factors controlling riffle scale hyporheic exchange flows and their seasonal changes in a gaining stream a three dimensional groundwater flow model 1 subsurface flow within a single riffle of a low gradient gravel bed stream was modeled in three dimensions using modflow a finite difference groundwater flow model model simulations showed that exchange flows can only occur in this low gradient gaining stream because of a zone of alluvial sediment around the stream that has much higher permeability than the surrounding catchment k 10 4 m s 1 compared with k 10 6 to 10 8 m s 1 the key factors controlling exchange flow within the alluvial zone were identified as the hydraulic conductivity of the alluvium the hydraulic gradient between upstream and downstream ends of the riffle and the flux of groundwater entering the alluvium from the sides and beneath in the study riffle each of these factors changes with season causing a reversal of flow paths in the alluvium and a reduction in exchange flows from about 0 2 0 5 m 3 d per meter stream length in summer to about 0 008 0 04 m 3 d 1 per meter stream length during fall to spring the model also revealed that exchange flows are up to twice as strong but more variable at the sides of the stream than near the center and that vertical flow paths beneath the channel are more persistent under the range of conditions modeled than lateral flow paths into the banks

using the value of the crosscorrelation coefficient to locate microseismic events a procedure to locate seismic events uses the value of the crosscorrelation coefficient between waveforms of different events first an empirical relation between spatial event separation and maximum crosscorrelation coefficient is established for a subset of a priori located reference events then this relation is used to determine the hypocenters of an increasing number of events by a grid search strategy measured arrival time differences between s and p waves also constrain the location although the reference events are located by a standard method using the arrival time measurements at three or more receivers the correlation based location requires only one receiver the method has been applied to microseismic data recorded at a single borehole sensor during the 2004 05 injection experiment at the continental deep drilling site ktb in germany with the approach significantly more weak seismic events were located compared to the number of events recorded by a near surface receiver array and by inversion of arrival times the proposed location method is particularly well suited to locate small magnitude earthquakes within dense event clouds when too few arrival time observations for part of the events are available and standard location methods fail these conditions are frequently met in the case of microseismic monitoring of geothermal or enhanced oil recovery experiments

relative sea level rise and tidal development in the fundy tidal system previous studies of sea level and tidal amplification in the bay of fundy suggested a linear increase of tidal amplitude as relative sea level rose new data presented here are used in a numerical tidal model in an effort to reproduce paleotidal regimes over the last 7000 years five new sea level curves covering the last 4000 years and some previously published data extending the record back to 7000 years before present bp are used as the data base these data when used together with the tidal model indicate that tidal amplitudes increased much more rapidly between 7000 and 4000 years ago than in the period 4000 years ago to present it is also shown that changes in depth within the bay of fundy produce little effect on the tidal amplitudes whereas such variations in water depth on georges bank account for almost all the change this calculation of tidal amplitude changes allows calibration of sea level curves to be made for the bay of fundy using higher high water hhw indicators

micropaleontological documentation for early holocene fall of relative sea level on the atlantic coast of nova scotia the presence of a marsh sequence between two shallow water marine deposits in an offshore core from lunenburg nova scotia indicates fall of relative sea level followed by rise of relative sea level the marsh sequence is now 27 m below datum level with a c 14 date of 7 070 yr b p this sequence suggests that the glacial forebulge migrated through this area 7 000 yr ago that 27 m of submergence has occurred since then and that prior to 7 000 yr b p the site was characterized by low amplitude emergence this is at present the only sequence where the entire regression transgression record is preserved along this coast the accuracy required to demonstrate this can be obtained only by using established marsh foraminiferal zonations

distribution of bedrock and alluvial channels in forested mountain drainage basins mountain river networks often consist of both bedrock and alluvial channels1 5 the spatial distribution of which controls several fundamental geomorphological and ecological processes6 7 the nature of river channels can influence the rates of river incision and landscape evolution1 2 as well as the stream habitat characteristics affecting species abundance and aquatic ecosystem structure8 11 studies of the factors controlling the distribution of bedrock and alluvial channels have hitherto been limited to anthropogenic badlands12 here we investigate the distribution of channel types in forested mountain drainage basins and show that the occurrence of bedrock and alluvial channels can be described by a threshold model relating local sediment transport capacity to sediment supply in addition we find that valley spanning log jams create alluvial channels hospitable to aquatic life in what would otherwise be bedrock reaches the formation of such jams depends critically on the stabilizing presence of logs derived from the largest trees in the riverside forests suggesting that management strategies that allow harvesting of such trees can have a devastating influence on alluvial habitats in mountain drainage basins

tidal and sedimentary response to the late quaternary closure and opening of cook strait new zealand results from numerical modeling evidence from numerical modeling of the m2 tide supplemented by geological data reveals marked changes in the tidal and sedimentary regimes of cook strait over the last postglacial rise in sea level approximately 18 000 years b p when sea level was approximately 113 m the strait was reduced to a narrow bay by the emergence of a land bridge connecting the north and south islands of new zealand high sediment supply and low tidally induced bottom stress encouraged widespread deposition of fine sediment except at the bay mouth the narrows where localized high stress resulted in the transport of sediment to the deep ocean via cook strait canyons at 17 000 years b p approximately 88 m the bay reached maximum size and was near resonance with the oceanic tide resulting in high tidal amplitudes bottom stress and sediment movement at the narrows and bay head the land bridge was breached and cook strait was formed about 15 000 years b p approximately 75 m both the narrows and breach were subject to high bottom stress whereas the intervening area was a zone of convergent low stress and fine sediment deposition by 11 000 years b p approximately 40 m cook strait was well established and had a tidal response similar to the modern strait the rising sea levels inundated remnants of the land bridge to form the broad continental shelf approaches to cook strait today overall tidal stress is reduced and mud deposition prevails except on the inner shelf where periodic forcing by wind induced currents maintains a sandy substrate and in the narrows where a tidal phase difference of approximately 120 maintains a zone of high sediment movement

sea level rise and tidal power plants in the gulf of maine 1 the response of the bay of fundy and gulf of maine to large scale tidal power plants and future sea level rise is investigated using an established numerical tidal model free stream tidal turbines were simulated within the bay of fundy by implementing an additional bed friction term kt the present day maximum tidal power output was determined to be 7 1 gw and required kt 0 03 extraction at this level would lead to large changes in the tidal amplitudes across the gulf of maine with future slr implemented the energy available for extraction increases with 0 5 1 gw per m slr slr simulations without tidal power extraction revealed that the response of the semidiurnal tides to slr is highly dependent on how changes in sea level are implemented in the model when extensive flood defenses are assumed at the present day coast line the response to slr is far larger than when land is allowed to permanently flood for example within the bay of fundy itself the m2 amplitude increases with nearly 0 12 m per m slr without flooding but it changes with only 0 03 m per m slr with flooding we suggest that this is due to the flooding of land cells changing the resonant properties of the basin

comparison of two and three dimensional model simulation of the effect of a tidal barrier on the gulf of maine tides abstract two dimensional and three dimensional tide models were used to simulate the m2 tide in the gulf of maine model estimates of changes to the tide caused by a tidal barrier in the upper bay of fundy were made and compared tidal amplitudes in the presence of a barrier increased 30 50 cm for both models corroborating the results of previous studies by greenberg and by duff the three dimensional model uniformly produced postbarrier elevations of 3 5 cm less than the two dimensional model in the gulf of maine a comparison of model amplitudes and velocities with data for the existing m2 tide is provided for both models total frictional dissipation is also calculated for each model and compared finally the postbarrier amplitudes as predicted by each model are compared root mean square errors of m2 tidal amplitude and phase at 45 locations in the gulf of maine were 7 9 cm and 6 for the two dimensional model and 5 7 cm and 7 for the three dimensional model both models predicted essentially ident

catastrophic tidal expansion in the bay of fundy canada tidal models for the bay of fundy canada site of the highest recorded modern tide show that tidal amplification began in the early holocene and by ca 5000 bp the range was almost 80 of the present range empirical data consisting of 146 sea level index points and other observations appear to contradict model results aggregated relative sea level data for chignecto bay and minas basin show that rapid tidal expansion began ca 3400 bp however if we separate these two geographically separate data sets evidence for this rapid late holocene tidal expansion is confined to minas basin we explain this singularity by positing a barrier at the mouth of minas basin at the minas passage that delayed tidal expansion with the rapid breakdown of this barrier and near instantaneous tidal expansion water temperature dropped tidal currents and turbidity increased and the form of the inner estuary was changed from lagoonal mesotidal to macrotidal we argue that the catastrophic breakdown of the barrier is

