the effects of large organic debris on sediment processes and stream morphology in vermont abstract research conducted on a small third order stream in the green mountains of vermont suggests that large organic debris lod has an important influence on areal sorting and storage of sediment spacing of pool riffle sequences and channel geometry large organic debris forms local base levels that trap over 26 cubic meters of sediment and cause over 14 percent of the vertical drop along a 412 meter study reach on tiger brook vermont the local base levels created by large organic debris accumulations are the most important control on sediment storage between large bedrock knickpoints along the study reach focusing fine grained sediment deposition in areas stable at low and moderate discharges the micro steps created by these lod local base levels dominate gradient and sediment storage at short time scales between the slowly evolving large bedrock macrosteps the relation that exists among the volumes of standing timber adjacent to the channel lod and sediment stored behind lod seems to indicate that large organic debris causes a negative feedback type mechanism where channel degradation leads to increased standing timber recruitment and large organic debris sediment storage sites

instream wood loads in montane forest streams of the colorado front range usa abstract although several studies examine instream wood loads and associated geomorphic effects in streams of subalpine forests in the u s southern rocky mountains little is known of instream wood loads in lower elevation montane forests of the region we compare instream wood loads and geomorphic effects between streams draining montane forest stands of differing age old growth versus younger and disturbance history healthy versus infested by mountain pine beetles we examined forest stand characteristics instream wood load channel geometry pool volume and sediment storage in 33 pool riffle or plane bed stream reaches with objectives of determining whether i instream wood and geomorphic effects differed significantly among old growth younger healthy and beetle infested forest stands and ii wood loads correlated with valley and channel characteristics wood loads were standardized to drainage area stream gradient reach length bankfull width and floodplain area streams flowing through old growth forests had significantly larger wood loads and logjam volumes pairwise t tests as well as logjam frequencies kruskal wallis test residual pool volume and fine sediment storage around wood than streams flowing through younger forests wood loads in streams draining beetle infested forest did not differ significantly from those in healthy forest stands but best subset regression models indicated that elevation stand age and beetle infestation were the best predictors of wood loads in channels and on floodplains suggesting that beetle infestation is affecting instream wood characteristics wood loads are larger than values from subalpine streams in the same region and jams are larger and more closely spaced we interpret these differences to reflect greater wood piece mobility in subalpine zone streams stand age appears to exert the dominant influence on instream wood characteristics within pool riffle streams in the study area rather than beetle infestation although this may reflect the relatively recent nature

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

coarse sediment movement in the vicinity of a logjam in a neotropical gravel bed stream wood influences channel morphology by increasing channel roughness altering flow hydraulics and decreasing sediment transport in most fluvial systems where it is present in many locations the collection of wood into jams leads to even greater interruption of sediment transport by means of sediment impoundment and the creation of low velocity backwater flow zones we examined tracer clast movement near a wood jam in a neotropical gravel bed stream in order to evaluate the effect of wood mobility and piece transience on the ability of the jam to impede sediment transport we found that the jam had minimal influence on the passage of any individual clast with tracer clast mobilization and travel distance being best predicted by flow magnitude and grain size rather than location relative to the jam the rate of clast passage through the jam did not correlate with either the piece retention rate of the jam or with the density of the jam the jam did however temporarily trap a sediment wedge during a period when fluvially imported wood pieces blocked flow under a key wood piece diverting flow to a secondary flow path these results suggest that there is an upper bound on the flows in which wood is able to disrupt sediment transport and unlike for bedrock roughness elements this bound is frequently crossed at our study site

comparison of density cutters for snow profile observations an investigation was made to estimate the variance measurement errors and sampling error in currently accepted practices for manual snow density measurement carried out as part of snow profile observations using the available variety of density cutters a field experiment in dry snow conditions was conducted using a randomized block design to account for layer spatial variability cutter types included a 500 cm 3 aluminium tube 200 and 100 cm 3 stainless steel box types 200 cm 3 stainless steel wedge types and a 100 cm 3 stainless steel tube without accounting for variation due to weighing devices the range of values for accepted practice determined in this study included variation within individual cutters of 0 8 6 2 variation between cutters of 3 12 variation between cutter means and layer means of 2 7 and under sampling errors of 0 2 the results of a statistical analysis suggest that snow density measurements taken using various density cutters are significantly different from each other without adjustment for under sampling and given that the mean of all measurements is the accepted true value of the layer density variation exclusively between cutter types provides accepted practice measurements that are within 11 of the true density

investigating feedbacks in human landscape systems lessons following a wildfire in colorado usa abstract as human interactions with earth systems continue to intensify understanding the complex relationships among human activity landscape change and societal responses to those changes becomes increasingly important interdisciplinary research centered on the theme of feedbacks in human landscape systems serves as a promising focus for unraveling these interactions this paper examines the specific case of the 2012 waldo canyon fire of colorado where human responses after the fire to perceived threats of hydro geomorphological hazards included construction of tall fences at the base of a burned watershed these actions prompted feedbacks that promoted further landscape change that ultimately increased those hazards rather than dampening the hydro geomorphological effects of fire geomorphic analysis showed that the fences trapped particles that would naturally move through the system by flows with recurrence intervals greater than 3 3 years with the particles blocked by the fences the channel downstream became erosive because it was devoid of large particles that produce substantial hydraulic resistance channel incision prompted a second human response to pave the eroding channel which led to further incision downstream this cycle of positive feedbacks between human decision making and landscape change eventually led to a complete channelization of the stream channel downstream of the fences the explanation for the transformation of the post fire landscape therefore lies in the interacting human impacts and feedbacks rather than the expected post fire hydro geomorphological adjustments an initial agent based model capable of integrating social and hydro geomorphological data simulates these interacting impacts and feedbacks further refinement with more complete data input especially pertaining to human decision making at individual or local levels is required to fully demonstrate the utility and promise of this tool for application to geomorphic analysis

using lidar to characterize logjams in lowland rivers abstract logjams significantly influence watershed hydrology flow regime channel morphology and stability and processes in lowland rivers consequently logjams play a major role in the existence and conservation of the riparian and aquatic ecosystems along major waterways in this paper we attempt to detect and quantify logjams in river channels using lidar technology in conjunction with traditional fieldwork to the best of our knowledge lidar based analysis has not been used to characterize logjams in streams overall when applied in a lowland river environment lidar based analysis demonstrates a comprehensive solution for detecting logjams in relation to the fieldwork with a low rate of omission a filtered approach predicted the presence of 95 of fieldwork reported logjams a 5 rate of omission but also identified six logjams not identified in the field a 10 rate of commission a nonfiltered approach identified 87 of field reported logjams producing a 13 rate of omission and a 6 7 rate of commission dimension measurements were more consistent in the filtered lidar approach showing 53 34 and 90 of r2 improvements for the length width and height respectively over the unfiltered lidar values as vegetation cover hindered accurate delineation of logjam boundaries by lidar field and lidar measurements of nonvegetation obstructed logjams were more highly correlated than the field and lidar measurements of partially and completely vegetation obstructed logjams

