flow pattern and sediment transport in a braided river the torrent de st pierre french alps summary in order to bring some understanding on the mountain stream dynamics we report measurements of flow and sediment transport leveled in a proglacial gravel bed river the torrent de st pierre in the french alps the river exhibits a modest discharge 3 s during most of the glacier melting season a braiding plain developed thanks to the occurrence of a massive landslide providing a small and simplified study area quite similar to recent experimental studies a mass balance was established at the outlet of the braiding plain our measurements indicate that in the range of flows measured the dominating transport mode is suspension though less important bed load transport is far from being negligible dissolved load eventually appears to be very small compared to solid transport analysis of velocity profile measurements shows that in this highly turbulent and shallow stream the use of a logarithmic form fails to recover the velocity profile and to estimate the shear velocity of the flow a uniform chezy like relationship is shown to be valid for the velocity with friction a coefficient considered as constant over the range of our measurements accordingly the only relevant velocity for transport description is the average velocity coupled measurements of bed load and velocity show that bed load transport is related to the average velocity through a power law eventually a correlation between bed load transport and suspended load transport is evidenced and discussed

turbidity and suspended sediment dynamics in small catchments in the nepal middle hills the himalayan environment has until recently been perceived to be in a critical state of environmental decline resulting from rapid population growth and associated land use change recent research however has emphasized the di culty of developing an objective appraisal of the state of the environment in a region where empirical data are scarce and unstructured and where an understanding of the spatial and temporal dynamics of natural environmental processes remains highly uncertain this paper presents results from an intensive three year project designed to help address the regional empirical de cit establish detailed baseline environmental data and to gain an insight into storm period and seasonal suspended sediment dynamics the instrumentation calibration and analysis of high frequency infrared turbidimetric records from a number of small subcatchments in the nepal middle hills are reported storm period and seasonal variation in turbidity and suspended sediment are examined and hysteresis patterns explored and explained a variety of methods to estimate seasonal suspended sediment yield in a mixed land use catchment are examined and found to vary by up to a factor of ve despite the inherent uncertainty all estimates of catchment sediment yield are found to be high with respect to erosion plot studies from the local area and this suggests the importance of riparian and channel erosion as major sediment sources a nding consistent with other regional studies copyright 1999 john wiley sons ltd

the effects of seasonal changes to in stream vegetation cover on patterns of flow and accumulation of sediment abstract in stream macrophytes are typically abundant in nutrient rich chalk streams during the spring and summer months and modify the in stream environment by altering river flows and trapping sediments we present results from an inter disciplinary study of two river reaches in the river frome catchment dorset uk the investigation focused on how ranunculus water crowfoot the dominant submerged macrophyte in the study reaches modified patterns of flow and sediment deposition measurements were taken on a monthly basis throughout 2003 to determine seasonal patterns in macrophyte cover associated changes in the distributions of flow velocities and the character and amount of accumulated fine sediment within stands of ranunculus maximum in stream cover of macrophytes exceeded 70 at both sites flow velocities were less than 0 1 m s 1 within the stands of ranunculus and accelerated to 0 8 m s 1 outside the stands during the early stages of the growth of ranunculus fine sediment mostly accumulated within the upstream section of the plant but the area of fine sediment accumulation extended into the downstream trailing section of the plant later in the growing season the fine sediment accumulations were dominated by sand 63 1000 m with silts and clays 0 37 63 m comprising

