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

structural evolution of the latakia ridge and cyprus basin at the front of the cyprus arc eastern mediterranean sea abstract the active deformation front between the african and anatolian plates in the eastern mediterranean is delineated by the cyprus arc present plate kinematic vectors and earthquake data suggest that the movement along the eastern extent of the cyprus arc is largely sinistral strike slip it is however widely accepted that subduction took place beneath cyprus until the early miocene subduction has since thought to have become impeded by the collision of the eratosthenes seamount with the island of cyprus the deformation front of the cyprus arc is dominated by the latakia ridge a steep narrow high which merges gradually with the lower slope of the broad hecataeus rise in the west and extends to the northern levantine coast in the east where the expression of the ridge changes to a number of narrow northeast trending ridges and basins the latakia ridge has previously been interpreted as either a thrust culmination or a positive flower structure this study uses high resolution marine seismic reflection profiles to delineate the stratigraphic and structural architecture of the deformation front from seismic profiles four stratigraphic units bounded by major basin wide unconformities can be identified these units are eocene lower miocene miocene uppermost miocene messinian and pliocene quaternary the timing of deformation determined from growth stratal architectures on the flanks of the major structures show that two main phases of deformation characterize the structural history of the deformation front each of these phases represents a different kinematic regime a compressional regime dominated during the miocene whereas a strike slip regime dominated in the pliocene quaternary

discrete plio pleistocene phases of tilting and counterclockwise rotation in the southeastern aegean arc rhodos greece early pliocene formation of the south aegean left lateral strike slip system the island of rhodos represents an uplifted block in the largely submerged southeastern aegean forearc it has a complex history of subsidence uplift and counterclockwise rotation during the plio pleistocene in response to the interplay between large scale geodynamic processes in this paper we present a new chronostratigraphic framework for the continental pliocene apolakkia basin of southwestern rhodos we combine these time constraints with recently published chronostratigraphic data from the marine plio pleistocene basins of northeastern rhodos to reconstruct rotational and vertical motions our palaeomagnetic results identify two rotation phases for rhodos c 10 9 6 counterclockwise ccw rotation between 3 8 and 3 6 ma and c 17 6 ccw rotation since 0 8 ma between these phases rhodos tilted to the se drowning the southeastern coast to a depth of 500 600 m between 2 5 and 1 8 ma then to the nw which resulted in the re emergence of the drowned relief between 1 5 and 1 1 ma we relate the rotations of rhodos to incipient formation of the south aegean sinistral strike slip system and the foundering of the rhodos basin the previously shown absence of messinian evaporites in the deep marine rhodos basin in combination with the 3 8 ma onset of ccw rotation of rhodos constrains the onset of the formation of the south aegean strike slip system between 5 3 and 3 8 ma the formation of this strike slip system is probably related to the interplay of oblique collision between the southeastern aegean region and the northward moving african plate the westward motion of anatolia gravitational spreading of the overthickened aegean lithosphere and the recently postulated southwestward retreat of the african subducted slab along a subduction transform edge propagator fault

numerical simulation of overbank processes in topographically complex floodplain environments this article presents results from an investigation of the hydraulic characteristics of overbank flows on topographically complex natural river floodplains a two dimensional hydraulic model that solves the depth averaged shallow water form of the navier stokes equations is used to simulate an overbank flow event within a multiple channel reach of the river culm devon uk parameterization of channel and floodplain roughness by the model is evaluated using monitored records of main channel water level and point measurements of floodplain flow depth and unit discharge modelled inundation extents and sequences are assessed using maps of actual inundation patterns obtained using a global positioning system observational evidence and ground photographs simulation results suggest a two phase model of flooding at the site which seems likely to be representative of natural floodplains in general comparison of these results with previous research demonstrates the complexity of overbank flows on natural river floodplains and highlights the limitations of laboratory flumes as an analogue for these environments despite this complexity frequency distributions of simulated depth velocity and unit discharge data closely follow a simple gamma distribution model and are described by a shape parameter that exhibits clear systematic trends with changing discharge and floodplain roughness such statistical approaches have the potential to provide the basis for computationally efficient flood routing and overbank sedimentation models copyright 2002 john wiley sons ltd

