modeling flow in phreatic and epiphreatic karst conduits in the holloch cave muotatal switzerland the holloch cave is a site where the hydrodynamic behavior of a karst conduit network can be observed with a high degree of precision observed heads discharge rates conduit sizes and conduit lengths have been compiled into a simple hydrodynamic model in order to check their consistency it was possible to calibrate and satisfactorily fit the observed data model results show the following 1 flow models which are able to simulate turbulent flow in variably saturated conduit networks can adequately model conduit flow dominated karst systems 2 karst systems may be strongly nonlinear especially because of the presence of epiphreatic conduits 3 under certain circumstances storage in the epiphreatic conduits and in the fissured limestone matrix can be neglected 4 the typical effective hydraulic conductivity of karst conduits ranges between 1 and 10 m s 1 and the louis formula is adequate to calculate head losses in those conduits 5 indirect measurements of flow velocity using scallop size indicate values of 30 40 of the maximal annual discharge and velocity derived from pebble size indicates values of 150 of the maximal annual discharge

channel and floodplain response to recent abrupt climate change the tyne basin northern england this paper examines the timing nature and magnitude of river response in upland piedmont and lowland reaches of the tyne basin northern england to high frequency 20 30 year changes in climate and flood regime since 1700 ad over this period fluvial activity has been characterized by alternating phases of river bed incision and stability coinciding with non random decadal scale fluctuations in flood frequency and hydroclimate that appear to be linked to changes in large scale upper atmospheric circulation patterns episodes of widespread channel bed incision 1760 1799 1875 1894 1955 1969 result from a higher frequency of large floods 20 year return period and cool wet climate under meridional circulation regimes phases of more moderate floods 5 20 year return period corresponding to zonal circulation types 1820 1874 1920 1954 are characterized by enhanced lateral reworking and sediment transfer in upper reaches of the catchment and channel narrowing and infilling downstream rates of fluvial activity are reduced in intermediate periods 1800 1819 1895 1919 with no dominant circulation regime associated with lower flood frequency and magnitude the results of this study provide a valuable guide for forecasting probable drainage basin and channel response to future climate change

structure stability and transformation of contaminated lacustrine surface fine grained laminae an in situ annular flume sea carousel was deployed in hamilton harbour lake ontario to assess the structure stability and transformation of lacustrine surface fine grained laminae sfgl such laminae typify depositional lacustrine environments and occur at the sediment water interface the critical erosion thresholds erosion rates and internal friction coefficients were determined for natural undisturbed and physically disturbed sites in order to assess changes in bed stability sediment cores taken at each site were analyzed for bulk density using a ct scanner in order to provide an intercomparison of our results flocs and aggregates pumped from the flume during erosion experiments were analyzed for morphological characteristics using conventional optical microscopy and transmission electron microscopy to evaluate the mechanism and development of the sfgl and its structure a general three layer model is developed which depicts the organic flocs of the sfgl layer 1 compressing within a collapse zone layer 2 to form a consolidated bed layer 3 the sfgl was observed to be porous of low density and of high water content which possessed yield resistance due in part to binding by extracellular polymeric substances secreted by a colonized microbial population transmission electron microscopy observations showed an active biological community in the sediment promoting biostabilization time series of erosion thresholds and friction coefficients of the disturbed bed showed that the sfgl reconsolidated rapidly and increased in shear strength the artificial disturbance of the sediment resulted in incorporation of the sfgl and the collapse zone with the consolidated bed through mixing this stimulated the process of consolidation chiefly through removal of gas and breakdown of the organic fibril network reconsolidation began with the formation of a collapse zone at the surface of the disturbed sediment high friction coefficients and an increasing density with depth in the new surface layer indicated that rapid consolidation occurred after disturbance

out of phase holocene terraces in part of the north saskatchewan river basin alberta this study focuses on alluvial terraces in part of the north saskatchewan river valley near edmonton and in the small tributary valleys of whitemud and strawberry creeks the characteristic terrace morphologies and alluvial sediment sequences are briefly described but most importantly the deposits are radiocarbon dated for many sites twenty seven new 14c dates on bone wood charcoal and shell materials along with previously reported dates provide the chronological framework for the study occurrences of the mazama ash marker bed in terrace alluvium offer additional geochronological evidence the small tributary valleys have clearly developed in an out of phase manner relative to the main river valley which acts as their local base level despite the comparatively abundant geochronological evidence described here the explanation of alluvial terrace development in terms of predominant causal factors remains tantalizingly elusive

changes in streambank erodibility and critical shear stress due to subaerial processes along a headwater stream southwestern virginia usa despite more than 40 yr of research attributing temporal changes in streambank erosion rates to subaerial processes little quantitative information is available on the relationships between streambank erodibility kd and critical shear stress c and the environmental conditions and processes that enhance streambank erosion potential the study goal was to evaluate temporal changes in kd and c from soil desiccation and freeze thaw cycling soil erodibility and c were measured monthly in situ using a multiangle submerged jet test device soil moisture temperature and bulk density as well as precipitation air temperature and stream stage were measured continuously to determine changes in soil moisture content and state pairwise mann whitney tests indicted kd was 2 9 and 2 1 times higher p 0 0065 during the winter december march than in the spring fall april may october november and the summer june september respectively regression analysis showed 80 of the variability in kd was explained by freeze thaw cycling alone study results also indicated soil bulk density was highly influenced by winter weather conditions r2 0 86 bulk density was inversely related to both soil water content and freeze thaw cycling results showed that significant changes in the resistance of streambank soils to fluvial erosion can be attributed to subaerial processes water resource professionals should consider the implications of increased soil erodibility during the winter in the development of channel erosion models and stream restoration designs