large wood mobility processes in low order chilean river channels abstract large wood lw mobility was studied over several time periods in channel segments of four low order mountain streams southern chile all wood pieces found within the bankfull channels and on the streambanks extending into the channel with dimensions more than 10 cm in diameter and 1 m in length were measured and their position was referenced thirty six percent of measured wood pieces were tagged to investigate log mobility all segments were first surveyed in summer and then after consecutive rainy winter periods annual lw mobility ranged between 0 and 28 eighty four percent of the moved lw had diameters 40 cm and 92 had lengths 7 m large wood mobility was higher in periods when maximum water level h max exceeded channel bankfull depth h bk than in periods with flows less than h bk but the difference was not statistically significant dimensions of moved lw showed no significant differences between periods with flows exceeding and with flows less than bankfull stage statistically significant relationships were found between annual lw mobility and unit stream power for h max and h max h bk the mean diameter of transported wood pieces per period was significantly correlated with unit stream power for h 15 and h 50 the level above which the flow remains for 15 and 50 of the time respectively these results contribute to an understanding of the complexity of lw mobilization processes in mountain streams and can be used to assess and prevent potential damage caused by lw mobilization during floods

field measurements of three dimensional hydraulics in a step pool channel we investigated the effects of morphologic position and discharge on flow structure in a steep 0 10m m mountain channel by collecting three dimensional measurements of time averaged and turbulent velocity components with a sontek flowtracker handheld adv acoustic doppler velocimeter on a 30 m reach of a step pool channel in the colorado rockies velocity profiles were measured at morphologic positions characteristic of steep channels above steps step lips base of steps pools cascades runs and at five different discharges a marked three dimensionality of flow structure was documented in east st louis creek velocities in the streamwise component were the largest contributors to overall velocity vector magnitudes cross stream and vertical components contributed averages of 20 and 15 respectively to overall vector magnitudes turbulence intensities were especially multi dimensional however with large contributions to turbulent kinetic energy from the vertical component of velocity analysis of variance indicated that discharge and morphologic position significantly affected mean streamwise velocities with substantially higher velocities upstream from steps than in pools discharge and morphology effects on cross stream and vertical velocity components however were not significant discharge and morphologic position also significantly affected turbulence intensities for all flow components with the greatest turbulence intensities occurring in pools and at high discharges these results illustrate the strong discharge dependence of hydraulics in step pool channels where relative submergence of bedforms changes rapidly with discharge and the substantial spatial variation in hydraulics created by step pool sequences

experience with shear frames utilisation d une jauge a cisaillement pour des mesures in situ de la resistance au cisaillement dans l etude des stabilites des avalanches de plaques

bridging the gaps an overview of wood across time and space in diverse rivers abstract nearly 50 years of research focused on large wood lw in rivers provide a basis for understanding how wood enters rivers how wood decays breaks and is transported downstream and how at least temporarily stable wood influences channel geometry fluxes of water sediment and organic matter and the abundance and diversity of aquatic and riparian organisms field based studies have led to qualitative conceptual models and to numerical stimulations of river processes involving wood numerous important gaps remain however in our understanding of wood dynamics the majority of research on wood in rivers focuses on small to medium sized rivers defined using the ratio of wood piece size to channel width as channels narrower than the locally typical wood piece length small and slightly narrower than the longer wood pieces present medium although diverse geographic regions and biomes are represented by one or a few studies in each region the majority of research comes from perennial rivers draining temperate conifer forests regional syntheses most commonly focus on the pacific northwest region of north america where most of these studies originate consequently significant gaps in our understanding include lack of knowledge of wood related processes in large rivers dryland rivers and rivers of the high and low latitudes using a wood budget as an organizing framework this paper identifies other gaps related to wood recruitment transport storage and how beavers influence lw dynamics with respect to wood recruitment we lack information on the relative importance of mass tree mortality and transport of buried or surficial downed wood from the floodplain into the channel in diverse settings knowledge gaps related to wood transport include transport distances of lw and thresholds for lw mobility in small to medium rivers with respect to wood storage we have limited data on longitudinal trends in lw loads within unaltered large and great rivers and on fluctuations in lw load over time intervals greater than a few years other knowledge gaps relate to physical and ecological effects of wood including the magnitude of flow resistance caused by lw patterns of wood related sediment storage for diverse river sizes and channel geometry quantification of channel floodplain lw interactions and potential threshold effects of lw in relation to physical processes and biotic communities finally knowledge gaps are related to management of large wood and river corridors including understanding the consequences of enormous historical reductions in lw load in rivers through the forested portions of the temperate zone and how to effectively reintroduce and manage existing lw in river corridors which includes enhancing public understanding of the importance of lw addressing these knowledge gaps requires more case studies from diverse rivers as well as more syntheses and metadata analyses

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

a flume experiment on the formation of wood jams in rivers 1 a flume experiment is carried out to explore jamming of large woody debris lwd in streams with complex morphology occurring in mountain streams with in channel boulders or vegetation in braided rivers or in floodplains during flood events non rooted defoliated lwd is modeled using wood dowels and obstacles to motion are represented by vertical wood rods congested transport of lwd is simulated by insertion of a number 100 of dowels the final position of the dowels is mapped and the observed jams are classified according to their size and position the key member of each jam is identified and its trapping mechanism evaluated either by leaning against a single obstacle or by bridging two obstacles to mimic uncongested transport the experiment is repeated for single pieces of wood with subsequent removal longer dowels and shallower water result in shorter traveled distance wood pieces travel farther when congested transport is observed the traveled distance of the wood pieces can be modeled using a gamma distribution for both congested and uncongested transport jams instead display uniform traveled distance the number of pieces displays an exponential distribution the degree of uniformity in space of jams and wood pieces is evaluated using a neighbor k statistic wood pieces show considerable clustering while jams show sparse distribution eventually the relationship between jams magnitude and position is explored showing negative correlation model application is then discussed and some conclusions and future developments are outlined

a computer based system simulating snowpack structures as a tool for regional avalanche forecasting this paper describes the current state of a complete automatic system of three numerical models that simulate snow cover stratigraphy and avalanche risks for operational avalanche forecasting the first model safran estimates relevant meteorological parameters affecting snowpack evolution the second crocus is a snow numerical model which simulates the physical processes inside the snowpack and its stratigraphy the last model mepra is an expert system based on an assessment of snowpack stability it deduces natural and accidental avalanche risks to describe the great variability of the snowpack and the associated avalanche risks this automatic system simulates snow cover evolution and its stability for many typical slopes elevations and aspects representative of the different french massifs to achieve this result different kinds of validations have been carried out since winter 1981 they are mainly based on comparisons with different sets of measurements and on the opinion of users although the routinely obtained results do not yet take into account all small scale effects such as wind transport they have been considered as valuable information by avalanche forecasters since 1992 93 and used operationally since then