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

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

exhumation with a twist paleomagnetic constraints on the evolution of the menderes metamorphic core complex western turkey 1 much remains to be understood about the links between regional vertical axis rotations continental extension and shortening in western turkey miocene vertical axis rotations have been reported that occur simultaneously with the extensional exhumation of the menderes metamorphic core complex which has been related to back arc extension in the eastern part of the aegean back arc in this paper we explore the spatial and temporal relationships between vertical axis rotations in southwestern turkey and extensional unroofing of the menderes massif to this end we provide a large set of new paleomagnetic data from western turkey and integrate these with the regional structural evolution to test the causes and consequences of oroclinal bending in the aegean region the lycian nappes and bey daglari are shown to rotate 20 between 16 and 5 ma defining the eastern limb of the aegean orocline this occurred contemporaneously with the exhumation of the central menderes massif along extensional detachments and after the latest oligocene to early miocene exhumation of the northern and southern menderes massifs exhumation of the latter two was not associated with vertical axis rotations the lower miocene volcanics in the region from lesbos to usak to the north of the central menderes massif underwent a small clockwise rotation insignificant with respect to eurasia this shows that exhumation of the central menderes massif was associated with a vertical axis rotation difference between the northern and southern menderes massifs of 25 30 this result is in excellent agreement with the angle defined by the trends of buyuk menderes and alasehir detachments as well as the angle defined by the regionally curving stretching lineation pattern across the central menderes massif these structures define a pivot point rotation pole for the west anatolian rotations the rotation of the southern domain including the southern menderes massif the lycian nappes and bey daglari must have led to n s contraction east of this pole the eastern limit of the rotating domain is formed by the transpressional couple of the aksu thrust and kirkkavak fault in the center of the isparta angle previously reported clockwise rotations in the volcanic fields near afyon may be the result of distributed n s shortening east of the pivot point the precise accommodation of this shortening history remains open for investigation late oligocene to early miocene extension in the eastern part of the aegean back arc was ne sw oriented and likely bounded by a discrete transform this transform may be associated with an early evolution of the eastern aegean subduction transform edge propagator fault oroclinal bending in the west anatolian region is likely related to a reconnection of the eastern part of the aegean orocline with the african northward moving plate in tandem with roll back in the aegean back arc comparable to a recently postulated scenario for western greece

salt tectonics in two convergent margin basins of the cyprus arc northeastern mediterranean abstract seismic reflection profiles from the adana cilicia and iskenderun latakia basin complexes in the ne mediterranean sea show the presence of linked extensional contractional fault systems detached at the base of the messinian evaporites the extensional domain is developed within the thick proximal part of the plio quaternary delta succession in the inner part of each basin it is characterized by imbricate fans of listric normal faults which delineate turtle anticlines and their intervening syncline the faults sole into the gently southwest dipping detachment surface in the inner basins salt is largely evacuated toward the outer basins but remnants occur as rollers in the footwalls of the listric extensional faults and small subdued pillows beneath turtle anticlines the narrow synclines between the two turtle back growth anticlines record a more complicated history of rise and fall of the salt related to switch in vergence of the extensional fault fan a large salt wall is developed at the toe of the delta complex in both basins two wide peripheral sinks are present within the plio quaternary units on both flanks of the salt wall locally small segments of salt welds are present near the base of the salt wall the contractional domain is characterized by a relatively thin plio quaternary cover overlying a relatively uniform 500 800 ms thick salt substrate a series of salt cored growth folds are commonly associated with thrusts of variable vergence the halokinetic structures in the cilicia and latakia basins display a remarkable resemblance to detached and linked systems of extensional and contractional fault fans documented in classical salt provinces on passive margins the study area also resembles scaled experiments which document synchronous development of extensional and contractional fault systems detached in a ductile substrate however a number of differences also exist which may arise from several factors including the nature of ductility contrast between the ductile portion of the evaporite layer and the supra salt succession the thickness ratio of overburden to evaporite unit and the rate of progradation and the nature of sediment distribution during the evolution of the delta complex the special aspect of these associations of linked gravity driven extensional and contractional salt structures is that they are developed as a self contained system wholly situated within a plio quaternary transtensional basin