onset of recent rapid sea level rise in the western atlantic ocean a high resolution record of sea level change spanning the past 1000 years is derived from foraminiferal and chronological analyses of a 2 m thick salt marsh peat sequence at chezzetcook nova scotia canada former mean tide level positions are reconstructed with a precision of 0 055 m using a transfer function derived from distributions of modern salt marsh foraminifera our age model for the core section older than 300 years is based on 19 ams 14c ages and takes into account the individual probability distributions of calibrated radiocarbon ages the past 300 years is dated by pollen and the isotopes 206pb 207pb 210pb 137cs and 241am between ad 1000 and ad 1800 relative sea level rose at a mean rate of 17 cm per century apparent pre industrial rises of sea level dated at ad 1500 1550 and ad 1700 1800 cannot be clearly distinguished when radiocarbon age errors are taken into account furthermore they may be an artefact of fluctuations in atmospheric 14c production in the 19th century sea level rose at a mean rate of 1 6 mm yr between ad 1900 and ad 1920 sea level rise accelerated to the modern mean rate of 3 2 mm yr this acceleration corresponds in time with global temperature rise and may therefore be associated with recent global warming 2005 elsevier ltd all rights reserved

particle dynamics the continuum of bedrock to alluvial river segments abstract particle dynamics refers to production erosion transport and storage of particulate material including mineral sediment and organic matter particle dynamics differ significantly between the end members of bedrock and alluvial river segments and between alluvial river segments with different grain size distributions bedrock segments are supply limited and resistant to change with relatively slow linear adjustments and predominantly erosion and transport particle dynamics in alluvial segments in contrast are transport limited and dominated by storage of mineral sediment and production of organic matter alluvial segments are resilient to change with relatively rapid multidirectional adjustments and stronger internal influences because of feedbacks between particles and biota bedrock segments are the governors of erosion within a river network whereas alluvial segments are the biogeochemical reactors fundamental research questions for both types of river segments center on particle dynamics which limit network scale incision in response to base level fall bedrock segments and habitat biogeochemical reactions and biomass production alluvial segments these characterizations illuminate how the spatial arrangement of bedrock and alluvial segments within a river network influence network scale resistance and resilience to external changes in relative base level climate and human activities

hyporheic exchange due to channel spanning logs 1 the flow of river water around large woody debris lwd creates pressure gradients along the riverbed that drive a large zone of river groundwater mixing or hyporheic exchange flume experiments and numerical simulations show that river water downwells into the riverbed upstream of a channel spanning log and upwells downstream exchange rates are greatest near the log and decay exponentially with distance upstream and downstream we developed equations for bed pressure profiles and hyporheic exchange rates in the vicinity of a channel spanning log that can be used to evaluate the impact of lwd removal or reintroduction on hyporheic mixing the magnitude of pressure disturbance along the bed and thus hyporheic exchange increases with the fraction of channel depth blocked by the log and channel froude number exchange rates are relatively insensitive to relative depth of the log gap ratio at natural densities lwd in lowland streams drives reach averaged hyporheic exchange rates similar to a ripple covered bed however the length scales and residence times of hyporheic exchange due to lwd are greater by removing lwd from streams humans have altered patterns and rates of hyporheic exchange which influence habitat distribution and quality for invertebrates and fish

morphology and seismic stratigraphy of the inner continental shelf off nova scotia canada evidence for a 65 m lowstand between 11 650 and 11 250 c14 yr b p abstract nova scotia s position near the margin of large pleistocene ice sheets makes the scotian shelf region critical for evaluation of glaciation models and sea level change the sea floor of the inner scotian shelf was mapped using multibeam bathymetry a combination of conventional seismic and sonar techniques and sampling multibeam bathymetry provides an areal image of the sea floor combining this unique image with sub bottom seismic imaging the relationships between sea floor topography and the underlying strata were explored the inner continental shelf of nova scotia can be subdivided into five major terrain zones these are the 1 truncation zone 2 morainal zone 3 outcrop zone 4 basin zone and 5 scotian shelf end moraine complex the scotian shelf end moraine complex and basin zone are glacial depositional zones at the seaward edge of the inner shelf landward of these zones is a region of high relief bedrock with ridges and valleys largely devoid of surficial sediments extending from 80 to 120 m water depth outcrop zone this zone is interpreted as a relict bedrock surface preserved under frozen bed glacier conditions to the east of the outcrop zone in similar water depths are unmodified till ridges overlying bedrock morainal zone the truncation zone is a region of the inner shelf from 90 m to the present shoreline characterized by muted acoustic topography and planar erosional surfaces truncating bedrock and surficial sediments the truncation zone is subdivided into the valley subzone the transition subzone the platform subzone and the estuarine subzone the valley subzone is typified by sediment infilled valleys occurring in 75 to 90 m water depths these valleys contain seismic facies with a ponded style of deposition planed off at the sea floor or by erosional unconformities near the sea floor the transition subzone is marked by a relatively steep ramp and terraces the ramp at the type section extends from 75 to 65 m water depth the surface of the ramp can be either an erosional unconformity or a depositional surface formed by clinoform beds the 65 m former shoreline is interpreted as the top of the transition subzone ramp surface at one ramp locality clinoform beds form part of a progradational sequence called the sambro delta a mussel valve fragment mytilus edulis was obtained from a core in the foresets and radiocarbon dated an age of 11 650 110 yr b p was obtained adjusted for isotopic fractionation above 65 m the sea floor forms a low relief gently sloping erosional surface platform subzone estuarine deposits have been found above 50 m the new sea level curve constructed with the dated 65 m shoreline and recently published data is at variance with calculated rsl curves based on geophysical models primarily in the amplitudes and rates of rsl change reasons for the discrepancies may be late melting ice and regional variations in lithospheric strength and thickness

holocene relative sea level changes in the inner solway firth abstract bio and lithostratigraphic data from four sites from the inner solway firth allow an accurate reconstruction of holocene rsl changes in the estuary radiocarbon assays give eleven new sea level index points providing a total of 24 reliable index points for the inner solway firth these data show a consistent pattern of rapid rsl rise during the early holocene culminating in a mid holocene sea level maximum then a gradual fall to the present day level detailed analysis of this dataset quantifies for the first time differential crustal movement between the north and south shores of the solway firth these data are used to test the accuracy of quantitative isostatic rebound models of lambeck and peltier and show there is good general agreement between the data and the models especially during the early holocene the models predict the mid holocene sea level peak slightly later than shown by the data c 500 and c 2000 yr this may be partly due to lack of resolution in the models and for the south solway the maximum altitude at this peak is 1 and 2 5 m too high in the two models the data are also compared to the isobase models of the main postglacial shoreline showing slight diachroneity between the north and south shore but otherwise general agreement with the postulated age and indicating that the altitude of this feature is 1 3 m higher than suggested by the models

salt marsh aggradation in response to late holocene sea level rise at amherst point nova scotia canada a radiocarbon 14c chronology determined for plant macrofossils in exposed salt marsh sediments at amherst point nova scotia canada shows that the edge of the high salt marsh aggraded 7 5 m since 900 bc equivalent to a mean rate of 25 9 cm 100 yr 1 four phases of rapid aggradation 900 600 bc 100 bc ad 200 ad 700 1100 and ad 1600 to present were interspersed with three phases of slower aggradation 600 100 bc ad 200 700 and tentatively ad 1100 1600 the stepped pattern of marsh aggradation probably resulted from eustatic sea level fluctuations superimposed on background signals of crustal subsidence and tidal range expansion because the rate of high salt marsh aggradation lagged or exceeded the rate of higher high water hhw increase at various times the high salt marsh aggradation trend only approximates the trend of hhw increase the eustatic sea level fluctuations are estimated to have a range of at least 0 8 m

