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

wood storage in a wide mountain river case study of the czarny dunajec polish carpathians storage of large woody debris in the wide mountain czarny dunajec river southern poland was investigated following two floods of june and july 2001 with a seven year frequency within a reach to which wood was delivered only by bank erosion and transport from upstream wood quantities were estimated for eighty nine 100 m long channel segments grouped into nine sections of similar morphology results from regression analysis indicated the quantity of stored wood to be directly related to the length of eroded wooded banks and river width and inversely related to unit stream power at the flood peak the largest quantities of wood up to 33 t ha 1 were stored in wide multi thread river sections here the relatively low transporting ability of the river facilitated deposition of transported wood while a considerable length of eroded channel and island banks resulted in a large number of trees delivered from the local riparian forest in these sections a few morphological and ecological situations led to the accumulation of especially large quantities of wood within a small river area very low amounts of wood were stored in narrow single thread sections of regulated or bedrock channel high stream power facilitated transport of wood through these sections while the high strength of the banks and low channel sinuosity prevented bank retreat and delivery of trees to the channel considerable differences in the character of deposited wood existed between wide multi thread channel sections located at different distances below a narrow 7 km long channellized reach of the river wood deposited close to the downstream end of the channellized reach was highly disintegrated and structured into jams whereas further downstream well preserved shrubs and trees prevailed this apparently reflects differences in the distance of wood transport and shows that in a mountain river wider than the height of trees growing on its banks wood can be transported long distances along relatively narrow single thread reaches but is preferentially deposited in wide multi thread reaches copyright 2005 john wiley sons ltd

a novel method for determining residence times of river and lake sediments based on disequilibrium in the thorium decay series sediment fluxes in rivers have proved difficult to measure or model at timescales relevant to land and water resource management decisions determining transport rates and residence times is complicated by the intermittent movement and temporary storage of sediments in natural streams this paper presents a new tool for estimating the residence times of river borne sediments based on the observed disequilibria between the naturally occurring radionuclides 228ra and 232th in the thorium decay series disequilibrium between concentrations of 228ra half life 5 75 years and its long lived parent 232th has been observed in marine environments and in terrestrial freshwaters but has not been previously reported in fluvial sediments or soils here we report 228ra excesses in sandy stream and silty lake sediments from southeastern australia the excess is developed in hillslope soils in the catchment headwaters and begins to decay back to secular equilibrium once the sediment is finally removed from contact with the soil water the short half life of 228ra enables this process to be used to investigate fluvial sediment transfers and alluvial and lacustrine sediment storages over the past 30 years when combined with indicators of sediment source such as 226ra 232th and 230th 232th ratios observation of this excess should provide a useful new tool for examining the residence and transit times of bed load and suspended load sediments in streams and lakes

a sediment budget for a forested catchment in luxembourg and its implications for channel development in the forested catchments of the luxembourg keuper area deeply incised valleys have developed in which streambank erosion is a widespread phenomenon for one of the catchments in this area the schrondweilerbaach catchment a sediment budget was constructed in order to determine the relative contributions of the various channel and valley slope processes to sediment output streambanks contributed 53 percent of the output with bank scour and subsoil fall being the main processes while to a lesser extent bank material was supplied by bank failures splash erosion and soil creep the remaining 47 per cent of the sediment was derived from the valley slopes mainly through the combined action of rainsplash detachment and overland flow transport during the two years of investigations sediment output from the drainage basin almost equalled sediment input from streambanks and valley slopes the results of the measurements of the various streambank processes are integrated in a descriptive model for the present day widening of valley incisions in the study area and used to hypothesize the palaeohydrological development of the basin special attention is paid to the in direct effects of the forest vegetation on streambank erosion and sediment transport through the stream channel

