field project in contrast to previously documented improve 2 cases the 4 5 december event featured weaker cross barrier winds 15 20 m s 1 weaker moist static stability nm 0 006 s 1 and convective cells that preferentially intensified over oregon s modest coastal mountain range these cells propagated eastward and became embedded within the larger orographic precipitation shield over the windward slopes of the cascades the weather research and forecasting model version 2 2 at 1 33 km grid spacing was able to accurately replicate the observed evolution of the precipitation across western oregon as a result of the convective cell development the precipitation enhancement over the co

hydraulic resistance in overland flow during partial and marginal surface inundation experimental observations and modeling hydraulic resistance as a function of surface roughness inundation was evaluated in a set of experiments designed to simulate overland flow on a rough granular surface the data are compared with an additive drag model based on the contribution of individual elements to flow resistance and a mixing length model for estimating bulk flow resistance during partial inundation of the surface roughness the observed coefficient of drag per element is much higher than for an isolated element and a model based on element form drag alone underestimates the observed friction these high resistance values are strongly correlated with the hydrostatic wave drag estimated from the free surface deformation around elements the mixing length model incorporating a multiplier setting the hydraulically effective roughness height reliably reproduces the trends in resistance during marginal inundation this multiplier is shown to have a value similar to the root mean square of the surface height

macroscale surface roughness and frictional resistance in overland flow the hydraulics of overland flow on rough granular surfaces can be modelled and evaluated using the inundation ratio rather than the flow reynolds number as the primary dimensionless group determining the flow behaviour the inundation ratio describes the average degree of submergence of the surface roughness and is used to distinguish three flow regimes representing partially inundated marginally inundated and well inundated surfaces a heuristic physical model for the flow hydraulics in each regime demonstrates that the three states of flow are characterized by very different functional dependencies of frictional resistance on the scaled depth of flow at partial inundation flow resistance is associated with the drag force derived from individual roughness and therefore increases with depth and percentage cover at marginal inundation the size of the roughness elements relative to the depth of flow controls the degree of vertical mixing in the flow so that frictional resistance tends to decrease very rapidly with increasing depth of flow well inundated flows are described using rough turbulent flow hydraulics previously developed for open channel flows these flows exhibit a much more gradual decrease in frictional resistance with increasing depth than that observed during marginal inundation a data set compiled from previously published studies of overland flow hydraulics is used to assess the functional dependence of frictional resistance on inundation ratio over a wide range of flow conditions the data confirm the non monotonic dependence predicted by the model and support the differentiation of three flow regimes based on the inundation ratio although the percentage cover and the surface slope may be of importance in addition to the inundation ratio in the partially and marginally inundated regimes the reynolds number appears to be of significance only in describing well inundated flows at low to moderate reynolds numbers as these latter conditions are quite rare in natural environments the inundation ratio rather than the reynolds number should be used as the primary dimensionless group when evaluating the hydraulics of overland flow on rough surfaces 1997 by john wiley sons ltd

flow threads in surface run off implications for the assessment of flow properties and friction coefficients in soil erosion and hydraulics investigations soil surface microtopography produces non uniform surface run off in which narrow threads of relatively deep and fast ow move within broader shallower slower moving regions this kind of ow is probably widespread given that microtopography is itself common methods used to record the properties of surface run off include grid or transect based depth observations with a single mean ow speed derived by calculation from v q wd and the use of dye timing to estimate velocity with an effective mean depth calculated from d q wv because these methods allow only single ow eld mean values to be derived for v or d neither is well suited to non uniform ows the use of depth data to derive a ow eld mean v furthermore implicitly applies area weighting to the depth data likewise the use of dye speeds for v inherently overestimates mean v because dye dominantly follows the faster ow threads the associated errors in derived parameters such as friction coef cients are not readily quanti ed and appear not to have been addressed previously new eld experiments made on untilled soil surfaces in arid western nsw australia explore these circumstances and the implications for deriving meaningful measures of ow properties including friction coef cients on surfaces deliberately chosen for their very subtle microtopography average thread velocities are shown to be commonly 2 5 times greater than the ow eld mean and locally 6 7 times greater on the other hand non thread ow speeds lie below the ow eld mean on average reaching only 84 per cent of this value and often considerably less flow eld means conceal the existence of regions of the ow eld whose properties are statistically distinct results con rm that a reliance on ow eld average depths yields estimates of friction coef cients that are biased toward the shallower high roughness parts of the ow while if dye speeds are relied upon the results are biased toward the deeper smoother threads of ow a new approach to the evaluation of friction coef cients in non uniform ows is advanced involving the determination of separate coef cients for threads and non thread zones of the ow eld in contrast ow eld friction coef cients as they are customarily derived in run off plot experiments subsume these distinct coef cients in proportions that are generally unknown the value of such coef cients is therefore questionable copyright 2004 john wiley sons ltd

estimation of gravel bed river flow resistance numerous formulations have been proposed linking friction factors to the gravel bed river downstream hydraulic geometry data from 280 rivers show that existing gravel bed power and semilogarithmic formulations fail to correctly predict the friction factors a new gravel bed semilogarithmic formulation is developed using nonlinear statistical tools it considers the influence of the relative roughness the froude number the sediment mobility parameter and a cross sectional form factor the best fit is achieved by modifying the adjustment parameter and the interior of the logarithmic term of the universal velocity distribution equation

shingled sharp based shoreface sandstones depositional response to stepwise forced regression in a shallow basin upper triassic gassum formation denmark