saltmarsh sustainability throughout the holocene in boston harbor a new sea level curve for the lower gulf of maine and implications of recent anthropogenic alteration abstract saltmarsh evolution is closely linked to sea level rise slr and sediment supply in a regime of accelerating slr saltmarsh survival depends on the ability of the marsh platform to grow vertically through organic and inorganic accumulation and laterally via transgression over adjacent uplands in formerly glaciated settings the formation and maintenance of a saltmarsh are complicated by steep uplands low sediment availability isostatic rebound changes to tidal amplitudes and anthropogenic alteration while much work has examined the development of large saltmarshes in new england since the mid holocene and anthropocene little is known about the smaller isolated saltmarshes that form in pockets along the glaciated coastline we use radiocarbon dates from newly uncovered index points basal peat within boston harbor to date one of the oldest saltmarshes in the region 4 2 ka and calculate the polynomial relative sea level curve rslr for the lower gulf of maine taking into account tidal amplification throughout the holocene this study informs the historical persistence of isolated saltmarshes under varying rates of sea level rise magnitude as much as 2 mm yr 1 additionally we refine the timing and rates of the mid holocene sea level deceleration in this region between 2 8 and 3 3 ka slowing from 2 1 mm yr 1 to 0 5 mm yr 1 rslr determined from the past century of tide gauge data is 2 86 mm yr 1 five times greater than historic rates over the past 2000 years recent vertical accretion rates determined from marker horizons and 210pb data indicate that portions of boston harbor s saltmarshes are able to keep pace with current rslr however historical diking and ditching practices appear to have resulted in elevation loss and conversion from high saltmarsh platforms to low saltmarsh platforms largely influencing the amount of inorganic sediment needed to help maintain marsh surfaces these results highlight that knowledge of historical anthropogenic modifications and changes in hydroperiod are critical when interpreting vertical accretion results more importantly anthropogenic modification within sediment starved saltmarshes may be the cause for cannibalization of marsh shorelines whereby inorganic sediment eroded from marsh edges is recycled and delivered to the surface facilitating vertical accretion that offsets rslr under modern accelerated sea level rise and decreased sediment supply this cannibalization process may now be the only pathway for saltmarsh survival

effect of experimental wood addition on hyporheic exchange and thermal dynamics in a losing meadow stream 1 stream restoration structures such as large wood can enhance shallow river groundwater exchange or hyporheic exchange and alter temperature dynamics in restored reaches we added and then removed channel spanning logs in a second order mountain meadow stream to test short term impacts on hyporheic exchange streambed temperatures and surface water temperatures based on vertical seepage measurements and numerical simulations of hyporheic fluid and heat flow large wood addition increased hyporheic exchange and altered streambed temperatures in this losing stream meter scale hyporheic exchange cells formed beneath large wood upwelling pore water downstream of logs stabilized diel temperature cycles across 8 of the streambed creating localized but potentially valuable thermal refuge exchange rates were 0 1 of channel discharge too small to impact the range of diel temperature signals in surface water however the lag between downstream and upstream diel temperature signals was slightly greater with large wood which may indicate that surface storage zones rather than hyporheic storage zones increased thermal retardation losing conditions limited the spatial extent and rates of hyporheic exchange near large wood impacts of large wood reintroduction on hyporheic exchange depend on ambient groundwater discharge or recharge streambed permeability channel froude number large wood blockage ratio and large wood spacing in many streams large wood reintroduction may increase hyporheic habitat volume and complexity but may not increase exchange rates enough to alter surface water temperature or chemistry surface storage zones such as eddies and pools can still influence heat and solute retention in the channel

correlation of waveforms from closely spaced regional events abstract we studied the similarity of waveforms recorded at the high frequency element of the noress array from 137 events m l 0 8 to 2 1 in or near the mining districts of central sweden waveform correlations based on the covariance matrices of three component recordings and on maximum amplitudes were calculated from traces filtered between 2 5 and 4 0 hz in which band the signal to noise ratio consistently peaked for the waveforms a cutoff value for the correlations to separate waveforms with poor and good correlation values could be defined from the statistical uncertainty in back azimuth estimates of noress more than 80 per cent of the events could be grouped with hierarchical clustering into one large group of 98 events and five smaller groups the noress epicenters of the events in the large group were scattered over an area of 20 75 km an exponential decay of the waveform correlation with event separation d in km could be fitted to the data of this group exp d 8 taking noress epicenter uncertainties into account a procedure for location of close events based on correlation values is defined when applied to the large event group it limits the event epicenters to be within an area of about 4 km for one small event group high correlation values were obtained above 15 hz these frequencies are significantly higher than those reported in other studies and the so called quarter wavelength argument constrains the event epicenters to within 0 1 km

the influence of riparian vegetation on stream width eastern pennsylvania usa we surveyed adjacent reaches with differing riparian vegetation to explain why channels with forested banks are wider than channels with nonforested banks cross sections and geomorphic mapping demonstrate that erosion occurs at cutbanks in curving reaches while deposition is localized on active floodplains on the insides of bends our data indicate that rates of deposition and lateral migration are both higher in nonforested reaches than in forested reaches two dimensionless parameters and e explain our observations represents the influence of grassy vegetation on rates of active floodplain deposition it is 5 times higher in nonforested reaches than in forested reaches e is proportional to rates of cutbank migration it is 3 times higher in nonforested reaches than in forested reaches differences in width between forested and nonforested reaches are proportional to e in forested reaches channels are wide with banks that are difficult to erode dense tree roots create a low value of e and the channel migrates slowly e is high however because is very low shade from trees inhibits the growth of grass on active floodplains in nonforested reaches channels are narrow with banks that are easy to erode e is high and the channel migrates rapidly e is low however due to a very large value of grass grows readily on nonforested convex bank floodplains thus differences in width between forested and nonforested reaches are related to a balance between rates of cutbank erosion and rates of deposition on active floodplains implying that equilibrium widths develop to equalize rates of cutbank erosion and vegetation mediated rates of deposition on active flood plains these results suggest that accurate models of width adjustment should consider the combined effects of bank erodibility and floodplain depositional processes rather than focusing on these processes in isolation from one another

the effect of streambed topography on surface subsurface water exchange in mountain catchments a numerical hydrological simulation suggested that water exchange between stream channels and adjacent aquifers is enhanced by convexities and concavities in streambed topography at st kevin gulch an effluent stream in the rocky mountains of colorado subsurface hydraulic gradients and movement of ionic tracers indicated that stream water was locally recharged into well defined flow paths through the alluvium stream water filled flow paths in the alluvium referred to as substream flow paths returned to the stream a short distance downstream 1 to 10 m recharge to the substream flow paths occurred where stream water slope increased at the transition from pools 1 to steeper channel units 5 20 return of substream flow paths to the stream occurred where stream water slope decreased at the transition from steeper channel units to pools a net water flux calculation is typically used to characterize water and solute fluxes between surface and subsurface zones of catchments along our study reach at st kevin gulch the net inflow of water from subsurface to stream 1 6 ml s 1 m 1 underestimated the gross inflow 2 7 ml s 1 m 1 by 40 the influence of streambed topography is to enhance hydrological fluxes between stream water and subsurface zones and to prolong water sediment contact times these effects could have important consequences for solute transport retention and transformation in catchments

the influence of organic debris on channel morphology and bedload transport in a new zealand forest stream the behaviour and form of and bedload sediment transport through a 3 5 m wide forest stream have been monitored for nearly three years bedload transport is highly episodic and spatially variable and is controlled less by water discharge than by sediment availability organic debris in the channel creates temporary base levels and sites at which coarse sediment may remain stored for long periods collapse or disruption of log and debris jams makes sediment available for transport in only a small proportion of the runoff events that are actually competent to move the material even then sediment travels only a short distance before being redeposited frequently behind debris accumulations further downstream rates of sediment transport during a given runoff event can vary markedly over short distances along the stream again depending on whether sediment was made available for transport by log jam collapse upstream organic debris is therefore a major constraint on the application of physical laws and theories to explaining sediment movement in and the morphology of this stream

using waveform similarity to constrain earthquake locations abstract we demonstrate that the numerical value of the cross correlation between p or s waveforms commonly computed to determine differential travel times for earthquake relocation itself contains useful information about the relative location of the events this information can be used to supplement traditional travel time inversions especially when few stations are available and to investigate the heterogeneity that underlies the multiple scattering process

a comparison of present sea level linear trends from tide gauge data and radiocarbon curves in eastern canada abstract a comparison is made of the results for determinations of vertical crustal movements by means of two independent sources of data widely used in geodesy and geology tide gauge sea level linear trends and gradients of radiocarbon curves as a reference the map of vertical crustal movements of canada is added which was computed using not only tide gauge data but also geodetic levelling data these results show similar trends computed by both techniques but an average value of 0 1 m century greater for the sea level trends the map of vertical crustal movements is in good agreement with the trends provided by the gradients of radiocarbon curves

