ground penetrating radar and its use in sedimentology principles problems and progress abstract ground penetrating radar gpr also referred to as ground probing radar surface penetrating radar subsurface radar georadar or impulse radar is a noninvasive geophysical technique that detects electrical discontinuities in the shallow subsurface

changes in hydrologic regime by dams dams have major impacts on river hydrology primarily through changes in the timing magnitude and frequency of low and high flows ultimately producing a hydrologic regime differing significantly from the pre impoundment natural flow regime this paper presents the analysis of pre and post dam hydrologic changes from dams that cover the spectrum of hydrologic and climatic regimes across the united states our overall goals are to document the type magnitude and direction of hydrologic shifts because of impoundment using the entire database for the national inventory of dams nid for dams possessing longstanding u s geological survey usgs gages downstream we identified 21 gage stations that met length of record criteria encompassing an array of types of dams and spanning four orders of magnitude in contributing watershed area to assess hydrologic changes associated with dams we applied a hydrologic model the indicators of hydrologic alteration iha supplemented with orientation statistics for certain hydrograph parameters dams had significant impacts on the entire range of hydrologic characteristics measured by iha for many characteristics the direction and significance of effects were highly consistent across the 21 sites the most significant changes across these sites occurred in minimum and maximum flows over different durations for low flows the 1 day through 90 day minimum flows increased significantly following impoundment the 1 day through 7 day maximum flows decreased significantly across the sites at monthly scales mean flows in april and may tend to decline while mean flows in august and september increase other significant adjustments included changes in annual hydrograph conditions primarily in the number of hydrograph reversals that has generally increased for almost all sites following impoundment the number of high pulses has increased following impoundment but the average length declines the mean rate of hydrograph rise and fall has declined significantly these results indicate that the major pulse of dam construction during the previous century has modified hydrologic regimes on a nationwide scale for large and small rivers

quantifying channel development and sediment transfer following chute cutoff in a wandering gravel bed river abstract three dimensional morphological adjustment in a chute cutoff breach alluvial channel is quantified using digital elevation model dem analysis for a ca 0 7 km reach of the river coquet northumberland uk following cutoff in january 1999 channel and bar topography was surveyed using a total station on five occasions between february 1999 and december 2000 analysis of planform change coupled with dem differencing elucidates channel and barform development following cutoff and enables quantification of sediment transfers associated with morphological adjustment within the reach this exercise indicates an initial phase of bed scour followed by a period characterised by extensive bank erosion and lateral channel migration where erosion including bed scour totalled some 15 000 m3 of sediment the channel in the post cutoff disequilibrium state is highly sensitive to relatively low magnitude floods and provision of accommodation space by bank erosion encouraged extensive lateral bar development bar development was further facilitated by infilling of channels abandoned by repeated within reach avulsion and large scale aggradation of sediment lobes deposited by higher magnitude floods calculations indicate that at least 6600 m3 of sediment was deposited on emerging bars within the reach over the survey period and 2300 m3 deposited within the channel sediment losses from the reach may have exceeded 6500 m3

downstream hydrologic and geomorphic effects of large dams on american rivers abstract the hydrology and geomorphology of large rivers in america reflect the pervasive influence of an extensive water control infrastructure including more than 75 000 dams one hundred thirty seven of the very large dams each storing 1 2 km 3 10 6 acre feet of water or more alter the flows of every large river in the country the hydrologic effects of these very large dams emerge from an analysis of the stream gage records of 72 river reaches organized into 36 pairs one member of each pair is an unregulated reach above a dam whereas the other is a regulated reach downstream from the same structure comparison of the regulated and unregulated reaches shows that very large dams on average reduce annual peak discharges 67 in some individual cases up to 90 decrease the ratio of annual maximum mean flow 60 decrease the range of daily discharges 64 increase the number of reversals in discharge by 34 and reduce the daily rates of ramping as much as 60 dams alter the timing of high and low flows and change the timing of the yearly maximum and minimum flows in some cases by as much as half a year regional variation in rivers dams and responses are substantial rivers in the great plains and ozark ouachita regions have annual maximum mean flow ratios that are 7 times greater than ratios for rivers in the pacific northwest at the same time the ratio of storage capacity mean annual water yield for dams is greatest for interior western ozark ouachita and great plains rivers and least for pacific northwest streams thus in many cases those rivers with the highest annual variability have the greatest potential impact from dams because structures can exert substantial control over downstream hydrology the hydrologic changes by dams have fostered dramatic geomorphic differences between regulated and unregulated reaches when compared to similar unregulated reaches regulated reaches have 32 larger low flow channels 50 smaller high flow channels 79 less active flood plain area and 3 6 times more inactive flood plain area dams also affect the area of active areas the functional surfaces that are functionally connected to the present regime of the river regulated reaches have active areas that are 72 smaller than the active areas of similar unregulated reaches the geomorphic complexity number of separate functional surfaces per unit of channel length is 37 less in regulated reaches reductions in the size of hydrologically active functional surfaces are greatest in rivers in the great plains and least in eastern streams the largest differences in geomorphic complexity are in interior western rivers the shrunken simplified geomorphology of regulated large rivers has had direct effects on riparian ecology producing spatially smaller less diverse riparian ecosystems compared to the larger more complex ecosystems along unregulated reaches of rivers

