petrological statistical approach to interpret recent and subrecent lagoon subfacies idku nile delta of egypt abstract an approach combining petrology and statistics cluster analysis is developed to better distinguish a series of subfacies in surficial and short core samples from idku lagoon in the northwestern nile delta egypt the method integrates lithology physical and biogenic structures grain size and composition of the sand size fraction seven lithofacies eight grain size types and six clusters reveal comparable geographic distributions that are a direct response to geomorphic setting and depositional processes both of which have been modified by man although positioned in an arid setting and affected by anthropogenic factors land reclamation pollutants regional subfacies distribution patterns in idku lagoon are largely a function of the spatial configuration of freshwater dominated to brackish to higher salinity dominated near inlet zones typical of lagoons receiving significant freshwater input within idku a northern depositional province near the inlet and along the coastal sand barrier is defined by associations of terrigenous and coarse grained sediment types a southern province bounded by lagoon margins and marshes is characterized by finer grained sediment types with a high biogenic content recording lower energy levels the petrological statistical approach is used to identify and interpret lagoon subfacies in older to 6000 years b p core sections in idku region and in former abu qir lagoon additionally cluster analysis serves to determine specific lagoon subfacies from hand samples alone whether from surface grabs or cores this is based on a comparison of lithofacies and clusters determined for surficial and short core samples in the idku region to test the method a separate cluster analysis also using surficial and short core samples was used to define manzala lagoon subfacies in the northeastern nile delta results are generally comparable to those obtained in the idku study and show a close relation among manzala lagoon subfacies geomorphic configuration and depositional processes the petrological statistical method could be applied to other regions and also to the geological record

the red river fault system in the tonkin gulf vietnam abstract the red river fault system in the tonkin gulf offshore haiphong was studied using seismic profiles calibrated by deep wells well characterised left lateral strike slip occurred continuously within a narrow 30 km wide zone southwest of the vinh minh fault between 30 ma and 5 5 ma however the corresponding amount of offset probably does not exceed a few tens of kilometres no sign of post 5 5 ma right lateral motion can be detected prior to 30 ma there is a widespread extension in a wider 100 km wide zone which could be related to a significant amount of left lateral motion the motion of the fault splays to the northeast of the vinh minh fault prior to 30 ma was absorbed in the rifting of the gulf of beibu a 15 5 ma unconformity separates the transtensional regime from a later transpresional regime this 15 5 ma date coincides with the cessation of sea floor spreading in the south china sea

age origin and climatic controls on vegetated linear dunes in the northwestern negev desert israel abstract the stabilized northwestern nw negev vegetated linear dunes vld of israel extend over 1300 km 2 and form the eastern end of the northern sinai nw negev erg this study aimed at identifying primary and subsequent dune incursions and episodes of dune elongation by investigating dune geomorphology stratigraphy and optically stimulated luminescence osl dating thirty five dune and interdune exposed and drilled section were studied and sampled for sedimentological analyses and osl dating enabling spatial and temporal elucidation of the nw negev dunefield evolution in a global perspective the nw negev dunefield is relatively young though sporadic sand deposition has occurred during the past 100 ka dunes began to accumulate over large portions of the dunefield area only at 23 ka three main chronostratigraphic units corresponding to three osl age clusters were found throughout most of the dunefield indicating three main dune mobilizations late to post last glacial maximum lgm at 18 11 5 ka late holocene 2 0 8 ka and modern 150 8 years the post lgm phase is the most extensive and it defined the current dunefield boundaries it involved several episodes of dune incursions and damming of drainage systems dune advancement often occurred in rapid pulses and the orientation of vld long axes indicates similar long term wind directions the late holocene episode included partial incursion of new sand reworking of late pleistocene dunes as well as limited redeposition the modern sand movement only reactivated older dunes and did not lengthen vlds this aeolian record fits well with other regional aeolian sections we suggest that sand supply and storage in sinai was initiated by the late pleistocene exposure of the nile delta sands late pleistocene winds substantially stronger than those usually prevailing since the onset of the holocene are suggested to have transported the dune sands across sinai and into the northwestern negev our results demonstrate the sensitivity of vegetated linear dunes located along the northern fringe of the sub tropical desert belt to climate change i e wind and sediment supply

a predictive typology for characterising hydromorphology abstract whilst traditionally poorly quantified the link between physical habitat and ecological response in rivers is widely recognised and is currently rising up legislative and policy agendas in europe this is reflected in the water framework directive which dictates that hydromorphological condition of water bodies should be capable of supporting good ecological status methods are developed that integrate river system hydrology geomorphology and ecology and the complex interplay between these three variables whilst hydrological and biological methods for characterisation are relatively well established geomorphological methods are not effective characterisation of geomorphology physical habitat with full spatial coverage at a range of scales can be used to explore spatial interactions between habitat and biological data and potentially further our understanding of ecological response managers need to know what aspects of physical habitat and at which critical locations intervention will lead to greatest improvements in ecological condition this requires information on hydromorphological character and condition existing applied approaches for capturing geomorphological data are highly dependent on intensive fieldwork which is unlikely to be resourced at sufficiently extensive scales to meet management needs this paper outlines a typology approach for characterising the physical template of rivers it draws on a range of hydromorphological data to develop a framework for a channel typology with data collation from secondary sources followed by targeted fieldwork to i assess to what extent individual channel types are characteristic of field conditions and ii to collect information on reach scale variability within each type results suggest that characterisation of channel types based on stream power floodplain width and stream order does result in a distinct set of channel types field survey subsequently found that these types had a characteristic suite of patch scale habitat features flow types the approach was applied to a catchment where geomorphological processes exert a dominant control over physical habitat

selecting geomorphic variables for automatic river segmentation trade offs between information gained and effort required abstract identifying river segments with apparently distinct geomorphic characteristics but relatively homogeneous internal features may be critically helpful in designing network analysis for characterization environmental assessment and river management automatic segmentation procedures using geographic tools and statistical methods provide objective and replicable results in particular multivariate procedures may be appropriated for different purposes such as coping with the multiple dimensionality of river systems although there is an increasing number of studies dealing with segmentation using different sets of morphological variables the influence that the selected variables have on segmentation results is rarely assessed in this context we defined five combinations of frequently used geomorphic variables i e channel slope active channel width valley bottom width channel confinement and specific stream power and compared the obtained segmentation results we study the upper esla river network covering a total length of 294 km with the largest two rivers regulated by large dams variables were measured at successive river sections 200 m apart five segmentation results were obtained in which we compared the number and characteristics of the segments and the internal variability and the suitability of predicting river dynamics i e occurrence of bare and vegetated gravel bars the number of segments per kilometer of river and their average length were different among segmentations but varied much more across rivers than across segmentations in general segmentations including channel slope and active channel width performed better in predicting the occurrence of bare gravel bars than segmentations based on stream power or valley confinement when splitting the initial data set into regulated and non regulated segments differences in predicting the occurrence of gravel bars were found with better results in the case of non regulated rivers channel slope and active channel width showed a reduced explanatory power for the regulated reaches finally we conclude that primary geomorphic variables such as channel slope and active channel width were more efficient than secondary variables such as stream power which may encompass more information but needed additional data and the use of empirical models with greater effort and much uncertainty in the case of regulated rivers automatic segmentation including the affected variables e g active channel width may help in detecting differences in geomorphic sensitivity to river adjustments across the resulting segments downstream from the dams our results offer valuable insights into the selection of geomorphic variables for river segmentation analysis in which trade offs between the information gained and the effort required must be considered according to the respective research targets

