imaging near surface heterogeneities by natural migration of backscattered surface waves s u m m a r y we present a migration method that does not require a velocity model to migrate backscattered surface waves to their projected locations on the surface this migration method denoted as natural migration uses recorded green s functions along the surface instead of simulated green s functions the key assumptions are that the scattering bodies are within the depth interrogated by the surface waves and the green s functions are recorded with dense receiver sampling along the free surface this natural migration takes into account all orders of multiples mode conversions and non linear effects of surface waves in the data the natural imaging formulae are derived for both active source and ambient noise data and computer simulations show that natural migration can effectively image near surface heterogeneities with typical ambient noise sources and geophone distributions

spatial organization in the step pool structure of a steep mountain stream vogelbach switzerland 1 spatial organization in the step pool structure of a 1 58 km long section of the vogelbach a steep mountain stream average channel bed slope 0 17 m m in the alpthal basin switzerland is analyzed to evaluate the extent of randomness in the occurrence of steps and to isolate the potential hydraulic and topographic controls on step placement statistics of the observed step sequence are compared with those of random sequences generated by permutation from the observed step height distribution hydraulic and topographic controls on step placement are analyzed from step length and steepness distributions and relations between mean step properties and step height and channel gradient for both observed and random sequences results show that 1 observed step length distributions are statistically significantly different from randomly generated sequences 2 step steepness is significantly different in observed data because of a positive correlation between mean step length and height and it remains fairly constant for all step sizes 3 spatial organization in steps does not extend far beyond the nearest step and 4 the influence of channel gradient on step properties is insignificant and highly variable indicating that hydraulic rather than topographic controls are dominant for step placement in this stream although the vogelbach is a steep stream on the boundary between a cascading and step pool morphology where we would expect randomness to dominate spatial organization was nevertheless detected in many important aspects of the step pool geometry

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

stress directions in eastern north america determined to 4 5 km from borehole elongation measurements stress directions have been determined to depths of 4 5 km in eastern north america from borehole elongation measured by dipmeter calipers in 47 wells the average maximum horizontal stress directions are eastern canada n54 e 7 appalachian basin n58 e 8 and the illinois basin n89 w 5 stress directions determined for the illinois and appalachian basins are in agreement with published interpretations from hydraulic fractures and earthquake fault plane solutions new results from eastern canada and the appalachian basin show that stress directions are everywhere consistent with the midcontinent stress province these data suggest that the maximum horizontal stress does not rotate from the ene midcontinent trend to nw near the atlantic coast a directional analysis of hydraulic fractures petal centerline fractures and natural fractures from the appalachian basin shows that borehole elongation is systematically aligned perpendicular to the directions of hydraulic fractures centerline fractures and northeast striking natural fractures but is not systematically aligned with northwest striking natural fractures these observations indicate that borehole elongations provide reliable stress orientations

integrating borehole image logs with core a method to enhance subsurface fracture characterization image logs provide critical data for characterizing fractured reservoirs however the nature of such logs coupled with borehole modified stresses creates challenges that may lead to erroneous fracture interpretations we developed a methodology to integrate image logs core and geomechanical models to obtain high confidence fracture data sets derived from image logs the methodology starts with a detailed comparison of overlapping image logs and core first to properly shift them into alignment core to log shift and second to determine which features interpreted as fractures on image logs picks can be validated as fractures in core then we derive guidelines for interpreting image logs without core control to reduce the likelihood of false fracture picks geomechanical modeling is used to assist with quality control and interpretation of image logs where drilling induced tensile fractures occur we use a fractured carbonate reservoir to demonstrate the application of this methodology comparison of image log fracture picks with core led to an average rejection rate of greater than 50 of fractures picked on the image logs these high rejection rates are mostly caused by overinterpretation of discontinuous sinusoids and misidentification of sedimentary features and induced fractures we derived rules for interpreting high quality fractures 1 only sinusoids with continuity greater than 50 should be interpreted and 2 sinusoids with dip angles less than 55 should be excluded from the interpretation application of this methodology has provided much higher quality fracture orientation and frequency data than that resulting from interpretation of borehole images alone the improved fracture data set provides a more reliable basis for testing hypotheses and deriving models of fracture distribution