miocene recent evolution of the western antalya basin and its linkage with the isparta angle eastern mediterranean abstract interpretation of 9500 km of multichannel seismic reflection profiles showed the presence of two major tectonic histories in western antalya basin spanning from the miocene or older to the pliocene quaternary a prominent fold thrust belt affects the miocene succession in the offshore the thrusts swing from a nw se strike with sw vergence in the northeast of the mapped area to a more northerly strike with westerly vergence at the western shelf edge of the deep basin the miocene deformation appears to continue offshore from the westerly directed thrusting seen onshore that characterizes the eastern edge of the isparta angle the contraction is consistent with the counterclockwise miocene rotation of the western side of the isparta angle determined from paleomagnetic studies the thrust belt forms the western extremity of the wider regional aksu kyrenia misis oroclinal culmination the tectonic activity experienced a period of relative quiescence across the western antalya basin during the messinian a major kinematic change occurred in the pliocene when the regional strain was partitioned into three spatially localized tectonic domains an extensional domain confined to the pliocene quaternary unit 1 occupied the northeastern portion of the study area a predominantly extensional domain with a few re activated pre existing miocene contractional structures occupied the southern and central portion of the study area and an extensional and or transtensional domain occupied the continental shelf and slope in the westernmost antalya basin these complexities relate to strike slip motions as the crustal block within the isparta angle moved northwards relative to the blocks to the north

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

flow reversal over a natural pool riffle sequence a computational study a computational study is presented on the hydraulics of a natural pool riffle sequence composed of mixed cobbles pebbles and sand in the river lune northern england a depth averaged two dimensional numerical model is employed calibrated with observed data at the field site from the computational outputs the occurrence of longitudinally double peak zones of bed shear stress and velocity is found in particular at low discharge there exists a primary peak zone of bed shear stress and velocity at the riffle tail in line with the local maximum energy slope in addition to a secondary peak at the pool head as discharge increases the primary peak at the riffle tail at low flow moves toward the upstream side of the riffle along with the maximum energy slope showing progressive equalization to the surrounding hydraulic profiles concurrently the secondary peak due to channel constriction appears to stand at the pool head with its value increasing with discharge and approaching or exceeding the primary peak over the riffle the existence of flow reversal is demonstrated for this specific case which is attributable to channel constriction at the pool head a dynamic equilibrium model is presented to reconstruct the pool riffle morphology a series of numerical modelling exercises demonstrates that the pool riffle morphology is more likely produced by shallow flows concentrated with coarse sediments than deep flows laden with low concentrations of fine sediments it is concluded that channel constriction can but may not necessarily lead to competence reversal depending on channel geometry flow discharge and sediment properties

high resolution two dimensional spatial modelling of flow processes in a multi thread channel this paper describes application and testing of a two dimensional numerical flow model in a multi thread reach of a proglacial stream the model solves the depth averaged form of the navier stokes equations for open channel flow incorporating a two equation turbulence closure an analytical correction for the effects of secondary circulation and a rigid lid approximation the model requires as input the channel bed topography the water surface bed roughness and inflow discharge information and predicts the spatial distribution of depth averaged velocity and eddy viscosity the results have been subjected to intensive testing using simple assessment of numerical performance e g conservation of mass and momentum numerical convergence distributed sensitivity analysis and comparison of model predictions with field measurements of velocity the results are encouraging particularly given some of the difficulties in obtaining accurate distributed cross stream and downstream velocities distributed sensitivity analysis allowed more detailed consideration of the necessary development of the model this suggested that significant errors in the velocity predictions were largely a result of uncertainty in the specification of both the magnitude and the spatial variation of bed roughness secondly the two equation turbulence closure was observed to have little effect upon model predictions except in the vicinity of the side walls in applications of models of this type to irregular coarse bedded channels improvements in the specification of the topographic boundary condition specification and bed roughness are likely to be more important than a sophisticated turbulence closure scheme thirdly although the secondary circulation correction was observed to reproduce some of the expected streamwise transfer of momentum the effects were seen to be relatively small given the intensity of secondary circulation defined in field contexts the inability of the model to correct effectively for the momentum transfer associated with secondary circulation processes related to topographic discordance and shear generated turbulence suggests that further work is required in this respect 1998 john wiley sons ltd

