sulfide formation in reservoir carbonates of the devonian nisku formation alberta canada an ion microprobe study the processes affecting sulfur during diagenesis in carbonates have been investigated by ion microprobe analysis of 34s values of pyrite marcasite and anhydrite from the devonian nisku formation in the western canada sedimentary basin pyrite and marcasite from three nisku wells have 34s ranging between 35 and 20 cdt most lie between 35 and 5 cdt the 34s values of sulfides are heterogeneous within individual thin section sized samples varying by as much as 25 the 34s values increase by up to 50 with increasing well depth in two different nisku wells and 34s also increases by up to 15 as grain size increases from 40 to over 100 m in individual samples the appearance of native sulfur is accompanied by an increase of up to 30 in pyrite 34s values bulk and ion probe analyses of anhydrite are relatively uniform 34s 22 to 30 cdt the predominately low 34s values of nisku sulfides indicate bacterial sulfate reduction textural relations indicate that fe sulfide formation in nisku carbonates may have occurred by two different mechanisms much of the sulfide has 34s values that suggest that it was associated with bacterial sulfate reduction although most fe sulfides did not form until after pervasive matrix dolomitization depths of 300 1000 m other sulfide may have formed later during deep 4 km burial via thermochemical sulfate reduction the range in 34s values in a single thin section and correlations between pyrite morphology and isotopic values suggest that sulfate reduction was a very localized process and that the sulfate reduction environment varied considerably on a small scale

quasiperiodic southward moving waves in 630 nm airglow images in the equatorial thermosphere 1 we report quasiperiodic southward moving waves which are commonly observed in the oi 630 nm airglow images emission altitudes of 200 300 km near the equator in 2 year airglow observations at kototabang indonesia 0 2 s 100 3 e geomagnetic latitude of 10 4 the waves have predominantly east west phase fronts and repeatedly propagate southward with a velocity of 310 110 m s and a period of 40 15 min they are frequently observed in may july with an occurrence rate of 53 and are also observed in other seasons with occurrences of 20 the waves are observed in and to the south geomagnetically poleward of the equatorial ionospheric anomaly which is identified as an airglow enhancement region moving gradually to lower geomagnetic latitudes at the premidnight local times we suggest that gravity waves in the lower thermosphere below 300 km are a plausible cause of the observed quasiperiodic waves in the airglow images

channel response to extreme floods insights on controlling factors from six mountain rivers in northern apennines italy abstract this work addresses the geomorphic response of mountain rivers to extreme floods exploring the relationships between morphological changes and controlling factors the research was conducted on six tributaries of the magra river northern apennines italy whose catchments were affected by an extreme flood estimated recurrence interval 100 years in most of the basins on 25 october 2011 an integrated approach was deployed to study this flood including i analysis of channel width changes by comparing aerial photographs taken before and after the flood ii estimate of peak discharges in ungauged streams iii detailed mapping of landslides and analysis of their connectivity with the channel network channel widening occurred in 35 reaches out of 39 in reaches with channel slope results indicate that hydraulic variables alone are not sufficient to satisfactorily explain the channel response to extreme floods and inclusion of other factors such as lateral confinement is needed to increase explanatory capability of regression models concerning hydraulic variables this study showed that the degree of channel widening is more strongly related to unit stream power calculated based on pre flood channel width than to cross sectional stream power and to unit stream power calculated with post flood channel width this could suggest that most width changes occurred after the flood peak finally in terms of hazard it is crucial to document the type and magnitude of channel changes to identify controlling factors and most importantly to develop tools enabling us to predict where major geomorphic changes occur during an extreme flood

sediment characteristics of an extreme flood 1993 upper mississippi river valley the 1993 mississippi river flood was notable for its high magnitude long duration summer occurrence and low sediment discharge a field survey of a 70 km long reach in the vicinity of quincy illinois revealed that the event was characterized by 100 yr flood had remarkably little sedimentological or geomorphological impact on the flood plain within the study reach because the transport effectiveness of floods in large drainage basins is influenced by event sequencing in the same manner as floods in small watersheds and the cohesive flood plain soils were not susceptible to erosion