evaluating channel response to an extreme sedimentation event in the context of historical range of variability upper colorado river usa in may 2003 a breach in a large irrigation ditch within rocky mountain national park rmnp initiated a debris flow that entered lulu creek and the colorado river where 36 000 m3 of sediment substantially altered channel forms and processes we present a proof of concept to understand whether the 2003 disturbance is within the historical range of variability hrv and whether the recovery potential of the system is sufficient to adapt to the disturbance flow and sediment regimes and channel morphology and stability were monitored on lulu creek and the colorado river from 2004 to 2011 dominant channel response following the debris flow within lulu creek included step development bed armoring and channel widening step height to length ratios h l for three reaches on lulu creek are outside the hrv of reference channels with one reach approaching reference conditions erosion of approximately 23 of the debris fan volume occurred as a result of the long duration 2011 peak flow sediment within the lulu creek fan will persist for 30 190 years assuming current maximum and mean removal rates planform changes on the colorado river since the debris flow include an increase in single thread geometries with braided reaches where bar deposition occurred bedload transport and grain size analysis of bedload indicate translational spreading of a sand wave front with a dispersive component in steeper reaches lulu creek is returning to a condition of natural variability but the colorado river is outside the hrv expected for steep gradient pool riffle channels applying hrv to a situation where management questions require a longer term perspective and pre disturbance baseline data are limited is a useful approach the hrv analysis facilitates a better understanding of site variability and delineates the range of possibilities of channel form and process to achieve management goals copyright 2012 john wiley sons ltd

heat flow on the hawaiian swell and lithospheric reheating most oceanic volcanic centres caused by hotspot activity are surrounded by sea floor that is unusually shallow for its age1 2 there is increasing evidence that swells found on older sea floor like the hawaiian swell have formed from a broad scale reheating and thinning of the lithosphere as it passes over a mantle hotspot3 4 if the formation and subsequent disappearance of these swells are controlled by thermal processes they should have an above normal heat flux we present here the results from 95 new heat flow measurements on the hawaiian swell along the older part of the swell the heat flow is 20 25 higher than the normal heat flow for crust of this age this anomaly is consistent with the observed swell uplift the shape and amplitude of the heat flow anomaly require that the reheating be largely confined to the lower half of the lithosphere

mediated equilibrium the influence of riparian vegetation and wood on the long term evolution and behaviour of a near pristine river analysis of the contemporary geomorphology vegetation and in channel wood within the relatively pristine thurra river in southeastern australia provides insight into river behaviour prior to european disturbance this sand bed river has an extremely low channel capacity with a pronounced pool riffle morphology lateral migration rates are low 11 24 mm a 1 as are floodplain aggradation rates average d 0 27 mm a 1 sedimentological evidence is used to place contemporary channel dynamics within a 16 ka evolutionary framework the floodplain has continuously aggraded over this interval despite a number of avulsions and numerous meander cutoffs avulsions occur on a timeframe of once in 5 ka or more while cutoffs occur around once in 1 ka the morphology and evolution of the thurra river are appraised in terms of a mediated equilibrium condition in which channel capacity hydraulics bedload transport rates bank erosion rates and in channel deposition are substantially influenced by vegetation and wood within the channel and on the floodplain copyright 2002 john wiley sons ltd

thermal and mechanical constraints on the lithosphere beneath the marquesas swell the marquesas islands like most active or recently active hotspot chains lie on anomalously shallow sea floor and their subsidence history points to a fundamentally thermal origin for the swell1 as do heat flow and subsidence data for the swells beneath bermuda2 and hawaii3 4 here we apply a new linear filtering technique to geoid height and depth anomaly data over the marquesas to constrain the depth to the high temperature low density material responsible for elevating the swell we determine an isostatic compensation depth of 45 5 km for the swell and best fitting values for lithospheric flexural rigidity and island load density of 5 1022 n m and 2 700 kg m 3 respectively the swell s shallow compensation depth and low flexural rigidity call for anomalously high temperatures within the lithosphere5 6

