an approximation for the xu white velocity model in 1995 s xu and r e white described a method for estimating compressional and shear wave velocities of shaley sandstones from porosity and shale content their model was able to predict the effect of increasing clay content on compressional wave velocity observed in laboratory measurements a key step in the xu white method estimates dry rock bulk and shear moduli for the sand shale mixture this step is performed numerically by applying the differential effective medium method to the kuster toksoz equations for ellipsoidal pores this step is computationally intensive using reasonable assumptions about dry rock elastic properties this step can be replaced with a set of approximations for dry rock bulk and shear moduli numerical experiments show an extremely close match between velocities obtained with these approximations and velocities computed with the differential effective medium method these approximations simplify the application of the xu white method and make the method computationally more efficient they also provide insight into the xu white method for example these approximations show how the xu white model is related to the critical porosity model

frame moduli of unconsolidated sands and sandstones in this study we investigate the elastic moduli of the empty grain framework the frame moduli in unconsolidated sands and consolidated sandstones the work was done to improve the interpretation of seismic amplitude anomalies and amplitude variations with offset avo associated with hydrocarbon reservoirs we developed a laboratory apparatus to measure the frame poisson s ratio and young s modulus of unconsolidated sands at seismic frequencies 0 2 to 155 hz in samples approximately 11 cm long we used ultrasonic pulse velocity measurements to measure the frame moduli of consolidated sandstones we found that the correlation coefficient between the frame poisson s ratio a and the mineral poisson s ratio m is 0 84 in consolidated sandstones and only 0 28 in unconsolidated sands the range of a values in unconsolidated sands is 0 115 to 0 237 mean 0 187 standard deviation 0 030 and a cannot be estimated without core or log analyses frame moduli analyses of core samples can be used to cal

seismic attenuation and velocity dispersion in heterogeneous partially saturated porous rocks summary using a numerical approach we explore wave induced fluid flow effects in partially saturated porous rocks in which the gas water saturation patterns are governed by mesoscopic heterogeneities associated with the dry frame properties the link between the dry frame properties and the gas saturation is defined by the assumption of capillary pressure equilibrium which in the presence of heterogeneity implies that neighbouring regions can exhibit different levels of saturation to determine the equivalent attenuation and phase velocity of the synthetic rock samples considered in this study we apply a numerical upscaling procedure which permits to take into account mesoscopic heterogeneities associated with the dry frame properties as well as spatially continuous variations of the pore fluid properties the multiscale nature of the fluid saturation is taken into account by locally computing the physical properties of an effective fluid which are then used for the larger scale simulations we consider two sets of numerical experiments to analyse such effects in heterogeneous partially saturated porous media where the saturation field is determined by variations in porosity and clay content respectively in both cases we also evaluate the seismic responses of corresponding binary patchy type saturation patterns our results indicate that significant attenuation and modest velocity dispersion effects take place in this kind of media for both binary patchy type and spatially continuous gas saturation patterns and in particular in the presence of relatively small amounts of gas the numerical experiments also show that the nature of the gas distribution patterns is a critical parameter controlling the seismic responses of these environments since attenuation and velocity dispersion effects are much more significant and occur over a broader saturation range for binary patchy type gas water distributions this analysis therefore suggests that the physical mechanisms governing partial saturation should be accounted for when analysing seismic data in a poroelastic framework in this context heterogeneities associated with the dry frame properties which do not play important roles in wave induced fluid flow processes per se should be taken into account since they may determine the kind of gas distribution pattern taking place in the porous rock

investigation of rate of erosion of soils in embankment dams the slot erosion test and the hole erosion test have been developed to study the erosion characteristics of soil in cracks in embankment dams the erosion characteristics are described by the erosion rate index which measures the rate of erosion and the critical shear stress which represents the minimum shear stress when erosion starts values of the erosion rate index span from 0 to 6 indicating that soils can differ in their rates of erosion by up to 10 6 times the rate of erosion is shown to be dependent on the soil fines and clay sized content plasticity and dispersivity compaction water content density and degree of saturation and clay mineralogy and possibly the presence of cementing materials such as iron oxides coarse grained noncohesive soils in general erode more rapidly and have lower critical shear stresses than fine grained soils knowledge of the erosion characteristics of the soil in the core of an embankment dam aids in the assessment of the likelihood of dam failure due to piping erosion