erosion and channel changes due to extreme flooding in the fourmile creek catchment colorado abstract infrequent large magnitude geomorphic events generate quantifiable change on geologically short timescales and are crucial to understanding landscape evolution airborne lidar surveys and field measurements were used to investigate floodplain erosion and deposition along a 19 5 km reach of fourmile creek colorado that was devastated by severe flooding in 2013 that followed a 2010 wildfire 350 mm of rain fell on the fourmile catchment from september 9 15 2013 generating discharge that exceeded bankfull for 120 h at the orodell gage with local unit stream power 300 w m 2 throughout the study reach debris flows occurred on steep hillslopes and tributary channels in the most intensely burned areas lidar difference measurements and field studies highlight zones of local deposition along the study reach but demonstrate overall net erosion of 0 25 m for the 19 5 km reach of fourmile floodplain mainly by channel widening tributary junctions where debris flow sediment entered the floodplain and local decreases in unit stream power controlled some zones of deposition overall mass balance calculations show that a total sediment loss of 91 000 161 000 m3 from the fourmile creek floodplain and hillslopes which is broadly consistent with channel sediment flux estimates of 71 000 111 000 m3 measurements from the fourmile catchment demonstrate that floodplain erosion was a major source of sediment in the 2013 flood and demonstrate that infrequent events marked by long duration flooding and high total energy expenditure can account for a large fraction of total sediment transport in mountain streams

morphological and sedimentological responses of streams to human impact in the southern blue ridge mountains usa abstract morphological and sedimentological responses of streams to basin scale impact have been well documented for intensively agricultural or urban areas sensitivity thresholds of streams to modest levels of disturbance however are not well understood this study addresses the influence of forest conversion on streams of the southern blue ridge mountains a region that has received little attention with respect to human impact on stream channels basins were chosen for this study to represent the end members of the range of human impact in the area with the forest cover of the basin used as a proxy for level of impact ranging from about 70 100 regionally two pairs of lightly impacted 90 forest and moderately impacted 70 80 forest sub basins of the upper little tennessee river were identified for comparison reach characteristics e g slope drainage area and riparian cover were aligned in each pair to isolate contrasting forest cover as the primary driver of any detected differences in morphology and sedimentology a suite of standard cross sectional and longitudinal data was collected for each reach for characterization of the sedimentology and morphology of the streams difference of means tests were conducted to identify parameters significantly differing between the lightly and moderately impacted streams in both pairs consistent and significant differences within both pairs were demonstrated in bankfull width depth ratios baseflow wetted width and particle size on the stream bed both in the thalweg and throughout the channel bed the moderately impacted streams are narrower than the lightly impacted streams and the bed texture of the moderately impacted streams is finer than that of the lightly impacted streams the moderately impacted streams contain a higher percentage of

investigations of thermospheric ionospheric dynamics with 6300 a images from the arecibo observatory pilot observations were conducted at arecibo puerto rico using an all sky image intensified ccd camera system in conjunction with radar ionosonde and global positioning system gps diagnostic systems during the periods january 19 28 1993 and february 21 to august 22 1995 these represent the first use of campaign mode operations of an imager at arecibo for extended periods of f region observations the january 1993 period the so called 10 day run yielded a rich data set of gravity wave signatures perhaps the first case of direct imaging of thermospheric wave train properties in the f region the 6 month 1995 campaign revealed two additional optical signatures of f region dynamics a brightness wave in 6300 a passing rapidly through the field of view fov has been linked to meridional winds driven by the midnight temperature maximum mtm pressure bulge on may 3 1995 during a period of geomagnetic activity a 6300 a airglow depletion pattern entered the arecibo fov such effects represent the optical signatures of equatorial spread f instabilities that rise above the equator to heights near 2500 km thereby affecting arecibo s l 1 4 flux tube