pool and riffle characteristics in relation to channel gradient abstract the depths of pools relative to the dephts of runs and riffles were correlated with reach scale channel gradient along three rivers in coastal northern california the sample included 122 pools formed in channels with gradients from 0 172 to 0 002 relative pool depth on these rivers and relative distance between pools increase as channel gradient decreases mean pool riffle depth is 2 8 1 at the highest channel gradient and 6 2 1 at the lowest gradient while mean pool riffle length is 1 0 8 at high channel gradient and 1 1 8 at low channel gradient we hypothesize that these trends reflect changes in energy expenditure with decreasing gradient as a result of the flow s ability to erode its channel boundaries channel reaches with high gradients are characterized by resistant channel boundaries coarse material and relatively low discharge and total stream power channel reaches with low gradients have less resistant channel boundaries finger grained bed material and higher values of discharge and total stream power these changes in channel and flow characteristics with decreasing gradient result in flows in high gradient reaches expending a greater proportion of their energy in overcoming boundary and internal resistance with less energy available for channel bed scour and the formation of pools in their relatively resistant channels in contrast with less energy available for channel bed scour the channel bed creating deeper pools because the channel boundaries are less resistant and the proportion of flow energy available for sediment entrainment and transport should be greater

a comparison of stream bank erosion processes on forested and moorland streams in the balquhidder catchments central scotland stream bank erosion rates measured over a two year period on a moorland and a forested stream in the institute of hydrology s balquhidder paired catchments in central scotland were compared bank erosion rates are generally higher on the mainstream of the moorland catchment and highest in wintger on both streams bank erosion is correlated with the incidence of frost minimum temperatures measured on stream banks of the forested stream were an average of 3 7 c higher than on stream banks both outside the forest and on the moorland stream this makes the incidence of frost on forested stream banks half as frequent volumes of material eroded from the mainstreams were combined with bulk density measurements and it is estimated that erosion of the mainstream banks is contributing 1 5 and 7 3 per cent of the sediment yield of the forested and moorland catchments respectively analysis of the vertical distribution of erosion on the banks of both streams suggests an undercutting mechanism which is more pronounced in the moorland stream the influence of trees on bank erosion and possible implications for the management of forest streams are discussed 1997 by john wiley sons ltd

ethology of the trace fossil chondrites form function and environment abstract the behaviour of the iconic ichnogenus chondrites is re evaluated based on review of existing literature and analysis of novel data macroscopic thin section and esem edx observations ct scans and resin peels of modern analogues computer controlled serial grinding morphometric analysis and theoretical morphology the bedding plane expression of chondrites is well constrained by morphometry 1 the angle of dichotomy formed by a pair of adjacent branches is typically between 30 and 56 interquartile range mean 47 2 branching order is between 1 and 9 3 branches are on average nine times longer than wide in the third dimension downward branching is dominant but bundled shafts and upward branching may be present the size of chondrites increased markedly from the late jurassic to the late cretaceous suggesting that the tracemakers became larger and larger microfabric analysis of chondrites shows active fill or alternatively passive fill of empty tunnels by currents or clay percolation a new mechanism proposed herein the tracemakers built chondrites to obtain food 1 vermiform deposit feeders produced chondrites for searching for food in the sediment fodinichnion 2 asymbiotic bivalves built chondrites for cultivating and directly ingesting bacteria agrichnion 3 chemosymbiotic bivalves produced chondrites to provide symbionts with chemical agents chondrites was modified through the life of the tracemaker or it represented a part of the producer s lifespan chondrites and its modern tracemaker s is associated with a range of marine settings including well oxygenated dysoxic and space limited nucleocave environments as such chondrites is regarded as an extremotolerant ichnotaxon

analysis of sediment from steps in a small catchment in the polish carpathians in relation to the transition zone between the hillslope and fluvial system abstract an investigation to determine the transition zone between the hillslope system and the fluvial system in connection with the degree of differentiation of sediment located upstream and downstream of log steps ls and boulder steps bs was undertaken in the channel of a stream located in a small mountain catchment area in the silesian beskidy mts polish carpathians a stream channel into which large wood was introduced artificially several years ago granulometric analyses of 41 samples taken from upstream 21 and downstream 20 of steps were performed to analyze the effectiveness of log steps and boulder steps in the differentiation of mineral sediment it was demonstrated that log steps have a significant impact on the functioning of the channel by shaping its longitudinal profile and affecting the transport of mineral material whereas boulder steps retain less sediment showing the beneficial effects of artificial creation of log steps in mountain stream channels results of granulometric analyses suggested the location of the theoretical transition zone between the hillslope system and the fluvial system suggesting the location and range of this zone in small mountain catchment areas can change depending on the intensity and range of slope processes in the longitudinal profile of the channel