holocene evolution of bottom sediment distribution on the continental shelves of the bohai sea yellow sea and east china sea abstract coastline shifts due to transgression and regression can remodel tidal fields of continental shelves and this can control transport of sediments and modulate sediment distribution accordingly tidal currents have become the dominant hydrodynamic processes on the continental shelves of the bohai sea yellow sea and east china sea byecs since the transgression after the last glacial maximum lgm to examine the evolution of the bottom sediment distributions on the continental shelves of the byecs we simulated patterns of tides and tidal currents sediment transport and bottom sediment types sand mud and mixed sediments for five periods corresponding to sea level lowstands of 80 m 52 m and 30 m below present the holocene transgression maximum htm and the present the simulation shows that both sediment transport and shelf sediment distribution patterns were controlled by the strength type and asymmetry of tidal currents in the byecs since the lgm evolution of shelf sediment distribution patterns occurred in two stages 1 sediment emplacement and formation stage before the htm and 2 local adjustment after the htm the marked changes in coastline configuration since the lgm are the dominant factor controlling tide and tidal current evolution distribution of shelf sediment types in the byecs is closely related to tidal current fields during transgression after the lgm

influence of large woody debris on channel morphology and dynamics in steep boulder rich mountain streams western cascades oregon this study used 20 year records of stream channel change and wood to test hypotheses about the long term influence of large woody debris lwd on channel morphology channel stability and sediment dynamics in a steep boulder rich mountain stream we compared two nearly adjacent reaches of third order mack creek over the period 1978 1997 after virtually all wood was removed from the channel of the lower reach in 1964 we assessed the long term legacy of wood removal using repeated crosssection surveys streamflow data lwd inventory data and detailed mapping and longitudinal profile surveys at each of 11 cross sections in the upper reach and 19 in the lower reach we calculated areas of scour and fill in response to the two largest floods in the record we used quasi likelihood logistic regression models to test the proportion of each reach that experienced change between consecutive surveys over the entire record 1978 1997 as a function of flood return periods the longitudinal profile of the site without lwd was more variable than the reach with lwd at the finest scale f1 m due to a greater frequency of boulder steps but the reach with lwd was more variable at the channel unit scale lwd created steps 1 to 2 5 m high in the wood rich reach accounted for nearly 30 of the total channel fall and created low gradient upstream channel segments one to three channel widths long as a result both reaches have the same average slope about 9 but nearly three times as much of the channel in the wood rich reach had a slope of v5 as in the reach without wood 20 4 of total channel length vs 7 5 of channel length the reach with abundant lwd was less responsive to moderate streamflow events return period f5 years but it responded similarly to peak flows with a return period of about 10 to 25 years although the average magnitude of crosssection changes was the same during the largest flood in the record 25 year return period the reach without lwd experienced scour and coarsening of the bed surface whereas the reach with lwd experienced aggradation upstream of lwd features mack creek may be representative of many steep mountain streams in which channel structure is strongly influenced by nonfluvial processes a legacy of large boulders from glacial or mass movement processes and a legacy of dead wood from ecological processes sediment limited mountain streams with large boulders when deprived of lwd appear to exhibit less morphological variation at the channel unit scale to store less sediment and to release it more readily than those with lwd d 2002 elsevier science b v all rights reserved

impact of heterogeneity bed forms and stream curvature on subchannel hyporheic exchange 1 advection through hyporheic zones hz consisting of heterogeneous channel bend streambed deposits and their equivalent homogenous medium was investigated using finite difference groundwater flow and transport simulations and forward particle tracking the top prescribed head boundary was varied in order to mimic various stream channel head distributions resulting from the presence of bed forms and channel curvature flux calculations show that heterogeneity causes significant additional hz flux compared to an equivalent homogenous medium however the major cause of hz flux is a spatially periodic sinusoidal head distribution along the boundary representing the effect of bed forms the additional influence of heterogeneity on the total channel bed exchange and the overall hz geometry are increased when boundary head sinusoidal fluctuation is more subdued we present dimensionless numbers that summarize these relationships heterogeneity s influence is further magnified by considering the effect of channel curvature on boundary heads the simulations illustrate the dynamic influence of heterogeneity on the hyporheic zone since the various head boundaries employed in our modeling efforts are a proxy for different surface water conditions and bed form states that may occur during a single flood furthermore we show that residence times total tracking times of particles originating from the streambed follow a lognormal distribution in the presence of heterogeneity residence times can decrease or they can increase compared to residence times for homogeneous conditions depending on the relative positions of the heterogeneities and the bed forms hence streambed heterogeneity and stream curvature factors often neglected in previous modeling efforts combine with bed form configuration to dynamically determine hz geometry fluxes and residence time distributions

hydraulic and thermal effects of in stream structure induced hyporheic exchange across a range of hydraulic conductivities in stream structure induced hyporheic exchange and associated thermal dynamics affect stream ecosystems their importance is controlled by spatial variability of sediment hydraulic conductivity k we calibrated a computational fluid dynamics cfd model of surface and groundwater hydraulics near a channel spanning weir represents log dams boulder weirs to field data and varied k from 10 7 to 10 2 m s silt to gravel surface water stopped cresting the weir for k 10 3 m s non darcy hyporheic flow was also prevalent for k 10 3 m s and velocity errors using non cfd models ranged up to 32 2 we also modeled weir induced heat transport during summer as k increased from 10 7 to 10 3 m s weir induced hyporheic heat advection steadily increased cooling and buffering along hyporheic flow paths decreased with increasing k particularly above k 10 5 and 10 4 m s respectively vertical heat conduction between surface water and groundwater near the weir decreased with increasing k particularly for k 10 5 m s conduction between hyporheic flow paths and adjacent groundwater helped cool hyporheic flow downstream surface water cooling by hyporheic advection increased steadily with k as increases in hyporheic flow overwhelmed decreases in cooling along hyporheic flow paths yet such effects were small 0 016 c even at k 10 3 m s the largest thermal effect of weir induced exchange was therefore spatial expansion of subsurface diel variability particularly for k 10 5 m s which affects benthic habitat and chemical reactions the specific values of k where such trend shifts occur is likely variable among streams based on flow conditions but we expect the presence of such trend shifts to be widespread

in stream geomorphic structures as drivers of hyporheic exchange 1 common in stream geomorphic structures such as debris dams and steps can drive hyporheic exchange in streams exchange is important for ecological stream function and restoring function is a goal of many stream restoration projects yet the connection between in stream geomorphic form hydrogeologic setting and hyporheic exchange remains inadequately characterized we used the models hec ras modflow and modpath to simulate coupled surface and subsurface hydraulics in a gaining stream containing a single in stream geomorphic structure and to systematically evaluate the impact of fundamental characteristics of the structure and its hydrogeologic setting on induced exchange we also conducted a field study to support model results model results indicated that structure size background groundwater discharge rate and sediment hydraulic conductivity are the most important factors determining the magnitude of induced hyporheic exchange followed by geomorphic structure type depth to bedrock and channel slope model results indicated channel spanning structures were more effective at driving hyporheic flow than were partially spanning structures and weirs were more effective than were steps across most structure types downwelling flux rate increased linearly with structure size yet hyporheic residence time exhibited nonlinear behavior increasing quickly with size at low structure sizes and declining thereafter important trends in model results were observed at the field site and also interpreted using simple hydraulic theory thereby supporting the modeling approach and clarifying underlying processes

diatom based inference model for paleosalinity reconstructions in estuaries along the northeastern coast of argentina article i nfo the relationship between benthic diatom assemblages and environmental variables was analyzed in 40 sites at three estuaries from the northeastern coast of argentina by using multivariate analyses surface sediment samples were collected along the estuarine gradient and analyzed for diatoms organic matter water content and grain size water salinity ph turbidity and temperature were measured seasonally at every sampling site canonical correspondence analysis cca was applied in order to recognize which environmental variables correlated most closely with the distributions of diatom taxa salinity and sediment properties were identified as the most important variables influencing diatom distribution in the studied estuaries a two component weighted averaging partial least squares wa pls calibration model was developed to infer salinity based on diatom assemblages the reliability of the model was evaluated by the error of prediction rmsepjack knifed 4 42 and the correlation r 2 jack knifed 0 75 between observed and diatom inferred values the transfer function was applied to fossil diatom assemblages recovered from a holocene sequence from the argentinean coast the application of the model to the fossil record allowed quantitative inferences of salinity changes in southern south america improving the quality of the inferences performed