technical methodology for aster global dem at the core of the technical methodology for creating the advanced spaceborne thermal emission and reflection radiometer aster global digital elevation model gdem is the procedure for generating a global set of 1 latitude by 1 longitude tiles containing dem data in geographic latitude and longitude coordinates and with one arc second postings from scene based aster dems the aster gdem is comprised of all tiles which include at least 0 01 land in them each containing 3601 by 3601 elevation data points the tiles are created by stacking all observed scene dem data matched geographically to the tile container selecting valid data for each pixel removing abnormal data values and then averaging the remaining selected valid data to assign as the tile elevation data valid earth surface elevation values typically clump within a 40 m range and are assumed to be lower in elevation than residual cloud outliers the filtering process which assigns the tile elevation data is one of the most important parts of the gdem generation system the median based selection method is designed to efficiently select the valid data for each pixel the combination of cloud masked and non cloud masked data is another important part of the process to assign accurate elevation data for each pixel because the cloud masking capability is not perfect the algorithm used to combine both data is described the postprocessing for inland water bodies is successfully carried out to yield a flattened elevation value this postprocessing is essential to assign unique elevation values for each inland water body gdem tile elevation data include some residual anomalies mostly in areas with fewer than three valid stacked input scenes the correction method using existing reference data also is described

late quaternary tectonics and seismotectonics along the red river fault zone north vietnam abstract a study of active tectonic development in vietnam is of great importance right lateral strike slip offsets along the red river fault during the pliocene present are determined by analyzing tributaries quaternary alluvial fans river valley from landsat spot images detailed topographical maps and field observation along the sw fault of the red river right lateral offsets of stream channels range between 150 and 700 m mean offsets of 300 m drainage offsets 170 450 m are found on the eastern branch assuming the major phase of incision is visible in this area which is close to the red river delta due to the onset of riss glaciation using the average length of offset channels and a minimum rate of 100 150 mm yr for river propagation we estimate the horizontal slip rates of 2 9 1 7 mm yr for song chay fault 2 3 1 5 mm yr for red river left side fault and 2 1 1 5 mm yr for red river left side fault several active faults associated with it are observed in son la area the phong tho nam pia fault is clearly seen in the geomorphology which separates tu le and song da rift zones in normal fault segments striking nw se sw dipping is observed clearly from spot images in the field triangular facets indicate typical dip slip displacement based on different data vertical slip rate of phong tho nam pia fault is estimated to be 0 2 0 4 mm y for pliocene present 0 5 3 mm y for quaternary present and 0 6 1 7 for the present time based on various methods maximum credible earthquakes for different fault segments in vietnam were estimated

a phenomenon based approach to upslope contributing area and depressions in dems description of the terrain surface through digital elevation models dems strongly depends on data collection methods and dem data structures for efficiency and availability reasons regular point distributions are most common which yield artefacts such as depressions and preferential flow directions these facts need to be considered when natural phenomena are modelled as is shown for handling depressions and for estimation of flow paths and upslope contributing areas analysis of the main reasons for the occurrence of depressions shows that they usually better reflect the terrain than their surroundings thus the most common remedial method of raising depressions is rejected algorithms that cut a flow path from the depression through its bounding barrier are favoured instead several flow routing algorithms are evaluated for their behaviour in regular grids it is shown that the multiple flow direction mfd algorithm that distributes water from a grid cell to the lower of its eight neighbours proportionally to their elevation differences slope exhibits correct flow directions and the best rotation invariance it is suggested that the estimation of upslope contributing areas tcas is undertaken in two steps first a high quality flow direction data set is derived by a well behaved mfd algorithm or by subgrid modelling of flow paths secondly the upslope contributing areas are obtained by counting the upslope elements

spatial disaggregation and aggregation procedures for characterizing fluvial features at the network scale application to the rhone basin france network scale heterogeneity in fluvial forms and processes has been analyzed for decades through the field based characterization of a reduced number of sites spatially continuous data sets are increasingly available at a national scale e g digital elevation models or aerial orthophotographs and open up new possibilities to investigate spatial structures in stream networks the paper introduces a gis methodological framework to support and automate the large scale characterization of the fluvial system based on spatial disaggregation and aggregation procedures the spatial disaggregation consists in the longitudinal discretisation of geographical objects into relatively high resolution spatial units to characterize fluvial features continuously along stream networks because rivers are heterogeneous and hierarchically organized the spatial aggregation aims to delineate statistically pattern or process based spatial units to answer questions at appropriate scales the paper develops the gis implementation of the disaggregation and aggregation procedures for characterizing stream networks in a geomorphic perspective we illustrate the approach on the rhone network focusing on the characterization of three geographical objects commonly used in classification schemes the streamline the valley bottom and the active channel the latter on a limited area the spatial aggregation is automated using the threshold test of pettitt 1979 to detect change points in univariate data series and delineate homogeneous spatial units throughout the stream network we provide three simple application examples to illustrate the potentialities of the spatial aggregation to investigate spatial heterogeneity in stream networks finally insights limitations and future challenging issues emerging from the application of the methodological framework are discussed

high resolution basin extent observations and implications for understanding river form and process fifty years of fluvial studies have posited a variety of conceptual frameworks for characterizing river forms and processes throughout entire basins including hydraulic geometry the river continuum concept self organized criticality and sediment links this article uses basin extent high resolution observations of fluvial forms in the nueces river basin texas and yellowstone national park to evaluate the ability of these frameworks to characterize system behavior across a multitude of scales the nueces data were collected with remote sensing methods and the yellowstone data were collected through extensive field surveys the data resolution spatial extent and quality of these data sets allow direct comparison between the two areas the hyperscale comparison supports using of each these frameworks at specific scales but also indicates an irreducible amount of variation in both datasets across many different scales that is not captured by the conceptual frameworks moreover the scales and locations where one framework such as hydraulic geometry works well are often not the same scales and locations where another framework such as the river continuum concept works well because the conceptual frameworks appear to operate at scales and locations distinct from one another the measurement approaches necessary to observe them must also be at different scales and locations for example seeing self organized criticality in a river system is difficult without an extensive survey through space whereas the recognition of sediment links requires quite intense sampling in specific river regions we suggest that these separations between measurement scales represent an incommensurability issue in river studies making it very difficult to both communicate among and test between two or more competing theories making simultaneous hyperscale observations of the river is one approach to minimizing the theory ladeness of observation as deviations from different predictions can be plotted at every scale copyright 2010 john wiley sons ltd