suspended sediment fluxes in a high arctic glacierised catchment implications for fluvial sediment storage suspended sediment fluxes from the 68 km2 finsterwalderbreen catchment in svalbard were monitored intensively during the 1999 and 2000 melt seasons at proximal and distal ends of a 4 2 km2 proglacial area which has been deglacierised during the twentieth century measured distal sediment fluxes correspond to total catchment denudation rates of 2700 710 t km 2 year 1 1999 and 1800 350 t km 2 year 1 2000 hourly net sediment flux time series distal flux minus proximal flux isolating change within the proglacial area itself reveal that the proglacial area serves as both a source and a sink of sediment during different periods of the melt season and that the majority of sediment evacuation from the area occurs during discrete episodes of enhanced meltwater discharge the mean net flux from the proglacial area itself was 690 230 t km 2 year 1 1999 and 3800 1700 t km 2 year 1 2000 therefore in 1999 there was a net increase in sediment storage in the proglacial area aggradation and in 2000 there was a net decrease denudation the pattern of sediment storage change appears to be driven by the runoff regime with net storage occurring during a year of relatively episodic sediment transport in which relative supply exhaustion occurs and net release in a year of more sustained sediment transport when relative supply exhaustion is absent many more years monitoring would be required for any trend to emerge from the large interannual variability in sediment yield

sediment transport and siltation of brown trout salmo trutta l spawning gravels in chalk streams deposition rates of fine sediment into brown trout spawning gravels were measured at monthly intervals for a period of one year in a small channel of the river test hampshire data were also collected on stream discharge water depth flow velocity and suspended sediment concentrations deposition rates followed a seasonal pattern and were maximal during periods of high discharge in the late winter early spring when suspended sediment concentrations were high the material deposited in the spawning gravels included silts and fine sands 250 m that were transported in suspension and coarser fragments of low density tufalike material that were transported as bed load the ecological implications of fine sediment deposition for salmonid egg survival in chalk streams are considered

recognition of santorini minoan tephra in lake sediments from golhisar golu southwest turkey by laser ablation icp ms laser ablation inductively coupled plasma mass spectrometry la icp ms has been applied to the analysis of fine grained volcanic ash shards separated from a tephra layer deposited by the mid second millenniumbc minoan eruption of santorini or thera in holocene lake sediments from golhisar golu a small intramontane lake in southwest turkey in this study we have used minor isotopes of two major elements routinely determined by epma in tephrochronological studies as the internal standard in la icp ms analyses these are30si and57fe for fully quantitative and single internal standard multi element calibration so called semi quantitative analysis respectively the results show that the determination of trace elements by la icp ms is a quick and accurate method typical accuracies are better than 20 and precision measured as the mean rsd relative standard deviation is better than 15 for most petrogenetically significant trace elements these levels of precision actually reflect within sample heterogeneity as repeat analyses on the homogenous nist 612 glass standard show that instrument precision is typically 5 for most elements the level of accuracy and precision obtained during this study is quite acceptable in tephrochronological studies and provides us with the confidence to proceed to the analysis of single glass shards by using a modified small spot laser ablation system

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

suspended sediment load during floods in a small stream of the dolomites northeastern italy abstract suspended sediment load was analyzed in a small high gradient stream of the eastern italian alps which was instrumented to measure discharge and sediment transport the ratio of suspended to total sediment yield and the relations between sediment concentration and water discharge were analyzed for seven floods which occurred from 1991 to 1996 in summer and autumn from june to october different patterns of hysteresis in the relation between suspended sediment and discharge were related to types and locations of active sediment sources the within storm variation of particle size of suspended sediment during a major flood indicates a coarsening of transported material for increasing discharge an analysis of grain size has shown that erosion areas on hillslopes were the main sources of suspended load

sediment concentration versus water discharge during single hydrologic events in rivers relations between sediment concentration c and water discharge q for a hydrologic event such as a flood are studied qualitatively by analyzing smoothed temporal graphs discharge and concentration vs time in terms of mode spread and skewness comparing cq ratios at a given discharge on the rising and falling limbs of the discharge hydrograph provides a consistent reliable method for categorizing c q relations five common classes of such relations are single valued straight or curved clockwise loop counterclockwise loop single valued plus a loop and figure eight temporal graph mode and skewness influence the type of relation whereas temporal graph spread affects the details of the particular c q relation its graphical breadth shape orientation and plotted location field examples of the various types of relations are given including varieties that heretofore have received little attention such as the figure eight explanations for each type of c q relation are discussed