interaction between bed roughness and flow hydraulics in eroding rills govers 1992 showed that the flow velocity in rills eroding loose nonlayered materials could be predicted from knowledge of discharge only without significant slope or soil effect the objective of this paper is to investigate to what extent the observed slope independence of flow velocity in eroding rills can be explained by the interaction between rill bed roughness and flow hydraulics in a laboratory study two situations were compared 1 rills which can freely erode a uniform soil layer and 2 rills with a fixed bed geometry during the experiments rill discharge and flow velocity were recorded after each experiment a detailed topographic survey of the rill bed was carried out using a laser scanner from these data the main hydraulic variables mean values of flow depth wetted perimeter and hydraulic radius were estimated the experiments confirmed the slope independence of rill flow velocities on mobile beds when the bed is fixed the flow velocity in rills is clearly slope dependent the slope independence of flow velocity on mobile beds is due to a feedback between rill bed morphology and flow conditions the roughness amplitude which was assessed from the standard deviation of corrected height values and the frequency of macroroughness elements which was assessed by counting the number of peaks per unit length in a previously simplified longitudinal profiles both increase and tend to counteract the effect of the increase in slope gradient on rill flow velocity the final rill flow velocity appears to be characterized by a constant average froude number

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

high horizontal stresses in hudson bay canada breakouts in four wells in hudson bay suggest that the paleozoic section is currently subject to maximum horizontal compression about a northeast southwest axis with some local deflection in horizontal stress orientations related to faults the paleozoic section does not appear to be detached from the crystalline basement of the canadian shield despite the presence of thick silurian halite rich intervals the northeast southwest compressional axis documented in the hudson bay basin is compatible with stress orientations mat have been measured in other parts of cratonic north america leak off tests from three wells imply that contemporary horizontal stress magnitudes above 1500 m depth exceed present day overburden loads comparable relative magnitudes have been measured elsewhere in central canada finite element modelling suggests mat this phenomenon is due to the effects of glacial loading crustal rebound and spreading of the mid atlantic ridge

field investigation of rill and ephemeral gully erosion in the sparacia experimental area south italy abstract this paper reports the results of a field investigation aiming at characterizing the morphology and hydraulics of both rills and ephemeral gullies egs monitored at sparacia experimental area sicily italy the comparison between rill and interrill erosion measurements showed that sediment delivery processes occurred in some erosive events and that the rill erosion rate was dominant in many cases the measurements were used for testing both the empirical relationships between the channel rill egs and gully length and its eroded volume and among the morphological variables length width depth and volume describing the channelized process finally the rill and egs hydraulic geometry was modelled by three well known power equations relating the discharge with the mean flow velocity with the flow depth and with the width of each channel segment respectively the rill measurements also showed that the flow velocity was affected by the rill segment slope while the flow depth and width were controlled by the plot slope therefore three equations taking into account these slope effects were proposed to estimate the hydraulic characteristics of the rills monitored at the sparacia area

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

ambient noise tomography of the greater geneva basin in a geothermal exploration context the greater geneva basin is one of the key targets for geothermal exploration in switzerland until recently information about the subsurface structure of this region was mostly composed of well logs seismic reflection lines and gravity measurements as part of the current effort to further reduce subsurface uncertainty and to test passive seismic methods for exploration purposes we performed an ambient noise tomography of the greater geneva basin we used 1 5 years of continuous data collected on a temporary seismic network composed of 28 broadband stations deployed within and around the basin from the vertical component of the continuous noise recordings we computed cross correlation functions and retrieved rayleigh wave group velocity dispersion curves we then inverted the dispersion curves to obtain 2d group velocity maps and proceeded to a subsequent inversion step to retrieve a large scale 3d shear wave velocity model of the basin we discuss the retrieved features of the basin in the light of local geology previously acquired geophysical datasets and ongoing geothermal exploration the greater geneva basin is an ideal natural laboratory to test innovative geothermal exploration methods because of the substantial geophysical datasets available for comparison while we point out the limits of ambient noise exploration with sparse networks and current methodology we also discuss possible ways to develop ambient noise tomography as an affordable and efficient subsurface exploration method