the fluvial evolution of the holocene nile delta abstract the evolution of the nile delta the largest delta system in the mediterranean sea has both high palaeoenvironmental and archaeological significance a dynamic model of the landscape evolution of this delta system is presented for the period c 8000 4500 cal bp analysis of sedimentary data and chronostratigraphic information contained within 1640 borehole records has allowed for a redefinition of the internal stratigraphy of the holocene delta and the construction of a four dimensional landscape model for the delta s evolution through time the mid holocene environmental evolution is characterised by a transition from an earlier set of spatially varied landscapes dominated by swampy marshland to better drained more uniform floodplain environments archaeologically important pleistocene inliers in the form of sandy hills protruding above the delta plain surface known as turtlebacks also became smaller as the delta plain continued to aggrade while the shoreline and coastal zone prograded north these changes were forced by a decrease in the rate of relative sea level rise under high rates of sediment supply this dynamic environmental evolution needs to be integrated within any discussion of the contemporary developments in the social sphere which culminated in the emergence of the ancient egyptian state c 5050 cal bp

late quaternary stratigraphy and paleogeography of the eastern nile delta egypt abstract a petrological study of numerous sediment borings identifies the late pleistocene and holocene lithofacies in the northeastern nile delta of egypt a coarsening upward sequence characterizes the major holocene depocenters located along the northern margin of the present delta stratigraphic correlation of radiocarbon dated sections and mapping of key facies such as delta front mud reveal the locations of four major holocene delta lobes related to former distributary branches of the nile river mendesian pelusiac tanitic and pre modern damietta these lobes formed primarily of marine prodelta and delta front deposits interfinger geographically but radiocarbon dating indicates that their bases are not synchronous lobes developed for the most part since 8000 years b p i e as the rate of eustatic sea level rise began to decrease climatic and sediment discharge fluctuations lateral migrations of distributaries and isostatic subsidence of land are additional factors that affected the temporal and spatial distributions of the lobes paleogeographic maps reveal the changes with time in the distributions of different lobes and deltaic plain environments marsh lagoons and concomitant displacement of the coastline holocene sediment accumulation rates to 500 cm per 1000 years are calculated this is 10 times greater than that on the nile cone and 50 times greater than on the egyptian continental shelf the delta coastal margin in the study area migrated northward by as much as 50 km during the past 5000 years an average progradational rate of up to 10 m per year the general configuration of the present delta developed during the past millennium the major changes recently induced by man in this region coupled with a series of continuing natural phenomena slow rise in sea level coastal erosion subsidence have markedly affected the evolution of the delta petrological study of the nile delta sediments provides baseline reference information to help recognize changes in the recent geological past to help identify those taking place at present and possibly to help predict those likely to occur in this region in the future

characterizing physical habitats in rivers using map derived drivers of fluvial geomorphic processes abstract new understanding of fluvial geomorphological processes has successfully informed flood mitigation strategies and rehabilitation schemes in recent years however well established geomorphological assessments are location specific and demanding in terms of resource and expertise required and their routine application for regional or national river characterization although desirable is unlikely at present this paper proposes a framework based on gis procedures empirical relationships and the self organized map for the analysis and classification of map derived drivers of fluvial morphological processes the geomorphic controls analysed are channel gradient and hydrology specific stream power river order and floodplain extent the case study is a gravel bed river in england using the self organized map we analyse patterns of these controls along the river longitudinal profile and identify clusters of similar configuration the reciprocal relationships that emerge amongst the geomorphic controls reflect the hierarchical nature of fluvial systems and are consistent with the current theoretical understanding of fluvial processes field observations from the river habitat survey are used to prove the influence of geomorphic drivers on reach scale morphological forms six clusters are identified which describe six distinctive channel types these proved to be characterized by distinctive configurations of geomorphic drivers and specific sets of physical habitat features the method successfully characterizes the notable transitions in channel character along the river course the framework is suitable for regional or national scale assessments through automatic gis and statistical procedures with moderate effort

assessment of downstream trends in channel gradient total and specific stream power a gis approach geographic information systems gis analyses of digital elevation models dems coupled with catchment area based discharge estimation techniques provide a relatively simple means of modelling contiguous downstream trends in channel gradient total stream power and in riverscapes conducive to regime analysis also specific stream power for a small high relief coastal catchment in se australia good agreement was obtained between channel gradients derived from a 25 m cell size dem and field survey equivalents over distances of several kilometres indicating that channel gradients derived from dems can have a reasonable degree of absolute as well as relative accuracy over multi kilometre reach scales assessment of downstream rates of change in channel gradient and specific stream power across four river systems suggests that some of the river reaches most responsive to high magnitude floods occur in zones where these variables rapidly decrease downstream modelling of downstream trends in channel gradient total and specific stream power from catchment wide dems has potential to provide a framework with which to investigate conceptual and empirical models between channel gradient stream power and the form and dynamics of river systems

lateral geomorphic connectivity in a fluvial landscape system unraveling the role of confinement biogeomorphic interactions and glacial legacies abstract the rates at which sediment from the landscape is recruited to channel networks reflect lateral geomorphic connectivity and have significant implications for biophysical river systems by strongly influencing sediment supply regime such inputs control the dynamics and characteristics of the channel as well as the associated habitat and biota the main objective of this research was to disentangle the relative importance of geomorphic and biological factors which define spatial patterns in lateral connectivity by promoting or restricting bank erosion avulsions and slope failures focusing on a forested formerly glaciated mountain basin in the interior pacific northwest we combined extensive field surveys with remote sensing data lidar aerial imagery to obtain metrics representing this complex suite of landscape characteristics the interpretation of evidence yielded by correlations between these variables a regime model and qualitative observations suggest that at a multi decadal timescale between major landscape disturbances lateral connectivity patterns in sullivan creek may be to a large extent governed by a combination of biotic factors and glacial legacies in particular forest canopy metrics were key predictors of hillslope stability as well as bank and valley floor resistance suggesting a pivotal influence of root reinforcement on the other hand instream large wood abundance was closely related to channel splitting which reflects its role in promoting channel avulsions more extensive bank erosion in reaches dominated by drift deposits appeared to indicate glacial legacies furthermore a strong association between bank erosion and colluvial inputs suggested a close coupling within the channel hillslope system lateral confinement defined as the proportion of the channel length abutting against bedrock terraces fans and roads was negatively associated with channel braiding the relationships linking confinement with bank erosion and the magnitude of colluvial inputs negative and positive association respectively were relatively weak taken together findings emerging from this research suggest that better understanding of lateral geomorphic connectivity patterns in mountain river basins similar to our study site requires that both channel processes and broader biophysical landscape system be considered