intra event and inter seasonal behaviour of suspended sediment in flash floods of the semi arid northern negev israel abstract a better understanding of the relation between suspended sediment concentration and water discharge is gained by recognizing amongst other things the different impacts of two types of rainfall event wandering discrete convective or convectively enhanced high intensity storms and ubiquitous multi celled low intensity frontal storms in the levant the first type is characteristic of autumn and spring and the flushing of sediment by the instant onset of high intensity rainfall produces a clockwise hysteresis in the suspended sediment water discharge relation the second type is characteristic of winter and can be marked by either anticlockwise or no hysteresis in the suspended sediment water discharge relation sedimentary flushing is rarely apparent suspended sediment concentrations in flash floods resulting from convective storms are high typically 10 4 10 5 mg l 1 but correlation with water discharge is low r 0 57 in contrast frontal storm runoff carries lower suspended sediment concentrations typically 10 3 10 4 mg l 1 and correlation with water discharge is better r 0 78 this division assists in interpreting the high degree of scatter evident in the overall suspended sediment concentration water discharge relation but it reveals that much is yet to be learned about the interplay of the disposition of cellular storm tracks and sediment source areas

landscape response to tectonic and climatic forcing in the foredeep of the southern apennines italy insights from quaternary stratigraphy quantitative geomorphic analysis and denudation rate proxies we present new data about the morphological and stratigraphic evolution and the rates of fluvial denudation of the tavoliere di puglia plain a low relief landscape representing the northernmost sector of the pliocene pleistocene foredeep of the southern apennines the study area is located between the easternmost part of the southern apennine chain and the gargano promontory and it is characterized by several orders of terraced fluvial deposits disconformably overlying lower pleistocene marine clay and organized in a staircase geometry which recorded the emersion and the long term incision history of this sector since mid pleistocene times we used the spatial and altimetric distribution of several orders of middle to late pleistocene fluvial terraces in order to perform paleotopographic reconstruction and gis aided eroded volumes estimates then we estimated denudation rates on the basis of the terraces chronostratigraphy supported by published osl and aar dating middle to upper pleistocene denudation rates estimated by means of such an approach are slightly lower than 0 1 mm yr 1 in good agreement with short term data from direct and indirect evaluation of suspended sediment yield the analysis of longitudinal river profiles using the stream power erosion model provided additional information on the incision rates of the studied area middle to late quaternary uplift rates about 0 15 mm yr 1 calculated on the basis of the elevation above sea level of marine deposits outcropping in the easternmost sector of the study area are quite similar to the erosion rates average value thus suggesting a steady state fluvial incision the approach adopted in this work has demonstrated that erosion rates traditionally obtained by quantitative geomorphic analysis and ksn estimations can be successfully integrated to quantify rates of tectonic or geomorphological processes of a landscape approaching steady state equilibrium copyright 2014 john wiley sons ltd

effects of an extreme flood on river morphology case study karoon river iran abstract an extreme flood occurred on 14 april 2016 in the karoon river iran the occurred flood discharge was the highest discharge recorded over the last 60 years in the karoon river using the oli landsat images taken on 8 april 2016 before the flood and 24 april 2016 after the flood the geomorphic effects were detected in different land cover types within the 155 km long study reach the results show that the flood significantly affected the channel width and the main effect was high mobilization of channel sediments and severe bank erosion in the meandering reaches according to field surveys the flood occupied the channel corridor and even the floodplain parts however the channel pattern was not significantly altered although the results show that the average channel width increased from 192 to 256 m statistical results indicate a significant change for active channel width and sinuosity index at 99 confidence level for both indexes the flood induced morphological changes varied significantly for different land cover types along the karoon river specifically the channel has widened less in residential areas than in other land cover types because of the occurrence of bank protection structures however the value of bank retreat in residential and protected sides of the karoon river is more than what we expected during the study of extreme flood

analysis of the effects of human activities on the hydromorphological evolution channel of the saint maurice river downstream from la gabelle dam quebec canada abstract during the first half of the twentieth century many hydroelectric facilities were built in the saint maurice river watershed followed by other human activities in the second half of the century pleasure boating boom dismantling urbanization etc the goal of the study is to constrain the effects of these various types of human activities particularly those of the many dams in the watershed on the hydromorphological evolution of the saint maurice river downstream from the la gabelle dam power plant 43 000 km2 comparison of specific discharge in this river with streamflow measured in a natural river setting reveals a significant decrease in seasonal maximum flows aside from winter when daily maximum flows increased significantly also unlike natural rivers the long term trend in spring flows is not characterized by a significant change in mean downstream from the la gabelle plant these hydrological changes are linked to the inversion type management mode of the reservoirs built downstream from the plant as for the morphological evolution the longitudinal variability of bankfull width downstream from the plant shows two significant shifts in mean the first which was quasi abrupt took place downstream of the des forges rapid and the second which was gradual occurred upstream from the confluence of the saint maurice river with the st lawrence river above the point where the saint maurice splits into two branches comparison of aerial photographs taken at various times 1948 1964 1975 1996 and 2008 reveals no significant change in the mean of bankfull width over time however a significant increase in the surface area of islets located at the confluence was observed which is caused by sediment accumulation these sediments were likely derived from local bank erosion resulting from anthropogenic changes