channel reach morphology in mountain drainage basins a classification of channel reach morphology in mountain drainage basins synthesizes stream morphologies into seven distinct reach types colluvial bedrock and five alluvial channel types cascade step pool plane bed pool rime and dune ripple coupling reach level channel processes with the spatial arrangement of reach morphologies their links to hillslope processes and external forcing by confinement ripar ian vegetation and woody debris defines a process based framework within which to assess channel condition and response potential in mountain drainage basins field investigations demonstrate character istic slope grain size shear stress and roughness ranges for different reach types observations consistent with our hypothesis that alluvial channel morphologies reflect specific roughness configurations ad justed to the relative magnitudes of sediment supply and transport ca pacity steep alluvial channels cascade and step pool have high ratios of transport capacity to sediment supply and are resilient to changes in discharge and sediment supply whereas low gradient alluvial channels pool rime and dune ripple have lower transport capacity to supply ra tios and thus exhibit significant and prolonged response to changes in sediment supply and discharge general differences in the ratio of transport capacity to supply between channel types allow aggregation of reaches into source transport and response segments the spatial distribution of which provides a watershed level conceptual model linking reach morphology and channel processes these two scales of channel network classification define a framework within which to in vestigate spatial and temporal patterns of channel response in moun tain drainage basins

evaluation of alternative groundwater flow models for simulating hyporheic exchange in a small mountain stream summary groundwater flow models have been used to estimate the amount of exchange flow and the residence time distribution of stream water in the hyporheic zone however reliability of these predictions have not been tested we ask the questions 1 how reliable are hyporheic groundwater models in typical applications examining hyporheic exchange flows and 2 how does the reliability change with increased data availability and model sophistication we developed groundwater flow models of the hyporheic zone for a mountain stream in the hj andrews experimental forest oregon the models are based on surveyed topography and hydraulic conductivity k measurements from both slug tests and a well to well tracer test we developed several models using different methods to estimate two of the most uncertain parameters k and the depth and shape of the bedrock boundary we first tested the goodness of fit of each model to the water levels observed in a network of wells and piezometers results showed that differences among models in predicted heads were quite small whereas differences among estimated hyporheic fluxes varied by a factor of two we then tested the model predictions of tracer arrival times to each well in the network during a stream tracer injection comparison of simulated and observed travel times showed that increased model sophistication did not lead to improved model reliability because travel time predictions from the homogeneous model were equal to or better than the predictions from the heterogeneous models while general trends in solute breakthrough were correct in the models k data from even 37 wells in a 15 m by 50 m model domain were insufficient to characterize detailed arrival times accurately this suggests that geomorphic data may be sufficient to predict water fluxes through the subsurface and approximate travel times however for detailed analysis of solute transport pathways and breakthroughs intensive sampling of the subsurface may be necessary published by elsevier b v

proposed younger dryas glaciation of the eastern scotian shelf a refined synthesis of the stratigraphy of the scotian shelf is presented based on recently published borehole and seismic reflection data and detailed correlation along high resolution seismic profiles between the outer banks and the central basins one of the new stratigraphic units of the outer bank region is of glacigenic origin and represents the last glacial event near the margin of the shelf these deposits appear to be part of a morainal bank complex formed at a tidewater front a younger dryas age is proposed for the glacial deposits and the ice may have been widely distributed across the eastern scotian shelf evidence for the late glaciation is expressed in the central shelf area by an unconformity which on the bank areas is associated with subglacial meltwater channels 14c dates for the basin sediments of this region provide the most reliable chronology for the shelf stratigraphy the origin of sable island is closely related to the depositional history of the moraine and its surface has be

holocene tides of the wash u k the influence of water depth and coastline shape changes on the record of sea level change abstract tidal simulations are conducted using a numerical model to investigate the relative influence of water depth and coastline shape changes on the holocene tides of the wash tidal input to this model is obtained by running a nested series of models commencing with a model of the northeast atlantic results of both types of simulations are compared with those of other simulations incorporating all the palaeogeographic information available on both past water depths and coastline shapes around the wash the model employs six harmonic tidal constituents to obtain mean high water of spring tides mhwst altitudes the wash was a depositional embayment during the holocene and results of model simulations are compared with sea level indicators in the stratigraphy which record past mhwst altitudes tidal simulations for water depths reduced by 2 5 and 10 m compared with present sea levels generally give lower tidal amplitudes around the wash than found at present mhwst altitudes simulating the coastline shape for 3000 4000 and 5000 yrs b p utilising present water depths show similar patterns of tidal changes to those obtained from the palaeogeographic simulations however reduced water depth tidal simulations accord more closely with the palaeogeographic simulation results in terms of the magnitude of changes to mhwst altitudes than the palaeocoastline simulations this is due to the fact that the rise in mean sea level during the holocene is far greater than any change in the amplitude of tides in the wash palaeogeographic simulation model results for mhwst agree within experimental errors with sea level curve altitudes reasons for discrepancies include inaccuracies in model parameters or measurement errors in obtaining mhwst altitudes from the stratigraphy overall tidal heights increase with sea level rise towards the present day alterations to coastline shape and non uniform water depth changes for example due to sediment movements or coastal defence schemes must be taken into consideration when assessing changes to the tidal regime for different sea levels in coastal embayments in order to determine both the pattern and magnitude of tidal changes this applies to both past and possible future tidal simulations

constraints on relative earthquake locations from cross correlation of waveforms abstract cross correlations of filtered waveforms can be used to place strong constraints on relative locations of local earthquakes under the assumption that events producing very similar waveforms occur within a distance of one quarter of the shortest wavelength for which the similarity is observed tests using digital seismograms of mine blasts with known locations recorded by the university of utah seismic network support this quarter wavelength hypothesis application of this method can yield information on relative locations of earthquakes within source volumes of 1 km 3 or smaller which is seldom possible using arrival time data alone

changes in hyporheic exchange flow following experimental wood removal in a small low gradient stream 1 we investigated the response of hyporheic exchange flow hef to wood removal in a small low gradient gravel bed stream in southeast alaska using a series of groundwater models built to simulate hef for the initial conditions immediately after wood removal and 1 month 2 years 4 years and 16 years following wood removal the models were based on topographic surveys of the stream channel and surrounding floodplain and surveyed water surface elevations wses were used to assign stream boundary conditions using the groundwater flow model modflow and the particle tracking model modpath we calculated hyporheic exchange fluxes their residence time distributions and both longitudinal and plan view spatial patterns of downwelling and upwelling zones in the first few years streambed scour and sediment deposition smoothed the streambed and wse profile reducing hef also large contiguous patches of downwelling or upwelling were fragmented nearly doubling the total number of patches present on the streambed as the stream continued to adjust to the loss of wood those trends began to reverse accretion of sediment onto alternating bars resulted in better developed pool riffle morphology enhanced hef and increased residence times and also resulted in downwelling and upwelling zones coalescing into elongated patches along bar margins this study showed that the hyporheic zone is sensitive to changes in wood loading and that initial changes in hef resulting from the direct effects of wood removal were contrary to longer term channel adjustments to changes in wood loading

characterization of hydrogeologic properties for a multi layered alluvial aquifer using hydraulic and tracer tests and electrical resistivity survey a multi layered aquifer typical of riverbank alluvial deposits in korea was studied to determine the hydrologic properties the geologic logging showed that the subsurface of the study site was comprised of four distinctive hydrogeologic units silt sand highly weathered and fresh bedrock layers the electrical resistivity survey supplied information on lateral extension of hydrogeologic strata only partially identified by a limited number of the geologic loggings the laboratory column tracer test for the recovered core of the sand layer resulted in a hydraulic conductivity of 5 00 10 2 cm s the slug tests performed in the weathered rock layer yielded hydraulic conductivities of 4 32 7 72 10 4 cm s hydraulic conductivities for the sand layer calculated from the breakthrough curves of bromide ranged between 2 08 10 3 and 2 44 10 2 cm s with a geometric mean of 6 89 10 3 cm s which is 7 times smaller than that from the laboratory column experiment the trend of increasing hydraulic conductivity with an increase in tracer travel length is likely a result of the increased likelihood of encountering a high conductivity zone as more of the aquifer is tested the combined hydrogeologic site characterization using hydraulic tests tracer tests and column test with geologic loggings and geophysical survey greatly enhanced the understanding of the hydrologic properties of the multi layered alluvial aquifer