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

hydraulics and erosion in eroding rills rills often act as sediment sources and the dominant sediment and water transport mechanism for hillslopes six experiments were conducted on two soils and a uniform sand using three experimental methodologies the results of this study challenge the assumption often used in hydrologic and erosion models that relationships derived for sheet flow or larger channel flow are applicable to actively eroding rills velocity did not vary with slope and reynolds number was not a consistent predictor of hydraulic friction this result was due to interactions of slope gradient flow rate erosion and the formation of rill roughness bed structures and head cuts a relationship for rill flow velocities was proposed stream power was found to be a consistent and appropriate predictor for unit sediment load for the entire data set while other hydraulic variables were not the data for stream power and sediment load fit the form of a logistic curve r2 0 93 which is promising relative to recently proposed erosion models which are based on probabilistic particle threshold theory

observations of quasi stationary and shallow orographic snow clouds spatial distributions of supercooled liquid water and snow particles abstract on 25 february 1999 due to a winter monsoon after a cyclonic storm orographic snow clouds formed under conditions of weak cold advection on the western side of the central mountain range of japan in this study the ka band doppler radar and vehicle mounted microwave radiometer and 2d grey imaging probe were used to obtain unique datasets for analyzing the spatial distributions of microphysical structures of the snow clouds at the windward slope the liquid water path number concentration of snow particles 0 1 6 4 mm diameter and precipitation rate were found to be correlated with altitude the greater concentration of larger particles tended to appear up the slope the echo top was at about 2 5 km 30 dbz and the relatively strong echo region 3 dbz appeared at 5 km up the slope and extended nearly parallel to the slope according to the echo pattern the ice water path increased with terrain height and reached the maximum intensity at about 14 km up the slope these observations pro

flow simulation in a rock ramp fish pass abstractthe flow characteristics in a rock ramp fish pass can be significantly altered by the boulder arrangement this study used a three dimensional computational fluid dynamics solver to investigate flow characteristics for variations of discharge channel slope and boulder size spacing and pattern this study derived relationships for estimating water depth and velocity in a rock ramp fish pass as a function of discharge and structure geometry the flow resistance varies significantly with emergent boulder spacing and is nearly constant for submerged boulders this study derives relationships for the drag coefficient and submergence ratio to forecast average flow velocity using a flow resistance equation based on maximum velocity and a slow velocity zone this study recommends effective boulder spacing in the longitudinal and transverse directions for two different boulder patterns finally this study developed a design procedure for designing a rock ramp fish pass

resistance to overland flow on desert hillslopes abstract this study examines the relation between the darcy weisbach friction factor f and the reynolds number re for overland flow on six runoff plots in semiarid southern arizona the surfaces of these plots are irregular and covered with stones as overland flow increases the stones and microtopographic protuberances which constitute the major roughness elements are progressively inundated thereby altering the flow resistance analyses of 14 cross sections reveal that the resulting f re relations have two basic shapes convex upward and negatively sloping these shapes bear little resemblance to the conventional f re relation for shallow flow over a plane bed whose shape is a function of the state of flow rather they are explained in terms of the simultaneous operation of two processes the first is the progressive inundation of roughness elements and increase in their wetted upstream projected area as discharge increases this process causes f to increase the second is the progressive increase in the depth of flow over already inundated parts of the bed as discharge increases this process causes f to decline whether the f re relation has a positive or a negative slope depends on whether the first or second process dominates and this depends on the configuration of the bed and level of discharge these findings have profound implications for the mathematical modeling of overland flow on desert hillslopes whether a model is based on the saint venant equations or makes use of the kinematic wave approximation it requires the specification of a relation between f and re or surrogates thereof and the computed hydrograph is very sensitive to the form of this relation hitherto the most widely used relation has been the conventional one for shallow flow over a plane bed however the present study suggests that this relation does not apply to desert hillslopes additional field and laboratory studies are needed to learn more of the behavior and controls of f re relations on such hillslopes so that models of overland flow can employ more realistic relations and better simulate runoff hydrographs

