calibration of prism and avnir 2 onboard alos daichi the advanced land observing satellite alos nicknamed ldquodaichirdquo was successfully launched on january 24 2006 and it continues to work very well this paper describes the calibrations of two optical instruments onboard alos which are the panchromatic remote sensing instrument for stereo mapping prism and advanced visible and near infrared radiometer type 2 avnir 2 prism consists of three panchromatic radiometers and is used to derive a digital surface model dsm with high spatial resolution which is an objective of the alos mission avnir 2 has four radiometric bands from blue to near infrared which are used for investigating regional environment issues such as land use and land cover classifications and disaster monitoring in this paper we introduce the calibration and validation plan methodologies accuracy assessments of the standard products image quality evaluations for prism and avnir 2 and their results geometric calibration is important in generating a precise dsm by a stereo pair image of prism the relative geometric calibrations of both prism and avnir 2 are conducted by evaluating accuracies within one scene and evaluating sensor alignments as absolute calibration for absolute geometric accuracies we achieved 8 1 m for nadir looking images and 9 3 m for forward and backward looking images of prism we also achieved 114 2 m for avnir 2 prism is also radiometrically calibrated both relatively and absolutely prism relative radiometric calibration is accomplished by using acquired images over homogeneous targets such as oceans deserts ice and snow areas as well as nighttime observation simultaneously observed images with calibrated avnir 2 are used for absolute radiometric calibration by cross calibration the absolute radiometric accuracy of the prism nadir looking radiometer is similar to that of avnir 2

evaluation of morphometric parameters of drainage networks derived from topographic maps and dem in point of floods an evaluation of morphometric parameters of two drainage networks derived from different sources was done to determine the influence of sub basins to flooding on the main channel in the havran river basin balikesir turkey drainage networks for the sub basins were derived from both topographic maps scaled 1 25 000 and a 10 m resolution digital elevation model dem using geographic information systems gis blue lines representing fluvial channels on the topographic maps were accepted as a drainage network which does not depict all exterior links in the basin the second drainage network was extracted from the dem using minimum accumulation area threshold to include all exterior links morphometric parameters were applied to the two types of drainage networks at sub basin levels these parameters were used to assess the influence of the sub basins on the main channel with respect to flooding the results show that the drainage network of sub basin 4 where a dam was constructed on its outlet to mitigate potential floods has a lower influence morphometrically to produce probable floods on the main channel than that of sub basins 1 3 and 5 the construction of the dam will help reduce flooding on the main channel from sub basin 4 but it will not prevent potential flooding from sub basin 1 3 and 5 which join the main channel downstream of sub basin 4 therefore flood mitigation efforts should be considered in order to protect the settlement and agricultural lands on the floodplain downstream of the dam in order to increase our understanding of flood hazards and to determine appropriate mitigation solutions drainage morphometry research should be included as an essential component to hydrologic studies

dem analyses and morphotectonic interpretation the plio quaternary evolution of the eastern ligurian alps italy abstract the ligurian alps italy straddle a complex and ill defined tectonic transition that accommodates eurasia adria shortening driving concurrent growth of the western alps and northern apennines we focus on the plio quaternary landscape evolution of the eastern part of the ligurian alps with the goal of defining the active tectonics through an analysis of topography drainage networks and river long profiles the ligurian alps have a steep seaward facing escarpment with topographic features reminiscent of the geomorphic markers preserved on both actively uplifting coastlines and passive margins for example there are seaward facing benches that are thought to be uplifted marine terraces common to active margins but the drainage divide of the seaward escarpment shows clear evidence of recent northward migration into the po foreland a process consistent with escarpment retreat characteristic of passive or subsiding margins this study explores the active tectonics consistent with these diverse landscape evolution pathways our analysis reveals that rock type strongly throttles the development of topographic relief drainage networks and northward migration of the drainage divide however we also identify segments of the escarpment that indicate recent base level falls through an analysis of modeled channel steepness and comparison with mean hillslope gradient the base level falls are consistent with numerous barbed tributaries that are best explained as recent stream captures no significant correlation among the stream captures at the drainage divide suspected marine terraces at the coast ligurian sea bathymetry and active seismicity indicates that the escarpment is the footwall of a segmented normal fault this normal fault is embedded in a regionally subsiding margin where actively uplifting segments lead to a straightened pinned drainage divide whereas relatively inactive segments permit divide migration into the footwall block these results are broadly consistent with rock uplift increasing eastward toward genova across the long suspected alps apennine sestri voltaggio fault zone they highlight the respective roles of legacy structures rock type and localized rock uplift in constructing a landscape in an otherwise extending and subsiding crustal retrowedge of an active subduction plate boundary

physical modeling of an outflow event in howe sound british columbia outflow winds occur when differing air masses are separated by a coastal mountain barrier in extreme cases the cross barrier pressure gradient and the high degree of stratification often approaching a distinct layered structure result in channel winds which exhibit hydraulic features we present a study of outflow winds in howe sound british columbia a field investigation aimed specifically at locating and quantifying hydraulic effects was undertaken during the winter months of 1992 1993 microbarographs positioned in the region recorded pressure changes at discrete locations in the streamwise direction the pressures obtained during a severe outflow wind event which occurred from december 27 1992 to january 1 1993 show a highly variable lower layer depth suggestive of hydraulic control experiments were conducted with a three dimensional physical model that is geometrically and kinematically similar to howe sound synoptic conditions recorded during the outflow wind event in howe sound in december 1992 were used to determine appropriate model flow forcing the expanse of supercritical flow area was observed to be relatively sensitive to changes in along channel pressure gradient and downstream depth when compared to changes in discharge channel sinuosity and local topography appeared to force critical conditions at specific locations for example a channel bend combined with headlands was observed to force a situation where subcritical and supercritical streams flow side by side flow separation resulting in lateral shear discontinuities produced similar conditions these effects are discussed and put into context with field observations field and model results show good agreement

