development of partial rock veneers by root throw in a subalpine setting rock veneers stabilize hillslope surfaces occur especially in areas of immature soil and form through a variety of process sets that includes root throw near westcliffe colorado usa data were collected from a 20 500 m transect on the east slope of the sangre de cristo mountains ages of pit mound complexes with rock fragments exposed at the surface by root throw ranged from recent freshly toppled tree to unknown complete tree decay calculations based on dimensions of the pit mound complexes estimated time of tree toppling sizes of exposed rock fragments and percentage rock covers at pit mound complexes as well as within the transect area indicate that recent rates of root throw have resulted in only partial rock veneering since late pleistocene deglaciation weathering of rock fragments prevents development of an extensive rock veneer and causes a balance achieved within an estimated 700 years between the rates of rock fragment exposure by root throw and clast disintegration by chemical reduction the estimated rate of rock fragment reduction accounts for part of the fluvial sediment yields observed for forested subalpine areas of western north america copyright 2005 john wiley sons ltd

sources sinks and storage of river sediment in the atlantic drainage of the united states the history of sediment and its movement in the atlantic drainage demonstrate some of the difficulties of modeling sediment on a river basin scale soil erosion was accelerated by a factor of at least 10 when european settlers cleared forests and planted crops although increasing soil conservation practice and decreasing crop farming have since reduced the rates of erosion large quantities of eroded material are still stored on hillslopes and in stream valleys where they continue to augment the sediment loads of the rivers the sediment from this episode of erosion that is largely past can be expected to emerge from storage for many decades and perhaps even several centuries to come the reservoirs that have been built on many of the major rivers trap significant portions of the moving sediment which in some places may be remobilized by large floods essentially all the river sediment that reaches the atlantic coastal zone is trapped in estuaries and coastal marshlands probably less than 5 is deposi

the use of vertical wind shear versus helicity in interpreting supercell dynamics a series of idealized simulations of supercell storms are presented for environments representing straight through circular hodographs to clarify the character of the storm dynamics over the large spectrum of hodograph shapes commonly observed the primary emphasis is on comparing and contrasting recent theories of supercell dynamics based on updraft shear interactions storm relative environmental helicity sreh and beltrami flow solutions to help clarify the degree to which each theory can represent the essential storm dynamics one of the particular questions being addressed is whether storm dynamics are significantly different for straight versus curved hodographs which has become a point of some controversy over recent years in agreement with previous studies the authors find that the physical processes that promote storm maintenance rotation and propagation are similar for all hodograph shapes employed and are due primarily to nonlinear interactions between the updraft and the ambient shear associated with the localized development of rotation on the storm s flank significant correlations between the updraft and vertical vorticity are also observed across the shear spectrum and in agreement with predictions of linear theories associated with sreh this correlation increases for increasing hodograph curvature however storm steadiness and propagation must already be known or inferred for such concepts to be applied thus limiting the applicability of this theory as a true predictor of storm properties tests of the applicability of beltrami solutions also confirm reasonable agreement for purely circular hodographs for which the analytical solutions are specifically designed however analysis of the model results indicates that the terms ignored for such solutions representing the nonlinear effects associated with storm rotation are more significant than those retained over most of the hodograph spectrum which severely limits the general applicability of such analyses

spatial distribution of coarse woody debris dams in the lymington basin hampshire uk abstract debris dams of coarse woody debris have a significant influence on channel processes in forested areas but few detailed studies have been made of variations within a single basin results from previous research are standardised and show that average variations throughout basins include densities of debris dams up to 40 per 100 metres of channel and can involve a loading value of up to 225 kg per m2 of channel variations have been ascribed to distance downstream to channel width to land use effects to felling and to the management of coarse woody debris in streams this study of the lymington basin 110 4 km2 in drainage area shows that the input of storm debris resulting from blowdown accounts for 45 of the gross load the remaining 55 net load varies to distance downstream to land use with the greatest loads in deciduous woodland areas and according to management removal of debris from streams and multiple regression equations are provided it is deduced that as a consequence of long term management the present channel debris may be as little as 7 of the total net load that could have been present if no management had occurred