construction of a hydrologic model for estimating wadi runoff and groundwater recharge in the eastern desert egypt we constructed a hydrologic model to estimate the groundwater recharge rate for alluvial aquifers of the eastern desert from sporadic precipitation over the red sea hills to estimate initial losses over sub basins transmission losses through channel routing and downstream runoff we developed an integrated model combining spatial rainfall distribution an appropriate basin unit hydrograph and appropriate infiltration parameters watersheds and stream networks identified from digital terrain elevation data were verified by comparison with co registered landsat thematic mapper scenes and geologic maps records of a november 1994 storm event acquired from rain gauges along the nile river and the red sea shore were used to generate a spatial precipitation distribution for the study area a 2 hour design hyetograph was adopted from rain gauge data for the 1994 flood event the model was tested against records from the november 1994 flood event at the outlets of the tarfa and hammamat watersheds groundwater recharge rates were estimated for the alluvial aquifers within the major watersheds of the north eastern desert we estimated that during the 1994 flood event the ground water recharge through transmission losses ranged from 21 to 31 tarfa 15 8 x 10 sup 6 m sup 3 asyuti 20 x 10 sup 6 more m sup 3 qena 49 x 10 sup 6 m sup 3 hammamat 59 x10 sup 6 m sup 3 of the precipitated volume the initial losses ranged from 65 to 77 only 3 7 of the precipitation reached the watershed outlets archival data show that rainfall events of the size of the november 1994 storm or larger occur every 40 months thus the annual recharge rates for the tarfa asyuti qena and hammamat alluvial aquifers are estimated at 4 7 x 10 sup 6 m sup 3 6 x 10 sup 6 m sup 3 14 7 x 10 sup 6 m sup 3 and 17 7 x10 sup 6 m sup 3 respectively implications for the use of these renewable ground waters and similar water resources in other arid areas of egypt and in neighboring countries are clear less

estimation of runoff critical shear stress for soil erosion from soil shear strength abstract critical shear stress is an important soil parameter governing detachment by runoff which appears in numerous erosion models soil shear strength has been often presented as the best soil property to predict critical shear stress however only a few studies have documented the relationship between soil shear strength and critical shear stress and the results obtained have sometimes seemed contradictory this is why we have put together all available data about the relationship between critical shear stress and soil shear strength in order to analyse and discuss its significance and its generality results showed that contradictions between different studies mainly arise because total shear stress is a poor predictor of detachment on rough soils when grain shear stress is used rather than total shear stress a significant relationship between saturated soil shear strength and critical shear stress does exist soil shear strength may thus be used to predict critical grain shear stress however it is recalled that in general only total shear stress is predicted by erosion models which makes detachment predictions difficult on rough natural soils

analysing sand dominated channel systems for potential gas hydrate reservoirs using an avo seismic inversion technique on the southern hikurangi margin new zealand abstract gas hydrates have recently been recognised as a class of unconventional petroleum resource and the economic viability of gas production from hydrates is now being viewed as a realistic possibility within the next decade therefore potential offshore hydrate accumulations in the world class endowed gas hydrate province the hikurangi margin new zealand represent a significant medium to long term opportunity to meet the country s future energy requirements in this paper we delineate a potential gas hydrate reservoir in the east coast basin new zealand and quantitatively estimate its gas hydrate concentrations from 2d seismic data with no well information available the target is interesting for exploration since it shows evidence for gas hydrate bearing sands in particular buried channel systems we use a combined analysis of high resolution velocity analysis amplitude versus offset avo attribute and avo inversion to investigate whether we can identify regions that are likely to contain highly concentrated gas hydrates and whether they are likely to be sand dominated to estimate hydrate concentrations we apply a rock physics model our results indicate the presence of several up to 200 m thick zones that are likely to host gas hydrates with one location predicted to consist of high permeable channel sands and an inferred gas hydrate saturation of 25 these findings suggest significant amounts of gas hydrates may be present in high quality reservoirs on this part of the margin