characterizing fluvial systems at basin scale by fuzzy signatures of hydromorphological drivers in data scarce environments despite the relevance of river hydromorphology hymo for integrated water resource management consistent geomorphic information at the scale of whole river basin is still scarce especially in emerging economies in this paper we propose a new scalable and globally applicable framework to analyze and classify fluvial systems in data scarce environments the framework is based on a data driven analysis of a multivariate data set of 6 key hydro morphologic drivers derived using freely available remote sensing information and several in situ hydrological time series core of the framework is a fuzzy classifier that assigns a characteristic signature of hymo drivers to individual river reaches we demonstrate the framework on the red river basin a large trans boundary river basin in vietnam and china where human induced morphological change concretely endangering local livelihoods is contrasted by very limited hymo information the derived hymo information covers spatial scales from the entire basin to individual reaches it conveys relevant information on subbasin hydro morphologic characteristic as well as on local geomorphologic forms and processes the fuzzy classifier successfully distinguishes abrupt from continuous downstream change and spatially dissects the river system in segments with homogeneous hydro morphologic forcings successful numerical modelling of morphologic forms and process rates based on the hymo signatures indicates that the multivariate basin scale classification captures relevant morphological drivers outperforms an analysis based on local drivers only and can support river management from diverse morphology related perspectives over a wide range of scales

evolutionary multi scale analysis of river bank line retreat using continuous wavelet transforms jamuna river bangladesh in this study continuous wavelet transforms are used to explore spatio temporal patterns of multi scale bank line retreat along a 204 km reach of the jamuna river bangladesh a sequence of eight bank line retreat series derived from remotely sensed imagery for the period 1987 1999 is transformed using the morlet mother wavelet bank erosion is shown to operate at several characteristic spatial and temporal scales local erosion and bank line retreat are shown to occur in short well defined reaches characterised by temporal persistence at the same location and separated by relatively stable reaches in contrast evidence of downstream propagation of bank line retreat patterns is evident at larger spatial scales the intensity of localised bank line retreat i e at scales of 0 20 km is strongly related to the magnitude of monsoonal peak discharge but this relationship weakens as the spatial scale of erosion increases the potential of continuous wavelet analysis to enhancing our understanding of morphological evolution in complex fluvial systems with multi channel planforms is discussed

molluscan faunas and paleobathymetry of holocene sequences in the northeastern nile delta egypt abstract the fossil molluscan component serves as a valuable indicator of the paleobathymetric variations which occurred in the nile delta egypt during the past 7500 years paleobiocoenoses have been identified on the basis of molluscan faunas in three radiocarbon dated cores as part of a long term study to help interpret the holocene evolution of the northeastern delta one of these smithsonian boring s 21 near port said has been selected as a type core because it includes a near complete holocene coarsening upward sequence of distinct open marine to coastal lithofacies typical of this depocenter the fossil molluscan faunas comprising 59 species all of which are presently living in the mediterranean serve to determine approximate changes in paleodepth at this site with time in particular the recognized paleocommunities show a good correspondence with several infralittoral biocoenoses of unconsolidated mud and sand rich substrates of the present mediterranean terrigenous mud fine well sorted sands fine sands in very shallow water and superficial muddy sands in sheltered areas the methodology was applied to two other cores of near comparable age in this region smithsonian core s 31 and boring fadda 1 earlier studied by others these two were also selected because they are characterized by a holocene sequence of marine to coastal lithologies similar to core s 21 the approach used serves to determine temporal and spatial differences in paleobathymetry at the three sites this investigation shows that analysis of the faunas in subsurface sections serves to refine paleoenvironmental interpretations of the nile delta moreover the molluscan paleobiocoenoses are best evaluated in conjunction with the lithofacies in which they occur

morphology and dynamic sedimentology of the eastern nile delta shelf coleman j m roberts h h murray s p and salama m 1981 morphology and dynamic sedimentology of the eastern nile delta shelf mar geol 42 301 326 some 13 000 km of bathymetry and overlapping side scan sonar data were collected over a 4450 km2 area of the eastern nile river shelf these data coupled with more detailed surveys of selected areas including bottom sampling and current measurements contribute to the understanding of shelf morphology lithofacies relationships and sediment transport processes four morphologic zones were defined zone 1 smooth bottomed flocculated clays and silty clays extending from the shore line 40 km seaward to the 25 m contour zone 2 a sand belt 5 20 km wide extending eastward from the damietta mouth and curving toward the coast at the boundary of the study area dominant bottom features were migratory bedforms of various dimensions superimposed on linear sand ridges zone 3 smooth clay to silty clay bottom topography punctuated with distinct algal mounds the mounds up to 10 m relief are composed of living coralline algae which contribute coarse debris to the surrounding sediments zone 4 mud diapirs and shelf edge slumps characterize this distal part of the shelf and the upper slope sand on the inner shelf is actively migrating and probably does not represent a relict deposit the damietta distributary causes a large scale perturbation in the mean easterly drift along the egyptian coast unusually strong currents capable of transporting and reworking large volumes of sand are associated with an eddy trapped behind this feature the directionality of these currents and the curvature of the eddy axis correspond well to the distribution pattern of sand on the inner shelf

sediment load change in the yangtze river changjiang a review abstract extensive research into the changing sediment load throughout the yangtze river changjiang basin has been completed over recent years and it provides an ongoing example of how to evaluate the consequences of natural and anthropogenic impacts on sediment processing in a very large fluvial system this paper reviews these recent studies and critically assesses their findings regarding changes in sediment yield load both spatial and temporal variations grain size and rating curves as well as the morphodynamic response of the channel and delta we also discuss the factors driving these changes including climate change soil and water conservation measures dam construction and sand extraction and consider the likely future trends in sediment load based on a consideration of the major outcomes of and discrepancies between recent studies we conclude that sediment supply transport mobilization and deposition in this large river system are complicated by the heterogeneous nature of its morphology and climate as well as the progressive intensification of human activities therefore the identification and interpretation of hydrological and sedimentological changes in the yangtze basin can be difficult and an in depth study of the causal mechanisms of variations in sediment load and the impacts on the yangtze river system is urgently required

barrier formation on an actively prograding delta system the red river delta vietnam abstract an extensive barrier spit system 20 to 30 km long developed on the delta front platform of the ba lat delta within a relatively short period 10 20 years however it was not evident whether the formation was related to river floods typhoons or calm weather conditions or to cross shore or alongshore sediment transport mechanisms therefore a process based numerical model that simulates sediment transport and morphologic changes by waves tides wind and river flow is used to analyze the processes that govern this barrier formation the mechanism that initiates the barrier formation is concluded to be onshore transport by wave asymmetry of sediment previously transported seaward in the buoyant river plume the main mechanism that counteracts the barrier formation is probably destruction of the barrier by river flow during the subsequent transformation from a subaqueous barrier into a sub aerial barrier spit system overwashes and alongshore sediment transport become increasingly important this spit system therefore appears to be dominated by alongshore processes even though its initial formation is more strongly regulated by cross shore processes the importance of cross shore processes results in a minor contribution of typhoons to the initial formation of these barriers typhoons are not very important to destruction of barriers as well because wave energy is gradually dissipated over the gentle offshore profile which in turn results from river plume sedimentation

