valley scale morphology drives differences in fluvial sediment budgets and incision rates during contrasting flow regimes abstract high resolution topographic surveys using lidar and multibeam sonar can be used to characterize and quantify fluvial change this study used repeat surveys to explore how topographic change fluvial processes sediment budgets and aggradation and incision rates vary across spatial scales and across two contrasting decadal flow regimes in a regulated gravel cobble river a novel method for quantifying digital elevation model uncertainty was developed and applied to a topographic change detection analysis from 2006 2008 to 2014 during this period which had four modest 3 5 year floods most sediment was laterally redistributed through bank erosion and channel migration erosion primarily occurred in the floodplain 97 000 m 3 terraces 80 000 m 3 and lateral bars 58 000 m 3 while deposition occurred in the adjacent pools 73 000 m 3 fast glides 48 000 m 3 and runs 36 000 m 3 in contrast significantly higher magnitude and longer duration floods from 1999 to 2006 2008 caused sediment to be displaced longitudinally with the upstream reaches exporting sediment and the downstream reaches aggrading the river maintained floodplain connectivity during both periods despite different processes dominating the type of connectivity larger floods promoted overbank scour and avulsion while smaller floods promoted bank erosion and lateral migration this study explores and illustrates how the geomorphic response to contrasting flood regimes in a nonuniform river is highly dependent on which landforms are controlling hydraulics

reenvisioning velocity reversal as a diversity of hydraulic patch behaviours past research investigated the surpassing of mean velocity at riffle cross sections by that at pool cross sections for flows up to bankfull termed velocity reversals to understand one mechanism by which riffle pool relief is maintained this study reenvisioned the classic velocity reversal by documenting stage dependent changes to the locations of peak velocity without cross sections instead the dynamics of peak velocity patches were considered for flows spanning 0 2 to 22 times bankfull discharge through the use of a high resolution dem and two dimensional hydrodynamic modelling a remarkable diversity in peak velocity patch behaviour was found across discharges including gradual expansion and shifting as well as abrupt disappearance and emergence relative to the low flow patch locations these behaviours blended together to varying degrees to produce many reversals in peak velocity across morphological units but it took substantially higher than bankfull discharge for peak velocities to move from riffles and chutes to fast glides and pools the discharges at which reversals occurred among morphological units were significantly higher for the valley confined reach than for the anastomosing reach copyright 2016 john wiley sons ltd

the last glacial maximum and late glacial environmental and climate dynamics in the baikal region inferred from an oxygen isotope record of lacustrine diatom silica abstract the last glacial maximum and late glacial environmental and climatic variability in the baikal region southern siberia russia has been studied in a sediment sequence from lake kotokel located 2 km east of lake baikal using the oxygen isotope composition of diatom silica 18 o diatom the purification of diatom frustules involved the process of trimethylsilylation which has been shown to be suitable for preparation of diatoms for oxygen isotope analysis the lake kotokel 18 o diatom record presented here spans intervals from about 24 6 to 22 9 ka bp further referred to as last glacial maximum and 16 7 11 5 ka bp further referred to as late glacial displaying variations in the oxygen isotope composition between 26 7 and 31 2 overall high 18 o diatom values of about 29 to 31 during the two investigated intervals characterize a strongly evaporative lake system in a dry environment and suggest a lower than present lake level due to enhanced evaporation the lake kotokel diatom isotope record is roughly in line with the 60 n summer solar insolation pointing to a linkage to broader scale climate change but displays weaker reaction to short term climatic oscillations i e bolling allerod or younger dryas the climate warming at 14 3 ka bp is marked by negative spikes in the 18 o diatom record due to isotopically low melt water input from the mountainous hinterland

3d float tracking in situ floodplain roughness estimation this paper presents a novel technique to quantify in situ hydrodynamic roughness of submerged floodplain vegetation 3d float tracking this method uses a custom built floating tripod that is released on the inundated floodplain and tracked from shore by a robotic total station simultaneously an acoustic doppler current profiler adcp collects flow velocity profiles and water depth data roughness values are derived from two methods based on 1 run averaged values of water depth slope and flow velocity to compute the roughness based on the chezy equation assuming uniform flow 2 the equation for one dimensional free surface flow in a moving window a sensitivity analysis using synthetic data proved that the median value of the roughness derived using method 2 is independent of 1 the noise in water levels up to 9 mm 2 bottom surface slope and 3 topographic undulations the window size should be at least 40 m for a typical lowland river setup field measurements were carried out on two floodplain sections with an average vegetation height of 0 030 arnhem and 0 043 m dreumel method 1 resulted in a nikuradse roughness length of 0 08 m for both locations method 2 gave 0 12 m for arnhem and 0 19 m for dreumel in arnhem a spatial pattern of roughness values was present which might be related to fractional vegetation cover or vegetation density during the flood peak 3d float tracking proved a flexible and detailed method for roughness determination in the absence of waves and provided an unrestricted view from shore copyright 2008 john wiley sons ltd

overland flow and infiltration modelling for small plots during unsteady rain numerical results versus observed values this paper reports the development and application of a two dimensional model based on an explicit finite difference scheme coupling overland flow and infiltration processes for natural hillslopes represented by topographic elevation and soil hydraulics parameters this model allows modelling of hortonian overland flow and infiltration during complex rainfall events original procedures have been developed in order to simulate complex rainfall events on natural slopes the accuracy of the results is tested by comparison with experimental field data on the basis of calibrated soil and surface friction parameters good agreement between the calculated result and the measured data was found the scheme proposed was found to be appropriate the results of tests presented illustrate the effect of microtopography on the distribution of the flow depths the magnitude and direction of flow velocities and infiltration depths

thermal springs in lake baikal pore waters extracted from sediment cores were analyzed for their oxygen and hydrogen isotopic compositions and major ion chemistry to determine the source of water from a vent area for diffuse lake bottom thermal springs or seeps in frolikha bay northeastern lake baikal the delta sup 18 o values of pore waters range from minus 15 2 per thousand to minus 16 7 per thousand and delta d values range from minus 119 per thousand to minus 126 per thousand both isotopes determined relative to standard mean ocean water smow bottom water in lake baikal has a delta sup 18 o value of minus 5 6 per thousand and a delta d values of minus 120 per thousand pore waters in the vent area are significantly enriched in mg k ca and especially na and have the lowest delta d and delta sup 18 o values these pore waters are isotopically and chemically distinct from pore waters in other more typical parts of the lake the pore water isotopic data fall on a local meteoric water line and covariations in water isotopes and chemistry are not consistent with evaporation or hydrothermal water rock interaction the thermal springs represent discharging meteoric waters that have been gently heated during subsurface circulation and are largely unaltered isotopically chemical variations are most likely due to dissolution of subsurface evaporites

valley width variation influences riffle pool location and persistence on a rapidly incising gravel bed river abstract decades of research have demonstrated that gravel bed rivers exhibit multiple spatial scales of landform nonuniformity landform features such as valley wall oscillations alluvial fans terraces river meanders point bars boulder clusters and logjams contribute to river corridor heterogeneity further studies have shown that the locations of riffles and pools in gravel bed rivers are closely associated with the spatial pattern of river corridor morphological variability these studies imply but do not directly test that persistence of riffles and pools through time is also conditioned by landform variability mechanistically it may be hypothesized that overbank flows interact hydraulically with oscillating valley walls by way of a mechanism known as flow convergence routing in such circumstances can variation in valley width influence channel morphology forcing riffle pool location and persistence to address this question research was performed on a valley confined wandering gravel bed reach of the regulated lower yuba river california usa that is incising from reduced sediment supply and flow regulation after a historic period of mining related valley sedimentation this study quantified stream planform change 1984 2006 and elevation change 1999 2006 using eight aerial photo sets and two digital elevation models and it qualitatively assessed channel change in older aerial photos going back to 1937 analysis revealed that the river has undergone rapid incision 0 11 m year and planform change in response to frequent floods yet eight riffles persisted in the same locations which coincided with the locally wide areas of the valley longitudinal profiles revealed that deep pools were associated with long valley constrictions geomorphic analysis and design need to explicitly account for multiple scales of landform nonuniformity in order to rehabilitate natural fluvial processes

flood driven topographic changes in a gravel cobble river over segment reach and morphological unit scales regulated rivers generally incise below dams that cut off sediment supply but how that happens and what the consequences are at different spatial scales is poorly understood modern topographic mapping at meter scale resolution now enables investigation of the details of spatial processes in this study spatial segregation was applied to a meter scale raster map of topographic change from 1999 to 2008 on the gravel cobble regulated lower yuba river in california to answer specific scientific questions about how a decadal hydrograph that included a flood peak of 22 times bankfull discharge affected the river at segment reach and morphological unit scales the results show that the river preferentially eroded sediment from floodplains compared to the channel and this not only promoted valley wide sediment evacuation but also facilitated the renewal and differentiation of morphological units especially in the channel at the reach scale area of fill and mean net rate of elevational change were directly correlated with better connectivity between the channel and floodplain while the mean rate of scour in scour areas was influenced by the ratio of slope to bankfull froude number a ratio indicative of lateral migration versus vertical downcutting hierarchical segregation of topographic change rasters proved useful for understanding multiscalar geomorphic dynamics this article is protected by copyright all rights reserved