floodplain development based on selective preservation of sediments squamish river british columbia abstract in the conventional model of floodplain sediment accumulation mechanisms of floodplain growth are differentiated into lateral and vertical accretion processes in which within channel deposits are capped by overbank deposits in the high energy gravel based squamish river sediments laid down on bar surfaces are composed of trough and planar crossbedded coarse sands these sequences contrast incongruously with adjacent floodplain deposits which are composed in large part of vertically accreted fine sands atop coarse alluvial gravels using element analysis it is inferred that bar platform sediments are stripped away by chute channels which are subsequently infilled with lower energy deposits from this a model of floodplain growth based on selective preservation of bar platform sands and prefrential preservation of vertically accreted deposits is proposed this mechanism of sediment replacement occurs independent of channel planform type

modeling sediment transport using depth averaged and moment equations a 1d mathematical model to calculate bed variations in alluvial channels is presented the model is based on the depth averaged and moment equations for unsteady flow and sediment transport in open channels particularly the moment equation for suspended sediment transport is originally derived by the assumption of a simple vertical distribution for suspended sediment concentration by introducing sediment carrying capacity suspended sediment concentration can be solved directly from sediment transport and its moment equations differential equations are then solved by using the control volume formulation which has been proven to have good convergence numerical experiments are performed to test the sensitivity of the calibrated coefficients and k in the modeling of the bed deposition and erosion finally the computed results are compared with available experimental data obtained in laboratory flumes comparisons of this model with hec 6 and other numerical models are also presented good agreement

response of the columbia river fluvial system to holocene climatic change abstract an understanding of the response of a fluvial system to past climatic changes is useful for predicting its response to future shifts in temperature and precipitation to determine the response of the columbia river system to previous climatic conditions and transitions a well dated sequence of floodplain development in the wells reservoir region was compared with the paleoenvironmental history of the columbia river basin results of this comparison indicate that aggradation episodes occurring approximately 9000 8000 7000 6500 4400 3900 and 2400 1800 yr b p coincided with climatic transitions that share certain characteristics the inferred climates associated with aggradation had at least moderate rates of precipitation that occurred mainly in winter coupled with moderate winter temperatures such conditions would have resulted in the buildup of snowpacks and a high frequency of rain on snow events the warming and precipitation increases predicted for the pacific northwest under most co2 doubling scenarios are likely to repeat these conditions which could increase the frequency of severe sediment laden floods in the columbia river basin

dynamics and spatial variability of near bottom sediment exchange in the yangtze estuary china abstract this study was conducted to examine the spatial variations in the exchange between near bottom suspended and sea bottom sediments in the yangtze estuary and adjacent region as well as to explore the fate of suspended sediments in the study area the relationship between the sand silt and clay contents of the sediments was analyzed by log ratio analysis which revealed a non linear function for selective deposition and a wide range of grain size distributions in the estuary this finding does not conform to the nearly constant clay silt ratios reported for other tidal basins around the world due to non linear sediment mixing under complex hydrodynamic conditions the sediment exchange processes in the yangtze estuary were quantified based on the principle of mass balance the average grain size distribution of near bottom suspended sediments from the estuary showed that approximately 49 of the riverine sediments accumulated in the mouth bar area while the rest which is primarily composed of fine grained sediments is transferred to the outer estuary and deposited in the form of flocs the spatial distribution of the sediment exchange ratios demonstrated that small amounts of suspended sediment were deposited onto the seabed of the upper estuary exchange ratio 0 8 seaward of the river mouth which implies that this is the present day depocenter of yangtze mud the sediment exchange rates obtained by combining the dimensionless exchange ratios and bulk sediment accumulation rates were found to be 2 3 cm yr in the muddy depocenter which extends to the south of the river mouth from 122 e to 123 e longitude at 31 n latitude

processes and forms of an unstable alluvial system with resistant cohesive streambeds as a response to channelization projects undertaken near the turn of the 20th century and in the late 1960s upstream reaches and tributaries of the yalobusha river mississippi usa have been rejuvenated by upstream migrating knickpoints sediment and woody vegetation delivered to the channels by mass failure of streambanks has been transported downstream to form a large sediment debris plug where the downstream end of the channelized reach joins an unmodified sinuous reach classification within a model of channel evolution and analysis of thalweg elevations and channel slopes indicates that downstream reaches have equilibrated but that upstream reaches are actively degrading the beds of degrading reaches are characterized by firm cohesive clays of two formations of palaeocene age the erodibility of these clay beds was determined with a jet test device and related to critical shear stresses and erosion rates repeated surveys indicated that knickpoint migration rates in these clays varied from 0 7 to 12 m a 1 and that these rates and migration processes are highly dependent upon the bed substrate resistant clay beds of the porters creek clay formation have restricted advancement of knickpoints in certain reaches and have caused a shift in channel adjustment processes towards bank failures and channel widening channel bank material accounts for at least 85 per cent of the material derived from the channel boundaries of the yalobusha river system strategies to reduce downstream flooding problems while preventing upstream erosion and land loss are being contemplated by action agencies one such proposal involves removal of the sediment debris plug bank stability analyses that account for pore water and confining pressures have been conducted for a range of hydrologic conditions to aid in predicting future channel response if the sediment debris plug is removed to improve downstream drainage care should be taken to provide sufficient time for drainage of groundwater from the channel banks so as not to induce accelerated bank failures published in 2002 john wiley sons ltd