after the deluge mediterranean stagnation and sapropel formation in an east mediterranean marine core the upper sapropel begins soon after the start of a global event a very heavy precipitation which occurred in the equatorial latitudes during the late glacial early holocene this heavy precipitation in africa channelled by the nile river across 35 of latitude produced a low salinity surface layer in the east mediterranean in this confined basin with high bottom salinity the steep salinity gradient stratified the water column the stagnant bottom waters triggered the sapropel formation cretaceous sapropels in the tropical oceans may result from the same chain of events in warm humid climates with contrasting wet and dry seasonal rhythm

a method for the assessment and analysis of the hydromorphological condition of italian streams the morphological quality index mqi article i nfo a new index has been developed for the hydromorphological assessment of italian rivers the method was designed to comply with the eu water framework directive requirements but its use can be extended to other applications in river management the evaluation of stream morphological quality is preceded by a phase of river segmentation consisting ofan initial division of the network intoriver reaches with homogeneous morphological characteristics the evaluation procedure consists of a set of 28 indicators which were defined to assess longitudinal and lateral continuity channel pattern cross section configuration bed structure and substrate and vegetation in the riparian corridor these characteristics are analyzed in terms of geomorpholog ical functionality artificiality and channel adjustments indicators classes and the scoring system were defined based on expert judgement the scoringsystemleads tothe definition of the morphologicalquality index mqi application of the method to 102 river reaches covering a wide range of physical conditions and human pres sures of italian streams enabled the testing of the overall methodology and the refinement of the indicators and scores limitations strengths and the applicability of the method are also discussed in the paper

erratum earthquakes triggered by silent slip events on kīlauea volcano hawaii nature 442 71 74 2006 there was a plotting error in fig 1 that inadvertently displays earthquakes for the incorrect time interval the location of earthquakes during the two day long slow slip event of january 2005 are shown here in the corrected fig 1 because the incorrect locations were alsoused in the coulomb stress change csc calculation the error could potentially have biased our interpretation of the depth of the slow slip event although in fact it did not

itcz and enso like pacing of nile delta hydro geomorphology during the holocene abstract the nile valley accommodates the world s longest river and shaped the development of numerous complex societies providing a reliable source of water for farming and linking populations to sub saharan africa and the mediterranean sea its fertile delta lay at the heart of ancient egyptian civilization however little is known of its morpho sedimentary response to basin wide changes in holocene hydrology here we present two well resolved records from the nile delta based on 320 radiocarbon dates to reconstruct the timing and rhythm of catchment scale modifications during the past 8000 years on the orbital timescale we demonstrate that nilotic hydrology and sedimentation have responded to low latitude insolation forcing while on sub millennial timescales many of the major phases of deltaic modification were mediated by climate events linked to el nino southern oscillation type enso variability

making riverscapes real abstract the structure and function of rivers have long been characterized either by 1 qualitative models such as the river continuum concept or serial discontinuity concept which paint broad descriptive portraits of how river habitats and communities vary or 2 quantitative models such as downstream hydraulic geometry which rely on a limited number of measurements spread widely throughout a river basin in contrast authors such as fausch et al 2002 and wiens 2002 proposed applying existing quantitative spatially comprehensive ecology and landscape ecology methods to rivers this new framework for river sciences which preserves variability and spatial relationships is called a riverine landscape or a riverscape application of this riverscape concept requires information on the spatial distribution of organism scale habitats throughout entire river systems this article examines the ways in which recent technical and methodological developments can allow us to quantitatively implement and realize the riverscape concept using 3 cm true color aerial photos and 5 m resolution elevation data from the river tromie scotland we apply the newly developed fluvial information system which integrates a suite of cutting edge high resolution remote sensing methods in a spatially explicit framework this new integrated approach allows for the extraction of primary fluvial variables such as width depth particle size and elevation from these first order variables we derive second order geomorphic and hydraulic variables including velocity stream power froude number and shear stress channel slope can be approximated from available topographic data based on these first and second order variables we produce riverscape metrics that begin to explore how geomorphic structures may influence river habitats including connectivity patchiness of habitat and habitat distributions the results show a complex interplay of geomorphic variable and habitat patchiness that is not predicted by existing fluvial theory riverscapes thus challenge the existing understanding of how rivers structure themselves and will force development of new paradigms

human impacts to mountain streams mountain streams are here defined as channel networks within mountainous regions of the world this definition encompasses tremendous diversity of physical and biological conditions as well as history of land use human effects on mountain streams may result from activities undertaken within the stream channel that directly alter channel geometry the dynamics of water and sediment movement contaminants in the stream or aquatic and riparian communities examples include channelization construction of grade control structures or check dams removal of beavers and placer mining human effects can also result from activities within the watershed that indirectly affect streams by altering the movement of water sediment and contaminants into the channel deforestation cropping grazing land drainage and urbanization are among the land uses that indirectly alter stream processes an overview of the relative intensity of human impacts to mountain streams is provided by a table summarizing human effects on each of the major mountainous regions with respect to five categories flow regulation biotic integrity water pollution channel alteration and land use this table indicates that very few mountains have streams not at least moderately affected by land use the least affected mountainous regions are those at very high or very low latitudes although our scientific ignorance of conditions in low latitude mountains in particular means that streams in these mountains might be more altered than is widely recognized four case studies from northern sweden arctic region colorado front range semiarid temperate region swiss alps humid temperate region and papua new guinea humid tropics are also used to explore in detail the history and effects on rivers of human activities in mountainous regions the overview and case studies indicate that mountain streams must be managed with particular attention to upstream downstream connections hillslope channel connections process domains physical and ecological roles of disturbance and stream resilience