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

effects of coarse woody debris and its removal on a channel affected by the 1980 eruption of mount st helens washington during the may 18 1980 eruption of mount st helens washington a pyroclastic surge introduced large volumes of coarse woody debris cwd and fine grained sediment to clearwater creek approximately 15 km northeast of the summit effects of controlled cwd removal on sediment storage substrate and pool frequency and volume were measured in four reaches each with three 200 m segments from 1982 to 1990 in each reach the upstream segment served as a control with no debris removal and cwd was totally and selectively removed from the other two segments unique among similar experiments are the large size and volume of cwd and the large inputs of fine grained sediment except for segments of two reaches that received debris torrents the clearwater channel thalweg scoured until 1985 in three reaches total debris removal caused additional scour and coarsening of the bed surface compared to segments with no or partial debris removal pools contracted from 1982 to 1985 and expanded afterward especially in control segments total debris removal apparently caused pools to become shallower and in segments of low sinuosity decreased the frequency of major pools habitat complexity decreased after total debris removal as indicated by a decrease in the standard deviation of residual depth and an increase in the size of substrate patches

changes in woody debris and bed material texture in a gravel bed channel abstract this study investigated the response of bed material texture under two distinct periods of log jam conditions in a 900 m study reach of carnation creek vancouver island bc a field program extending over seven flood seasons coupled with existing streamflow records channel maps and low altitude aerial photography provides observations of jam stability and permeability surface and subsurface grain size as well as bed material fluxes sediment supply calibre streambed stability and sediment exchange near jams all jams functioned as partial dams throughout the field program but the overall perturbation of sediment transfers decreased when two jams were breached bed material texture exhibited the largest differences over the study reach during a period when log jams exerted a stronger influence over the passage of water and sediment at individual gravel bars most adjustments in surface and subsurface grain size constituted less than a 20 change in percentile values larger changes occurred primarily in subsurface sediment temporal patterns in bed material texture exhibited variation between bars but downstream of breached jams surface sediment conformed to the expected fining trend while the subsurface sediment increased in size surface and subsurface sediments evolved in the same direction only 64 of the time and the different magnitudes of adjustment caused local armor ratios to vary over time results highlight that the temporal dynamism of large woody debris lwd should be coupled with spatial considerations for effective stream restoration and management of streambed sediment

grim gravity model improvement using lageos grim3 l1 improved modeling of the earth s geopotential is one of the major tasks of satellite geodesy the availability of a new set of precise lageos satellite laser ranging slr data as well as seasat acquired observations enabled us to compute an improved solution in the grim model series the new geopotential grim3 l1 recombined the satellite perturbation normals of the former grim3 solution with new normal equation subsystems derived from an additional 16 months of lageos slr data oceanic 1 1 mean free air anomalies recovered from seasat altimetry an updated set of terrestrial 1 1 mean free air anomalies and several condition equations for zonal and resonant harmonics the combined normal equations were solved for a complete set of spherical harmonics up to degree and order 36 and the coordinates of 109 tracking stations comparisons with altimetry derived quantities terrestrial gravity anomalies from satellite to satellite tracking longitude accelerations of 24 hour satellites and satellite orbit fits show a substantial improvement over previous grim solutions and indicate that the lageos data have contributed considerably to the reliable estimation of the long wavelength portion of the gravity field

large woody debris and flow resistance in step pool channels cascade range washington abstract total flow resistance measured as darcy weisbach f in 20 step pool channels with large woody debris lwd in washington ranged from 5 to 380 during summer low flows step risers in the study streams consist of either 1 large and relatively immobile woody debris bedrock or roots that form fixed or forced steps or 2 smaller and relatively mobile wood or clasts or a mixture of both arranged across the channel by the stream flow resistance in step pool channels may be partitioned into grain form and spill resistance grain resistance is calculated as a function of particle size and form resistance is calculated as large woody debris drag combined grain and form resistance account for less than 10 of the total flow resistance we initially assumed that the substantial remaining portion is spill resistance attributable to steps however measured step characteristics could not explain between reach variations in flow resistance this suggests that other factors may be significant the coefficient of variation of the hydraulic radius explained 43 of the variation in friction factors between streams for example large woody debris generates form resistance on step treads and spill resistance at step risers because the form resistance of step pool channels is relatively minor compared to spill resistance and because wood in steps accentuates spill resistance by increasing step height we suggest that wood in step risers influences channel hydraulics more than wood elsewhere in the channel hence the distribution and function not just abundance of large woody debris is critical in steep step pool channels