reconstructing hydrological variability in lake baikal during mis 11 an application of oxygen isotope analysis of diatom silica in this paper we reconstruct hydrological variability in lake baikal during marine isotope stage 11 mis 11 427 362 ka bp from oxygen isotope analysis of diatom silica highest d 18 odiatom values are found during mis 11 3 highlighting the dominance of hydrological input from rivers flowing into the south and central basins of lake baikal especially the selenga river hydrological input from south basin rivers dominated for over 30 ka however there is evidence from both biogenic silica and d 18 odiatom records for an abrupt cooling event at ca 390 ka bp stadial conditions at this time are coincident with an iceberg discharge event into the north atlantic the decline in d 18 odiatom values suggests increasing proportion of hydrological input from rivers to the north of lake baikal due to greater influence of winter precipitation and snow melt after a period of interstadial conditions during the early stages of mis 11 1 biogenic silica and d 18 odiatom values decline mirroring the slow growth in northern hemisphere ice sheets despite rigorous cleaning procedures palaeoclimatic inferences need to be treated with caution due to contamination of the d 18 odiatom record during stadial and glacial periods contamination of the d 18 odiatom record is even more significant natural environment research council nerc copyright 2008 reproduced with the permission of nerc published by john wiley sons ltd

a mixing layer theory for flow resistance in shallow streams 1 a variety of surface roughness characterizations have emerged from nineteenth and twentieth century studies of channel hydraulics when the water depth h is much larger than the characteristic roughness height ks roughness formulations such as manning s n and the friction factor f can be explicitly related to the momentum roughness height zo in the log law formulation for turbulent boundary layers thereby unifying roughness definitions for a given surface however when h is comparable to or even smaller than ks the log law need not be valid using a newly proposed mixing layer analogy for the inflectional velocity profile within and just above the roughness layer a model for the flow resistance in shallow flows is developed the key model parameter is the characteristic length scale describing the depth of the kelvin helmholtz wave instability it is shown that the new theory originally developed for canopy turbulence recovers much of the earlier roughness results for flume experiments and shallow gravel streams this study is the first to provide such a unifying framework between canopy atmospheric turbulence and shallow gravel stream roughness characterization the broader implication of this study is to support the merger of a wealth of surface roughness characterizations independently developed in nineteenth and twentieth century hydraulics and atmospheric sciences and to establish a connection between roughness formulations across traditionally distinct boundary layer types

gis based simulation of erosion and deposition patterns in an agricultural landscape a comparison of model results with soil map information abstract this paper presents a relatively simple two dimensional hillslope erosion deposition model the model differs from most geomorphological models in that it does not assume that erosion by surface wash is always transport limited as a first test the model is applied to an agricultural catchment in central belgium here patterns of past erosion and deposition can be deduced from information contained in the belgian soil map so that a qualitative validation of the model results is possible the results indicate that a simple model formulation allows to reproduce the basic pattern of erosion and deposition as it is observed in the landscape this confirms the major influence of topography on erosion and deposition patterns in such landscapes and indicates that in some cases a simple model formulation may well be sufficient to allow adequate modelling of landscape evolution

modeling overland flow and soil erosion on nonuniform hillslopes a finite volume scheme 1 this paper presents a finite volume scheme for coupling the saint venant equations with the multiparticle size class hairsine rose soil erosion model a well balanced monotone upstream centered schemes for conservation laws hancock muscl hancock method is proposed to minimize spurious waves in the solution arising from an imbalance between the flux gradient and the source terms in the momentum equation additional criteria for numerical stability when dealing with very shallow flows and wet dry fronts are highlighted numerical tests show that the scheme performs well in terms of accuracy and robustness for both the water and sediment transport equations the proposed scheme facilitates the application of the hairsine rose model to complex scenarios of soil erosion with concurrent interacting erosion processes over a nonuniform topography

the paleoclimatology of lake baikal a diatom synthesis and prospectus abstract the paleoclimatic archive held in lake baikal sediments is of significant importance given the lake s position in one of the world s most continental regions where there are few continuous high quality records spanning the quaternary here i review diatom and associated biogenic silica records from lake baikal sediments and provide a paleoclimatic synthesis of changes at various timescales over the quaternary i initially highlight major climatic and hydrological aspects of lake baikal as understanding the contemporary system both regionally and within the lake are fundamental to understanding past change interpreted from the sedimentary archive in this respect special attention is given to factors that can affect the integrity of the diatom record most notably dissolution processes these mechanisms are likely to have had a relatively greater impact on the preservation of diatom valves during glacial periods because of overall lower diatom productivity lower diatom numbers and relative increased dissolution during cold periods explains the lack of diatoms and low biogenic silica concentrations found in the lake sediments during glacial periods the biogenic record highlights the nature of the 100 ka cycle especially during the last 800 ka although there is also a strong precessional component further work is needed to reassess biological responses in lake baikal with respect to different orbital forcing mechanisms together with their impacts on evolution and speciation of diatoms the biological record from lake baikal confirms that the last interglacial in central asia lasted approximately 10 5 ka productivity in the lake as inferred from diatom biovolume accumulation rates exhibits millennial scale variability with the occurrence of centennial scale reductions in diatom biomass throughout the last interglacial period the most severe reduction in diatom biomass at c 120 ka bp is concurrent with millennial scale cooling in the north atlantic region links to changes in north atlantic ocean thermohaline circulation via teleconnections are also evident in the nature of the abrupt ecological changes in the lake throughout the last 60 ka linked to ice rafting into the north atlantic otherwise known as heinrich events new robust radiocarbon chronologies for sediments deposited during the late glacial and holocene in lake baikal allow detailed multi decadal records to be constructed for the last 14 000 years cooling events associated with millennial scale cycles are also apparent in the lake baikal record and both the diatom record and oxygen isotope record of the diatom silica highlight that biological responses to these abrupt events are almost simultaneous comparisons made between lake baikal records with others worldwide highlights that many of the holocene cooling events are associated with melt water outburst from the laurentide ice sheet and changes in solar insolation during the last 1000 years snow cover on lake baikal has been inferred from past diatom assemblages and is closely linked to weakening of the north atlantic oscillation allowing increasing intensity of the siberian high to develop and during the 17th and 18th centuries in the last 150 years diatom species have been shown to be sensitive indicators of recent warming however impacts from future global warming will be complex and are likely to impact not only on the balance between endemic and cosmopolitan diatoms throughout the lake but on the balance between siliceous and non siliceous algae and sources of primary productivity

oxygen and hydrogen isotope systematics of lake baikal siberia implications for paleoclimate studies we interpret oxygen and hydrogen isotope data for water samples from lake baikal siberia its tributaries and other local rivers and local precipitation in terms of the known water budget for the modern lake in order to gain insight into past limnological and climatic processes that influenced the lake lake baikal is remarkably uniform in its isotopic composition i80 15 8 0 2 0 6d 123 f 2 0 and lies slightly to the right of the global meteoric water line which suggests significant evaporation water is supplied to the lake by over 300 rivers and streams the oxygen isotope values 8180 of the rivers in the baikal catchment range from 13 4 to 21 2 0 the hydrogen isotope values sd for the same area range from 103 to 156 0 both these ranges generally conform to the global meteoric water line the weighted average isotopic composition of input to the lake rivers plus precipitation is 15 2 0 for 6 0 and 116 0 for 6d values higher than those of the modern lake therefore the isotopic composition of the modem lake cannot be related to the modern input through simple evaporation instead modeling of the isotopic mass balance of the lake suggests that inputs precipitation and influx from rivers and outputs evaporation and outflow are not at a steady state equilibrium under current climate conditions we found previous input to the lake had lower zy o and 6d values than modern input which reflects cooler climates in the past compared with modern conditions under constant climate conditions steady state conditions are not expected to be reached by the lake for at least 700 yr because of its large size and the long residence time of water in the lake

processes of deep water renewal in lake baikal deep water renewal in lake baikal siberia the world s deepest lake and largest lake by volume is relatively fast water age calculated from tritium and helium as well as from chlorofluorocarbons does not exceed 19 yr relative saturation of dissolved oxygen typically exceeds 80 the equation of state of baikal water was determined including the effect of dissolved ions and silicic acid based on nearly 600 ctd profiles taken between 1993 and 1995 two mechanisms of deep water mixing were identified 1 in spring cold and relatively saline water from the selenga the major inflow to the lake forms a density plume that reaches the bottom of the central basin during april and early may due to entrainment of lake water the plume transports about 125 km of water per year to the deepest part of the basin later in spring the river water forms the thermal bar observed along the eastern shore there are indications that parts of the selenga are also plunging to the deep part of the southern basin 2 at academician ridge separating the cold and saline water of the central basin from the warmer and slightly less saline water of the northern basin horizontal mixing results in a water mass that can sink on either side of the sill whereas in the central basin the water mass stays at intcrmediatc depth in the northern basin it sinks to the decpcst part more detailed data are needed to quantify this density flux no indication of a wind induced thermobaric instability was found

effect of raindrop splash and transversal width on soil erosion laboratory flume experiments and analysis with the hairsine rose model the parameter consistency of the one dimensional hairsine rose h r erosion model under conditions of significant rainfall splash was examined to account for the splash characteristic length scale and its interaction with the transverse erosion width experiments were carried out using erosion flumes of the same length 6 m but different widths with sediment concentrations measured at the flume exits total sediment concentration and the concentration of seven size fractions 1000 m were measured at high rainfall intensity 60 mm h and with a gentle slope 2 2 the conditions employed ensured that erosion was predominantly precipitation driven the experimental results showed that raindrop splash affected particularly the sediment breakthrough from the wider flumes flumes 1 and 2 1 and 0 5 m wide respectively however the raindrop splash effect was less significant in observed sediment concentrations from the narrower flumes flumes 3 and 4 both 0 25 m wide for these flumes the detached sediment was affected by the transversal width of the flume in that an amount of detached sediment adhered to the barriers instead of being removed in the overland flow the one dimensional h r model was fitted to the experimental results and good agreement was found in particular for the finer size classes the data for the coarser grain sizes were more scattered suggesting sediment motion by mechanisms other than as a suspension in the overland flow e g rolling along the soil surface the optimized parameters indicated that the shield layers where the shield consists of redeposited eroded sediment of the wider flumes 1 and 2 developed within 5 10 min from the start of the experiment whereas in the narrower flumes 3 and 4 they never fully developed the optimized detachment rates were consistent with previous findings but the estimated thickness of the deposited layer was too small to provide complete protection of the original soil against raindrop detachment indicating that the shield was not uniform the experimental design allowed us to investigate directly the effect of flow non uniformity on soil erosion by inclusion of an offset drainage point in flume 4 the observations taken during and after the experiment as well as surface elevation data confirmed the noticeable impact of non uniform flow on the erosion process