engineered channel controls limiting spawning habitat rehabilitation success on regulated gravel bed rivers in efforts to rehabilitate regulated rivers for ecological benefits the flow regime has been one of the primary focal points of management strategies however channel engineering can impact channel geometry such that hydraulic and geomorphic responses to flow reregulation do not yield the sought for benefits to illustrate and assess the impacts of structural channel controls and flow reregulation on channel processes and fish habitat quality in multiple life stages a highly detailed digital elevation model was collected and analyzed for a river reach right below a dam using a suite of hydrologic hydraulic geomorphic and ecological methods results showed that despite flow reregulation to produce a scaled down natural hydrograph anthropogenic boundary controls have severely altered geomorphic processes associated with geomorphic self sustainability and instream habitat availability in the case study given the similarity of this stream to many others we concluded that the potential utility of natural flow regime reinstatement in regulated gravel bed rivers is conditional on concomitant channel rehabilitation

use of slope creation for rehabilitating incised regulated gravel bed rivers 1 gravel bedded channels often become incised and degraded below dams gravel can be added to the channel to rehabilitate hydrogeomorphic conditions including those promoting salmon spawning when implemented without increasing bed slope gravel addition at downstream riffles back floods upstream riffles a 2 year gravel augmentation project was done to test the efficacy of a new method for slope creation riffle to riffle slope was raised from 0 002 to 0 008 by adding gravel to the most upstream riffle when gravel was added to the next downstream riffle a year later riffle to riffle slope decreased to the sought after 0 004 after the study the area of high quality chinook salmon spawning habitat increased 471 the number of redds observed went from 62 to 161 during the study despite a 50 decline of in river spawners this eliminates variations in migrant population size and hatchery take as alternative explanations slope creation can be a useful aid for rehabilitating regulated rivers

flow convergence routing hypothesis for pool riffle maintenance in alluvial rivers 1 the velocity reversal hypothesis is commonly cited as a mechanism for the maintenance of pool riffle morphology although this hypothesis is based on the magnitude of mean flow parameters recent studies have suggested that mean parameters are not sufficient to explain the dominant processes in many pool riffle sequences in this study two and three dimensional models are applied to simulate flow in the pool riffle sequence on dry creek california where the velocity reversal hypothesis was first proposed these simulations provide an opportunity to evaluate the hydrodynamics underlying the observed reversals in near bed and section averaged velocity and are used to investigate the influence of secondary currents the advection of momentum and cross stream flow variability the simulation results support the occurrence of a reversal in mean velocity and mean shear stress with increasing discharge however the results indicate that the effects of flow convergence due to an upstream constriction and the routing of flow through the system are more significant in influencing pool riffle morphology than the occurrence of a mean velocity reversal the hypothesis of flow convergence routing is introduced as a more meaningful explanation of the mechanisms acting to maintain pool riffle morphology

a stochastic model of hydraulic variations within stream channels 1 this paper presents a stochastic model of the joint depth and velocity probability distribution in stream channels model input is restricted to simple measures of channel geometry hydraulic distributions are quantified using two independent hydraulic variables each a function of velocity and depth and varying either longitudinally or laterally within a stream channel the stochastic model provides a useful tool for exploring relations between fine scale hydraulic variations and channel geometry one application is modeling fine scale hydraulic habitat conditions in stream channels

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

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

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

investigating two dimensional finite element predictions of floodplain inundation using fractal generated topography two dimensional finite element hydraulic models have been developed to simulate river flood flows at high spatial and temporal resolutions over river reach lengths of 1 60 km such models have been shown to be capable of simulating bulk flow however model redesign to predict spatially distributed hydraulic variables has been constrained by lack of suitable topographic and hydraulic data here we begin this development process using a hypothetical river channel floodplain domain where the topographic surface is parameterized using scaling information derived from a fractal analysis of a real floodplain dtm this is used to test the relative effect of the boundary friction calibration numerical model grid resolution topography sampling error and floodplain relative height on model predictions of outflow discharge inundation extent and local hydraulic variables simulations indicate that model calibration is the dominant factor affecting the above three quantities moreover model sensitivity to spatially uniform change is shown to be simple for bulk flow and inundation extent but spatially complex for local hydraulics the study has a number of implications for model calibration and set up procedures as well as indicating the need to develop a new suite of analysis techniques for this class of model 1998 john wiley sons ltd