establishing sediment budgets for two small lowland agricultural catchments in the uk sediment budgets have been established for two small 4 km2 lowland agricultural catchments by using 137cs measurements sediment source fingerprinting and more traditional monitoring techniques to quantify the individual components of the budget the gross and net erosion rates for the fields on the catchment slopes were estimated using 137cs measurements within selected fields which encompassed a representative range of slope angles slope lengths and land use these estimates were extrapolated over the entire catchment using a simple topographically driven soil erosion model terrain based gis tbgis superimposed on a dem to derive catchment average gross and net erosion rates suspended sediment yields were measured at the catchment outlets and sediment source fingerprinting techniques were used to establish the relative contributions from the catchment surface subsurface tile drains and eroding channel banks to the sediment yields in channel and wetland storage were quantified using both direct measurements and 137cs measurements the sediment budgets established for the catchments highlighted the importance of subsurface tile drains as a pathway for sediment transfer accounting for ca 60 and 30 of the sediment output from the two catchments erosion from channel banks contributed ca 10 and 6 of the sediment output from the two catchments although the suspended sediment yields from these catchments were considered high by uk standards ca 90 t km 2 year 1 the sediment delivery ratios ranged between 14 and 27 indicating that a major proportion of the mobilised sediment was stored within the catchments in field and field to channel storage were shown to be of similar magnitude but storage of sediment in the channel system and associated wetlands was relatively small representing 5 of the annual suspended sediment yield

erosion thresholds and suspended sediment yields waipaoa river basin new zealand characteristics of the suspended sediment load in the waipaoa river new zealand and in two of its tributaries mangatu and te arai rivers are examined for evidence of different dominant erosion processes in the basins upstream different shapes of the suspended sediment concentration water discharge relations lead to differences in long term average yield event yield magnitude frequency relations and relative importance of large flows and rare events in the mangatu river frequent runoff events 2 1 are relatively more important to the long term yield 11 540 t km yr half of the long term average load is transported by events with return periods less than 1 year and there is little evidence of an erosion threshold limitation on sediment supply this is consistent with the predominance in the mangatu basin of hillslope erosion processes that involve scour by surface and channelized runoff particularly gully erosion this contrasts with the te arai river where sediment concentration tends to be much lower at low and moderate flows frequent runoff events transport less of the long term yield 4600 t km 2 yr than do rarer large magnitude flood events event sediment yields are an order of magnitude lower during events with subannual return periods and half of the long term average load is transported during events with a return period of 2 years some of these characteristics appear to result in part from two populations of runoff events in the te arai basin nonetheless they are consistent with field evidence that most of the sediment supplied to the te arai stream network is generated by shallow landslides which are activated once a rainfall threshold is exceeded

establishing fine grained sediment budgets for the pang and lambourn locar catchments uk summary an integrated approach to data collection combining the use of 137cs measurements sediment source fingerprinting bed sediment surveys and conventional river monitoring has been successfully employed to establish the fine grained sediment budgets of two lowland groundwater fed catchments in the uk gross surface erosion is higher on cultivated land pang 55 263 t yr 1 or 507 t km 2 yr 1 lambourn 79 997 t yr 1 or 437 t km 2 yr 1 than on pasture pang 1960 t yr 1 or 140 t km 2 yr 1 lambourn 1425 t yr 1 or 95 t km 2 yr 1 in both study areas and a substantial proportion of the mobilized sediment is sequestered within the fields pang 28 058 t yr 1 or 228 t km 2 yr 1 lambourn 55 575 t yr 1 or 281 t km 2 yr 1 and between the individual fields and the river channel network pang 28 672 t yr 1 or 233 t km 2 yr 1 lambourn 24 782 t yr 1 or 125 t km 2 yr 1 the sediment contribution from banks and subsurface sources is relatively low and typically ca 5 t yr 1 in the pang and ca 11 t yr 1 in the lambourn representing only about 1 of the suspended sediment output from each study catchment the mean level of fine grained sediment storage in the main channel system is equivalent to 38 pang and 21 lambourn of the respective mean annual suspended sediment yields of the two catchments the estimated sediment delivery ratio for both study catchments is ca 1

