stabilization of a gravel channel by large streamside obstructions and bedrock bends jacoby creek northwestern california jacoby creek bed width 12 m bankfull discharge 32 6 m 3 s contains stationary gravel bars that have forms and positions controlled by numerous large streamside obstructions bedrock outcrops large woody debris and rooted bank projections and bedrock bends bank projection width and bar volume measured in 104 channel segments 1 bed width long are significantly cross correlated at lags of 1 3 and 4 indicating the tendency for large obstructions and bends to form bars 3 to 4 bed widths downstream and 1 bed width upstream all of the 18 bars downstream of large obstructions or bends in the study reach were along the obstruction side of the channel or outside bank of the bend most of the pools 85 were next to large obstructions or in bends conversely 92 of large obstructions or bends had pools comparison of the volume of four bars with volumetric bar changes and volume of bedload transported during four high flow events suggests that rates of sediment transport were sufficient to cause major changes in bars during bankfull events the only important channel changes observed in 4 yr however have been associated with the movement of large woody debris and with changes in the angle at which the flow approaches an obstruction a general model is proposed that large obstructions and nonalluvial bends stabilize the form and location of gravel bars bars are stabilized by two related mechanisms 1 large obstructions and bends cause intense quasi steady secondary circulation in scour holes that terminate upstream bars at fixed locations obstruction width channel deflection scour hole width and bed width were measured at 26 obstructions these data show that obstructions wider than approximately one third of the bed form pools spanning the entire channel and thus terminating bars smaller obstructions form scour holes contained within a single bar 2 bars are deposited upstream of large obstructions and sharp bends because of backwater reductions in stream power bars are deposited downstream because flow energy is expended around obstructions and bends and because the flow expands downstream of constrictions that result from large obstructions the formation of bars and pools inherent in many gravel channels can thus be enhanced and fixed in position by flow structures set up around large obstructions and bends formed of resistant materials

large scale dam removal on the elwha river washington usa river channel and floodplain geomorphic change abstract a substantial increase in fluvial sediment supply relative to transport capacity causes complex large magnitude changes in river and floodplain morphology downstream although sedimentary and geomorphic responses to sediment pulses are a fundamental part of landscape evolution few opportunities exist to quantify those processes over field scales we investigated the downstream effects of sediment released during the largest dam removal in history on the elwha river washington usa by measuring changes in riverbed elevation and topography bed sediment grain size and channel planform as two dams were removed in stages over two years as 10 5 million t 7 1 million m3 of sediment was released from two former reservoirs downstream dispersion of a sediment wave caused widespread bed aggradation of 1 m greater where pools filled changed the river from pool riffle to braided morphology and decreased the slope of the lowermost river the newly deposited sediment which was finer than most of the pre dam removal bed formed new bars largely pebble granule and sand material prompting aggradational channel avulsion that increased the channel braiding index by almost 50 as a result of mainstem bed aggradation floodplain channels received flow and accumulated new sediment even during low to moderate flow conditions the river system showed a two to tenfold greater geomorphic response to dam removal in terms of bed elevation change magnitude than it had to a 40 year flood event four years before dam removal two years after dam removal began as the river had started to incise through deposits of the initial sediment wave 1 2 million t of new sediment 10 of the amount released from the two reservoirs was stored along 18 river km of the mainstem channel and 25 km of floodplain channels the elwha river thus was able to transport most of the released sediment to the river mouth the geomorphic alterations and changing bed sediment grain size along the elwha river have important ecological implications affecting aquatic habitat structure benthic fauna salmonid fish spawning and rearing potential and riparian vegetation the response of the river to dam removal represents a unique opportunity to observe and quantify fundamental geomorphic processes associated with a massive sediment influx and also provides important lessons for future river restoration endeavors

yangtze river derived sediments in the southwestern south yellow sea provenance discrimination and seasonal transport mechanisms abstract the southwestern south yellow sea sys is influenced by tremendous sediment loads derived from the yellow river huanghe and the yangtze river changjiang however the influence of yangtze river sediments and their transport mechanism in this area remain unresolved in this study we present the grain size clay minerals and elemental compositions of surface sediments from the southwestern sys together with an analysis of field observation seawater salinity and suspended sediment data to investigate the provenance and transport mechanism of the sediments discrimination diagrams of clay minerals cr th vs sc al and rare earth elements rees indicate that the southwestern sys sediments are mainly derived from the old yellow river subaqueous delta and the yangtze river interestingly yangtze sediments enter the sys in ways that differ seasonally in summer yangtze sediments may be transported into the central sys by the dispersion of changjiang diluted water cdw and may also be transported northwestward by the subei coastal current scc to the area off the jiangsu coast in winter the yangtze derived sediments deposited off the jiangsu coast in summer are transported into the central and or even north sys under the combined effects of the scc yellow sea coastal current yscc and yellow sea warm current yswc throughout the transport processes there is an alternation between a source and sink of yangtze sediments off the jiangsu coast the coast serves as a sink of yangtze sediments in summer but as a source of sys sedimentation in winter the depositional and transport mechanisms of yangtze derived sediments are closely associated with seasonal variations in the circulation system of the sys

normalization of excess 210pb with grain size in the sediment cores from the yangtze river estuary and adjacent areas implications for sedimentary processes the fallout radionuclide 210pb has been widely used as an environment tracer for estimating deposition rates and revealing sedimentary processes however a comprehensive evaluation of different gr

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

potbellies wasp waists and superparamagnetism in magnetic hysteresis because the response of a magnetic substance to an applied field depends strongly on the physical properties of the material much can be learned by monitoring that response through what is known as a magnetic hysteresis loop the measurements are rapid and quickly becoming part of the standard set of tools supporting paleomagnetic research yet the interpretation of hysteresis loops is not simple it has become apparent that although classic single domain pseudo single domain and multidomain loops described in textbooks occur in natural samples loops are frequently distorted having constricted middles wasp waisted loops or spreading middles and slouching shoulders potbellies such complicated loops are often interpreted in oversimplified ways leading to erroneous conclusions the physics of the problem have been understood for nearly half a century yet numerical simulations appropriate to geological materials are almost unavailable in this paper we discuss results of numerical simulations using the simplest of systems the single domain superparamagnetic sd sp system examination of the synthetic hysteresis loops leads to the following observations 1 wasp waisting and potbellies can easily be generated from populations of sd and sp grains 2 wasp waisting requires an sp contribution that saturates quickly resulting in a steep initial slope and potbellies require low initial slopes the sp contribution approaching saturation at higher fields the approach to saturation is dependent on volume hence the cube of grain diameter therefore there is a very strong dependence of hysteresis loop shape on the assumed threshold size 3 we were unable to generate potbellies using an sp sd threshold size as large as 30 nm and wasp waists cannot be generated using a threshold size as small as 8 nm the occurrence of both potbellies and wasp waists in natural samples is consistent with a room temperature threshold size of some 15 nm 5 4 simulations using a threshold size of 15 20 nm with populations dominated by sp grain sizes that is with a small number of sd grains produce synthetic hysteresis loops consistent with measured hysteresis loops and transmission electron microscopic observations from submarine basaltic glass 5 simulations and measurements using two populations with distinct coercivity spectra can also generate wasp waisted loops a relatively straightforward analysis of the resulting loops can distinguish the latter case from wasp waisting resulting from sp sd behavior

clay mineralogy indicates the muddy sediment provenance in the estuarine inner shelf of the east china sea abstract the estuarine inner shelf mud regions of the east china sea ecs are valuable for studying the source to sink processes of fluvial sediments deposited since the holocene in this study we present evidence of the provenance and environmental evolution of two cores s5 2 and jc07 from the estuarine inner shelf regions of the ecs over the past 100 years based on 210pb dating high resolution grain size measurements and clay mineral analyses the results indicate that the clay mineral assemblages of cores s5 2 and jc07 are dominated by illite followed by kaolinite and chlorite and present scarce amounts of smectite a comparison of these clay mineral assemblages with several major sources reveals that the fine sediments on the estuarine inner shelf of the ecs represent a mixture of provenances associated with the yangtze and yellow rivers as well as smaller rivers however the contribution of each provenance has varied greatly over the past hundred years as indicated by the down core variability due to strong sediment reworking and transport on the inner shelf and the reduction of the sediment load from the yangtze river basin in the mud region of the yangtze river estuary the sediment from 1930 to 1956 was primarily derived from the yangtze river although the yellow river was also an important influence from 1956 to 2013 the yellow river contribution decreased whereas the yangtze river contribution correspondingly increased in the zhe min mud region the yangtze river contributed more sediment than did other rivers from 1910 to 1950 however the yangtze river contribution gradually decreased from 1950 to 2013 moreover the other small rivers accounted for minor contributions and the east asian winter monsoon eawm played an important role in the sediment transport process in the ecs our results indicate that the weakening strengthening of the eawm and a decrease in the sediment load of the yangtze river influenced the transport and fate of sediment on the estuarine inner shelf of the ecs

channel adjustments following two dam removals in wisconsin 1 we examined channel response following the removal of low head dams on two lowgradient fine to coarse grained rivers in southern wisconsin following removal channels eroded large quantities of fine sediment resulting in deposition 3 5 km downstream at one site baraboo river upstream changes were rapid and included bed degradation minimal bank erosion and sediment deposition on channel margins and new floodplain sand was transported through the former impoundment and temporarily deposited downstream at the second site koshkonong river head cut migration governed channel adjustments a deep narrow channel formed downstream of the headcut with negligible changes upstream of the head cut fluvial changes were summarized in a conceptual channel evolution model that highlighted 1 similarities between adjustments associated with dam removal and other events that lower channel base level and 2 the role of reservoir sediment characteristics particle size cohesion in controlling the rates and mechanisms of sediment movement and channel adjustment index terms 1815 hydrology erosion and sedimentation 1824 hydrology geomorphology 1625 1857 hydrology reservoirs surface keywords dams dam removal channel evolution model

a new rock magnetic approach to selecting sediments for geomagnetic paleointensity studies application to paleointensity for the last 4000 years the hypothesis that the ratio of detrital remanent magnetization to anhysteretic remanent magnetization drm arm for sediment samples is a measure of relative geomagnetic paleointensity is critically evaluated by two distinct approaches one approach is a detailed rock magnetic examination of the implicit assumptions of the drm arm method and the construction of a selection process by which to identify sediments that conform to requirements satisfying these assumptions sediments are uniform with respect to drm arm ratio if they contain magnetite in the 1 15 ym particle size range as the predominant magnetic mineral and have variations in magnetite content of less than 20 30 times the minimum concentration the drm arm ratios of these sediments should provide estimates of relative geomagnetic paleointensity relative particle size variations in magnetite are detected with a plot of anhysteretic susceptibility xarm versus low field susceptibility x and the size range 1 15 m is approximately identified by high field hysteresis parameters a rock magnetic evaluation of leboeuf lake sediments with these techniques indicates that these sediments are suitable for a relative plaeointensity study the second approach to evaluating the drm arm ratio as a measure of relative paleointensity is direct comparison with absolute paleointensity data a comparison between the leboeuf lake estimates and thellier thellier results from the western united states supports the conclusion that suitable sediments can record geomagnetic paleointensity fluctuations