transport of suspended solids from a karstic to an alluvial aquifer the role of the karst alluvium interface this study focuses on the coupled transport of dissolved constituents and particulates from their infiltration on a karst plateau to their discharge from a karst spring and their arrival at a well in an alluvial plain particulate markers were identified and the transport of solids was characterised in situ in porous and karstic media based on particle size analyses sem and traces transport from the sinkhole to the spring appeared to be dominated by flow through karst particulate transport was apparently conservative between the two sites and there was little difference in the overall character of the particle size distribution of the particulates infiltrating the sinkhole and of those discharging from the spring qualitatively the mineralogy of the infiltrating and discharging material was similar although at the spring an autochthonous contribution from the aquifer was noted chalk particles eroded from the parent rock by weathering in contrast transport between the spring and the well appears to be affected by the overlying alluvium particles in the water from the well showed evidence of considerable size sorting additionally sem images of the well samples showed the presence of particles originating from the overlying alluvial system these particles were not found in samples from the sinkhole or the spring the differences between the particulates discharging from the spring and the well indicate that the water pumped from the alluvial plain is coming from the karst aquifer via the very transmissive complex geologic interface between the underlying chalk formation and the gravel at the base of the overlying alluvial system

the use of overbank sediment for geochemical mapping and contamination assessment results from selected english and welsh floodplains abstract overbank sediment profiles from floodplains in england and wales contain a record of both natural geochemical patterns and those showing the influence of man s activities it has been suggested that this characteristic can be used to allow maps to be compiled which show human impact on the fluvial geochemical environment studies reviewed in this paper however show that a single overbank profile very rarely spans the period from before anthropogenic disturbance through to the industrial revolution and later significant lateral variations in metal concentrations occur also over a relatively small area in overbank sediments of the same general age these and the nature of vertical changes in chemistry make the choice of sample sites and sampling interval within a profile difficult even sediments which appear uncontaminated may record anthropogenic influences from activities such as deforestation and agriculture a means of dating the sediment and an appreciation of river erosion and sedimentation histories are shown to be essential in order to ensure that maps intended to depict natural geochemical variations are based on material deposited before disturbance of the catchment by human activity these considerations and associated costs may render overbank sediment non viable as a regional geochemical mapping medium

influence of coherent flow structures on the dynamics of suspended sediment transport in open channel flow the influence of suspended sediments on coherent flow structures has been studied by simultaneously measuring the longitudinal and vertical components of the instantaneous velocity vector and the instantaneous suspended particle concentration with an acoustic particle flux profiler the measurements were carried out in clear water and in particle laden open channel flows in both cases they clearly show the predominance of ejection and sweep phases that are part of a burst cycle the analysis further demonstrates the importance of the ejection and sweep phases in sediment resuspension and transport ejections pick up the sediment at the bed and carry it up through the water column close to the surface it is shown that ejections and sweeps are in near equality in the near bottom layer whereas ejections clearly dominate in the remaining water column the implications of these results for sediment transport dynamics are discussed

holocene alluvial fan and terrace formation in the bowland fells northwest england in the bowland fells lancashire northwest england in the headwater valleys of the hodder river system is a suite of holocene fluvial landforms debris cones and alluvial fans at tributary junctions and river terraces along the main valleys post date late pleistocene forms and pre date the modern valley floor alluvial forms eight 14c dates from wood samples incorporated within the terrace and fan deposits have allowed two main phases of holocene erosion to be identified with debris cone fan deposition taking place after c 5400 bp but before c 1900 bp and again at c 900 bp some of the fans and cones are complex with deposits attributable to both phases others are simple and attributable only to the later phase in the headwaters an upper terrace at c 5400 bp pre dates the cones and a lower terrace is contemporaneous with the first debris cone phase lower downvalley the youngest of three terraces date from c 5000 bp or earlier indicating that the sequence is less complex downstream

holocene evolution of a lowland scottish landscape kirkpatrick fleming part iii fluvial history mapping and radiocarbon dating of fluvial terrace fragments along the greater length of the kirtle water resulted in the definition of five major terrace surfaces correlations with proxy records of climate change part i and anthropogenic activity part ii are made to understand causal mechanisms in fluvial behaviour the limitations of such correlations are emphasized the highest terrace kirtle i is thought to be of devensian lateglacial age the remaining four are of holocene age an early holocene gravel aggradation kirtle ii may have been sustained from c 7250 14c years bc until close to c 455 cal bc the establishment of alnus on floodplains may have led to channel stability incision after c 3250 cal bc may have been due to greater discharges at a time of deteriorating climate terrace kirtle iii is undated prior to aggradation of terrace kirtle iv beginning at around cal ad 300 a period of lowered fluvial activity and floodplain stability is recorded from c 850 cal bc anthropoge