laminaset geometries in fine grained shallow marine sequences core data from the rannoch formation north sea and outcrop data from the kennilworth member utah usa and the bencliff grit dorset uk sandbodies from storm dominated marine and marginal marine environments commonly contain intervals of laminated fine sandstones a characteristic of such lamination is the presence of low angle cross lamination in order to model correctly the effects of such lamination on a waterflood of an oil bearing shoreface sequence it was necessary to quantify the geometry of the laminaset elements this challenge has been greatly complicated by the lack of outcrop of the formation of interest the middle jurassic rannoch formation of the north sea only occurs in the subsurface where it is not possible in core to measure the aspect ratio of laminasets directly in this study the laminaset geometry data that can be obtained from core e g apparent set thicknesses were collected for the rannoch formation these data were compared with similar data from potential outcrop analogues in 1 the cretaceous kennilworth member of the blackhawk formation in utah usa and 2 the upper jurassic bencliff grit from the dorset coast uk a quantitative analysis of laminaset geometries has been used to compare subsurface core with potential outcrop analogues the rannoch formation core is characterized by numerous low angle truncations we have measured these features in two wells means of 7 2 and 12 1 mean apparent set thicknesses were 0 24 and 0 19 m in the outcrop sections studied truncation angles ranged from 9 6 to 13 4 and mean set thicknesses from 0 24 to 0 34 m mean bounding surface dips of 5 8 and 8 6 and mean laminaset lengths of 2 3 and 4 1 m were also measured directly in the field and by using photomosaics on the basis of this comparison the kennilworth member in utah was found to be the most suitable and the geometries i e aspect ratios measured there were used to generate an appropriate geometry of rannoch laminaset geometries for use in engineering studies laminaset length 2 0 m laminaset thickness 0 2 m

turbulent flow and sand transport over a cobble bed in a laboratory flume abstractimproving the prediction of sand transport downstream of dams requires characterization of the interaction between turbulent flow and near surface interstitial sands the advanced age and impending decommissioning of many dams have brought increased attention to the fate of sediments stored in reservoirs sands can be reintroduced to coarse substrates that have available pore space resulting from periods of sediment starved flow the roughness and porosity of the coarse substrate are both affected by sand elevation relative to the coarse substrate therefore the turbulence characteristics and sediment transport over and through these beds are significantly altered after sediment is reintroduced past work by the writers on flow over sand filled gravel beds revealed that the fine sediment level controls the volume of material available for transport and the area of sediment exposed to the flow the present work expands on the gravel bed experiments by conducting similar measurements of turbulent f

a sediment transport equation for interrill overland flow on rough surfaces a model for predicting the sediment transport capacity of turbulent interrill flow on rough surfaces is developed from 1295 flume experiments with flow depths ranging from 3 4 to 43 4 mm flow velocities from 0 09 to 0 65 m s 1 reynolds numbers from 5000 to 26 949 froude numbers from 0 23 to 2 93 bed slopes from 2 7 to 10 sediment diameters from 0 098 to 1 16 mm volumetric sediment concentrations from 0 002 to 0 304 roughness concentrations from 0 to 0 57 roughness diameters from 1 0 to 91 3 mm rainfall intensities from 0 to 159 mm h 1 flow densities from 1002 to 1501 kg m 3 and flow kinematic viscosities from 0 913 to 2 556 10 6 m2 s 1 stones cylinders and miniature ornamental trees are used as roughness elements given the diverse shapes sizes and concentrations of these elements the transport model is likely to apply to a wide range of ground surface morphologies using dimensional analysis a total load transport equation is developed for open channel flows and this equation is shown to apply to interrill flows both with and without rainfall the equation indicates that the dimensionless sediment transport rate is a function of and therefore can be predicted by the dimensionless shear stress its critical value c the resistance coefficient u u the inertial settling velocity of the sediment wi the roughness concentration cr and the roughness diameter dr the model has the form 1 where and testing reveals that the model gives good unbiased predictions of in flows with sediment concentrations less than 0 20 flows with higher concentrations appear to be hyperconcentrated and to have sediment transport rates higher than those predicted by the model copyright 2001 john wiley sons ltd

stratigraphic development mineral sources and preservation of marine placers from pleistocene terraces in southern oregon u s a abstract marine placers containing economic minerals chromite ilmenite magnetite and zircon have been extensively studied in pleistocene coastal deposits of southwest oregon the two largest placers occur on adjacent uplifted terraces south of a prominent headland cape arago and include the older seven devils placer covering 11 km 2 and containing 1 1 10 7 m 3 placer sand heavy minerals 50 weight abundance and the younger pioneer placer covering about 0 9 km 2 and containing 9 10 5 m 3 placer sand the most highly enriched beds of placer ore containing at least 6 chromite by weight are generally concentrated in the bottom 1 4 m of terrace stratigraphic sections upsection sequences of nearshore to inner shelf facies in the seven devils deposit and beach to eolian dune facies in the pioneer deposit respectively indicate placer formation during 1 marine transgression and 2 sea level high stand with beachface progradation microprobe analyses of opaque minerals establish local river sources of placer minerals for both seven devils and pioneer deposits in contrast younger terrace and modern beach deposits are supplied by distant river sources 100 150 km south as well as local rivers indicating increasing net northward littoral drift during successive marine transgressions placer thickness in the seven devils and pioneer deposits are controlled in part by platform gradient and paleo tidal range respectively placer development and preservation in this high wave energy active margin setting are strongly controlled by paleo shoreline orientation and littoral cell bounding headlands