geomorphic effects flood power and channel competence of a catastrophic flood in confined and unconfined reaches of the upper lockyer valley southeast queensland australia flooding is a persistent natural hazard and even modest changes in future climate are believed to lead to large increases in flood magnitude previous studies of extreme floods have reported a range of geomorphic responses from negligible change to catastrophic channel change this paper provides an assessment of the geomorphic effects of a rare high magnitude event that occurred in the lockyer valley southeast queensland in january 2011 the average return interval of the resulting flood was similar to 2000 years in the upper catchment and decreased to similar to 30 years downstream a multitemporal lidar derived dem of difference dod is used to quantify morphological change in two study reaches with contrasting valley settings confined and unconfined differences in geomorphic response between reaches are examined in the context of changes in flood power channel competence and degree of valley confinement using a combination of one dimensional 1 d and two dimensional 2 d hydraulic modelling flood power peaked at 9800 w m 2 along the confined reach and was 2 3 times lower along the unconfined reach results from the dod confirm that the confined reach was net erosional exporting similar to 287 000 m 3 of sediment whilst the unconfined reach was net depositional gaining similar to 209 000 m 3 of sediment 70 of the amount exported from the upstream confined reach the major sources of eroded sediment in the confined reach were within channel benches and macrochannel banks resulting in a significant increase of channel width in the unconfined reach the benches and floodplains were the major loci for deposition whilst the inner channel exhibited minor width increases the presence of high stream power values and resultant high erosion rates within the confined reach is a function of the higher energy gradient of the steeper channel that is associated with knickpoint development dramatic differences in geomorphic responses were observed between the two adjacent reaches of contrasting valley configuration the confined reach experienced large scale erosion and reorganisation of the channel morphology that resulted in significantly different areal representations of the five geomorphic features classified in this study c 2013 elsevier b v all rights reserved

performance evaluation of three dem based fluvial terrace mapping methods the availability of high resolution digital elevation models dems derived from airborne light detection and ranging lidar surveys has spurred the development of several methods to identify and map fluvial terraces the post glacial landscape of the sheepscot river watershed maine where land use change has produced fill terraces upstream of historic dam sites was selected to implement a comparison between terrace mapping methodologies at four study sites within the watershed terraces were manually mapped on lidar dem derived hillshade images to facilitate the comparison among fully and semi automated dem based procedures including 1 spatial relationships between interpreted terraces and surrounding natural topography 2 feature classification algorithms and 3 the terex terrace mapping toolbox each method was evaluated based on its accuracy and ease of implementation the four study sites have varying longitudinal slope 0 0008 0 006 m m channel width 5 30 m surrounding landscape relief 20 80 m type and density of surrounding land use and mapped surficial geologic units all methods generally overestimate terrace areas average predicted area 210 of manually defined area with the most accurate results achieved within confined river valleys surrounded by the steep hillslopes accuracy generally decreases for study sites surrounded by low relief landscapes predicted areas ranged 4 953 of manual delineations we conclude with the advantages and drawbacks of each method tested and make recommendations for the scenarios where the use of each method is most appropriate copyright 2016 john wiley sons ltd