estimation of runoff critical shear stress for soil erosion from soil shear strength abstract critical shear stress is an important soil parameter governing detachment by runoff which appears in numerous erosion models soil shear strength has been often presented as the best soil property to predict critical shear stress however only a few studies have documented the relationship between soil shear strength and critical shear stress and the results obtained have sometimes seemed contradictory this is why we have put together all available data about the relationship between critical shear stress and soil shear strength in order to analyse and discuss its significance and its generality results showed that contradictions between different studies mainly arise because total shear stress is a poor predictor of detachment on rough soils when grain shear stress is used rather than total shear stress a significant relationship between saturated soil shear strength and critical shear stress does exist soil shear strength may thus be used to predict critical grain shear stress however it is recalled that in general only total shear stress is predicted by erosion models which makes detachment predictions difficult on rough natural soils

effect of particle density and inflow concentration of suspended sediment on bedload transport in rill flow laboratory flume experiments were carried out to evaluate the effect of particle density on bedload transport of sand sized particles and the effect of a suspended load of clay particles kaolinite on bedload transport of sand sized particles in rill flow conditions three materials in the range 400 600 m were selected to simulate bedload transport of primary particles and aggregates sand 2650 kg m3 crushed brick 2450 kg m3 and anthracite 1300 1700 kg m3 in the two first experiments two different methods were applied to determine bedload transport capacity of coarse particles for various conditions of flow discharge from 2 to 15 l min and slope 2 2 3 and 4 in the third experiment clear water was replaced with kaolinite water mixture and bedload transport capacity of crushed brick particles was determined for a 4 slope and different concentrations of kaolinite 0 7 41 and 84 g l the results showed that bedload transport increased significantly with the decrease in particle density but the effect of particle density on transport rates was much less important than flow discharge velocity measurements of clear flow flow mixed with coarse particles and coarse particles confirmed the existence of a differentiation between suspended load and bedload in these experimental conditions suspended load of kaolinite did not affect bedload rates of crushed brick particles three transport capacity formulae were tested against observed bedload rates a calibration of the foster formula revealed that the shear stress exponent should be greater than 1 5 the low and the govers unit stream power usp equations were then evaluated the low equation was preferred for the prediction of bedload rates of primary particles but it was not recommended in the case of aggregates of low density because of the limited experimental conditions applied to derive this equation copyright 2008 john wiley sons ltd

the major and minor element geochemistry of lake baikal funding for u s participation in the fieldwork and sample collection was provided by the u s national science foundation funding for the analytical work was obtained by various means

significant decadal channel change 58 67 years post dam accounting for uncertainty in topographic change detection between contour maps and point cloud models abstract construction of digital elevation models dems and the subtraction of dems between different points in time as a method to determine temporal patterns of scour and fill is a highly valuable procedure emerging in geomorphology these dems of differences dods must be assessed for error in order to distinguish actual topographic change from uncertainty and surface error current methods include 1 uniformly excluding all values that fall below a minimum threshold 2 using a spatially variable approach such as the construction of minimum level of detection lod grids or 3 the creation of a fuzzy inference system although spatially variable methods for determining error have been more accurate in excluding noise without discarding large amounts of meaningful data a challenge remains in performing dods against preexisting contour based maps for which no original point data are available the goals of this study were to 1 develop a method that overcomes the unknown point density of contour and other historical data sets and allows for some assessment of dod uncertainty on the basis of information on topographic variability 2 perform comprehensive uncertainty analysis testing to understand the opportunities and constraints associated with this new method and 3 report and interpret the overall pattern and volume of decadal topographic change for a regulated river 67 years post dam in light of alternate conjectured mechanisms of post dam longitudinal profile adjustment the key feature of the new approach is the introduction of a high density artificial point grid that samples the topographic variability evident in the available historical data set the testbed used to develop and assess this new dod method was the 37 5 km lower yuba river california historical data consisted of 0 6 m contours from a 1999 survey while a more detailed point cloud was available for the most recent survey in 2006 2008 to evaluate uncertainty in the method this study applied seven different uncertainty metrics of varying strictness t 1 t 1 96 uniform 0 3 m exclusion t 1 plus uniform 0 3 m exclusion t 1 with lod minimum at 0 3 t 1 96 plus uniform 0 3 m exclusion and t 1 96 with lod minimum at 0 3 and two different dod adjustment methods exclusion and subtraction a stringent approach involving joint use of the contour half interval and the spatially distributed lod grid at a 95 confidence limit excluded 44 3 of the study area from spatial assessment of channel change and volumetric change computation this preferred approach yielded an estimated 2 518 million m 3 of total scour and 2 455 million m 3 of total fill in 7 9 years after considering different mapping epochs the net annual average export was 17 000 m 3 32 500 tons to the feather river and a river valley sediment yield of 2205 tons km 2 year this amount is 36 of the post dam annual yield of gravel and cobble to the upstream reservoir that blocks sediment conveyance into the study domain suggesting that the lowland system is still highly dynamic 67 years after the dam was built the scientific significance of this is that the response of rivers to dams can be far more long lasting and complex depending on the suite of cumulative societal impacts to rivers the ability to account for spatially explicit dod uncertainty i e data retention when uncertainty is low and data removal when uncertainty is high when comparing historic contour based and modern point cloud based dems will allow for more detailed and reliable dods and sediment budgets in these cases

relationships between mesoscale morphological units stream hydraulics and chinook salmon oncorhynchus tshawytscha spawning habitat on the lower yuba river california an expert based approach was used to identify 10 morphological unit types within a reach of the gravel bed regulated yuba river california that is heavily utilized by spawning chinook salmon oncorhynchus tshawytscha analysis of these units was carried out using two dimensional hydrodynamic modeling field based geomorphic assessment and detailed spawning surveying differently classified morphological units tended to exhibit discrete hydraulic signatures in most cases the froude number adequately differentiated morphological units but joint depth velocity distributions proved the most effective hydraulic classification approach spawning activity was statistically differentiated at the mesoscale of the morphological unit salmon preferred lateral bar riffle and riffle entrance units these units had moderately high velocity unit median 0 45 m s 1 and low depth unit median 0 6 m but each exhibited a unique joint depth velocity distribution a large proportion of redds 79 were associated with conditions of convective flow acceleration at riffle and riffle entrance locations in addition to reflecting microhabitat requirements of fish it was proposed that the hydraulic segregation of preferred from avoided or tolerated morphological units was linked to the mutual association of specific hydraulic conditions with suitable caliber sediment that promotes the provision and maintenance of spawning habitat

floodplain roughness parameterization using airborne laser scanning and spectral remote sensing abstract floodplain roughness parameterization is one of the key elements of hydrodynamic modeling of river flow which is directly linked to exceedance levels of the embankments of lowland fluvial areas the present way of roughness mapping is based on manually delineated floodplain vegetation types schematized as cylindrical elements of which the height m and the vertical density the projected plant area in the direction of the flow per unit volume m 1 have to be assigned using a lookup table this paper presents a novel method of automated roughness parameterization it delivers a spatially distributed roughness parameterization in an entire floodplain by fusion of casi multispectral data with airborne laser scanning als data the method consists of three stages 1 pre processing of the raw data 2 image segmentation of the fused data set and classification into the dominant land cover classes khat 0 78 3 determination of hydrodynamic roughness characteristics for each land cover class separately in stage three a lookup table provides numerical values that enable roughness calculation for the classes water sand paved area meadows and built up area for forest and herbaceous vegetation als data enable spatially detailed analysis of vegetation height and density the hydrodynamic vegetation density of forest is mapped using a calibrated regression model herbaceous vegetation cover is further subdivided in single trees and non woody vegetation single trees were delineated using a novel iterative cluster merging method and their height is predicted r 2 0 41 rse 0 84 m the vegetation density of single trees was determined in an identical way as for forest vegetation height and density of non woody herbaceous vegetation were also determined using calibrated regression models a 2d hydrodynamic model was applied with the results of this novel method and compared with a traditional roughness parameterization approach the modeling results showed that the new method is well able to provide accurate output data the new method provides a faster repeatable and more accurate way of obtaining floodplain roughness which enables regular updating of river flow models

a reassessment of late glacial holocene diatom oxygen isotope record from lake baikal using a geochemical mass balance approach we present a new palaeoenvironmental record of hydrological variability in lake baikal based on re modelled delta o 18 diatom values of diatom silica delta o 18 modelled where the residual contaminants are identified and compensated for using electron optical imaging and whole sample geochemistry delta o 18 modelled interpretations are based on the balance between rivers with high delta o 18 values and rivers with low delta o 18 values isotopic variability is related to latitudinal differences in precipitation which feed these rivers the delta o 18 modelled record suggests that rather moist conditions prevailed in the lake baikal region during the latter stages of the younger dryas throughout the holocene episodes of low delta o 18 modelled values are in general in good agreement with increases in percentage haematite stained grains in north atlantic sediments indicative of ice rafted debris events rivers with southerly catchments dominate fluvial input especially between c 3 3 and 2 cal ka bp concurrent with high precipitation in the lake baikal region copyright c 2011 john wiley sons ltd