incomplete self similarity and flow velocity in gravel bed channels velocity measurements previously carried out using both a miniature current flowmeter and an acoustic doppler velocimeter are used to verify the applicability of the incomplete self similarity theory to deduce the velocity profile in a gravel bed channel then for the velocity profiles having the maximum value below the free surface and for the s shaped profiles the power velocity distribution is corrected using a new divergence function for each value of the depth sediment ratio the nondimensional friction factor parameter is calculated by integration of the measured velocity distributions in the different verticals of the cross section finally a semilogarithmic flow resistance equation is empirically deduced

well bore bottom stress concentration and induced core fractures the orientation spacing and shape of drilling induced disking petal and petal centerline fractures in core commonly are remarkably uniform these fractures result from concentrations of in situ stress by the well bore bottom hole cavity and in oriented core their strikes commonly have been used as indicators of the horizontal principal stress directions however an understanding of how these varied fractures are produced has been limited by the lack of detailed knowledge of the distribution of stresses near the bottom hole in this paper we present our result of studying these stress concentrations using full three dimensional finite element modeling for a variety of applied far field in situ stress conditions and as a function of core stub length in nearly all cases purely tensional concentrated stresses are generated within the core by the compressive in situ stresses the directions and magnitudes of these tensions vary with the applied stress indicating the morphology of many of the observed drilling induced core fractures cupped shape disking fractures result from a state of uniform horizontal biaxial stress these fractures also initiate within the rock at the root of the core stub as the horizontal stresses become more anisotropic the point of fracture initiation shifts to the surface of the core and saddle shaped core disks are possible such fractures strike in the direction of the most compressive in situ horizontal principal stress increasing the magnitude of the overburden stress eventually results in petal and copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received april 1 1996 revised manuscript received december 2 1996 final acceptance june 19 1997 2institute of geophysics meteorology and space physics department of physics university of alberta edmonton alberta canada e mail yongyi phys ualberta ca doug phys ualberta ca this work is supported in part by nserc lithoprobe supporting science grant nserc and the alberta oil sand technology and research authority d schmitt acknowledges the assistance of the a v humboldt foundation during revisions of this paper constructive reviews and comments of b r kulander j c lorenz and s l dean were greatly appreciated this paper is lithoprobe submission number 882

structural analysis of cores and cuttings from the toa baja puerto rico borehole deformation structures in core samples and well cuttings from the toa baja borehole in puerto rico obtained from depths of 580 to 2700 meters can be divided into two major categories 1 structures resulting from compression and shear and 2 structures formed by extension generally the first ones are older and they are somewhat more abundant at horizons where fault zones occur as deduced from dipmeter readings and televiewer log these structures may have formed during an eocene thrusting event recognized regionally in puerto rico the extensional structures which almost always crosscut the compressional ones are filled with zeolite calcite prehnite or quartz there is poor correspondence between the abundance of these fractures and the position of the major fault zones the largest abundance of veins occurs between 1700 and 2100 meters depth they may be related to a phase of regional extension during the late paleogene