bay sedimentation as controlled by regional crustal behaviour local tectonics and eustatic sea level changes coquimbo formation miocene pliocene bay of tongoy central chile abstract the north facing bay of tongoy in central chile is flanked by topographic highs in the west and east during the miocene and pliocene the bay extended inland at least 30 km farther south than a present it was filled with muds sands coquinas and gravel during a series of transgressions and regressions related to regional and local tectonic movements combined with global sea level variations 87sr 86sr and microfossil dating indicates transgressions between 11 9 11 2 ma 10 1 9 5 ma 9 0 7 3 ma 6 3 5 3 ma 4 3 2 2 ma and 1 7 1 4 ma the regional tectonic behaviour of the crust shows general uplifting from 10 5 ma to 6 9 ma associated with subduction of the juan fernandez ridge jfr beneath this part of the continent subsidence followed between 6 9 and 2 1 ma in the wake of the southeastward migrating jfr the subsequent subduction of an oceanic plateau similar to the jfr caused rapid uplift that led to the final emergence of the bay above sea level the puerto aldea normal fault along the western limit of the study area was reactivated during the regional uplift and subsidence events with reverse faulting occurring during the latter phase sporadic fault reactivation probably triggered the rapid changes in water depth reflected in the recorded vertical succession of facies

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

effects of macro scale bed roughness geometry on flow resistance 1 flow field over macro roughness elements as for example in flow conditions such as of steep mountain streams is investigated by means of a theoretical model and a laboratory study with the main aim of understanding the influence of concentration and planimetric disposition of grain roughness on flow resistance a theoretical model for the average velocity distribution profile over a bed with macro roughness elements is developed herein the model is based on a two layer approach which takes into account the displacement of the main flow due to the drag around the roughness the laboratory study is composed of an extensive set of flume experiments in the case of steep slopes and large relative roughness conditions for a given flow discharge and bed slope various experiments have been carried out with different pattern and spacing of the roughness elements constituted by river pebbles application of the theoretical model to the experimental results enables the determination of how flow resistance is affected by the macro roughness in particular it appears that when the concentration of the roughness is within an optimal range flow resistance is maximum

experimental validation of a 2d overland flow model using high resolution water depth and velocity data summary this paper presents a validation of a two dimensional overland flow model using empirical laboratory data unlike previous publications in which model performance is evaluated as the ability to predict an outlet hydrograph we use high resolution 2d water depth and velocity data to analyze to what degree the model is able to reproduce the spatial distribution of these variables several overland flow conditions over two impervious surfaces of the order of one square meter with different micro and macro roughness characteristics are studied the first surface is a simplified representation of a sinusoidal terrain with three crests and furrows while the second one is a mould of a real agricultural seedbed terrain we analyze four different bed friction parameterizations and we show that the performance of formulations which consider the transition between laminar smooth turbulent and rough turbulent flow do not improve the results obtained with manning or keulegan formulas for rough turbulent flow the simulations performed show that using keulegan formula with a physically based definition of the bed roughness coefficient a two dimensional shallow water model is able to reproduce satisfactorily the flow hydrodynamics it is shown that even if the resolution of the topography data and numerical mesh are high enough to include all the small scale features of the bed surface the roughness coefficient must account for the macro roughness characteristics of the terrain in order to correctly reproduce the flow hydrodynamics

high frequency eustatic sea level changes during the middle to early late ordovician of southern jordan indirect evidence for a darriwilian ice age in gondwana abstract the middle to early late ordovician hiswah and dubaydib formations in southern jordan provide a well constrained sedimentary record of 4th and 3rd order relative sea level change along the northern tectonically quiescent subpolar gondwana continental margin cyclic deposition occurred on a wave and storm dominated microtidal shelf dominated by shoreface and offshore transition zone facies cycles are commonly bounded by amalgamated bounding surfaces sb ts or sb mfs and are characterised by stacked transgressive systems tracts tsts the small facies dislocation across key sequence bounding surfaces indicates a 15 50 m change in relative sea level fourth order sequences are hypothesized to be paced by the long eccentricity 405 kyr cycle and consequently 3rd order sequences are calculated to be 1 2 m y and 2 4 m y long these correlate with the global eustatic sea level curve in comparison with mesozoic and cenozoic sequence stratigraphical data we conclude that the 1 2 m y cycles correspond with long obliquity cycles predominant in icehouse conditions and the 2 4 m y cycles with the long eccentricity cycle predominant during greenhouse conditions we propose a darriwilian ice age during which orbitally induced cold snaps caused the expansion and amalgamation of small medium scale ice sheets the reduced size of the correlative positive carbon isotope excursion compared to that in the hirnantian may indicate that the darriwilian ice sheets only reached the sea in a few places the absence of glacio terrestrial deposits of middle ordovician age is most likely due to subsequent glacial erosion during repeated ice advances up to and including those in the hirnantian the existence of darriwilian ice sheets is consistent with zooplankton province distributions that indicate a polar front at 40 s during the ice age it is likely that polar ice existed throughout the ordovician