geospatial organization of fluvial landforms in a gravel cobble river beyond the riffle pool couplet abstract morphological units mu are landforms with distinct local form process associations at 1 10 channel widths scale that may be the fundamental building blocks describing the geomorphic structure of a river past research has disproportionately focused on the two mus of pool and riffle conjecturing that they are the central linked couplet in the process form association the goal of this study was to delineate and map spatially explicit fluvial landforms in two dimensional planview within a gravel cobble bed river using two dimensional hydrodynamic delineation and then to statistically examine mu geospatial patterns for indicators of deterministic geomorphic control this procedure is not discharge dependent like mesohabitat methods but gets at the geometry of underlying landforms statistical testing confirmed that eight delineated in channel mu types comprise a complex and diverse channel morphology in which pools and riffles are not directly coupled specifically gravel cobble river channels 1 exhibit nonrandom spatial organization of their longitudinally and laterally variable landform morphology 2 consist of a variety of mu types not just pools and riffles and 3 show distinct mu collocations and avoidances with riffles linked to chutes and runs while pools are linked to slackwaters and glides planview mu delineation with two dimensional hydrodynamic modeling provides a bottom up approach to understanding and linking channel morphology with ecosystem services and geomorphic processes and is being used to guide river management and rehabilitation strategies

holocene oxygen isotope record of diatoms from lake kotokel southern siberia russia and its palaeoclimatic implications the oxygen isotope composition of diatom silica d 18 odiatom from marine and lake sediments is helpful for the interpretation of the past climate and environments especially when complemented by other proxy records this paper presents a holocene oxygen isotope record of diatoms from lake kotokel located 2 km east of lake baikal in southern siberia russia the isotope record displays variations in d 18 odiatom from 23 7 to 30 3 from about 11 5 ka bp until today comparing the isotope composition of recent lake kotokel water mean d 18 o 12 to that of the most recent diatom sample d 18 o 27 5 an isotope fractionation in the right order of magnitude was calculated the kotokel d 18 o diatom record is controlled by changes in the isotopic composition of the lake water rather than by

evaluation of the simple settling theory for predicting sediment deposition by overland flow experiments were conducted in the laboratory to evaluate the influence of sediment concentration sediment grain size distribution bed slope and flow discharge on sediment deposition rates and patterns associated with a reduction in bed slope the experimental data clearly indicate that sediment deposition by overland flow is a very selective process fine particles remain almost entirely in suspension and coarse particles are deposited quickly analysis of the data shows that up to a critical unit discharge a simple settling equation without a transport term assuming continuous mixing of the sediment and water gives a good prediction of the overall sediment delivery ratio and the grain size distribution of the deposited and the exported sediment however there are some discrepancies for the clay the coarse silt and the sand fractions the assumption of continuous mixing is tested by investigating the sedimentation patterns of very narrow size classes the observed decrease of sediment concentration versus distance from the inflow point for these individual sediment size classes closely agrees with the prediction assuming continuous mixing when the critical unit discharge is exceeded hydraulic properties of the overland flow do influence the sediment delivery outcomes at discharges exceeding the threshold value the simple settling theory underpredicts the sediment delivery ratio in these hydraulic conditions a transport term needs to be incorporated into the simple settling theory it is shown that the transport capacity and the re entrainment model yield similar expressions for the description of sediment transport by overland flow over an area of net deposition the experimental data indicate that the re entrainment of previously deposited sediment is non selective copyright 1999 john wiley sons ltd

uranium series disequilibrium sedimentation diatom frustules and paleoclimate change in lake baikal abstract the large volume of water approximately one fifth of the total surface fresh water on the planet contained in lake baikal in southeastern siberia is distinguished by having a relatively high concentration of uranium ca 2 nm and together with the surface sediments an unusually high234u238u alpha activity ratio of 1 95 about 80 of the input of uranium to the lake with a234u238u ratio of 2 0 comes from the selenga river profiles of uranium as well as the extent of isotopic disequilibrium in a 9 m sediment core collected on academic ridge generally show high values during interglacial periods corresponding to high diatom frustule numbers difr and biogenic silica bsi data that have been reported elsewhere during glacial periods low difr and bsi uranium progeny 234u and230th were in secular equilibrium with low concentrations of their parent238u radionuclide distributions were interpreted in terms of a quantitative model allowing for adsorption of riverine inputs of uranium onto two classes of sedimenting particles with differing238u232th ratios and uranium progeny in secular equilibrium if the234u238u activity ratio of adsorbed uranium has remained constant mean sedimentation rates can be independently estimated as 3 6 0 6 and 3 7 0 9 cm kyr 1 for the decay of234u and in growth of230th respectively these rates are consistent with a mean rate of 3 76 cm kyr 1 calculated by optimization of the correspondence between adsorbed238u and 18o in dated oceanic sediments the adsorbed uranium apparently tracks variable river flow during interglacials and is drastically reduced during periods of glaciation evidently uranium has not been significantly redistributed within baikal sediments over at least the past 250 kyr and is a unique biologically non essential tracer for climate sensitive processes which provide their own internal geochronometers potentially useful for ages up to 1 myr bp

two dimensional hydraulic flood modelling using a finite element mesh decomposed according to vegetation and topographic features derived from airborne scanning laser altimetry airborne scanning laser altimetry lidar is an important new data source that can provide two dimensional river flood models with spatially distributed floodplain topography for model bathymetry together with vegetation heights for parameterization of model friction methods are described for improving such models by decomposing the model s finite element mesh to reflect floodplain vegetation features such as hedges and trees having different frictional properties to their surroundings and significant floodplain topographic features having high height curvatures the decomposition is achieved using an image segmentation system that converts the lidar height image into separate images of surface topography and vegetation height at each point the vegetation height map is used to estimate a friction factor at each mesh node the spatially distributed friction model has the advantage that it is physically based and removes the need for a model calibration exercise in which free parameters specifying friction in the channel and floodplain are adjusted to achieve best fit between modelled and observed flood extents the scheme was tested in a modelling study of a flood that occurred on the river severn uk in 1998 a satellite synthetic aperture radar image of flood extent was used to validate the model predictions the simulated hydraulics using the decomposed mesh gave a better representation of the observed flood extent than the more simplistic but computationally efficient approach of sampling topography and vegetation friction factors on to larger floodplain elements in an undecomposed mesh as well as the traditional approach using no lidar derived data but simply using a constant floodplain friction factor use of the decomposed mesh also allowed velocity variations to be predicted in the neighbourhood of vegetation features such as hedges these variations could be of use in predicting localized erosion and deposition patterns that might result in the event of a flood copyright 2003 john wiley sons ltd

geochemical mass balances of major elements in lake baikal major element mass balances for lake baikal are calculated with mostly previously published data for soluble fluxes and new unpublished data for riverine suspended particulate matter chemistry physical transport seems to be the most important riverine process the elements ca mg and na seem to be very mobile in the weathering mantle and k and si seem to be relatively mobile a comparison of elemental input output budgets and mass accumulation rates mar in bottom sediments shows that most major elements except ca si and mn have comparable riverine particulate matter fluxes and mars the addition of wet atmospheric deposition fluxes results in an excess of ca mg and na entering the lake the additive effect of these excess inputs during a 40 year period amounts to undetectable concentration increases in the water column if erosion of weathered bedrock is the source of most dissolved and all particulate matter transported to the lake theoretical elemental fluxes can be calculated with al as the conservative element flux ratios observed theoretical range from 0 7 to 2 2 but most fall within the acceptable range of 0 7 l 5 major rock forming elements are carried by rivers as weathering products and there are minimal biogeochemical processes that modify these inputs as suspended particulate matter accumulates in the bottom sediments of the lake in terms of continental paleoclimatic reconstruction lake baikal represents a unique opportunity in that its long continuous history of sedimentation in a northern latitude continental setting affords scientists the ability to compare continental and marine records for the last 30x 10 yr environmental change as documented from the sedimentary record is assumed to result from changes in the concentrations of various sedimentary components owing to external forces that either act on the drainage basin directly or cause changes in the lake s properties for example a drop in temperature can cause a decline in chemical and mechanical weathering as well as a lowering and species shift in primary productivity within the lake thus it is important to determine whether the sedimentary record reflects climatic imprints that can be distinguished from diagenetic overprints this paper is part of a series describing the geochemical mass balances of major minor and nutrient elements in lake baikal in order to ascertain whether this important lake is at steady state with respect to chemical inputs and whether diagenesis plays a significant role in determining the biogeochemical cycle of these elements additionally such massbalance calculations may provide a foundation for assessing the impact of human influences on the baikal basin this paper deals with the rock forming elements ca mg na k al si fe mn that constitute the major mass of

modelling floodplain flows using a two dimensional finite element model a prototype two dimensional finite element flow model for depth averaged free surface flows was developed for floodplain environments limited refinement of the model s physical representation was undertaken and the enhanced scheme applied to an 11 km river channel floodplain reach in the u k preliminary model results indicate that this modelling approach can be used to identify dynamic variations in the flow field parameters over length scales of the order of 10 100 m potentially such data have the ability to permit detailed analysis of short term floodplain sedimentary dynamics

modeling the erosion process over steep slopes approximate analytical solutions abstract analytical expressions are developed for the rainfall runoff erosion process on steep hillslopes subjected to time varying rainfall events the erosion equation is essentially represented as a first order reaction with the reaction rate being represented by the soil erodibility the analytical transient solutions are based upon the assumption that the flow and sediment discharge have a constant relationship as during steady state conditions the analytical solution for the sediment discharge performs well when compared with numerical and experimental results the approximate analytical solution for the concentration profile is the asymptotic limit of the transient numerical solutions an error analysis shows that the analytical solutions improve with increasing slope length and that the solution model presented here is applicable to a wide range of physical situations

depositional and tectonic framework of the rift basins of lake baikal from multichannel seismic data recent multichannel seismic reflection data from lake baikal located in a large active continental rift in central asia image three major stratigraphic units totaling 3 5 to 7 5 km thick in four subbasins a major change in rift deposition and faulting between the oldest and middle rift units probably corresponds to the change from slow to fast rifting in early pliocene time inferred from on land studies a minor modification of fault patterns characterizes the youngest unit a brief comparison of the basins of lake baikal with those of the east african rift system highlights differences in structural style that can be explained by differences in age and evolution of the surrounding basement rocks