erosion quantification in the small marly experimental catchments of draix alpes de haute provence france calibration of the etc rainfall runoff erosion model abstract erosion rates measured for 15 years in the small ranging from 0 13 ha to nearly 1 km2 and steep 30 75 mountainous marly basins of draix south alps france are over 100 tons ha year in a badland area devoid of vegetation in a similar basin reforested at the end of the 19th century the sediment yield is considerably reduced less than 3 tons ha year the analysis of the sediment yield of these torrents reveals the importance of the erosion processes on slopes at the scale of the elementary gully and the influence of deposition transport and scouring processes as soon as the channel network of the basin is developed these processes were modelled by a hydrosedimentologic model developed by cemagref for flood torrent erosion and called etc etc is an integrated spatialized and global model working at the event scale the rainfall runoff component and the solid transport component which involves scouring deposition and armouring are well developed on the other hand the erosion component is not yet a physically based model as the knowledge on the elementary processes is not enough quantitative the etc model was used on a badland basin of 86 ha in area the laval and has shown its ability to simulate both water and sediment flows in mountainous and steep basins the erosion modelling highlighted the need for a better representation of the slope processes and for more information on the storing of sediments in the channel network observations carried out on the influence of the vegetation cover patterns and the links between slopes and channels should be taken into account to improve the model

macrophytes and suspension feeding invertebrates modify flows and fine sediments in the frome and piddle catchments dorset uk summary this research investigated the ecosystem engineering by in stream macrophytes dominated by ranunculus spp and associated suspension feeding blackfly larvae diptera simuliidae for five reaches in the frome and piddle catchments dorset uk over one annual growth cycle 2003 this paper focuses on the modification of flow velocities and the trapping of fine sediment particles in stream macrophyte growth was extensive with maximum percentage cover of 80 recorded in september and october 2003 the macrophyte cover significantly altered flow patterns and flow velocities within and between the macrophyte stands the reduced flow velocities within the plants promoted sediment trapping reaching volumes of 0 085 m3 of fine sediment trapped per metre square of vegetation at one site the effective particle sizes of the sediments trapped within ranunculus stands were dominated by the 250 500 m fraction from march to july 2003 whereas a higher proportion of smaller fractions occurred from october to december faecal pellets were highly abundant in the sediments trapped within ranunculus stands up to 2 2 108 faecal pellets per m2 and their dimensions total size range 25 400 m fall within the dominant size fraction of the trapped sediments our findings demonstrate the need to consider the biogenic component of the fine sediments in chalk streams in future studies of sediment and nutrient dynamics

interplay of stream subsurface exchange clay particle deposition and streambed evolution 1 hyporheic exchange mixing of stream water with pore water beneath the stream is responsible for the transport of many ecologically relevant substances across the stream subsurface interface this process is dependent on both the streamflow conditions and sedimentary properties but the complex nature of fluvial systems has presented a barrier to the development of mechanistic understanding of the dynamics of stream subsurface interactions this work presents the results of a controlled study to examine in detail the relationship between stream subsurface exchange fluxes delivery of suspended sediments to the hyporheic region fine particle accumulation in the streambed and alteration of sedimentary properties laboratory flume experiments were used to observe kaolinite clay deposition in a sand bed and the resulting alteration of hyporheic exchange fluxes solute and suspended sediment exchange with clean sand beds is predicted well by a fundamental model for bed form driven advective pumping exchange however substantial accumulation of clay in the bed causes an alteration of the pore water flow environment which reduces both water flux across the stream subsurface interface and subsequent particle deposition measurement of bulk solute exchange and direct observation of clay accumulation in the bed both indicate that transported fine particles are preferentially removed near the stream subsurface interface clogging of inflow regions produces heterogeneous subsurface clay deposits even when the bed is initially homogeneous this behavior is also predicted by the fundamental colloid pumping model these results contradict the accepted view that suspended sediments will generally deposit in the deepest regions of the bed and thus clog the bed from the bottom upward our results indicate that clogging of the streambed surface will often isolate deeper regions of the bed from the streamflow so that even relatively low amounts of suspended sediments can substantially degrade streambed habitat