gravel sediment routing from widespread low intensity landscape disturbance current river basin missouri during the last 160 years land use changes in the ozarks have had the potential to cause widespread low intensity delivery of excess amounts of gravel sized sediment to stream channels previous studies have indicated that this excess gravel bedload is moving in wave like forms through ozarks drainage basins the longitudinal areal distribution of gravel bars along 160 km of the current river missouri was evaluated to determine the relative effects of valley scale controls tributary basin characteristics and lagged sediment transport in creating areas of gravel accumulations the longitudinal distribution of gravel bar area shows a broad scale wave like form with increases in gravel bar area weakly associated with tributary junctions secondary peaks of gravel area with 1 8 4 1 km spacing disturbance reaches are superimposed on the broad form variations in valley width explain some but not all of the short spacing variation in gravel bar area among variables describing tributary drainage basin morphometry present day land use and geologic characteristics only drainage area and road density relate even weakly to gravel bar areal inventories a simple channel network based sediment routing model shows that many of the features of the observed longitudinal gravel distribution can be replicated by uniform transport of sediment from widespread disturbances through a channel network these results indicate that lagged sediment transport may have a dominant effect on the synoptic spatial distribution of gravel in ozarks streams present day land uses are only weakly associated with present day gravel inventories and valley scale characteristics have secondary controls on gravel accumulations in disturbance reaches copyright 1999 john wiley sons ltd

chronology of the oldest supracrustal sequences in the palaeoarchaean barberton greenstone belt south africa and swaziland abstract zircon age data for felsic metavolcanic rocks of the sandspruit and theespruit formations the two oldest supracrustal components in the palaeoarchaean barberton greenstone belt show that these two successions are time equivalent and constitute one single volcanic event at ca 3530 ma the sandspruit felsic rocks are ubiquitously metasomatized intensely deformed and intruded by and tectonically interlayered with ca 3450 ma granitoid sills that are probably part of the theespruit pluton one metasomatized sandspruit sample contains abundant metamorphic zircons with a weighted mean 207pb 206pb age of 3220 1 1 6 ma reflecting a widespread metamorphic event in parts of the eastern kaapvaal craton in south africa and swaziland several samples of felsic metavolcanic rocks of the theespruit formation confirm a previously established magmatic emplacement age of ca 3530 ma but slightly older rocks up to 3552 ma were found in the easternmost exposure of the theespruit sequence near the south african swaziland border and may represent a lower lithostratigraphic level than exposed farther west hf in zircon isotopic data for most felsic metavolcanic rocks confirm earlier results suggesting that these rocks predominantly originated from melting of a felsic continental basement possibly related to the oldest ca 3660 3550 ma components of the ancient gneiss complex in swaziland however several sandspruit samples also suggest that a juvenile source was involved in their generation perhaps a mafic underplate we see no evidence in the geochemistry and isotopic signatures of felsic volcanic rocks of the sandspruit and theespruit formations for partial melting of a metabasaltic protolith and for palaeoarchean oceanic crust that formed in connection with subduction we rather favor a plateau type setting on older continental crust

impact of historic land use change on sediment delivery to a chesapeake bay subestuarine delta historic land use in the chesapeake bay drainage basin induced large fluxes of fluvial sediment to subestuarine tributaries stratigraphic and palaeoecologic analyses of deltaic deposits may be used to infer changes on the landscape but are not sufficient to quantify past sediment supply when viewed as an inverse boundary value problem reconstruction of the sediment supply function may be achieved by combining deltaic sedimentation chronologies with an equation governing delta progradation we propose that the diffusion equation is appropriate for simulating delta progradation and obtaining the sediment supply function provided a suitable diffusion constant d can be determined three new methods for estimating d are presented for the case of estuarine deltas when the inverse boundary value technique was applied to otter point creek a tidal freshwater delta at the head of bush river in upper chesapeake bay d values ranged from 3763 to 6199 m2 a 1 delta growth simulations showed a 1740 1760 initial pulse a 1760 1780 erosive redistributive interval a 1780 1920 growth period and a 1920 present erosive redistributive era coupling of simulated delta elevations with an empirical plant habitat predictive equation allowed for comparison of predicted versus actual relative habitat areas also the model yielded reconstructed watershed erosion rates and stream suspended sediment concentrations that could be useful for development of water quality regulations copyright 2001 john wiley sons ltd