earthquakes triggered by silent slip events on kīlauea volcano hawaii silent earthquakes or slow slip events happen so slowly that they cannot be detected by conventional seismographs but now the availability of gps data means that they can be followed in detail segall et al report on a series of small earthquakes on k lauea volcano hawaii the earthquakes at depths of 7 to 8 km appear to be triggered by otherwise silent slow slips though small triggered earthquakes of this type can be used to help quantify the increased hazard due to slow slip events slow slip events or silent earthquakes have recently been discovered in a number of subduction zones including the nankai trough1 2 3 in japan cascadia4 5 and guerrero6 in mexico but the depths of these events have been difficult to determine from surface deformation measurements although it is assumed that these silent earthquakes are located along the plate megathrust this has not been proved slow slip in some subduction zones is associated with non volcanic tremor7 8 but tremor is difficult to locate and may be distributed over a broad depth range9 except for some events on the san andreas fault10 slow slip events have not yet been associated with high frequency earthquakes which are easily located here we report on swarms of high frequency earthquakes that accompany otherwise silent slips on k lauea volcano hawaii for the most energetic event in january 2005 the slow slip began before the increase in seismicity the temporal evolution of earthquakes is well explained by increased stressing caused by slow slip implying that the earthquakes are triggered the earthquakes located at depths of 7 8 km constrain the slow slip to be at comparable depths because they must fall in zones of positive coulomb stress change triggered earthquakes accompanying slow slip events elsewhere might go undetected if background seismicity rates are low detection of such events would help constrain the depth of slow slip and could lead to a method for quantifying the increased hazard during slow slip events because triggered events have the potential to grow into destructive earthquakes

holocene evolution of the northeastern corner of the nile delta abstract the constructive phase of the modern nile delta as manifested in a 48 m section drilled east of the suez canal commenced in very early holocene times sands rich in marine fauna were deposited in the littoral zone and the shoreline was more than 20 km landward of its present day position subsequently clays and silts were dumped from the nile distributaries and the marine faunal spectrum became very limited and brackish later in early and middle holocene times the sediments deposited were rich in freshwater delta plain diatoms and pollen and in allochthonous fern spores from the tropics indicating proximity of a distributary mouth the middle part of the section 22 5 17 5 m is very poor in faunal and floral remains pollen grains from sabkha vegetation are abundant the environment which seems lagoonal and slightly hypersaline is related to the sea regression in middle holocene times euryhaline pelecypods dating from about 3000 yr b p are abundant around the 8 m depth upward there is an increase in pollen grains from sabkhas the section is poor in diatoms and those present are mostly euryhaline and lagoonal allochthonous spores derived from the nearby pelusiac branch are abundant between 3000 and 2000 yr b p the constructive phase of the modern delta terminated and winnowed sands began accreting in front of the delta plain

downstream variation in stream power abstract stream power has a significant influence on many form and process attributes of the fluvial system using a similar approach to that suggested by d m lawler in 1992 and 1995 a model is developed to explore how stream power might vary in the downstream direction based on the assumption that the longitudinal profile of the river has an exponential form no particular discharge is necessarily specified but near bankfull flows are regarded as significant morphologically and one such discharge is the focus here total stream power per unit channel length qs is predicted to peak at an intermediate location the position of which depends on the ratio b where b and are the downstream rates of change of discharge and slope respectively if b is a relatively conservative quantity then the form of the longitudinal profile and in particular its degree of concavity will have the major influence on the position of maximum stream power specific stream power w is even more sensitive to and is expected to peak closer to the headwaters about half way between source and the location of the stream power maximum although this will depend on how channel width w varies with distance from source the model is tested along three connected streams of different size in the catchment of the river trent taking advantage of a relationship between mean annual flood and link magnitude which enables this near bankfull discharge to be estimated at any point within the network the model is verified in so far as stream power does attain a mid basin maximum but the observed and predicted locations of the maxima do not always correspond largely because of the distinctive variation in discharge and especially slope along individual pathways for example maximum power lies far downstream along the trent because of the large increase in mid basin discharge associated with a series of large closely spaced tributaries the importance of slope is borne out by the near headwater locations for specific power maxima which tend to be further upstream than predicted along all three rivers as a result of the steepness of upper reaches the variety of geomorphic settings produces deviations from expectation which has implications for the movement and storage of material in the fluvial system

multi scale factors controlling the pattern of floodplain width at a network scale the case of the rhone basin france abstract in this study the floodplain width fw was assessed for the entire rhone catchment river network 32 160 km long to highlight controlling factors the fw data which is measured every kilometre on a digital elevation model dtm is aggregated into spatial homogenous segments using a pettitt break detection test resulting in aggregated geographical objects ago based on these agos an analysis of the variability of the floodplain width was performed the general pattern for the rhone network shows a downstream increase in fw related to the concept of river continuum this general pattern explains ca 30 of the variation in fw deviations from this general trend are however large values for floodplain widths are normalized for catchment scale to study deviations that do not depend on scale effects based on a conceptual model the main environmental parameters influencing fw were identified these parameters include lithology and different parameters that influence the river profile such as base level changes and tectonics sediment load and discharge an analysis of catchment wide patterns shows that the main variations on the scaling effect are caused by lithology superposed on this general scaling pattern disturbed by lithological variations are the variations in floodplain width caused by disturbances in the geomorphic system which influence floodplain slope sediment and water discharge and which include inherited landscapes although large data sets become increasingly available and the applied methodology reduces data noise data availability and quality still hampers studies at a larger scale nevertheless such information sources are becoming crucial because they are more and more accessible and diverse and the analysis is now easier with the increasing capacities of gis technologies as a result they are becoming very complementary to field studies to understand geomorphic processes at wider spatial and longer temporal scales in a sense the tradition of geomorphology may evolve in the next years with image data providing additional evidence of earth evolution

dam impacts on the changjiang yangtze river sediment discharge to the sea the past 55 years and after the three gorges dam 1 in 5 recent years 2000 2004 the changjiang yangtze river has discharged past datong 600 km from the river mouth an average of 250 million tons mt of sediment per year a decrease of more than 40 since the 1950s and 1960s whereas water discharge at datong has increased slightly water and sediment discharge data from the upper middle and lower reaches of the river suggest that the reduction of the changjiang sediment load has occurred in two phases between 1950 and 2002 following the closure of the danjiangkou reservoir on the hanjiang tributary in 1968 and following the installation of numerous dams and water soil conservation works in the jialingjijang catchment after 1985 as the three gorges dam tgd started operating in 2003 the changjiang entered a third phase of sediment reduction with annual sediment loads at datong less than 200 mt yr upon completion of the three gorges dam tgd in 2009 the sediment load at datong will decrease to 210 mt yr for the first 20 years then will recover to 230 mt yr during 2030 2060 and will reach 310 mt yr during 2060 2110 from the sediment budget and sediment erosion data for the changjiang subaqueous delta it can be assumed that the delta will be eroded extensively during the first five decades after tgd operation and then will approach a balance during the next five decades as sediment discharging from tgd again increases

