numerical modelling of downstream migrating antidunes a numerical model is presented that compute the geometrical dimensions and movement of downstream migrating antidunes the model solves the navier stokes equations together with the k epsilon turbulence model to find the water flow field over the bedforms a two dimensional width averaged grid is used the bed elevation changes are computed by solving the convection diffusion equation for suspended sediments and bed load together with the engelund hansen sediment transport formula the free surface is computed with an algorithm based on water continuity in the surface cells non orthogonal adaptive grids were used moving vertically with the computed location of the bed and the free water surface the numerical model was tested on data from a physical model study where regular downstream migrating antidunes had been observed the numerical model started out with a flat bed and the trains of antidunes formed over time many of the physical processes observed in earlier studies were replicated by the numerical model four dune parameters were computed in the current tests the antidune wavelength height and celerity together with the average water depth the antidune wavelengths were best predicted with an accuracy of 3 8 compared with the measurements the antidune heights were computed with a deviation of 11 25 compared with an empirical formula the water depths over the antidunes were predicted with an accuracy of 3 9 related to the measured values the average antidune celerity was the parameter with largest deviation for the coarsest grid it was overpredicted with 37

geometry of ripples and dunes a kinematic theory for lower regime bedform shape is presented and examined in the light of extensive bedform data observed in large prototype channels depending upon the extent of bedform maturity the theory predicts uniquely defined nondimensional shapes for upstream faces these shapes are borne reasonably well by the observed data in spite of large variation in bedform size the length of upstream face relative to the wavelength is randomly distributed with most probable value of 0 614 which is close to the value 0 667 predicted by the theory for mature ripples and dunes

bed configuration and hydraulic resistance in alluvial channel flows a new approach for predicting alluvial channel resistance in the framework of the familiar manning equation is proposed the new method proposes a relation for the manning coefficient that incorporates directly the role of bed configuration in determining alluvial bed resistance a relation for bed form height is developed which is then used as an independent variable to account for the resistance due to bed form drag the method was applied to a large body 969 flows of river and flume data with satisfactory agreement with the observed values mean normalized errors for predicted flow depths and velocities were about 10 for all 969 flows the procedure can be applied to natural streams with compound channels since variable roughness for the main channel and overbank sections can be computed separately in this approach prediction accuracy was generally better for flows that were clearly in the lower regime ripple or dune or in the upper regime flat bed or antidune but larger errors were associat

sand dune geometry of large rivers during floods the geometry of lower regime bed forms in several large sand bed rivers is investigated during average and flood conditions the van rijn method is revised because it generally underpredicts the dune height of most large rivers around the world during floods in large sand bed rivers upper regime plane bed is not necessarily obtained when t 25 both parameters describing dune height and dune steepness do not decrease as the transport stage parameter t increases in the range 10 t 25 the analysis of bed form data during large floods on the meuse river and the rhine river branches indicates that both the dune height and length generally increase with discharge while dune steepness remains relatively constant a reasonable approximation of the wavelength is 6 5 h where h is the flow depth the dune height varies as a function of the depth h and median grain size d50 estimates can be obtained by 2 5 h 0 7d0 350

flow separation and shear stress over angle of repose bed forms a numerical investigation large asymmetric bed forms commonly develop in rivers the turbulence associated with flow separation that develops over their steep lee side is responsible for the form shear stress which can represent a substantial part of total shear stress in rivers this paper uses the delft3d modeling system to investigate the effects of bed form geometry and forcing conditions on flow separation length and associated turbulence and bed form shear stress over angle of repose 30 lee side angle bed forms the model was validated with lab measurements that showed sufficient agreement to be used for a systematic analysis the influence of flow velocity bed roughness relative height bed form height water depth and aspect ratio bed form height length on the variations of the normalized length of the flow separation zone the extent of the wake region where the turbulent kinetic energy tke was more than 70 of the maximum tke the average tke within the wake region and the form shear stress were investigated form shear stress was found not to scale with the size of the flow separation zone but to be related to the product of the normalized extent of the wake region extent of the wake region extent of water body above the bed form and the average tke within the wake region the results add to understanding of the hydrodynamics of bed forms and may be used for the development of better parameterizations of small scale processes for application in large scale studies