suspended sediment exchange through the sub tropical richmond river estuary australia a balance approach major sources of suspended sediments and their exchanges with the continental shelf for the richmond river estuary were investigated during two hydrological years of the major sources of suspended sediment inputs into the richmond river estuary fluvial input from the upper catchment area was about 92 99 of the total yearly balance and more than 90 of this fluvial sediment was transported into the estuary during less than 5 time of the year the richmond river estuary received net sediment input of about 1 2 of the total yearly balance from the continental shelf during dry seasons when upper catchment freshwater input was less than 45 106 m3 bank erosion in the richmond river estuary was least 1 during low to moderate floods mainly due to river training works and large mangrove coverage along the banks percentage of sediment export from the richmond river estuary depends on the magnitude of floods which was evident from 47 export during dry year when the estuary experienced a minor flood compared to 88 export during the wet year when the estuary experienced one minor and one moderate flood

non synchronous response of adjacent floodplain systems to holocene environmental change abstract two adjacent upland floodplains are compared to establish the local response of floodplains to environmental change radiocarbon dating the analysis of sedimentary exposures terrace mapping aerial photography and archaeological evidence are used to examine late quaternary valley fill sediments on the afon tanat and the afon vymwy in the upper severn basin wales uk the alluvial stratigraphy of the two floodplain systems consists of late devensian last glacial fluvio glacial sediments at the valley margins deposited under a braided outwash river regime holocene age terraces with floodplain and palaeochannel deposits composed of gravels overlain by silty sands are inset into this older unit and were formed by meandering fluvial channel systems a combination of field and laboratory data demonstrates that from the mid late holocene the two floodplain systems had divergent development the afon vyrnwy has remained vertically stable for the last ca 4000 yrs whereas the adjacent afon tanat continued to be vertically and laterally active both floodplain systems have been affected by late quaternary climatic fluctuations and anthropogenic activity from the bronze age to the roman period but local geomorphic gradient controls combined with a possibly greater focus of anthropogenic activity in the tanat catchment may explain the differential evolution of the two systems the data demonstrate that multiple reach scale studies are essential for revealing significant stages in the chronology and historical development of fluvial systems

suspended sediments in karst spring waters near massa tuscany italy the marble quarries of the alpi apuane supply some of the world s finest ornamental stone scanning electron microscopy of sediments emerging from cartaro grande one of the major apuane springs reveals that sediments produced by the cutting of the marble are worked through the groundwater system during storm events at concentrations of up to 12 574 mg l 1 sediment loads during single storm events reach at least 83 t the minimum annual sediment load for the 12 months to may 2000 was 300 t however due to off the scale discharge and turbidity data this quantity may be as high as 1 000 t equating to a mean suspended sediment concentration of 80 mg l 1 and an annual sediment yield of 100 t km 2 this remarkably high sediment flux is not surprising given that 440 000 t of marble is removed annually from the colonnata basin

flood alluviation and entrenchment holocene valley floor development and transformation in the british uplands the morphology sedimentary properties and sequence of recent coarse grained flood deposits and earlier holocene alluvial fills were investigated in thinhope burn a small 12 km2 catchment in the northern pennine uplands northern england twenty one large flood events are recorded by distinctive cobble boulder bars sheets and splays and boulder berms and lobes lichenometric analysis showed that all but one of these floods dated from the mid eighteenth century the timing of large floods between 1766 and 1960 corresponds with major hydroclimatic trends evident in northern britain and northwest europe over this period discharge estimates suggest that flood magnitudes have decreased since the mid eighteenth century channel and flood plain metamorphosis in late roman times and in the eighteenth century following major valley floor entrenchment locally as much as 8 m would appear to have been caused by increased runoff and flood magnitude this was linked to a shift to a wetter climate with flow augmented by iron age and roman woodland clearance and drainage of the catchment in more recent times results from this study suggest that current models of longer term holocene and pleistocene valley floor development in the british uplands may need to be re evaluated

terraced fills of pleistocene and holocene age in the rheidol valley wales the legacy of repeated pleistocene glaciations has endowed many welsh river valleys with locally thick successions of glacial and alluvial sediments investigations of a well preserved flight of terraced sediments with good exposures at capel bangor on the afon rheidol mid wales has allowed its quaternary valley fill stratigraphy to be examined in detail study has revealed five terraced fills consisting of seven distinct sedimentary units these range from late devensian ice contact and ice marginal deposits to holocene high sinuosity stream sediments with episodes of man induced accelerated deposition of fine grained alluvium and to aggradation and subsequent incision associated with historic metal mining examination of general sedimentary properties e g granulometry sedimentary structures terrace surface morphology show both differences in the pattern and controls of deposition and also progressive changes over late devensian and holocene times the sediments of the rheidol valley record the response and subsequent recovery of a drainage basin to glaciation and the increasing influence of man on sediment yields channel processes and sediment quality