source and depositional processes of the surface sediments and their implications on productivity in recent past off mahanadi to pennar river mouths western bay of bengal abstract spatial distribution and depositional processes of surface sediments along 4 transects from 27 to 2825 m water depth off mahanadi godavari krishna and pennar river mouths from western part of bay of bengal were studied using grain size clay minerals organic carbon nitrogen phosphorus calcium carbonate and metal concentration grain size distribution of surface sediments has revealed that overall the sediment size decreased with increasing water depth away from the coast which indicates a transport direction from west to east and also north to south in the study area high sand content and tio 2 values at shallow water depth indicate their terrigenous source and relatively high energy conditions prevailed near the shore off mahanadi river mouth illite was the dominant clay mineral while off godavari krishna pennar river mouths smectite was the dominant clay mineral indicating input from felsic and mafic rocks respectively slightly higher ti off godavari krishna rivers as compared to mahanadi also suggested mafic source for the sediments large illite concentration in the northern part of study area supports its major supply from himalayas furthermore the decreased illite concentration southwards indicates dilution of ganges borne clays from river inputs of peninsular region possible loss of energy of ganges waters during transport inhibits the southward movement of sediments along transect off mahanadi the c n ratio varied from 6 53 to 9 43 indicating a mixed source for organic matter derived from terrestrial as well as marine along godavari krishna and pennar river mouth regions the c n ratio varied between 8 19 and 13 54 indicating increased terrestrial organic matter input supplied through the rivers all transects showed higher c n values in shallower regions c n ratio in most of the sediments was higher than redfield ratio except in deeper areas off mahanadi where they are closer to redfield ratio however n p and c p ratios were lower than the redfield ratio indicating significant limitation of p in the area calcium carbonate concentration in this region was low due to increased clay loads which cause dilution of carbonates the turbidity occurring near river mouths due to suspension of fine particles creates oxidizing conditions under such oxygenated waters preservation of organic carbon and phosphorus is less possible thereby estimating reduced productivity than actual mn excess values observed in this region may also represent oxic waters prevalent in the region high fe excess values off mahanadi godavari and pennar indicate additional iron input from terrigenous source in addition ferric hydroxide minerals from the red beds off visakhapatnam must have contributed to fe excess the al ti ratios were distinctly different off the mouth of mahanadi godavari and krishna at 9 06 6 35 and 3 97 respectively suggesting that they are possibly provenance signatures of these three rivers and could be useful as typical end members

geochemical and isotopic signatures of surficial sediments from the western continental shelf of india inferring provenance weathering and the nature of organic matter abstract bottom sediments from thirteen transects sampled mainly at depth contours of 30 100 and 200 m along the western continental margin of india falling in two offshore sectors from dwaraka to goa and cape comorin to goa were analyzed for calcium carbonate major elements in silicate fraction trace and rare earth elements in the bulk fraction and carbon and nitrogen isotopes in organic matter to understand the provenance of sediments weathering patterns in the source areas and nature of organic matter major elements such as si ti mg and discrimination plots involving alkalies and silica have shown a distinct north south provinciality with the source signatures pointing at deccan basalt for sediments in the north from dwaraka to goa and gneisses and granulites of south india in the south shale normalized ree patterns and ree content suggest additional local sources mainly in the southwest coast of india degree of alteration determined using chemical index of alteration cia plagioclase index of alteration pia and a cn k plots have suggested that the sediments are moderately weathered despite the intense orographic rainfall in the source area variability in degree of chemical weathering is seen with the change in provenance in general the sediments north of goa with a provenance of deccan basalts show a higher chemical weathering index corg n molar ratios are mostly between 10 and 12 minimum and maximum being 6 9 and 14 respectively which are closer to values for marine organic matter this is corroborated by marine 13c values 18 2 to 21 6 while they broadly fall within the marine values heavier values are seen in northern transects off porbandar and dwaraka where the sediments have a provenance different from those in the south this could be due to a higher contribution from c4 type vegetation in the north consistent with heavier 13c values in terrestrial plants in source regions heavier 15n values are observed for the northern transects north of ratnagiri which is supported by the intense denitrification in the northern arabian sea

seasonal variations of sediment discharge from the yangtze river before and after impoundment of the three gorges dam abstract over the past decades 50 000 dams and reforestation on the yangtze river changjiang have had little impact on water discharge but have drastically altered annual and particularly seasonal sediment discharge before impoundment of the three gorges dam tgd in june 2003 annual sediment discharge had decreased by 60 and the hysteresis of seasonal rating curves in the upper reaches at yichang station had shifted from clockwise to counterclockwise in addition the river channel in middle lower reaches had changed from depositional to erosional in 2002 during the four years 2003 2006 after tgd impoundment 60 of sediment entering the three gorges reservoir was trapped primarily during the high discharge months june september although periodic sediment deposition continues downstream of the tgd during most months substantial erosion has occurred supplying 70 million tons per year mt y of channel derived sediment to the lower reaches of the river if sand extraction 40 mt y is taken into consideration the river channel loses a total of 110 mt y during the extreme drought year 2006 sediment discharge in the upper reaches drastically decreased to 9 mt only 2 of its 1950 1960s level because of decreased water discharge and tgd trapping in addition dongting lake in the middle reaches for the first time changed from trapping net sediment from the mainstem to supplying 14 mt net sediment to the mainstem severe channel erosion and drastic sediment decline have put considerable pressure on the yangtze coastal areas and east china sea

observation of glacial isostatic adjustment in stable north america with gps 1 motions of three hundred and sixty global positioning system gps sites in canada and the united states yield a detailed image of the vertical and horizontal velocity fields within the nominally stable interior of the north american plate by far the strongest signal is the effect of glacial isostatic adjustment gia due to ice mass unloading during deglaciation vertical velocities show present day uplift 10 mm yr near hudson bay the site of thickest ice at the last glacial maximum the uplift rates generally decrease with distance from hudson bay and change to subsidence 1 2 mm yr south of the great lakes the hinge line separating uplift from subsidence is consistent with data from water level gauges along the great lakes showing uplift along the northern shores and subsidence along the southern ones horizontal motions show outward motion from hudson bay with complex local variations especially in the far field although the vertical motions are generally consistent with the predictions of gia models the horizontal data illustrate the need and opportunity to improve the models via more accurate descriptions of the ice load and laterally variable mantle viscosity

immediate changes in stream channel geomorphology aquatic habitat and fish assemblages following dam removal in a small upland catchment abstract dam removal is becoming an increasingly important component of river restoration with 1100 dams having been removed nationwide over the past three decades despite this recent progression of removals the lack of pre to post removal monitoring and assessment limits our understanding of the magnitude rate and sequence of geomorphic and or ecological recovery to dam removal taking advantage of the november 2012 removal of an old 190 year old 6 m high run of river industrial dam on amethyst brook 26 km2 in central massachusetts we identify the immediate eco geomorphic responses to removal to capture the geomorphic responses to dam removal we collected baseline data at multiple scales both upstream 300 m and downstream 750 m of the dam including monumented cross sections detailed channel bed longitudinal profiles embeddedness surveys and channel bed grain size measurements which were repeated during the summer of 2013 these geomorphic assessments were combined with detailed quantitative electrofishing surveys of stream fish richness and abundance above and below the dam site and throughout the watershed and visual surveys of native anadromous sea lamprey petromyzon marinus nest sites post removal assessments were complicated by two events 1 upstream knickpoint migration exhumed an older ca late eighteenth century intact wooden crib dam 120 m upstream of the former stone dam and 2 the occurrence of a 10 20 year ri flood 6 months after removal that caused further upstream incision and downstream aggradation now that the downstream reach has been reconnected to upstream sediment supply the predominant geomorphic response was bed aggradation and associated fining 30 60 reduction at dam proximal locations aggradation ranged from 0 3 to 1 m where a large woody debris jam enhanced aggradation although less pronounced distal locations still showed aggradation with a mean depth of deposition of 0 20 m over the 750 m downstream reach post removal but pre flood bed surveys indicate 2 m of incision had migrated 25 m upstream of the former reservoir before encountering the exhumed dam which now acts as the new grade control limiting progressive headcutting approximately 1000 m3 of sediment was evacuated in the first year with 67 of the volume occurring by pre flood process driven e g changes in base level controls the combination of changes in channel bed sedimentology the occurrence of a large magnitude flood and the emergence of the new crib dam that is a likely barrier to fish movement was associated with major reductions in abundance and richness in sites downstream and immediately upstream adjacent to the former dam in post removal sampling at the same time we documented the presence of four species of fish including sea lamprey which were not present above the dam prior to removal indicating that upstream passage has been achieved and we also documented lamprey spawning activity at sites immediately below the dam which had previously been unsuitable owing to an excessively coarse and armored riverbed our results point to the importance of interactions between dam removal and flood disturbance effects with important implications for short and long term monitoring and assessment of dam impacts to river systems

sediment delivery to the three gorges 2 local response abstract information on soil erosion and sediment yields is very limited in the immediate vicinity of the three gorges project tgp although the inceptisols developed on triassic shales and sandstones in this area are known to be highly susceptible to erosion estimated sediment yields for a small reservoir catchment yiwanshui in changshou county downstream of chongqing are high around 3500 t km 2 a 1 and similar to the data from 38 reservoir investigations in sichuan basin but exceeding the yields estimated in the feasibility studies for the tgp the high sediment yield reflects severe soil erosion due to cultivation aligned with slope on steep slopes which is very common throughout sichuan basin and particularly in the tgp area the total sediment delivered to the yangtze from the tgp area has been estimated using small reservoir data and sediment load measured at hydrological stations these are comparable with previous estimates but there is much temporal variability in sediment supply from different parts of the three gorges region suggesting the importance of local impact on sediment flux resettlement of agricultural activity around the three gorges reservoir is likely to further enhance soil erosion temporal changes in sediment yields are reconstructed by using caesium 137 137cs dating techniques they indicate significant changes resulting from human activity and rainfall variability during the past four decades comparing reservoir sedimentation against erosion estimates on catchment soils derived from measurements indicates that 84 of eroded soil is delivered to the reservoir and the remainder is deposited in valley floor paddy fields it is estimated that over 60 of sediment is contributed from arable land the trap efficiency of small catchment reservoirs such as yiwanshui may be an important control on sediment delivery to the main channel of the upper yangtze

the subglacial origin of the lake agassiz ojibway final outburst flood arc shaped scours sandwaves and channels on the hudson bay seafloor suggest that the catastrophic drainage of lake agassiz ojibway occurred as a subglacial flood beneath the laurentide ice sheet which covered northern north america

the assessment of landslide susceptibility mapping using random forest and decision tree methods in the three gorges reservoir area china landslide susceptibility mapping is an indispensable prerequisite for landslide prevention and reduction at present research into landslide susceptibility mapping has begun to combine machine learning with remote sensing and geographic information system gis techniques the random forest model is a new integrated classification method but its application to landslide susceptibility mapping remains limited landslides represent a serious threat to the lives and property of people living in the zigui badong area in the three gorges region of china as well as to the operation of the three gorges reservoir however the geological structure of this region is complex involving steep mountains and deep valleys the purpose of the current study is to produce a landslide susceptibility map of the zigui badong area using a random forest model multisource data gis and remote sensing data in total 300 pre existing landslide locations were obtained from a landslide inventory map these landslides were identified using visual interpretation of high resolution remote sensing images topographic and geologic data and extensive field surveys the occurrence of landslides is closely related to a series of environmental parameters topographic geologic landsat 8 image raining data and seismic data were used as the primary data sources to extract the geo environmental factors influencing landslides thirty four layers of causative factors were prepared as predictor variables which can mainly be categorized as topographic geological hydrological land cover and environmental trigger parameters the random forest method is an ensemble classification technique that extends diversity among the classification trees by resampling the data with replacement and randomly changing the predictive variable sets during the different tree induction processes a random forest model was adopted to calculate the quantitative relationships between the landslide conditioning factors and the landslide inventory map and then generate a landslide susceptibility map the analytical results were compared with known landslide locations in terms of area under the receiver operating characteristic curve the random forest model has an area ratio of 86 10 in contrast to the random forest whole factors wf random forest 12 major factors 12f decision tree wf decision tree 12f the final result shows that random forest 12f has a higher prediction accuracy meanwhile the random forest models have higher prediction accuracy than the decision tree model subsequently the landslide susceptibility map was classified into five classes very low low moderate high and very high the results demonstrate that the random forest model achieved a reasonable accuracy in landslide susceptibility mapping the landslide hazard zone information will be useful for general development planning and landslide risk management