effects of horizontal and vertical grid spacing on mixing in simulated squall lines and implications for convective strength and structure abstractthe sensitivity of an idealized squall line to horizontal and vertical grid spacing is investigated using a new approach simulations are first performed at a horizontal grid spacing of 1 km until the storm reaches its mature stage the model output is then interpolated to smaller and larger grid spacings and the model is restarted using the interpolated state plus small thermodynamic perturbations to spin up small scale motions this framework allows an investigation of the sensitivity of the storm to changes in without complications from differences in storm initiation and early evolution the restarted simulations reach a quasi steady state within approximately 1 h results demonstrate that there are two dependent regimes with the transition between regimes occurring for between 250 and 500 m some storm characteristics such as the mean convective core area change substantially for 250 m but show limited sensitivity as is decreased below 250 m despite better resolving smaller scale turbu

little river revisited thirty five years after hack and goodlett abstract in possibly the first detailed study to relate geomorphology vegetation and hydrology at a watershed scale hack and goodlett 1960 documented variation in the eastern forest with topograhic positions of cove side slope and nose runoff identified as convergent parallel or divergent supported forest types respectively of northern hardwood oak and yellow pine the study conducted in the little river basin of northwestern virginia also described effects on landforms and vegetation of a catastrophic flood that occurred in june 1949 field investigations conducted nearly 4 decades later review selected parts of the study by hack and goodlett 1960 replicate data provide a basis to evaluate interpretations of hack and goodlett to document geomorphic change within the little river basin since the 1949 flood and to identify vegetation change in uplands and bottomlands results suggest that change to hillslope landforms has been minor since 1949 but that changes have occurred to the little river and its tributaries seemingly during flow events of 1952 1955 and 1985 change in areal extent of forest types was not detected change in the relative abundances of dominant species may have resulted from 20th century fire suppression

observed and numerically simulated structure of a mature supercell thunderstorm abstract through the interactive use of doppler radar analyses and a three dimensional numerical storm simulation the detailed structure of a supercell tornadic storm is analyzed this storm named the del city storm occurred in central oklahoma on 20 may 1977 the storm exhibits certain important features which are essential to maintaining its longevity and which promote the storm s transition to its tornadic phase these features are strongly influenced by the rotational character of the storm separates the precipitation from the updraft and which orients the resulting downdrafts to which reinforce low level convergence along the gust front and sustain the storm analyses of air parcel and rain trajectories within the storm provide a detailed visualization of this internal structure these trajectories reveal that air parcels rising through the cyclonically rotating updraft actually turn anticyclonically with height owing to the influence of the storm relative environmental wind field downdraft traj

the role of vertical wind shear in modulating maximum supercell updraft velocities abstractobserved supercell updrafts consistently produce the fastest mid to upper tropospheric vertical velocities among all modes of convection two hypotheses for this feature are investigated

geomorphic and vegetative characteristics along three northern virginia streams geometry sediment and woody vegetation data were collected from bottomland geomorphic surfaces at valley sections along three gaged perennial streams of northern virginia the basins of the streams differ widely in topography and physiography mean discharges vary from 0 196 to 323 m3 per sec prevalent surfaces identified were the depositional bar the active channel shelf the flood plain and terraces the stages corresponding to active channel shelf levels were equivalent to flow durations of 5 to 13 stages corresponding to flood plain levels were equivalent to discharges with 1 4 to 2 0 yr recurrence intervals the discharge data and statistical tests of geomorphicsurface sediment and vegetative data suggest that the various alluvial features are formed and maintained by hydraulically controlled sorting processes analysis of woody plant and geomorphic data shows that each surface supports characteristic species some of which are nearly unique to a surface tests of sediment type with species distribution showed lower correlation than that of geomorphic surface with species it is inferred that plant distributions largely are controlled by flow frequency and intensity and that plants may help to identify geomorphic levels and potential for flood damage