flow and form in rehabilitation of large river ecosystems an example from the lower missouri river abstract on large intensively engineered rivers like the lower missouri the template of the physical habitat is determined by the nearly independent interaction of channel form and flow regime we evaluated the interaction between flow and form by modeling four combinations of modern and historical channel form and modern and historical flow regimes the analysis used shallow slow water shallow water habitat swh defined as depths between 0 and 1 5 m and current velocities between 0 and 0 75 m s as an indicator of habitat that has been lost on many intensively engineered rivers and one that is thought to be especially important in rearing of young fishes two dimensional hydrodynamic models for modern and historical channels of the lower missouri river at hermann missouri indicate substantial differences between the two channels in total availability and spatial characteristics of swh in the modern channel swh is maximized at extremely low flows and in overbank flows whereas the historical channel had substantially more swh at all discharges and swh increased with increasing discharge the historical channel form produced 3 7 times the swh area of the modern channel regardless of flow regime the effect of flow regime is evident in increased within year swh variability with the natural flow regime including significant seasonal peaks of swh associated with spring flooding comparison with other reaches along the lower missouri river indicates that a channel form is the dominant control of the availability of habitat even in reaches where the hydrograph is more intensively altered and b rehabilitation projects that move toward the historical condition can be successful in increasing topographic diversity and thereby decreasing sensitivity of the availability of habitat to flow regime the relative efficacy of managing flow and form in creating swh is useful information toward achieving socially acceptable rehabilitation of the ecosystem in large river systems

logging effects on sediment flux observed in a pollen based record of overbank deposition in a northern california catchment a palynological approach was used to estimate overbank deposition rates in a forested catchment affected by logging the palynological approach uses downcore variations in total fossil pollen and fossil pollen assemblage to calculate rates of overbank deposition and has a distinct advantage over radioisotopic approaches in that it is not limited by radioactive decay using this approach we determined that overbank deposition rates increased over 400 per cent within years of logging events and that the increased rates persisted for less than 4 years after logging induced deposition peaked overbank deposition decreased over 60 per cent relative to the pre logging background values the decreased deposition rates persisted for over 40 years the immediate effect of logging in this catchment was to induce mass wasting events in hollows that produced rapidly travelling sediment pulses in the subsequent recovery period reduced sediment loading occurred as a result of a reduction in the volume of sediment available for transport the reduction in sediment load led to a reduction in overbank deposition rates until subsequent logging disturbances destabilized and emptied other hollows

late miocene recent evolution of the finike basin and its linkages with the beydaglari complex and the anaximander mountains eastern mediterranean abstract interpretation of 2500 km of high resolution multi channel seismic reflection profiles shows that the finike basin evolved during the pliocene quaternary as the result of dramatic subsidence associated with loading of large imbricate thrust panels that carry the western tauride mountains in the north in the late miocene the stacked seaward prograded quaternary deltas presently resting at 1000 1500 m water depths corroborate the rapid subsidence of the region the ubiquitous presence of evaporites in the 2000 2400 m deep antalya basin and their absence in the 3000 3200 m deep finike basin suggest that the morphology of the finike basin and environs must have been considerably different during the messinian and that this region must have remained above the depositional base of evaporites during this time the transition from the messinian to the pliocene quaternary is marked by partitioning of stress into several discrete spatial domains a dextral strike slip fault zone developed along the western antalya basin extending from the apex of the isparta angle southward into the anaximander mountains this fault zone referred to as the antalya fault zone transected the anaximander mountains sensu lato separating the anaxagoras mountain from the anaximander and anaximenes mountains hence the finike basin sirri erinc plateau and the anaximander and anaximenes mountains remained part of the onland beydaglari block and experienced 20 counterclockwise rotation during the late miocene we envisage the boundaries of the beydaglari block as the burdur fethiye fault zone in the west the newly delineated antalya fault zone in the east and the east west trending sector of the sirri erinc plateau in the southwest kinematic evaluation of the structural elements mapped across the finike basin and the sirri erinc plateau suggest that two additional strike slip zones developed during the pliocene quaternary relaying the stress between the antalya fault zone in the east and the pliny strabo fault zone in the west