geochemistry of river borne clays entering the east china sea indicates two contrasting types of weathering and sediment transport processes the east china sea is characterized by wide continental shelf receiving a huge input of terrigenous matter from both large rivers and mountainous rivers which makes it an ideal natural laboratory for studying sediment source to sink transport processes this paper presents mineralogical and geochemical data of the clays and bulk sediments from the rivers entering the east china sea aiming to investigate the general driving mechanism of silicate weathering and sediment transport processes in east asian continental margin two types of river systems tectonically stable continental rivers and tectonically active mountainous rivers coexist in east asia as the direct weathering products clays can better reflect the silicate weathering regimes within the two river systems provenance rock types are not the dominant factor causing silicate weathering intensity difference existed in the east asian rivers the silicate weathering intensity of tectonically stable river basins is primarily driven by monsoon climate and the sediment transfer is relatively slow because of natural trapping process and increasing damming effect the geochemistry of these river borne sediments can thus indicate paleo weathering intensities in east asian continent in contrast silicate weathering intensity in tectonically active mountainous rivers is greatly limited by strong physical erosion despite the high temperature and highest monsoon rainfall the factors controlling silicate weathering in tectonically active catchments are complex and thus it should be prudent to use river sediment records to decipher paleoclimate change these two different silicate weathering regimes and sediment transport processes are manifestations of the landscape evolution and overall dominate the sedimentation in asian continental margin

hyperpycnal plume formation from riverine outflows with small sediment concentrations a series of laboratory experiments has been conducted in order to elucidate the sediment induced mixing processes accompanying riverine outflows specifically the discharge of a warm fresh particle laden fluid over a relatively dense cool brine in a parameter regime analogous to recently acquired field measurements hypopycnal surface plumes were subject to a convective instability driven by some combination of heat diffusing out of the warm fresh sediment laden plume and particle settling within it convection was robust in the presence or absence of intense turbulence at sediment concentrations as low as 1 kg m 3 and took the form of millimetre scale sediment laden fingers descending from the base of the surface plume a consequence of the convective instability of the original hypopycnal plume is the generation of a hyperpycnal bottom riding flow the experiments presented here indicate that natural river outflows may thus generate hyperpycnal plumes when sediment concentrations are 40 times less than those required to render the outflow heavy relative to the oceanic ambient the resulting hyperpycnal plumes may play an important role in transporting substantial quantities of sediment to the continental slope and beyond

large scale dam removal on the elwha river washington usa erosion of reservoir sediment abstract base level lowering of reservoirs impounding upstream sediment supply triggers a series of channel evolution steps such as degradation lateral erosion and redeposition that can dramatically alter the reservoir landscape and decouple the relationship between stream power and sediment supply many case studies exist for small dam removals with a few years of sediment storage or dam breaches triggering instantaneous large sediment releases however quantitative information for a controlled drawdown initiating erosion of a large sediment deposit is rare we investigate reservoir sediment response to the phased and concurrent drawdown of two reservoirs on the elwha river washington usa during the largest dam removal in history by measuring changes in reservoir topography and channel morphology as a function of base level lowering river discharge and cohesion after two years the elwha dam was completely removed and three quarters of glines canyon dam were removed reservoir drawdown increments of 3 to 5 m were sufficient to initiate channel degradation and delta progradation across the width of the receding reservoir redistributing decades of accumulated delta sediment throughout the reservoir while the lake still remained the first year of dam removal resulted in up to 5 m of incision through the lake aldwell delta down to the predam surface and in just over 20 m of incision through the lake mills delta in contrast delta progradation resulted in a few meters of deposition in lake aldwell and 2 to 10 m in lake mills on top of prodelta and lakebed deposits in coarse noncohesive sediment a braided channel developed and widened up to tenfold across the entire width of the reservoir the most extensive lateral erosion occurred in noncohesive deposits during multiweek hold periods coinciding with flows greater than the mean annual flow but less than a 2 year flood peak channel widening in more cohesive fine sediments of the prodelta and lakebed was less than half of that in the coarse noncohesive delta sediments dam removal resulted in the erosion and downstream release of 23 of the sediment in lake aldwell 1 12 0 07 million m3 and 37 of the sediment in lake mills 5 95 0 12 million m3 representing nearly four decades of sediment supply from the upstream watershed within a two year time frame a significant portion of the reservoir sediment is expected to remain as sediment terraces within the reservoir landscape but additional erosion is expected after the remainder of the glines canyon dam is removed and during future floods until the river reaches quasi equilibrium after phased dam removal the reservoir landscape consists of a series of sediment terraces of varying heights composed of prograded coarse sediment overlying fine lakebed deposits the predam surface is exposed along the river corridor and abundant 1 to 3 m stumps from pre removal forests create unique morphology where the river interacts with the predam landscape

itrax description and evaluation of a new multi function x ray core scanner a new automated multi function core scanning instrument named itrax has been developed that records optical radiographic and elemental variations from sediment half cores up to 1 8 m long at a resolution as fine as 200 m an intense micro x ray beam focused through a flat capillary waveguide is used to irradiate samples to enable both x radiography and x ray fluorescence xrf analysis data are acquired incrementally by advancing a split core via a programmable stepped motor drive through the flat rectangular section x ray beam traditional xrf determination of element composition in sediments provides high quality data but it takes a considerable time and normally consumes gram quantities of material that is often only available in limited quantities the itrax core scanner non destructively collects optical and x radiographic images and provides high resolution elemental profiles that are invaluable for guiding sample selection for further destructive detailed sampling this paper presents a description of the construction characteristics and capabilities of the itrax system high resolution itrax data obtained from sediment cores are also presented and compared with results from traditional wavelength dispersive xrf analysis at lower resolution finally some recent technical developments linked to the second generation itrax are presented

hydrodynamic sorting and transport of terrestrially derived organic carbon in sediments of the mississippi and atchafalaya rivers abstract over the course of two years four cruises were conducted at varying levels of discharge in the lower mississippi and atchafalaya rivers mr and ar where grab samples were collected from sand and mud dominated sediments the tetramethylammonium hydroxide tmah thermochemolysis method was used to determine sources of terrestrially derived organic carbon oc in these two sediment types to examine the effects of hydrodynamic sorting on lignin sources in river sediments average lignin concentrations in the lower mr were 1 4 1 1 mg goc 1 at english turn et and 10 4 27 4 mg goc 1 at venice using these concentrations annual lignin fluxes to the gulf of mexico from tidal and estuarine mud remobilization at et and venice were 3 1 2 5 10 5 kg and 11 4 30 0 10 5 kg respectively much of the lignin derived materials in muddy sediments appeared to be derived from non woody grass like sources which should decay more quickly than the woody materials typically found in the sandy deposits the average total oc 1 93 0 47 of english turn sands yields an annual flux of 0 34 0 09 10 9 kg lignin flux in the english turn sands 3 6 2 6 mg gc 1 using the numbers above would be 12 2 9 4 10 5 kg the extensive amounts of sand sized woody materials coffee grinds found in the sandy sediments in both the ar and mr are likely derived from woody plant materials this is the first time it has been demonstrated that sandy sediments in the mr provide an equally important pathway compared to muds for the transport of terrestrially derived organic matter to the northern gulf of mexico using the ar average oc in sand 1 16 0 72 we estimated an annual flux of oc to the shelf of 0 13 0 07 10 9 kg lignin flux for ar sands was estimated to be 12 4 12 1 10 5 kg despite the high error associated with these numbers we observe for the first time that the flux of lignin in sandy sediments in the ar to the northern gulf of mexico is comparable to that found in the mr these results further support the likelihood of grain size related hydrodynamic sorting of terrestrially derived organic carbon in the lower mississippi and atchafalaya rivers suggesting that there is a distinct sandy sediment organic fraction contributed by major rivers to the global carbon cycle

channel evolution after dam removal in a poorly sorted sediment mixture experiments and numerical model dam removal is commonly used for river restoration however there are still some uncertainties associated with dam removal mainly related to the sediment transport rates released downstream from the deposit that had previously filled the impoundment this research studies the physical response to dam removal in the antecedent deposit by answering the following questions a how does an initial channel excavated into the deposit evolve and b what is the time distribution of the material released during the early stages of the process these goals are achieved by an experimental campaign using a poorly sorted mixture of sediment in the antecedent deposit the research shows that for the given conditions of our experiments the rate at which the sediment is released depends on the height of the removed dam the water discharge and the maximum potential volume of sediment to be eroded this investigation provides new insights of the width evolution when the sediment is composed of a poorly sorted mixture this evolution is linked to the bed degradation rates channel narrows during a rapid incisional phase and subsequently widens when bed degradation rates decrease channel width changes propagate upstream as a convection like perturbation associated with a kinematic wave starting at the location of the antecedent dam these features are modeled through a new numerical model accounting for mixtures more specifically a set of equations has been derived for the variation of bed elevation channel bottom width and bed grain size distribution which when solved numerically describe the observed channel processes

effects of sediment pulses on bed relief in bar pool channels to further develop prediction of the range of morphological adjustments associated with sediment pulses in bar pool channels we analyze channel bed topographic data collected prior to and following the removal of two dams in oregon marmot dam on the sandy river and brownsville dam on the calapooia river we hypothesize that in gravel bed bar pool channels the response of bed relief to sand and gravel sediment pulses is a function of initial relief and pulse magnitude modest increases in sediment supply to initially low relief sediment poor cross sections will increase bed relief and variance of bed relief via bar deposition modest increases in sediment supply to initially high relief cross sections characteristic of alternate bar morphology will result in decreased bed relief and variance of relief via deposition in bar adjacent pools these hypothesized adjustments are measured in terms of bed relief which we define as the difference in elevation between the pool bottom and bar top we evaluate how relief varies with sediment thickness where both relief and mean sediment thickness at a cross section are normalized by the 90th percentile of observed relief values within a reach prior to a sediment pulse field measurements generally supported the stated hypotheses demonstrating how introduction of a sediment pulse to low relief reaches can increase mean and variance of relief while introduction to high relief reaches can decrease the mean and variance of bed relief at least temporarily in general at both sites the degree of impact increased with the thickness of sediment delivered to the cross section results thus suggest that the analysis is a useful step for understanding the morphological effects of sediment pulses introduced to gravel bed bar pool channels copyright 2015 john wiley sons ltd

magnetic evidence for yellow river sediment in the late holocene deposit of the yangtze river delta china abstract sediment source identification is critical for understanding delta evolution processes and for managing delta sustainability particularly for deltas experiencing significant recent fluvial sediment discharge sediment sources for the yangtze river delta yrd are commonly assumed to be derived from the yangtze river despite the fact that the yrd is a tide dominated delta that can receive marine sourced sediments in addition to fluvial inputs in particular potential contributions from the neighbouring sediment laden yellow river when it discharged into the yellow sea during 1128 1855 ce remains unclear here we present provenance analysis of three cores from the northern yrd using size specific magnetic characterizations we find that magnetic properties of sediments younger than 400 years have large differences among the studied cores comparison of magnetic properties to potential sources including the major yangtze river tributaries i e jinsha river jialing river and han river and old yellow river oyr indicates that the northern core received enhanced yellow river sediment loads over the last 400 years while the southern core had a dominant yangtze influence which is most pronounced in size fractions less than 16 m this interpretation is supported by geochemical results the documented spatial sediment source heterogeneity is caused by differences in tidal fluvial interaction among delta distributary channels our results imply that the neighbouring oyr delta to the north exerts a remote influence on the yrd through longshore transport this coastal connectivity between deltas should be assessed when forecasting future tide dominated delta changes in the context of global change