modeling sediment entrainment and transport processes limited by bed armoring abstract a sediment transport model including a bed armoring algorithm is used to ascertain the potential importance of bed armoring processes the parameters that control the bed armoring effects on the suspension of granular sediments in the marine environment are examined using the numerical model and data from the eel shelf results for the shelf indicate that bed armoring controls the total suspended sediment load and affects the across shelf gradients of suspended material the armoring effects are too significant to be neglected in most analyses of shelf and nearshore sediment transport and this is especially relevant for models that are developed to represent large scale and long term sedimentary regimes a principal controlling parameter is the thickness of the active layer and the dynamics of this layer are not well known

design and installation of a novel automatic erosion monitoring system process inference in geomorphology is hindered by a lack of information on the true temporal distribution of contemporary erosional and depositional activity to tackle this problem a low cost automatic monitoring system based on the photo electronic erosion pin peep sensor has been developed the peep is essentially an array of photosensitive cells enclosed within a transparent tube and connected by cable to a datalogger when inserted into an eroding landform subsequent retreat of the face exposes more photosensitive cells to light which increases peep voltage output deposition decreases sensor outputs the logged signals thus reveal the magnitude timing and frequency of erosion and deposition events with much greater precision than has hitherto been possible measurement principles electronic and physical design calibration field installation problems and prospects and pilot results from a river bank erosion site are discussed the peep system appears to have great potential for disentangling competing hypotheses in geomorphological process studies and in building and testing erosion and sediment transport models of high temporal resolution

scour of cohesive soil by submerged circular turbulent impinging jets this paper introduces a method for estimating the scour in cohesive soils produced by a submerged vertical circular turbulent impinging jet determining scour in cohesive soils is a complex problem partly because the clay particles within the soil are held together by electrochemical forces that are not easily quantifiable as well erosion occurs in many forms such as the removal of individual particles or as large chunks of soil results of a laboratory study of scour by a circular impinging jet of a cohesive soil consisting of 40 clay 53 silt and 7 fine sand are presented analysis based on the mechanics of the impinging jets shows that the dimensions of the scour hole at an equilibrium state of scour are a function of the momentum flux from the jet the impingement height for large impingement heights the viscosity and density of the eroding fluid and the critical shear stress of the soil mass erosion was the predominant type of erosion observed

comparison of linear and nonlinear models for cohesive sediment detachment rill erosion hole erosion test and streambank erosion studies abstractcohesive sediment detachment is typically modeled for channels levees spillways earthen dams and internal erosion by using a linear excess shear stress approach however mechanistic nonlinear detachment models such as the wilson model have recently been proposed in the literature questions exist as to the appropriateness of nonlinear relationships between applied shear stress and the erosion rate therefore the objective of this research was to test the appropriateness of linear and nonlinear detachment models for cohesive sediment detachment using three data sets 1 rill erodibility studies across a limited range of applied shear stress 0 9 21 4 pa 2 hole erosion tests hets across a wide range of applied shear stress 12 6 62 0 pa and 3 streambank erodibility as quantified by jet erosion tests jets for the linear excess shear stress equation and the nonlinear wilson model across a small range of shear stress 1 4 pa the wilson model was also incorporated into the bank st

gap flow in an alpine valley during a shallow south fohn event observations numerical simulations and hydraulic analogue this paper examines the three dimensional structure and dynamics of southerly hybrid gap mountain flow through the wipp valley wipptal austria observed on 30 october 1999 using high resolution observations and model simulations the observations were obtained during a shallow south fohn event documented in the framework of the mesoscale alpine programme map three important data sources were used the airborne differential absorption lidar leandre 2 the ground based doppler lidar teaco2 and in situ measurements from the national oceanic and atmospheric administration p 3 aircraft this event was simulated down to 2 km horizontal resolution using the non hydrostatic mesoscale model meso nh the structure and dynamics of the flow were realistically simulated the combination of high resolution observations and numerical simulations provided a comprehensive three dimensional picture of the flow through the wipptal in the gap entrance region brenner pass austria the low level jet was not solely due to the channelling of the southerly synoptic flow through the elevated gap part of the wipptal flow originated as a mountain wave at the valley head wall of the brenner pass downstream of the pass the shallow fohn flow had the characteristics of a downslope windstorm as it rushed down towards the inn valley inntal and the city of innsbruck austria downhill of the brenner pass the strongest flow was observed over a small obstacle along the western side wall the nosslachjoch rather than channelled in the deeper part of the valley just to the east further north the low level jet was observed in the centre of the valley approximately halfway between brenner pass and innsbruck where the along axis direction of the valley changes from north to north north west the low level jet was observed to be deflected to the eastern side wall of the wipptal interaction between the stubaier alpen the largest and highest topographic feature to the west of the wipptal and the south westerly synoptic flow was found to be the primary mechanism responsible for the deflection the along and cross valley structure and dynamics of the flow were observed to be highly variable due to the influence of surrounding mountains localized steep slopes within the valley and outflows from tributaries the gschnitztal and the stubaital to the west of the wipptal for that shallow fohn case observations and simulations provided a large body of evidence that downslope flow created thinning thickening fluid and accelerations decelerations reminiscent of mountain wave hydraulic theory along the wipptal two hydraulic jump like transitions were observed and simulated i on the lee slope of the nosslachjoch and ii in the gschnitztal exit region a hydraulic solution of the flow was calculated in the framework of reduced gravity shallow water theory the down valley evolution of the froude number computed using leandre 2 p 3 flight level and teaco2 measurements confirmed that these transitions were associated with super to subcritical transitions copyright 2002 royal meteorological society