sediment transfer and transformation of an alluvial valley floor the river south tyne northumbria u k the amounts of alluvial storage and the mechanisms responsible for the dispersal of sediment associated with historic metal mining are examined for a 115 year timespan on a 22 km reach of the river south tyne northern england analysis of lateral and vertical channel change over this period the extent of actively reworked gravels and identification of metals in alluvial units show five sedimentation zones separated by more stable reaches aggradation in the late nineteenth century was followed by a period of storage and local reworking and then incision some reaches show short term storage of sediment injected from tributaries which may be dispersed by floods there is some evidence of transfer of sediment bodies downvalley within sedimentation zones and of a sediment wave movement between zones in lower parts of the south tyne investigated present day incision the variation in the area of actively reworked gravel spreads and the widespread dispersal of fine grained toxic metal mining wastes all have practical implications the intricate response of the channel system to historic changes in sediment supply is not readily described by either a complex response model or a simple translatory wave

sediment carbon fate in phreatic karst part 2 numerical model development and application abstract the authors develop a numerical model to elucidate time distributed processes controlling sediment carbon fate in phreatic karst sediment carbon processes simulated in the new numerical model include in conduit erosion and deposition sediment carbon transport surficial fine grained laminae evolution carbon pool mixing microbial oxidation and the understudied process of sediment carbon exchange during equilibrium transport the authors perform a model evaluation procedure that includes generalized likelihood uncertainty estimation to quantify uncertainty of the model results modeling results suggest that phreatic karst conduits sustain sediment transport activity long after surface storm events cease the sustained sediment transport has the potential to shift the baseflow sediment yield of the phreatic karst to be on par with stormflow sediment yield the sustained activity is suggested to promote the exchange of sediment carbon between the water column and subsurface karst deposits during equilibrium sediment transport conditions in turn the sediment carbon exchange impacts the mixing of new and old carbon pools and the flux of carbon from phreatic karst integrated numerical model results from this study support the concept that phreatic karst act as a biologically active conveyor of sediment carbon that temporarily stores sediment turns over carbon at higher rates than surface streams and recharges degraded carbon back to the fluvial system the numerical modeling method adopted in this paper shows the efficacy of coupling carbon isotope fingerprinting with water quality modeling to study sediment carbon in phreatic karst

a sensitive high resolution record of late holocene climatic change from a raised bog in northern england proxy climatic data in the form of plant macrofossils have been analysed from a 5 m core from bolton fell moss cumbria uk detailed analysis of peat from the upper 50 cm of this core is used to demonstrate a strong correlation between changes in the relative proportion of taxa and known climatic changes over the last 1000 years the record of changes in bog vegetation contained within the peat profile is used to reconstruct changes in bog surface wetness for the latter half of the holocene as bog surface wetness is directly controlled by the prevailing climatic conditions this reconstruction can be viewed as a proxy climate record twelve radiocarbon age estimates on the 5m core suggest that between 50 and 500 cm peat accumulated at a relatively constant rate of 12 4 yr cm 1 the regular sampling intervals thus provide a time series of past bog surface wetness spectral analyses of this series indicates that wetness changes are cyclic with a ca 800 year periodicity

in channel surficial fine grained sediment laminae part ii chemical characteristics and implications for contaminant transport in fluvial systems samples of surficial fine grained laminae sfgl were collected in three south western ontario rivers each sediment sample was subjected to a sequential extraction procedure designed to partition particulate metals cd pb cu zn into five operationally defined fractions 1 exchangeable 2 bound to carbonates 3 bound to fe mn oxides 4 bound to organic matter and 5 residual particulate phosphus was sequentially extracted from the sediment samples into three fractions 1 non apatite inorganic p 2 apatite p and 3 organic p the major accumulate phases of trace metals in sfgl are carbonates fe mn oxides and organic matter the content of naip in sfgl ranged from 17 to 38 of total particulate p compared with suspended and bed sediments levels of p and trace metals in sfgl were lower at the study sites a conceptual overview of physical chemical and biological processes influencing formation of sfgl and the potential role of this fine grained sediment for contaminant transport in fluvial systems is presented

karst groundwater resources in the countries of eastern mediterranean the example of lebanon the hydrogeological study of some karst systems in lebanon shows important storage capacity up to 27 billions m3 for zarka system the spring of orontes river their geological and morphological settings as well as their hydrodynamic function show structures developed below the level of present springs probably up to several hundreds meters at depth since miocene those carbonate formations were subject to a remarkable instability of their base levels variations of sea level of which the messinian salinity crisis is the major phase and effects of the alpine orogenesis combined with climate variations to develop complex multiphased karst systems karstification occurs frequently in the whole formation often deeply below sea level or underneath sediment filling of continental basins the surface karst landscape is often intensely eroded those multiple superimposed karst phases give the carbonate aquifers their large extension and storage capacity these karst aquifers show the typical easy restoration of storage they have the ability to bear large interannual recharge variations and support exploitation under high pumping rates however these aquifers have some disadvantages for sustainable management in some regions successful boreholes which allow high pumping rates also induce uncontrolled exploitation another consequence is natural seawater intrusion as well as the submarine discharge of fresh groundwater in coastal aquifers those carbonate aquifers are subject to important economical stress which jeopardizes their durability the systematic study and understanding of carbonate aquifers in eastern mediterranean is a preliminary condition to any integrated and sustainable management of water resources studies in progress in lebanon may serve as examples to the whole region