the kinematic structure of a wasatch mountain winter storm during ipex iop3 the influence of orographic circulations on the precipitation structure of a wasatch mountain winter storm is examined using observations collected during the third intensive observing period iop3 of the intermountain precipitation experiment ipex the event featured the passage of a midlevel 700 550 hpa trough followed 3 h later by a surface trough prior to and during the midlevel trough passage large scale southwesterly flow impinged on the wasatch mountains low level confluence was observed between this southwesterly flow and along barrier southerly flow within 20 40 km of the wasatch mountains this confluence zone which moved toward the wasatch mountains during and following the passage of the midlevel trough was accompanied by low level convergence and precipitation enhancement over the upstream lowlands dual doppler analysis revealed the presence of a shallow along barrier jet near the base of the wasatch mountains that was surmounted by southwesterly cross barrier flow at mid and uppermountain levels this cross barrier flow produced strong 1 2 m s 1 ascent as it interacted with the steep windward slopes of the wasatch mountains where precipitation was roughly double that observed in the lowlands upstream flow deflection and splitting were also observed near the highest terrain features a narrow region of strong subsidence which at times exceede d2ms 1 was found to the lee of the wasatch and based on radar imagery appeared to modulate hydrometeor spillover aloft processes contributing to the evolution of the near barrier flow field including topographic blocking diabatic effects and surface friction contrasts are discussed

interactions between topographic airflow and cloud precipitation development during the passage of a winter storm in arizona abstract a case study showing comparisons between observations and numerical simulations of the passage of a winter storm over complex terrain is presented the interactions between the mesoscale and cloud environments and the microphysical and dynamical processes are addressed using both observations and numerical simulations a three dimensional time dependent nested grid model was used to conduct numerical simulations of the three dimensional airflow and cloud evolution over the mogollon rim and adjacent terrain in arizona the modeling results indicated that the flow patterns and cloud liquid water clw were closely linked to the topography to a large extent gravity waves excited by the flow over the mountains determine the distribution of clouds and precipitation the waves extend through deep layers of the atmosphere with substantial updrafts and downdrafts at times exceeding 5 m s 1 the simulated vertical velocities and horizontal wavelengths of about 20 km were in good agreement with the air

flow resistance in concentrated overland flow on rough slope surfaces field experiments have been done on simulated flows over different rough pre rill and rill bed surfaces the purpose of the experiments was to evaluate the hydraulic roughness properties of these bed surfaces conventional equations describing the relation of the resistance coefficient to the reynolds number for flow in closed conduits or open channels can also be applied to shallow flows provided the boundary values of the reynolds number which discriminate between the various flow regimes are adapted when the reynolds number is less than 100 the flow regime is laminar above this figure the flow is either transitional or turbulent depending on the roughness of the bed surface the degree of turbulence can be deduced from a morphological description of the pre rill and rill bed surface roughness

quartz cementation history of sandstones revealed by high resolution sims oxygen isotope analysis abstract evaluating the timing and origin of quartz cement is central to understanding how porosity is lost in sandstones during burial kinetic models of quartz cementation have been calibrated using large scale datasets but have never been tested at the microscopic level at which cement forms here we use high precision in situ oxygen isotope analyses on sandstone from the jurassic ness formation from the north sea to reveal the growth history of single quartz overgrowths to a resolution of 2 m measured 18o cement range from 28 to 20 v smow in early to late cement and are consistent with quartz cementation models that propose the bulk of quartz precipitates as a continuous process beginning at 60 70 c quantitative x ray diffraction analyses and clay mineralogical analysis of interbedded shales are inconsistent with a silica source from shale implying that silica for the cement is sourced internally to the sand these isotope data are broadly consistent with predictive conceptual quartz cementation models and provide a critical link from micron scale measurements to basin scale predictions and observations

rill hydraulics on a semiarid hillslope southern arizona seventy field experiments were conducted in seven rills located on a semiarid rangeland hillslope underlain by gravelly soils at walnut gulch arizona the rills which are characterized by wide shallow cross sections and gravel covered beds have mean at a station hydraulic geometry exponents of b 0 33 f 0 34 and m 0 33 although the differences between these values and typical values of b 0 30 f 0 40 and m 0 30 for cropland rills are not statistically significant they are thought to be real as cropland rills often have more rectangular cross sections and steeper sides than the rangeland rills under study for rills formed in silty loamy soils govers developed an empirical relation between mean flow velocity and discharge emphasizing the generality of this relation he suggested that it may be used as a simple means of routing runoff through rills he also noted that this relation appeared to be unaffected by either slope or soil materials the present data represent rills underlain by coarser and somewhat more varied gravel rich soils these data do not conform to govers relation and a multiple regression analysis reveals that slope and soil materials either directly or indirectly through bed roughness exert almost as much influence on flow velocity as does discharge three alternative methods are developed for predicting flow velocity in the rills under study all three methods give good results with the largest root mean square deviation being 3 115 cm s 1