the geomorphic evolution and sediment balance of the lower rhone river southern france over the last 130 years hydropower dams versus other control factors article i nfo atthe end of thelittleice age lia agriculturalpractices and successive phasesof channel management involv ing embankments and dams however the respective roles of these various control factors in modifying sedi ment storage and channel stability are often difficult to identify the aim of this paper is to determine the main factors that have driven morphological changes over the past 130 years on the 120 km long downstream reach of the rhone river a gis based analysis of maps and aerial photographs available since 1860 coupled with chrono stratigraphic data on the river s alluvial deposits has enabled quantification of sediment storage and erosion in different morphological units changes measured include riverbed incision narrowing of the main channel in relation with accumulation of fine sediments along the channel margins and reduction of sed iment input at the mouth on the basis of local and reach scale sediment balances we show that these changes are synchronous with engineering works carried out at the end of the nineteenth century and beginning of the twentieth century a period that coincided with a decline in river sediment inputs largely generated by human activities the early stabilisation of mountain slopesresulting from a decline inrural agriculture rural exodus re forestation and engineered torrent control has had a much greater impact in geomorphically transforming the rhone than dams and gravel mining the major identified causes of river destabilisation in the world this calls for caution in the all too common and wholesale attribution of declining sediment budgets of european rivers

fluoride occurrence in publicly supplied drinking water in estonia a study was undertaken to examine the content and spatial distribution of fluoride in drinking water water samples 735 from public water systems covering all estonian territory were analysed using spadns method in order to specify the natural source of fluoride the chemistry data from five aquifer systems utilised for water supply were included into the study fluoride concentrations in tap water to a great extent ranged from 0 01 to 6 95 mg l drinking water in southern estonia where terrigenous middle devonian aquifer system is exploited has a fluoride concentration lower than recommended level 0 5 mg l thus promoting susceptibility to dental caries the western part of the country is supplied by water with excess fluoride content 1 5 6 9 mg l groundwater abstracted for drinking purposes originates from ordovician and silurian carbonate rocks the content of fluoride in silurian ordovician aquifer system is associated with the groundwater abstraction depth and the main controlling factors of dissolved fluoride are the ph value and the chemical type of water

scales and causes of heterogeneity in bars in a large multi channel river rio parana argentina to date published studies of alluvial bar architecture in large rivers have been restricted mostly to case studies of individual bars and single locations relatively little is known on how the depositional processes and sedimentary architecture of km scale bars vary within a multi km reach or over several 100s km downstream this study presents ground penetrating radar gpr and core data from 11 km scale bars from the rio parana argentina the investigated bars are located between 30 km upstream and 540 km downstream of the rio parana rio paraguay confluence where a significant volume of fine grained suspended sediment is introduced into the network bar scale cross stratified sets with lengths and widths up to 600 m and thicknesses up to 12 m enable the distinction of large river deposits from stacked deposits of smaller rivers but are only present in half the surface area of the bars up to 90 of bar scale sets are found on top of finer grained ripple laminated bar trough deposits bar scale sets make up as much as 58 of the volume of the deposits in small incipient mid channel bars but this proportion decreases significantly with increasing age and size of the bars contrary to what might be expected a significant proportion of the sedimentary structures found in the rio parana is similar in scale to those found in much smaller rivers in other words large river deposits are not always characterised by big structures that allow a simple interpretation of river scale however the large scale of the depositional units in big rivers causes small scale structures such as ripple sets to be grouped in thicker co sets which indicate river scale even when no obvious large scale sets are present the results also show that the composition of bars differs between the studied reaches upstream and downstream of the confluence with the rio paraguay relative to other controls on downstream fining the tributary input of fine grained suspended material from the rio paraguay causes a marked change in the composition of the bar deposits compared to the upstream reaches the sedimentary architecture of the downstream reaches in the top 5 m of mid channel bars shows i an increase in the abundance and thickness up to m scale of laterally extensive 100s of metres fine grained layers ii an increase in the percentage of deposits comprised of ripple sets to 40 in the upper bar deposits and iii an increase in bar trough deposits and a corresponding decrease in bar scale cross strata