automatic procedures for river reach delineation univariate and multivariate approaches in a fluvial context abstract segmenting the continuum of rivers into homogeneous reaches is an important issue in river research and management automatic procedures provide significance objectivity and repeatability although univariate techniques are frequently used to identify river reaches multivariate approaches offer a more integrative context three nonparametric methods multi response permutation procedures mrpp with an advance in the significance level estimation the pettitt and mann kendall tests are applied for segmenting the river based on three geomorphic variables valley width active channel width and channel slope systematically measured in a gis environment the cited techniques have been applied to the curueno river nw spain to illustrate the methods we analyse reach distribution along the river longitudinal profile the methods successfully characterize the evident transitions along fluvial systems and also others less noticeable the three methods provide more reaches according to valley width and less reaches according to channel slope 18 0 and 3 7 reaches on average respectively in contrast to the mann kendall test mrpp and pettitt tests provide more stable segmentations when significance level varies however the pettitt test provides irregular segmentations for regular patterns the mrpp both univariate and multivariate applications enables a wider scope for the segmentation issue which is useful in diverse aspects of fluvial domain

delineation of the riparian zone in data scarce regions using fuzzy membership functions an evaluation based on the case of the naryn river in kyrgyzstan abstract riparian zones contain important ecosystems with a high biodiversity and relevant ecosystem services from a process point of view riparian zones are characterized by the interaction of hydrological geomorphological and ecological processes consequently their boundary is dynamic and blurred as it depends on not only the local valley morphology but also the hydrological regime this makes a delineation of riparian zones from digital elevation data a challenging task as it should represent this blurred nature of riparian zone boundaries while the application of high resolution topography from lidar and hydraulic models have become standard in many developed countries studies and applications in remote areas still commonly rely on the freely available coarse resolution digital elevation models in this article we present the delineation of riparian zones from the srtm 1 elevation model and fuzzy membership functions for the naryn river in kyrgyzstan having a length of approximately 700 km we evaluate the extraction of the underlying channel network as well as the different indicator variables the maximum user s accuracy for the delineation of riparian zones along the entire naryn river is 82 14 reflecting the uncertainty arising from the heterogeneity of the riverscape as well as from the quality of the underlying elevation data despite the uncertainty the fuzzy membership approach is considered as an appropriate method for riparian zone delineation as it reflects their dynamic transitional character and can be used as indicator of connectivity within a riverscape

digital modelling of landscape and soil in a mountainous region a neuro fuzzy approach abstract research on genetic relationships between soil and landforms has largely improved soil mapping recent technological advances have created innovative methods for modelling the spatial soil variation from digital elevation models dems and remote sensors this generates new opportunities for the application of geomorphology to soil mapping this study applied a method based on artificial neural networks and fuzzy clustering to recognize digital classes of land surfaces in a mountainous area in north central venezuela the spatial variation of the fuzzy memberships exposed the areas where each class predominates while the class centres helped to recognize the topographic attributes and vegetation cover of each class the obtained classes of terrain revealed the structure of the land surface which showed regional differences in climate vegetation and topography and landscape stability the land surface classes were subdivided on the basis of the geological substratum to produce landscape classes that additionally considered the influence of soil parent material these classes were used as a framework for soil sampling a redundancy analysis confirmed that changes of landscape classes explained the variation in soil properties p 0 01 and a kruskal wallis test showed significant differences p 0 01 in clay hydraulic conductivity soil organic carbon base saturation and exchangeable ca and mg between classes thus the produced landscape classes correspond to three dimensional bodies that differ in soil conditions some changes of land surface classes coincide with abrupt boundaries in the landscape such as ridges and thalwegs however as the model is continuous it disclosed the remaining variation between those boundaries

remote sensing planform and facies analysis of the plain of tineh egypt for the remains of the defunct pelusiac river abstract the pelusiac branch was a distributary river in the nile delta that splits off from the main trunk of the nile river as it flowed toward the mediterranean at approximately 25 a d it was chocked by sand and silt deposits from prograding beach accretion processes the lower course of the river and its bifurcation point from the trunk of the nile have been hypothesized based on ancient texts and maps as well as previous research but results have been inconsistent previous studies partly mapped the lower course of the pelusiac river in the plain of tineh east of the suez canal but rapid urbanization related to the inauguration of the peace canal mega irrigation project has covered any trace of the linear feature reported by these previous studies the present study used multispectral remote sensing data of geoeye 1 and landsat tm to locate and accurately map the course of the defunct pelusiac river within the plain of tineh remote sensing analysis identified a linear feature that is 135 m wide at its maximum and approximately 13 km long it extends from the pelusium ruins to the suez canal just north of the peace canal this remotely located linear feature corresponds to the path of the pelusiac river during roman times planform geomorphology was applied to determine the hydrological regime and paleodischarge of the river prior to becoming defunct planform analysis derived a bankfull paleodischarge value of 5700 m 3 s 1 and an average discharge of 650 m 3 s 1 using the reach average for the interpreted pelusiac river the derived values show a river distributary similar in discharge to the modern dammed damietta river field work completed in april of 2012 derived four sedimentary lithofacies of the upper formation on the plain that included pro delta delta front and delta plain depositional environments diatom and fossil mollusk samples were also identified that support coastal beach and lagoonal environments of deposition measured section columns and a shoreline parallel transect were also constructed to portray the paleogeography of the mediterranean coastline in the plain of tineh at 25 a d and indicate that the sampled study area is the downdrift margin of an asymmetric delta with barrier lagoon systems

fluvial geomorphology and river engineering future roles utilizing a fluvial hydrosystems framework abstract river engineering is coming under increasing public scrutiny given failures to prevent flood hazards and economic and environmental concerns this paper reviews the contribution that fluvial geomorphology can make in the future to river engineering in particular it highlights the need for fluvial geomorphology to be an integral part in engineering projects that is to be integral to the planning implementation and post project appraisal stages of engineering projects it should be proactive rather than reactive areas in which geomorphologists will increasingly be able to complement engineers in river management include risk and environmental impact assessment floodplain planning river audits determination of instream flow needs river restoration and design of ecologically acceptable channels and structures there are four key contributions that fluvial geomorphology can make to the engineering profession with regard to river and floodplain management 1 to promote recognition of lateral vertical and downstream connectivity in the fluvial system and the inter relationships between river planform profile and cross section 2 to stress the importance of understanding fluvial history and chronology over a range of time scales and recognizing the significance of both palaeo and active landforms and deposits as indicators of levels of landscape stability 3 to highlight the sensitivity of geomorphic systems to environmental disturbances and change especially when close to geomorphic thresholds and the dynamics of the natural systems and 4 to demonstrate the importance of landforms and processes in controlling and defining fluvial biotopes and to thus promote ecologically acceptable engineering challenges facing fluvial geomorphology include gaining full acceptance by the engineering profession widespread utilization of new technologies including gps gis image analysis of satellite and airborne remote sensing data computer based hydraulic modeling and geophysical techniques dovetailing engineering approaches to the study of river channels which emphasize reach scale flow resistance shear stresses and material strength with catchment scale geomorphic approaches empirical predictions bed and bank processes landform evolution and magnitude frequency concepts producing accepted river channel typologies fundamental research aimed at producing more reliable deterministic equations for prediction of bed and bank stability and bedload transport and collaboration with aquatic biologists to determine the role and importance of geomorphologically and hydraulically defined habitats