variations in flood magnitude effect relations and the implications for flood risk assessment and river management abstract in spite of major physical impacts from large floods present river management rarely takes into account the possible dynamics and variation in magnitude impact relations over time in flood risk mapping and assessment nor incorporates feedback effects of changes into modelling using examples from the literature and from field measurements over several decades in two contrasting environments a semi arid region and a humid temperate region temporal variations in channel response to flood events are evaluated the evidence demonstrates how flood physical impacts can vary at a location over time the factors influencing that variation on differing timescales are examined the analysis indicates the importance of morphological changes and trajectory of adjustment in relation to thresholds and that trends in force or resistance can take place over various timescales altering those thresholds sediment supply can also change with altered connectivity upstream and changes in state of hillslope channel coupling it demonstrates that seasonal timing and sequence of events can affect response particularly deposition through sediment supply duration can also have a significant effect and modify the magnitude relation lack of response or deposits in some events can mean that flood frequency using such evidence is underestimated a framework for assessment of both past and possible future changes is provided which emphasises the uncertainty and the inconstancy of the magnitude impact relation and highlights the dynamic factors and nature of variability that should be considered in sustainable management of river channels

measurement of river bank and cliff erosion from sequential lidar and historical aerial photography abstract the methodology and errors involved in determining the meander migration rates and amount of sediment produced by river bank and cliff erosion over five decades along a 16 and 28 km reach of the waipaoa river new zealand are described the reach average meander migration rates 0 22 and 0 12 m a 1 respectively are low by international standards for rivers of comparable size suggesting considerable stability of the river planform the contribution of sediment from bank and cliff erosion 74 3 and 23 3 kt a 1 respectively to suspended sediment load is also low

morphological impacts of flow events of varying magnitude on ephemeral channels in a semiarid region abstract flows in ephemeral channels in semiarid areas are only occasional and channel changes are episodic but the flash floods can be devastating and have major geomorphological impacts data on morphological impacts of flows in semiarid areas are needed to increase understanding of the dynamics and variability of geomorphic responses in such channels for this purpose nine reaches of river channel in three catchments in se spain the nogalte torrealvilla and salada have been sites for measurement of flows and their effects over the period 1997 2012 the sites encompass a range of channel size channel morphology substrate vegetation and position within the catchments a major difference is between schist and marl bedrock areas peak flow stage has been recorded and topography surveyed at frequent intervals and after major flow events over the 16 year period an average of 0 5 flow events per year has been recorded at the schist sites and an average of one per year at the marl sites but occurrence has been highly variable from year to year threshold daily rainfall for channel flow is mostly 15 20 mm but higher rainfalls do not always produce flow one to two major floods have occurred in each of the catchments in the period including the extreme flood event of september 2012 in the nogalte catchment measured morphological changes have occurred between 2 and 10 times at the monitored sites the same size flow can have differing effects depending on the state of the system low flow can mobilise sediment without producing much morphological change the long term trajectory of the reaches and the sediment substrate has a major influence on response to events channel change is governed by threshold values of hydraulic conditions the measurements provide an indication of the scale of maximum erosion and deposition that occurs within the channels and on the floodplains over a range of flow magnitudes and the flow impacts that need to be considered in management

impact of reach geometry on stream channel sensitivity to extreme floods predicting spatial and temporal variations in bank erosion due to extreme floods presents a long standing challenge in geomorphology we develop two methodologies for rapid regional scale assessments of stream reaches susceptible to channel widening the first proposes that channel widening occurs when unit stream power exceeds a critical threshold 300 w m2 the second is motivated by the observation that widening often occurs at channel bends we introduce a new metric the bend stress parameter which is proportional to the centripetal force exerted on a concave bank we propose that high centripetal forces generate locally high bank shear forces and enhance channel bank erosion we test both metrics using the geomorphic signature of tropical storm irene 2011 on the white and the saxtons rivers vermont specifically we test if reaches where significant channel widening occurred during irene required one or both metrics to exceed threshold values we observe two distinct styles of channel widening where unit stream power and bend stress parameter are high widening is usually due to bank retreat elsewhere widening is usually due to the stripping of the upstream end of mid channel islands excluding widening associated with the stripping of the heads of mid channel islands almost all the widening 98 occurred along reaches identified as susceptible to widening the combined metrics identify up to one quarter of the reaches lacking susceptibility to channel widening copyright 2014 john wiley sons ltd