a study of seismic reflection imaging using microearthquake sources abstract we present a method for processing three component digital recordings of microearthquakes to obtain near vertical reflection profiles in regions of shallow seismicity the processing includes magnitude and focal depth normalization and event stacking where stacking is by small localized groups with ray theoretical time and distance corrections applied to compensate for varying focal depths in areas with high seismicity this procedure allows earthquakes to be treated as controlled sources to probe layered structures of the deep crust and upper mantle the validity of our approach is examined using aftershocks of the borah peak idaho earthquake m s 7 3 several thousand events occurred in a nnw trending zone about 10 km wide 75 km long and 15 km deep a small 10 10 km array of nine university of wisconsin three component triggered short period digital seismographs was installed in the region of aftershock activity over a 10 day period about 1000 useable events were recorded of which about 120 have been used for this study hypocenters have been computed using both p and s wave arrivals the latter being essential for stable solutions of events outside the network the borah peak data have been processed to obtain shear wave reflection profiles for the central station station 8 of the digital station array the stacked shear wave transverse record sections reveal coherent reflections from horizons at mid crustal to moho depths the most prominent reflections are from crustal discontinuities in the depth range 18 28 km coherent reflections can be obtained only through stacking which is necessary to improve the signal to noise ratio the major sources of data scatter as manifested by smearing of reflections on the stacked records are crustal heterogeneity and errors in the determination of focal depth and origin time

sedimentation rates and patterns in beaver ponds in a mountain environment abstract sediment depth was measured at several sites within each of eight beaver ponds in glacier national park montana and sediment samples wen collected from five of these ponds accumulation rates of sediments far exceeded published rates from boreal forest landscapes in eastem and central north america pond area strongly predicts volume of sedimentation textural differences illustrated spatial variations associated with position in a pond and along a pond sequence organic matter content was significantly higher in older ponds and has ramifications for the development of the benthos and the long term storage of matter in ponds the role of beavers as biogeomorphic agents is profound but requires further elucidation to distinguish between fluvial sediment deposition in ponds and sediment deposition associated with beaver excavational activity

the regulation of tornado intensity by updraft width abstractstrong to violent tornadoes cause a disproportionate amount of damage in part because the width and length of a tornado damage track are correlated to tornado intensity as now estimated through enhanced fujita scale ratings the tendency expressed in the observational record is that the most intense tornadoes are often the widest herein the authors explore the simple hypothesis that wide intense tornadoes should form more readily out of wide rotating updrafts this hypothesis is based on an application of kelvin s circulation theorem which is used to argue that the large circulation associated with a wide intense tornado is more plausibly associated with a wide mesocyclone because a mesocyclone is strictly speaking a rotating updraft the mesocyclone width should increase with increasing updraft width a simple mathematical model that is quantified using observations of mesocyclones supports this hypothesis as do idealized numerical simulations of supercellular thunderstorms

the structure and classification of numerically simulated convective storms in directionally varying wind shears abstract using a three dimensional numerical cloud model we investigate the effects of directionally varying wind shear on convective storm structure and evolution over a wide range of shear magnitudes as with a previous series of experiments using unidirectional wind shear profiles weisman and klemp the current results evince a spectrum of storm types ranging from short lived single cells at low shears multicells at intermediate shears to supercells at high shears with a clockwise curved hodograph the supercellular growth is confined to the right flank of the storm system while multicellular growth is favored on the left flank an analysis of the dynamic structure of the various cells reveals that the quasi steady supercell updrafts are strongly enhanced by dynamically induced pressure gradients on the right flank of the storm system we use this feature along with other related storm characteristics such as updraft rotation to propose a dynamically based storm classification scheme following

are supercells resistant to entrainment because of their rotation abstractthis research investigates a hypothesis posed by previous authors which argues that the helical nature of the flow in supercell updrafts makes them more resistant to entrainment than nonsu