assessment of intermediate fine sediment storage in a braided river reach southern french prealps this paper presents a field investigation on river channel storage of fine sediments in an unglaciated braided river the bes river located in a mountainous region in the southern french prealps braided rivers transport a very large quantity of bedload and suspended sediment load because they are generally located in the vicinity of highly erosive hillslopes consequently these rivers play an important role because they supply and control the sediment load of the entire downstream fluvial network field measurements and aerial photograph analyses were considered together to evaluate the variability of fine sediment quantity stored in a 2 5 km long river reach this study found very large quantities of fine sediment stored in this reach 1100 t per unit depth 1 dm given that this reach accounts for 17 of the braided channel surface area of the river basin the quantities of fine sediment stored in the river network were found to be approximately 80 of the mean annual suspended sediment yields ssys 66 200 t year 1 comparable to the ssys at the flood event scale from 1000 t to 12 000 t depending on the flood event magnitude these results could explain the clockwise hysteretic relationships between suspended sediment concentrations and discharges for 80 of floods this pattern is associated with the rapid availability of the fine sediments stored in the river channel this study shows the need to focus on not only the mechanisms of fine sediment production from hillslope erosion but also the spatiotemporal dynamics of fine sediment transfer in braided rivers copyright 2010 john wiley sons ltd

interactions of phosphorus with sediments in the river swale yorkshire uk the ultimate fate of inorganic phosphorus in natural waters is to a large degree determined by interactions with sediments the interactions in river bed sediments have been investigated by a combination of methods using surface sediments 2 mm in diameter collected from a 55 km stretch of the river swale in yorkshire uk the sediments were analysed by digestion fe ca and p clay mineralogy and their equilibrium phosphate concentration all the equilibrium phosphate concentrations were below 2 mol dm 3 which is much less than the concentration in the overlying water and indicates a net uptake of phosphorus by the sediments experiments in a fluvarium channel with a coarse sediment also showed that the release and uptake of soluble phosphorus was towards a steady state concentration in the overlying solution consistent with measurements of the equilibrium phosphate concentration a kinetic model describing the net uptake of soluble reactive phosphorus by river sediments was applied to chemical data collected during an intensive monitoring exercise in the catchment copyright 1999 john wiley sons ltd