modeling river dune development and dune transition to upper stage plane bed large asymmetric bedforms known as dunes commonly dominate the bed of sand rivers due to the turbulence generation over their stoss and lee sides dunes are of central importance in predicting hydraulic roughness and water levels during floods in steep alluvial rivers dunes are observed to grow rapidly as flow strength increases undergoing an unstable transition regime after which they are washed out in what is called upper stage plane bed this transition of dunes to upper stage plane bed is associated with high transport of bed sediment in suspension and large decrease in bedform roughness in the present study we aim to improve the prediction of dune development and dune transition to upper stage plane bed by introducing the transport of suspended sediment in an existing dune evolution model in addition flume experiments are carried out to investigate dune development under bed load and suspended load dominated transport regimes and to get insight in the time scales related to the transition of dunes to upper stage plane bed simulations with the extended model including the transport of suspended sediment show significant improvement in the prediction of equilibrium dune parameters e g dune height dune length dune steepness dune migration rate dune lee side slope both under bed load dominant and suspended load dominant transport regimes the chosen modeling approach also allows us to model the transition of dunes to upper stage plane bed which was not possible with the original dune evolution model the extended model predicts change in the dune shapes as was observed in the flume experiments with decreasing dune heights and dune lee slopes furthermore the time scale of dune transition to upper stage plane bed was quite well predicted by the extended model

stratigraphic and tectonic features of the middle pleistocene sedimentary and volcanic deposits in the area of rome italy the analysis of a large number of stratigraphic logs from boreholes as well as an extensive field survey suggests that the middle pleistocene sedimentary deposits in the area of rome can be subdivided into two groups each one characterised by a different stratigraphy and tectonic setting a north eastern sector corresponding to the eastern urban area of rome and a south western sector corresponding to the ponte galeria area in the north eastern sector the distribution of sediments is influenced by vertical block faulting showing a predominantly north south trend superimposed on a middle pleistocene ne sw extensional tectonic domain in the south western sector we suggest that the ponte galeria formation auct can be subdivided into two depositional sequences that can be linked to isotope stages 19 and 21 in addition a sedimentary hiatus is proposed at the top of the ponte galeria sequence it corresponds to the deposition of a continental succession in the north eastern sector before the emplacement of pyroclastic deposits from the colli albani and sabatini volcanic districts the correlation between these two depositional sequences that have been identified and the oxygen isotope time scale allowed us to extend our investigation across to the urban area of rome where we have recognised six sedimentary cycles all of pleistocene age which have been tentatively related to particular isotopes stages

40ar 39ar geochronology of roman volcanic province tephra in the tiber river valley age calibration of middle pleistocene sea level changes the close proximity of the roman volcanic province to the tyrrhenian sea coastline provides a unique opportunity to combine clastic stratigraphy with 40 ar 39 ar geochronology to constrain the timing of pleistocene sea level oscillations the main eruptions from the monti sabatini volcanic district occurred during the interval 560 280 ka and the alban hills volcanic district main eruptions span 560 350 ka the interfingering of volcanics from these two centers with fluvial and shallow marine sediments of the tiber river and delta provides a datable relative sea level record for this portion of middle pleistocene time we calculate the timing of glacial terminations using analytical errors only then assess age uncertainties that include analytical plus systematic errors the latter is required to compare 40 ar 39 ar ages with those from other dating methods terminations iii v and vi occur at 278 261 285 ka 95 confidence interval 430 422 442 ka and 534 520 541 ka respectively when only analytical uncertainties are used to calculate the ages of bracketing volcanic horizons the confidence interval expands significantly when full external errors are considered with predicted ages of 276 258 289 ka 430 416 448 ka and 533 512 548 ka for the terminations the resultant 40 ar 39 ar chronology is generally consistent with the deep sea 18 o record of sea level change tuned to earth9s obliquity cycle for glacial terminations vi v and iii in addition the 40 ar 39 ar constrained tiber river delta sea level record has the added benefit of identifying when coastal sections respond to complex multistep terminations