identifying patchy saturation from well logs gassmann s 1951 equations relate the elastic bulk ksat and shear gsat moduli of a fully saturated rock to the elastic bulk and shear moduli of the dry rock frame kdry and gdry respectively porosity and the bulk moduli of the mineral phase ks and pore fluid kf

assessment of gas hydrate saturations in the makran accretionary prism using the offset dependence of seismic amplitudes we estimate the saturations of gas hydrate and free gas based on measurements of seismic reflection amplitude variation with offset avo for a bottom simulating reflector coupled with rock physics modeling when we apply the approach to data from a seismic line in the makran accretionary prism in the arabian sea the results reveal lateral variations of gas hydrate and free gas saturations of 4 29 and 1 7 5 respectively depending on the rock physics model used to relate seismic velocity to saturation our approach is simple and easy to implement

velocity determination for pore pressure prediction overpressured formations exhibit several of the following properties when compared with a normally pressured section at the same depth dutta 2002 1 higher porosities 2 lower bulk densities 3 lower effective stresses 4 higher temperatures 5 lower interval velocities and 6 higher poisson s ratios

impact of the geomorphology and soil management on the development of waterlogging in closed drainage basins of egypt and saudi arabia this paper investigates the interplay of the catchment geomorphology hydrology and soil properties on the development of waterlogging and land degradation within different dry land catchments in egypt and saudi arabia multi temporal remote sensing data of the landsat thematic mapper and enhanced thematic mapper were collected and processed to detect the land cover changes and development of cultivations within the two areas the shuttle radar topography mission digital elevation model were hydrologically processed to delineate the catchment morphometrical parameters and to examine the spatial distribution of cultivated fields and their relation to the extracted drainage networks the fluvial channels of the farafra oasis have largely been obliterated by the prevailing aridity and often buried under aeolian deposits the soil of these areas are mainly lithic with a high calcium carbonate content thus limiting the downward percolation of excess irrigation water and therefore develop perched water table and seepage through the buried fluvial channels on the other hand the cultivations of tabuk catchment which has similar geomorphologic setting to the farafra oasis have shown no signs for waterlogging this situation is could be related to the different soil properties the spatial distribution of cultivated areas and the adopted irrigation methods via pivots the inactive alluvial channels landforms and irrigation methods have to be considered when planning for a new cultivation in dry land catchments to better control waterlogging hazard the dry drainage concept can be implemented as the drainage and seepage water which can be conveyed into certain abandoned playas for evaporation

integration of geological investigations with multi gis data layers for water resources assessment in arid regions el ambagi basin eastern desert egypt water resources assessment in arid lands is of a particular interest not only in scientific terms but also under the concept of sustainable development the study area el ambagi basin represents a remote arid area with a scarcity of data the measured effective porosity and permeability revealed high potentialities of the nubian sandstone and oligocene sediments the hydrogeologic setting indicates favorable conditions for groundwater accumulation where there is an opportunity of recharge and thus the sustainability of the groundwater the research approach is based on geological investigations as well as several data layers in the gis environment including landforms lithology slope soil morphometric parameters structural lineaments and geophysical data several specific sites were suggested as targets for future groundwater explorations the studied basin contains four sub basins which have an intensive drainage network the morphometric parameters revealed that they have potential for surface runoff occurrence and also for groundwater recharge two of the investigated sub basins show high hazard degrees and should be protected to avoid flash floods the estimated runoff volume from a single rainfall event 27 mm can reach 3316 42 103 m3 hence management of rainwater harvesting and protection measures against flash floods are necessary a future water resources management strategy based on results of the multidisciplinary study is proposed