streambank erosion rates and loads within a single watershed bridging the gap between temporal and spatial scales abstract the importance of streambank erosion to watershed scale sediment export is being increasingly recognized however few studies have quantified bank erosion and watershed sediment flux at the basin scale across temporal and spatial scales in this study we evaluated the spatial distribution extent and temporal frequency of bank erosion in the 5218 ha walnut creek watershed in iowa across a seven year period we inventoried severely eroding streambanks along over 10 km of stream and monitored erosion pins at 20 sites within the watershed annual streambank recession rates ranged from 0 6 cm yr during years of hydrological inactivity to 28 2 cm yr during seasons with high discharge rates with an overall average of 18 8 cm yr the percentage of total basin export attributed to streambank erosion along the main stem of walnut creek ranged from 23 to 53 large variations in individual site annual rates and percentage of annual load suggested that developing direct relationships between streambank erosion rates and total sediment discharge may be confounded by the timing and magnitude of discharge events storage of sediments within channel system and the remobilization of eroded material

assessing global digital elevation models using the runway method the advanced spaceborne thermal emission and reflection radiometer versus the shuttle radar topography mission case the accuracy of global digital elevation models gdems or dems i e the advanced spaceborne thermal emission and reflection radiometer aster and the shuttle radar topography mission srtm has been reassessed using the runway method the runway method uses the vertical profiles of runways as reference data to which corresponding profiles extracted from investigated dems are compared the major advantage of the runway method is that only the source of instrument induced errors of dems is captured this ultimate effect is achieved due to the flatness and the homogeneous materials from which runways are constructed a cross comparison of the two dems has helped to highlight a few important facts both exhibit a negative elevation bias and the aster dem contains outliers that may be relatively easy to detect and correct particularly in flat terrain

comparison of basin morphometry analyses derived from different dems on two drainage basins in turkey morphometric analyses provide important data about basins and their drainage networks many data sources which are produced from different techniques can be used in this analysis two areas which have similar areal and formal features but have different vegetation density were selected as study areas kabisre and koyunluyusufozu basin selected parameters were implemented to both basins using five different datasets aster gdem srtm dem alos dsm 30 m and topo dems 30 m and 10 m the topo dems were produced from 1 25 000 scaled digitized topographical maps the morphometric analyses result of topo dems 10 m resolution was used as the benchmark data for comparing the results of the other data sources as a result srtm dems gave the most compatible results with the results of reference data for the study area of kabisre basin that has heavy vegetation and the alos dsms gave the closest results to the reference data in study area on koyunluyusufozu basin that is deprived of vegetation

critical shear stress of bimodal sediment in sand gravel rivers a new model for the critical shear stress and the transport of graded sediment is presented the model is based on the size distribution of the bed surface and can be used to compute sediment transport rates in numerical simulations with an active layer model this model makes a distinction between unimodal and bimodal sediments it is assumed that all size fractions of unimodal sediments have the same critical shear stress while there is selective transport for the gravel fractions of bimodal sediments a recently published laboratory transport data set is used to calibrate our model

influence of sediment structure on erosional strength and density of kaolinite sediment beds the role of sediment pore water chemistry and the resulting particle structure in determining the erosional stability of settled cohesive sediment beds in rivers lakes and estuaries is examined kaolinite sediment is used as the surrogate sediment in this experimental investigation with the beds settled from concentrated suspensions the bed stability with respect to erosion or resuspension is measured in a laboratory flume as a function of sediment pore water chemistry the chemical properties varied are sediment ph ionic strength and natural organic matter the remolded bed sample is prepared from a sediment suspension having controlled chemical properties that is allowed to settle into the flume bed where its erosional strength and density are determined with depth in the sample different structures of settled beds are observed with changes in chemical parameters under low ph and low organic content conditions the initial suspension before settling is flocculated the resulting settled beds show strong stratification with respect to erosional strength but weak stratification of bulk density with depth on the other hand under high ph or high organic content conditions at low ionic strength the initial suspension is dispersed the resulting settled beds have lower erosional strength and weak stratification of erosional strength with depth but strong stratification of bulk density with depth this research shows that the relationship between erosional strength and bulk density of a settled bed depends strongly on the structure of the sediment particle associations as determined by pore water chemistry

a conceptual framework for shear flow induced erosion of soft cohesive sediment beds this paper proposes a conceptual framework for erosion of cohesive sediment beds we focus on cohesive beds distinguishing between floc erosion surface erosion and mass erosion by our definition surface erosion is a drained soil mechanical process whereas mass erosion occurs under undrained conditions the eroding shear stress is modeled through a probability density function this yields a continuous description of floc erosion and surface erosion as a function of mean bed shear stress furthermore we assume a distribution for the bed strength the mean values of the bed strength are derived from soil mechanical theory assuming that the surface erosion rate is limited by the swelling rate from the undrained shear strength in the bed to its drained value at its surface the rate of erosion then relates to the undrained shear strength of the soil and its consolidation swelling coefficient the critical shear stress for erosion is slightly larger than the true cohesion of the bed i e the drained strength and follows a power law relation with the plasticity index the conceptual framework proposed herein has been validated against a limited number of experimental data and has a series of advantages above other methods of direct measuring erodibility as it is inexpensive and can be used to attain space covering information on the sediment bed moreover the use of bulk soil mechanical parameters accounts implicitly for the effects of organic material though the role of e g macrophytobenthos mats and or bioturbation is difficult to capture a priori

measurements of sediment erosion and transport with the adjustable shear stress erosion and transport flume soil and sediments play an important role in water management and water quality issues such as water turbidity associated contaminants reservoir sedimentation undesirable erosion and scour and aquatic habitat are all linked to sediment properties and behaviors in situ analysis is necessary to develop an understanding of the erosion and transport of sediments sandia national laboratories has recently patented the adjustable shear stress erosion and transport asset flume that quantifies in situ erosion of a sediment core with depth while affording simultaneous examination of transport modes bedload versus suspended load of the eroded material core erosion rates and ratios of bedload to suspended load transport of quartz sediments were studied with the asset flume the erosion and transport of a fine grained natural cohesive sediment were also observed experiments using quartz sands revealed that the ratio of suspended load to bedload sediment transport is a function of grain diameter and shear