an appraisal of the velocity reversal hypothesis for stable pool riffle sequences in the river severn england the velocity reversal hypothesis is the linchpin for a number of recent conceptual models pertaining to sediment sorting and the maintenance of pool riffle sequences in gravel bedded streams the literature in support of the hypothesis together with published adverse criticism is reviewed it is concluded that convincing evidence for the ubiquitous occurrence of such a reversal in a range of channel geometries is currently unavailable continuity considerations indicate that riffles need to be considerably wider than pools for a reversal in the mean velocity to occur under conditions of subcritical flow high stage and stable morphology these observations are substantiated by a detailed study of the hydraulic geometry of stable pool riffle sequences in the river severn england neither the sectionally averaged velocity nor the near bed shear velocity is sensibly greater in the pools than over the riffles during bankfull or near bankfull flow instead a tendency towards equalization of the values of average hydraulic variables is noted as discharge increases a detailed investigation of the three dimensional character of the flow is required to demonstrate whether the entrainment forces within pools can locally exceed those over neighbouring riffles unusual behaviour of the energy gradient over riffles during moderate discharges is related to backwater effects as mediated by the spacing of the riffles the hydraulic data are used to comment on the stability of the test reaches in the context of the development of the river severn in the vicinity of shrewsbury

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

modelling three dimensional flow structures and patterns of boundary shear stress in a natural pool riffle sequence fluid sediment interactions control river channel forms and processes analysis of spatial hydraulic patterns and the resulting boundary shear stress are required to aid understanding of river system behaviour in this paper the hydraulic processes active in a natural pool riffle sequence are simulated using a three dimensional computational fluid dynamics cfd model methods employed for the prescription of model boundary conditions are outlined model calculations are assessed using comparisons with field observations acquired over a range of flows simulations are then used to illustrate flow structures and patterns of boundary shear stress for a near bankfull and an intermediate flow event results are used to assess existing theories that seek to explain the development and maintenance of pool riffle sequences simulated results suggest that near bed velocities and bed shear stresses decrease on riffles and increase in pools as discharge increases model simulations indicate that secondary flow acts to route near bed flow over the downstream side of riffles and into the pool head away from the centre of pools implications for sediment transport and pool maintenance are discussed

supporting aquatic habitat remediation in the detroit river through numerical simulation abstract successful habitat remediation begins with an understanding of the geomorphic processes e g flow regime and sediment transport that maintain desired habitats although field surveys can provide information on site conditions field measurements are limited to spatial temporal extents and resolutions that do not always meet the level of detail required to determine the best remediation design for the underling geomorphic processes at a given site however hydraulic models are capable of predicting flow characteristics at fine resolutions over large spatial extents and can be developed to supplement field surveys hydraulic models were used in conjunction with field surveys to guide the placement of three fish spawning habitats reefs in the detroit river model predictions were used to identify reef placement minimizing flow disruptions that could encourage sediment deposition over the reefs following reef construction we revisited the hydraulic models to evaluate their ability to predict the influence of reef design and placement on flow patterns and further examine the influence of the reefs on localized flow heterogeneity at a resolution relevant to fish

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

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

the oligocene recent evolution of the mesaoria basin cyprus and its western marine extension eastern mediterranean abstract the neogene stratigraphic and structural evolution of the mesaoria basin and kyrenia range is studied using multi channel seismic reflection profiles from their western marine extension the region north of the front of the troodos larnaka culmination constitutes a crustal scale s verging thick skinned linked imbricate thrust system comprising most of the forearc region north of the present day cyprus arc in the eocene thrust activity gave rise to the prominent growth of the troodos larnaka culmination and concurrent imbrication further north in the forearc region creating the root of the kyrenia fold thrust belt northward retreat of the active thrust front in the oligocene miocene led to the development of a foredeep across the root of the kyrenia fold thrust belt with a prominent depositional foredeep ramp situated at the current front of this belt crustal contraction continued in the miocene along the front of the troodos larnaka culmination leading to the progressive shoaling of the basin carried on the backlimb of this culmination in the late miocene thrust activity became widespread in the forearc region with structural contraction being focussed on the kyrenia fold thrust belt pliocene thrust activity in the forearc region is primarily focussed on the kyrenia fold thrust belt with much uplift occurring in the mid late pliocene but continuing to the present the mesaoria basin evolved in the miocene to pliocene as a piggy back basin our data negate earlier models that postulate a phase of crustal extension in the forearc region during the oligocene to mid late pliocene