variation of the apparent compensation depth of hotspot swells with age of plate abstract most oceanic hotspot swells are associated with anomalously shallow seafloor and broad geoid anomalies these depth and geoid anomalies are generally positively correlated and linearly related the linear relationship can be used to infer an apparent depth of isostatic compensation of the swell we have analysed geoid and depth anomalies over 23 oceanic hotspot swells almost the majority of oceanic hotspots and deduced the apparent depth of compensations of these features the data indicate a linear increase of the compensation depth with the square root of seafloor age t on the order of 7 km m y 1 2 this trend is comparable to that predicted by conductive cooling models for the deepening of the isotherms inside the oceanic lithosphere

contrasting patterns of wood storage in mountain watercourses narrower and wider than the height of riparian trees abstract large wood exerts a beneficial influence on the functioning of riverine and riparian ecosystems but can be also the source of flood risk several studies have recognised a trend of decreasing amounts of large wood on unit channel area with increasing width of mountain streams this study verifies whether this trend can also be generalised for wide mountain rivers longitudinal wood distribution was compared for two watercourses in the polish carpathians second to fourth order kamienica stream 14 m wide on average and the fifth order czarny dunajec river with a mean width of 52 m in the stream both the number and the mean mass of wood deposits were unrelated to channel width and this was reflected in a lack of the relationship between total wood storage the amount of stored wood per channel length and channel width in turn specific wood storage the amount of stored wood per channel area decreased nonlinearly with increasing channel width in the wide czarny dunajec the number and the mean mass of wood deposits increased as the river widened and this was reflected in a marked trend of increasing total wood storage with increasing river width here the width related variation in total wood storage was so high that it overcame the influence of increasing channel area on calculated values of specific wood storage which also increased with increasing river width this study shows that different mechanisms known to govern large wood retention in the channels narrower and wider than the height of riparian trees are reflected in the contrasting patterns of wood storage in mountain watercourses of different relative width different relations between the tendencies of total and specific wood storage in the two types of channels emphasise the need of identifying the spatial density and the total amount of large wood

influence of large woody debris on the morphology of six central european streams the impact of large fallen trees on channel form is described for six short stream sections in central europe influenced by large woody debris lwd sections five of which are compared to nearby reference sections free of lwd reference sections three dimensional models of streambed topography were generated by surveying cross sections with a spacing of 1 per 1 15 channel width parameters derived from digital terrain models and cross sections compared between lwd sections and reference sections include the extent of pools bars and cutbanks streambed and bank complexity cross sectional area width depth and cross section complexity as described by andrle s math geol 26 1994 83 angle measurement technique amt analysis a measure of the deviation of a cross section line from a straight line structural diversity is greater in lwd sections at almost all spatial scales particularly in terms of pool volume mann whitney u test p 0 01 and cross section complexity described by median angle of amt analysis mann whitney u test p 0 05 large pools are clearly associated with large fallen trees and attain volumes up to 36 m3 with the exception of the ratio of one lwd section where the fallen tree is oriented parallel to flow the ratio of pool volume to bed planimetric area ranges from 424 to 693 m3 ha which is in the upper range reported for small high gradient streams in oregon nw america 229 755 m3 ha can j fish aquat sci 47 1990 1103 pool volume of lwd sections is strongly correlated to the blockage ratio spearman rank order correlation rs 0 93 p 0 01 differences in channel morphology between the lwd sections and reference sections indicate a strong morphologic control of large woody debris in these central european stream sections