gap winds and wakes sar observations and numerical simulations the nature of terrain induced gap winds and wakes in the atmosphere is examined using surface wind data from synthetic aperture radar sar and the shallow water equations the shallow water model is used to predict the types of wake jet wind patterns that might occur behind an idealized pair of bell shaped hills with a gap between them a regime diagram is constructed based on the width of the gap and the upstream froude number specific predictions of the model are found to compare moderately well with sar data from four examples of airflow near unimak island in the aleutian chain the model predicts the observed wakes and jets including jets that exceed the upstream speed theoretical analysis considers the relative importance of rising terrain and narrowing valley walls in the acceleration of gap winds wind speeds in the wake region are controlled by the bernoulli function and regional pressure gap winds therefore are streams of air that have avoided bernoulli loss over the terrain by passing through gaps the speed of gap winds can exceed the upstream speed only in ridgelike situations when the regional leeside pressure is lower than the upstream pressure

application of morphometry in neotectonic studies at the eastern edge of the parana basin santa catarina state brazil article i nfo the neotectonic evolution of the eastern edge of the parana basin in the santa catarina state brazil was investi gated using field data and detailed morphometric analysis along an east west section analysis included gener ation of maps of isobase hydraulic gradients hypsometry incision of drainage basins drainage asymmetry and anomalous morphological features all these maps generated results that agreed with field data and helped define recent faults in directions close to n s and e w both probably reactivated faults of the parana basin and the basement geomorphological features identified in topographic maps possibly related to neotectonism have a close agreement with our observations in the field the asymmetry of basins as analysed by the t index method proved to be compatible with the influence of a e w compressive tectonic regime and showed a move ment from w to e application of the hypsometric integral technique helped establish a correlation between the younger basins with structures trending n s 30 the n s faults were related to a compressional stress field shmax close to e wa nd shmin stress minimum around n s thereby establishing a tectonic context of structures developed in a transpressive regime the compressional field was caused by the subduction of the nazca tectonic plate below the south american plate whereas the transcurrent component exploited pre existent e w structures when the atlantic ocean was opening

may the shields theory be extended to cohesive and adhesive benthic sediments 1 a threshold criterion for incipient motion of cohesive adhesive sediments based on moment balance and dimensional considerations is here developed the criterion discriminates between single particles and flocs critical conditions and induces a modification to the traditional shields curve commonly adopted for noncohesive particles this modification is particularly effective for the smaller size particles but tending to vanish for the larger ones the proposed approach is validated on the basis of experiments performed on sediment cores sampled at different depths from seven lakes with different trophic conditions and organic matter content the incipient motion conditions are evaluated by means of an original procedure based on image analysis techniques which enables the entrainment between single particles and flocs to be distinguished the adhesion force which is mainly due to the biological activity at the sediment water interface is estimated following the proposed criterion and it is found to depend on the organic matter content in particular the cores sampled in the littoral photic zone are characterized by a bell shaped dependence between adhesion coefficient and organic matter content which is typical for indicators of biological activity of the littoral ecosystems

the influence of clay on the threshold of movement of fine sandy beds the erosion threshold i e surface shear strength of mixed sediment deposits has been tested under the action of unidirectional currents mean critical speeds 4 mm above the bed ranging from 12 4 cm s 1 to 18 2 cm s 1 or simulated waves mean critical periods ranging from 2 0 s to 6 7 s for near bed wave amplitudes of 0 28 0 57 m using an oscillating tray in a rectangular recirculating flume the sediment mixtures investigated consisted of angular fine grained quartz sands d50 152 5 and 215 m and cohesive estuarine mud the investigation has shown that the cohesive material increases generally the erosion threshold of sandy deposits the rate of increase is smaller for mud contents 30 clay mineral content 11 14 by dry weight and is attributed to an increase of the internal angle of friction when the clay mineral content exceeds 11 14 by dry weight then the sand particles are not in contact with each other consequently the clay component controls the erodibility of the sediment mixture finally a prolonged and intense stress history can increase considerably by a factor of 1 3 1 7 the original erosion threshold value of these sediments

stable width and depth of gravel bed rivers with cohesive banks an analytical model is developed to determine the influence of the bank stability on the stable width and depth of alluvial gravel bed rivers with cohesive banks the formulation of the model is based on the assumption that the stable width corresponds with an optimum condition that is equivalent to the maximum bed load transporting capacity the optimum condition develops when the channel banks are at their limiting stability with respect to either mass failure or fluvial erosion two basic channel types are identified bank height and bank shear constrained mass failure stability is estimated using a simple total stress approach a method for estimating the critical bank shear stress based on model calibration is proposed analysis of field data indicates that the effect of the bank vegetation on bank stability can be expressed in terms of the critical bank shear stress the average critical bank shear stress value calculated for riverbanks covered by vegetation with well developed root networks was fo

cohesive material erosion by unidirectional current the initiation of motion of consolidated cohesive sediments under a unidirectional flow of clear water was studied experiments were performed in a flume tunnel capable of providing a bed shear stress up to 26 pa and a velocity of 3 5 m s 3 mm above the bed samples were prepared in a specially designed press using a carefully controlled consolidation procedure critical shear stress and velocity were found to increase with compressive strength vane shear strength plasticity index clay content and consolidation pressure