detailed recording of gully morphology in 3d through image based modelling abstract the ability to understand gully erosion development is closely related to our ability to quantify the morphology of gullies at present various technologies are at hand to collect data at increasing levels of detail however many of the developed technologies are time consuming difficult to apply or expensive as an alternative image based modelling offers a cost efficient flexible and rapid method to quantify gully morphology from photographs taken in the field in this study the use of image based modelling was tested and fine tuned to quantify the morphology of four gully heads in contrasting biophysical environments prone to gully erosion two bank gullies in central belgium and two permanent gullies in northern ethiopia ground photographs n 88 235 were taken with a reflex canon eos 450d camera having a 20 mm wide angle lens with a fixed focal length the data collection occurred during days of 30 100 cloud cover and after removing excessive vegetation in the gullies processing of the photographs occurred in photoscan 1 0 2 software using the semi automated structure from motion multi view stereo sfm mvs workflow and allowed to produce 3d digital elevation models with accuracies that range from millimetres to centimetres in addition for the same surface 2 5d models were created in arcgis gully morphological properties were derived and included cross sections total volume and volume of undercut walls and soil pipe inlets for the volume calculation optocat software was used cross sections were also quantified by tape meter measurements when compared to 3d models cross sections quantified from tape meter measurements and from 2 5d models underestimate the cross sectional area by

effect of saltating sediment load on the determination of the mean velocity of overland flow where overland flow velocity is measured using dye or salt tracing the mean velocity is often determined by multiplying the velocity of the leading edge of the tracer plume by a correction factor flume experiments show that a varies with both reynolds number and sediment load for sediment free flow over a sand covered bed is less than the theoretical value of 0 67 in laminar flow and increases rapidly with reynolds number in transitional flow and more slowly with reynolds number in turbulent flow for sediment laden flow decreases as sediment load increases in transitional and turbulent flows saltating sediment extracts momentum from the flow causing velocities near the bed to decrease and to decrease a multiple regression equation is developed which can be used to predict the value of from reynolds number and sediment load in transitional and turbulent overland flows

longitudinal velocity patterns and bed morphology interaction in a rill present day understanding of rill dynamics is hampered by a lack of detailed data on velocity distributions in rills the latter are dif cult to collect with traditional techniques due to the very low water depths and the relatively high ow velocities in rills the objectives of this paper were to investigate the feasibility of miniaturized acoustic doppler velocimeter madv measurements in rill ow and to explore longitudinal variations in ow velocities and their relationship with rill bed morphology detailed data on longitudinal ow velocity were required to achieve these objectives a 1 8 m long rill was formed freely in a ume at 5 slope and 0 001 m3 s 1 discharge rill topography was characterized by an alternation of steps and pools the ume surface was then xed to preserve rill roughness a topographical scanning of the entire ume surface was made velocity was measured with a madv along the rill and at different depths flow depth in a longitudinal direction was also measured using an elevation gauge a strong relationship exists between rill topography and ow hydraulics over steps ow was unidirectional and rapidly accelerating until a threshold froude number fn value between 1 3 and 1 7 was reached and a hydraulic jump occurred leading to the formation of a pool in the pool the ow pattern was multidirectional and complex the ow was subcritical when leaving the pool and accelerated over the next step until the threshold froude number value was again reached energy loss in the rill was concentrated in the pools mainly due to the action of a hydraulic jump this mechanism of energy dissipation appeared to be an essential factor in rill formation and bedform evolution copyright 2004 john wiley sons ltd

channel morphology gradient profiles and bed stresses during flood in a step pool channel abstract the stability of a step pool channel is investigated on the basis of measurements during a median annual flood the study reaches range in gradient from 5 to 10 and the flow was 3 m3 s 1 in an 8 m wide channel the estimated shear stress based on the channel gradient was 102 pa which implies that the channel ought to move half meter class boulders calculations of the shear stress using flow resistance equations yield values of about 30 pa these figures imply that the largest boulders in the channel could be moved in fact the channel is stable the effective stress remains well below the threshold to move the large structure forming boulders the steps are stable structures that result from interlocking of the larger stones they are semi randomly located depending on the location of keystones that are deposited in the channel by debris flows or fall out of the banks the high variation in step pool wavelength step height residual pool depth and pool length is indicative of the random nature of step location and structure along a reach there is no convincing evidence that special conditions govern their formation