sources and distributions of sedimentary organic matter in the columbia river drainage basin washington and oregon1 nonwoody angiosperm tissues and gymnosperm woods are the major types of vascular plant debris in bottom sediments from 16 sites within the columbia river and its tributaries in tributary sediments relative abundances of these types of tissue vary regionally and are consistent with drainage basin vegetation within the extensively dammed main river vascular plant debris mixtures are more uniform indicating downstream mixing of sedimentary material from reservoir to reserwoir vascular plant tissues account for an average of a third of the total sedimentary organic matter at the 16 river sites the remaining organic material has an atomic c n of 10 l 5 and a stable carbon isotope composition similar to average land plants organic matter in sediments of the columbia river system is generally enriched in nonwoody angiosperm tissues and ligninpoor organic matter in comparison to columbia river derived organic matter in modern marine sediments from the southern washington continental shelf

sources and distribution of terrigenous organic matter delivered by the atchafalaya river to sediments in the northern gulf of mexico abstract suspended sediments ss from the atchafalaya river ar and the mississippi river and surficial sediment samples from seven shallow cross shelf transects west of the ar in the northern gulf of mexico were examined using elemental oc c n isotopic 13c 14c and terrigenous biomarker analyses the organic matter om delivered by the ar is isotopically enriched 24 5 and relatively degraded suggesting that soil derived om with a c4 signature is the predominant om source for these ss the shelf sediments display oc values that generally decrease seaward within each transect and westward parallel to the coastline a strong terrigenous c n 29 signal is observed in sediments deposited close to the mouth of the river but values along the remainder of the shelf fall within a narrow range 8 13 with no apparent offshore trends depleted stable carbon isotope 13c values typical of c3 plant debris 27 are found near the river mouth and become more enriched 22 to 21 offshore the spatial distribution of lignin in shelf sediments mirrors that of oc with high lignin yields found inshore relative to that found offshore water depth 10 m the isotopic and biomarker data indicate that at least two types of terrigenous om are deposited within the study area relatively undegraded c3 plant debris is deposited close to the mouth of the ar whereas more degraded isotopically enriched soil derived om appears to be deposited along the remainder of the shelf an important input from marine carbon is found at the stations offshore from the 10 m isobath quantification of the terrigenous component of sedimentary om is complicated by the heterogeneous composition of the terrigenous end member a three end member mixing model is therefore required to more accurately evaluate the sources of om deposited in the study area the results of the mixing calculation indicate that terrigenous om soil derived om and vascular plant debris accounts for 79 of the om deposited as inshore sediments and 66 of om deposited as offshore sediments importantly the abundance of terrigenous om is 40 higher in inshore sediments and nearly 85 higher in offshore sediments than indicated by a two end member mixing model such a result highlights the need to reevaluate the inputs and cycling of soil derived om in the coastal ocean

sediment delivery to the three gorges 1 catchment controls abstract the paper examines sediment yield and its response to catchment disturbance and environmental variables in the upper yangtze basin where the attention of environmentalists has been drawn to the three gorges project tgp information about the source and conveyance of sediment from the catchment area to the three gorges reservoir has implications for management strategies methodologies for establishing the relationships between land cover climatic and topographic variables with sediment yield are introduced the analysis uses a sediment load data set containing 250 stations with up to 30 years of measurement a 1 1 km resolution land cover database and variables extracted from various geodatabases the mean sediment load delivered from the yangtze upstream of chongqing is 318 mt a 1 but the contribution from the jialing tributary is higher in terms of specific sediment yield at 928 t km 2 a 1 long term sediment yield at yichang has not exhibited an upward trend despite the evidence for increased soil erosion within the basin examination of sediment response to catchment disturbance and spatial variability in relation to controlling variables has been undertaken in an attempt to predict future sedimentation impacts time series analysis illustrates that significant increases in sediment yield have occurred over about 8 of the catchment area while about 3 have experienced decreasing sediment yields the latter are associated with major reservoir schemes on the tributaries of the yangtze when the spatial pattern of sediment yields within the basin is analysed natural climatic and topographic factors explain most of the variability in the relatively sparsely populated western part of the upper yangtze basin but do not afford very good prediction in the more populated eastern part incorporation of land cover information does not provide additional explanation of spatial variability examination of the response of sediment delivery to catchment disturbance and environmental variables provides an illustration which may have some lessons for the management of the sedimentation problem in the three gorges reservoir and a basis for modelling future changes in sediment delivery

distribution and sources of organic matter in surface sediments of the eastern continental margin of india the sources and distribution of organic matter om in surface sediments of the eastern continental margin of india including the region influenced by river discharge were investigated using content molar c n ratios and stable isotopes of carbon and nitrogen despite relatively high water column integrated chlorophyll a concentrations were found in the continental shelf than the slope however the lower sediment organic carbon soc was found in the former than the latter region suggesting that in situ production did not play significant role on preservation of soc in the coastal bay of bengal the broad range of 13 c of soc 23 2 to 16 7 suggests that om is a broad mixture of terrestrial and marine om relative contributions from terrestrial c3 and c4 plants and marine sources are quantified as 34 23 and 43 respectively indicating that dominant source of allochthonous om 57 in the coastal bay of bengal relatively higher contribution of om from c4 plants were found in the sediments at off river krishna indicating that this region received detritus of agricultural crops such as jowar bajra and sugar cane which are dominant in its drainage basin during sw monsoon this study revealed that relatively high om preserved in the slope than shelf region along the coastal bay of bengal and the composition of om is primarily controlled by the type of agricultural crops and vegetation in the drainage basin of the river

distinguishing sediments from the yangtze and yellow rivers china a mineral magnetic approach the yellow river and the yangtze river contribute 10 of the global fluvial sediment flux to the oceans proper characterization of the sediments of the two rivers is critical to the knowledge of their fate in the marginal seas of the west pacific ocean magnetic measurements have been made on bulk sediments as well as on separated particle size fractions of representative samples from the yellow and yangtze river estuaries with the purpose of providing an efficient means of differentiating both groups of river sediments from each other we found that on average the yangtze river estuary sediments have relatively higher ferrimagnetic mineral contents and ferrimagnetic to antiferromagentic ratios compared with the yellow river estuary sediments a diagram of saturated isothermal remanent magnetization sirm versus the demagnetization parameter s 100 can clearly distinguish sediments from the two rivers detailed magnetic measurements carried out on particle size fractions provide additional confirmation

deglacial and postglacial paleoseismological archives in mass movement deposits of lakes of south central quebec investigation of seismic activity in eastern canada is important for natural hazard management as two major active seismic zones with many historical records are located in the region the western

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

time and the persistence of alluvium river engineering fluvial geomorphology and mining sediment in california abstract river managers need to understand fluvial systems as they change through time many river systems are presently in a state of flux as a result of substantial anthropogenic changes to water and sediment regimes and channel hydraulics yet historical approaches to understanding river systems rarely receive adequate attention because historical methodologies are not conducive to the application of quantitative analysis while there is limited precision in most historical reconstructions the information derived from these studies constrains other interpretations and is essential to a full understanding of the behavior of fluvial systems geomorphology provides a perspective on river systems in which time at various scales is interwoven into practical and theoretical aspects of scientific inquiry thus geomorphology is important to our understanding of not only physical systems but also fundamental concepts of time this study examines channel morphological changes in the bear and american basins brought about by two episodes of sedimentation from hydraulic gold mining the primary event was the production of more than 1 billion m3 of sediment throughout the northern sierra nevada from 1853 to 1884 which caused aggradation in many channels across the sierra foothills and sacramento valley assumptions by both engineers and geomorphologists that morphologic responses to this event were ephemeral that sediment loads have returned to previous levels and that deposits have stabilized are not borne out by field and historical data in the sacramento valley a secondary sedimentation event not previously studied was the production of at least 24 million m3 of sediment during a period of licensed mining from 1893 to 1953 this episode of sedimentation has been largely overlooked as a geomorphic hydrologic or water quality event yet channel morphologic responses in phase with mining during this period are demonstrated systematic changes in stage discharge relationships reflect channel morphological changes that are relevant to flood risk assessments stability of engineering structures on floodplains and geomorphic interpretations

large scale dam removal on the elwha river washington usa fluvial sediment load abstract the elwha river restoration project in washington state includes the largest dam removal project in united states history to date starting september 2011 two nearly century old dams that collectively contained 21 3 million m3 of sediment were removed over the course of three years with a top down deconstruction strategy designed to meter the release of a portion of the dam trapped sediment gauging with sediment surrogate technologies during the first two years downstream from the project measured 8 200 000 3 400 000 tonnes of transported sediment with 1 100 000 and 7 100 000 t moving in years 1 and 2 respectively representing 3 and 20 times the elwha river annual sediment load of 340 000 80 000 t y during the study period the discharge in the elwha river was greater than normal 107 in year 1 and 108 in year 2 however the magnitudes of the peak flow events during the study period were relatively benign with the largest discharge of 292 m3 s 73 of the 2 year annual peak flow event early in the project when both extant reservoirs still retained sediment despite the muted peak flows sediment transport was large with measured suspended sediment concentrations during the study period ranging from 44 to 16 300 mg l and gauged bedload transport as large as 24 700 t d five distinct sediment release periods were identified when sediment loads were notably increased when lateral erosion in the former reservoirs was active or reduced when reservoir retention or seasonal low flows and cessation of lateral erosion reduced sediment transport total suspended sediment load was 930 000 t in year 1 and 5 400 000 t in year 2 of the total 6 300 000 3 200 000 t of suspended sediment load 3 400 000 t consisted of silt and clay and 2 900 000 t was sand gauged bedload on the lower elwha river in year 2 of the project was 450 000 360 000 t bedload was not quantified in year 1 but qualitative observations using bedload surrogate instruments indicated detectable bedload starting just after full removal of the downstream dam using comparative studies from other sediment laden rivers the total ungauged fraction of

can coarse bedload pass through weirs abstract restoring active bedload transfer in human impacted rivers has received increasing attention in recent years notably in response to the european water framework directive wfd which requires that the continuity of rivers not be disturbed by anthropogenic features such as dams or weirs the bocq river 233 km2 a moderate gradient stream in wallonia belgium has a hydraulic resource that was formerly largely exploited with 74 weirs up to 2 3 m high along 43 km we examined the effects of seven old abandoned weirs on bedload transport for three different types of weirs defined by the presence and position of the sluice gate system first the volume estimates of bedload stored in reservoirs indicated that despite their old age the reservoirs were not completely filled between 25 and 50 filled compared to the reservoir volume capacity and did not evolve very much since 1990 second the grain size analysis of bed material upstream downstream and within the reservoirs and the direct measurements of sediment transport slag particles and pit tagged pebbles demonstrated that bedload continues to be transported out of the reservoir even though the selective trapping of coarser elements was observed within the reservoir particles in the range of the median can pass over the crest of weirs but the coarser elements tend to remain in the reservoirs this trapping effect is mitigated when the weir has open or collapsed flushing gates that facilitate bedload transfer this indicates that weirs act as leaky barriers that allow bedload to pass through although the individual geomorphic setting plays a primary role in determining the local sediment continuity these findings suggest that river connectivity is less impacted than initially thought and is likely to increase over time as old weirs gradually fall into disrepair this needs to be acknowledged when planning barrier removal projects