high spatial resolution mapping of surface velocities and depths for shallow overland flow point measurements of flow rate depth or velocity are not sufficient to validate overland flow models particularly when the interaction of the water with the soil surface creates a complex flow geometry in this study we present the coupling of two techniques obtaining spatial data of flow depths and surface velocity measurements for water depths as low as 1 mm overland flow experiments were performed in the laboratory at various flow rates and slopes on two surfaces the first surface was 120 cm by 120 cm showing three undulations of sinusoidal shape with an amplitude of 1 cm and a wavelength of 20 cm while the second was a 60 cm by 60 cm moulded reproduction of a seedbed with aggregates up to 2 cm in size large scale particle image velocimetry lspiv was used for velocity measurements with a sub centimetre spatial resolution an instantaneous profile laser scanner was used to map flow depths with a sub millimetre spatial resolution a sensitivity analysis of the image processing of the lspiv showed good robustness of the method comparison with measurements performed with hot film anemometer and salt velocity gauge showed that lspiv surface velocities were representative of the flow water depths measured with the laser scanner were also in good agreement with single point measurements performed with a dial indicator spatially distributed flow rates could be computed by combining both presented techniques with a mean relative error less than 20 copyright 2012 john wiley sons ltd

resistance equation for large scale roughness a theory of flow resistance for large scale roughness is developed the main points of which are supported by a flume study from which the outline of a process based resistance equation is determined rivers with large scale roughness have steep slopes and depths of the same order of magnitude as the bed material size flow resistance depends on the form drag of the roughness elements and their disposition in the channel theoretical considerations show resistance to be a function of reynolds number froude number roughness geometry and channel geometry these processes are examined using the results of flume experiments based on five different roughness beds and a wide range of flows semi empirical analysis supports the theory and allows the development of a theoretical power law resistance equation which accounts for most of the processes a summary of the data is presented for use in other research studies

accumulation and preservation of reworked marine pyrite beneath an oxygen rich devonian atmosphere constraints from sulfur isotopes and framboid textures abstract the devonian appalachian basin provides a unique window to the unusual geochemical conditions required to form and preserve detrital metal sulfide deposits during the oxygen rich phanerozoic eon the devonian leicester pyrite member a marine transgressive lag occurs in the northern appalachian basin of western new york and is a reworked and redeposited acid resistant residuum dominated by a wide range of pyritic clasts in the absence of carbonate grains these iron sulfide grains include 10 2 m nodules framboids and pyritized fossil material e g cephalopods burrows and steinkerns a previous model for the formation of the leicester pyrite member requires establishment of a strong and persistent density and chemical stratification in the appalachian basin although this model permits erosion under the low oxygen conditions required for pyrite preservation little geochemical evidence has been provided in corroboration and the chemical conditions responsible for the formation deposition and preservation of the pyrite lag have remained speculative using a combined geochemical and petrographic approach focusing on the pyritic fraction and emphasizing sulfur isotopes and pyrite framboid size distributions the specific redox conditions responsible for the formation of the leicester pyrite member are addressed the wide ranges of textural and isotopic data observed for the leicester pyrite member with 34s values that range from 22 to 54 at a single location are consistent with the general idea of lag concentration of pyritic debris formed under diverse diagenetic and possibly water column syngenetic conditions energy propagation possibly storm related along the redox transition of the pycnocline and chemocline would have favored pyrite preservation while still permitting enough oxidation and concomitant acid production to dissolve associated hydrodynamically equivalent carbonate debris intermittence in the stability of water column stratification would have enhanced this oxidation although an association with the overall oxygen deficiency that characterized the deposition of the overlying geneseo shale member is demonstrated by the occurrence of microlaminated geneseo shale member like clasts within the leicester pyrite member our geochemical results confirm that during times of atmospheric oxygenation pyrite reworking and lag formation require high energy but low oxygen conditions at pycnocline depths in a subaqueous marine setting while not unique to the leicester pyrite member the specific sets of environmental conditions required for pyrite preservation differ from those of the fluvial settings in which archean detrital pyrite and uraninite deposits formed we suggest therefore that the presence of phanerozoic pyrite lags such as the leicester pyrite member does not compromise the utility of archean detrital pyrite as a paleoredox proxy delineating early deficiency of atmospheric oxygen

estimation of flow resistance in gravel bedded rivers a physical explanation of the multiplier of roughness length the need to estimate velocity and discharge indirectly in gravel bedded rivers is a commonly encountered problem semilogarithmic friction equations are used to estimate mean velocity using a friction factor obtained from depth and grain size information although such equations have a semi theoretical basis in natural gravel bed channels an empirical constant 6 8 or 3 5 has to be introduced to scale up the characteristic grain size d50 or d84 to represent the effective roughness length in this paper two contrasting approaches are used to suggest that the multiplier of characteristic grain size is attributable to the effect of small scale form resistance reflecting the occurrence of microtopographic bedforms in gravel bedded environments first spatial elevation dependence in short detailed bed profiles from a single gravel bedded river is investigated using semivariogram and zero crossing analyses this leads to objective identification of two discrete scales of bed roughness associated with grain and microtopographic roughness elements second the autocorrelation structure of the three dimensional near bed velocity field is examined to identify regularities associated with eddy shedding and energy losses from larger grains and microtopographic bedforms apart from improving the capacity to determine friction factors for velocity and discharge estimation the findings have implications in general for the initial motion of gravelly bed material