a quantitative three dimensional depositional model of gravelly braided rivers a quantitative three dimensional depositional model of gravelly braided rivers has been developed based largely on the deposits of the sagavanirktok river in northern alaska these deposits were described using cores wireline logs trenches and ground penetrating radar profiles the origin of the deposits was inferred from observations of 1 channel and bar formation and migration and channel filling interpreted from aerial photographs 2 water flow during floods and 3 the topography and texture of the river bed at low flow stage this depositional model quantitatively represents the geometry of the different scales of strataset the spatial relationships among them and their sediment texture distribution porosity and permeability in the model are related to sediment texture the geometry of a particular type and scale of strataset is related to the geometry and migration of the bedform type e g ripples dunes bedload sheets bars associated with deposition of the strataset in particular the length to thickness ratio of stratasets is similar to the wavelength to height ratio of associated bedforms furthermore the wavelength and height of bedforms such as dunes and bars are related to channel depth and width therefore the thickness of a particular scale of strataset i e medium scale cross sets and large scale sets of inclined strata will vary with river dimensions these relationships between the dimensions of stratasets bedforms and channels mean that this depositional model can be applied to other gravelly fluvial deposits the depositional model can be used to interpret the origin of ancient gravelly fluvial deposits and to aid in the characterization of gravelly fluvial aquifers and hydrocarbon reservoirs

architecture of channel belt deposits in an aggrading shallow sandbed braided river the lower niobrara river northeast nebraska abstract architecture of recent channel belt deposits of the niobrara river northeast nebraska usa records the response of a sandy braided river to rapid base level rise up to 3 m of aggradation has occurred within the lower 14 km of the niobrara river since the mid 1950s as a result of base level rise at the confluence of the niobrara and missouri rivers aerial photographs and channel surveys indicate that the lower niobrara has evolved from a relatively deep stable channel with large bank attached braid bars to a relatively shallow aggrading channel with braid bars and smaller secondary channels architecture of channel belt deposits associated with the recent aggradation has been defined using ground penetrating radar gpr and vibracores the channel belt deposits exhibit a series of amalgamated channel fills and braid bar complexes i e macroforms radar facies identified in the gpr data represent architectural elements of the braid bar complexes large and small bedforms two dimensional 2 d and three dimensional 3 d dunes and channels individual braid bars appear to consist of basal high flow and upper low flow components preservation of the complete high flow bar geometry is generally incomplete due to frequent migration of smaller scale secondary channels within the channel belt i e braided channel network at low discharges the large scale stratification of the braid bar deposits is dominated by cross channel and upstream accretion elements of downstream accretion are also recognized these accretion geometries have not been documented previously in similar sandy braided rivers braid bar deposits with low flow modification e g incision by secondary channels are recognized in the deeper portions of the deposits imaged by gpr preservation of braid bars with both high and low flow components is a result of the rapid base level rise and channel bed aggradation experienced by the niobrara river over the past 45 years recent avulsion of the river channel allowed preservation of the upper low flow component of the braid bar deposits i e bar top sequences the relative abundance and stratigraphic position of the amalgamated channels and braid bar complexes within the channel belt deposits constitute a signature of the recent base level rise