characteristics distribution and geomorphic role of large woody debris in a mountain stream of the chilean andes the paper presents an analysis of amounts characteristics and morphological impact of large woody debris lwd in the tres arroyos stream draining an old growth forested basin 9 1 km2 of the chilean southern andes large woody debris has been surveyed along a 1 5 km long channel section with an average slope of 0 07 and a general step pool cascade morphology specific wood storage is very high 656 710 m3 ha 1 comparable to that recorded in old growth forested basins in the pacific northwest half of the lwd elements were located on the active floodplain and around two thirds of lwd elements were found in accumulations different types of log jam were observed some heavily altering channel morphology log steps and valley jams while others just line the channel edges bankfull bench jams log steps represent approximately 22 of all steps whereas the elevation loss due to lwd log steps and valley jams results in 27 loss of the total stream potential energy about 1600 m3 of sediment is stored in the main channel behind lwd structures corresponding to approximately 150 of the annual sediment yield copyright 2007 john wiley sons ltd

transport of large woody debris in the presence of obstacles flume experiments were carried out to investigate the motion of large woody debris lwd in rivers as influenced by the presence of obstacles non rooted defoliated lwd was modelled by placing properly scaled wooden dowels placed into controlled water flow obstacles were represented by wooden rods randomly placed into the flume with a specified probability distribution the results provide the probability of lodging of the dowels and statistics of the distance travelled their relationships with flow rate and depth dowel length and spatial density of the obstacles is explored this yields a general theoretical framework to approach lwd transport in rivers by combining random factors with deterministic dimensionless variables

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

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

temporal variations of large wood abundance and mobility in the blanco river affected by the chaiten volcanic eruption southern chile abstract the aim of this study is to analyze the temporal variation in abundance and transport of in channel wood along a river affected by a volcanic eruption considering the mobility and retention rates in detail the 2008 eruption of chaiten volcano southern chile severely affected the blanco river basin causing changes in channel morphology and large wood lw dynamics along the fluvial corridor of the river a fourth order stream on the southern slope of the volcano temporal dynamics of lw were investigated from january 2015 until march 2016 in three 80 m long study reaches of the active channel in the lower course of the river every wood element 1 m in length and 0 1 m in diameter within the active channel of each reach was georeferenced measured tagged and characterized wood mobility rate defined as the number of tagged wood pieces repositioned or not found within each study reach to total tagged lw in the same reach and retention rate defined as the number of tagged lw pieces found within each study reach to total tagged wood pieces in the same reach were calculated considering two periods one in summer and one in autumn winter a regional flood frequency analysis estimated flood magnitude defining a recurrence interval of 1 year for summer floods and 10 25 years for autumn winter floods results highlighted how eight years after the eruption the types of lw are still influenced by the impacts of pyroclastic density currents on riparian vegetation the characteristics and abundance of monitored lw are typical of a river system with frequent wood transport the mobility rate ranges between 42 and 94 during the summer and autumn winter period respectively while the wood volume decreases during the summer and increases in autumn winter large wood mobility was also found to vary according to the predominant morphological settings with lower values in narrower channels compared to wider wetted areas in this context the greatest abundance of lw was detected after the higher floods corresponding to an input of lw up to 285 35 m3 ha 1 along the blanco river ordinary floods deliver lw mainly through fluvial transport and bank erosion during higher floods appears as an additional and important wood recruitment process the bank erosion processes with up to 5200 m2 of eroded area confirmed the widening tendency occurring in river systems following volcanic disturbances as there are dead riparian trees along the easily erodible banks it is reasonable to suppose that the blanco river will continue to widen for a long period recruiting and transporting downstream huge volumes of lw in this context these analyses appear of fundamental importance to better manage the river system also for decreasing hazards to the downstream village of chaiten

frequency of large in channel wood in eastern oklahoma ecoregions and its association with channel morphology abstract regional climate geology vegetation and land use influence hydrogeomorphic processes which influence stream channel form and the recruitment and transport of wood in streams we studied relationships between channel morphology and frequencies of large in channel wood in three upland ecoregions of eastern oklahoma where streams contain high fish diversity and valuable sport fisheries we surveyed 138 streams for wood within the boston mountains n 30 ozark highlands n 30 and ouachita mountain n 78 ecoregions our study investigated whether 1 the frequency of large wood differed among ecoregions 2 channel morphology influenced the distribution of large wood within and among ecoregions and 3 a relationship existed between the frequency and size of trees in the riparian zone and the frequency of large wood within and among ecoregions the frequency of single large wood pieces did not differ among ecoregions or vary with drainage area however the presence of one or more wood accumulation 2 to 4 pieces increased with drainage area and increased at a higher rate in the boston mountains and ozark highlands than in the ouachita mountains the frequency of single wood pieces decreased in narrower channels with larger substrates but increased in larger stream channels overall no association existed between riparian tree density and in channel wood in study reaches we discuss these results in the context of wood recruitment and transport and highlight key questions that remain regarding wood in eastern oklahoma streams

wood controls on pool spacing step characteristics and sediment storage in headwater streams of the northwestern cascade mountains abstract wood influences channel morphology in headwater streams by creating steps and pools in the longitudinal profile and trapping sediment we used field data from 32 headwater stream reaches in the northwestern cascade mountains to test the hypotheses that 1 larger diameter classes of large wood lw defined as pieces with diameter 10 cm and length 0 5 m are critical step keying materials in headwater channels despite narrow channel widths 1 4 m 2 wood keyed steps trap more sediment than clast and root keyed steps and 3 the negative relationship between lw frequency and the distance between pools observed elsewhere in large streams extends to headwater streams we found that the frequency of step key pieces peaked in the 20 40 cm diameter class similarly 40 100 cm diameter pieces were disproportionately associated with key piece function compared to their overall association with step formation wood with diameter

does reintroducing large wood influence the hydraulic landscape of a lowland river system abstract our understanding of the effectiveness of reintroduced large wood for restoration is largely based on studies from high energy river systems by contrast few studies of the effectiveness of reintroducing large wood have been undertaken on large low energy lowland river systems river systems where large wood is a significant physical feature on the in channel environment this study investigated the effect of reintroduced large wood on the hydraulic landscape of the barwon darling river australia at low flows to achieve this the study compared three hydraulic landscapes of replicated reference naturally wooded control unwooded and managed wood reintroduced treatments on three low flow periods these time periods were prior to the reintroduction of large wood to managed reaches several months after the reintroduction of large wood into the managed reaches and then more than four years after wood reintroduction following several large flood events hydraulic landscapes of reaches were characterised using a range of spatial measures calculated from velocity measurements taken with a boat mounted acoustic doppler profiler we hypothesised that reintroduced large wood would increase the diversity of the hydraulic landscape at low flows and that managed reaches would be more similar to the reference reaches our results suggest that the reintroduction of large wood did not significantly change the character of the hydraulic landscape at the reach scale after several months p 0 16 or several years p 0 29 overall the character of the hydraulic landscape in the managed reaches was more similar to the hydraulic landscape of the control reaches than the hydraulic landscape of the reference reaches at low flows some variability in the hydraulic landscapes was detected over time and this may reflect reworking of riverbed sediments and sensitivity to variation in discharge the lack of a response in the low flow hydraulic landscape to the reintroduction of large wood is inferred because the character the size and complexity of individual pieces and positioning of large wood in managed reaches did not mimic that of reference reaches effectively despite the abundance of wood pieces being similar in the reference and managed reaches the results of this study highlight the importance of understanding the natural character and distribution of large wood on hydraulic landscapes in large low energy lowland river systems especially when reintroducing large wood for river management purposes