impacts of extremely asymmetrical polar ice sheets on the east asian summer monsoon during the mis 13 interglacial abstract marine isotope stage mis 13 500 ka ago was a relatively weak interglacial according to the benthic 18o and antarctic ice core records however proxy records from the northern hemisphere indicate that mis 13 was at least as warm as or even warmer than more recent interglacials with an extremely strong summer monsoon and possible melting of the greenland ice sheet in this study assuming an asymmetric hemispheric climate we investigate the response of the east asian summer monsoon to various greenland and antarctic ice sheet sizes using a set of sensitivity experiments with the hadcm3 model through factor separation analysis results show that with no greenland ice sheet and a large antarctic ice sheet there is an enhancement of summer monsoon precipitation in the east asian monsoon region of up to 7 in agreement with the direction of change from proxy reconstructions for china this enhancement is associated with a stronger land sea thermal contrast more water vapor transport to east asia and a northward shift of the intertropical convergence zone the response to the greenland ice sheet removal is related to thermodynamic and topographical effects that influence the east asian monsoon through an orographically induced wave train the response to the larger antarctic ice sheet involves stronger upwelling of circumpolar deep water in the southern ocean melts the sea ice leading to a warmer sst this warming propagates to the north affecting the east asian summer monsoon

erodibility of cohesive streambeds in the loess area of the midwestern usa excess stress parameters critical shear stress c and erodibility coefficient k d for degrading channels in the loess areas of the midwestern usa are presented based on in situ jet testing measurements critical shear stress and k d are used to define the erosion resistance of the streambed the jet testing apparatus applies hydraulic stresses to the bed and the resulting scour due to the impinging jet is related to the excess stress parameters streams tested were primarily silt bedded in texture with low densities which is typical of loess soils results indicate that there is a wide variation in the erosion resistance of streambeds spanning six orders of magnitude for c and four orders of magnitude for k d erosion resistance was observed to vary within a streambed from streambed to streambed and from region to region an example of the diversity of materials within a river system is the yalobusha river basin in mississippi the median value of c for the two primary bed materials naheola and porters creek clay formations was 1 31 and 256 pa respectively streambeds composed of the naheola formation are readily eroded over the entire range of shear stresses whereas only the deepest flows generate boundary stresses great enough to erode streambeds composed of the porters creek clay formation therefore assessing material resistance and location is essential in classifying and modelling streambed erosion processes of these streams

suitability of transport equations in modelling soil erosion for a small loess plateau catchment erosion models have not often been applied to very steep terrain such as the gully catchments of the chinese loess plateau the purpose of this research was to evaluate the suitability of a number of transport equations for use in erosion modelling under loess plateau conditions to do this the equations were programmed into the lisem model which was applied to the 3 5 km2 danangou catchment in the rolling hills region of the loess plateau previous evaluations of transport equations used either flume tests or river sections and did no spatial modelling the results show that some equations predicted physically impossible concentrations defined as above 1060 g l the results were evaluated by using two methods 1 by comparing predicted and measured sedigraphs and sediment yield at the catchment outlet and 2 by comparing the fraction of the catchment in which physically impossible transport capacities occurred the results indicated that for the small grain sizes high density flows and steep slopes of the gully catchments on the loess plateau the shields parameter attained very high values furthermore the transport threshold can usually be neglected in the equations most of the resulting equations were too sensitive to slope angle abrahams schoklitsch yalin bagnold low and rickenmann so that transport rates were overpredicted for steep slopes and underpredicted for gentle slopes the yang equation appeared to be too sensitive to grainsize the govers equation performed best mainly because of its low slope dependency and is therefore recommended for erosion models that simulate sediment transport by flowing water in conditions with small grain sizes and steep slopes

karst flash flood forecasting in the city of nimes southern france in southern france karst flash floods may be the result of two potentially cumulative phenomena floods from highly localized events that mostly occur during autumn and are locally known as cevenol rain events floods exacerbated by recent rainfall events that contributed to saturation of the aquifer before the storm event thereby increasing runoff in any case flash floods occurring in a karst landscape are directly linked to the structure and hydraulic properties of the karst aquifer a methodology was developed for the city of nimes for forecasting these dangerous events based on the study and modelling of karst aquifer response to rain events this work was composed of i definition of how the nimes system functions leading to a conceptual model ii modelling of this conceptual model iii definition of a tool for hazard management presented as an abacus and tested on particular strong rainfall event

modelling of the functioning of karst aquifers with a reservoir model application to fontaine de vaucluse south of france summary this work deals with a rainfall discharge model applied to a well known karst aquifer a new approach is developed in order to minimize the fitting parameters here some of the model parameters do not result from a simple fitting as it was the case with earlier models i e some of them were assessed from the hydrograph analysis the conceptual model of the functioning is based on a production function based on a simple calculation of effective rainfall and a transfer function consisting of two reservoirs a slow discharge reservoir transfers the low flow and a rapid discharge reservoir feeds the high flow the model has three fitted parameters plus one for its initialisation three parameters are deduced from the hydrograph analysis over the entire time series for example the recession coefficient of the slow discharge reservoir is determined from the hydrodynamic analysis of the recession mangin a 1975 contribution a l etude hydrodynamique des aquiferes karstiques 3eme partie constitution et fonctionnement des aquiferes karstiques annales de speleologie 30 1 210 124 this model was tested over a ten years period on the fontaine de vaucluse french karst system the first hydrological year is used for fitting the model the nine other cycles validate the modelling the good quality of the model is proved by the nash criterion of 92 3 on the validation period moreover the simulation results were validated by a statistical analysis of measured and simulated time series the model successfully simulates both the high and low flow at the same time also it estimates the water volumes available in the different parts of the aquifer and it proposes a management tool capable of predicting the evolution of the discharge in different climate conditions