changing river styles in response to weichselian climate changes in the vecht valley eastern netherlands abstract in the vecht valley eastern netherlands distinct changes in fluvial style and erosional phases took place from the middle part pleniglacial of the last glacial to the holocene a low energetic laterally inactive river changed around 41 ka into a higher energetic river accompanied by a distinct erosional phase even higher energetic conditions occurred during the late pleniglacial when a braided river was active fluvial activity diminished in the vecht valley towards the end of the late pleniglacial as aeolian processes became much more dominant the river became confined to a much more narrow flood plain where it incised at the onset of the late glacial deposits of two kinds of river types can be recognized in the late glacial low energetic probably meandering and braided the vecht became and remained meandering during the holocene the observed fluvial changes and erosional phases are most likely the result of climatically induced changes in the water sediment discharge ratio several distinct climate changes occurred since the middle pleniglacial some of them not all are reflected by changes in fluvial styles the response of vegetation to climate changes appears to be an important factor as it determined bank and soil stability and therefore sediment supply but also evapotranspiration rates which influenced discharge characteristics a model explaining the fluvial response to climate change is presented and discussed by the example from the vecht river incision took place at the onset of a cooler period when the discharge increased before the vegetation cover was destroyed incision also occurred as a response to warmer climate conditions but with a time lag depending on the time needed to establish a vegetation cover dense enough to decrease sediment supply and increase evapotranspiration rates

sharp crested breaking surface waves observed from a ship based stereo video system abstracta new ship based stereo video system is used to observe breaking ocean waves i e whitecaps as three dimensional surfaces evolving in time first the stereo video measurements of all waves breaking and nonbreaking are shown to compare well with statistical parameters from traditional buoy measurements next the breaking waves are detected based on the presence of whitecap foam and the geometry of these waves is investigated the stereo measurements show that the whitecaps are characterized by local extremes of surface slope though the larger scale crest to trough steepness of these waves is unremarkable examination of 103 breaking wave profiles further demonstrates the pronounced increase in the local wave steepness near the breaking crest as estimated using a hilbert transform these crests are found to closely resemble the sharp corner of the theoretical stokes limiting wave results suggest that nonlinear wave group dynamics are a key mechanism for breaking as the phase speed of th

changes in river regime after the construction of upstream reservoirs this article presents and analyses many years of investigations in china on the fluvial processes downstream of impounding and detention reservoirs the study covers the change in hydrograph the recovering of sediment concentration along the river course the degradation of stream bed the adjustment of longitudinal profile the coarsening of bed material the change in channel width and the trend of channel pattern variation for alluvial streams downstream of impounding reservoirs without confluence of major tributaries the degradation may extend to a great distance below the dam in the process of reducing the sediment carrying capacity of the flow to match the diminished sediment supply the coarsening of bed material is a factor of equal if not greater importance as compared with the flattening of channel gradient in places where the flow has not been sufficiently cut down and the bank is erosive non resistant a receding of banklines may take place in concurrence with the deepening of the river bed below detention reservoirs even if the total runoff and sediment supply remain essentially unchanged the modification of the hydrograph is sufficient to enhance the deterioration of the downstream channel

recent channel adjustments in alluvial rivers of tuscany central italy drastic channel adjustments have affected the main alluvial rivers of tuscany central italy during the 20th century bed level adjustments were identified both by comparing available topographic longitudinal profiles of different years and through field observations changes in channel width were investigated by comparing available aerial photographs 1954 and 1993 98 bed incision represents the dominant type of vertical adjustment and is generalized along all the fluvial systems investigated the arno river system is the most affected by bed level lowering up to 9 m whereas lower incision generally less than 2 m is observed along the rivers of the southern part of the region human disturbances appear to be the dominant factors of adjustments the main phase of vertical change occurred during the period 1945 80 in concomitance with the phase of maximum sediment mining activity at the regional scale the second dominant type of adjustment that involved most of the rivers in the region consists of a narrowing of the active channel based on measurements of channel width conducted on aerial photographs 38 of the reaches analysed experienced a narrowing greater than 50 of the initial channel width the largest values of channel narrowing were observed along initially braided or sinuous with alternate bars morphologies in the southern portion of the region a regional scheme of channel adjustments is derived based on initial channel morphology and on the amounts of incision and narrowing different styles of channel adjustments are described rivers that were originally sinuous with alternate bars to braided generally became adjusted by a moderate incision and a moderate to intense narrowing in contrast sinuous meandering channels mainly adjusted vertically with a minor amount of narrowing copyright 2003 john wiley sons ltd