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

neighborhood matters patterns and controls on wood distribution in old growth forest streams of the colorado front range usa abstract we surveyed wood characteristics along four headwater channel segments of the colorado front range with drainage areas of 8 82 km2 stream lengths surveyed range from 3025 to 8980 m and together include a total of 15 706 pieces of wood time since last disturbance in the form of a stand killing fire varied from 31 to 500 years individual pieces of wood were highly aggregated at length scales of 1 to 150 m trends among jams were more weakly developed but jams tended to be more segregated at lengths 300 m with jams along individual channels being aggregated segregated or random multiple linear regressions failed to produce highly predictive models to explain the response variables of wood load piece dimensions or characteristics of jams other than jam volume which correlated with drainage area and wood load but examination of downstream patterns suggests that local valley and channel geometry valley bottom width gradient and sequence of longitudinal channel changes exert a stronger influence on patterns of wood distribution than either time since last forest disturbance or progressive downstream trends associated with increasing drainage area the longitudinal sequences of wood recruitment sources forest stand age and channel geometry together exert an important control on reach scale wood load and aggregation wood loads in streams draining old growth 250 years forests of the colorado front range are low compared to old growth sites in other regions of the world which we interpret to reflect decreased retention of wood recruited to the streams

a probabilistic multidimensional approach to quantify large wood recruitment from hillslopes in mountainous forested catchments abstract large wood lw plays a key role in physical chemical environmental and biological processes in most natural and seminatural streams however it is also a source of hydraulic hazard in anthropised territories recruitment from fluvial processes has been the subject of many studies whereas less attention has been given to hillslope recruitment which is linked to episodic and spatially distributed events and requires a reliable and accurate slope stability model and a hillslope channel transfer model the purpose of this study is to develop an innovative lw hillslope recruitment estimation approach that combines forest stand characteristics in a spatially distributed form a probabilistic multidimensional slope stability model able to include the reinforcement exerted by roots and a hillslope channel transfer procedure the approach was tested on a small mountain headwater catchment in the eastern italian alps that is prone to shallow landslide and debris flow phenomena the slope stability model that had not been calibrated provided accurate performances in terms of unstable areas identification according to the landslide inventory auc 0 832 and of lw volume estimation in comparison with lw volume produced by inventoried landslides 7702 m3 corresponding to a recurrence time of about 30 years in the susceptibility curve the results showed that most lw potentially mobilised by landslides does not reach the channel network only about 16 in agreement with the few data reported by other studies as well as the data normalized for unit length of channel and unit length of channel per year 0 116 m3 km and 0 4 m3 km y 1 this study represents an important contribution to lw research a rigorous and site specific estimation of lw hillslope recruitment should in fact be an integral part of more general studies on lw dynamics for forest planning and management and positioning in channel wood retention structures

linking the effective thermal conductivity of snow to its shear strength and density 1 the effective thermal conductivity of snow keff is a crucial climatic and environmental variable here we test the intuition that keff is linked to microstructural and mechanical properties by attempting to relate keff to density snow and to shear strength measured with a handheld shear vane we performed 106 combined measurements of keff snow and in the alps svalbard arctic alaska and near the north pole covering essentially all snow types we find a good correlation between keff and snow which is not significantly different from that of sturm et al 1997 the correlation between keff and a combination of and snow is stronger than with density alone we propose an equation linking keff w m 1 k 1 snow kg m 3 and pa keff 7 114 10 5 snow 0 333 2 367 10 2 this equation places constraints on the calculation of keff snow and in avalanche warning models where is a key variable for our samples we calculate from measured values of keff and snow using our equation and compare the value to that predicted by the french mepra avalanche warning model which uses density and grain type as input data mepra and the prediction of based on keff and snow agree within 8 mepra agrees with observations within 11 calculating from density only yields values 55 lower than measured showing the interest of using additional data to predict

log step and clast interactions in mountain streams in the central cascade range of washington state usa article i nfo field surveys of log steps in high gradient streams investigate the interactions between log steps and clasts to assesswhethersecond growthwoodcanformlogstepscapableof diverting flowandactingassignificant rough ness elements similar to those formed by old growth wood we measure the functional log diameter and step height as well as visually estimate the clast size in the step of 102 log steps in 15 high gradient streams in the centralcascaderangeofwashington usa wecomparestepheightdatatomeasurementsofmaximumbankfull depthtomeasurethe capability of log steps to divert flowrelativeto theirclastsizeand log diameter stepheight positively correlates with functional log diameter p b 0 001 and clast size additionally a threshold clast size exists above which functional log diameter more strongly correlates with step height indicating that clast size can limit step height we find that steps with cobble or larger n64 mm clasts in the step are 3 7 times more likely to reach or exceed bankfull depth than steps with smaller than cobble clasts in the step we conclude that it is necessary for steps formed by small logs to have large clasts in the step in order to reach bankfull depth act as significant roughness elements and create flow diversions implying that the potential for second growth forests to maintain log steps similar to those formed by old growth logs depends on the size of bed material

distribution and dynamics of large woody debris and organic matter in a low energy meandering stream this field based study using a combination of bed sediment sampling and large woody debris lwd tracking explores the storage of organic matter and mobility of lwd in poplar creek a low energy meandering river that contains a diverse arrangement of large woody debris lwd this research addresses the following questions 1 does lwd influence the spatial pattern of the storage of benthic organic matter in meander bends 2 how mobile is the lwd in low gradient meandering systems 3 do characteristics of lwd such as length bankfull channel width ratio affect movement based on detailed sampling of sediment and lwd monitoring this study provides a detailed representation of the influence of lwd on the storage of benthic organic matter in meander bends as well as a detailed documentation of the mobility of lwd in the study reach this study has demonstrated that 1 lwd strongly influences patterns of storage of benthic organic matter in low gradient meander bends 2 removal of lwd from meander bends in low gradient systems can substantially reduce the storage of benthic organic matter and 3 the lwd within the study reach at poplar creek is highly mobile the high mobility of lwd observed in this study contrasts with the rates observed in high gradient systems and suggests that lwd influenced patterns of storage of organic matter are temporally variable and that storage of benthic organic matter occurs in pulses interspersed with transport that are keyed to the mobility of lwd although lwd may exert an equally significant control over patterns of storage of organic matter in high and low gradient systems the differences in the mobility rates of lwd suggest a fundamental difference in the dynamics of lwd mediated organic matter between low and high gradient systems

bed surface adjustments to spatially variable flow in low relative submergence regimes in mountainous rivers large relatively immobile grains partly control the local and reach averaged flow hydraulics and sediment fluxes when the flow depth is similar to the size of these grains low relative submergence heterogeneous flow structures and plunging flow cause spatial distributions of bed surface elevations textures and sedimentation rates to explore how the bed surface responds to these flow variations we conducted a set of experiments in which we varied the relative submergence of staggered hemispheres simulated large boulders between runs all experiments had the same average sediment transport capacity upstream sediment supply and initial bed thickness and grain size distribution we combined our laboratory measurements with a 3d flow model to obtain the detailed flow structure around the hemispheres the local bed shear stress field displayed substantial variability and controlled the bedload transport rates and direction in which sediment moved the divergence in bed shear stress caused by the hemispheres promoted size selective bedload deposition which formed patches of coarse sediment upstream of the hemisphere sediment deposition caused a decrease in local bed shear stress which combined with the coarser grain size enhanced the stability of this patch the region downstream of the hemispheres was largely controlled by a recirculation zone and had little to no change in grain size bed elevation and bed shear stress the formation development and stability of sediment patches in mountain streams is controlled by the bed shear stress divergence and magnitude and direction of the local bed shear stress field