channel planform as a non controlling factor in fluvial sedimentology the case of the squamish river floodplain british columbia abstract channel planform styles demonstrate a continuum of variability whereas end member situations may exhibit diagnostic sedimentologic characteristics non end member situations may be exceedingly difficult to reliably differentiate the relevance of channel planform based sedimentologic differentiation of fluvial depositional units has been questioned for some time e g jackson 1978 bridge 1985 brierley 1989a despite reservations outlined in these papers facies models and interpretations of depositional suites in the rock record continue to be applied in terms of channel planform style this paper describes a test of this principle in one particular depositional setting the squamish river in southwestern british columbia is a high energy gravel based river in a fjord setting in a 20 km reach this river displays a distinct downstream gradation in channel planform type from braided through wandering gravel bed to meandering assemblages of bedform scale facies units on bar surfaces in this river do not differ by planform type brierley 1989a rather facies associations relate directly to the pattern of morphostratigraphic units on bar surfaces brierley 1991a when analysed in floodplain exposures sediment sequences which are equivalent to morphostratigraphic units are termed elements these elements are defined in terms of their geometry bounding surface and sediment characteristics detailed analysis of floodplain deposits in the braided wandering gravel bed and meandering reaches of the squamish river demonstrates that just as assemblages of bedform scale facies cannot be differentiated by planform style neither can assemblages of floodplain elements indeed for the squamish river the type character and spatial association of these elements cannot be differentiated reliably at the channel planform scale this indicates the limited relevance of planform differentiation of sedimentary environments under transitional planform situations such as those of high energy gravel bed rivers in confined valleys in such situations sediment inventory at the element scale provides greater insight into mechanisms of floodplain evolution than can be provided by interpretation at either the channel bedform or channel planform scales

a holocene alluvial sequence in the lower tyne valley northern britain a record of river response to environmental change palaeoenvironmental investigations have been made of late quaternary sediments infilling the lower tyne valley at scotswood newcastle upon tyne 18 km upstream from the mouth of the river attention has focused on the holocene alluvial sedimentary sequence using sedimentological geochemical and palynological analyses holocene valley floor development from c 7500 bp has been largely dominated by a tendency towards river aggradation with some limited lateral and vertical reworking of sediments four alluvial fills have been identified and dated to 1 c 7500 4800 bp 2 from c 2590 bp up to the early first millennium ad and possibly as late as medieval times 3 between the medieval period and the early seventeenth century and 4 between the seventeenth and nineteenth centuries episodes of incision are dated to c 4800 2590 bp and to the period following the early seventeenth century marked variations in the rates and nature of sedimentation and erosion appear to coincide with rising post glacial

changes in the isotopic and chemical composition of ground water resulting from a recharge pulse from a sinking stream abstract the little river an ephemeral stream that drains a watershed of approximately 88 km 2 in northern florida disappears into a series of sinkholes along the cody scarp and flows directly into the carbonate upper floridan aquifer the source of water supply in northern florida the changes in the geochemistry of ground water caused by a major recharge pulse from the sinking stream were investigated using chemical and isotopic tracers and mass balance modeling techniques nine monitoring wells were installed open to the uppermost part of the aquifer in areas near the sinks where numerous subterranean karst solution features were identified using ground penetrating radar during high flow conditions in the little river the chemistry of water in some of the monitoring wells changed reflecting the mixing of river water with ground water rapid recharge of river water into some parts of the aquifer during high flow conditions was indicated by enriched values of delta 18 o and delta deuterium 1 67 to 3 17 per mil and 9 2 to 15 6 per mil respectively elevated concentrations of tannic acid higher more radiogenic 87 sr 86 sr ratios and lower concentrations of 222 rn silica and alkalinity compared to low flow conditions the proportion of river water that mixed with ground water ranged from 0 10 to 0 67 based on binary mixing models using the tracers 18 o deuterium tannic acid silica 222 rn and 87 sr 86 sr on the basis of mass balance modeling during steady state flow conditions the dominant processes controlling carbon cycling in ground water are the dissolution of calcite and dolomite in aquifer material and aerobic degradation of organic matter

the role of the surface fine grained laminae in low gradient streams a model approach abstract this contribution presents a model approach to simulate the erosion entrainment deposition and burial of the surface fine grained laminae sfgl in low gradient streams we hypothesized that sfgl transport acts as a geomorphic control of the erosion and transport of sediment sources in a bedrock controlled low gradient stream with fluvial deposits located in central kentucky usa results indicate that the sfgl development and temporary storage on the streambed surface plays a key role in maintaining an equilibrium streambed the sfgl provides an easily erodible sediment source that satisfies the transport capacity of the stream during low to moderate flow events and thus protects deeper streambed sediment and streambank sediments from erosion modeling results showed that the simulation period was characterized by low to moderate hydrologic events which flush the sfgl from the stream and high flow events which deposit fine sediments into the sfgl during the former transported sediments were dominated by sediments of sfgl origin i e 89 of sediments during the latter 33 of sediment input to the stream is deposited to the sfgl which shows its importance as a temporary sink our model results support a novel concept that the ephemeral sfgl layers can satisfy sediment transport capacity of flow at low to moderate flows and thus protect other sources from erosion while perhaps the bedrock low gradient stream studied provides an end member to sfgl control future research might investigate the importance of sfgl control in other stream systems