the importance of high resolution monitoring in erosion and deposition dynamics studies examples from estuarine and fluvial systems abstract erosion and deposition processes lie at the centre of geomorphological explanation but progress in understanding has been limited by a lack of appropriate high resolution monitoring methodologies which permit detection of erosion and deposition dynamics this paper presents a case for monitoring erosion and deposition at high temporal resolutions and uses hypothetical approaches supported by example erosion and deposition events and analyses drawn from estuarine and fluvial systems the paper first presents testable hypotheses to demonstrate the complexity of possible event combinations sequences and juxtapositions for the erosion driving forces which underpin the need for high resolution monitoring second it summarises recent improvements to the photo electronic erosion pin peep automatic erosion and deposition monitoring system including the novel concept of thermal consonance timing tct which is particularly promising because it helps to define the timing of nocturnal events and through the entire hydrograph third example results are discussed from high resolution monitoring of bank erosion at a tidal site at burringham on the river trent in northern england tidal banks are revealed to be much more dynamic than previous conventional monitoring has indicated a key result is that because the high resolution approach allows erosional and depositional activity to be assigned to specific periods of tidal inundation it becomes possible for the first time routinely to produce event based erosion 36 mm h 1 and deposition rates 4 5 and 8 4 mm h 1 such rate determinations are potentially very useful in the field validation of sedimentological and geomorphological models including grain settling and resuspension theory fourth through a longer term of aggregated daily data a striking 2 week cycle of deposition and erosion emerges which correlates most strongly with spring neap tidal cycling but is moderated by wind stress effects sediment was deposited on the bank relatively quickly over 4 5 days but then removed by erosion rather slowly over 9 10 days fifth the dangers of low resolution monitoring are illustrated by comparing the daily peep data set with a series resampled at a lower 14 day frequency to simulate the information generated by conventional resurvey methodologies the low frequency series failed adequately to represent the cyclicity mean range variability and trend of bank elevation changes and without this dynamics information rate and process definition is very difficult largely because of self concealing activity sixth a useful advance is illustrated by the fluvial erosion sequence for the river wharfe n england this shows how tct can generate rare and important results with the definition of the precise time of an erosion event within the hydrograph bank retreat here occurred very quickly after initial inundation and within 4 h of the flow peak information which can be used to define thresholds for entrainment e g critical shear stresses such high resolution monitoring helps to unravel some of the erosional effects of complex sequences combinations and juxtapositions of similar or different forcing events finally high resolution approaches have been adopted worldwide for fluvial estuarine mudflat and canal systems but considerable potential exists for their development and use in these and other contexts e g gully hillslope beach and dune environments to improve understanding and modelling of geomorphological processes more widely

input and output mass flux correlations in an experimental braided stream implications on the dynamics of bed load transport through the development of a model experiment it is shown that there exists a correlation between input and output sediment fluxes in a micro scale braided stream that remains valid regardless of the stability of the braided river this correlation has some important consequences on the mechanics of bed load transport by braided rivers it enables the definition of both a dimensionless stream power and a dimensionless transport efficiency these dimensionless variables in turn permit the definition of a braided river stability criterion with regard to bed load transport the existence of such a correlation also suggests that the average critical shear stress or slope of motion may depend on the flux of mass input to the system using these findings together with a one dimensional exner equation for the conservation of mass a kinematic wave equation for the average evolution of the riverbed is eventually derived and its significance analyzed

deposition and storage of fine grained sediment within the main channel system of the river tweed scotland thispaperassessestheimportanceofdepositionandstorageoffine grained c 150m sedimentonthefloodplainsand bedsofthemain non tidal channelsoftherivertweed 4390km 2 scotland andtwoofitstributaries riverteviotand ettrick water caesium 137 analysis of floodplain sediment cores has been used to estimate average rates of overbank sedimentation during the last 30 to 40 years average values for individual transects ranged from 016 to 218 kg m 2 a 1 013to2 2m ma 1 themeanforthe10transectsinvestigatedwas129kgm 2 a 1 1 3m ma 1 thetotalamountoffine sediment deposited was estimated to be about 44 000 t a 1 the fine grained sediment stored in the channel bed was quantifiedusingresuspensiontechniques averagevaluesforindividualsitesrangedfrom012to096kgm 2 themeanfor the10sitesinvestigatedwas056kgm 2 thetotalamountofsedimentstoredonthechannelbedofthemainchannelsystem at the time of sampling was estimated to be about 4300 t comparison of these estimates of floodplain and channel storage with the estimated suspended sediment loadfor the river tweed at the downstream gauging site atnorham indicates that floodplainsedimentationandchannelbedstoragerepresentabout40and4percent respectively oftheannualloadoffine sedimentdeliveredtothemainchannelsystem erosionofchannelbankswillreintroducetheequivalentofabout30percent of the floodplain deposited sediment back into the channel the residence time of the fine grained sediment stored on the channel bed is probably less than one year but that of sediment deposited on the floodplain is likely to be considerably longer conveyance losses associated with overbank deposition have important implications for the routing of sediment throughfluvialsystemsandtheinterpretationofdownstreamsedimentyields copyright 1999johnwiley sons ltd