strike slip faulting and block rotation a possible triggering mechanism for lava flows in the alban hills abstract it is suggested in this paper that two distinct tectonic triggers tapping different depths of a magma reservoir may be the cause of nearly contemporaneous eruptions of lava flows and ignimbrites in the alban hills the area between the alban hills and rome underwent alternating regional extensional and strike slip faulting during the middle pleistocene the geometries of the main structural dislocations in quaternary strata combined with a statistical analysis of drainage network trends show a structural pattern that is consistent with local strain partitioning in transpressive zones at strike slip fault bends superimposed on regional extension based on this analysis it is suggested that local clockwise block rotation between parallel n s strike slip faults might have generated local crustal decompression allowing relatively volatile free magma to rise from deep reservoirs beneath the alban hills triggering peripheral fissure lava flows in contrast the main ignimbrite eruptions appear to tap shallow volatile rich magma reservoirs and are controlled by extensional processes

flow resistance and bed form geometry in a wide alluvial channel 1 this paper explores the underlying mechanism of flow resistance in a wide alluvial channel with bed forms on the basis of published data it is shown that the grain roughness can be taken as equal to 2 times the median diameter of the bed sediment an empirical equation for the bed form roughness has been proposed and it depends on the bed form height and bed form steepness the influence of the bed form length and height on the total bed shear stress and energy slope is deliberated and empirical expressions for the length of the separation zone behind the bed forms are also proposed the study proposed an equation to compute the total bed shear stress as a function of the grain and bed form roughness as well as the important role of the bed form geometry in the overall flow resistance in alluvial channels the model is tested and verified against 670 flume measurements and 1540 field observations the computed and measured energy slopes are in good agreement with close to 71 of all data sets within the 20 error band

strain partitioning in transpression zones abstract transprcssional strain acting upon structurally anisotropic rocks can be partitioned into separate deformational domains of pure shear and simple shear this contrasts with homogeneous transpression in which both the pure shear and the simple shear strain components are uniformly distributed across the zone of deformation structural weaknesses capable of partially or fully accommodating one component of deformation include lithological contacts rheological heterogeneities and faults or shear zones situated within the deformation zone or lying along its boundaries partitioning of transprcssional strain can occur when stress is applied oblique to pre existing structural weaknesses or can occur during later stages of progressive strain when the early deformation of isotropic rocks imparts sufficient anisotropy to allow subsequent strain to be partitioned partitioning of transpressional strain into domains lying parallel to the deformation zone boundaries can be distinguished from fault stepped transpression in which strain is partitioned along the length of a segmented fault zone mesofracture analysis of rocks affected by mid devonian deformation on both sides of the highland boundary fault zone hbfz in central scotland shows that strain was not homogeneous the mesofracture data suggest that regional north south compression orientated oblique to the pre existing ne sw trending hbfz was partitioned into separate deformational domains the hbfz accommodated most of the simple shear component whilst the rocks flanking the zone were deformed predominantly by pure shear a contemporary example is the san andreas fault in central california where analyses of neo tectonic stresses show that the direction of principal compression is perpendicular to the fault zone many examples of the partitioning of transpressional strain have also been recognised at destructive plate margins where the direction of plate motion is oblique to the edge of the over riding plate

using both free surface effect and sediment transport mode parameters in defining the morphology of river dunes and their evolution to upper stage plane beds doi 10 1061 asce hy 1943 7900 0000873 dunes are common bed forms in sand bed rivers and are of central interest in water management purposes due to flow separation and associated energy dissipation dunes form the main source of hydraulic roughness a large number of dune dimension data sets was compiled and analyzed in this study 414 experiments from flumes and the field showing a significantly different evolution of dune height and length in flows with low froude numbers negligible free surface effects and flows with high froude numbers large free surface effects for high froude numbers 0 32 0 84 relative dune heights are observed to grow only in the bed load dominant transport regime and start to decay for u w s suspension number exceeding 1 dunes in this case are not observed for suspension numbers greater than 2 5 for low froude numbers 0 05 0 32 relative dune heights continue to grow from the bed load to suspended load dominant transport regime dunes in this case are not observed for suspension numbers greater than 5 it was concluded that for reliable predictions of dune morphology and their evolution to upper stage plane beds it is essential to address both free surface effects and sediment transport mode