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

the dependence of numerically simulated convective storms on vertical wind shear and buoyancy abstract the effects of vertical wind shear and buoyancy on convective storm structure and evolution are investigated with the use of a three dimensional numerical cloud model by varying the magnitude of buoyant energy and one directional vertical shear over a wide range of environmental conditions associated with severe storms the model is able to produce a spectrum of storm types qualitatively similar to those observed in nature these include short lived single cells certain types of multicells and rotating supercells the relationship between wind shear and buoyancy is expressed in terms of a nondimensional convective parameter which delineates various regimes of storm structure and in particular suggests optimal conditions for the development of supercell type storms applications of this parameter to well documented severe storm cases agree favorably with the model results suggesting both the value of the model in studying these modes of convection as well as the value of this representation i

the influence of vertical wind shear on moist thermals abstractalthough it is well established that vertical wind shear helps to organize and maintain convective systems there is a longstanding colloquial notion that it inhibits the development of dee

interactions between semi natural vegetation and hydrogeomorphological processes abstract within britain lowland heaths and floodplain forests are rapidly disappearing from the landscape this paper considers the hydrogeomorphological significance of these two types of semi natural vegetation cover using research results gathered from a drainage basin in the new forest southern england whilst heathland vegetation communities are closely adjusted to the soil water hydrological regime floodplain forests have a distinctive and significant influence on the geomorphology of river channels both of these types of interaction are not only of hydrogeomorphological interest but provide an essential foundation for the effective management and restoration of catchments and rivers containing these types of vegetation cover

riparian vegetation and fluvial geomorphic processes abstract riparian vegetation and fluvial geomorphic processes and landforms are intimately connected parts of the bottomland landscape relations among vegetation processes and landforms are described here for representative streams of four areas of the united states high gradient streams of the humid east coastal plain streams great plains streams and stream channels of the southwestern united states vegetation patterns suggest that species distributions in the humid east are largely controlled by frequency duration and intensity of floods along channelized streams vegetation distribution is largely controlled by variation in fluvial geomorphic processes cycles of degradation and aggradation in response to increases in channel gradient associated with channelization similarly riparian vegetation of great plains streams may be controlled by fluxes in sediment deposition and erosion along braided streams patterns of riparian vegetation in semi arid regions may be most closely related to patterns of water availability unlike most other streams in more humid environments channel equilibrium conditions control stability of the coincident fluvial landform and attendant vegetation pattern throughout the continent in most situations riparian vegetation patterns are indicative of specific landforms and thus of ambient hydrogeomorphic conditions

the role of vegetation and bed level fluctuations in the process of channel narrowing abstract a catastrophic flood ire 1965 on plum creek a perennial sandbed stream in the western great plains removed most of the bottomland vegetation and transformed the single thalweg stream into a wider braided channel following eight years of further widening associated with minor high flows a process of channel narrowing began in 1973 narrowing continues today the history of channel narrowing was reconstructed by counting the annual rings of 129 trees and shrubs along a 5 km reach of plum creek near louviers colorado sixty three of these plants were excavated in order to determine the age and elevation of the germination point the reconstructed record of channel change was verified from historical aerial photographs and then compared to sediment stratigraphy and records of discharge and bed elevation from a streamflow gaging station in the study reach channel narrowing at plum creel occurs in two ways first during periods of high flow sand and fine gravel are delivered to the channel temporarily raising the general bed level subsequently several years of uninterrupted low flows incise a narrower channel second during years of low flow vegetation becomes established on the subaerial part of the present channel bed in both cases surfaces stabilize as a result of vegetation growth and vertical accretion of sediment