modeling the contribution of m2 tidal amplification to the holocene rise of mean high water in the gulf of maine and the bay of fundy abstract increase in the m2 principal lunar semi diurnal component of the tidal range is an important contributor to the postglacial rise of the high tide level in the gulf of maine and the bay of fundy in addition to relative sea level rise the increase occurred as the shape of this semi enclosed embayment changed with sea level rise and its natural period approached resonance with the m2 tide a three dimensional tide model 3dens predicts the following m2 tidal ranges averaged for the gulf of maine bay of fundy as a percentage of the present range 54 59 at 7000 yrs b p 73 at 5000 yrs b p 78 at 4000 yrs b p 85 at 3000 yrs b p 94 at 2000 yrs b p and 98 at 1000 yrs b p with a predicted sea level rise of 0 15 0 90 m by the year 2100 m2 tidal range may increase 0 3 1 9

effects on bedload transport of experimental removal of woody debris from a forest gravel bed stream experimental removal of woody debris from a small gravel bed stream in a forested area resulted in a four fold increase in bedload transport at bankfull discharge this was caused by increased transportability of sediment previously stored upslope of debris buttresses or in low energy hydraulic environments related to debris bank erosion delivered additional sediment to the channel and transport energy was increased by an inferred increase in the component of total boundary shear stress affecting grains on the bed increased transport following debris removal in may 1987 continued throughout the entire autumn storm season through late november 1987 indicating persistent adjustment of the stream bed and banks despite marked response to earlier flows as large as bankfull stream bed adjustments included development of a semi regular sequence of alternate bars and pools many of which were spaced independently of former pool locations

middle and late holocene sea level changes in eastern maine reconstructed from foraminiferal saltmarsh stratigraphy and ams 14c dates on basal peat abstract a relative sea level history is reconstructed for machiasport maine spanning the past 6000 calendar years and combining two different methods the first method establishes the long term 10 3 yr trend of sea level rise by dating the base of the holocene saltmarsh peat overlying a pleistocene substrate the second method uses detailed analyses of the foraminiferal stratigraphy of two saltmarsh peat cores to quantify fluctuations superimposed on the long term trend the indicative meaning of the peat the height at which the peat was deposited relative to mean tide level is calculated by a transfer function based on vertical distributions of modern foraminiferal assemblages the chronology is determined from ams 14 c dates on saltmarsh plant fragments embedded in the peat the combination of the two different approaches produces a high resolution replicable sea level record which takes into account the autocompaction of the peat sequence long term mean rates of sea level rise corrected for changes in tidal range are 0 75 mm yr between 6000 and 1500 cal yr b p and 0 43 mm yr during the past 1500 years the foraminiferal stratigraphy reveals several low amplitude fluctuations during a relatively stable period between 1100 and 400 cal yr b p and a sea level rise of 0 5 m during the past 300 years

holocene history of bedford basin nova scotia foraminifera dinoflagellate and pollen records three piston cores from bedford basin a silled coastal inlet provide the basis for a micropaleontological study of postglacial to recent sediments five faunal units four foraminiferal one arcellacean are found in core 79 11 a surface assemblage followed by deep estuarine marginal marine transition and freshwater arcellacean assemblages the other cores contain only expanded marine sequences the top of the transition zone in core 79 11 has a c 14 age of 5830 230 years bp indicating a rise in sea level of at least 20 m the sill depth during the holocene four dinoflagellate assemblage zones are found in core 79 11 the first o centrocarpum b tepikiense is typical of a silled basin with marine water of near normal salinity the second p conicoides cyst c indicates a temperate marine environment with strong fluvial influence marginal marine the third p limbatum is dominated by freshwater cysts and the fourth dinocyst sp a is dominated by subarctic brackish water cysts fo

a high resolution study of tides in the delaware bay past conditions and future scenarios 1 tides in the delaware bay usa have been modeled from 7000 years before present 7 ka to the present day and for selected future sea level rise scenarios 100 years 300 years historic bathymetries were constructed through use of glacial isostatic adjustment models and a very high spatial resolution 100 m was used at the shoreline future bathymetries were obtained by extrapolating these glacial isostatic adjustment models and applying an additional eustatic sea level rise it was found that tides in the lower bay have remained fairly constant through time but that tides in the upper bay have increased steadily from about 4 ka to the present day a nearly 100 increase in total the future runs demonstrated spatially complex behavior with tidal range changes of up to 10

a comparison of observed and theoretical postglacial relative sea level in atlantic canada two extreme models of late wisconsinan ice cover in atlantic canada and the northeastern u s a are shown to produce postglacial relative sea level curves that bracket existing field observations at six sites throughout the region this suggests that the true late wisconsinan ice distribution is probably intermediate to the two contrasting reconstructions proposed both ice models predict the existence of four relative sea level zones an innermost zone closest to the centre of glaciation in which relative sea level falls continuously throughout postglacial time an outermost zone in which it rises continuously and two transitional zones in which it first falls and then rises in varying proportions according to the distance from the ice margin the distinctive forms of the relative sea level curves are probably representative of each of the zones and are unlikely to be significantly perturbed even by large local ice readvances they therefore establish patterns with which future field data are expected to conform the form that the geological record of relative sea level change is likely to take within each zone is discussed and promising settings for the collection of new data are proposed the common practice of separating relative sea level into an isostatic and a eustatic component is analysed and shown to be incorrect as usually applied the practice is also shown to be unnecessary because the models discussed in this paper predict changes in relative sea level that can be compared directly with the observations

effect of instream wood on vertical water flux in low energy sand bed flume experiments 1 in streams interaction of current with bed forms and solid objects can produce vertical water flux across the streambed instream wood is a major obstacle to flow and alters the bed topography of natural sand bed streams in the present experimental study in large circulating flumes simulating sand bed streams with low constant slope we compared systems with and without natural quantities of wood the introduction of wood resulted in the production of irregular bed forms as a result flow resistance tripled and vertical water flux across the streambed increased by a factor of 1 8 to 2 5 the mixing depth was spatially variable and seemed unrelated to the local bed form after the addition of wood surface water mixed deeper into the sediments and the total sediment pore water volume involved in mixing increased by factors of 1 2 to 1 5 the practice of increasing instream wood should be a valuable tool for hyporheic rehabilitation of degraded sand bed streams

polarization and coherence of 5 to 30 hz seismic wave fields at a hard rock site and their relevance to velocity heterogeneities in the crust abstract except for its very onset the p wave of earthquakes and chemical explosions observed at two narrow aperture arrays on hard rock sites in the adirondack mountains have a nearly random polarization the amount of energy on the vertical radial and transverse components is about equal over the frequency range 5 to 30 hz for the entire seismogram the spatial coherence of the seismograms is approximately exp cf x where c is in the range 0 4 to 0 7 km 1 hz 1 f is frequency and x is the distance between array elements vertical radial and transverse components were quite coherent over the aperture of the array indicating that the transverse motion of the compressional wave is a property of relatively large 10 6 m 3 volumes of rock and not just an anomaly caused by a malfunctioning instrument poor instrument rock coupling or out crop scale effects the spatial coherence is approximately independent of component epicentral azimuth and range and whether p or s wave coda is being considered at least for propagation distances between 5 and 170 km these results imply a strongly and three dimensionally heterogeneous crust with near receiver scattering in the uppermost crust controlling the coherence properties of the waves

influence of glacial isostatic adjustment on tide gauge measurements of secular sea level change modem tide gage records of secular sea level change are strongly contaminated by the ongoing influence of glacial isostatic adjustment in this paper we employ an accurate high resolution model of the glacial isostatic adjustment process to filter this signal from time series consisting of annual mean heights observed on over 500 tide gages from which records of duration longer than 10 years are available these records are all contained in the archive of the permanent service for mean sea level at bidston in the united kingdom prior to removal of the isostatic adjustment contamination from these records the secular sea level change signal is seen to exhibit both rising and falling levels depending upon geographic location with regions of falling level corresponding to those that were ice covered during the last glaciation event of the present ice age after filtering the geographic heterogeneity in rates is considerably reduced so much so that a globally coherent component consisting of a rise of sea level at a rate of 2 4 0 9 mm yr 1 is revealed this could conceivably be driven by the greenhouse effect although no particular mechanism has been unambiguously identified by our analyses we investigate the impact of a number of different variants of the analysis procedure upon the inferred global signal