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

a long term estimate of bedload and suspended sediment yield derived from reservoir deposits abstract the draw down of pinmacher reservoir ayrshire west scotland in 1988 exposed sedimentary sequences entrapped since impoundment in 1903 the sole surface influent an ungauged second order stream drains a mainly undisturbed upland catchment most of the floor of the small basin is coated with mud however below the inflow a normally subaqueous delta of gravelly sand has accumulated examination of sections has enabled the construction of an isopachyte map from which the volume of deposits has been evaluated taking account of trap efficiency sediment water content and bulk densities the total sediment yield from the pinmacher catchment is 51 1 t km 2 year 1 on the assumption that the deltaic and lacustrine sequences respectively represent the bed and suspended fractions of the influent stream load long term 85 years average yields for the two components of 23 3 t km 2 year 1 and 27 8 t km 2 year 1 may be discriminated thus bedload accounts for ca 46 of the total load whilst the quantification of long term bedload transport remains elusive this study provides an unusually long record moreover analysis of the delta stratigraphy demonstrates two major and 21 additional flood events during the history of impoundment

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

thermal origin of the hawaiian swell heat flow evidence and thermal models the lithospheric reheating hypothesis for the origin of the hawaiian swell has been tested by heat flow measurements along the swell between hawaii and midway ninety five measurements at eight carefully selected sites show that the heat flux on the swell increases systematically from near normal values 52 2 mw m 2 near hawaii to values near midway 59 2 mw m 2 about 20 25 higher than normal for lithosphere of that age 110 m y this heat flow pattern is qualitatively consistent with a deep seated thermal anomaly created in a lithospheric plate moving across a fixed heat source modeling of the heat flow and bathymetry data on the hawaiian swell strongly suggest that the swell is caused by a rapid heating within 40 to 50 km depth of normal 90 m y old lithosphere over a relatively broad 500 1000 km region near hawaii this model is also consistent with gravity and geoid anomalies associated with the swell which require a low density region in the lower lithosphere and with flexure studies of seamounts in the hawaiian chain which indicate that the rigidity of the lithosphere is not significantly reduced by the reheating appendices a c are available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j82 005 1 00 payment must accompany order

geoid height versus topography for oceanic plateaus and swells oceanic plateaus and swells are a major component of the seafloor topography yet they remain among the most poorly understood features this is especially true of the oceanic plateaus which show large variations in crustal thickness to determine the depth and mode of compensation for 53 of the largest plateaus and swells we analyzed the relationship between geoid height and topography in polygonal areas containing each feature both geoid height and topography were first band pass filtered 400 km i 4000 km to isolate the signal associated with local compensation from flexural and deep mantle signals the ratio of geoid height to topography was then determined by fitting a straight line to the data except for nine of the smaller features there is a high correlation between geoid height and topography that is positive in accordance with airy and thermal compensation models eighteen features have high geoid topography ratios that cannot be explained by the airy compensation model of crustal thickening these features thermal swells are partially supported by thermal buoyancy forces in the lower half of the lithosphere the ratios are highest for active hot spot swells and decay with the thermal age of the swell to values consistent with airy compensation of the enduring volcanic edifice the remaining features plateaus have lower geoid topography ratios in agreement with the airy compensation model those plateaus with average height greater than 4 km are thought to be continental fragments the shorter plateaus tend to be volcanic features modified continental plateaus presumably small fragments of extended and intruded continental margin crust cluster around heights of n3 km overlapping the range associated with oceanic plateaus since the origin of many plateaus is poorly understood this global geoid topography analysis provides a new technique for comparing the deep structure of oceanic plateaus and swells