channel changes due to river regulation the case of the piave river italy this paper deals with the channel changes of the piave river in the eastern alps italy which have occurred during this century in response to human interventions in the fluvial system the flow regime and the sediment supply of the river have been considerably altered by hydroelectric dams flow diversions and gravel mining in addition river dynamics have been affected by the construction of streambank protection structures to document these changes a historical analysis was performed using maps and aerial photographs morphological features that were examined included planform configuration channel width braiding index and bed elevation the results indicate that as a consequence of decreases in the flows and sediment supply remarkable channel changes have occurred in the river during this century especially during recent decades the channel has undergone a general narrowing with a decrease in average width to 35 per cent of its initial value while the braiding index has decreased from about 3 to 1 5 in several reaches the planform pattern has changed from braided to wandering the observed trends of channel change suggest that the river has not yet reached a new equilibrium condition and it may therefore be predicted that reductions in width and braiding intensity are likely to continue in the immediate future copyright 1999 john wiley sons ltd

medium and short term channel planform changes on the rivers tay and tummel scotland abstract channel planform change was analysed using a variety of data sources for the medium term 25 years and

dams and geomorphology research progress and future directions dams impose changes of flow and sediment transfer that drive changes of channel form along the downstream regulated river these changes have been described for more than 50 years but process form relationships have only been advanced with the establishment of a conceptual framework during the 1970s and then the extension of monitoring data and advancement of remote sensing technologies particularly over the past 20 years this paper reviews these developments and identifies three influential themes i channel dynamics ii the role of riparian vegetation and iii channel change as the driver of ecological change changes can be rapid in semi arid regions but elsewhere relaxation periods may extend to millenia in these latter cases regime or steady state models should be replaced by models of transient states applied to the reach scale in order to respond to the needs of river managers over decadal timescales

sedimentological effects and stratigraphic implications of a rare high stage flow in an evolving braided to anabranching stream with riparian woodland abstract low frequency 1 in 25 years high stage flows on the south platte and upper platte rivers in nebraska usa during september october 2013 produced sedimentary effects that are unaccounted for in depositional models of that fluvial system being superimposed on a historically recent trend of channel belt abandonment and encroachment of woody vegetation these outcomes are even more useful for comparison with the wider sedimentary record rooted vegetation particularly riparian trees played a major role in determining where erosion and sedimentation occurred outside of the main perennially flowing channels effects of the 2013 event include 1 small pebble to cobble sized gravel in various bar top and flood channel settings 2 common current or sediment shadows including streamlined sediment shadow bars several meters or more in length which formed downstream from rooted trees and logjams 3 sand lobes that prograded into densely wooded abandoned parts of the historical channel belt at angles of as much as 85 from average downstream flow 4 large scours some approaching 2 m in depth many of which formed behind trees near the diffluences of flood channels and the main channel 5 deposits of sand that were baffled by nonwoody or shrubby vegetation in the abandoned channel belt and 6 local accumulations of large woody debris in front of rooted trees as cross flood channel dams and rarely as walls alongside flood channels in an aggrading system these features should be preserved as a distinctive set of sedimentary structures which may be interpretable as evidence for episodic major flows in a system in which woody vegetation has encroached widely onto the channel belt

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

morphology and evolution of bars in a wandering gravel bed river lower fraser river british columbia canada a hierarchical typology for the channels and bars within aggradational wandering gravel bed rivers is developed from an examination of a 50 km reach of lower fraser river british columbia canada unit bars built by stacking of gravelly bedload sheets are the key dynamic element of the sediment transfer system linking sediment transport during individual freshets to the creation development and remoulding of compound bar platforms that have either a lateral or medial style primary and secondary unit bars are identified respectively as those that deliver sediment to compound bars from the principal channel and those that redistribute sediment across the compound bar via seasonal anabranches and smaller channels the record of bar accretion evident in ground penetrating radar sequences is consistent with the long term development of bar complexes derived from historical aerial photographs for two compound bars inter annual changes associated with individual sediment transport episodes are measured using detailed topographic surveys and longer term changes are quantified using sediment budgets derived for individual bars from periodic channel surveys annual sediment turnover on the bars is comparable with the bed material transfer rate along the channel indicating that relatively little bed material bypasses the bars bar construction and change are mainly accomplished by lateral accretion since the river has limited capacity to raise bed load onto higher surfaces styles of accretion and erosion and therefore the major bar form morphologies on fraser river are familiar and consistent with those in gravelly braided channels but the wandering style does exhibit some distinctive features for example 65 year histories reveal the potential for long sequences of uninterrupted accretion in relatively stable wandering rivers that are unlikely in braided rivers