the spatial variability of overbank sedimentation on river floodplains abstract river floodplains are important landforms and information on rates and patterns of overbank sediment deposition is essential for understanding their development such information is also needed for validating existing overbank floodplain flow and sediment transport and deposition models the use of bomb derived 137cs for documenting rates of overbank sediment deposition on river floodplains offers the potential for assembling data for a large number of points on a floodplain and therefore for investigating the spatial patterns involved this approach also overcomes some of the operational and sampling problems encountered in traditional monitoring techniques the study reported uses 137cs measurements on sediment cores to investigate the spatial variability of sediment deposition on selected floodplain reaches of five british lowland rivers attention is given both to the overall reach and to more detailed investigations of small areas the observed spatial patterns of sediment deposition are interpreted in terms of the major controls involved which include the floodplain microtopography and morphology the relationship between the grain size composition of deposited sediment and sedimentation rate is also considered

spatial dynamics of overbank sedimentation in floodplain systems abstract floodplains provide valuable social and ecological functions and understanding the rates and patterns of overbank sedimentation is critical for river basin management and rehabilitation channelization of alluvial systems throughout the world has altered hydrological and sedimentation processes within floodplain ecosystems in the loess belt region of the lower mississippi alluvial valley of the united states channelization the geology of the region and past land use practices have resulted in the formation of dozens of valley plugs in stream channels and the formation of shoals at the confluence of stream systems valley plugs completely block stream channels with sediment and debris and can result in greater deposition rates on floodplain surfaces presently however information is lacking on the rates and variability of overbank sedimentation associated with valley plugs and shoals we quantified deposition rates and textures in floodplains along channelized streams that contained valley plugs and shoals in addition to floodplains occurring along an unchannelized stream to improve our understanding of overbank sedimentation associated with channelized streams feldspar clay marker horizons and marker poles were used to measure floodplain deposition from 2002 to 2005 and data were analyzed with geospatial statistics to determine the spatial dynamics of sedimentation within the floodplains mean sediment deposition rates ranged from 0 09 to 0 67 cm y at unchannelized sites 0 16 to 2 27 cm y at shoal sites and 3 44 to 6 20 cm y at valley plug sites valley plug sites had greater rates of deposition and the deposited sediments contained more coarse sand material than either shoal or unchannelized sites a total of 59 of 183 valley plug study plots had mean deposition rates 5 cm y the geospatial analyses showed that the spatial dynamics of sedimentation can be influenced by the formation of valley plugs and shoals on channelized streams however responses can vary restoration efforts in the region need to have basinwide collaboration with landowners and address catchment scale processes including the geomorphic instability of the region to be successful

transport and deposition of large woody debris in streams a flume experiment abstract large woody debris lwd is an integral component of forested streams of the pacific northwest and elsewhere yet little is known about how far wood is transported and where it is deposited in streams in this paper we report the results of flume experiments that examine interactions among hydraulics channel geometry transport distance and deposition of floating wood these experiments were carried out in a 1 22 m wide 9 14 m long gravel bed flume using wooden dowels of various sizes as surrogate logs channel planforms were either self formed or created by hand and ranged from meanders to alternate bars floating pieces tended to orient with long axes parallel to flow in the center of the channel pieces were deposited where channel depth was less than buoyant depth typically at the head of mid channel bars in shallow zones where flow expanded and on the outside of bends we hypothesize that the distance logs travel may be a function of the channel s debris roughness a dimensionless index incorporating ratios of piece length and diameter to channel width depth and sinuosity travel distance decreased as the ratio of piece length to both channel width and radius of curvature increased but the relative importance of these variables changed with channel planform large pieces can move further than our debris roughness models predict if greater than 50 of the active channel area is deeper than the buoyant depth of the piece or if momentum is high enough to carry pieces across shallows our debris roughness model allows first order prediction of the amount of wood transport under various channel geometries