the 1989 1990 seismic swarm in the alban hills volcanic area central italy abstract a long seismic swarm has been recorded by a digital microseismic network that the istituto nazionale di geo fisica ing deployed from april 1989 to march 1990 in the alban hills quaternary volcanic region about 20 km southeast of rome the network consisted of thirteen digital stations equipped with four six component weak motion and strong motion sensors three three component and six vertical weak motion seismometers including both broad band and short period sensors more than 3000 earthquakes were detected during about one year of operation the data recorded during the sequence provided an unprecedented opportunity to resolve details of the seismogenic features of this area that has experienced earthquakes since the roman age although the temporal distribution of seismicity reveals a volcanic type swarm activity the recorded seismic signals show medium high frequency waveforms and clear s wave arrivals typical of tectonic earthquakes about 1100 earthquakes in a magnitude range between m d 1 5 and md 4 0 have been located the seismicity delineates a 6 12 km 2 nw se elongated region that corresponds to the area where the most recent 0 027 ma phreato magmatic activity took place almost no earthquakes occurred beneath the central cone and the eastern side of the caldera the seismicity is shallow and is mostly concentrated in two clusters that are offset laterally and are at sligthly different depths 3 5 and 4 6 km the fault plane solutions of the strongest earthquakes reveal a ne sw extension consistent with the regional orientation of the stress field along the apenninic chain as obtained by other seismo logical data

spatial variability in river sediments and its link with river channel geometry 1 this study explores the link between spatial variability within fluvial sedimentary strata and river channel geometry this link is then used to determine the macrodispersion coefficients for solute transport in groundwater flow in river deposits in doing that we combine concepts from sedimentology geostatistics and the stochastic lagrangian theory of subsurface transport it is proposed to analyze the spatial variability of river sediments in terms of transition probabilities the transition probabilities can be determined from the averages and variances of the lengths of stratasets and their volumetric fractions using concepts developed by carle and fogg 1996 and ritzi 2000 strataset length scales are shown to correlate well with the geometry of the river channel and its bed forms and can be determined indirectly from aerial photogrammetry and more directly through surface ground penetrating radar surveys stratal dimensions can also be related using lagrangian transport analysis to macrodispersivity of subsurface transport this allows relationships between the geometry of river channels and subsurface transport parameters of associated fluvial deposits for demonstration the longitudinal macrodispersivity in a compound bar deposit in the gravelly braided sagavanirktok river was investigated

bed material discharge prediction for nonuniform bed sediments an important element for simulating the evolution of a riverbed with nonuniform sediments is the reliable prediction of sediment discharge for each size fraction which is essential for simulating

geometry and migration characteristics of bedforms under waves and currents part 2 ripples superimposed on sandwaves this paper presents results of a series of detailed measurements of geometric and migrating characteristics of ripples superimposed upon sandwaves under the action of combined waves and currents velocity measurements within the fluid surface wave characteristics and 3d mapping of the bottom were recorded with an acoustic doppler velocimeter adv an acoustic water level sensor and a 32 composite element array of sub aquatic acoustic sensors respectively bottom records were statistically analyzed to obtain height length and migration rates of ripples experiments examined ripple heights and wavelengths for the mobility factors as defined in eq 4 and the reynolds wave number within the ranges 10 88 and 16 103 rew 5 105 respectively measured values were compared with laboratory and field data together with semi empirical and analytical formulae from the literature good correlation was obtained when plotting measured ripple length and length in dimensionless form as a function of the reynolds wave number rew under a given hydraulic condition it was observed that ripples with different geometric characteristics may coexist at different locations over the sandwave ripple steepness is presented as a function of the shields parameter although characterized with rather large scatter finally average ripple migration speed is presented as a function of the shields parameter and the mobility number