hydrologic and geomorphic changes resulting from episodic glacial lake outburst floods rio colonia patagonia chile glacial lake outburst floods glofs are a prominent but poorly understood cryospheric hazard in a warming climate we quantify the hydrologic and geomorphic response to 21 episodic glofs that began in april 2008 using multitemporal satellite imagery and field observations peak discharge exiting the source lake became progressively muted downstream at 40 60 km downstream where the floods entered and traveled down the main stem rio baker peak discharges were generally 1 2 times the peak annual discharge of this system chile s largest river by volume as such caution must be applied to empirical relationships relating lake volume to peak discharge as the latter is dependent on where this observation is made along the flood path the glofs and subsequent periods of free drainage resulted in 40 m of incision the net removal of 25 106 m3 of sediment from the source lake basin and a nonsteady channel configuration downstream these results demonstrate that glofs sourced from low order tributaries can produce significant floods on major main stem rivers in addition to significantly altering sediment dynamics

recent human impacts on the morphological evolution of the yangtze river delta foreland a review and new perspectives abstract this paper reviews the morphological change in the yangtze river delta due to increasing human impacts from three major aspects the first is the reduction of sediment supply to the ocean due to dam construction soil conservation and sand mining within the yangtze river basin the reduced sediment supply has decreased the progradation rate of the delta and triggered erosion in the front of the delta the second impact relates to the reclamation of intertidal wetlands by human activities since the 1950s approximately 1100 km 2 of intertidal land has been embanked resulting in the disappearance of salt marshes and even the entire intertidal zone along some sections of the coastline the third change in the delta due to human interference is the construction of deep waterway structures at the mouth bar which has greatly modified the local hydrodynamics and morphology sediment accretion has increased significantly in these areas as a result of sheltering by these deep waterway structures this review shows that human activities have severely altered the natural balance among the hydrodynamics and sediment supply affecting the morphological features of the yangtze river watershed and delta human impacts on the morphological evolution of deltaic coasts in general are becoming an increasingly concern and more attention should be paid to the management and mitigation of these effects

environmental magnetism principles and applications 1 in environmental magnetism rock and mineral magnetic techniques are used to investigate the formation transportation deposition and postdepositional alterations of magnetic minerals under the influences of a wide range of environmental processes all materials respond in some way to an applied magnetic field and iron bearing minerals are sensitive to a range of environmental processes which makes magnetic measurements extremely useful for detecting signals associated with environmental processes environmental magnetism has grown considerably since the mid 1970s and now contributes to research in the geosciences and in branches of physics chemistry and biology and environmental science including research on climate change pollution iron biomineralization and depositional and diagenetic processes in sediments to name a few applications magnetic parameters are used to routinely scan sediments but interpretation is often difficult and requires understanding of the underlying physics and chemistry thorough examination of magnetic properties and of the environmental processes that give rise to the measured magnetic signal is needed to avoid ambiguities complexities and limitations to interpretations in this review we evaluate environmental magnetic parameters based on theory and empirical results we describe how ambiguities can be resolved by use of combined techniques and demonstrate the power of environmental magnetism in enabling quantitative environmental interpretations we also review recent developments that demonstrate the mutual benefit of environmental magnetism from close collaborations with biology chemistry and physics finally we discuss directions in which environmental magnetism is likely to develop in the future

the magnetic signature of rapidly deposited detrital layers from the deep labrador sea relationship to north atlantic heinrich layers rock magnetic parameters from deep labrador sea piston core p 094 are useful for recognizing rapidly deposited detrital layers some of which correlate with north atlantic heinrich layers variations in magnetic properties and lithology distinguish two classes of rapidly deposited detrital layers during the last ice age 1 seven detrital carbonate dc layers have high carbonate content and mean magnetite grain diameters about 4 times greater than the background sediments 2 six low detrital carbonate ldc layers have very similar magnetic properties to dc layers but low carbonate content similar to the background sediments the magnetite associated with dc and ldc layers is well sorted and relatively uniform within and between layers ice rafted detritus ird recognized by increased percentage of the 125 micron grain size fraction and by high magnetic susceptibility is associated with most dc and ldc layers but is not the dominant detrital constituent the correspondence of dc and ldc layers with increased grain size of well sorted magnetite but not with coarse fraction content precludes ice rafting as the primary depositional mechanism dc and ldc layers may have been deposited from suspended sediment derived from turbidite activity in the nearby northwest atlantic mid ocean channel namoc this interpretation is supported by a piston core p 013 from a greenland rise site largely but not completely outside the influence of the namoc the association of dc layers with ird and the apparent age correlation of dc layers to north atlantic heinrich layers suggest that the ice advances which produced the ird in p 094 and in correlative north atlantic heinrich layers also triggered turbiditic flows down the namoc several dc and ldc layers however do not correlate with recognized heinrich layers but appear to be coeval with recently discovered high frequency ird rich layers in the north atlantic

distribution and dispersal of clay minerals on the western continental shelf of india abstract sediment samples distributed over a distance of 1700 km from the inner continental shelf of western india were analysed for their clay mineral content by x ray diffraction the clay minerals present in the sediments in order of abundance are montmorillonite kaolinite illite chlorite and gibbsite based on the abundance of montmorillonite and kaolinite four clay mineral provinces on the continental shelf have been demarcated these are 1 the montmorillonite kaolinite illite chlorite province off the gulf of kutch 2 the montmorillonite rich zone off the gulf of cambay 3 a transition zone on the central parts of the shelf and 4 a relatively montmorillonite poor gibbsite province on the southwestern part of the shelf source rock influence on clay mineral composition appears to be more important than physical transport the southwest monsoon drift in the present case in the northwestern part of the study area the high velocity tidal streams of the macrotidal gulf of kutch act as dynamic barriers to longshore sediment dispersal leading to distinct clay mineral assemblages on the shelf north and south of the gulf mouth

a centennial tribute to g k gilbert s hydraulic mining debris in the sierra nevada abstract g k gilbert s 1917 classic monograph hydraulic mining debris in the sierra nevada is described and put into the context of modern geomorphic knowledge the emphasis here is on large scale applied fluvial geomorphology but other key elements e g coastal geomorphology are also briefly covered a brief synopsis outlines key elements of the monograph followed by discussions of highly influential aspects including the integrated watershed perspective the extreme example of anthropogenic sedimentation computation of a quantitative semidistributed sediment budget and advent of sediment wave theory although gilbert did not address concepts of equilibrium and grade in much detail the rivers of the northwestern sierra nevada were highly disrupted and thrown into a condition of nonequilibrium therefore concepts of equilibrium and grade for which gilbert s early work is often cited are discussed gilbert s work is put into the context of complex nonlinear dynamics in geomorphic systems and how these concepts can be used to interpret the nonequilibrium systems described by gilbert broad basin scale studies were common in the period but few were as quantitative and empirically rigorous or employed such a range of methodologies as pp105 none demonstrated such an extreme case of anthropogeomorphic change

dredging and canal gate technologies in portus the ancient harbour of rome reconstructed from event stratigraphy and multi proxy sediment analysis ancient harbours are rich archives of human environment interaction however dating harbour deposits and correlating their stratigraphy is a major challenge because of typically high sedimentation rates over short periods and possible curative dredging events portus the maritime harbour of rome at the height of the roman empire was a port complex composed of basins and canals connecting the commercial harbour to rome via the tiber river sediment core cps1 in the narrowest of these canals canale traverso is located centrally in what was the capital city s commercial hub and contains a continuous harbour depositional record with average sedimentation rates greater than 1 cm per year here we use piston coring high resolution core scanning and a multi proxy sediment analysis including for the first time paleo and rock magnetism and bulk and clay mineralogy in order to overcome the problems of dating harbour deposits and correlating their stratigraphy the method allowed precise identification of major reworked events including a dredged deposit and a hyperpycnal deposit which improve the chronostratigraphy and water depth reconstruction and sheds light on harbour technologies at the height of the roman empire a debris layer with abundant ceramic fragments and rocks marks the decommissioning of canale traverso and provides a new chronostratigraphic marker at portus multi proxy riverine input signatures point to the possible use of canal gate technology for water flow management

mineralogical and isotopic evidence for the sediment provenance of the western south yellow sea since mis 3 and implications for paleoenvironmental evolution abstract changing sediment provenance and related paleoenvironmental evolution since marine isotope stages mis 3 have been investigated based on accelerator mass spectrometry ams 14c and optically stimulated luminescence osl dating of core csdp 01 recovered from the western south yellow sea sys based on our results sea level fluctuations and monsoonal climate variations are identified as the principal factors driving these changes sea level fluctuations determined the accommodation space in the shelf area while the monsoonal climate controlled the sediment supply capacity from river to sea mineral and sr nd isotopic records reveal the major contribution of the paleo changjiang river yangtze river to the study core area during the early mid mis 3 which likely defined the northern limit of the paleo changjiang delta at that time high sediment supply and limited accommodation space led to the development of sediment fed systems on the sys shelf resulting in a high preservation potential for thick stacking and overlapping deltaic sediments along with deltaic progradation core sediment provenance gradually transformed from the paleo changjiang river to the paleo huanghe river yellow river near the late mis 3 implying that the paleo huanghe river likely emptied into the sys and built a large delta during the mis 3 interval a strong summer monsoon during the early mis 1 interval was favorable for the changjiang to deliver abundant sediments to the study core area a weak summer monsoon during the mid late mis 1 when the coastline had retreated to nearly its present day position decreased the changjiang and huanghe supply to the study area low sediment supply and sufficient accommodation space gave rise to the development of sediment starved systems during this period nd values fluctuated between the changjiang and huanghe sources at that time suggesting that sea bed erosion materials are the main sediment contribution to the study area in general sedimentary evolution in the western sys since mis 3 is a good example of river sea interaction in the marginal seas of southeast asia in which sea level and monsoonal climate changes should play an important role

progradation speed of tide dominated tidal flats decreases stronger than linearly with decreasing sediment availability and linearly with sea level rise we use the results of a one dimensional morphodynamic model and the basis of the lagrangian equilibrium state maan et al 2015 https doi org 10 1002 2014jf003311 to derive a quantitative relationship between the progradation speed of tidal flats and the suspended sediment concentration in their adjacent waters and show that the speed increases more than linearly with the concentration we also show that horizontally prograding flats rise vertically with sea level rise at the expense of their horizontal speed via a linear relationship if accretion rates are insufficient to keep up with sea level rise however the intertidal flat submerges and retreats landward at the same time we apply the obtained relationships to the yangtze estuary to estimate the critical sediment concentration level below which a shift from progradation to retreat can be expected

variations of the monsoon regime during the upper quaternary evidence from carbon isotopic record of organic matter in north indian ocean sediment cores abstract the 13 c 12 c ratios and contents of organic carbon in deep sea sediment cores of the north indian ocean have been compared for the different climatic stages as determined by oxygen isotope stratigraphy using the differences in the 13 c values between marine and terrestrial organic matter the terrestrial contribution to the eastern gulf of bengal and the andaman sea has been determined for modern and glacial times the geographical distribution of the terrestrial organic carbon linked to sea surface circulation shows that during the last glacial period the ne monsoon circulation was the dominant feature the organic carbon abundance within the sediment which is related to local productivity was greater during glacial times in the areas where production depends on the ne monsoon strength coast of north india in the arabian sea and andaman sea suggesting its reinforcement

classification of geomorphological effects downstream of dams abstract the effects of dams on downstream geomorphology are reviewed and a typology is devised consisting of nine cases the classification can be seen as a further development of lane s balance between water discharge sediment load grain size and river slope depending on changes in released water flow and changes in released sediment load relative to the transport capacity of the flow it is possible to estimate resulting cross sectional geomorphology the longitudinal extent of changes and their variability with time and the tributary response to altered mainstream cross section changes are also discussed