application of high resolution sequence stratigraphy to northwest hutton field northern north sea implications for management of a mature brent group field the middle jurassic brent group reservoirs in northwest hutton comprise shallow marine marginal marine and coastal plain reservoir sandstones of both channelized and sheet geometries the connectivity and production characteristics of these sandstones can be predicted through the application of high resolution sequence stratigraphic correlation techniques the broom formation overlies a basal brent sequence boundary and is a lowstand to transgressive systems tract tidal estuarine complex the overlying rannoch formation comprises shoreface sands that represent a highstand systems tract the overlying etive formation is a multilayer fluvial to estuarine channelized system of near fieldwide development interpreted as incised valley fills the superjacent ness formation is genetically related to the etive and is the main oil bearing interval over much of the field the lower ness comprises mouth bar parasequences and is interpreted to be a transgressive systems tract to the etive lowstand the upper ness is a nonmarine delta plain succession interpreted as a highstand systems tract upper ness channel sands typically correlate between several wells and are oriented west east an interval of widespread stacked channels indicates a change in drainage orientation and is related to a high frequency relative sea level fall the uppermost reservoir unit is the tarbert formation related to a further major sequence boundary original repeat formation tester data support a stratigraphically well connected reservoir model compartmentalization exists and is due to stratigraphic layering laterally persistent mudstones creating low vertical permeability and variable dimensions of channels and valley fills

overland flow in wetlands vegetation resistance emergent wetland vegetation frequently provides most of the resistance to flow of surface water stems are typically spaced many diameters apart therefore fluid friction should be computed from drag on single objects not channel or packed bed equations complication arises from vertical variation of vegetation density and nonoriented spatial variation of soil elevations further flows are often in the transition region between laminar and turbulent and the manning equation is therefore not appropriate a detailed approach requires knowledge of statistical distributions of wetland ground elevation depth and velocity ground slopes are typically in the range of 0 1 100 cm km however the depth range is small so the combined effects recorrelate to a simple power law equation for dense emergent vegetation with spatial uniformity on the scale of 10 m parameters in the model can be estimated with sufficient accuracy from vegetation and soil surveys combined with relatively little hydrologic data dat

very coarse grained beaches as a response to generalized sea level drops in a complex active tectonic setting pleistocene marine terraces at the cadiz coast sw spain abstract the studied pleistocene deposits at the cadiz coast are located on the current intertidal zone or at cliffs parallel to the actual coast 6 50 m a s l from the localities of el puerto de santa maria to chiclana five sequences of very coarse grained beaches have been recognized and dated they unconformably overlie pliocene units and are formed by clast supported conglomerate and coarse grained sandstone chronological ages 87 sr 86 sr and ams 14 c analysis and stratigraphic correlation stand that the oldest marine terrace is the one placed topographically higher and towards the se of cadiz city dated as early pleistocene 1 3 ma after it the sea retreatment produces subaerial exposure of sequence 1 and the development of several calcrete profiles and a paleokarst subsequent sea level rises allow the sedimentation of sequences 2 3 and 4 during early middle pleistocene 1 to 0 8 ma in areas close to cadiz city with subaerial exposure recorded at the top of sequences 3 and 4 during the very upper pleistocene sedimentation of sequence 5 occurs towards the se of cadiz city based on the spatial position of sequence 5 we can conclude that this area constituted a downthrown block during the latest pleistocene in relation to neotectonic processes and diapirism sandstone framework hybrid arenites reveals that main source areas for these marine terraces include units from the betic orogene betic external zones triassic and jurassic rocks and the gibraltar arc the guadalquivir basin passive margin iberian massif the guadalquivir foreland basin marine miocene and pliocene record and local inputs of pleistocene units the siliciclastic supplies from sources were mainly constant during the sedimentation of all set of sequences suggesting maturation processes as reworking and recycling of homogenized sediments during transport early diagenetic processes have been identified as carbonate cementation neomorphism and dissolution outlining the deduced sea level fluctuations during deposition of pleistocene sequences the marine terraces arrangement and its comparison with regionally adjacent areas allows to deduce that the southern and central portuguese coast iberian massif and of the southern and southeastern spanish coast betic orogene were predominantly tectonically raising during pleistocene however the cadiz gulf coast formerly guadalquivir foreland basin was mainly sinking during the same time interval