origin of hysteresis in bed form response to unsteady flows 1 field and laboratory studies indicate that changes in riverbed morphology often lag changes in water discharge this lagged response produces hysteresis in the relationship between water discharge and bed form geometry to understand these phenomena we performed flume experiments to observe the response of a sand bed to step increases and decreases in water discharge for an abrupt rise in discharge we observed that bed forms grew rapidly by collision and merger of bed forms migrating with different celerities growth rate slowed as bed forms approached equilibrium with the higher discharge regime after an abrupt discharge drop bed form decay occurred through formation of smaller secondary bed forms in equilibrium with the lower discharge which cannibalized the original relict features we present a simple model framework to quantitatively predict time scales of bed form adjustment to flow changes based on equilibrium bed form heights lengths and celerities at low and high flows for rising discharge the model assumes that all bed form collisions result in irreversible merger due to a dispersion of initial celerities for falling discharge we derive a diffusion model for the decay of relict high stage features our models predict the form and time scale of experimental bed form adjustments additional experiments applying slow and fast triangular flood waves show that bed form hysteresis occurs only when the time scale of flow change is faster than the modeled and measured bed form adjustment time we show that our predicted adjustment time scales can also be used to predict the occurrence of bed form hysteresis in natural floods

influence of lateral water withdrawal on bed form geometry in a channel in flood protection engineering side weirs or overflow dams are used to divert water in a controlled way into flood plains as soon as the discharge capacity of the main channel is reached because of the lateral loss of water the sediment transport capacity is reduced resulting in local sediment deposition near the side overflow moreover bed form characteristics such as length height steepness and stoss and lee slope angle are affected by the lateral water withdrawal both phenomena are responsible for an increased side overflow intensity compared with plane bed conditions the results from a systematic flume study show that the shape of observed bed forms is highly threedimensional and that three distinct regions along the channel axis can be identified the first one extends from the channel entrance to the upstream weir corner the second one comprises the reach of the weir and the third one represents the reach downstream of the weir the description of bed form shape by approaches from literature shows reasonable agreement with measured bed form geometry

shape and dimensions of stationary dunes in rivers the shape and dimensions length height of sand dunes in rivers are calculated by use of the measured bed shear stress distribution downstream a rearward facing step the transport of sediment is split up into bed load and suspended load which makes it possible to explain the transition to plane bed the model can predict flow resistance curves in alluvial streams

dynamic routing of flow resistance and alluvial bed form changes from the lower to the upper regime on the basis of a strouhal number and the definition of the control factor m a new routing to calculate the energy slope in the lower and upper alluvial regimes is proposed the control factor m representing the interactions in alluvial rivers is reckoned as a bed form index while the flow evolves through transition the control factor m decreases from m 2 associated with two dimensional fully developed dunes to m 1 associated primarily with in phase waves the way to predict the value of the control factor m is drawn from a previously published criterion for delineating the upper regime and is calibrated with experimental data on several data from flumes and rivers the routing is tested and compared with other methods from the literature it appears that the new routing is the most robust because it allows researchers to obtain low averages of the discrepancy ratio for a wide range of ratios between the water depth and the median sediment diameter on a selection of contrasted freshet events the new routing allows for the capture of the primary dynamic of the flow resistance decrease

effect of non migrating bars on dune dynamics in a lowland river as dunes and larger scale bed forms such as bars coexist in rivers the question arises whether dune dynamics are influenced by interaction with the underlying bed topography the present study aims to establish the degree in which dune characteristics in two and three dimensions are influenced by an underlying topography dominated by non migrating bars as a case study a 20km stretch in the waal river in the netherlands is selected which represents a sand bed lowland river at this location longitudinal training dams ltds have recently been constructed to ensure sufficient navigation depth during periods with low water levels and to reduce flood risk by using data covering two year long periods before and after ltd construction the robustness of the results is investigated before ltd construction dune characteristics show large variability both spatially and temporally with dunes being longer lower less steep and having a lower lee side angle when they are located on bar tops the correlation between dune characteristics and the underlying bed topography is disrupted by unsteady conditions for which the dunes are in a state of transition the bar pattern causes tilting of dune crest lines which may result from a transverse gradient in bed load sediment transport as a result of ltd construction the hydraulic and morphological conditions have changed significantly despite this the main conclusions still hold which strengthens the validity of the results