riffle pool maintenance and flow convergence routing observed on a large gravel bed river abstract geomorphologists have studied and debated over the processes responsible for natural riffle pool maintenance for decades most studies have focused on small wadable rivers but they lack much description of overbank flood conditions or a spatially explicit characterization of morphodynamics in this study 1 m horizontal resolution digital elevation models were collected from a riffle pool run sequence before and after an overbank flood with a 7 7 year recurrence interval on the relatively large gravel bed lower yuba river california digital elevation model differencing was used to quantify the magnitude and pattern of flood induced morphodynamic change cross section based analysis and two dimensional hydrodynamic modeling of flows ranging from 0 147 to 7 63 times bankful discharge were completed to evaluate the hydraulic mechanisms responsible for the observed topographic changes one key finding was that riffle pool relief increased by 0 42 m confirming the occurrence of natural hydrogeomorphic maintenance spatially complex patterns of scour and deposition exceeding 0 15 m at the scale of subwidth morphological units were reasonably predicted by the two dimensional mechanistic model that accounts for convective acceleration the one dimensional cross section based method underperformed the two dimensional model significantly consequently multiple scales of channel non uniformity and a dynamic flow regime caused the observed maintenance of the pool riffle morphology through the mechanism of flow convergence routing proposed by macwilliams et al macwilliams m l wheaton j m pasternack g b kitanidis p k street r l 2006 the flow convergence routing hypothesis for riffle pool maintenance in alluvial rivers water resources research 42 w10427 doi 10 1029 2005wr004391

numerical modelling of floodplain hydraulics and suspended sediment transport and deposition a numerical model is presented for the prediction of floodplain inundation extents flow depths and velocities and patterns of suspended sediment dispersion and deposition the model employs a simplified and novel treatment of fluid flow and a conventional convection diffusion mass balance relationship for suspended sediment transport and deposition these relationships are solved over a finite difference grid with a relatively fine nodal spacing which enables a detailed representation of complex floodplain topography the model is applied to a 600 m reach of the river culm devon uk continuous records of river stage and suspended sediment concentration monitored at the upstream boundary of the study reach provide the data needed to operate the model these data are supplemented by measurements of the in situ settling characteristics of the suspended sediment load model predictions of overbank flow depths and velocities and patterns of suspended sediment concentrations and deposition amounts are presented predicted patterns of overbank deposition are described and compared with field measurements obtained with the aid of astroturf sedimentation traps grain size distributions obtained for samples of deposited sediment retrieved from the sedimentation traps are also examined and compared with model predictions the results of both the field measurement programme and modelling work are shown to have significant implications for the representation of floodplain topography and suspended sediment particle size and settling properties in numerical simulations of overbank processes 1998 john wiley sons ltd

effects of lidar derived spatially distributed vegetation roughness on two dimensional hydraulics in a gravel cobble river at flows of 0 2 to 20 times bankfull abstract the spatially distributed effects of riparian vegetation on fluvial hydrodynamics during low flows to large floods are poorly documented drawing on a lidar derived meter scale resolution raster of vegetation canopy height as well as an existing algorithm to spatially distribute stage dependent channel roughness this study developed a meter scale two dimensional hydrodynamic model of 28 3 km of a gravel cobble bed river corridor for flows ranging from 0 2 to 20 times bankfull discharge with and without spatially distributed vegetation roughness results were analyzed to gain insight into stage dependent and scale dependent effects of vegetation on velocities depths and flow patterns at the floodplain filling flow of 597 49 m 3 s adding spatially distributed vegetation roughness parameters caused 8 0 and 7 4 increases in wetted area and mean depth respectively while mean velocity decreased 17 5 vegetation has a strong channelization effect on the flow increasing the difference between mid channel and bank velocities it also diverted flow away from densely vegetated areas on the floodplain vegetation stands caused high velocity preferential flow paths that were otherwise unaccounted for in the unvegetated model runs for the river as a whole as discharge increases overall roughness increases as well contrary to popular conception

floodplain inundation response to climate valley form and flow regulation on a gravel bed river in a mediterranean climate region abstract floodplain inundation regime defines hydrological connectivity between river channel and floodplain and thus strongly controls structure and function of these highly diverse and productive ecosystems we combined an extensive lidar data set on topography and vegetation long term hydrological records as well as the outputs of hydrological and two dimensional hydraulic models to examine how floodplain inundation regimes in a dynamic regulated gravel cobble river in a mediterranean climate region are controlled by reach scale valley morphology hydroclimatic conditions and flow regulation estimated relative differences in the extent duration and cumulative duration of inundation events were often as large as an order of magnitude and generally greatest for large and long duration events the relative impact of flow regulation was greatest under dry hydroclimatic conditions although the effects of hydroclimate and flow impairment are larger than that of valley floor topography the latter controls sensitivity of floodplain hydroperiod to flow regime changes and should not be ignored these quantitative estimates of the relative importance of factors that control floodplain processes in mediterranean semiarid rivers contributes to better understanding of hydrology and geomorphology of this important class of channels we also discuss implications of our findings for processes that shape floodplain habitat for riparian vegetation and salmonid fish especially in the context of ecological restoration

revealing the natural complexity of topographic change processes through repeat surveys and decision tree classification title revealing the natural complexity of topographic change processes through repeat surveys and decision tree classification short title decision tree classification of topographic change processes authors joshua r wyrick a gregory b pasternack b a lafayette college 740 high street easton pa 18042 b university of california davis one shields drive davis ca 95616 corresponding author tel 1 610 330 5735 e mail wyrickj lafayette edu fax 1 keywords topographic change dem differencing river morphology regulated rivers geomorphic change abstract topographic change processes tcps are the mechanisms by which a landscape is interpreted to be experiencing landform deformation and are defined by the specific actions occurring within a contiguous localized region that cause sediment to be either deposited or eroded past topographic change studies have mostly been focused at the site scale the goal of this study was to identify and delineate spatially explicit tcp

correction factors in the determination of mean velocity of overland flow the velocity of overland flow has been conventionally measured using tracers but it is difficult to measure the mean flow velocity directly because the centroid of the tracer plume is not easily identified consequently previous investigators have measured the velocity of the leading edge of the plume and multiplied it by a correction factor to obtain an estimate of mean velocity an alternative method is to measure the velocity of the peak concentration in the tracer plume and multiply this velocity by another correction factor to estimate mean velocity to investigate the controls of and and develop predictive models for these correction factors 40 experiments were performed in a flume with a mobile sand bed multiple regression analyses reveal that both and vary inversely with slope and directly with reynolds number the derived regression equations may be used to calculate the mean velocity of other shallow overland flows at least within the range of slope and reynolds number for which the equations were developed in the experiments slope ranged from 2 7 to 10 and reynolds number from 1900 to 12 600

modeling of two dimensional overland flow a two dimensional hydrodynamic and numerical model for overland flow is developed in this paper the model allows spatial variations in hillslope physical characteristics including surface roughness infiltration and microtopography the accuracy of the model is tested by comparison with characteristic based solutions and experimental data the results of these tests indicate that the model is accurate and has good stability and convergence properties the application of the model to two dimensional overland flow on hillslopes is demonstrated by applying it to surfaces with spatially variable roughness infiltration and microtopography these simulations show that microtopography is the dominant factor causing spatial variation in overland flow depth velocity and direction

roughness coefficients and velocity estimation in well inundated sheet and rilled overland flow without strongly eroding bed forms even with the flow of water over a soil surface in which roughness elements are well inundated and in less erosive situations where erosional bed forms are not pronounced the magnitude of resistance coefficients in equations such as those of darcy weisbach chezy or manning vary with flow velocity at least using both original laboratory and field data and data from the literature the paper examines this question of the apparent variation of resistance coefficients in relation to flow velocity even in the absence of interaction between hydraulics and resulting erosional bed forms resistance equations are first assessed as to their ability to describe overland flow velocity when tested against these data sources the result is that manning s equation received stronger support than the darcy weisbach or chezy equations though all equations were useful the second question addressed is how best to estimate velocity of overland flow from measurements of slope and unit discharge recognizing that the apparent flow velocity variation in resistance coefficients is probably a result of shortcomings in all of the listed resistance equations a new methodology is illustrated which gives good agreement between estimated and measured flow velocity for both well inundated sheet and rill flow comments are given on the predictive use of this methodology copyright 1999 john wiley sons ltd

turbulent velocity profiles and boundary shear in gravel bed rivers vertical profiles of turbulent streamwise velocities in several new zealand gravel bed rivers are investigated field measurements made at high and low flows with electronic pitot tubes show logarithmic velocity profiles to extend over much of the flow depth for the gravel bed rivers studied the velocity at 0 6 of the total depth was generally a good indicator of depth averaged flow velocity an unambiguous definition of flow depth is adopted to deal with situations where the bed is uneven or moving when hydraulic roughness z sub 0 is defined as a fitted parameter of a logarithmic velocity profile the river data indicate that the profile origin displacement below the tops of roughness elements scales with z sub 0 no direct relation between z sub 0 and bed material size is evident under mobile bed conditions for these conditions a relation between hydraulic roughness and u squared is identified with u also derived as a log profile parameter a flow resistance equation using this relation is verified by comparison with mobile bed laboratory measurements in which u is not fitted from velocity profiles

psem_2d a physically based model of erosion processes at the plot scale 1 this paper presents the development and first applications of the plot soil erosion model 2d psem 2d infiltration is computed using a green and ampt model overland flow is computed using the depth averaged two dimensional unsteady flow equations saint venant equations and soil erosion is computed by combining the equation of mass conservation of sediment and a detachment transport coupling model for erosion by runoff a shear stress approach is used to determine the transport capacity the formation of a covering cohesionless layer as a result of depositing sediment and action of rainfall impact before runoff is considered the erosion processes involved are rainfall and runoff detachment of original soil rainfall redetachment and overland flow entrainment of sediment from the deposited layer and deposition the model uses a single representative particle size complex rainfall events on natural slopes can be simulated the accuracy of the predictions for erosion of planar surfaces is tested by comparison with observed data obtained from experiments and with an analytical solution good agreement between the calculated results and measured data was found a sensitivity analysis was also performed limitations related to the description of overland flow on plane soil surface are pointed out finally an application to a nonplanar natural surface of 75 m2 illustrated the distribution of erosion and sedimentation over the plot