geomorphological impacts of an extreme flood in se spain abstract long term field studies in semiarid ephemeral streams are rare these geomorphic data are essential for understanding the nature of the processes in order to develop modelling for risk assessments and management an extreme flood event on 28 september 2012 affected the murcia region of se spain including long tem monitoring sites on two fluvial systems in the guadalentin basin the nogalte and torrealvilla detailed morphological data were collected before and immediately after the event and the amount of morphological change erosion and deposition have been related to peak flow conditions at the sites on the nogalte channel peak flow reached 2500 m3 s 1 at the downstream end of the catchment in less than 1 h the event had a recurrence interval of 50 years based on rainfall records and damage to old irrigation structures the major effect in the braided gravel channel of the nogalte was net aggradation with massive deposition in large flat bars the measured changes in bankfull capacity were highly correlated with most hydraulic variables net changes in cut and fill in cross sections on the nogalte were highly related to peak discharge and stream power but much less so to measures of hydraulic force velocity shear stress unit stream power relationships of amount of erosion to hydraulic variables were much weaker than for amount of deposition which was largely scaled to channel size and flow energy changes on the torrealvilla were much less than on the nogalte and net erosion occurred at all sites sites on the nogalte channel in schist exhibited higher deposition than those of the torrealvilla sites on marl for the same hydraulic values overall less morphological change took place in the extreme event on the nogalte than predicted from some published hydraulic relations probably reflecting the high sediment supply and the hydrological characteristics of the event the results demonstrate the high degree of adjustment of these channels to the occasional high magnitude flash flood events and that such events need to be allowed for in management the detailed quantitative evidence produced by these long term monitoring sites provide valuable rare data for modelling morphological response to flood events in ephemeral channels

coordinated study of coherent radar backscatter and optical airglow depletions in the central pacific 1 equatorial plasma depletions have well known seasonality and solar cycle behavior except for a few well instrumented sectors much of these data have come from satellite sounding and in situ observations we present a climatology of optical airglow images and 50 mhz coherent backscatter from the pacific sector from solar maximum january 2002 to solar minimum january 2009 in contrast to in situ observations we find that depletion activity remains quite high into solar minimum however the depletions and associated backscatter appear later in the evening and backscatter persists longer at solar minimum furthermore we present individual nights that illustrate the day to day variability of depletion formation and their relationship to coherent backscatter echoes the echoes originate from the depleted regions early in the evening but disappear as the night progresses

geomorphic impact and system recovery following an extreme flood in an upland stream thinhope burn northern england uk abstract quantitative assessments of the impacts of extreme floods on channel morphology are rare real time kinematic rtk gps surveys of a 500 m reach of the thinhope burn an upland gravel bed stream in the uk taken in 2003 and 2004 permitted an assessment of geomorphic work whilst the channel was at steady state a large flood that occurred on 17 july 2007 resulted in a catastrophic impact to the thinhope burn valley floor the reach was re surveyed after the event in 2007 and again in 2008 and in 2011 digital elevation models were produced from the survey data which allowed the spatial patterns of erosion and deposition and volumetric changes between surveys to be established a total of 5202 m3 of deposition and 2125 m3 of erosion was recorded in the reach following the flood event field walking of the catchment and comparison of aerial photographs for 2003 and 2007 suggested that most of the material mobilised had originated from existing sediment held in terraces and paleoberms on the valley floor although slope failures were evident including peat slides in the headwaters delivery of sediment from coupling zones to the channel was thought to play a secondary role in the geomorphic response shown by the channel similarly large volumes of erosion and deposition were found after resurveys in 2008 and 2011 suggesting that the system was still in its relaxation phase the results obtained in this investigation coupled with historical information on the flood history of thinhope burn dating back to 1766 suggested that rare large floods are the geomorphically effective flows in the catchment

geomorphic impacts of flash flooding in a forested headwater basin abstract geomorphic impacts of a july 2001 flood in the hungry mother basin near marion virginia were examined to shed light on the relationships between channel characteristics and the frequency of channel modifying discharges creeks in the study area have been observed for many years with no significant channel changes since at least 1985 the 2001 flood had a recurrence interval of 200 years and caused the only channel change bank erosion and transport of coarse channel material observed in recent decades the paucity of fines in channels before or after the flood and the absence of sub sand sized material in the flood deposits indicates that normal frequent well below bankfull flows are sufficient to transport the apparently limited supply of fines the large particles transported during the 2001 flood after years of inactivity indicate that relatively rare floods are necessary to mobilize this material this suggests the notion of a bimodal dominant discharge on the one hand frequent flows considerably below bankfull levels are sufficient to maintain the channel and prevent significant accumulation of fine sediments and organic matter on the other hand rare floods are necessary to transport the coarser bed material and erode channel banks in the hungry mother area bed material has no relationship to normal flows or to flows with recurrence intervals on the order of 1 3 years bankfull discharge is apparently not related to either the maintenance or channel changing dominant discharges these results suggest that the use of channel dimensions and or bed material as surrogate indicators of hydrologic regimes can be quite complicated and that in some streams bankfull flow has no particular significance in terms of sediment transport and channel modifications