focussed fluid flow on the hikurangi margin new zealand evidence from possible local upwarping of the base of gas hydrate stability the southern hikurangi subduction margin is characterized by significant accretion with predicted high rates of fluid expulsion bottom simulating reflections bsrs are widespread on this margin predominantly occurring beneath thrust ridges we present seismic data across the porangahau ridge on the outer accretionary wedge the data show high amplitude reflections above the regional bsr level based on polarity and reflection strength we interpret these reflections as being caused by free gas we propose that the presence of gas above the regional level of bsrs indicates local upwarping of the base of gas hydrate stability caused by advective heatflow from upward migrating fluids although we cannot entirely rule out alternative processes simplified modelling of the increase of the thermal gradient associated with fluid flow suggests that funnelling of upward migrating fluids beneath low permeability slope basins into the porangahau ridge would not lead to the pronounced thermal anomaly inferred from upwarping of the base of gas hydrate stability focussing of fluid flow is predicted to take place deep in the accretionary wedge and or the underthrust sediments above the high amplitude reflections sediment reflectivity is low a lack of lateral continuity of reflections suggests that reflectivity is lost because of a destruction of sediment layering from deformation rather than gas hydrate related amplitude blanking structural permeability from fracturing of sediments during deformation may facilitate fluid expulsion on the ridge a gap in the bsr in the southern part of the study area may be caused by a loss of gas during fluid expulsion we speculate that gaps in otherwise continuous bsrs that are observed beneath some thrusts on the hikurangi margin may be characteristic of other locations experiencing focussed fluid expulsion

investigation of geotechnical parameters affecting electrical resistivity of compacted clays abstractthe use of resistivity imaging ri in subsurface investigation has increased in recent years ri is a non destructive method and provides a continuous image of the subsurface however only qualitative evaluation of the subsurface can be obtained from ri the correlations between ri results and geotechnical engineering properties of soils have become important for site investigation using this method the primary objective of the current study was to determine the geotechnical parameters affecting electrical resistivity of compacted clays understanding the influential factors will be helpful in determining the correlations between ri results and geotechnical properties of soil the effects of moisture content unit weight degree of saturation specific surface area percentages of pores and ion composition on soil resistivity were investigated soil samples used were classified as highly plastic clay ch according to the unified soil classification system high energy x ray fluorescence tests

effects of digital elevation model map scale and data resolution on a topography based watershed model the effects of digital elevation model dem map scale and data resolution on watershed model predictions of hydrologic characteristics were determined for topmodel a topography based watershed model the effects of topography on watershed hydrology are represented in topmodel as the distribution of ln a tan b where ln is the napierian logarithm a is the upslope area per unit contour length and tan b is the gravitational gradient the minimum maximum mean variance and skew values of the ln a tan b distribution were computed from 1 24 000 scale 24k dems at 30 and 90 m resolutions and from 1 250 000 scale 250k dems at 90 m resolution for 71 areas in pennsylvania new york and new jersey an analysis of topmodel showed that model predictions of the depth to the water table the ratio of overland flow to total flow peak flow and variance and skew of predicted streamflow were affected by both the dem map scale and data resolution further topmodel analyses showed that the effects of dem map scale and data resolution on model predictions were due to the sensitivity of the predictions to the mean of the ln a tan b distribution which was affected by both dem map scale and data resolution dem map scale affected the mean of the ln a tan b distribution through its influence on the mean of the ln a distribution which characterizes land surface shape and the mean of ln 1 tan b distribution which characterizes land surface slope dem resolution in contrast affected the mean of the ln a tan b distribution primarily by its influence on the mean of the ln a distribution