geology geography and humans battle for dominance over the delivery of fluvial sediment to the coastal ocean abstract sediment flux to the coastal zone is conditioned by geomorphic and tectonic influences basin area and relief geography temperature runoff geology lithology ice cover and human activities reservoir trapping soil erosion a new model termed bqart in recognition of those factors accounts for these varied influences when applied to a database of 488 rivers the bqart model showed no ensemble over or underprediction had a bias of just 3 across six orders of magnitude in observational values and accounted for 96 of the between river variation in the long term 30 years sediment load or yield of these rivers the geographical range of the 488 rivers covers 63 of the global land surface and is highly representative of global geology climate and socioeconomic conditions based strictly on geological parameters basin area relief lithology ice erosion 65 of the between river sediment load is explained climatic factors precipitation and temperature account for an additi

yangtze river of china historical analysis of discharge variability and sediment flux hydrological records covering a 100 year period from the upper middle and lower yangtze river were collected to examine the temporal and spatial distribution of discharge and sediment load in the drainage basin the yangtze discharge as expected increases from the upper drainage basin downstream only an estimated 50 of the discharge is derived from the upper yangtze with the rest being derived from the numerous tributaries of the middle and lower course however the distribution of sediment load along the yangtze is the reverse of that observed for discharge with most of the sediment being derived from the upper basin a dramatic reduction in sediment load by 0 8 108 tons year occurs in the middle yangtze because of a marked decrease in slope and the change to a meandering pattern from the upper yangtze rock sections considerable siltation also occurs in the middle yangtze drainage basin as the river cuts through a large interior dongting lake system sediment load in the lower yangtze while significantly less than that of the upper river is somewhat higher than the middle yangtze because of additional load contributed by adjacent tributaries a strong correlation exists between the discharge and sediment load along the yangtze drainage basin during the dry season as lower flows carry lower sediment concentration during the wet season a strong correlation is also present in the upper yangtze owing to the high flow velocity that suspends sand on the bed however a negative to poor correlation occurs in the middle and lower yangtze because the flow velocity in these reaches is unable to keep sand in suspension transporting only fine grained particles downstream hydrological data are treated for 30 years 1950 1980 when numerous dams were constructed in the upper yangtze drainage basin at yichang and hankou hydrological stations records revealed a decreasing trend in annual sediment load along with slightly reduced annual discharge at the same stations this can be interpreted as the result of water diversion primarily for agriculture sediment load at datong further downstream is quite stable and not influenced by slightly reduced discharge furthermore sediment concentration at the three hydrological stations increased which can be attributed to sediment loss in association with intensifying human activity especially in the upper drainage basin such as deforestation and construction of numerous dams mean monthly sediment load of these 30 years pulses about 2 months behind discharge implying dam released sediment transport along the entire river basin during the high water stage

long term elevated post eruption sedimentation at mount pinatubo philippines post eruption sedimentation rates from two basins draining mount pinatubo philippines are compiled and extended through a d 2009 to compare short term predictions with long term yields the pasig potrero and sacobia rivers were covered by 1 km 3 of thick pyroclastic flow deposits during the 1991 eruption of mount pinatubo blanketing 30 of each basin with highly erodible sediments erosion of these deposits led to some of the highest sediment yields ever recorded yields peaked in 1991 and declined exponentially for the first decade following the eruption deposition on the aggrading alluvial fan shows that sedimentation rates from 2001 to 2009 were almost twice as high as an exponential decay model would predict with rates that have leveled off and are no longer declining exponentially patterns of long term sedimentation are similar to those of the north fork toutle river washington state united states at mount st helens with two phases of erosion and sediment export in the first erosion of hillslope tephra and carving of the initial valley network lead to high sediment yields that decline exponentially over 5 10 yr in the second phase continued valley widening and fluvial instability maintain high sediment yields for at least two decades a comparison of post eruption deposition with pre eruption yields indicates that century to millennial scale sedimentation is dominated by sediment associated with discrete eruptive events

soil organic matter as an important contributor to late quaternary sediments of the tropical west african continental margin the contribution of soil organic matter som to continental margins is largely ignored in studies on the carbon budget of marine sediments detailed geochemical investigations of late quaternary sediments 245 0 ka from the niger and congo deep sea fans however reveal that corg ntot ratios and isotopic signatures of bulk organic matter 13corg in both fans are essentially determined by the supply of various types of som from the river catchments thus providing a fundamentally different interpretation of established proxies in marine sciences on the niger fan increased corg ntot and 13corg up to 17 were driven by generally nitrogen poor but 13c enriched terrigenous plant debris and som from c4 c3 vegetation entisol domains grass and tree savannah on young sandy soils supplied during arid climate conditions opposite humid climates supported drainage of c3 c4 vegetation alfisol ultisol domains forest and tree savannah on older developed clay bearing soils that resulted in lower corg ntot and 13corg 20 in the niger fan record sediments from the congo fan contain a thermally stable organic fraction that is absent on the niger fan this distinct organic fraction relates to strongly degraded som of old and highly developed kaolinite rich ferallitic soils oxisols that cover large areas of the congo river basin reduced supply of this nitrogen rich and 12c depleted som during arid climates is compensated by an elevated input of marine om from the high productive congo up welling area this climate driven interplay of marine productivity and fluvial som supply explains the significantly smaller variability and generally lower values of corg ntot and 13corg for the congo fan records this study emphasizes that ignoring the presence of som results in a severe underestimation of the terrigenous organic fraction leading to erroneous paleoenvironmental interpretations at least for continental margin records furthermore burial of som in marine sediments needs more systematic investigation combining marine and continental sciences to assess its global relevance for long term sequestration of atmospheric co2

tidal impacts on the subtidal flow division at the main bifurcation in the yangtze river delta flow division at bifurcations in the yangtze estuary has received ample attention since it may control the pathways of terrestrial sediments over downstream river branches including the 12 5 m deepwater navigation channel while some efforts have been made to interpret flow division at the bifurcations of the yangtze estuary little attention has been paid to the role of tides flow division at estuarine bifurcations is made complicated by tides that propagate from the outlet of the tidal channels into the delta to quantify the tidal influence on the distribution of river discharge and more generally to understand the mechanisms governing the subtidal flow division at the tidally affected bifurcation in the yangtze river delta a two dimensional hydrodynamic model is employed in this model the landward boundary is chosen beyond the tidal limit where the tidal motion has faded out entirely the seaward boundary is chosen such that the river discharge does not influence the water level subtidal discharges are decomposed using the method of factor separation to distinguish between the effects of tides river discharge and river tide interactions on the subtidal flow division results indicate that tides modify the river discharge distribution over distributary channels in the yangtze river delta particularly in the dry season a significant difference in the subtidal flow division during spring tide and neap tide shows that the tidally averaged flow division over the distributaries in the delta greatly depends on tidal amplitude by varying the river discharge at the landward boundary and amplitudes and phases of the principal tidal constituents at the seaward boundary of the established model the sensitivities of the subtidal flow division to the river discharge and tidal amplitude variation were investigated in detail generally the tidal impacts on the subtidal flow division are around 12 to 22 with river discharge varying from 30 000 m3s 1 to 20 000 m3s 1 this effect on the flow distribution can even overwhelm the effects induced by river discharge based on geometry only when the flow discharge is lowest furthermore the fortnightly tidal cycle plays an important role in enhancing the inequality of the subtidal flow division caused by the m2 tidal component solely at the tidal bifurcation in the yangtze river delta during low flow

molecular evidence for lignin degradation in sulfate reducing mangrove sediments amazonia brazil abstract molecular lignin analyses have become a powerful quantitative approach for estimating flux and fate of vascular plant organic matter in coastal and marine environments the use of a specific molecular biomarker requires detailed knowledge of its decomposition rates relative to the associated organic matter and its structural diagenetic changes to gain insight into the poorly known processes of anaerobic lignin diagenesis molecular analyses were performed in the sulfate reducing sediment of a north brazilian mangrove organic matter in samples representing different diagenetic stages i e fresh litter a sediment core and percolating water was characterized by alkaline cuo oxidation for lignin composition element c n and stable carbon isotope analyses on the basis of these results and on a balance model long term in situ decomposition rates of lignin in sulfate reducing sediments were estimated for the first time the half life t 1 2 of lignin derived from mangrove leaf litter mainly rhizophora mangle was 150 yr in the upper 1 5 m of the sediment associated organic carbon from leaf tissue was depleted to 75 within weeks followed by a slow mineralization in the sediment t 1 2 300 yr unlike the known pathways of lignin diagenesis even highly degraded lignin did not show any alterations of the propyl or methoxyl side chains as evident from stable acid to aldehyde ratios and the proportion of methoxylated phenols vanillyl and syringyl phenols aromatic ring cleavage is probably the principal mechanism for lignin decay in the studied environment cinnamyl phenols were highly abundant in mangrove leaves and were rapidly depleted during early diagenesis thus the cinnamyl to vanillyl ratio could be used as a tracer for early diagenesis even under the sulfate reducing conditions syringyl phenols were removed from dissolved organic matter in interstitial water probably by sorption onto the sediment suspended organic matter in a mangrove creek showed a different lignin signature than its source namely sedimentary organic matter or mangrove litter with clear evidence for propyl side chain oxidation this was probably attributable to erosion of aerated thin sediment surface layers during mangrove inundation although particulate and dissolved organic matter in the mangrove creek have a common source their compositional patterns were different because of different pathways of release degradation and transport to the creek

high resolution multiproxy records of sedimentological changes induced by dams in the sept iles area gulf of st lawrence canada abstract a multiproxy approach was performed on two sediment box cores sampled in the nw gulf of st lawrence in order to better understand the impacts of recent climatic or land use changes on the sedimentary regime in the proximal offshore zone multibeam and seismic surveys allowed for the careful selection of coring sites the chronology of the cores was established by 210 pb measurements and validated with coinciding historical weather events recorded in both cores confirming that the sediments are recent last 370 years the lithological variations in the cores were quantified using 1 stratigraphic markers and grain size measurements 2 high resolution x ray micro fluorescence xrf and 3 physical and magnetic tracers the grain size measurements allowed the identification of a major flood around ad 1844 4 years whereas a drastic decrease in variations and in the median grain size d50 occurred around ad 1900 highlighting the offshore impact of the sm1 dam construction on the sainte marguerite river in the early 1900s sedimentological variations have been investigated by wavelet analysis using xrf data and the sharp disappearance of high frequencies

temporal and spatial variations in magnetic properties of suspended particular matter in the yangtze river drainage and their implications abstract as the largest river of china the yangtze river transports large amounts of sediments to the adjacent oceans provenance of these ancient marine sediments can only be deciphered when the source to sink process of modern sediments in the yangtze river is fully understood many methods have been used to study the provenance of river sediment and an environmental magnetic method is applied in this study because of its fast nondestructive advantages magnetic properties of suspended particulate matter spm along the yangtze river were measured to provide a holistic understanding about magnetic properties of sediments in this river and its controlling factors the results indicate that the dominant magnetic mineral in spm is magnetite with a small contribution of hematite and goethite significant spatial variation was observed in most of the magnetic parameters which primarily reflects the distribution of major geologic units along the drainage area of the river anthropogenic influences are also recorded in the magnetic parameters the three gorges dam results in a dramatic decrease of magnetic minerals in the downstream reaches since its construction in 2003 in addition small variations in magnetic properties of spm are found along water depth together with a clear seasonal shift at datong station this seasonal variation of magnetic properties of spm is driven by variability in both hydrology and source contributions this complicates the use of magnetic parameters for provenance studies magnetic properties of sediments in rivers are capable of tracing provenance areas but caution must be taken into account