bed morphology and generation of step pool channels flume experiments have been carried out to study the formation processes and the bed morphology of step pool channels from the experiments different step types and step configurations could be distinguished depending on the stream power these step types can be seen as an image of the generation mechanisms of step pool systems these results suggest that the bed roughness geometry develops towards a condition that provides the maximum possible bed stability for a given grain size distribution in contrast to a variety of other studies antidunes did not contribute to the generation of the step structures however the data of the presented study fits well into the region of antidune formation proposed by kennedy for sand bed rivers this observation points out that step pool field data located in the kennedy region do not inevitably prove that antidunes played a role in step development it is rather proposed that in kennedy s region of antidune formation there exist hydraulic conditions where the flow resistance is maximized it is suggested that such maximum flow resistance is associated with an optimal distance between the bedforms and their height independently of whether these are antidunes in sand and gravel bed rivers or step pool units in boulder bed streams the considerations of the kennedy region of antidune formation and the analysis of planform step types depending on stream power both suggest that steep channels have a potential for self stabilization by modifying the step pool structure towards a geometry that provides maximum flow resistance and maximum bed stability copyright 2008 john wiley sons ltd

morphological organization of a steep tropical headwater stream the aspect of channel bifurcation abstract channel characterization and instream wood surveys demonstrate the spatial complexity of an ungauged tropical headwater stream hws in the tilaran mountains of costa rica throughout the stream course we characterized 29 individual reaches based on their morphological organization and instream wood occurrences bifurcated reaches were the most numerous and consistently distributed they also had the highest values of wood abundance and loading and contained the majority of unattached instream wood we selected two bifurcated reaches for ultrahigh resolution terrestrial laser scanning tls surveys orthographic tls produced millimeter resolution point cloud data sets from which 2 cm planimetric resolution digital elevation models dems of the channel surface were derived for both reaches cross sectional surveys of these dems using the river bathymetry toolkit rbt produced hydraulic geometries at two flow levels high and low for every meter length of channel reach we input these geometries into a one dimensional analytical model to demonstrate the downstream evolution of mean stream power through varying morphology elements mean stream power variation displays a regular pattern through the vertical modulation of step pool sequences but this regular pattern is lost through channel widening and bifurcation reach geometric data indicates that increasing width to depth ratio is the most notable feature of channel bifurcation and corresponds to a reduction in slope and roughness variation this primary understanding of channel dynamics denotes the complex organization of a tropical hws and promotes further research into tropical hws systems

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

wood retention and transport in tropical headwater streams la selva biological station costa rica article i nfo wood in tropical streams has the potential to be more mobile than wood in otherwise similar temperate streams because of the warm and humid conditions that promote decay and the more frequent and flashier floods of the tropics to test this hypothesis we monitored all large wood pieces for 2 3 years in 10 50 m long reaches of old growth headwater streams in la selva biological station costa rica annual wood retention rates for pieces ranged from 0 55 to 0 91 among the sites and retention rates by volume ranged from 0 67 to 0 99 assuming steady state wood load which is reasonable for la selva these rates are equivalent to mean residence times of 2 2 10 6 years for pieces and 3 0 83 2 years for a volume of wood calculating mean residence time from the weighted average of retention rates gives an average residence time of 4 9 years for a piece of wood and 6 9 years for a volume of wood these values are less than those reported for old growth temperate forests supporting our hypothesis mobility of individual pieces was best predicted by piece length relative to stream width lr higher lr led to lower mobility channel gradient s higher s led to higher mobility and piece integration into the channel unattached pieces were 2 6 times more mobile than attached ramp or bridge pieces temporal variation in retention rates was well explained by variation in peak flow all four of these factors have also been observed to influence mobility in the temperate zone the higher mobility of wood in our study site relative to the temperate rainforest of the pacific northwest may be explained by the flashy and frequent floods the high decay rate or the branching morphology of the native trees but differentiating the role of these factors particularly flow and decay will be complicated by their covariation across climates

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 numerical model to simulate snow cover stratigraphy for operational avalanche forecasting laws of snow metamorphism have been introduced in a numerical model which simulates the evolution of temperature density and liquid water profiles of snow cover as a function of weather conditions to establish these laws the authors have summarized previous studies on temperature gradient and on wet snow metamorphism and they have also conducted metamorphism experiments on dry or wet fresh snow samples an original formalism was developed to allow a description of snow with parameters evolving continuously throughout time the introduction of laws of metamorphism has improved significantly the derivation of the settlement of internal layers and of snow covered albedo which depend on the simulated stratigraphy i e the type and size of snow grains of different layers of the snow cover the model was tested during a whole winter season without any re initialization comparison between the simulated characteristics of the snow cover and the observations made in the field are described in detail the model proved itself to be very efficient in simulating accurately the evolution of the snow cover stratigraphy throughout the whole winter season

properties of small instream wood as a logjam clogging agent implications for clogging dynamics based on wood density water content and depositional environment abstract in cooperation with large instream wood lw within logjams small instream wood sw can control downstream flux of sediment and particulate organic matter and can play an important role for stream ecosystems however information regarding the density and moisture content of sw which affects wood transport wood decay and mass loading is limited here we investigated the sw properties i e density under field conditions in situ density basic density volumetric water content and depositional environment of sw sampled from five logjams and their backwater areas in two headwater streams second and third order streams surrounded by mixed broadleaf conifer forests in western japan the in situ density ranged from 0 49 to 1 25 g cm 3 and pieces with densities 1 0 g cm 3 accounted for 45 of all samples additionally the in situ density of sw closely related to the volumetric water content r2 0 76 rather than the basic density as an index of solidity or decay condition of wood the sw that was partially submerged in water had a higher volumetric water content than sw exposed to air these results indicate that a nonfloating transport cannot be ignored as an important mechanism for sw movement and that in situ density depends not on the solidity of the wood but on water sorption by sw however waterlogged sw should be well decayed because it has a lower basic density than air exposed and sediment buried sw we conclude that the moisture conditions of the depositional environment can affect subsequent transport and decay processes of sw moreover most waterlogged and sediment buried sw because of its high in situ density 1 0 g cm 3 may contribute to clogging between the channel bed and lw that initiate a logjam during future movements