watershed erosion modeling using the probability of sediment connectivity in a gently rolling system abstract sediment connectivity has been shown in recent years to explain how the watershed configuration controls sediment transport however we find no studies develop a watershed erosion modeling framework based on sediment connectivity and few if any studies have quantified sediment connectivity for gently rolling systems we develop a new predictive sediment connectivity model that relies on the intersecting probabilities for sediment supply detachment transport and buffers to sediment transport which is integrated in a watershed erosion model framework the model predicts sediment flux temporally and spatially across a watershed using field reconnaissance results a high resolution digital elevation models a hydrologic model and shear based erosion formulae model results validate the capability of the model to predict erosion pathways causing sediment connectivity more notably disconnectivity dominates the gently rolling watershed across all morphologic levels of the uplands including microtopography from low energy undulating surfaces across the landscape swales and gullies only active in the highest events karst sinkholes that disconnect drainage areas and floodplains that de couple the hillslopes from the stream corridor results show that sediment connectivity is predicted for about 2 or more the watershed s area 37 days of the year with the remaining days showing very little or no connectivity only 12 8 0 7 of the gently rolling watershed shows sediment connectivity on the wettest day of the study year results also highlight the importance of urban suburban sediment pathways in gently rolling watersheds and dynamic and longitudinal distributions of sediment connectivity might be further investigated in future work we suggest the method herein provides the modeler with an added tool to account for sediment transport criteria and has the potential to reduce computational costs in watershed erosion modeling

application of modflow for simulating groundwater flow in the trifilia karst aquifer greece karst aquifers can have a complex flow as a result of the formation of large conduits from dissolution features as a result a three dimensional finite difference groundwater flow model equivalent porous media may not apply as the dual porosity nature of karst features and the effects of turbulent flow cannot be directly simulated statistical analysis of karst hydrographs of the trifilia aquifer in greece showed the existence of a slightly karstified mass with high primary porosity that regulates the flow an equivalent porous media model was developed to simulate the trifilia karst aquifer using modflow steady state and transient state calibration gave encouraging results for the equivalent porous media approach which does not consider pipe flow or turbulence detailed hydrogeological research conducted in the area helped define the aquifer hydraulic conductivity zones and extent and flux to from the aquifer only hydraulic conductivity and specific yield were adjusted during calibration as the flux to from the system was considered known and applied as boundary conditions small mean absolute and rms piezometric head error of the model under both steady and transient state conditions were achieved

in channel surficial fine grained sediment laminae part i physical characteristics and formational processes an in channel surficial depositional feature surficial fine grained laminae composed of loosely bound fine sediment deposited during low flow conditions has often been observed in river systems in south western ontario the physical characteristics of this feature have been determined by a direct observation image analysis system this sediment consists primarily of flocculated fine grained material the size distributions of surficial fine grained laminae and suspended sediment were not significantly different each distribution is bimodal in nature and shows a characteristic grain size deficiency in the 4 5 m size range this observation suggests that flocculation and not low discharge or low competence is the dominant mechanism for the formation of surficial fine grained laminae under conditions of low flow in fluvial systems of south western ontario a quantitative assessment of this feature shows its potential importance as a source of fine grained sediment and associated contaminants for downstream transport

late holocene channel and floodplain development in a wandering gravel bed river the river south tyne at lambley northern england geomorphological analyses of the morphology lithostratigraphy and chronology of holocene alluvial fills in a 2 75 km long piedmont reach of the wandering gravel bed river south tyne at lambley in northumberland northern england have identified spatial and temporal patterns of late holocene channel and floodplain development and elucidated the relationship between reach and subreach scale channel transformation and terrace formation five terraced alluvial fills have been dated to periods sometime between c 1400 bc ad 1100 ad 1100 1300 ad 1300 1700 ad 1700 1850 and from ad 1850 to the present palaeochannel morphology and lithofacies architecture of alluvial deposits indicate that the past 3000 years has been characterized by episodic channel and floodplain change associated with development and subsequent recovery of subreach scale zones of instability which have been fixed in neither time nor space cartographic and photographic evidence spanning the past 130 years suggests channel transformation can be accomplished in as little as 50 years the localized and episodic nature of fluvial adjustment at lambley points to the operation of subreach scale controls of coarse sediment transfers these include downstream propagation of sediment waves as well as internal controls imposed by differing valley floor morphology gradient and boundary materials however the preservation of correlated terrace levels indicates that major phases of floodplain construction and entrenchment have been superimposed over locally complex patterns of sediment transfer reach scale lateral and vertical channel adjustments at lambley appear to be closely related to climatically driven changes in flood frequency and magnitude with clusters of extreme floods being particularly important for accomplishing entrenchment and reconfiguring the pattern of localized instability zones confinement of flood flows by valley entrenchment and contamination of catchment river courses by metal rich fine sediments following recent historic mining operations have combined to render the south tyne at lambley increasingly sensitive to changes in flood regimes over the past 1000 years copyright c 2000 john wiley and sons ltd