developing detailed records of relative sea level change using a foraminiferal transfer function an example from north norfolk uk this paper provides a brief overview of the transfer function approach to sea level reconstruction using the example of two overlapping sediment cores from the north norfolk coast uk the advantages and limitations of the transfer function methodology are examined while the selected cores are taken from different sites and display contrasting patterns of sedimentation the foraminiferal transfer function distils comparable records of relative sea level change from both sequences these reconstructions are consistent with existing sea level index points from the region but produce a more detailed record of relative sea level change transfer functions can extract sea level information from a wider range of sedimentary sub environments this increases the amount of data that can be collected from coastal deposits and improves record resolution the replicability of the transfer function methodology coupled with the sequential nature of the data it produces assists in the compilation and analysis of sea level records from different sites this technique has the potential to bridge the gap between short term instrumental and long term geological or geophysical records of sea level change

on the postglacial isostatic adjustment of the british isles and the shallow viscoelastic structure of the earth summary observations of postglacial relative sea level rsl history at sites beyond the margins of the main accumulations of wu rm wisconsin devensian ice may be invoked to test the accuracy of global models of the glacial isostatic adjustment process the existing database of rsl time series for the british isles forms a continuous network of sites that sample the coasts of scotland england and wales fairly uniformly and which may be especially important in this regard not only are these 14c data for the holocene epoch of very high quality in terms of our knowledge of the coastal environment and relationship to palaeo sea level of each age measurement but they are especially numerous and relate to an island that was itself partly glaciated in the north essentially ice free in the south and located well outboard of the massive ice sheet that covered fennoscandia at the last glacial maximum lgm taken together the time series from 55 distinct locations allow us to perform a fairly stringent test of the recently formulated ice 4g vm2 global model of the isostatic adjustment process even without modification this model has been shown to fit most of the time series in the uk data set rather well in order to satisfy very recently published a priori constraints on the maximum thickness of the scottish ice sheet however we find that the lithospheric thickness the feature of the radial viscoelastic structure to which the rebound data from scotland are most sensitive must be somewhat reduced whereas the assumed thickness of the lithosphere in ice 4g vm2 was near to 120 km best fits to the scottish data require a lithospheric thickness near to 90 km this reduced value for lithospheric thickness agrees exceedingly well with the latest estimates of this earth property based on the inversion of oceanic geoid and topography data as the asymptotic thickness characteristic of the oldest ocean floor this would appear to be the best possible a priori estimate for the thickness of the cratonic lithospheres upon which the largest ice sheets of the late pleistocene are known to have rested we also demonstrate explicitly that inferences of the shallow viscoelastic structure beneath the british isles are strongly influenced by the details of the history of deglaciation at remote locations at antarctica in particular

hyporheic exchange with heterogeneous streambeds laboratory experiments and modeling 1 hyporheic exchange is generally analyzed with the assumption of a homogeneous hyporheic zone in reality streambed sediments have a heterogeneous structure and this natural heterogeneity produces spatially variable interfacial fluxes and complex hyporheic exchange patterns to assess the basic effects of sediment structure on hyporheic exchange we performed salt and dye injection experiments in a recirculating laboratory flume with two heterogeneous sediment beds characterized by negative exponential correlated random hydraulic conductivity fields dye injections showed that the hyporheic flow structure was controlled by the spatial relationship of bed forms to high and low permeability regions of the streambed as no existing model could represent these effects we developed a new finite element model to calculate the pore water flow field resulting from the interaction of the bed form induced boundary head distribution and the heterogeneous sediment structure a numerical particle tracking approach was then used to assess the resulting hyporheic exchange the combined flow transport model did an excellent job of predicting the complex hyporheic flow pathways in the heterogeneous bed and the net hyporheic exchange up to t 30 hours the heterogeneous hydraulic conductivity field caused both greater spatial variability in the water flux through the bed surface and a greater average interfacial flux than would have occurred with a homogeneous bed the layered correlation structure of the streambed produced an effective anisotropy that favored longitudinal pore water flow and caused a relatively rapid decrease of the mean pore water velocity with depth as a result solute penetration into the bed was confined to a more shallow region than would have occurred with a homogeneous bed the combination of faster near surface transport and shallower solute penetration produced a shorter mean hyporheic residence time on the basis of the combination of experimental results and model simulations we conclude that the structural heterogeneity of streambed sediments produces more spatially limited hyporheic exchange that occurs with greater spatial variability and at a higher overall rate

holocene relative sea level movements along the north norfolk coast uk abstract relative changes in holocene sea level are reconstructed from foraminiferal assemblages in seven cores recovered from the intertidal zone of north norfolk eastern england a total of 33 radiocarbon and infra red stimulated luminescence dates provide a detailed chronological framework for these changes a transfer function approach developed from modern uk foraminiferal datasets establishes a series of 21 new sea level index points for this coastline which are combined with 18 existing index points and a further number of limiting values errors associated with changing tidal ranges through the holocene are reduced by adopting recently developed tidal models for this period this new approach allows the use of foraminiferal assemblages to be extended from the upper saltmarsh environment traditionally used for sea level studies to lower elevations in the tidal frame and include clastic detrital sediments the results confirm the previously observed trend of continuously rising sea levels in this area during the last 10 000 years which is consistent with a glacial isostatic adjustment model relative sea level rsl rises from an observed minimum of approximately 13 50 m od at about 7500 cal bp to approximately 4 0 m at about 5300 cal bp which equates to a mean rise of c 4 3 mm yr 1 subsequently rsl rose gradually to present levels although there is evidence that a minor reverse in this trend occurred between 4000 and 2000 cal bp when sea level fell by about 1 m to c 3 5 m the rate of land subsidence for north norfolk is 0 54 0 03 mm yr 1 inverse of late holocene sea level rise

sea level in time and space revolutions and inconvenient truths in this paper we identify four revolutions that in our view have shaped the study of sea level changes in recent decades i the search for eustasy one of the most hotly debated issues in the 1960s is still relevant as models of glacial isostatic adjustment gia require input of the amount of meltwater transferred to the world s oceans following the demise of the large pleistocene ice sheets ii resolution of sea level archives all sea level archives have limitations in their resolving power but are we willing to define these from studies of salt marsh deposits and corals it is highly likely that climate driven metre scale sea level fluctuations have not occurred during the middle and late holocene iii rapid sea level changes improved coring technology has resulted in the suggestion of meltwater pulses during the last deglaciation low frequency high magnitude events have been documented along seismically active shorelines and provide information on seismic hazards and storm impacts iv merging of empirical sea level investigations and models much sea level research in the past two decades has embraced the integration of models and field derived data providing testable hypotheses and insights into processes we conclude with some reminders about the inconvenient truths that keep the sea level scientist honest

a new holocene relative sea level curve for western brittany france insights on isostatic dynamics along the atlantic coasts of north western europe abstract this study presents new relative sea level rsl data that were obtained in the finistere region western tip of brittany france and the implications those data have for the understanding of the isostatic dynamics across north western europe and more specifically along the atlantic and channel coasts new stratigraphic sequences were obtained and analyzed to derive 24 new sea level index points in which 6 are basal these new data considerably increase the knowledge we have of the rsl evolution along the coasts of western brittany since the last 8 kyr b p from this new dataset rsl was estimated to rise continuously over the last 8 kyr with a major inflection at ca 6 kyr cal bp our results show large vertical discrepancies between the rsl records of brittany and south western uk with the latter plotting several meters below the new data from this comparison we suggest that the two regions underwent a very different pattern and or amplitude of subsidence during the last 8 kyr which has implications for the spatial and temporal pattern of the peripheral bulge of the european ice sheets we compared our data against predictions from glacio isostatic adjustment models gia models there are large misfits between rsl observations and the predictions of the global ice 5g vm2a peltier 2004 glac1 b tarasov and peltier 2002 tarasov et al 2012 briggs et al 2014 and regional uk models biis bradley et al 2009 bradley et al 2011 kuchar kuchar et al 2012 which can t be resolved through significant changes to the deglaciation history and size of the british irish ice sheet paleo tidal modelling corrections indicate regional changes in the tidal ranges played a negligible role in the data model misfits hence we propose that the misfits are due to some combination of i unaccounted mass loss of far field ice sheets antarctic ice sheet or laurentide ice sheet ii unresolved differences in the deglaciation history and size of the fennoscandian ice sheet or more likely iii significant lateral variations in the earth s structure across the english channel