large wood lw 3d accumulation mapping and assessment using structure from motion photogrammetry in the laboratory abstract a structure from motion sfm photogrammetry based methodology for precise mapping of large wood lw accumulations in fluvial systems is presented the technique may be useful for routine inventory and rapid volume estimation of complex lw structures that tend to divert or obstruct flow in rivers our methodology is validated by means of laboratory experiments ranging from elementary to complex arrangements of lw components and organic fine material ofm seven experimental setups were used as the basis for i manual approximations of 2 5d and 3d geometric reference volumes ii 2 5d volume models based on mesh geometry iii a closed watertight 3d mesh from an unorganized point cloud and iv estimates of porosity a commercially available sfm photogrammetry software package pix4dmapper was used for point cloud and simplified mesh generation in order to obtain more precise volumes 3d surface models are required accordingly we generated 3d watertight mesh models of the unorganized point cloud using the screened poisson surface reconstruction psr technique the pix4d volume tool 2 5d resulted in an overestimation 2 9 to 52 7 of the geometric volume 3d due to the convex hull approximation of the geometry normal to the surface plane psr 3d resulted in more precise volumes showing deviations from the geometric volume 3d in a range of 15 9 to 10 6 as the algorithm could capture concavities and involuted surfaces on the accumulation assuming that the difference between 3d and 2 5d volume models represents many of the voids visible within or on the surface of the deposit this volume can be used as an estimate of porosity our assessment suggests that image based sfm methodology is well suited for further investigations in lw research due to its time and cost efficiency in comparison with other conventional surveying techniques the methodology can be used to generate high quality point cloud and mesh models of log jam formations these may be used by river managers and researchers to quantify accumulation volume and thus gain a better understanding of lw composition and the influence of wood geometry on hydraulic flow conditions

global mean sea surface based upon the seasat altimeter data a mean sea surface map has been computed for the global ocean areas between 70 n latitude and 62 s latitude based upon the 70 day set of seasat altimeter data recorded in 1978 a combination of regional crossover adjustment techniques and a global reference surface using the best available geodetic parameters for seasat has formed the basis for the computation the overall rms value of the crossover residuals in the open ocean areas was 13 cm after the adjustment a contour map of the crossover residuals is very similar in nature to earlier contour maps of the collinear pass results for mesoscale variability the mean sea surface is presented in the form of a global contour map a 0 5 0 5 grid and a computerilluminated image

depth and geoid anomalies over oceanic hotspot swells a global survey the broad depth and geoid anomalies associated with 23 hotspot swells in oceanic areas have been analyzed maximum height and geographical extent of the topographic swell and of the geoid anomaly as well have been measured for each hotspot the results indicate a clear increase of the topographic swell height with age of the underlying lithosphere from values in the range 300 500 m at young ages to values in the range 1 500 2 000 m at ages larger than 100 ma the geoid anomaly amplitude also increases with plate age from nearly zero close to mid ocean ridges to 6 8 m over old plates on the other hand the geographical extent of the swell does not show any clear relationship with plate age the mean lateral extent of swells range from 1 000 to 1 500 km swells located close to spreading ridges show a significant non zero depth anomaly but are associated with negligible geoid signal these results complete those of a previous study where the apparent compensation depth of oceanic hotspot swells was showed to increase linearly with the square root of plate age and coincide roughly with the base of the thermal lithosphere this trend may either be interpreted in terms ofmore lithospheric thinning or dynamical support besides both seem necessary to explain the observed bathymetry in proportion evolving with aging of the lithosphere less

subsurface flow in lowland river gravel bars geomorphic and hydraulic processes which form gravel bars in large lowland rivers have distinctive characteristics that control the magnitude and spatial patterns of infiltration and exfiltration between rivers and their immediate subsurface environments we present a bedform infiltration relation together with a set of field measurements along two reaches of the san joaquin river ca to illustrate the conditions required for infiltration and exfiltration of flow between a stream and its undulating bed and a numerical model to investigate the factors that affect paths and residence times of flow through barforms at different discharges it is shown that asymmetry of bar morphology is a first order control on the extent and location of infiltration which would otherwise produce equal areas of infiltration and exfiltration under the assumption of sinusoidal bedforms hydraulic conductivity varies by orders of magnitude due to fine sediment accumulation and downstream coarsening related to the process of bar evolution this systematic variability not only controls the magnitude of infiltration but also the residence time of flow through the bed the lowest hydraulic conductivity along the reach occurred where the difference between the topographic gradient and the water surface gradient is at a maximum and thus where infiltration would be greatest into a homogeneous bar indicating the importance of managing sand supply to maintain the ventilation and flow through salmon spawning riffles numerical simulations corroborate our interpretation that infiltration patterns and rates are controlled by distinctive features of bar morphology