mapping the response of riparian vegetation to possible flow reductions in the snake river idaho abstract this study was initiated to determine the general effects of potential flow reductions in the middle snake river swan falls dam downstream to the idaho oregon border on its riparian vegetation considerable water from the river is currently used to irrigate the adjacent snake river plain and increased demand for water in the future is likely the problem was subdivided into several research components including field investigation of the existing riparian vegetation and river environment hydrological modeling to calculate the effects of one flow scenario on hydrological regime and integration of vegetation and hydrological modeling results with a geographic information system gis to map the riverbed island and bank conditions under the scenario flow field work was conducted in summer 1990 riparian vegetation along 40 u s geological survey cross sections was sampled at approximately 1 25 mile intervals within the 50 mile long study area cross section and flow data were provided by the u s geological survey gis mapping of land water cover using arc info was based on 1987 aerial photographs riverbed contour maps were produced by linking cross section data topographic contouring software anudem and gis the maps were used to spatially display shallow areas in the channel likely to become vegetated under reduced flow conditions the scenario would reduce flow by approximately 20 160 maf and lower the river an average of 0 5 ft the scenario flow could cause a drop in the elevation of the riparian zone comparable to the drop in mean river level and expansion of the lower riparian zone into shallow areas of the channel the gis maps showed that the shallow areas of the channel more likely to become vegetated under the scenario flow are located in wide reaches near islands some possible ecological consequences of the scenario flow include a greater area of riparian habitat reduced flow velocity and sedimentation in shallow channels leading to channel deactivation increased island visitation and nest predation by predatory mammals due to loss of a water barrier between some islands and banks and larger populations of alien plant species in the new riparian vegetation

fluvial processes and vegetation glimpses of the past the present and perhaps the future abstract most research before 1960 into interactions among fluvial processes resulting landforms and vegetation was descriptive since then however research has become more detailed and quantitative permitting numerical modeling and applications including agricultural erosion abatement and rehabilitation of altered bottomlands although progress was largely observational the empiricism increasingly yielded to objective recognition of how vegetation interacts with and influences geomorphic process a review of advances relating fluvial processes and vegetation during the last 50 years centers on hydrologic reconstructions from tree rings plant indicators of flow and flood frequency parameters hydrologic controls on plant species regulation of sediment movement by vegetation vegetative controls on mass movement and relations between plant cover and sediment movement extension of present studies of vegetation as a regulator of bottomland hydrologic and geomorphic processes may become markedly more sophisticated and widespread than at present research emphases that are likely to continue include vegetative considerations for erosion modeling response of riparian zone forests to disturbance such as dams and water diversion the effect of vegetation on channel and bottomland dynamics and rehabilitation of stream corridors research topics that presently are receiving attention are the effect of woody vegetation on the roughness of stream corridors and hence processes of flood conveyance and flood plain sedimentation the development of a theoretical basis for rehabilitation projects as opposed to fully empirical approaches the effect of invasive plant species on the dynamics of bottomland vegetation the quantification of below surface biomass and related soil stability factors for use in erosion prediction models and the effect of impoundments on downstream narrowing of channels and accompanying encroachment of vegetation bottomland vegetation partially controls and is controlled by fluvial geomorphic processes the purposes of this paper are to identify and review investigations that have related vegetation to bottomland features and processes to distinguish the present status of these investigations and to anticipate future research into how hydrologic and fluvial geomorphic processes of bottomlands interact with vegetation

what is the intrinsic predictability of tornadic supercell thunderstorms abstracta 25 member ensemble of relatively high resolution 75 m horizontal grid spacing numerical simulations of tornadic supercell storms is used to obtain insight on their intrinsic predictabil