bedform migration and bed load transport in some rivers and tidal environments reliable field data obtained by directly measuring bed load transport of fine to coarse grained bed material are extremely scarce mainly because of the difficulty of sampling accurately therefore the verification of bed load transport formulae is largely based on flume experiments which refer to unrealistic shallow water conditions in this study some bed load transport formulae were tested against data from natural environments as an alternative to ascertaining the bed load transport rate by sampling the bed load the transport rate was deduced from data on bedform height and bedform celerity for this purpose 43 sets of data from rivers representing a wide range of bed material bedform dimensions and hydraulic conditions were collected as were some sets of data from tidal settings two formulae were used for the prediction of the bed load transport the formula of van rijn 1981 and the kalinske 1947 formula as approximated by elzerman frijlink 1951 and in the present study slightly modified for application to tidal waters both the bed load function of van rijn and the modified formula of kalinske frijlink require data which are easily obtained and that can be measured accurately at those stages of the flow when bed load transport was high the van rijn function tended to overestimate that transport for flow stages when bed load transport was low the opposite was true the modified kalinske frijlink function gave consistently good results 86 of the transport rates predicted using the river data were within 0 5 2 0 times the values actually measured

the geomorphic effectiveness of a large flood on the rio grande in the big bend region insights on geomorphic controls and post flood geomorphic response abstract since the 1940s the rio grande in the big bend region has undergone long periods of channel narrowing which have been occasionally interrupted by rare large floods that widen the channel termed a channel reset the most recent channel reset occurred in 2008 following a 17 year period of extremely low stream flow and rapid channel narrowing flooding was caused by precipitation associated with the remnants of tropical depression lowell in the rio conchos watershed the largest tributary to the rio grande floodwaters approached 1500 m 3 s between a 13 and 15 year recurrence interval and breached levees inundated communities and flooded the alluvial valley of the rio grande the wetted width exceeding 2 5 km in some locations the 2008 flood had the 7th largest magnitude of record however conveyed the largest volume of water than any other flood because of the narrow pre flood channel conditions record flood stages occurred we used pre and post flood aerial photographs channel and floodplain surveys and 1 dimensional hydraulic models to quantify the magnitude of channel change investigate the controls of flood induced geomorphic changes and measure the post flood response of the widened channel these analyses show that geomorphic changes included channel widening meander migration avulsions extensive bar formation and vertical floodplain accretion reach averaged channel widening between 26 and 52 occurred but in some localities exceeded 500 the degree and style of channel response was related but not limited to three factors 1 bed load supply and transport 2 pre flood channel plan form and 3 rapid declines in specific stream power downstream of constrictions and areas of high channel bed slope the post flood channel response has consisted of channel contraction through the aggradation of the channel bed and the formation of fine grained benches inset within the widened channel margins the most significant post flood geomorphic changes have occurred at and downstream from ephemeral tributaries that contribute large volumes of sediment

dams on the mekong cumulative sediment starvation the mekong river largely undeveloped prior to 1990 is undergoing rapid dam construction seven dams are under construction on the mainstem in china and 133 proposed for the lower mekong river and tributaries we delineated nine distinct geomorphic regions for which we estimated sediment yields based on geomorphic characteristics tectonic history and the limited sediment transport data available we then applied the 3w model to calculate cumulative sediment trapping by these dams accounting for changing trap efficiency over time and multiple dams on a single river system under a definite future scenario of 38 dams built or under construction cumulative sediment reduction to the delta would be 51 under full build out of all planned dams cumulative sediment trapping will be 96 that is once in channel stored sediment is exhausted only 4 of the predam sediment load would be expected to reach the delta this scenario would have profound consequences on productivity of the river and persistence of the delta landform itself and suggests that strategies to pass sediment through around dams should be explored to prevent the consequences of downstream sediment starvation