bed form geometry in sand bed flows a new method is proposed for predicting relative bed form height h d in sand bed flows the proposed method is based on the concept of relating energy loss due to form drag to the head loss across a sudden expansion in open channel flows a unique feature of the proposed method is that it can be applied to various bed forms i e ripples dunes antidunes standing waves and transitional bed regimes that occur in alluvial flows the relation thus developed was applied to a large number 251 flows 14 different data sets of laboratory and river data and was found to give good agreement with the observed h d values in a comparison of prediction accuracies with seven existing relationships the proposed method was found to give significantly better agreements with the observed data future improvements in the prediction of h d will depend on improved formulations of the two parameters incorporated in the present relation i e energy loss coefficient k and the relative bed form length l d for various b

sediment transport part iii bed forms and alluvial roughness a method is presented that makes the classification of bed forms the prediction of the bed form dimensions and the effective hydraulic roughness of the bed forms feasible the proposed relationships are based on the analysis of reliable flume and field data a verification analysis using about 1 500 alternative reliable flume and field data shows good results in predicting the hydraulic roughness friction factor for field conditions the proposed method yields considerably better results than previously proposed methods which are reviewed here the proposed method has also been used to predict the flow depth and the total bed material load

ripples on stream bed some 30 years ago john f kennedy laid the foundations for the description of the geometry of sand waves on stream beds by the potential flow model since then the analysis has been extensively refined and extended but no rigorous description of the small features called ripples exists the present study attempts a stock taking of the data and the various behavioral concepts with the aim of encouraging researchers to improve our knowledge of the physics of features called ripples various trends are identified from the data it is deduced that ripples act as roughness elements of the boundary the ripple troughs are filled with the energy consuming lee vortices the main flow is over the ripple crests and lee vortices and does not interact with the bed geometry the roughness layer of ripples and vortices is within the constant shear layer and is affected by the flow depth only as far as it affects the velocity distribution and alters the shear stress on the bed

f phlogopites in the alban hills volcanic district central italy indications regarding the role of volatiles in magmatic crystallisation abstract a systematic analysis of micas contained in effusive pyroclastic and hypabyssal rocks of the alban hills volcanic district ahvd central italy was made in order to characterise minerals of pyroclastic units for tephrostratigraphy and to obtain as much information as possible on the activity of volatiles in this magmatic system the phlogopite shows a large range of f contents between 0 50 and 7 50 wt that make it possible to discriminate different ahvd lithologies in particular micas of lava groundmass are characterised by extremely high f up to 7 50 wt and ba up to 9 70 wt contents seldom or never found in other magmatic ultrapotassic rocks moreover the micas of pyroclastics ultramafic cumulates and holocrystalline inclusions made up of leucite clinopyroxene and phlogopite hereafter italites show mg mg fe values between 0 65 and 0 90 that are not correlated with f contents the variations in f contents observed in the ahvd micas do not appear to be due to a temperature effect or pressure changes but they may be due to variations in the h 2 o and co 2 activities in the magma chamber they make it possible to differentiate three crystallisation environments in the ahvd magmatic system the first one had elevated co 2 activity and formed the italites near the carbonate contact these rocks represent at least those enriched in clinopyroxene without skarn minerals the hypabyssal crystallisation of the ahvd magmas at the periphery of magma chamber the second one characterised by a higher water activity is represented by the micas of the ultramafic cumulates and pyroclastic scorias and is located in the inner part of magma chamber the third environment the groundmass of the lavas it is not related with the previous ones and is characterised by the absence of water and by a high f activity in general our results suggest that the compositional variations observed in the micas al si ti ba reflect different h 2 o activities inversely correlated with f activity in the magma chamber