predicting the type location and magnitude of geomorphic responses to dam removal role of hydrologic and geomorphic constraints abstract using a dam removal on the ashuelot river in southern new hampshire we test how a sudden spatially non uniform increase in river slope alters sediment transport dynamics and riparian sediment connectivity site conditions were characterized by detailed pre and post removal field surveys and high resolution aerial lidar data and locations of erosion and deposition were predicted through one dimensional hydrodynamic modeling the homestead dam was a 200 year old 4 m high 50 m wide crib dam that created a 9 5 km long relatively narrow reservoir following removal an exhumed resistant bed feature of glaciofluvial boulders located 400 m upstream and 2 5 m lower than the crest of the dam imposed a new boundary condition in the drained reservoir acting as a grade control that maintained a backwater effect upstream during the 15 months following removal non uniform erosion in the former reservoir totaled 60 000 m3 equivalent to 9 3 cm when averaged across the reservoir net deposition of 10 700 m3 was measured downstream of the dam indicating most sediment from the reservoir was carried more than 8 km downstream beyond the study area the most pronounced bed erosion occurred where modeled sediment transport increased in the downstream direction and deposition occurred both within and downstream of the former reservoir where modeled sediment transport decreased in the downstream direction we thus demonstrate that spatial gradients in sediment transport can be used to predict locations of erosion and deposition on the stream bed we further observed that bed incision was not a necessary condition for bank erosion in the former reservoir in this characteristically narrow and shallow reservoir lacking abundant dam induced sedimentation the variable resistance of the bed and banks acted as geomorphic constraints overall the response deviated from the common conceptual model of knickpoint erosion and channel widening due to dam removal with thousands of dams likely to be considered for removal or repair in the coming decades this study helps to advance predictions of the geomorphic response to dam removal and contributes to a broader understanding of the variability in both style and timing of fluvial responses to disturbances

large scale dam removal on the elwha river washington usa source to sink sediment budget and synthesis abstract understanding landscape responses to sediment supply changes constitutes a fundamental part of many problems in geomorphology but opportunities to study such processes at field scales are rare the phased removal of two large dams on the elwha river washington exposed 21 3 million m3 or 30 million tonnes t of sediment that had been deposited in the two former reservoirs allowing a comprehensive investigation of watershed and coastal responses to a substantial increase in sediment supply here we provide a source to sink sediment budget of this sediment release during the first two years of the project september 2011 september 2013 and synthesize the geomorphic changes that occurred to downstream fluvial and coastal landforms owing to the phased removal of each dam the release of sediment to the river was a function of the amount of dam structure removed the progradation of reservoir delta sediments exposure of more cohesive lakebed sediment and the hydrologic conditions of the river the greatest downstream geomorphic effects were observed after water bodies of both reservoirs were fully drained and fine silt and clay and coarse sand and gravel sediments were spilling past the former dam sites after both dams were spilling fine and coarse sediments river suspended sediment concentrations were commonly several thousand mg l with 50 sand during moderate and high river flow at the same time a sand and gravel sediment wave dispersed down the river channel filling channel pools and floodplain channels aggrading much of the river channel by 1 m reducing river channel sediment grain sizes by 16 fold and depositing 2 2 million m3 of sand and gravel on the seafloor offshore of the river mouth the total sediment budget during the first two years revealed that the vast majority 90 of the sediment released from the former reservoirs to the river passed through the fluvial system and was discharged to the coastal waters where slightly less than half of the sediment was deposited in the river mouth delta although most of the measured fluvial and coastal deposition was sand sized and coarser 0 063 mm significant mud deposition was observed in and around the mainstem river channel and on the seafloor woody debris ranging from millimeter size particles to old growth trees and stumps was also introduced to fluvial and coastal landforms during the dam removals at the end of our two year study elwha dam was completely removed glines canyon dam had been 75 removed full removal was completed 2014 and 65 of the combined reservoir sediment masses including 8 mt of fine grained and 12 mt of coarse grained sediment remained within the former reservoirs reservoir sediment will continue to be released to the elwha river following our two year study owing to a 16 m base level drop during the final removal of glines canyon dam and to erosion from floods with larger magnitudes than occurred during our study comparisons with a geomorphic synthesis of small dam removals suggest that the rate of sediment erosion as a percent of storage was greater in the elwha river during the first two years of the project than in the other systems comparisons with other pacific northwest dam removals suggest that these steep high energy rivers have enough stream power to export volumes of sediment deposited over several decades in only months to a few years these results should assist with predicting and characterizing landscape responses to future dam removals and other perturbations to fluvial and coastal sediment budgets

sources and distribution of organic matter in thirty five tropical estuaries along the west coast of india a preliminary assessment abstract studies characterizing the sources of organic matter om to the west coast of india wci and its continental shelf are limited this study examined sedimentary om in 35 estuaries along the wci using molecular biomarkers lignin phenol elemental ratio c n and stable carbon isotope 13c values multivariate statistical techniques such as cluster analysis identified similar sedimentary chemical properties among the estuaries and their distribution patterns highlight the strong control of geographical provenance on sedimentary om composition from south to north along the wci results of an end member mixing model reveal that terrigenous sources c3 plants c4 plants and soil contribute 80 of estuarine om with the remaining 20 derived from marine sources marine plankton and estuarine macrophytes in the estuaries of large rivers such as the narmada and sabarmati rivers c4 plants and soil om were found to be the dominant contributors of om which is likely the result of an abundance of c4 vegetation and agriculture in their catchment areas high oc organic carbon content of sediments 0 5 5 from the wci estuaries indicates that large amounts of om are present in the sediments the sources of om plant and soil shift substantially throughout the study area corresponding to changes in land use patterns along the western ghats sediments with low nitrogen contents c n 15 20 and degraded lignin ad al v 0 4 0 6 and dhba v 0 16 0 34 were observed in all estuaries indicating humification and or degradation of om originating from terrestrial plants bio degradation and soil de mineralization the collective results of this study illustrate the benefits of using biomarkers lignin phenols along with c n and 13c values for evaluating land use changes and the impacts of land use changes on aquatic ecosystems

rates and processes of channel response to dam removal with a sand filled impoundment 1 dam removal projects are playing an increasingly important role in stream restoration and offer unparalleled opportunities to study sediment dynamics following disturbance we used the removal of the 4 m high merrimack village dam mvd on the souhegan river in southern new hampshire to measure processes and rates of channel evolution in a sand filled impoundment from 2007 to 2010 we repeatedly surveyed 11 cross sections and the longitudinal profile and collected sediment samples to measure changes in channel morphology and bed texture the dam removal in august 2008 resulted in a nearly instantaneous base level drop of 3 9 m and caused a two phased channel response the initial process driven phase 2 months was characterized by rapid incision and removal of the impounded sand up to 1013 t d 1 followed by channel widening once incised to base level the rate of sediment removal slowed 30 7 t d 1 and adjustments became event driven and the former impoundment segmented into a nonalluvial section and an alluvial section with erosion and deposition influenced by vegetation on the channel banks two years after the dam removal and two high magnitude floods the river has excavated 79 of the original sediment continued response will be substantially influenced by the establishment of bank vegetation within the former impoundment and the magnitude and frequency of high discharge events initial channel development and sediment erosion occurs rapidly weeks to months in sand filled impoundments but excavation of the remaining sediment occurs more slowly depending on vegetation feedbacks and flood events

towards a sediment and organic carbon budget for hudson bay abstract a preliminary sediment and organic carbon budget is constructed for the hudson bay marine system based on published literature and new data collected from nine rivers and 13 sediment boxcores the budget considers the main inputs of terrestrial and marine components of sediment and organic carbon and the main sinks sediment burial and losses oxidation export to hudson strait sedimentation rates 0 032 0 23 g cm 2 yr 1 were estimated from 210 pb profiles and a sediment advection diffusion model in our cores and in two cores collected previously by lockhart et al lockhart w l et al 1998 fluxes of mercury to lake sediments in central and northern canada inferred from dated sediment cores biogeochemistry 40 163 173 sedimentation rates implied by the 210 pb profiles were verified against profiles of 137 cs and for some of the cores contaminant pb the sediment sink in hudson bay was estimated at 138 64 10 6 t a 1 by applying the average sedimentation rate to the area of active sedimentation in the bay 15 of the seafloor calculated according to a regional sedimentation map developed from seismic data josenhans h w et al 1988 preliminary seismostratigraphic and geomorphic interpretations of the quaternary sediments of hudson bay natural resources canada the known sediment sources to hudson bay include river input 11 6 6 10 6 t a 1 subaerial coastal erosion 8 4 10 6 t a 1 marine primary production 24 2 17 10 6 t a 1 and atmospheric deposition 0 5 10 6 t a 1 based on the available data the modern sediment input 44 3 18 10 6 t a 1 represents only about one third of the apparent sediment sink in hudson bay resuspension and lateral transport of shallow water deposits primarily glacigenic and winnowing from topographic highs likely consequences of the exceptional continuous relative sea level rsl fall in hudson bay provides a plausible source for the 116 10 6 t a 1 imbalance using organic carbon and 13 c values in the cores we estimate the burial of particulate organic carbon poc in sediments at 1 3 0 6 10 6 t c a 1 of which 80 is marine the importance of reworked glaciomarine carbon to the burial flux is difficult to estimate because modern autochthonous primary production provides a large source of poc to the system 16 1 7 10 6 t c a 1 and its degradation is not well constrained the 0 58 10 6 t c a 1 terrestrial carbon estimated to be transported as part of the redistributed sediment load accounts for almost one half the total terrigenous poc inputs to the bay if sediment and oc supply and burial in the hudson bay system are presently responding to the history of isostatic rebound as proposed here the task of predicting and measuring the additional consequences of river diversions and climate change e g sea ice permafrost runoff is rendered considerably more difficult

natural streams and the legacy of water powered mills gravel bedded streams are thought to have a characteristic meandering form bordered by a self formed fine grained floodplain this ideal guides a multibillion dollar stream restoration industry we have mapped and dated many of the deposits along mid atlantic streams that formed the basis for this widely accepted model these data as well as historical maps and records show instead that before european settlement the streams were small anabranching channels within extensive vegetated wetlands that accumulated little sediment but stored substantial organic carbon subsequently 1 to 5 meters of slackwater sedimentation behind tens of thousands of 17th to 19th century milldams buried the presettlement wetlands with fine sediment these findings show that most floodplains along mid atlantic streams are actually fill terraces and historically incised channels are not natural archetypes for meandering streams

importance of hydrology on channel evolution following dam removal case study and conceptual model abstracta slow draining reservoir on the u s east coast was monitored to identify the processes governing channel evolution upstream of a dam removal channel evolution was documented through cross section surveys sediment size analysis discharge measurements and visual assessments of vegetative growth the reservoir drained slowly allowing for an analysis of channel evolution and identification of the morphometric parameters defining the path and time required for a channel to reach dynamic equilibrium channel evolution was a multidirectional process and evolving channel reaches actively migrated laterally while alternating between aggradation and degradation channel formation was dominated primarily by the hydrologic regime at the time of dam removal and secondarily by the ability of vegetation to establish and stabilize the channel form the importance of seasonal site hydrology over the minimum time required for channel evolution and the process through which the channel evolves indicates the