modeling channel morphodynamic response to variations in large wood implications for stream rehabilitation in degraded watersheds abstract anthropogenic modification of forests has often decoupled streams from riparian ecosystems and altered natural wood recruitment processes extensive research has shown that large wood significantly impacts channel dynamics especially in small and intermediate sized forested streams where wood pieces are similar in length to channel width and many stream rehabilitation efforts now involve the addition of large wood to streams the primary objective of this research is to investigate the relation between large wood and reach scale channel morphology and hydraulics using a physical model in order to better inform stream rehabilitation programs and future modeling efforts four experiments each comprising numerous five hour runs were conducted using a froude scaled stream table with wood loads scaled to 0 m3 m2 0 011 m3 m2 0 016 m3 m2 and 0 022 m3 m2 the addition of large wood significantly decreased the reach averaged velocity in all experiments and was associated with decreased sediment transport and increased sediment storage in the reach increases in bed and water surface slope compensated for the loss of energy available to transport sediment and enabled the system to reach a new steady state within the equivalent of 6 to 9 years adding wood increased pool frequency as well as the variability in cross sectional depth while causing the reach to undergo a transition from a plane bed to a riffle pool morphology retention of fine sediment increased the availability of fish spawning substrate while increased water stage improved connectivity between the channel and the floodplain the changes in habitat complexity were generally related to the wood load added to the reach but were also dependent on the orientation and arrangement of the pieces these results demonstrate that wood may exert a primary control on channel morphodynamics and the availability of aquatic habitat in intermediate sized streams and suggest that the benefits from stream rehabilitation efforts are highly dependent on project scale the relatively long time needed to realize habitat benefits demonstrates that long term monitoring of rehabilitation projects is necessary

influence of large woody debris on morphological evolution of incised sand bed channels this paper documents the influence of large woody debris lwd on the morphological evolution of unstable degrading sand bed rivers in the yazoo basin north mississippi usa the study was performed as part of the demonstration erosion control dec project twenty three river reaches were studied with the aim of determining whether the presence of lwd was beneficial or detrimental to the recovery of stability in degrading sand bed river systems and to provide the geomorphic understanding necessary to underpin enhanced lwd management strategies the results demonstrate that locations of lwd inputs volumes of lwd stored in different reaches and number of jams per unit channel length are causally related to the morphological processes occurring during different stages of adjustment in these unstable incised fluvial systems and may be explained using a channel evolution model cem the net impact of lwd jams on reach scale sediment budgets was found in general to be positive that is jams trap more sediment than they mobilise this suggests that lwd probably accelerates rather than retards recovery of a stable longitudinal profile and channel configuration following incision field typing of lwd jams based on their impacts on the flow pattern reveals that jam type is a function of the size of large key elements in the jam in relation to the channel width a debris jam classification scheme is proposed on this basis with the spatial relationship between jam type and drainage basin area expressed using a dimensionless function of the ratio between channel width and average riparian tree height the scheme features four jam types underflow dam deflector and flow parallel bar head each of which has a different morphological impact on local channel geometry these jam types may be used to classify lwd jams as an aid in determining appropriate management strategies according to their location within the drainage basin

using structure from motion photogrammetry to assess large wood lw accumulations in the field abstract river systems in forested catchments are strongly influenced by wood and sediment loading from both natural e g mass wasting and anthropogenic forestry sources in order to effectively manage impacts on property infrastructure and the broader ecosystem as well as to better assess the interactions between large wood lw channel morphology and flow hydraulics more efficient and accurate surveying techniques are required we present an evaluation of structure from motion sfm photogrammetry and point cloud based techniques for capturing the geometry and volume of lw in the field wood accumulations can be notoriously complex 3d objects with multi scalar features and thus difficult to quantify with photogrammetric methods we introduce a novel workflow to generate volumetric information of organic material accumulations using sfm and a suite of meshing algorithms the volumes of two accumulations are assessed individually using several meshing techniques and are compared with more conventional volume estimates results show volumetric variations of