reevaluating dune scaling relations abstract in sand bedded rivers dunes dominate sediment transport and flow resistance dunes are also commonly preserved in fluvial deposits as cross stratified units that record their size shape and migration rates prediction of dune dimensions is therefore important for forecasting modern river channel dynamics as well as reconstructing past fluvial environments on earth and other planets predictions are often made by assuming that the formative flow depth h sets dune dimensions with height scaling as 1 6h and length as 5h yet there is a suite of other scaling relations that link dune dimensions to other variables like grain size transport stage and froude number here we present a new compilation of flow and dune dimension data to evaluate scaling relations the data reveal approximately two orders of magnitude variation in dune height and length at any given flow depth dune heights in shallow flows 2 5 m are often more symmetric have lower lee angles are relatively shorter in height than 1 6h and have a wider range of observed heights for a given depth none of the scaling relations predict the observations exceptionally well likely because of natural variability in dune dimensions and because they do not explicitly account for the apparent scaling break that occurs at 2 5 m we propose new simple depth scaling relations with added statistical uncertainty for the prediction of dune height and length from flow depth as well as flow depth from dune height we conclude that shallow and deep flow dunes exhibit different scaling due to a change in the dominant process controls as dunes get larger

sediment convection diffusion and bedform length in connection with the mechanics of ripples and dunes the governing equations of convection diffusion of suspended sediment in two dimensional flow fields over ripples or dunes are solved by the finite element method the role of suspended sediment in determining the steady bedform length is theoretically investigated the postulate that in the case of steady bedforms the diffusive flux vector at any point on the stoss must point into the interior of the flow region divides mathematically acceptable solutions into two categories 1 physically acceptable solutions and 2 physically unacceptable solutions the marginal solutions which lie on the common boundary between the two classes in the solution space are of special interest they represent steady bedforms with minimum length under the prevailing flow conditions and they are conjectured to correspond to the steady bedforms occurring in nature finally the theory is compared with the physical observations made in flumes canals and rivers t

flow resistance over mobile bed in an open channel flow this paper deals with the underlying mechanism of flow resistance in an alluvial channel the effects of sidewall and bed form on flow resistance einstein s divided hydraulic radius approach and engelund s energy slope division approach are reexamined these two approaches assume that the shear stress on a mobile bed is the summation of shear stresses caused by skin friction and bed form using a different approach this paper presents a theoretical relationship between the total bed shear stress with grain and bed form shear stresses the contribution of sidewall on the total bed shear stress is also discussed the writers found that the size of bed form plays a significant role for the flow resistance and developed relevant expressions for the length of the separation zone behind the bed forms in addition a systematical approach has been developed to compute the flow velocity in an alluvial channel this approach is tested and verified against 5 989 flume and field measurements the computed and mea

low magnitude earthquakes in rome structural interpretation and implications for the local stress field on 1995 june 12 a ml 3 6 earthquake occurred in the cecchignola area of southern rome a detailed structural investigation of this area and an analysis of macroseismic and instrumental data indicate a seismogenic area for the local low magnitude seismicity that affects the city of rome a peripheral volcanic field in cecchignola shows that the local seismicity could be related to the same volcanotectonics that affects the colli albani alban hills region fracture field emission is proposed for the emplacement of about 2 5 km3 of lava which developed a small plateau that was subsequently intruded by the feeder dyke of a large ignimbrite the geometry of this dyke as well as the faults disrupting the lava field indicates ne sw extension younger tectonic features show a nw striking 3 in the studied area suggesting that dextral n s strike slip displacement generated structures that are not compatible with the local present day stress field characterized by a ne striking 3 an analysis of focal solutions and the spatial distribution of the 1995 june 12 microearthquake sequence suggests an e w seismogenic structure whose trend is atypical of the structural setting of the area the present study identifies surface faulting with the same trend as the focal mechanisms in the epicentral area and suggests that these faults represent an inactive surface expression of the deeper structures it is also suggested that these structures originated during a different tectonic regime and are presently reactivated at depth by the ne sw extension the general ne orientation of the t axes from focal mechanisms for the colli albani earthquakes and for the 1995 june 12 cecchignola event strongly supports a regional interpretation for the present day stress field previously observed only in the colli albani area it is likely that a combination of different tectonic styles during the last 600 kyr is necessary to explain the structural features of the cecchignola area and of the central tyrrhenian sea margin of italy in general