controls on the spacing and geometry of rill networks on hillslopes rain splash detachment initial hillslope roughness and the competition between fluvial and colluvial transport 1 rill networks have been a focus of study for many decades but we still lack a complete understanding of the variables that control the spacing of rills and the geometry of rill networks e g parallel or dendritic on hillslopes in this paper we investigate the controls on the spacing and geometry of rill networks using numerical modeling and comparison of the model results to terrestrial laser scanner derived topographic data from rill networks formed in physical experiments the landscape evolution model accounts for the transport of sediment due to rain splash and fluvial entrainment as well as the deposition of sediment being advected by the overland flow in order to develop realistic rill networks in the model we find that it is necessary to incorporate the effects of raindrop impact within the fluvial sediment transport process model results are only consistent with those of experiments when raindrop aided fluvial sediment transport is accounted for dendritic networks are often predicted by the model in cases of high initial topographic roughness and high rates of advective fluvial sediment transport relative to diffusive colluvial transport parallel networks form within numerical experiments in low roughness cases under a wide range of relative advective and diffusive transport rates as well as in high roughness cases in which diffusive sediment transport is high relative to advective transport the transition from dendritic to parallel rill networks is shown to occur gradually rather than being associated with a particular threshold finally based on a balance between diffusive and advective sediment transport processes we predict that the mean spacing between parallel rills scales with the square root of the ratio of diffusivity to channel erodibility

the structure and development of the baikal rift depression abstract the baikal rift depression located in southeastern siberia is one of the best investigated intra continental rift structures in the world in addition to being the site of comprehensive studies by russian geo scientists for decades the baikal depression is now the subject of new international investigations using advanced technical means and technologies the present paper summarizes the principal results concerning the morphostructure of the baikal rift the stratigraphy of the cenozoic deposits and the stages of the baikal depression development based on cross sections which exhibit the impact of both tectonic and climatic processes the development of the baikal depression occurred through two stages i the pre crypto rift stage of the late cretaceous eocene and ii active rifting of the oligocene recent the second stage is divided into several steps and substeps separated by tectonic phases formation of the baikal rift zone appears to be related to the indo eurasian plate collision related to a model of passive rifting the uplifted shoulders of the depression have a complex morphostructure overlain by cenozoic deposits which are thin and restricted in area the near marginal zones of the rift are largely defined by the system of longitudinal blocks of different width surfaces of the blocks are inclined either to the uplifted shoulder of the rift bound by listric faults typical for western edges of the depression or to the axis of the depression cenozoic deposits on the blocks consist of accumulative plains composed primarily of thick lacustrine sequences

measurement and modelling of high resolution flow velocity data under simulated rainfall on a low slope sandy soil the study presented here is focussed on the question of the hydraulic nature of the threshold that allows a rill to start a rainfall simulation experiment was carried out to produce high resolution flow velocity data the experiment employed a 10 m 4 m experimental plot with a 1 slope which had been previously eroded and had a small rill formed in the middle the experiment consisted of a 2 h 15 long rainfall at a constant intensity of 69 mm h 1 surface elevation was measured before rainfall at a horizontal resolution of 2 5 cm across and 5 cm along the slope direction during rainfall flow velocities were measured at 68 locations on the plot with the salt velocity gauge technology an automated miniaturized device based on the inverse modelling of the propagation of a salt plume the experiment led to the collection of flow velocity measurements which are novel in three ways i the small size of the measured section which was only 10 cm long and 1 cm wide ii the wide range of measured flow velocities which ranged from 0 006 m s 1 to 0 27 m s 1 and iii the large number of measured locations the flow velocity field was simulated with three models psem 2d solves the saint venant equations in 2d mahleran uses a 1d kinematic wave in the slope direction coupled with a 2d flow routing algorithm and rillgrow2 which involves an empirical runoff algorithm that is close in principle to the diffusion wave equation in 2d the darcy weisbach friction factor ff and the infiltration parameters were calibrated in all cases to investigate the capabilities of the different models to reproduce flow hydraulics compatible with the onset of rilling in a first set of numerical experiments ff was set uniform and calibration used only the hydrograph the comparison of simulated and observed flow velocity field showed that psem 2d was the most satisfying model at the cost of longer computational time mahleran gave surprisingly good results with regards to the simplicity of the model and its low computational needs however all models largely underestimated the highest velocity values located in the rill furthermore none of the models was able to simulate the reynolds re and froude fr numbers the next numerical experiment was done with psem 2d non uniform ff values were calibrated by fitting the simulated flow velocity field to the observed one the latter simulation produced realistic simulations of re and fr the hydraulic conditions at the transition from interrill flow to rill flow are discussed the results support the theory that supercritical flows are a necessary condition for a rill to emerge from a smooth surface

hydraulics and erosion in eroding rills rills often act as sediment sources and the dominant sediment and water transport mechanism for hillslopes six experiments were conducted on two soils and a uniform sand using three experimental methodologies the results of this study challenge the assumption often used in hydrologic and erosion models that relationships derived for sheet flow or larger channel flow are applicable to actively eroding rills velocity did not vary with slope and reynolds number was not a consistent predictor of hydraulic friction this result was due to interactions of slope gradient flow rate erosion and the formation of rill roughness bed structures and head cuts a relationship for rill flow velocities was proposed stream power was found to be a consistent and appropriate predictor for unit sediment load for the entire data set while other hydraulic variables were not the data for stream power and sediment load fit the form of a logistic curve r2 0 93 which is promising relative to recently proposed erosion models which are based on probabilistic particle threshold theory

evaluating a multiclass net deposition equation in overland flow conditions 1 the movement of sediment and related pollutants in overland flow from the point of erosion to a stream normally occurs through a series of deposition zones here we present the evaluation of a new multiclass model of sediment transport through these zones this model simulates size selective net deposition as a result of simultaneous deposition by settling and nonselective reentrainment of previously deposited sediment hairsine et al 2002 sander et al 2002 multiclass sediment deposition models provide a useful basis for simulating off site effects of soil erosion but information on the grain size composition of deposited and exported sediment is crucial for calibrating and evaluating such models therefore the multiclass sediment deposition model was tested using detailed experimental data information on the amount of sediment deposition on the grain size distribution of the deposited and exported sediment and on the spatial pattern of the deposits was collected during sediment deposition experiments calibration of the multiclass model using one part of these data was performed by adjusting the fraction of stream power available for sediment reentrainment by minimizing errors between both simulated and observed total outflow sediment concentration and grain size distribution of the exported sediment evaluation was conducted using the other part of the data over a wide range of conditions the evaluation shows that the deposition equation is capable of reasonably simulating the observed size selectivity of the deposition process however the model is not capable of simulating correctly the spatial pattern of the deposited sediment because of simplifications used in the hydraulic model

constraining modern day silicon cycling in lake baikal constraining the continental silicon cycle is a key requirement in attempts to understand both nutrient fluxes to the ocean and linkages between silicon and carbon cycling over different time scales silicon isotope data of dissolved silica 30sidsi are presented here from lake baikal and its catchment in central siberia as well as being the world s oldest and voluminous lake lake baikal lies within the seventh largest drainage basin in the world and exports significant amounts of freshwater into the arctic ocean data from river waters accounting for 92 of annual river inflow to the lake suggest no seasonal alteration or anthropogenic impact on river 30sidsi composition the absence of a change in 30sidsi within the selenga delta through which 62 of riverine flow passes suggests a net balance between biogenic uptake and dissolution in this system a key feature of this study is the use of 30sidsi to examine seasonal and spatial variations in dsi utilization and export across the lake using an open system model against deepwater 30sidsi values from the lake we estimate that 20 24 of dsi entering lake baikal is exported into the sediment record while highlighting the impact that lakes may have upon the sequestration of continental dsi mixed layer 30sidsi values from 2003 and 2013 show significant spatial variability in the magnitude of spring bloom nutrient utilization with lower rates in the north relative to south basin

hydrological instability during the last interglacial in central asia a new diatom oxygen isotope record from lake baikal last interglacial variability is commonly used as an analogue for variability in a future warmer world pervasive cycles are increasingly apparent in last interglacial archives although studies in continental regions are under represented here we provide a new isotopic record of diatom silica 18odiatom spanning c 127 5 115 ka bp from lake baikal in central asia peak rain fed discharge occurred c 125 4 ka bp shortly after july insolation maximum and initiation of siberian soil development between 127 and 119 7 ka bp there are six marked fluctuations in 18odiatom values with a pacing of approximately 1 26 0 3 ka similar to fluctuations of within lake productivity fluctuations in 18odiatom values show good agreement with patterns in atlantic meridional overturning circulation amoc supporting hypothesis of strong teleconnections via the westerlies between the north atlantic and central asia two periods of low 18odiatom values are especially notable the earliest between c 126 5 and 126 ka bp is concurrent with the final stages of the heinrich 11 the second between 120 5 and 119 7 ka bp is also concurrent with an increase in ice rafted debris in the north atlantic aquatic productivity in lake baikal increased between 119 7 and 117 4 ka bp before declining to the top of the record 115 ka bp concomitant with a shift to predominately cool steppe catchment vegetation however isotopic composition of discharge into lake baikal provides evidence for strong penetration of westerlies into central asia during the latter stages of the last interglacial variability in 18odiatom values was compared between the last interglacial and the holocene millennial scale variability was significantly more stable during the last interglacial possibly linked to diminished influence of freshwater discharge on amoc during periods of higher global mean temperatures