the quaternary development of tributary channels to the nile river at kom ombo area eastern desert of egypt and their implication for groundwater resources the dry wadis ephemeral channel constituting the main tributaries to the nile river in kom ombo are structurally and tectonically controlled and exhibit complex drainage pattern this complicated drainage pattern is inherited from the morpho tectonic evolution of the ancestral nile river protonile which drained the eastern desert during the middle pleistocene a digital elevation model derived from shuttle radar topography mission data is used to delineate the contemporary drainage networks and their catchments satellite images acquired during a flash flood event were used to validate the delineated watershed divides and flow pathways particularly where the courses of dry wadis are interlocked currently the westward flow of wadi abu suberah is derived from a small area in the eastern desert as the palaeo upper reaches of this wadi were captured due to tectonic movements along nw se and n s faults by wadis in the kharit and elewa areas the influence of these tectonic movements on groundwater distribution is also shown where the deep nubian aquifer discharges its water into the quaternary aquifer through fault planes the northward flowing protonile main course has tectonically shifted from the gallaba plain in the western desert eastward to the current nile river course this shift has produced several cut off segments of the palaeo tributary drainage that was originally flowing westward towards the old protonile main course in the gallaba plain however these segments have reversed their surface run off flow directions eastward towards the current nile course they could include potential groundwater resources as their alluvium may be still recharged by the nile river copyright 2010 john wiley sons ltd

paleoflood hydrology and extraordinary flood events paleoflood hydrology is the study of past or ancient flood events the most accurate technique involves the analysis of slackwater deposits and paleostage indicators swd psi slackwater deposits are sand and silt emplaced from suspension in exceptionally deep high velocity floods that characterize narrow deep canyons in resistant geologic materials these and other paleostage indicators are used to establish hydraulic grade lines for the generating flow events favorable sites for slackwater deposition include channel margin areas where stresses and velocities are reduced below critical values necessary to maintain fine grained bedload material sand and silt in suspension computerized procedures for hydraulic flow modeling are used to tie the elevations of the highest slackwater deposits to surveyed river cross sections the flood discharges calculated by this method can be calibrated through the study of modern floods on gaged rivers correlation of multiple swd psi sites along a river reach is used to identify the maximum paleostage achieved by a given flood advances in the dating of flood deposits permit estimates of flood frequency to be made extending over a data base of thousands of years the major geochronologic tool is radiocarbon dating of various kinds of organic matter intercalated with the slackwater deposits an important development is the use of the tandem accelerator mass spectrometer for direct measurement of 14c tiny blebs of charcoal seeds and other organics can be analyzed in order to date ancient flood deposits of hydrologic significance since swd psi studies yield very accurate determinations of paleoflood ages and magnitudes there is a pressing need for new statistical procedures that make optimum use of the information content in paleoflood records for flood frequency analysis nevertheless swd psi paleoflood hydrology has moved beyond the research phase its use should be encouraged in evaluating past experience of extraordinary floods at appropriate hazardous sites

experimental quantification of the seismoelectric transfer function and its dependence on conductivity and saturation in loose sand under certain circumstances seismic propagation within porous media may be associated to a conversion of mechanical into electromagnetical energy known as a seismoelectromagnetic phenomemon the propagation of fast compressional p waves is more specifically associated to manifestations of a seismoelectric field linked to fluid flow within the pores the analysis of seismoelectric phenomena which requires combining the theory of electrokinetics to biot s theory of poroelasticity provides us with a transfer function noted e u that links the coseismic seismoelectric field e to the seismic acceleration u in order to measure the transfer function we have developed an experimental set up enabling seismoelectric laboratory observation in unconsolidated quartz sand within the kilohertz range the investigation focused on the impact of fluid conductivity and water saturation over the coseismic seismoelectric field during the experiment special attention was given to the accuracy of electric field measurements we concluded that in order to obtain a reliable estimate of the electric field amplitude the dipole from which the potential differences are measured should be of much smaller length than the wavelength of the propagating seismic field time lapse monitoring of the seismic velocities and seismoelectric transfer functions were performed during imbibition and drainage experiments in all cases the quantitative analysis of the seismoelectric transfer function e u was in good agreement with theoretical predictions while investigating saturation variations from the residual water saturation to full saturation we showed that the e u ratio undergoes a switch in polarity at a particular saturation s also implying a sign change of the filtration traducing a reversal of the relative fluid displacement with respect to the frame this sign change at critical saturation s stresses a particular behaviour of the poroelastic medium the dropping of the coseismic electric field to zero traduces the absence of relative pore fluid displacements representative of a biot dynamically compatible medium we concluded from our experimental study in loose sand that measurements of the coseismic seismoelectric coupling may provide information on fluid distribution within the pores and that the reversal of the seismoelectric field may be used as an indicator of the dynamically compatible state of the medium