investigating a floodplain scaling relation using a hydrogeomorphic delineation method 1 floodplains are critical landscape features that are highly distinguished from neighboring uplands in terms of their hydrologic geomorphologic biogeochemical and ecological processes thus an essential step in floodplain studies is the determination of the lateral floodplain extent and its variability within a basin recent advances in topographic mapping and gis based analysis provide a means for developing automated techniques to determine floodplain extent in this study we propose a hydrogeomorphic floodplain delineation which links a simplified inundation algorithm with the river basin properties we utilize the method to investigate the physical controls on floodplain formation as captured by scaling relations between floodplain width and contributing area our hypothesis is that an efficient delineation grounded in hydrogeomorphic theory can improve our understanding of floodplain geometry across a range of conditions we test the method for two distinct watersheds a humid catchment in italy and an ephemeral basin in new mexico and note the existence of power law scaling of the floodplain width after averaging over stream orders an analysis of the algorithm parameters is conducted to identify possible limitations further systematic tests are needed to establish the generality of the floodplain scaling and its control on floodplain processes

channel planform geometry and slopes from freely available high spatial resolution imagery and dem fusion implications for channel width scalings erosion proxies and fluvial signatures in tectonically active landscapes article i nfo the rapid expansion of high spatial resolution optical sensors and imagery over the last decade presents ex ceptional opportunities for quantifying visible attributes of geomorphic systems in this study we detail a simple robust methodology changeom to extract continuous channel width and centerline datasets for single thread channels using freely available high spatial resolution imagery currently available in google earth and bing maps comparisons with a global dataset of field and lidar derived channel widths indicate minimal errors associated with the imagery and changeom methodology b1 overall while examples from the goriganga river indian himalaya and the yakima river wa usa emphasize the benefit of em pirical width values over established channel width scalings in deciphering fluvial responses to complex landscape forcings in tectonically active regions additionally accurate centerline delineation from the changeom methodology provides improved sinuosity measurements and when fused with coarse resolution digital elevation models dems removes along profile shortening and coincident increases in reach scale channel slope lastly comparisons of aster gdem v2 srtm v4 1 and lidar channel profiles extracted in moderate to high relief regions demonstrate the inferiority of the aster gdem for channel slope calcula tions despite the apparent spatial resolution advantages 9 the methodology presented here will facili tate new discoveries in the fluvial environment that have historically been difficult due to access and imagery resolution issues and provide greater perspective on channel signatures and responses to a host of landscape forcings especially in tectonically active bedrock and lower order drainage systems

disturbance stream incision and channel evolution the roles of excess transport capacity and boundary materials in controlling channel response abstract channel incision is part of denudation drainage network development and landscape evolution rejuvenation of fluvial networks by channel incision often leads to further network development and an increase in drainage density as gullies migrate into previously non incised surfaces large anthropogenic disturbances similar to large or catastrophic natural events greatly compress time scales for incision and related processes by creating enormous imbalances between upstream sediment delivery and available transporting power field examples of channel responses to antrhopogenic and natural disturbances are presented for fluvial systems in the mid continent and pacific northwest usa and central italy responses to different types of disturbances are shown to result in similar spatial and temporal trends of incision for vastly different fluvial systems similar disturbances are shown to result in varying relative magnitudes of vertical and lateral widening processes and different channel morphologies as a function of the type of boundary sediments comprising the bed and banks this apparent contradiction is explained through an analysis of temporal adjustments to flow energy shear stress and stream power with time numerical simulations of sand bed channels of varying bank resistance and disturbed by reducing the upstream sediment supply by half show identical adjustments in flow energy and the rate of energy dissipation the processes that dominate adjustment and the ultimate stable geometries however are vastly different depending on the cohesion of the channel banks and the supply of hydraulically controlled sediment sand provided by bank erosion the non linear asymptotic nature of fluvial adjustment to incision caused by channelization or other causes is borne out in similar temporal trends of sediment loads from disturbed systems the sediments emanating from incised channels can represent a large proportion of the total sediment yield from a landscape with erosion from the channel banks generally the dominant source disturbances that effect available force stream power or flow energy or change erosional resistance such that an excess of flow energy occurs can result in incision channel incision therefore can be considered a quintessential feature of dis equilibrated fluvial systems

a stability criterion inherent in laws governing alluvial channel flow the stability criterion of maximum flow efficiency mfe has previously been found inherent in typical alluvial channel flow relationships and this study investigates the general nature of this criterion using a wider range of flow resistance and bedload transport formulae for straight alluvial channels in which the effect of sediment sorting is insignificant our detailed mathematical analysis demonstrates that a flow efficiency factor e occurs generally as the ratio of sediment bedload discharge qs to stream power qs in the form of when e is maximized i e qs is maximized or is minimized maximally efficient straight channel geometries derived from most flow resistance and bedload transport formulae are found compatible with observed bankfull hydraulic geometry relations this study provides support for the use of the criteria of mfe maximum sediment transporting capacity and minimum stream power for understanding the operation of alluvial rivers and also addresses limitations to the direct application of its findings copyright 2002 john wiley sons ltd

recent subsidence and northeast tilting of the nile delta egypt abstract sediment borings collected in the nile delta of egypt many of them radiocarbon dated indicate that the entire northern sector of this major depositional center in the eastern mediterranean is presently subsiding mapping of the base of the holocene deltaic facies which is dated at about 8000 6500 yrs b p reveals that differential lowering of the northern delta plain is preferentially accentuated toward the northeast long term subsidence rates at or near the coast averaged for the mid to upper holocene range from about 0 1 to 0 25 cm yr between alexandria and the north central delta margin rates increase markedly eastward to a maximum of about 0 5 cm yr in the port said manzala lagoon region and this rapid lowering explains the presence of thick marine delta lobe sequences of holocene age in cores in the northeastern delta in contrast only reworked remnants of holocene marine delta lobe deposits of the earlier river nile branches which once flowed to the north and northwest are preserved seaward of the present north delta coast subsidence has induced marked environmental changes particularly with respect to coastal erosion and salt water incursion the asymmetric pattern of saline ground water here attributed in part to the northeast tilt of the delta plain has serious implications for agricultural development in this intensely cultivated region

subsidence in the northeastern nile delta rapid rates possible causes and consequences holocene fluvial and marine deposits have accumulated in a graben like structure on the northeastern margin of the nile delta this part of the delta which includes lake manzala port said and the northern suez canal has subsided rapidly at rates of up to 0 5 centimeter per year since about 7500 years ago this subsidence has diverted at last four major distributaries of the nile river into this region the combined effects of continued subsidence and sea level rise may flood a large part of the northern delta plain by as much as 1 meter by the year 2100 the impact of continued subsidence now occurring when sediment input along the coast has been sharply reduced because of the aswan high dam is likely to be substantial particularly in the port said area and as far inland as south of lake manzala