dissipative analogies of step pool features from rills to mountain streams abstract in this paper the dissipative similarity of step pool units at different spatial scales ranging from rills to streams is analyzed this investigation benefits from the latest theoretical advances in open channel flow resistance high resolution topography from close range photogrammetry applied to rill erosion and the availability of published data from literature on step pool streams at first the integration of a power velocity distribution allowed to obtain a theoretically based expression of darcy weisbach friction factor in which function and exponent of the velocity profile are included then this theoretically deduced flow resistance relationship is calibrated and tested by flow measurements carried out in rill reaches where the step pool units occurred in particular the proposed function is calibrated using the measurements corresponding to 88 rill reaches shaped on a plot having a slope equal to 14 22 and 24 and the calibrated equation is also positively tested with measurements carried out in 48 rill reaches shaped on a 26 sloping plot for the rill flow the developed analysis stated that the friction factor is characterized by estimate errors which are less than or equal to 15 for 86 of cases and less than or equal to 10 for 70 of cases using measurements of flow velocity water depth width and bed slope measurements carried out in 109 reaches of step pool streams this investigation demonstrates that the theoretical flow resistance equation can be applicable to step pool streams carrying out a specific calibration of the function the comparison between the darcy weisbach friction factor values measured in streams and step pool rills demonstrates that in the stream features the friction factor values are on average higher than those related to rills with step pool sequences in conclusion the comparison between rills and streams with step pool units highlights that the same theoretical flow resistance equation can be applied even if a scale effect between the two features is detected

origin of step pool systems in mountain streams mountain streams very often present a step pool aspect antidune formation alone dispersion and sorting theory or velocity reversal as advocated for the origin of riffle pool sequences do not explain how steps and pools form experiments have been conducted to clarify their origin it was found that the step pool aspect appears after high flows had deformed the bed during the presented tests a self armoring process occurred which resulted in a stabilization of the bed when coarsening of the top layer was little classic antidunes resulted an important coarsening was accompanied by a structuring of the bed into roughness elements whose spacing did correspond to maximum flow resistance the substantial increase in resistance was an essential factor in bed stabilization

step pool formation models and associated step spacing step pool bedforms develop under conditions of high flow rates and high sediment influx and transport rates step setting events are capable of mobilizing and rearranging the large step forming grain sizes thus observations of the processes of step formation are limited to flume experiments the results of laboratory experiments involving active transport of widely sorted sediment including large grains whose deposition readily formed steps are presented over 350 step formations were observed and documented creating a large data set for detailing and evaluating step formation processes existing step formation models focus on step development from antidunes particle clusters transverse ribs or depositional berms or from a hydraulic regime that includes cascade flow and hydraulic jumps these models were developed using field measurements of artificial grade control structures or stable step pool systems during low flow conditions or degradational flume experiments where flows elucidated the step pool bedform in the channel profile but did not create equilibrium transport of the large step forming clasts this research evaluates the pre existing formation models and proposes three new models the rough bed exhumation and dune models the rough bed model was dominant throughout the experiments followed by the exhumation model and then the dune model a single model was not responsible for all step formations the rough bed exhumation and dune models all influenced step development and every step sequence was created through a mixture of formation processes this research generated a large data set where each step spacing is paired with the corresponding step formation model making it possible to identify a distinct exclusion zone length for each model thus given knowledge of the step formation model the minimum distance to the next step downstream can be predicted from the final spacing of a step sequence it may be possible to deduce the likely formation mechanisms active during a step resetting event copyright 2007 john wiley sons ltd

a boom in boomless seismology taking advantage of cheap long lasting sensors developed by the oil and gas industry seismologists are increasingly exploring the top 10 kilometers of the crust with dense surveys of hundreds or even thousands of seismometers what s more the surveys are being operated passively which means that ambient noise from earth is used to illuminate the subsurface passive surveys are cheaper and easier to permit than active surveys which rely on explosives or vibrations from special thumper trucks seismologists predict that the dense surveys will yield precision imaging of magma chambers underneath volcanos and earthquake rupture zones along faults