downhole log evidence for the coexistence of structure ii gas hydrate and free gas below the bottom simulating reflector in the south china sea abstract stratigraphic layered pore filling gas hydrates are identified above the bottom simulating reflector bsr using the well log and core data acquired at sites w11 and w17 during the third gas hydrate drilling expedition conducted by china s geological survey guangzhou marine geological survey gmgs3 in the south china sea a seismic profile near site w17 reveal the presence of two bsrs i e double bsr which we show to relate to zones of structure i gas hydrate i bsr and structure ii gas hydrate ii bsr well log data from site w17 between the i bsr projected depth of 250 mbsf and ii bsr projected depth of 330 mbsf showed anomalous responses for gas hydrate bearing sediments with high resistivity high s wave velocity and alternating high and low p wave velocities pressure core data support the interpretation that structure ii gas hydrate occurs at a depth of 263 mbsf at site w17 the cross plot between log derived neutron and density porosities reveals a free gas bearing layer at a depth of 258 270 mbsf suggesting gas hydrate coexists with free gas between the i bsr and the ii bsr synthetic seismograms generated from the p wave velocity and density logs further support the presence of free gas in this section based on the coexistence of hydrate free gas and water the simplified three phase equation stpe was modified to simultaneously estimate free gas and hydrate saturations beneath the i bsr from p wave and s wave velocity logs assuming uniform or patchy distributions of free gas the estimated free gas and hydrate saturations together with gas compositions from pressure core samples collectively indicate that structure ii gas hydrate and free gas are interbedded and coexist below the i bsr at site w17 our study of the coexistence of gas hydrate and free gas between the double bsr at site w17 provides new insights into gas hydrate systems in nature that contain more complex gas chemistries

estimating rock porosity and fluid saturation using only seismic velocities evaluation of the fluid content in deep earth reservoirs or fluid contaminants in shallow earth environments has required the use of geophysical imaging methods such as seismic reflection prospecting interpretation of seismic velocities and amplitudes is based on theories of fluid saturated and partially saturated rocks that have been available since the 1950s here we present a new synthesis of the same physical concepts that uses compressional wave velocities together with shear wave velocities in a scheme that is much simpler to understand and apply yet yields detailed information about porosity and fluid saturation magnitudes and spatial distribution the key idea revolves around the fact that the density and the lame elastic parameter are the only two parameters determining seismic velocities that also contain information about fluid saturation at low enough frequencies gassmann s well known equations show that the shear modulus is independent of the fluid saturation level we use these facts to

hydraulic erosion of cohesive riverbanks abstract this study identifies and assesses the controls on hydraulic erosion of cohesive riverbanks on a 600 m reach of an urban ephemeral stream with active bank erosion we examined hydraulic bank erosion by separating estimated bank shear stress into four properties magnitude duration event peak and variability the values of these independent variables were used as a bank erosion context at three transects stepwise regression showed that the event peak maximum peak of excess shear stress best predicts cohesive bank erosion at the two transects with moderate critical shear stresses 1 93 4 08 n m 2 while the variability all peaks of excess shear stress best predicts erosion at the transect with low critical shear stress 0 95 n m 2 these results suggest that the amount of hydraulic erosion of cohesive riverbanks is dictated by flow peak intensities finally the results of this study were combined with results from previous bank erosion studies to produce a conceptual model for estimating bank erosion rates based on their silt clay content

predicting soil erodibility using electrical resistivity tomography abstractscour is responsible for approximately 60 of all bridge collapses in the united states a large number of bridges are listed in the national bridge inventory as scour critical however ev