multiple paths to straths a review and reassessment of terrace genesis abstract strath terraces an important tool in tectonic geomorphology have been attributed to climatic tectonic volcanic and human activity yet the pathways connecting external forcings to the channel response leading to terrace formation are highly variable and complex to better understand variability and controls on the pathways between forcing and terrace formation we created a comprehensive database of 421 strath terraces from peer reviewed literature and noted the strath age and rock type the ascribed forcing climate tectonics volcanoes or humans or whether the cause was unascribed and the pathway between forcing and strath incision or planation study authors identify climate tectonics volcanoes and humans as the forcing for 232 55 20 5 8 2 and 5 1 strath terraces in our compilation respectively a forcing was not identified for the remaining 156 37 terraces strath terraces were dated using 14 different methods 71 of terraces in our database are dated using methods such as radiocarbon and optically stimulated luminescence that date planation and give a maximum age of incision 16 of terraces are dated with methods that give a minimum age of incision and 14 use a variety of methods for which a generalization about incision age cannot be made that the majority of terrace studies use planation ages to understand terrace formation highlights the necessity of knowing the relative timescales of incisional and planation phases which has so far been quantified in only a handful of studies in general rivers in arid regions plane straths in interglacial periods when discharge and sediment transport capacity increase whereas temperate rivers plane in glacial or interglacial periods when sediment supply increases heterogeneities in rock strength between watersheds further control how sediment is produced and when straths are planed globally these regional and watershed controls result in strath planation and incision during all parts of the glacial cycle terraces with no identified forcing in our database reach a maximum frequency during the late holocene 4 kya present and could potentially be explained by regional deforestation and increased anthropogenic fire frequency regionally active tectonics and climate fluctuations deforestation and fires by reducing the supply of wood to streams decrease instream sediment retention and could convert alluvial channels to bedrock thus promoting strath incision the regional and watershed controls on strath formation highlighted in our database as well as the possibility of anthropogenic forcings on strath terrace formation in the late holocene illustrate the importance of explicitly establishing the pathway between forcing and strath terrace formation in order to accurately interpret the cause of strath formation

do the coarsest bed fractions and stream power record contemporary trends in steep headwater channels abstract three stream channels that were devoid of evidence of past debris flows and one headwater channel that contained debris flow deposits in the flysch western carpathians czech republic were selected to test relationships between in channel processes bed sediments and unit stream power calculated for bankfull and q 20 flows contemporary depositional or erosional trends in the examined headwaters were linked with bed sediments that were represented by the coarsest cobble and boulder fraction with a mean calculated from the five largest particles the downstream trends of the unit stream power were derived for a bankfull discharge and a well documented 20 year flood event in addition the flow competences during the discharges were calculated using indirect bedload transport measurements downstream fining of the cobble and boulder fraction was observed in all of the studied headwaters and unique downstream variations of the unit stream power were calculated for the longitudinal profiles the single thread streams that were devoid of evidence of debris flow events exhibited direct relations between the coarsest sediment size and the unit stream power especially as calculated for the 20 year flood event and for erosional depositional trends of the channel the downstream coarsening of the bed material that was accompanied by an increase in the unit stream power was usually observed in the case of deeply incised 0 5 m above the assumed bankfull depth channel reaches the calculated competence of the 20 year flow was up to twofold higher than that required to entrain the largest bed particle diameters in those channel reaches and even the bankfull flow was potentially capable of transporting the coarsest bed particles in certain of the reaches on the other hand some depositional channel reaches evidently led to the disconnectivity of transport of the coarsest bed material even in the case of the 20 year flood event the longitudinal profile of the channel that had evidence of past debris flows did not clearly show a direct relationship between boulder size and calculated unit stream power and contemporary channel trends this finding reflected the presence of significantly coarser bed material which points to a higher stability of the debris flow influenced channel during ordinary floods when compared to fluvially dominated headwaters that are devoid of debris flows

flood and debris flow interactions with roads promote the invasion of exotic plants along steep mountain streams western oregon this study examines the interactions among geomorphic and biogeographic processes that govern the invasion by two contrasting exotic plant species a shrub scotch broom cytisus scoparius and an herb foxglove digitalis purpurea over several decades of road and stream networks in the h j andrews experimental forest in western oregon distributions of c scoparius and d purpurea were mapped along hillslopes and streams in 1993 2002 and 2003 the mapped distributions were related to debris flow pathways and changes in stream morphology interpreted from field surveys and air photos over the period 1993 to 2003 laboratory trials examined the response of seed germination to scarification to test effects of transport by debris flows soaking to test effects of fluvial transport and substrate texture to test effects on establishment c scoparius and d purpurea were present along roads and in clearcuts in the andrews forest from the 1970s to 2003 but invaded the stream lookout creek only after debris flows and floods during an extreme storm in 1996 laboratory trials demonstrated that seeds could germinate on a variety of substrates after scarification and flood transport mapping and air photo gis analysis indicated that the distributions of exotic plants were located on freshly scoured bars and floodplains adjacent to the active channel downstream of seed sources along roads that were connected to the main stem of lookout creek by road ditch drainage systems and debris flow paths this paper outlines a conceptual model for the invasion of exotic plants highlighting the connectivity between road and stream networks provided by geomorphic processes in steep forested landscapes

morphological patterns of headwater streams based in flysch bedrock examples from the outer western carpathians abstract a channel reach morphology of mountain headwater streams results from the balance between fluvial and hillslope processes a large dataset n 102 of channel reaches coming out from flysch mid mountains was evaluated and compared with streams occurring in other environments two new channel reach morphologies were distinguished with respect to their differences in the ratio of sediment supply to transport capacity bedrock cascades and step rapids the chaining of channel reach morphologies by gradient criteria and the parameters of channel gradient and bankfull width related to the basin area show similar trends when compared to other recent studies by contrast bankfull depth indicates its independence on increasing basin area significant downstream coarsening of bed material occurs only in alluvial stepped bed morphologies cascades step pools and step rapids mainly due to strong slope channel coupling processes moreover the specific ratio of bankfull width and d90 predicts the interlocking of boulder steps as well as well developed step pool morphology an amount of large woody debris is closely related to the activity of strict local forest management in evaluated channels as a significant decrease in large woody debris pieces is observed with increasing basin area

the thermal conductivity of seasonal snow twenty seven studies on the thermal conductivity of snow k eff have been published since 1886 combined they comprise 354 values of k eff and have been used to derive over 13 regression equation and predicting k eff vs density due to large and largely undocumented differences in measurement methods and accuracy sample temperature and snow type it is not possible to know what part of the variability in this data set is the result of snow microstructure we present a new data set containing 488 measurements for which the temperature type and measurement accuracy are known a quadratic equation where is in g cm 3 and k eff is in w m 1 k 1 can be fit to the new data r 2 0 79 a logarithmic expression can also be used the first regression is better when estimating values beyond the limits of the data the second when estimating values for low density snow within the data set snow types resulting from kinetic growth show density independent behavior rounded grain and wind blown snow show strong density dependence the new data set has a higher mean value of density but a lower mean value of thermal conductivity than the old set this shift is attributed to differences in snow types and sample temperatures in the sets using both data sets we show that there are well defined limits to the geometric configurations that natural seasonal snow can take

measuring specific surface area of snow by near infrared photography the specific surface area ssa is considered an essential microstructural parameter for the characterization of snow photography in the near infrared nir spectrum is sensitive to the ssa we calculated the snow reflectance from calibrated nir images of snow pit walls and measured the ssa of samples obtained at the same locations this new method is used to map the snow stratigraphy the correlation between reflectance and ssa was found to be 90 calibrated nir photography allows quantitative determination of ssa and its spatial variation in a snow profile in two dimensions within an uncertainty of 15 in an image covering 0 5 1 0 m 2 even layers of 1 mm thickness can be documented and measured spatial maps of ssa are an important tool in initializing and validating physical and chemical models of the snowpack