advances in the continuous monitoring of erosion and deposition dynamics developments and applications of the new peep 3t system abstract in most episodic erosion and deposition systems knowledge of the timing of geomorphological change in relation to fluctuations in the driving forces is crucial to strong erosion process inference and model building validation and development a challenge for geomorphology however is that few studies have focused on geomorphological event structure timing magnitude frequency and duration of individual erosion and deposition events in relation to applied stresses because of the absence of key monitoring methodologies this paper therefore a presents full details of a new erosion and deposition measurement system peep 3t developed from the photo electronic erosion pin sensor in five key areas including the addition of nocturnal monitoring through the integration of the thermal consonance timing tct concept to produce a continuous sensing system b presents novel high resolution datasets from the redesigned peep 3t system for river bank system of the rivers nidd and wharfe northern england uk and c comments on their potential for wider application throughout geomorphology to address these key measurement challenges relative to manual methods of erosion and deposition quantification continuous peep 3t methodologies increase the temporal resolution of erosion deposition event detection by more than three orders of magnitude better than 1 second resolution if required and this facility can significantly enhance process inference results show that river banks are highly dynamic thermally and respond quickly to radiation inputs data on bank retreat timing fixed with peep 3t tct evidence confirmed that they were significantly delayed up to 55 h after flood peaks one event occurred 13 h after emergence from the flow this suggests that mass failure processes rather than fluid entrainment dominated the system it is also shown how by integrating turbidity instrumentation with tct ideas linkages between sediment supply and sediment flux can be forged at event timescales and a lack of sediment exhaustion was evident here five challenges for wider geomorphological process investigation are discussed this event based dynamics approach based on continuous monitoring methodologies appears to have considerable wider potential for stronger process inference and model testing and validation in many areas of geomorphology

morphometrical analysis of two tropical mountain river basins of contrasting environmental settings the southern western ghats india the morphometric analysis of river basins represents a simple procedure to describe hydrologic and geomorphic processes operating on a basin scale a morphometric analysis was carried out to evaluate the drainage characteristics of two adjoining mountain river basins of the southern western ghats india muthirapuzha river basin mrb in the western slopes and pambar river basin prb in the eastern slopes the basins forming a part of the proterozoic high grade southern granulite terrain of the peninsular india are carved out of a terrain dominantly made of granite and hornblende biotite gneisses the western ghats forming the basin divide significantly influences the regional climate i e humid climate in mrb while semi arid in prb the survey of india topographic maps 1 50 000 and shuttle radar topographic mission digital elevation data were used as the base for delineation and analysis both river basins are of 6th order and comparable in basin geometry the drainage patterns and linear alignment of the drainage networks suggest the influence of structural elements the rb of either basins failed to highlight the structural controls on drainage organization which might be a result of the elongated basin shape the irregular trends in rb between various stream orders suggest the influence of geology and relief on drainage branching the dd values designate the basins as moderate to well drained with lower infiltration rates the overall increasing trend of rl between successive stream orders suggests a geomorphic maturity of either basins and confirmed by the characteristic i hyp values the re values imply an elongate shape for both mrb and prb and subsequently lower vulnerability to flash floods and hence easier flood management the relatively higher rr of prb is an indicative of comparatively steeply sloping terrain and consequently higher intensity of erosion processes further the derivatives of digital elevation data slope aspect topographic wetness index and stream power index showing significant differences between mrb and prb are useful in soil conservation plans the study highlighted the variation in morphometric parameters with respect to the dissimilarities in topography and climate

applicability of reduced gravity shallow water theory to atmospheric flow over topography abstractapplicability of the reduced gravity shallow water rgsw theory to a shallow atmospheric layer capped by an inversion underneath a deep stratified atmosphere over a two dimensional ridge has been investigated using linear analysis and nonlinear numerical simulations two key nondimensional parameters are identified namely and where g is the reduced gravity acceleration h0 is the rgsw layer depth and n and u are the buoyancy frequency and wind speed respectively in the layer above the inversion if j and are around unity or larger the response of the rgsw flow over the ridge can be significantly modified by pressure perturbations aloft any jumplike perturbations in the rgsw layer rapidly decay while propagating away from the ridge as the perturbation energy radiates into the upper layer with j and much less than unity rgsw theory is more adequate for describing rgsw flows in addition inversion splitting occurs downstream of a jump when where ni is the buoyancy frequency in the

erosion tests on four intact ontario clays erosion tests were carried out on four natural intact cohesive soils from ontario using laboratory flume tests with both clear water and water with sand in suspension it was found that erosion was initiated at discontinuities the critical shear stresses were low and were not related to the geotechnical properties of the soils higher rates of erosion occurred with the sand suspension and erosion appeared to be controlled by the movement of the sand particles it is suggested that where the eroding water contains particles in suspension such as in river beds and along shorelines of cohesive soil erosion may be controlled by the size of the particles rather than the properties of the cohesive soil or the eroding water key words erosion cohesive soil flume test

the stability of fine grained sediments from the fraser river delta the stability and erodibility of benthic fine grained sediments on the foreshore and upper foreslope of the fraser river delta were measured using thein situbenthic flume sea carousel the erosion threshold c 0 which varied between 0 11 and 0 50 pa was inversely related to erosion rate it was also proportional to sediment wet bulk density b in the form c 0 7 10 4 b 0 47 this trend agreed with those obtained from four other sites across canada that encompassed a wide range in sediment densities 1000 b 2000 kg m 3 erosion threshold shields parameter c was positively related to grain reynolds number over the silt clay size range 0 01 re 5 c 2 86re0 58 this was similar to earlier findings for water saturated sediment this trend is also in continuity with published threshold values measured in biostabilized sand 5 re 50 copyright 1997 academic press limited three erosion types were observed type ia erosion was a surface phenomenon caused by the presence of a thin organic fluff layer it occurred at current speeds less than 0 3 m s 1 type 1b erosion asymptotically decaying with time characterized the mid portions of each erosion time series and occurred at current speeds of 0 3 0 9 m s 1 type i ii erosion transitional was largely found on the foreslope and occurred at current speeds in excess of 0 8 m s 1 the erosion process began in all cases under turbulent transitional flows the change from type i to type ii erosion corresponded to the onset of turbulent rough flows 60 re 70 this is supported by video observations which showed type i erosion to be largely the result of entrainment of small aggregates and flocs whereas type ii erosion was the result of enlargement of surface irregularities and subsequent undercutting and release of large aggregates mean erosion rate em was independent of either azimuthal current speed or bed shear stress it was largely constant throughout each deployment and varied between 1 4 and 7 4 10 4 kg m 2 s 1