combined palaeoflood and rainfall runoff assessment of mountain floods spanish pyrenees abstract this paper reports a comparative study of the use of palaeohydrological and hydrological techniques to estimate magnitude and frequency of floods applied to two high gradient small catchments located in the spanish central pyrenees the aras basin 18 6 km2 the montardit basin 15 2 km2 palaeohydrological palaeoflood techniques based on palaeostage indicators and the application of both manning s equation and critical flow equation were used to estimate discharge values corresponding to seven cross sections of the montardit stream this method yielded discharges ranging from 7 to 112 m3 s 1 palaeoflood and historical flood analyses indicated a greater frequency of high magnitude events for both the aras and montardit basins than suggested by the application of two different methodologies based on precipitation data the rational and the unit hydrograph methods the 1996 aras basin flood was modelled using the unit hydrograph method with most reliable results 217 m3 s 1 obtained using a semidistributed basin model for small ungauged mountain basins palaeoflood reconstruction provides an excellent tool to obtain past flood discharges on which to base the calibration of parameters e g runoff threshold used in rainfall runoff methods it is proposed that the combined results of long term flood record analysis based on palaeoflood and historical data and of standard hydrometeorological methods will aid in the assessment of flood risks for application to the design of emergency measures and floodplain management in ungauged mountain streams

practical seismic petrophysics the effective use of log data for seismic analysis a quick scan of the seg web site shows that the phrase seismic petrophysics has been used explicitly in the title of a paper or abstract six times the earliest of which was by williams et al in 1996 the hugoton cross well survey a direct look at stratigraphy seismic petrophysics and shale anisotropy however the first attempt at a definition and an expanded description of seismic petrophysics was published by wayne pennington in the leading edge in 1997 seismic petrophysics an applied science for reservoir geophysics he defines seismic petrophysics as follows the purposeful application of rock physics theory as calibrated by laboratory and well measurements to the interpretation of seismic data

case histories in soil and rock erosion woodrow wilson bridge brazos river meander normandy cliffs and new orleans levees this lecture presents four case history examples of erosion processes because the topic of soil and rock erosion is relatively underdeveloped in geotechnical engineering an introduction precedes the case histories to describe some fundamental aspects of erosion erosion involves the soil or rock through its erodibility the water through its velocity and the geometry of the obstacle through its size and shape knowledge of these three components is needed for any erosion problem to be studied and solved a set of fundamental issues are addressed in the first part including an erodibility classification for soils and rocks an explanation of the stresses imposed by the water on the soil water or rock water interface and an explanation of how the geometry impacts the problem the woodrow wilson bridge case history outlines a new and less conservative method to compute the scour depth and gives examples of bridge scour calculations the brazos river meander case history outlines a new method to predict m

integration of remote sensing and gis for modelling flash floods in wadi hudain catchment egypt this paper presents a new approach to modelling flash floods in dryland catchments by integrating remote sensing and digital elevation model dem data in a geographical information system gis the spectral reflectance of channels affected by recent flash floods exhibit a marked increase due to the deposition of fine sediments in these channels as the flood recedes this allows the parts of a catchment that have been affected by a recent flood event to be discriminated from unaffected parts using a time series of landsat images using images of the wadi hudain catchment in southern egypt the hillslope areas contributing flow were inferred for different flood events the srtm3 dem was used to derive flow direction flow length active channel cross sectional areas and slope the manning equation was used to estimate the channel flow velocities and hence the time area zones of the catchment a channel reach that was active during a 1985 runoff event that does not receive any tributary flow was used to estimate a transmission loss rate of 7 5 mm h 1 given the maximum peak discharge estimate runoff patterns resulting from different flood events are quite variable however the southern part of the catchment appears to have experienced more floods during the period of study 1984 2000 perhaps because the bedrock hillslopes in this area are more effective at runoff production than other parts of the catchment which are underlain by unconsolidated quaternary sands and gravels due to high transmission loss runoff generated within the upper reaches is rarely delivered to the alluvial fan and shalateen city situated at the catchment outlet the synthetic gis based time area zones on their own cannot be relied on to model the hydrographs reliably physical parameters such as rainfall intensity distribution and transmission loss must also be considered copyright 2009 john wiley sons ltd