influence of the ancestral sweetgrass arch on sedimentation of the lower cretaceous bootlegger member north central montana abstract in north central montana the bootlegger member of the upper lower cretaceous blackleaf formation is well exposed near great falls and at one locality in the sweetgrass hills in both areas bootlegger strata comprise four stratigraphic successions in the great falls study area each succession consists of an upward coarsening shoaling package of interbedded very fine sandstone and shale grading upward into fine to medium sandstone abruptly overlain by a transgressive erosion surface and capped in many places by a conglomeratic transgressive lag deposit the stacking of these successions is attributed to episodic changes of relative sea level probably related to episodic reactivation of the ancestral sweetgrass arch during episodes of arch uplift accommodation space was reduced a d caused the bootlegger shoreline to prograde eastward subsequently because of arch subsidence and or the ongoing basinwide eustatic rise the shoreline migrated westward erosion associated with transgressive shoreface retreat was most intense near the crest of the arch as a result in the western study area which lies above the arch crest successions are thin and typically consist only of inner shelf strata lithofacies 1 strata deposited in shallower environments were removed mainly by later transgressive erosion by contrast in the eastern area farther from the arch crest the upward shoaling part of each succession is more completely preserved at the end of bootlegger time however movement of the arch either ceased or simply could no longer keep pace with the eustatic ri e consequently the shoreline continued to transgress westward and only fossiliferous silt and mud accumulated in a distal shelf environment this marked a eustatic drowning and termination of rhythmic bootlegger sedimentation

a linear theory of orographic precipitation a linear theory of orographic precipitation is developed including airflow dynamics condensed water advection and downslope evaporation the formulation extends the widely used upslope model vertically integrated steady state governing equations for condensed water are solved using fourier transform techniques closed form expressions are derived for special cases for more general cases the precipitation field is computed quickly by multiplying the terrain transform by a wavenumber dependent transfer function five length scales are included in the model mountain width a buoyancy wave scale the moist layer depth and two condensed water advection distances the efficiency of precipitation in the model is sensitive to the decay of the forced ascent through the moist layer and to the advection of condensed water downwind into the region of descent the strong influence of horizontal scale on precipitation pattern and amount predicted by the model is discussed the model is illustrated by applying it to the olympic mountains in washington state

flow resistance caused by large scale bank roughness in a channel systematic experimental investigations have been performed under steady flow conditions in a channel whose banks are equipped with large scale rectangular roughness elements the purpose was to determine the flow resistance owing to such macrorough banks the practical motivation of the study is to see how morphological restoration of banks in channelized rivers such as lateral cavities influences the steady flow characteristics the experiments performed in 40 different geometrical configurations revealed various two dimensional flow characteristics in the bank cavities created by the roughness elements compared to the prismatic reference channel the overall head loss of the flow is governed by the existence of different phenomena such as vertical mixing layers wake zones recirculation gyres coherent structures and skin friction the analysis of the experiments for steady flow conditions showed that the flow resistance is significantly increased in the macrorough configurations because of the disturbance of the bank geometry inducing large scale depressions the additional flow resistance attributable to macroroughness has been related to the forms of the banks by separating the observed flow behavior into a normal recirculating a reattachment and a square grooved flow type macrorough flow resistance formulas according two different approaches could be developed that are in good agreement with the laboratory experiments

numerical simulations of orographic gravity waves in flows which back with height numerical simulations are carried out to determine the steady state gravity wave structure above a circularly symmetric bell shaped hill when the wind backs with height two types of idealized basic state flow are considered one representing the advection of a uniform baroclinic shear flow and the other being a flow of constant speed but with a wind vector that rotates uniformly in height of particular interest is the nature of the critical level processes that must appear at all heights due to the three dimensionality of the wave field and the rotation of the wind vector as suggested by linear theory a critical level or asymptotic wake is found downwind of the hill at any height where downwind refers to the wind at that level only for small hills where the nondimensional mountain height unity the simulated vertical momentum flux profiles are in very good agreement with linear hydrostatic wave theory if it is assumed that wave component critical level absorption is total i e no wave transmission or reflections are permitted the vertical momentum fluxes generated by a 1 km high hill show nonlinear enhancement by a factor of about 1 5 an interesting feature of the gravity wave field generated by this 1 km mountain is an asymptotic wake that is dominated by a single intense shear layer in which the richardson number is order unity

the pulse of calm fan deltas abstract at the heart of interpreting the history of earth surface evolution preserved in the rock record is distinguishing environmental allogenic forcing from internally generated autogenic noise allogenic deposits classically have been recognized by their cyclic nature which apparently results from periodic changes in base level sediment supply or tectonics autogenic deposits which are quite variable in their origin and scale are caused by the nonlinearity of sediment transport and might be expected to have a random or scale free fractal signature here we describe a robust mechanism that generates cyclic deposits by an autogenic process in experimental fan deltas sheet flow over the fan surface induces deposition and an increase in fluvial slope and curvature to a point where the surface geometry is susceptible to a channelization instability similar to channel initiation on hillslopes channelized flow results in incision and degrading of the fan surface to a lower slope releasing a

friction factor evaluation in gravel bed rivers field data gathered from 43 river reaches of calabria southern italy were employed to develop a theoretically based equation for predicting the f friction factor that takes into account both the froude number and the sediment mobility parameter the river reaches investigated have 1 reasonably uniform and relatively low flow 2 no appreciable vegetation in the channel bed and banks 3 a fully developed turbulent flow 4 a friction slope greater than 0 2 5 small and intermediate scale roughness 6 a mobility parameter greater than the critical value in more than 50 of the cases and 7 a froude number between 0 20 1 30 statistical techniques were used to derive an equation for estimating f that takes into account the physical processes controlling flow resistance beyond the range of the collected data