sticky thermals evidence for a dominant balance between buoyancy and drag in cloud updrafts abstractthe vertical velocities of convective clouds are of great practical interest because of their influence on many phenomena including severe weather and stratospheric moistening however the magnitudes of forces giving rise to these vertical velocities are poorly understood and the dominant balance is in dispute here an algorithm is used to extract thousands of cloud thermals from a large eddy simulation of deep and tropical maritime convection using a streamfunction to define natural boundaries for these thermals the dominant balance in the vertical momentum equation is revealed cloud thermals rise with a nearly constant speed determined by their buoyancy and the standard drag law with a drag coefficient of 0 6 contrary to suggestions that cloud thermals might be slippery with a dominant balance between buoyancy and acceleration cloud thermals are found here to be sticky with a dominant balance between buoyancy and drag

the influences of effective inflow layer streamwise vorticity and storm relative flow on supercell updraft properties abstractthe relationship between storm relative helicity srh and streamwise vorticity s is frequently invoked to explain the often robust connections between effective inflow layer eil srh a

simulations of shallow supercell storms in landfalling hurricane environments abstract numerical simulations of the convective storms that form in tornado producing landfalling hurricanes show that shallow supercells are possible even though buoyancy is limited because ambient lapse rates are close to moist adiabatic updrafts generally reach peak intensity at low levels often around 2 km above the surface by comparison a simulated midlatitude supercell typical of the great plains of the united states exhibits a pronounced increase in storm size both horizontally and vertically at low levels however the hurricane spawned storms may contain updrafts that rival or exceed in intensity those of great plains supercells at similar levels simulations made using a tornado proximity sounding from the remnants of hurricane danny in 1985 produce a small but intense supercell a finding consistent with the available observational evidence although the amplitude of parcel buoyancy is often small in hurricane environments its concentration in the strongly sheared lower troposphere pro

the influence of the shear induced pressure gradient on thunderstorm motion abstract in the present investigation we propose a simple theory to explain how a veering environmental wind shear vector can cause an initially symmetric updraft to grow preferentially to the right of the shear vector and acquire cyclonic rotation the explanation offered is based on linear theory which predicts that interaction of the mean shear with the updraft produces favorable vertical pressure gradients along its right flank to asses the validity of linear theory for large amplitude updrafts the three dimensional shallow anelastic equations are numerically integrated using a simple parameterization for latent heating within a cloud and the linear and nonlinear forcing terms are separately analyzed these results suggest that although the nonlinear effects strongly promote splitting of the updraft the linear forcing remains the dominant factor in preferentially enhancing updraft growth on the right flank we believe this differential forcing is a major contributor to the observed predominance o

natural streams and the legacy of water powered mills gravel bedded streams are thought to have a characteristic meandering form bordered by a self formed fine grained floodplain this ideal guides a multibillion dollar stream restoration industry we have mapped and dated many of the deposits along mid atlantic streams that formed the basis for this widely accepted model these data as well as historical maps and records show instead that before european settlement the streams were small anabranching channels within extensive vegetated wetlands that accumulated little sediment but stored substantial organic carbon subsequently 1 to 5 meters of slackwater sedimentation behind tens of thousands of 17th to 19th century milldams buried the presettlement wetlands with fine sediment these findings show that most floodplains along mid atlantic streams are actually fill terraces and historically incised channels are not natural archetypes for meandering streams

a mass flux scheme view of a high resolution simulation of a transition from shallow to deep cumulus convection in this paper an idealized high resolution simulation of a gradually forced transition from shallow nonprecipitating to deep precipitating cumulus convection is described how the cloud and transport statistics evolve as the convection deepens is explored and the collected statistics are used to evaluate assumptions in current cumulus schemes the statistical analysis methodologies that are used do not require tracing the history of individual clouds or air parcels instead they rely on probing the ensemble characteristics of cumulus convection in the large model dataset they appear to be an attractive way for analyzing outputs from cloud resolving numerical experiments throughout the simulation it is found that 1 the initial thermodynamic properties of the updrafts at the cloud base have rather tight distributions 2 contrary to the assumption made in many cumulus schemes nearly undiluted air parcels are too infrequent to be relevant to any stage of the simulated convection and 3 a simple model with a spectrum of entraining plumes appears to reproduce most features of the cloudy updrafts but significantly overpredicts the mass flux as the updrafts approach their levels of zero buoyancy a buoyancy sorting model was suggested as a potential remedy the organized circulations of cold pools seem to create clouds with larger sized bases and may correspondingly contribute to their smaller lateral entrainment rates our results do not support a mass flux closure based solely on convective available potential energy cape and are in general agreement with a convective inhibition cin based closure the general similarity in the ensemble characteristics of shallow and deep convection and the continuous evolution of the thermodynamic structure during the transition provide justification for developing a single unified cumulus parameterization that encompasses both shallow and deep convection