fault mechanics and the kinematics of block rotations in many strike slip tectonic settings large rotations up to 100 of crustal blocks have been inferred from paleomagnetic data these blocks are bounded by sets of parallel faults which accommodate the relative motion between the blocks as regional deformation progresses simple geometrical considerations require that the faults must also rotate in this paper we show that on the basis of mechanical considerations the amount of fault rotation permissible under a stationary stress field is limited to 20 to 45 consequently block rotations that are larger than 40 or 45 require more than one set of accompanying faults to accommodate the block rotation examples of such multiple sets with 40 to 45 between them as predicted by the model were recognized in sistan iran in yerington the lake mead area nevada and in southern california

seismicity and fault kinematics through the eastern transverse ranges california block rotation strike slip faulting and low angle thrusts hypocentral locations and first motion data from the southern california seismic network are used to infer the present pattern of deformation along the southern san andreas fault the study area lies between the san jacinto fault and desert hot springs and includes the san bernardino mountains and san gorgonio pass this region has some of the deepest earthquakes observed anywhere along the entire san andreas system exhibits a complex surface geology characterized by both right and left lateral faults has high topographic relief as a result of recent uplift and is a potential site for the nucleation of a great earthquake although this area is unusually seismogenic little activity can be directly associated with major throughgoing faults seismicity is also generally absent in the upper 5 km the predominant style of faulting above 10 12 km is oblique slip with a large reverse component the spatial distribution of relocated hypocenters and first motion data suggests the presence of a system of left slip faults striking northeast this pattern of faulting in conjunction with an unusual set of normal and reverse focal mechanisms is interpreted as the clockwise rotation of a small set of crustal blocks subject to regional right lateral shear at depths greater than about 10 km seismicity defines a wedge shaped volume undergoing pervasive internal deformation on a combination of strike slip and low angle thrust faults velocity structures determined from earthquake arrival times suggest a low velocity zone at about 10 km below the san bernardino mountains but not below the san jacinto mountains this is nearly the same depth as the transition between the two layers of different kinematic behavior seen south of the mill creek mission creek branch of the san andreas fault and the maximum depth of seismicity seen north of that fault the low velocity zone and the transition between block rotations and the deeper deformation may thus correspond to a detachment under much of this region and would imply that the overthrust san bernardino mountains are allochthonous the present pattern of seismic deformation in shocks of small to moderate size may only characterize the interval between large earthquakes and may change systematically as the region prepares to accommodate large right lateral displacements

correlation of fluviodeltaic aggradational sections with glacial climate history a revision of the pleistocene stratigraphy of rome volcanic horizons interbedded with fluviodeltaic clastic sediments of the tiber and fosso galeria river valleys near rome provide a unique opportunity to date five middle pleistocene fining upward aggradational sections 40 ar 39 ar ages from the interbedded volcanic beds illustrate that aggradation occurred on an approximate 100 k y cycle and was initiated by sea level rise associated with glacial melting the age constraint additionally shows that aggradation occurs rapidly in response to sea level change and thus ages from volcanic strata within the aggradational sections provide high resolution constraint on the timing of relative sea level rise the established chronology is consistent with other glacial proxies and their radioisotopically or orbitally based time scales for the timing of glacial terminations vi and v but is significantly older than most records for the timing of termination iii ultimately the age of each termination should be determined by radioisotopic means and to that end the work here shows that fluviodeltaic sedimentology provides valuable information for middle pleistocene time scale calibration