effects of coarse woody debris on morphology and sediment storage of a mountain stream system in western oregon effects of coarse woody debris cwd on channel morphology and sediment storage were investigated at five sites representative of first order to fifth order streams in the steep and bedrock confined stream first second order interaction between the channel and cwd was limited except where breakage upon falling produced cwd pieces shorter than channel width channel widening steepening and sediment storage associated with cwd were observed predominantly in third to fifth order streams variation in channel width and gradient was regulated by cwd in the fifth order stream most of the cwd pieces derived from the riparian forest interacted directly with the channel without being suspended by sideslopes in this system cwd promoted lateral channel migration but sediment storage was temporary with annual release and capture

neotectonic history of eastern maine evaluated from historic sea level data and 14c dates on salt marsh peats we constructed a local relative sea level curve for eastern maine from 14 c dates on salt marsh peats to evaluate potential holocene neotectonic activity this sea level chronology indicates that contrary to suggestions made previously low elevations of late glacial shoreline features in eastern maine are not related to neotectonic activity during the past 5 ka a comparison between seismicity and tide gauge records leads to the conclusion that there is no relation between seismic activity and contemporary subsidence of eastern coastal maine we propose that eastern maine has not been affected by anomalous subsidence during at least the past 5 ka

stream channel erosion and change resulting from riparian forests forested stream banks compared to grassed ones can destabilize stream channels by promoting erosion four reaches of coon creek wisconsin each with long term grassed and forested subreaches were examined grassed reaches were narrower and had smaller channels bankfull cross sections than forested reaches suggesting that grassed channel reaches stored about 2100 to 8800 m 3 more sediment per kilometre than forested reaches available evidence suggests that conversion of riparian forests to grass would allow storage of sediment along channels possibly decreasing downstream sediment yields these findings are important as many grassed riparian corridors are rapidly reverting to forest because of economic conditions and governmental policies

the quaternary stratigraphy of southwest sable island bank eastern canada three boreholes ten vibrocores and high resolution seismic reflection records were analyzed to reconstruct the stratigraphy of the topmost 50 m of the sedimentary column of southwest sable island bank the sequence is complex owing to the effects of two low stands of sea level two periods of ice influence and two periods of open water during the past 40 000 yr a low stand at 98 m occurred at 28 000 to 32 000 yr b p a second low stand occurred at 110 m between 13 000 and 15 000 yr b p ice covered the region prior to 32 000 yr b p and from 11 000 to 10 000 yr b p open water prevailed at other times the sequence of sediments follows the formational subdivision of king and the member subdivision of amos and knoll the sable island sand and gravel formation is subdivided into three members trough bedded sand cross bedded sand and conformably bedded sand the conformably bedded sand formed under heavy sea ice and represents the younger dryas event the uppermost two members result from shelf sediment reworking the emerald silt formation is subdivided into four members channel gravel upper stratified sand fines barren gravelly sand and lower stratified sand fines and two regional discontinuities r1 and r2 the coarser grained facies of the channel gravel and barren gravelly sand members are the result of reworking during late and mid wisconsinan transgressions of sable island bank the upper stratified sand fines member is interpreted as an open water marine deposit formed during the scotian stade the lower stratified sand fines member is interpreted as a glacio marine deposit formed during the digby stade

holocene land and sea level changes in great britain analysis of more than 1200 radiocarbon dated samples that constrain relative sea levels in great britain over the past 16 000 yr provides estimates of current land level changes negative of relative sea level change maximum relative land uplift occurs in central and western scotland ca 1 6 mm yr 1 and maximum subsidence is in southwest england ca 1 2 mm yr 1 sediment consolidation arising from autocompaction as the sediment accumulates and from land drainage increases the subsidence in areas with thick sequences of holocene sediments with an average effect equivalent to at least an extra ca 0 2 mm yr 1 land subsidence but more in parts of southeast england 0 5 1 1 mm yr 1 modelled changes in tidal range during the mid to late holocene in eastern england suggest that the calculated rate of land subsidence is overestimated unless such changes are quantified the effect is most significant for large coastal lowlands the fenland and humber ca 0 5 and 0 6 mm yr 1 that were tidal embayments during the mid to late holocene

relative sea level changes glacial isostatic modelling and ice sheet reconstructions from the british isles since the last glacial maximum while contributing 1 m equivalent eustatic sea level rise the british isles ice sheet produced glacio isostatic rebound in northern britain of similar magnitude to eustatic sea level change or global meltwater influx over the last 18 000 years the resulting spatially variable relative sea level changes combine with observations from far field locations to produce a rigorous test for quantitative models of glacial isostatic adjustment local ice sheet history and global meltwater influx after a review of the attributes of relative sea level observations significant for constraining large scale models of the isostatic adjustment process we summarise long records of relative sea level change from the british isles and far field locations we give an overview of different global theoretical models of the isostatic adjustment process before presenting intercomparisons of observed and predicted relative sea levels at sites in the british isles and far field for a range of earth and ice model parameters in order to demonstrate model sensitivity and the resolving power available from using evidence from the british isles for the first time we show a good degree of fit between relative sea level observations and predictions that are based upon global earth and ice model parameters independently derived from analysis of far field data with a terrain corrected model of the british isles ice sheet that includes extensive glaciation of the north sea and western continental shelf that does not assume isostatic equilibrium at the last glacial maximum and keeps to trimline constraints of ice surface elevation we do not attempt to identify a unique solution for the model lithosphere thickness parameter or the local scale detail of the ice model in order to provide a fit for all sites but argue that the next stage should be to incorporate an ice sheet model that is based on quantitative glaciological model simulations we hope that this paper will stimulate this debate and help to integrate research in glacial geomorphology glaciology sea level change earth rheology and quantitative modelling copyright 2006 john wiley sons ltd

source to mainstream hydrochemical water changes in a channel head in the young glacial area pomeranian lakeland poland abstract a channel head is a zone where hydrological changes occur that shape the chemical features of water during the final stage of underground flow and the beginning of the surface water cycle the study aims were as follows i to characterise spatial water chemistry patterns ii to establish the role played by the hyporheic zone in the chemical transformations associated with the groundwater that supplies the first order stream and iii to identify the factors that control the chemical composition transformations that occur in headwater alcoves the analysis was performed on three sets of samples taken at the arnowo channel head situated in the young glacial landscape of the parseta drainage basin nw poland the performed hydrochemical measurements showed that the waters found in the alcoves displayed a mosaic pattern with spatial variability in the levels of trace metals and nutrients in turn geogenic ions featured in the mineralogical petrographic compositions of deposits found in headwater catchments such as ca2 hco3 mg2 and na showed low temporal variability and small differences among the various sampled headwater alcoves these results indicated that the majority of spatial variance associated with the chemical composition of water is driven by the transformation of groundwater discharges in the hyporheic zone the locations of hydrochemical transformation hotspots can be explained by the influences of critical physical variables such as the intensity of seepage erosion sediment texture bottom microtopography groundwater discharge characteristics water temperatures and the diversity of groundwater fed vegetation hydrochemical studies performed in the ground and surface water contact zones within a channel head can identify the underlying causes of changes to water chemistry which in turn can facilitate the protection of water resources against unfavourable changes that may affect the water quality at the headwater catchment

using foraminiferal transfer functions to produce high resolution sea level records from salt marsh deposits maine usa quantitative analyses of foraminiferal distributions along the coast of maine are used to provide transfer functions for reconstruction of sea level changes from fossil foraminiferal assemblages the indicative meaning of fossil assemblages is most accurately predicted by a training set that incorporates live and dead foraminifera and that uses flooding duration not height as the predictor variable sea level records are produced for two sites in maine usa a middle marsh site in scarboro and a high marsh site in machiasport these records offer temporal resolution of five to seven years and span the past century they are compared with instrumental data from a nearby tidal station to assess their accuracy strong correlations are found between the geologic records and the observational data in particular between the foraminiferal record from machiasport and the tide gauge record from eastport r2 0 83 p 0 005 thus a foraminifera based transfer function approach offers great potential for reso