evaluation of sediment transport formulae and detachment parameters in eroding rills using psem_2d and the water erosion prediction project wepp database 1 the numerical model psem 2d is applied to reproduce the rill experiments described by elliot et al 1989 for five different textured soils psem 2d is a two dimensional water flow and erosion model incorporating the first order detachment transport coupling model the infiltration parameters and the friction factor are calibrated to reproduce both the flow discharges and the flow velocities measured by elliot et al 1989 values of the determined friction factors are higher for the cohesive soils compared to the noncohesive soils four sediment transport capacity formulae for rills are tested the yalin the low the unit stream power govers usp and the effective stream power govers esp equations these equations do not require any calibration the erosion parameters for the first order detachment transport coupling model come from the water erosion prediction project wepp database they were calibrated by elliot et al 1989 using observed data and the rill component of wepp the govers usp formula gives the best results for the cohesive soils nevertheless none of the equations performs well for the noncohesive soils the study also focuses on the results obtained for the barnes nd the bonifay and the collamer soils to explore the implication of the detachment transport coupling model on the spatial erosion patterns along the rills a detachment limiting regime is produced over the whole rill for the barnes nd soil a transport limiting regime is reached over a very short flow distance for the bonifay soil and a detachment limiting regime in the upper part along with a transport limiting regime in the lower part of the rills is experienced for the collamer soil

revealing the natural complexity of fluvial morphology through 2d hydrodynamic delineation of river landforms abstract fluvial landforms at the morphological unit scale 1 10 channel widths are typically delineated and mapped either by breaking up the one dimensional longitudinal profile with no accounting of lateral variations or by manually classifying surface water patterns and two dimensional areal extents in situ or with aerial imagery mapping errors arise from user subjectivity varying surface water patterns when the same area is observed at different discharges and viewpoints and difficulty in creating a complete map with no gaps or overlaps in delineated polygons this study presents a new theory for delineating and mapping channel landforms at the morphological unit scale that eliminates in field subjective decision making adds full transparency for map users and enables future systemic alterations without having to remap in the field delineation is accomplished through a few basic steps first near census topographic and bathymetric data are used in a two dimensional hydrodynamic model to create meter scale depth and velocity rasters for a representative base flow second expert judgment and local knowledge determine the number and nomenclature of landform types as well as the range of base flow depth and velocity over each type this step does require subjectivity but it is transparent and adjustable at any time third the hydraulic landform classification is applied to hydraulic rasters to quickly completely and objectively map the planform pattern of laterally explicit landforms application of this theory will reveal the true natural complexity yet systematic organization of channel morphology

estimation of effective aerodynamic roughness of walnut gulch watershed with laser altimeter measurements a new method to estimate the effective aerodynamic roughness of a complex landscape is presented high resolution elevation profiles measured with an airborne laser altimeter have been used to compute geometrical parameters of three landscape elements of the walnut gulch experimental watershed arizona mean crop height its standard deviation and the frequency distribution as a function of penetration depth of plant elements hit by the laser beam have been calculated for short segments 1 m measured over intervening grass between shrubs longer segments have been applied to obtain the mean height and spacing of taller shrubs and trees finally laser profiles covering the entire watershed gave the mean amplitude and wavelength of hillocks and ridges the aerodynamic roughness length of the intervening grass is estimated using the ratio of standard deviation to vegetation height corrected for instrument noise times mean height an effective roughness length which parameterizes the total stress due to grass and taller shrubs and trees is calculated first finally a watershed scale effective roughness length is calculated combining the amplitude and wavelength of hillocks and ridges with the roughness length obtained in the previous step

siliceous deep sea sponge monorhaphis chuni a potential paleoclimate archive in ancient animals abstract the deep sea sponge monorhaphis chuni forms giant basal spicules which can reach lengths of 3 m they represent the largest biogenic silica structures on earth that is formed from an individual metazoan the spicules offer a unique opportunity to record environmental change of past oceanic and climatic conditions a giant spicule collected in the east china sea in a depth of 1110 m was investigated the oxygen isotopic composition and mg ca ratios determined along center to surface segments are used as geochemical proxies for the assessment of seawater paleotemperatures calculations are based on the assumption that the calculated temperature near the surface of the spicule is identical with the average ambient temperature of 4 c a seawater temperature of 1 9 c is inferred for the beginning of the lifespan of the monorhaphis specimen the temperature increases smoothly to 2 3 c to be followed by sharply increased and variable temperatures up to 6 10 c in the outer part of the spicule the inferred seawater temperature is about 4 c the lifespan of the spicule can be estimated to 11 000 3000 years using the long term trend of the inferred temperatures fitted to the seawater temperature age relationships since the last glacial maximum specimens of monorhaphis therefore represents one the oldest living animals on earth the remarkable temperature spikes of the ambient seawater occurring 9500 3100 years b p are explained by discharges of hydrothermal fluids in the neighborhood of the spicule the irregular lamellar organization of the spicule and the elevated mn concentrations during the high temperature growth are consistent with a hydrothermal fluid input

unsteady soil erosion due to rainfall impact a model of sediment sorting on the hillslope a new method is presented for predicting sediment sorting associated with soil erosion by raindrop impact for non equilibrium conditions the form of soil erosion considered is that which results from raindrop impact in the presence of shallow overland flow itself where the flow is not capable of eroding sediment the method specifically considers early time runoff and erosion when sediment leaving an eroding area is generally finer and thus may have a higher potential for transport of sorbed pollutants the new mechanism described is the formation of a deposited layer on the soil surface which is shown to lead to sediment sorting during an erosion event the deposited layer is taken to have two roles in this process to temporarily store sediment on the surface between successive trajectories and to shield the underlying soil from erosive stresses equations describing the dynamics of the suspended sediment mixture and the deposited layer are developed by integrating these equations over the length of eroding land element and over the duration of the erosion event an event based solution is proposed which predicts total sediment sorting over the event this solution is shown to be consistent with experimentally observed trends in enrichment of fine sediment predictions using this approach are found to only partly explain measured enrichment for sets of experimental data for two quite different soils but to be in poor agreement for an aridsol of dispersive character it is concluded that the formation of the deposited layer is a significant mechanism in the enrichment of fine sediment and associated sorbed pollutants but that processes in the dispersive soil are not as well described by the theory presented

continental climate response to orbital forcing from biogenic silica records in lake baikal changes in insolation caused by periodic changes in the earth s orbital parameters provide the primary forcing for global ice ages1 6 but it is not clear to what extent the climates in continental interiors are controlled directly by regional variations in insolation and to what extent they are driven instead by the highly nonlinear response of the oceans and ice sheets here we investigate this question using the record of biogenic silica in lake baikal as a proxy for climate change in this high latitude mid continental region we find a good correlation between this record and that of marine oxygen isotopes4 over the past 250 kyr the baikal record exhibits both a strongly nonlinear component manifested in a 100 kyr periodicity and weaker direct insolation components manifested in the 41 kyr obliquity and 23 and 19 kyr precession orbital cycles these results show that even though extreme continental climates such as this are influenced directly by insolation variations they are dominated by the nonlinear rhythm of the oceans and ice sheets

investigating the behaviour of two dimensional finite element models of compound channel flow this paper describes results from a recent study concerning the numerical modelling of compound channel flow using two generalized two dimensional finite element codes specifically adapted to floodplain studies rma 2 and telemac 2d by application to an 11 km reach of the river culum devon uk simulations are developed to investigate the impact of numerical technique mesh resolution and topographic parameterization on model results the research is shown to raise a number of issues concerning the construction calibration and validation of two dimensional finite element models for this flow problem 1997 by john wiley sons ltd

deep ventilation of lake baikal waters due to spring thermal bars increase of density due to mixing cabbeling instability in a spring thermal bar in lake baikal results in the sinking of cold surface water t 3 2 3 4 c w 0 3 cm s 1 below the profile of tmd this density increase generates forced convection and subsequent movement of cold water along the underwater slope to maximum depths cooling of deep and near bottom waters caused by forced convection is compensated during other seasons of the year by eddy heat flux directed toward the bottom on a long term basis vertical temperature profiles in deep waters remain constant

modelling flood hydraulics and overbank deposition on river floodplains this paper outlines a numerical model for the prediction of floodplain inundation sequences overbank deposition rates and deposit grain size distributions the model has two main components first a simplified hydraulic scheme which predicts floodwater flow depths and velocities and second a sediment transport element which employs a mass balance relation describing suspended sediment dispersion by convective and diffusive processes and sediment deposition as a function of particle settling rates these relationships are solved numerically on a finite difference grid that accurately replicates the complex topographic features typical of natural river floodplains the model is applied to a 600 m reach of the river culm devon u k using data derived from a range of field and laboratory techniques continuous records of river stage and suspended sediment concentration provide the model s upstream boundary input requirements these are supplemented by measurements of the in situ settling characteristics of the suspended sediment load the model s sediment transport component is calibrated with the aid of a dataset of measured overbank deposition amounts derived from flood events over a 16 month period the model is shown to predict complicated floodwater inundation sequences and patterns of suspended sediment dispersion and deposition which are largely a product of the complex topography of the floodplain these results compare favourably with observations of overbank processes and are an improvement over those of previous models which have employed relatively simple representations of floodplain geometry 1997 by john wiley sons ltd

floodplain friction parameterization in two dimensional river flood models using vegetation heights derived from airborne scanning laser altimetry two dimensional 2 d hydraulic models are currently at the forefront of research into river flood inundation prediction airborne scanning laser altimetry is an important new data source that can provide such models with spatially distributed floodplain topography together with vegetation heights for parameterization of model friction the paper investigates how vegetation height data can be used to realize the currently unexploited potential of 2 d flood models to specify a friction factor at each node of the finite element model mesh the only vegetation attribute required in the estimation of floodplain node friction factors is vegetation height different sets of flow resistance equations are used to model channel sediment short vegetation and tall and intermediate vegetation the scheme was tested in a modelling study of a flood event that occurred on the river severn uk in october 1998 a synthetic aperture radar image acquired during the flood provided an observed flood extent against which to validate the predicted extent the modelled flood extent using variable friction was found to agree with the observed extent almost everywhere within the model domain the variable friction model has the considerable advantage that it makes unnecessary the unphysical fitting of floodplain and channel friction factors required in the traditional approach to model calibration copyright 2003 john wiley sons ltd