sediment records of the influence of river damming on the dynamics of the nelson and churchill rivers western hudson bay canada during the last centuries two gravity cores 778 and 780 sampled at the nelson river mouth and one 776 at the churchill river mouth in western hudson bay canada were analyzed in order to identify the impact of dam construction on hydrology and sedimentary regime of both rivers another core 772 was sampled offshore and used as a reference core without a direct river influence core chronology was established using 14c and 210pb measurements cores 778 and 780 show greater variability than the others and the physical chemical magnetic and sedimentological properties measured on these cores reveal the presence of several hyperpycnites indicating the occurrence of hyperpycnal flows associated with floods of the nelson river these hyperpycnal flows were probably caused by ice jam formation which can increase both the flow and the sediment concentration following the breaching of such natural dams however these hyperpycnites are only observed in the lower parts of cores 778 and 780 it was not possible to establish a pr

rapid reservoir erosion hyperconcentrated flow and downstream deposition triggered by breaching of 38 m tall condit dam white salmon river washington condit dam on the white salmon river washington a 38 m high dam impounding a large volume 1 8 million m3 of fine grained sediment 60 sand 35 silt and clay and 5 gravel was rapidly breached in october 2011 this unique dam decommissioning produced dramatic upstream and downstream geomorphic responses in the hours and weeks following breaching blasting a 5 m wide hole into the base of the dam resulted in rapid reservoir drawdown abruptly releasing 1 6 million m3 of reservoir water exposing reservoir sediment to erosion and triggering mass failures of the thickly accumulated reservoir sediment within 90 min of breaching the reservoir s water and 10 of its sediment had evacuated at a gauging station 2 3 km downstream flow increased briefly by 400 m3 s 1 during passage of the initial pulse of released reservoir water followed by a highly concentrated flow phase up to 32 sediment by volume as landslide generated slurries from the reservoir moved downstream this hyperconcentrated flow analogous to those following volcanic eruptions or large landslides draped the downstream river with predominantly fine sand during the ensuing weeks suspended sediment concentration declined and sand and gravel bed load derived from continued reservoir erosion aggraded the channel by 1 m at the gauging station after which the river incised back to near its initial elevation at this site within 15 weeks after breaching over 1 million m3 of suspended load is estimated to have passed the gauging station consistent with estimates that 60 of the reservoir s sediment had eroded this dam removal highlights the influence of interactions among reservoir erosion processes sediment composition and style of decommissioning on rate of reservoir erosion and consequent downstream behavior of released sediment

bedload transport over run of river dams delaware u s a abstract we document the detailed morphology and bed sediment size distribution of a stream channel upstream and downstream of a 200 year old run of river dam on the red clay creek a fifth order stream in the piedmont of northern delaware and combine these data with hec ras modeling and bedload transport computations we hypothesize that coarse bed material can be carried through run of river impoundments before they completely fill with sediment and we explore mechanisms to facilitate this transport only 25 of the accommodation space in our study site is filled with sediment and maximum water depths are approximately equal to the dam height all grain size fractions present upstream of the impoundment are also present throughout the impoundment a characteristic coarse grained sloping ramp leads from the floor of the impoundment to the crest of the dam a 2 3 m deep plunge pool has been excavated below the dam followed immediately downstream by a mid channel bar composed of coarse bed material similar in size distribution to the bed material of the impoundment the mid channel bar stores 1472 m3 of sediment exceeding the volume excavated from the plunge pool by a factor of 2 8 these field observations are typical of five other sites nearby and suggest that all bed material grain size fractions supplied from upstream can be transported through the impoundment up the sloping ramp and over the top of the dam sediment transport computations suggest that all grain sizes are in transport upstream and within the impoundment at all discharges with return periods from 1 to 50 years our computations suggest that transport of coarse bed material through the impoundment is facilitated by its smooth sandy bed model results suggest that the impoundment is currently aggrading at 0 26 m year but bed elevations may be recovering after recent scour from a series of large floods during water year 2011 2012 we propose that impoundments upstream of these run of river dams behave as long pools that adjust their bed elevation and texture to transport the load supplied by the watershed rather than as impounded reservoirs with little bed material transport capacity scour may only occur during episodic high flows followed by aggradation during periods of low flow

isotopic constraints of sedimentary inputs and organic carbon burial rates in the saguenay fjord quebec abstract the saguenay fjord quebec has exceptionally high sedimentation rates resulting in up to 100 m thick holocene sequences filling some of its basins partly due the frequent occurrence of rapidly deposited layers landslides seismic events floods in the present study special attention is paid on the incidence of such events on organic carbon oc fluxes sources and burial rates using physical sedimentological geochemical and isotopic measurements on 4 sediment cores raised from the inner basin of the fjord and the adjacent baie des ha ha in these cores rapidly deposited layers rdl include notably a turbidite linked to a major earthquake in 1663 a landslide layer dating from 1971 saint jean vianney landslide and a flood layer from 1996 compared with background sediments rdl are characterized by low oc contents 3 contents 2 and low 13 c values in oc 13 c oc values 26 8 0 2 and c n ratios 17 7 1 7 in the pre industrial pre 1663 fjord sediments indicate that most sedimentary organic matter om was then of terrigenous origin paper mill activity during the 20th century has resulted in om fluxes growing almost exponentially until the mid 1960s when major changes in industrial practices and the implementation of environmental regulations during the 1970s and later on reduced the amount of industrial om discharged into the fjord this industrial om shows an isotopic signature of 26 34 0 02 and c n ratios 20 not unlike those of the regional terrestrial om oc burial rates since the 1663 earthquake varied between 20 and 290 gc m 2 yr 1 rdl seem to favour oc preservation in the fjord by reducing bioturbation and both oxic and anoxic oc degradation and by contributing themselves to higher carbon burial rates therefore transitional environments such as the saguenay fjord could represent significant long term carbon sinks

sediment deposition and erosion during the extreme flood events in the middle and lower reaches of the yangtze river abstract floods often are accompanied by intensified soil erosion and thus high sediment supply from the catchment into the main channel of the river this paper examined the sediment processes especially deposition and erosion during the two extreme flood years in 1954 and 1998 in the middle and low reaches of the yangtze river the total amount of sediment supplied to the middle and lower reaches from yichang hankou and hankou datong was 1095 mt in 1954 and 855 9 mt in 1998 or 176 and 137 of the averaged 622 mt a from 1950 to 2006 a high deposition occurred in the floodplains lakes and channels along the section yichang hankou both in 1954 and 1998 the total deposition reached 635 mt and 499 mt in 1954 and 1998 or 138 and 124 of the sediment load measured at the datong station respectively however different processes in the downstream section hankou datong during the two flood events were found severe erosion 140 mt happened in 1954 but only a slight erosion occurred 22 mt in 1998 thus the floodplains and channels in the middle and lower reaches of the yangtze river play an important role in regulating sediment discharge during extreme flood events the heavy deposition in the middle reaches effectively reduced the amount of sediment discharged into the river mouth and thus acted as a major depocenter in the extreme flood year the results also suggested that the yichang hankou tended to shift from a depositional section to an erosional section whereas the hankou datong changed from an erosion dominated section to a deposition dominated section even before the three gorges reservoir infilling in 2003 it is anticipated that this tendency would be accelerated and the historical role of sediment regulation by the two reaches could eventually be changed due to the reduced sediment supply from the upper yangtze

sedimentary laminae in muddy inner continental shelf sediments of the east china sea formation and implications for geochronology abstract the sedimentary rhythm is well developed in the environment which is controlled by strong seasonal climate changing condition this rhythm is important for sediment core dating purpose in this study we examine muddy sediments on the inner continental shelf of the east china sea that are influenced under seasonal change of the east asian monsoon we use ensemble empirical mode decomposition eemd method to process sediment grain size and x radiograph negatives grayscale value data in three sediment cores from this area and use the results to analyze the patterns of sedimentary variability and the causes of cyclic variability of the sedimentary process the variability in the grain size and grayscale values of the core sediments has three components the high frequency variability low frequency variability and a secular trend among these components the high frequency component reflects variability on annual time scale can be well recognized we suggest that the annual variability is derived from seasonal variation in the sediment flux from the yangtze river to the sea as well as the east asian monsoon s impact on the sedimentary dynamics of the east china sea s inner continental shelf however the other variability is hard to identify which cycles there are this variability may reflect decadal winter monsoon oscillation and human activity of dam construction in the yangtze river each annual variability presents a varve in the sediment sequence which can be used to determine the sediment deposition rate and accurately date the core sediment we found that the average deposition rates of the three cores from north to south on the inner shelf were 3 1 cm yr 1 0 cm yr 0 9 cm yr indicating that the yangtze derived sediment decreased with the increasing distance from the yangtze estuary to the shelf the deposition rate of each core varies over time and the maximum deposition rate can be 3 5 times greater than the minimum rate the sediment ages obtained from varve chronology and radiometric dating are fairly consistent on a centennial scale differing only by 2 5 years thus varve counting is a useful supplementary approach to radiometric age dating for constructing chronologies for core sediment in shelf seas influenced by monsoons

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

earthquake and flood induced turbidites in the saguenay fjord quebec a holocene paleoseismicity record abstract a 38 m long piston core from the deep basin of the saguenay fjord quebec recorded rapidly deposited layers rdl interpreted to represent major floods and earthquakes over the past 7200 years high resolution physical magnetic and sedimentological analyses revealed at least 14 rdl generally with a sandy base and a light gray color interbedded with hemipelagic sediments digital x radiography and grain size analyses at

characterizing the depositional settings for sedimentary organic matter distributions in the lower yangtze river east china sea shelf system grain size distributions total organic carbon toc and total nitrogen tn concentrations and toc tn ratios c n were analysed for surface sediments from the lower yangtze river east china sea ecs shelf system hierarchical cluster analysis of grain size parameters mode mean sorting skewness and kurtosis has been employed to characterize grain size compositions the results suggest there are five grain size compositional types type i v that fingerprint distinct depositional conditions in areas with high sedimentation rates hydrological sorting preferentially enriches the fraction coarser than 6 4o 12 m in shallow seafloor sediments water depth 30 m and thus forms grain size compositional type i shallow and type ii deep in the open shelf where modern sediment supply is very limited grain size types iii v are identified according to different winnowing intensity overall toc contents significantly correlate with mud proportions suggesting muddy sediments are the primary control on om accumulation however de association of terrestrial om from fine sediments in the estuary and the occurrence of presumably relict om in the open shelf exert additional controls on om dispersal and carbon cycling in the ecs by considering geography oceanography sediment source and the relation between sedimentation conditions and sedimentary om distributions we define six depositional settings the lower river the estuary the coast the offshore upwelling area the erosional area and the open shelf these settings describe the sediment dispersal and associated organic matter cycling in the lower yangtze river ecs shelf system

metals in suspended sediments from the changjiang yangtze river and huanghe yellow river to the sea and their comparison thirty five samples of suspended sediments were collected at datong station and lijin station the basin wide control stations of the changjiang yangtze river and the huanghe yellow river during flood and dry seasons in 2000 and 2001 concentrations of 15 elements fe mg ca al na k ti mn ba sr pb cu zn v and ni in these samples were measured by icp aes the results indicated that fe al ti mn ba cu zn v and ni concentrations in the changjiang sediments in may flood season were quite close to those in november dry season whereas mg ca na k sr concentrations were slightly higher and pb was relatively lower in the dry season ti ba sr and zn concentrations in huanghe sediments varied little in august flood season and december dry season while mg ca al na and k concentrations were higher by approximately 30 and fe mn pb cu zn v and ni concentrations were lower in flood season concentrations of most metals except ca na and sr were much higher in changjiang sediments than those in the huanghe such differences of metal concentrations in sediments from these two rivers could be ascribed to their different sediment sources and weathering processes within their corresponding river basin particularly since the 1980s pb and zn concentrations in changjiang sediments have increased significantly due to the releases of waste contaminants from human activities while the variations for these two elements in the huanghe samples were very little due to the elevated river bed in the lower reaches