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

stability analysis of semicohesive streambanks with concepts coupling field and laboratory investigations to quantify the onset of fluvial erosion and mass failure abstractthe overarching goal of this study is to perform a comprehensive bank stability analysis that is phenomenologically sound by considering both mass failure and fluvial erosion the nature of this study is twofold first field and experimental analyses are conducted to generate data for channel cross section properties soil index properties and mechanical and erosional strengths at two sites in a representative midsize midwestern stream in southeastern iowa that is subjected to frequent flash floods and characterized by active fluvial erosion and cantilever failure second the channel surveys and data obtained from the field and laboratory analyses are used as input parameters for an established one dimensional channel evolution model namely the conservational channel evolution and pollutant transport system concepts version 2 0 langendoen and alonso 2008 to estimate the factor of safety for mass failure fsm and fluvial erosion fsf and simulate the bank retreat as a result of eithe

mechanistic detachment rate model to predict soil erodibility due to fluvial and seepage forces abstractthe erosion rate of cohesive soils is typically computed using an excess shear stress model based on the applied fluvial shear stress however no mechanistic approaches are available for incorporating additional forces such as groundwater seepage into the excess shear stress model parameters seepage forces are known to be significant contributors to streambank erosion and failure the objective of this research was to incorporate seepage forces into a mechanistic fundamental detachment rate model to improve the predictions of the erosion rate of cohesive soils the new detachment model which is referred to as the modified wilson model was based on two modified dimensional soil parameters b0 and b1 that included seepage forces due to localized groundwater flow the proposed model provided a general framework for studying the impact of soil properties fluid characteristics and seepage forces on cohesive soil erodibility equations were presented for deriving the material parameters from bot

quantitative measurement of the scour resistance of natural solid clays the erosion of clayey soils is a complex phenomenon that includes various types of erosive actions a tentative classification of erosion processes is proposed this paper concentrates on the scour resistance of solid clays available prediction methods are reviewed generally they propose relationships between physical or mechanical parameters and the critical hydraulic shear stress tau sub c that defines a boundary between no erosion and erosion it became apparent that the physicochemical parameters of both the clay and eroding water control the erosion process however subsequent studies on these parameters have yet to yield reliable predictions of natural clay erodibility from indirect measurements an erosion testing program was therefore performed on three quebec clays with the improved rotating cylinder technique in this test intact or remolded samples can be tested physicochemical parameters can be controlled and the hydraulic shear stress tau and the erosion rate e can be adequately determined a relatively complete and accurate graph of e versus tau including e values for tau values lower than critical can be established previous and present research underline the need to exert a strict control of all clay and water parameters including that of sample preparation in order to adequately simulate a field problem

the importance of high resolution monitoring in erosion and deposition dynamics studies examples from estuarine and fluvial systems abstract erosion and deposition processes lie at the centre of geomorphological explanation but progress in understanding has been limited by a lack of appropriate high resolution monitoring methodologies which permit detection of erosion and deposition dynamics this paper presents a case for monitoring erosion and deposition at high temporal resolutions and uses hypothetical approaches supported by example erosion and deposition events and analyses drawn from estuarine and fluvial systems the paper first presents testable hypotheses to demonstrate the complexity of possible event combinations sequences and juxtapositions for the erosion driving forces which underpin the need for high resolution monitoring second it summarises recent improvements to the photo electronic erosion pin peep automatic erosion and deposition monitoring system including the novel concept of thermal consonance timing tct which is particularly promising because it helps to define the timing of nocturnal events and through the entire hydrograph third example results are discussed from high resolution monitoring of bank erosion at a tidal site at burringham on the river trent in northern england tidal banks are revealed to be much more dynamic than previous conventional monitoring has indicated a key result is that because the high resolution approach allows erosional and depositional activity to be assigned to specific periods of tidal inundation it becomes possible for the first time routinely to produce event based erosion 36 mm h 1 and deposition rates 4 5 and 8 4 mm h 1 such rate determinations are potentially very useful in the field validation of sedimentological and geomorphological models including grain settling and resuspension theory fourth through a longer term of aggregated daily data a striking 2 week cycle of deposition and erosion emerges which correlates most strongly with spring neap tidal cycling but is moderated by wind stress effects sediment was deposited on the bank relatively quickly over 4 5 days but then removed by erosion rather slowly over 9 10 days fifth the dangers of low resolution monitoring are illustrated by comparing the daily peep data set with a series resampled at a lower 14 day frequency to simulate the information generated by conventional resurvey methodologies the low frequency series failed adequately to represent the cyclicity mean range variability and trend of bank elevation changes and without this dynamics information rate and process definition is very difficult largely because of self concealing activity sixth a useful advance is illustrated by the fluvial erosion sequence for the river wharfe n england this shows how tct can generate rare and important results with the definition of the precise time of an erosion event within the hydrograph bank retreat here occurred very quickly after initial inundation and within 4 h of the flow peak information which can be used to define thresholds for entrainment e g critical shear stresses such high resolution monitoring helps to unravel some of the erosional effects of complex sequences combinations and juxtapositions of similar or different forcing events finally high resolution approaches have been adopted worldwide for fluvial estuarine mudflat and canal systems but considerable potential exists for their development and use in these and other contexts e g gully hillslope beach and dune environments to improve understanding and modelling of geomorphological processes more widely

a new technique for the automatic monitoring of erosion and deposition rates the rates and processes of erosion and deposition of soils and sediments are subjects of widespread and increasing concern in the earth and environmental sciences process inference from field studies however has been hampered by a lack of information on the precise magnitude frequency and timing of erosional and depositional activity because no automatic monitoring technique has hitherto been available i describe here an automatic photo electronic erosion pin peep system which apparently for the first time allows quasi continuous time series of erosion and deposition data to be collected example results from a river bank site show how the peep system helps to define the true temporal distribution of geomorphological change quantify the erosional impact of individual forcing events and discriminate between competing hypotheses of process control in erosional and depositional contexts the system should thus allow more effective testing of erosion models of high temporal resolution and facilitate a more rigorous linking of catchment sediment output to supply dynamics