the self organization of step pools in mountain streams abstract spontaneous autogenic self organization has been described in numerous geomorphic systems but it has not been investigated in detail with respect to coarse bedforms in general or step pools in particular in this paper we review the spatial organization of step pool systems and present example evidence of step pool development as an autogenic self organization process we then outline the mathematical language for defining spatially divergent self organization and test these ideas using two unique field examples from oregon andrews experimental forest and california baxter creek where step pools developed from planar beds in artificially manipulated channels results show that step pool development is consistent with a spatially divergent self organization phenomenon entropy increases as initially undifferentiated planar channels diverge into steps and pools then declines when a series of steps and pools of consistent size and spacing is established signifying stability in the system the self organization process is accompanied by increasing flow resistance and decreasing slope through increasing the vertical sinuosity of the step pool profile and creation of low or negative gradient pool areas suggesting a minimization of stream power the self adjustment of the step pool bed profile over time represents another manifestation of a general process that results in rhythmic patterns on the surface of earth

precipitation patterns control the distribution and export of large wood at the catchment scale large wood lw plays an important role in river ecosystems but lw laden floods may cause serious damage to human lives and property the relationship between precipitation patterns and variations in lw distribution and export at the watershed scale is poorly understood to explore these linkages we examined differences in lw distribution as a function of channel morphologies in six watersheds located in southern and northern japan and analysed the impacts of different precipitation patterns on the fluvial export of lw from river catchments in southern japan intense rainfalls caused by typhoons or localized torrential downpours initiate landslides and debris flows that introduce massive amounts of lw into channels gravel bars formed by frequent flood events are widely prevalent and the lw temporarily stored on these bars is frequently moved and or broken into smaller pieces by floods in these systems fluvial export of lw is supply limited with smaller accumulations and shorter residence times than in northern japan conversely in northern japan where typhoons and torrential downpours rarely occur lw is mostly recruited by bank erosion tree mortality and windthrow into channels rather than by landslides and debris flows recruited pieces accumulate in log jams on valley floors particularly on floodplains supporting mature forests resulting in larger accumulations and longer residence times in these watersheds fluvial export of lw is transport limited and the pieces gradually decompose during long term storage as log jams copyright 2015 john wiley sons ltd

mapping coastal morphodynamics with geospatial techniques cape henry virginia usa abstract the advent and proliferation of digital terrain technologies have spawned concomitant advances in coastal geomorphology airborne topographic light detection and ranging lidar has stimulated a renaissance in coastal mapping and field based mapping techniques have benefitted from improvements in real time kinematic rtk global positioning system gps varied methodologies for mapping suggest a need to match geospatial products to geomorphic forms and processes a task that should consider product and process ontologies from each perspective towards such synthesis coastal morphodynamics on a cuspate foreland are reconstructed using spatial analysis sequential beach ridge and swale topography are mapped using photogrammetric spot heights and airborne lidar data and integrated with digital bathymetry and large scale vector shoreline data isobaths from bathymetric charts were digitized to determine slope and toe depth of the modern shoreface and a reconstructed three dimensional antecedent shoreface triangulated irregular networks were created for the subaerial cape and subaqueous shoreface models of the cape beach ridges and sets for volumetric analyses results provide estimates of relative age and progradation rate and corroborate other paleogeologic sea level rise data from the region swale height elevations and other measurements quantifiable in these data provide several parameters suitable for studying coastal geomorphic evolution mapped paleoshorelines and volumes suggest the virginia beach coastal compartment is related to embryonic spit development from a late holocene shoreline located some 5 km east of the current beach

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

wood mediated geomorphic effects of a jokulhlaup in the wind river mountains wyoming a jokulhlaup burst from the head of grasshopper glacier in wyoming s wind river mountains during early september 2003 five reaches with distinct sedimentation patterns were delineated along the dinwoody creek drainage this paper focuses on a portion of the jokulhlaup route where erosion of the forested banks created 16 large logjams spaced at longitudinal intervals of tens to hundreds of meters aggradation within the main channel upstream from each logjam created local sediment wedges and the jams facilitated overbank deposition during the jokulhlaup field surveys during 2004 and 2006 documented logjam characteristics and associated erosional and depositional features as well as initial modification of the logjams and flood deposits within the normal seasonal high flow channel overbank deposits have not been altered by flows occurring since 2003 field measurements supported three hypotheses that i logjams present along the forested portions of the jokulhlaup route are larger and more closely spaced than those along adjacent otherwise comparable stream channels that have not recently experienced a jokulhlaup ii logjams are not randomly located along the jokulhlaup route but instead reflect specific conditions of channel and valley geometry and flood hydraulics and iii the presence of logjams facilitated significant erosional and depositional effects this paper documents a sequence of events in which outburst floodwaters enhance bank erosion and recruitment of wood into the channel and thus the formation of large logjams these logjams sufficiently deflect flow to create substantial overbank deposition in areas of the valley bottom not commonly accessed by normal snowmelt peak discharges and through this process promote valley bottom aggradation and sediment storage changes in the occurrence of glacier outburst floods thus have the potential to alter the rate and magnitude of valley bottom dynamics in these environments which is particularly relevant given predictions of worldwide global warming and glacial retreat processes observed at this field site likely occur in other forested catchments with headwater glaciers

fire floods and woody debris interactions between biotic and geomorphic processes fire and floods interact in the riparian zone as processes that structure plant communities and landforms although much of the immediate impact of fire is on the vegetation fire related changes in runoff sediment supply riparian vegetation and woody debris volume have ongoing geomorphic impacts on the valley floor consequent hydrogeomorphic changes in turn affect the composition and distribution of vegetation this paper reviews these interactions and provides an example of how fires and floods intersect to supply burnt trees as woody debris because the temporal and spatial distribution of woody debris is initially controlled by patterns of tree mortality ecological disturbances like fire can be an important source for pulses of woody debris in riparian systems to understand these interactions we examine woody debris inputs 3 years after a wildfire in the riparian gallery forests of the western transverse ranges california within our sample of 339 burned stems snags fell in distinctive patterns species were variable in susceptibility to falling and fell at greater rates at sites with greater subsequent flooding discordance between the species composition of fallen snags and that of overall burned stems indicates that variability in forest composition must be considered in predicting post disturbance inputs of woody debris variation in snagfall timing among species suggests that woody debris inputs are likely to occur in multiple sequential pulses after wildfire the role of flooding is superimposed on this ecological influence as the timing and spatial variability of floods affect the recruitment of woody debris from the supply of snags created by fire