impact of variations in upper level shear on simulated supercells abstractit has previously been suggested based on limited observations that vertical wind shear in the upper troposphere is a key control on supercell morphology with the low precipitation high precipitation and classic archetypes favored under strong weak and moderate shear respectively the idea is that with increasing upper level shear uls hydrometeors are transported farther from the updraft by stronger storm relative anvil level winds limiting their growth and thereby reducing precipitation intensity the present study represents the first attempt to test this hypothesis using idealized simulations of supercells performed across a range of 6 12 km shear profiles contrary to expectations there is a significant increase in surface precipitation and an associated strengthening of outflow winds as uls magnitude is increased from 0 to 20 m s 1 these changes result from an increase in storm motion which drives stronger low level inflow a wider updraft and enhanced condensation a further

european impacts on downstream sediment transfer and bank erosion in cobargo catchment new south wales australia abstract upland valley fills in cobargo catchment on the south coast of new south wales represent substantial sediment source zones contemporary channels within these fills are up to 8 m deep and 50 m wide for catchment areas 2 virtually all banks are eroding downstream of this sediment source zone sediment transfer zones are characterised by sinuous channels that are partially choked by sands released from upland valley fills coarse sands stored in point bars deflect flow to outer banks where colluvial footslopes are eroded approximately 50 of banks are eroding in this section of the catchment other than the 10 km river reach upstream of the river mouth the remainder of the catchment is a bedrock confined sediment throughput zone characterised by fluctuations in channel bed elevation the downstream 10 km of the catchment is a sediment accumulation zone in which erosion is restricted to occasional concave banks prior to european settlement of cobargo catchment upland valley fills were largely unincised and middle transfer reaches of the catchment comprised swamps vegetation clearance along with disturbance and drainage of swamps transformed discontinuous water courses into continuous channels working from a base point of intact upland valley fills almost 50 of available material has been removed from the upper catchment sediment source zone contributing 2 9 10 6 m 3 of material to the lower catchment of this roughly 65 has been stored along the channel bed and floodplain this gives a total sediment contribution to the delta of 1 0 10 6 m 3 sufficient materials are stored in transient storage units along transfer zones to maintain current rates of sediment throughput to the delta for several decades cobargo catchment experienced dramatic acceleration of channel incision and bank erosion processes within a few decades following european settlement of the catchment i e around 1830 transition in landscape form and associated sediment delivery were rapid with a negligible lag interval i e within a few decades of disturbance however given the extensive volume of sediment released from upland valley fills landscape recovery i e refilling of upland valleys will likely take thousands of years

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

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

stream channel erosion and change resulting from riparian forests forested stream banks compared to grassed ones can destabilize stream channels by promoting erosion four reaches of coon creek wisconsin each with long term grassed and forested subreaches were examined grassed reaches were narrower and had smaller channels bankfull cross sections than forested reaches suggesting that grassed channel reaches stored about 2100 to 8800 m 3 more sediment per kilometre than forested reaches available evidence suggests that conversion of riparian forests to grass would allow storage of sediment along channels possibly decreasing downstream sediment yields these findings are important as many grassed riparian corridors are rapidly reverting to forest because of economic conditions and governmental policies