drainage networks from grid digital elevation models current algorithms that deduce the drainage network from a digital elevation model dem represented by a regular array of surface elevations share a fault unless the terrain is rugged the derived water channels tend to flow in parallel lines along preferred directions engendered by the sampling grid orientation we present a simple solution to the problem a second difficulty is the presence of noise that creates artificial pits we briefly describe a method which deals with pits in what we believe to be a more efficient manner for virtual memory environments than previous efforts our system has treated dems of nearly 9 000 000 pixels we show how depth first search of the resulting drainage network permits segmentation of the dem into basins by various criteria analysis of stream sediment anomaly dilution profiles improved hydrological models and other applications

effects of bed structure on erosion of cohesive sediments data from two recent papers are used to illustrate the effects of change of structure of fine sediment on erosion rates the paper by roberts et al presents erosion rates as functions of bed bulk density and shear stress ranges of densities were obtained by allowing various times for consolidation and the erosion tests were made where the density was nearly constant with depth a marked change in the linear relation between erosion rate and density is presented that is attributed to a change of bed structure the paper by zreik et al presents erosion rate data for a thin layer near the surface of a bed formed by sedimentation the linear relation between amount of overburden removed and bed strength also has a marked change that can be attributed to a change of bed structure the initial structures are described as aggregates of aggregates and the changes are shown to be progressive collapse of the larger to smaller interaggregate pores due to thermal motion biased by overburden pressure to a nearl

morphometric analysis of the river thamirabarani sub basin in kanyakumari district south west coast of tamil nadu india using remote sensing and gis the quantitative analysis of the drainage morphometric system is vital to understand the hydrological and environmental interaction and its processes of an area the present study deals with quantitative characteristics of morphometry of steep slope and short length sub basin of r thamirabarani in kanyakumari district tamilnadu india using geospatial technology in this study the digital elevation model data product aster dem landsat etm image and survey of india topographical map were used to delineate slope relief and drainage system structures such as drainage pattern stream order stream network and stream length of the sub basin using arcgis 9 3 software the morphometric analysis deals with hydrologic processes such as stream frequency bifurcation ratio circulatory ratio and length of overland flow of the sub basin area and their influences on the local morphologic landforms the quantitative measurement of these characteristics is used to explore the basin s contribution to the hydrological cycle and the shape size and formation of the local landscapes in the region moreover the hypsometric analysis and denudation rate were estimated for understanding the quantitative geomorphological characteristics of the sub basin the relationship of the morphometric parameters reveals that the drainage network is strongly controlled by geological and geomorphological structures of the area the geometry of streams exhibits dendritic drainage pattern associated with coarse drainage texture in primary order of streams present on hilly terrain surface and semi dendritic pattern in higher stream order flow on less elevated surface with gentle slope the drainage density of the study area ranges from 0 1 to 1 89 km km2 and the maximum density value was found along the higher stream order the mean bifurcation ratio of this area is 4 21 and the high ratio was measured between the third and fourth order of stream segments the morphometry of this area is depicted by the length of the stream segment drainage pattern and stream flow direction which are influenced by relief steep slope and local geological structure furthermore the sub basin is found to be strongly elongated in shape with a length of 42 78 km and the circularity ratio of this area is measured as 0 33 and elongation ratio as 0 57 the textural dissection of the landforms shows low drainage density in the high elevated hilly terrain in the north and high level in the plain areas in the southern part the values of the circulatory ratio length of overland flow and elongation ratio are relatively close to one another and the relationship among them shows their influences on the process of surface runoff and sediment deposition along the estuary landforms in the study area moreover it is observed that the hypsometric curve of this study area is characterized by convex up shape in nature and represents the youth stage inequilibrium of landscapes consequently the hypsometric integral value 0 49 reflects the distribution of a major volume of the landmass 435 32 km2 at relatively low elevations 180 m the morphometric parameters induced denudation rate of this study area is 65 14 t km2 year and indicates the occurrence of a wide range of denudation intensities throughout the sub basin which is relatively proportional to the suspended sediment yield that is transported in the suspension per unit area based on the realistic output it is proved that remote sensing and gis are effective tools for morphometric studies of the drainage basin

understanding mass fluvial erosion along a bank profile using peep technology for quantifying retreat lengths and identifying event timing this study provides fundamental examination of mass fluvial erosion along a stream bank by identifying event timing quantifying retreat lengths and providing ranges of incipient shear stress for hydraulically driven erosion mass fluvial erosion is defined here as the detachment of thin soil layers or conglomerates from the bank face under higher hydraulic shear stresses relative to surface fluvial erosion or the entrainment of individual grains or aggregates under lower hydraulic shear stresses we explore the relationship between the two regimes in a representative us midwestern stream with semi cohesive bank soils namely clear creek ia photo electronic erosion pins peeps provide for the first time in situ measurements of mass fluvial erosion retreat lengths during a season the peeps were installed at identical locations where surface fluvial erosion measurements exist for identifying the transition point between the two regimes this transition is postulated to occur when the applied shear stress surpasses a second threshold namely the critical shear stress for mass fluvial erosion we hypothesize that the regimes are intricately related and surface fluvial erosion can facilitate mass fluvial erosion selective entrainment of unbound exposed mostly silt sized particles at low shear stresses over sand sized sediment can armor the bank surface limiting the removal of the underlying soil the armoring here is enhanced by cementation from the presence of optimal levels of sand and clay select studies show that fluvial erosion strength can increase several fold when appropriate amounts of sand and clay are mixed and cement together hence soil layers or conglomerates are entrained with higher flows the critical shear stress for mass fluvial erosion was found to be an order of magnitude higher than that of surface fluvial erosion and proceeded with higher approximately 2 4 times erodibility the results were well represented by a mechanistic detachment model that captures the two regimes copyright 2017 john wiley sons ltd