influence of large wood on channel morphology and sediment storage in headwater mountain streams fraser experimental forest colorado abstract large fallen wood can have a significant impact on channel form and process in forested mountain streams in this study four small channels on the fraser experimental forest near fraser colorado usa were surveyed for channel geometries and large wood loading including the size source and characteristics of individual pieces the study is part of a larger effort to understand the impact of mountain pine beetle infestation on a suite of watershed properties here we present baseline data collected at the onset of widespread tree mortality channels range from 1 5 to 2 m in width with slopes ranging from 3 to 10 median d 50 streambed particle sizes range from gravel to very coarse gravel channels are characterized as cascade step pool and plane bed over varying scales large wood loads ranged from about 0 4 to 1 0 piece per meter length of channel which is comparable to values reported for other colorado sites much of the wood showed indications of being in place for long periods of time decayed rotten broken into ramps and partially buried in beds and banks nearly all surveyed reaches contained steps formed from small boulders and or logs significant portions of the elevation drop in some of the reaches were made up by log steps though the percentages varied 0 to 60 individual log steps trap a portion of the coarse sediment moved as bedload forming wedge shaped accumulations upstream of the logs the particle size distributions for measured bedload and step accumulations largely overlapped but more so for the coarse ends of the distributions suggesting a trapping inefficiency for the finer component of bedload estimates of the total volume of sediment stored behind log steps were approximately an order of magnitude greater than the mean sediment volume exported on an annual basis as determined from measured accumulations in weir ponds the particle size distribution of sediment in the ponds ranging from sand to medium gravel is considerably finer than sediment stored in steps the series of comparisons between storage volumes particle size distributions and sediment export suggests that log steps effectively trap coarse sediment moved in these small streams and act as a series of check dams that inhibit channel erosion but may be less effective at trapping finer sediment sand and small gravel

interactions between instream wood and hydrogeomorphic development within recently deglaciated streams in glacier bay national park alaska the physical and structural characteristics of instream wood were examined within five streams that represented 200 years of stream development following glacial recession within glacier bay national park alaska wood characteristics altered with watershed age as terrestrial succession progressed and wood was recruited into the riverine environment the influence of wood characteristics on the development of geomorphic diversity and hydraulic variability within the streams were assessed using detailed habitat mapping sediment analysis and hydraulic assessment using an acoustic doppler current profiler at a number of transects upstream downstream and adjacent to wood results show that the size complexity and orientation of wood accumulations are the main drivers in determining the degree of influence instream wood have on stream geomorphic and hydraulic complexity adjacent terrestrial vegetation must be of a sufficient stage of development in terms of size and maturity in order to elicit significant hydrogeomorphic changes to benefit aquatic biota such as fish macroinvertebrates and plants

simulated wood budgets in two mountain streams abstract large wood lw recruitment transport and storage were evaluated over a century in gregory and riley creeks haida gwaii british columbia by modeling a reach scale lw budget using two frameworks for output lw loss through decay and downstream transport and loss through depletion at reach and at watershed scales mass movement and bank erosion dominated inputs and fluvial transport was an important flux term in several reaches large wood recruitment by mortality was relatively minor in comparison large proportions of the in channel lw were stored in jams with a mean age of 40 50 years overall both modeling approaches yielded reasonable stored lw predictions in the study creeks with the omission inclusion of transport responsible for the largest differences between models modeled storage generally was within 30 of that measured in the field and our results illustrate the large temporal variation in storage resulting from episodic inputs of lw from hillslopes

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

wood storage in three mountain streams of the southern andes and its hydro morphological effects this study analyses large wood lw storage and the associated effects on channel morphology and flow hydraulics in three third order mountain basins drainage area 9 12 km2 covered in old growth nothofagus forests ranging from the temperate warm chilean andean cordillera to the sub antarctic tierra del fuego argentina amount characteristics and dimensions of large wood 10 cm diameter 1 m long were recorded as well as their effects on stream morphology hydraulics and sediment storage results show that major differences in lw abundance exist even between adjacent basins as a result of different disturbance histories and basin dissection massive lw volumes i e 1000 m3 ha 1 can be reached in basins disturbed by fires followed by mass movements and debris flows potential energy dissipation resulting from wood dams is about a quarter of the total elevation drop in two streams with a gross sediment volume stored behind wood dams of around 1000 m3 km 1 which appears to be of the same order as the annual sediment yield finally the presence of wood dams may increase flow resistance by up to one order of magnitude copyright 2007 john wiley sons ltd

channel reach morphology controls of headwater streams based in flysch geologic structures an example from the outer western carpathians czech republic a detailed measurement of 93 channel reaches that were classified with an adjusted montgomery buffington 1997 reach scale system provided comprehensive information of approximately 9 at a reach parameters the channel gradient the bankfull width the bankfull depth d90 the percentage of resistant rocks in the bed sediment the number of pieces of large woody debris valley confinement direct sediment inputs and the presence of fluvial accumulations in the stream channel in addition the quantified intensity of sediment transport i e ratio between sediment supply and transport capacity in longitudinal stream profiles during flood events has been estimated by the one dimensional bedload transport model tomsed which was validated in two local streams the principal component analysis of the at a reach parameters did not reveal significant groups of channel reach morphologies thus the selected parameters that exclude sediment transport dynamics within stream longitudinal profile cannot reliably distinguish or predict individual channel reach morphologies nevertheless the channel gradient represented the most significant single explanatory variable for stepped bed morphologies the addition of bedload transport parameters demonstrated that limited sediment supply streams and streams with limited transport capacities featured different successions of the channel reach morphologies in terms of the channel gradient and subsequently the fluvial continuity the bedrock cascades and step pools were significant for the first case whereas cascade and step rapid morphology often occurred in higher sediment supply conditions

mobility of large woody debris lwd jams in a low gradient channel abstract mobility of large woody debris lwd in low gradient channels is an important but often overlooked transport process the majority of studies on lwd have focused on its role in geomorphic and ecologic river processes when jams extend across the width of the channel they have the potential to retain sediment and alter the channel profile when jams obstruct only a portion of the channel they can re direct flow altering patterns of scour and deposition the boundary complexity created by lwd has a recognized role in riverine ecosystems which has led to programs of replacing lwd in channel corridors where it was previously removed although lwd jams are common in rivers around the world they have been studied most intensely in steep forested channel reaches where they are often found to be stable channel features it is not fully known how much of the information on lwd from steep forested channels will transfer to other channel types whereas it may be reasonable to assume that the ecological benefits of lwd are similar in low gradient channels research has shown that a much higher rate of lwd transport occurs in low gradient channels with jams mobilized on timescales of 10 0 10 2 years this study evaluates the distribution and mobility of lwd over 72 km of the san antonio river a low gradient channel in southeast texas lwd jam locations were identified for 2003 and 2007 using a combination of aerial photography and field mapping each jam was cataloged according to its location in the channel cross section and the amount of channel area blocked during the four year period all the lwd jams were mobilized including those jams extending across the channel width although easily mobilized 34 jams re form in the same locations creating 34 channel locations with persistent lwd jams data from the san antonio river are applied to two models developed to predict lwd mobility and transport distances to assess the applicability of each model to a low gradient channel the locations of stable or recurring lwd jams were matched to model results where predicted lwd transport distances were equal to measured lwd jam spacing model results showed good agreement with the mean and median spacing of lwd jams when given input parameters specific to the channel and wood species the ability to predict where lwd jams will persist over time in a low gradient channel has application in watershed management persistent lwd jams can exert a greater influence on channel morphology and may require active management