source storage and mobilisation of fine sediment in a chalk stream system concern for sediment problems in the upper river piddle dorset including accumulation of fine sediment on the channel bed and elevated turbidity levels during periods of stable flow provided the stimulus for a detailed field investigation of the sediment dynamics of this chalk stream system undertaken during the period november 1991 to april 1993 two monitoring stations were established at south farm piddletrenthide and lawrence mede piddlehinton and estimates of suspended sediment load were obtained for these two sites in addition suspended sediment concentrations and bed sediment loadings were regularly sampled at several other sites sediment traps were deployed at ten representative sites along the river channel field observations of sediment sources and pathways were made during storm events and a sediment source fingerprinting study was undertaken estimates of annual suspended sediment yield provided values of 9 12 t km 2 year 1 which must be seen as low by uk standards elevated suspended sediment concentrations were not restricted to storm events but occurred throughout the monitoring period in response to remobilisation of sediment stored in the channel the evidence provided by the sediment loads recorded at the two monitoring stations by the sediment traps and by the measurements of bed sediment loading indicated that substantial amounts of sediment accumulated in the channel of the upper and middle reaches of the river during the winter months and that this slug of sediment was slowly transmitted downstream during the following summer fingerprinting of the transported sediment and of potential sources indicated that the dominant source of suspended sediment was likely to be surface soil from cultivated areas field reconnaissance surveys undertaken during storm events indicated that substantial inputs of surface runoff and suspended sediment entered the stream much of this sediment is however stored within the channel system and slowly transmitted downstream copyright 1999 john wiley sons ltd

a freeze sampling technique suitable for coarse river bed material abstract a freeze sampling technique is described that has proven successful in sampling coarse stream bed gravels under flowing water the utility of the technique is demonstrated with examples of grain size characteristics and void ratios of deposits

floodplain stages in the braided ngaruroro river new zealand this study investigates floodplain deposits in the braided ngaruroro river new zealand to characterize and quantify the spatial extent of deposits at different stages of development using a sequence of aerial photography depositional surfaces were mapped and then assigned a floodplain development stage based on age the discharge causing inundation and field observations of sediment and vegetation characteristics the ensemble of floodplain deposits makes up 40 of the river valley the remainder being the active river bed stabilizing bars and mature floodplains dominate the floodplain ensemble while the existence of stabilizing bars points to a recent shift or fluctuation in controlling conditions the extent and location of mature units suggest an earlier change in hydrologic and sediment supply conditions that limited braidtrain mobility mosaics of different aged deposits range from simple two stage mosaics to more complex arrangements of three and four stages in the rapid evolution from stabilized bars to mature floodplains a large amount of fine grained sediment is stored in the ngaruroro river valley highlighting the possibility of finding extensive fine grained facies in the ancient sedimentary record of braided systems understanding floodplain ensembles and their controls will contribute to effective restoration of braided rivers

groundwater management and coal bed methane development in the powder river basin of montana summary coal bed methane cbm development will eventually pump more than 124 000 ha m of groundwater or more than 40 of the recharge from the coal seam and sandstone aquifers of the montana portion of the powder river basin prb this will relieve the hydrostatic pressure by causing a drawdown in the potentiometric surface and drawing groundwater from storage and natural discharges to release the methane gas a numerical groundwater flow model simulated drawdown that will exceed 90 m in the middle of the cbm fields with 6 m drawdown extending up to 29 km from the fields simulation results indicate that river flux will decrease up to 40 and drawdown will encompass hundreds of wells and springs recovery requires up to 45 years for significant decreases in river flux to recover and is not complete for 200 years cbm development impacts can be mitigated in two ways first reinjecting produced water into depleted coal seams would replenish the lost storage so that recovery would draw less groundwater from long distances second rapid infiltration basins near potentially affected rivers could decrease the short term river flow depletion modeled artificial recharge replaced up to 4000 ha m of deficit in the depleted coal seams and is a feasible option for mitigating some effects of cbm development reinjection would be more effective if the development period were lengthened