seasonal variations of seismic velocities in the san jacinto fault area observed with ambient seismic noise s u m m a r y we observe seasonal seismic wave speed changes dv v in the san jacinto fault area and investigate several likely source mechanisms velocity variations are obtained from analysis of 6 yr data of vertical component seismic noise recorded by 10 surface and six borehole stations we study the interrelation between dv v records frequency dependent seismic noise properties and nearby environmental data of wind speed rain ground water level barometric pressure and atmospheric temperature the results indicate peak to peak seasonal velocity variations of 0 2 per cent in the 0 5 2 hz frequency range likely associated with genuine changes of rock properties rather than changes in the noise field phase measurements between dv v and the various environmental data imply that the dominant source mechanism in the arid study area is thermoelastic strain induced by atmospheric temperature variations the other considered environmental effects produce secondary variations that are superimposed on the thermal based changes more detailed work with longer data on the response of rocks to various known external loadings can help tracking the evolving stress and effective rheology at depth

flow velocity profiles in gravel bed rivers velocity measurements carried out in a rectangular laboratory flume having a gravel bed are presented the measurements are carried out for four different bed shapes characterized from different concentrations of coarser elements and for the two conditions of small and large scale roughness the analysis showed that the dean profile is usable to establish the velocity profile for both hydraulic conditions for small scale hydraulic condition an indirect estimate procedure of the coefficients of dean profile is proposed

the morphologic structure of step pools in mountain streams abstract step pool sequences in streams in the santa monica mountains of southern california impart a characteristic morphologic structure that varies with slope but despite the strong association with slope that suggests a direct process control analysis of 464 step pools in 13 study reaches reveals the relationship to reflect correlation but not necessarily causality the direct control on step height is particle size whereas discharge is the probable causal process determining step wavelength because both particle size and discharge generally change with channel slope downstream a slope variation with step wavelength and height is the apparent indirect geometric result a conceptual model of process form linkages is proposed based on these results whereby the step pool morphology is produced by positive relationships between wavelength and discharge and between height and particle size the model offers new insights for explaining the step pool morphology and it is potentially useful in channeling future efforts toward the appropriate scales and variables

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

drilling induced core fractures and in situ stress the relationship between the shapes of drilling induced core fractures and the in situ state of stress is developed the stress concentrations at the well bore bottom are first determined using a complete three dimensional finite element analysis existing in situ compressional stresses generate large tensions in the immediate vicinity of the bottom hole which are sufficient to rupture the rock tensile fracture trajectories within these concentrated stress fields are predicted using a simple model of fracture propagation these modeled fracture trajectories resemble well the observed shapes of drilling induced core disking petal and petal centerline fractures further this agreement suggests that both the shape of the drilling induced fracture and the location at which it initiates depends on the in situ stress state existing in the rock mass prior to drilling the core fractures contain substantial information on in situ stress conditions in all faulting regimes the coring induced fractures initiate near the bit cut except for most cases under thrust faulting regime where the fracture initiates on the well bore axis further under thrust faulting conditions only disk fractures appear possible both petal and disking fractures can be produced in strike slip and normal faulting regimes depending upon the relative magnitudes between the least compressive horizontal principal stress and the vertical overburden stress the predicted fracture shapes are in good qualitative agreement with observations of drilling induced fractures described in the literature from laboratory experiments and field programs in which in situ stresses are measured by other means the relationship of the morphology of coring induced fractures and in situ stresses suggests that the fractures can be used as independent complementary indicators in identifying stress regimes

characteristic dimensions of the step pool bed configuration an experimental study 1 the dominant dimension of the step pool bed form is its spacing which is determined by the locations at which large step forming grains are deposited we conducted laboratory experiments involving active transport of widely sorted sediment including large grains whose deposition readily formed steps direct observation of step development indicates that deposition of step forming grains was predominantly associated with bed roughness impeding transport or with earlier flow and transport conditions not contemporaneous with step development neither mechanism is likely to occur at regular locations on the bed measured step spacing was found to follow a poisson distribution supporting the conclusion that steps do not develop in preferred or regular locations this contrasts with previous arguments that regular step spacing develops in response to deposition forced at regular locations beneath water surface waves we observe neither the regular distribution nor the associated depositional mechanism although the observed step distribution is well defined with a strong mode that could be interpreted as indicating regular spacing