observations of flow and sediment entrainment on a large gravel bed river constant discharge reservoir releases on the trinity river california provide an unusual opportunity to unambiguously relate flow and gravel entrainment on a large gravel bed river bed shear stress 0 was estimated using local observations of depth averaged velocity gravel entrainment was measured using large tracer gravel installations lateral variability of 0 is large even for straight channels with simple trough like geometry no simple relation exists between local and cross section mean values of 0 fine grains less than 8 mm 20 30 of the bed material are transported at lower discharges than coarse grains scour to the base of the bed surface layer occurs at a dimensionless shear stress g 0 035 for g formed using local 0 and the median grain size of the gravel portion of the bed the dimensionless reference transport rate w 0 002 often used as a surrogate for the threshold of grain motion occurs at nearly the same g at smaller g entrainment and transport rates decrease rapidly becoming vanishingly small at g 0 031 even at very small gravel transport rates all sizes are transported although the coarsest sizes are in a state of partial transport in which only a portion of the exposed grains are entrained both entrainment and cumulative transport observations suggest that maximum scour depth for plane bed transport is slightly less than twice the surface layer thickness

hydrologic and topographic variability modulate channel change in mountain rivers summary the relationships between flow hydrology topography and channel change in mountain rivers is important to understanding landscape evolution the structure and persistence of aquatic habitat and also the physiochemical cycling of upstream derived organic and inorganic materials there is a paucity of detailed studies that analyze the joint roles of hydrology and topography in controlling multiple mechanisms of channel change in mountain rivers in this study gravel and cobble channel change in a bedrock river canyon were analyzed in light of a controlled yet natural experiment where 4491 metric tonnes of rounded gravel and cobble was augmented below a sediment barrier dam in a 1200 m long mountain river reach that had no prior sources of rounded gravel or cobble and still experiences floods above the bankfull discharge the overall study goal was to investigate how flow hydrology can modulate multiple channel change processes depending on the topographic features engaged by the flow channel change was assessed via differencing of high resolution repeat topographic and bathymetric surveys along with cm scale aerial photography post injection statistical tests used to implicate topographic feature specific mechanisms of channel change that vary with discharge included analyzing geomorphic covariance structures of flow dependent width bed elevation and channel change as well as autocorrelation of flow width spatial series stage dependent topographic steering was inferred from associations of erosion and deposition with changes in 2d model derived flow directions at multiple discharges a variety of mechanisms of channel change were qualitatively and quantitatively confirmed including particle hiding topographic steering eddying and flow convergence no single mechanism explained the observed patterns of channel change but rather it is thought that process blending occurs as modulated by the interactions of flow hydrology with complex topography results from this study suggest that both existing channel boundary variability and input hydrologic variability work together to create hydrodynamic spatial patterns that control the fate and transport of sediments in mountain rivers and ultimately their spatial structure

the application of computational fluid dynamics to natural river channels three dimensional versus two dimensional approaches this paper addresses the recent trend in fluvial geomorphology towards using computational fluid dynamics to explore the adjustment between flow processes sediment transport and river channel morphology it aims to evaluate the extent to which three dimensional 3d models improve predictive ability and prediction utility compared to two dimensional 2d applications this is achieved through comparing the predictions of both 3d and 2d models with high quality field data identical boundary conditions obtained from a confluence within a gravel bed river system with high relative roughness are defined for each model evaluation of the 3d model suggests that there is a fundamental limitation upon model predictive ability due to problems of specifying topographic complexity however comparison with the 2d model shows that the 3d model has a higher predictive ability particularly if the 2d model is not corrected for the effects on flow structure of secondary circulation further the 3d model provides more reliable estimates of bed shear stress and other more useful information such as the three dimensional flow field important for mixing processes this suggests that there is significant merit in the move towards 3d models but that research is required to incorporate methods developed in other fields for dealing with boundary condition uncertainties

error propagation for velocity and shear stress prediction using 2d models for environmental management pasternack g b gilbert a t wheaton j m buckland e m 2006 error propagation for velocity and shear stress prediction using 2d models for environmental management journal of hydrology 328 1 2 227 241 sponsorship us fish and wildlife service contracting entity for calfed bay delta ecosystem restoration program cooperative agreement dcn 113322g003