digital elevation model networks demon a model of flow over hillslopes for computation of contributing and dispersal areas current algorithms for computing contributing areas from a rectangular grid digital elevation model dem use the flow routing model of o callaghan and mark 1984 which has two major restrictions 1 flow which originates over a two dimensional pixel is treated as a point source nondimensional and is projected downslope by a line one dimensional moore and grayson 1991 and 2 the flow direction in each pixel is restricted to eight possibilities we show that large errors in the computed contributing areas result for any terrain topography divergent convergent or planar we present a new model called digital elevation model networks demon which avoids the above problems by representing flow in two dimensions and directed by aspect demon allows computation of both contributing and dispersal areas demon offers the main advantage of contour based models e g moore et al 1988 the representation of varying flow width over nonplanar topography while having the convenience of using rectangular grid dems

hydraulic physical modeling and observations of a severe gap wind abstract strong gap winds in howe sound british columbia are simulated using a small scale physical model model results are presented and compared with observations recorded in howe sound during a severe gap wind event in december 1992 hydraulic theory is utilized to explain along channel variation in wind field observations affirm the findings of the physical modeling with both indicating the presence and location of controls and hydraulic jumps in the wind layer hydraulic behavior is found to change as the synoptic pressure gradient and the flow rate increase in particular field results indicate two distinct hydraulic situations one during relatively weak wind the other which is more strongly controlled during the period of peak wind an additional comparison is made with output from the computer model hydmod of jackson and steyn numerical simulations configured for the conditions present in howe sound during the december 1992 event indicate channel hydraulics and thus spatial wind spee

influence of cohesion on the incipient motion condition of sediment mixtures 1 previous investigations on initiation of motion and erosion of cohesive sediment mixtures have not included gravel within the mixtures experimental results on the incipient motion characteristics of cohesive sediment mixtures containing gravel are presented in this paper the sediment used consisted of fine gravel mixed with clay in proportions varying from 10 to 50 by weight and fine gravel with fine sand mixed in equal proportion with clay proportions again varying from 10 to 50 by weight the stages of the incipient condition of motion were visually identified three modes of initiation of motion of cohesive sediment mixtures were noticed namely pothole erosion line erosion and mass erosion the modes of initiation of motion changed mainly with clay percentages in the mixture its antecedent moisture characteristics and the applied shear stress analysis of the experimental data from the present study and the literature revealed that depending upon the flow and sediment characteristics the critical shear stress of the incipient motion condition in cohesive sediment mixtures can be up to 50 times larger than the critical shear stress of cohesionless sediments having similar arithmetic mean size as the cohesive sediments on the basis of dimensional considerations a relationship is proposed for the determination of critical shear stress of the incipient motion condition in cohesive sediment mixtures also containing gravel the variables namely clay percentage void ratio and unconfined compressive strength of the sediment bed are noticed to be the main parameters controlling the incipient motion condition of the cohesive sediments in the absence of cohesion the proposed relationship reduces to the critical shear stress for the incipient motion condition of the cohesionless sediment mixture having the same arithmetic mean size the condition for the threshold of erosion of cohesive sediment mixtures by the flow is thus parameterized in the present study

hydraulic aspects of fohn winds in an alpine valley this study examines the applicability of single layer hydraulic theory to alpine fohn winds in the example of the flow in the brenner pass region austria italy the south fohn is described as the gap flow over the pass and along the associated wipp valley numerical shallow water simulations for a wide range of initial conditions including shallow and deep fohn cases are discussed and compared with selected measurements collected within the mesoscale alpine programme map the observational analyses are based on doppler and aerosol backscatter lidar data for a specific fohn case and on surface observations and radiosoundings for all fohn cases observed within the 70 day map special observing period sop radiosoundings at a location upstream south and downstream north of the brenner pass reveal that the average map sop fohn case had subcritical flow south and nearly critical flow north of the brenner pass the hydraulic model indicates flow transition to a supercritical state near the pass a hydraulic jump 2 km further north mainly subcritical flow in the upper wipp valley except near the brenner and especially for shallow fohn a tendency to becoming supercritical in the lower wipp valley the model results suggest that the vertical topographic contraction exerts stronger control for the flow at the brenner gap than the lateral contraction in accordance with doppler lidar measurements the hydraulic model captures the decrease of the wind speed in the across valley direction from east to west in the northern part of the valley this asymmetric flow pattern is a result of the complex valley geometry rather than of the influence of upper level synoptic winds as suggested in a previous study for some observed cases the strength of the temperature inversion at the top of the fohn layer decreased across the brenner pass presumably due to entrainment processes consequently the reduced gravity decreased as well there are two major reasons for the only moderate agreement between the hydraulic parameters retrieved from soundings and those provided by the model the model assumes a constant value of reduced gravity and the calculation of hydraulic parameters for fohn cases without a strong and sharp temperature inversion is ambiguous essential flow patterns in the simulated fields such as the location of the pressure minimum and wind speed maxima compare well with the surface observations along a valley transect indications for a steeply amplified or breaking gravity wave resembling a hydraulic jump to the lee of the two mountain ridges are found in lidar observations as well as in the simulations copyright 2004 royal meteorological society

secondary current effects on cohesive river bank erosion 1 the emphasis of this research was placed on the development of a methodology that allows 1 an adequate representation of the distribution of the near bank shear stress s when secondary currents are present and 2 estimation of the critical erosional strength cr and other sediment erodibility parameters for fluvial erosion these two factors combine to form the overarching objective of this investigation which was carried out in union flat creek a stream with pronounced cross sectional irregularities located within the loess region of the palouse basin of washington state united states the study has shown that the presence of the secondary currents increases the magnitude of the depth averaged sidewall shear stress at least by a factor of 2 0 it was also found that the ratio of the maximum to the depth averaged sidewall shear stress is greater than 5 these findings suggest therefore that use of the may be a good approximation of the fluid shear stress magnitude for simple channel geometries but not for natural channels characterized by complex geometries the measured critical erosional strength cr 4 16 pa was comparable with the findings of other laboratory and field studies that also focused on palouse sediments