hydraulics and basin morphometry of the largest flash floods in the conterminous united states abstract the maximum rainfall runoff floods measured by indirect methods in small basins 0 39 370 km2 in the conterminous united states are examined this analysis identified twelve floods that were the largest ever measured these floods all occurred in semiarid to arid areas for eleven of the twelve largest rainfall runoff floods measured in small basins by the slope area method values of hydraulic depth hydraulic radius width depth ratio n value mean velocity velocity head coefficient froude number water surface energy and channel slopes shear stress and unit stream power are tabulated estimated composite n values weighted by subsection conveyance range from 0 028 to 0 048 with a mean of 0 038 mean velocities ranged from 3 47 to 9 97 m s 1 froude numbers ranged from 0 81 to 2 49 with 9 of 12 floods having values greater than 1 00 water surface energy and channel slopes vary considerably for each flood energy slope always was less than water surface slope by values of 1 104 channel slope was greater than energy slope in eight floods shear stresses ranged between 61 and 855 n m 2 and unit stream power from 212 to 8131 w m 1 floods in these small basins produced shear stresses and unit stream powers several hundred times greater than floods in large rivers floods on other small streams with smaller unit discharges produced greater shear stresses and stream powers this indicates that the force of a flood is controlled by the depth slope product not absolute discharge in the twelve watersheds studied basin relief ranged from 165 to 1280 m elongation ratios ranged from 0 55 to 0 80 the number of first order streams basin magnitude ranged from 10 to 4297 drainage density ranged from 4 1 to 10 9 km km 2 basin slope ranged from 0 0043 to 0 2486 relief ratio ranged from 0 0097 to 0 34 ruggedness number ranged from 0 69 to 7 17 and first order channel frequency ranged from 5 1 to 38 6 km 2 elongation ratios were larger and drainage density and first order channel frequency lower than other small flash flood prone basins in the united states these twelve basins have neither the most favorable morphometric characteristics which contribute to flash flood peaks nor did the storms causing these flash floods have the greatest short duration intensities maximum flood peaks originate from an optimal combination of basin morphology and physiography and storm intensity

an approach to combined rock physics and seismic modelling of fluid substitution effects the aim of seismic reservoir monitoring is to map the spatial and temporal distributions and contact interfaces of various hydrocarbon fluids and water within a reservoir rock during the production of hydrocarbons the fluids produced are generally displaced by an injection fluid we discuss possible seismic effects which may occur when the pore volume contains two or more fluids in particular we investigate the effect of immiscible pore fluids i e when the pore fluids occupy different parts of the pore volume the modelling of seismic velocities is performed using a differential effective medium theory in which the various pore fluids are allowed to occupy the pore space in different ways the p wave velocity is seen to depend strongly on the bulk modulus of the pore fluids in the most compliant low aspect ratio pores various scenarios of the microscopic fluid distribution across a gas oil contact goc zone have been designed and the corresponding seismic properties modelled such goc transition zones generally give diffuse reflection regions instead of the typical distinct goc interface hence such transition zones generally should be modelled by finite difference or finite element techniques we have combined rock physics modelling and seismic modelling to simulate the seismic responses of some gas oil zones applying various fluid distribution models the seismic responses may vary both in the reflection time amplitude and phase characteristics our results indicate that when performing a reservoir monitoring experiment erroneous conclusions about a goc movement may be drawn if the microscopic fluid distribution effects are neglected

bounds on low frequency seismic velocities in partially saturated rocks the most common technique for estimating seismic velocities in rocks with mixed pore fluid saturations is to use gassmann s relations with an effective fluid whose density and compressibility are averages of the individual pore fluid properties this approach is applicable only if the gas oil and brine phases are mixed uniformly at a very small scale so the different wave induced increments of pore pressure in each phase have time to diffuse and equilibrate during a seismic period in contrast saturations that are heterogeneous over scales larger than the characteristic diffusion length i e patchy saturation will always lead to higher seismic velocities than if the same fluids are mixed uniformly at a fine scale critical saturation scales separating uniform from patchy behavior are typically of the order 0 1 1 cm for laboratory measurements and tens of centimeters for field seismic frequencies for low seismic frequencies velocities corresponding to patchy and homogeneous saturations represent a