case study effect of submerged aquatic plants on turbulence structure in a lowland river interactions of aquatic plants with turbulent flows in fluvial systems have attracted considerable interest while there have been recent advances in theories that describe vegetation flow interactions in idealized laboratory flows their practical application is still problematic due to limited knowledge of effects caused by heterogeneously patchy distributed plants in naturally formed vegetative mosaics in rivers this paper reports on a study in a lowland river aimed at quantification and parameterization of vegetation effects on redistribution of mean and turbulent characteristics of the flow and their consequences for hydraulic resistance the measurements were carried out in summer on a river reach with a patchy mosaic dominated by submerged flexible aquatic plants and repeated at the same water level in early spring before the plants start growing this design of the study allowed for quantitative evaluation of the effects caused by flow plants interactions on bulk flow parameters at comparable submergences of riverbed roughness elements sediment grains and sand bars the study indicates that symmetrical quasi two dimensional open channel flow structure in unvegetated riverbed was transformed into highly fragmented complex flow pattern spatially arranged by patches and free paths in the mosaic despite complexities and three dimensionality of the flow normalized mean velocity profiles in the patches were satisfactory described by hyperbolic tangent function while flow in the free paths similarly to unvegetated channel was in a reasonable agreement with the conventional logarithmic law

virtual manipulation of topography to test potential pool riffle maintenance mechanisms in this study numerical experimentation with two dimensional hydraulic modeling of pool riffle river topography drawing on the testbed data from the classic keller 1971 study was used to investigate the effect of synthetically manipulating topography on the occurrence and magnitude of velocity and shields stress reversals in a pool riffle sequence reversals in velocity and shear stress have been used to explore mechanisms of pool riffle maintenance while shields stress a combined measure of transport capacity and substrate erodibility is emerging in importance the original site topography was modeled alongside six altered ones to evaluate the sensitivity of hydraulic reversals to subtle morphology five incrementally wider pools and a filled pool the caamano 2009 criterion a simplified geometric threshold for predicting velocity reversals was applied to each terrain to evaluate its utility the original pool riffle topography was just over the threshold for a velocity reversal and well over the threshold for a strong shields stress reversal overall pool widening caused a predominantly local response with change to pool hydraulics and no change in section averaged velocity in the riffle beyond the initial widening of 10 filling in the pool significantly increased the magnitude of reversals whereas expanding it eliminated the occurrence of a reversal in mean velocity though the shields stress reversal persisted because of strong differentiation in bed material texture using shields stress as a reversal parameter enabled the quantification of pool modification effects on pool riffle resiliency the caamano 2009 criterion accurately predicted reversal occurrence for the altered terrains with exaggerated effects but failed to predict the weak reversal for the original topography two dimensional modeling coupled with previously accepted hydrologic geomorphic and engineering analyses is vital in project design and evaluation prior to construction

evaluating data constraints on two dimensional finite element models of floodplain flow abstract a prototype two dimensional finite element model for the simulation of flood flows is presented this is shown to have significant advantages over other methods of flow simulation for compound meandering channels such as the ability to predict dynamic inundation zones in particular this paper demonstrates that reasonable predictions may be obtained on the basis of extremely sparse data sets such as topographic maps and available flow monitoring records finally a more rigourous method of determining the most suitable modelling approach in a given situation is called for

modeling complex flow structures and drag around a submerged plant of varied posture although vegetation is present in many rivers the bulk of past work concerned with modeling the influence of vegetation on flow has considered vegetation to be morphologically simple and has generally neglected the complexity of natural plants here we report on a combined flume and numerical model experiment which incorporates time averaged plant posture collected through terrestrial laser scanning into a computational fluid dynamics model to predict flow around a submerged riparian plant for three depth limited flow conditions reynolds number 65 000 110 000 plant dynamics were recorded through high definition video imagery and the numerical model was validated against flow velocities collected with an acoustic doppler velocimeter the plant morphology shows an 18 reduction in plant height and a 14 increase in plant length compressing and reducing the volumetric canopy morphology as the reynolds number increases plant shear layer turbulence is dominated by kelvin helmholtz type vortices generated through shear instability the frequency of which is estimated to be between 0 20 and 0 30 hz increasing with reynolds number these results demonstrate the significant effect that the complex morphology of natural plants has on in stream drag and allows a physically determined species dependent drag coefficient to be calculated given the importance of vegetation in river corridor management the approach developed here demonstrates the necessity to account for plant motion when calculating vegetative resistance

integration of high resolution topographic data with floodplain flow models two dimensional hydraulic models of floodplain flow are at the forefront of current research into flood inundation mechanisms but they are however currently constrained by inadequate parameterization of topography and friction primarily due to insufficient or inaccurate data this paper reviews the effects of topographic representation on flood inundation extent prediction and presents initial results of a flood simulation using a new topographic parameterization surface produced from airborne lidar laser induced direction and ranging data copyright 2000 john wiley sons ltd

modelling soil erosion in a clayey subsurface drained agricultural field with a three dimensional flush model summary soil erosion is an important environmental issue in agricultural areas of northern europe where clayey soils are prevalent clayey soils are routinely subsurface drained to accelerate drainage which creates an additional discharge route for suspended sediment previously assessment of the sediment load from clayey fields has been difficult because process based models were only able to simulate sediment loads via surface runoff a new distributed process based erosion model was developed and incorporated into the flush modelling system to fulfil this void the model facilitates simulation of spatially distributed soil erosion on the field surface and sediment loads via surface runoff and subsurface drainflow soil erosion on the field surface is simulated with the two dimensional sediment continuity equation coupled with hydraulic and rain drop splash erosion sediment settling and transport capacity processes subsurface sediment transport in macropores is described with the three dimensional advection dispersion equation the model was applied to a clayey subdrained field section 3 6 ha in southern finland the results demonstrated the capability of the model to simulate soil erosion and sediment transport in terms of the match between the measured 2669 kg ha 1 and modelled 2196 kg ha 1 sediment loads via surface runoff and the measured 2937 kg ha 1 and modelled 2245 kg ha 1 loads via drainflow during the validation period of 7 months the model sensitivity analysis pointed out the importance of the flow model parameters in simulation of soil erosion through their control on the division of total runoff into surface runoff and drainflow components the key parameters in the erosion model were those that affected hydraulic and splash erosion rates the model application in the experimental field suggested that both hydraulic and splash erosion were the factors behind the sediment losses during the growing season and early autumn whereas high sediment loads in late autumn were caused by hydraulic erosion due to overland flow in tilled soil

modelling suspended sediment deposition on a fluvial floodplain using a two dimensional dynamic finite element model abstract in this paper we outline a new numerical model for predicting floodplain sediment deposition resulting from out of bank flow in reach scale natural compound channels simulation of this problem requires models capable of dealing with the hydraulic and sediment transport effects of a dynamically moving inundation front as well as a complex set of flow processes including momentum exchange between main channel and floodplain spillage of water across meander loops and the impact of complex topography whilst the treatment of dynamic moving boundary problems is difficult but attainable in finite element hydraulic codes the necessity to include dry areas within the model generates a number of problems that numerical solvers for fluvial sediment transport have to date failed to overcome accordingly we develop a two dimensional finite element approach that specifically accounts for sediment transport in domains undergoing wetting and drying the hypothesis that at the reach scale a two dimensional depth averaged representation of flow and suspended sediment is able to reproduce observed deposition patterns is then tested against average annual rates determined using 137 caesium analysis of floodplain sediments using reasonable parameterisation and no calibration of the sediment transport component the developed model is able to replicate an encouraging amount of the observed spatial variability in this data set whilst further testing of both the hydraulic and sediment transport components of the model is undoubtedly required the results provide an initial assessment of reach scale process dominance for floodplain systems

using 7be measurements to estimate the relative contributions of interrill and rill erosion abstract rapid and reliable methods for estimating the relative contribution of interrill and rill erosion during a rainfall event are needed to provide an improved understanding of soil erosion processes and to develop process based soil erosion prediction models use of the radionuclide 7 be in controlled experiments provides a means of addressing this need and this paper reports an experimental study aimed at refining and testing procedures employed to estimate the relative contribution of the two components of erosion four experimental plots area 5 2 m and 10 15 20 and 25 slope filled with a loessial soil manually tilled and kept free of weeds with herbicides were subjected to high intensity rainfall 91 8 120 6 mm h 1 in order to induce rill development the evolution of the rill network was documented photographically during the rainfall events and the runoff and sediment output from the plots were collected and measured the sediment was recovered from the runoff and its mass and 7 be activity were measured the yang model reported previously was used to estimate the relative contributions of interrill and rill erosion from the 7 be activity of the exported sediment and this model was further refined to take account of the dynamic growth of the rills during the rainfall event the results from the experiments were also used to develop a simple empirical linear model for estimating the relative contributions of interrill and rill erosion from the 7 be measurements a comparison of the results provided by the three models showed some differences in the estimates of the magnitude of the relative contributions although their trend during the event was similar the estimates provided by the empirical linear model tended to be higher than those obtained using the refined model and lower than those generated by the yang model but were closer to those provided by the refined model which was seen as being theoretically the most accurate model the basis of the empirical linear model was simpler than that of other models since only a few easily obtained parameters were required in practical terms the empirical linear model therefore has important advantages and is judged to provide acceptable results further work is required to test its applicability under a wider range of conditions