the impact of exceptional events on erosion bedload transport and channel stability in a step pool channel sediment transport in the erlenbach a small stream with step pool morphology in the canton of schwyz switzerland has been monitored for more than 20 years during this time three exceptional events events with high sediment yield and long return times that have a large effect on channel morphology have impacted the stream and partly or completely rearranged the existing step pool morphology in the aftermath of the events sediment transport rates at a given discharge and total sediment yield remained elevated for about a year or longer for the last event dated on the 20 june 2007 observations of boulder mobility and step destruction were used to interpret channel stability boulders with median diameters of up to 135 cm and estimated weights of more than 2 5 tons have moved during the 2007 event using hydraulic observations and shear stress calculations boulders up to 65 cm in diameter were predicted to have been fully mobile in peak conditions even if form resistance and increased critical stresses needed for the initiation of motion in steep streams were taken into account for two of the events estimated peak shear stresses at the bed exceeded 1000 pa calculated both from observations of the flow hydraulics and from boulder mobility this suggests that highly energetic flows occur relatively frequently in small steep streams and that large boulders can be transported by fluvial processes in such streams the observations have potential significance for hazard risk mitigation stream engineering and restoration copyright 2009 john wiley sons ltd

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

significance of coring induced fractures in mesaverde core northwestern colorado several types of mechanically induced fractures occur in mesaverde core from the u s department of energy s multiwell experiment wells two of these types of fractures have significance for the determination of in situ stress orientations scribe line fractures originate at orientation grooves on the surface of the core and are initiated by scribing knives in the core barrel minutes after the core is cut free from the surrounding rock in sandstone core these fractures strike parallel to the maximum in situ horizontal stress direction that has been determined in these wells by anelastic strain recovery measurements coring induced petal and petal centerline fractures form just below the advancing core bit their strike is also controlled by the in situ stress field loc lly however strike may be secondarily influenced by shear stress created by bit rotation reorienting petal fracture strikes in the direction of rotation nevertheless in many situations the orientations of these two types of fractures may be used to determine the orientation of the horizontal in situ stress field if the core is oriented even in unoriented core the relative orientation between in situ stress and natural fractures may be determined

modeling the topography of shallow braided rivers using structure from motion photogrammetry abstract recent advances in computer vision and image analysis have led to the development of a novel fully automated photogrammetric method to generate dense 3d point cloud data this approach termed structure from motion or sfm requires only limited ground control and is ideally suited to imagery obtained from low cost non metric cameras acquired either at close range or using aerial platforms terrain models generated using sfm have begun to emerge recently and with a growing spectrum of software now available there is an urgent need to provide a robust quality assessment of the data products generated using standard field and computational workflows to address this demand we present a detailed error analysis of sub meter resolution terrain models of two contiguous reaches 1 6 and 1 7 km long of the braided ahuriri river new zealand generated using sfm a six stage methodology is described involving i hand held image acquisition from an aerial platform ii 3d point cloud extraction modeling using agisoft photoscan iii georeferencing on a redundant network of gps surveyed ground control points iv point cloud filtering to reduce computational demand as well as reduce vegetation noise v optical bathymetric modeling of inundated areas and vi data fusion and surface modeling to generate sub meter raster terrain models bootstrapped geo registration as well as extensive distributed gps and sonar based bathymetric check data were used to quantify the quality of the models generated after each processing step the results obtained provide the first quantified analysis of sfm applied to model the complex terrain of a braided river results indicate that geo registration errors of 0 04 m planar and 0 10 m elevation and vertical surface errors of 0 10 m in non vegetation areas can be achieved from a dataset of photographs taken at 600 m and 800 m above the ground level these encouraging results suggest that this low cost logistically simple method can deliver high quality terrain datasets competitive with those obtained with significantly more expensive laser scanning and suitable for geomorphic change detection and hydrodynamic modeling