seeding of equatorial plasma depletions by polarization electric fields from middle latitudes experimental evidence 1 it is well known that large wedges of depleted plasma often form in the equatorial ionosphere after sunset irregularities in and around these depletions cause scintillation on trans ionospheric radio paths as well as strong vhf backscatter the ultimate stage of depletion growth is controlled by a collisional interchange instability however the initiation stages remain the subject of debate depletions formed in the first 1 3 hours after sunset are probably seeded by instability processes operating in the valley region from 150 250 km however depletions that form later in the evening do not benefit from the rapid pre reversal enhancement of the zonal electric field nor the sheared flow of the evening vortex we investigate evidence from airglow images and vhf coherent backscatter that a polarization electric field associated with an ionospheric instability process at middle latitudes may induce the formation of post midnight depletions at the geomagnetic equator during geomagnetically quiet periods

geomorphic response to an extreme flood in two mediterranean rivers northeastern sardinia italy analysis of controlling factors abstract a high magnitude low frequency flash flood affected two ungauged rivers northeastern sardinia italy on 18 november 2013 this study investigates the response of channel reaches in a mediterranean environment featuring different morphological settings i e alluvial semialluvial and bedrock boundaries with the aims of i detecting the morphological effects of this large flood and ii analyzing a range of morphological and hydraulic variables as potential controlling factors of channel response channel widening was the dominant geomorphic response observed and it occurred at different magnitudes among the study subreaches within individual subreaches channel width increased from 1 1 to 6 2 times the pre flood width a significant trend in channel widening is observed especially in alluvial subreaches where the narrowest channels were prone to enlarge more compared to the widest channels considerable erosion of valley sides also occurred in confined and partly confined semialluvial and bedrock subreaches a range of parameters influenced the geomorphic role of the flood and a series of selected morphological and hydraulic controlling factors showed robust correlations with changes in channel width although correlations were stronger in alluvial subreaches analysis and documentation of channel response and its variability through different morphological settings is crucial to provide a basis from which to forecast future river sensitivity to geomorphic adjustment to high magnitude floods and improve flood management strategies

geomorphological change detection of an urban meander loop caused by an extreme flood using remote sensing and bathymetry measurements a case study of karoon river iran abstract flooding and flood inundation are key hydrological characteristics of meander loop rivers however the effects of extreme floods on river morphology and spatial patterns of erosion and deposition are poorly understood a detailed geomorphologic change detection and sediment erosion process caused by an extreme flood more than 100 year recurrence interval discharge on 14 apr 2016 was surveyed for a single urban meander loop of the karoon river iran the studied meander loop is located next to the city of the ahavz and has a centerline length of about 14 km the bathymetry in 8892 stable points was measured also the detailed bathymetry layers for before 8 apr 2016 and after 24 apr 2016 the extreme flood event were compared geomorphological change detection gcd results show that in the studied reach about 106 ha of bank erosion was detected with a total volume of approximately 450 600 m3 furthermore total volume of surface lowering and the total volume of surface rising volumes that were obtained were 95421 6 m3 and 98619 0 m3 respectively the talweg length of the studied meander loop decreased about 126 m and the average depth decreased from 3 71 m to 3 14 m after the flood event channel widening as a consequence of the extreme flood was found to be about 21 m 17 the findings of this study indicate that extreme floods play an important role in the sediment budget and morphological evolution of meandering rivers

impact of a large flood on mountain river habitats channel morphology and valley infrastructure abstract the biala river polish carpathians was considerably modified by channelization and channel incision in the twentieth century to restore the biala establishing an erodible corridor was proposed in two river sections located in its mountain and foothill course in these sections longer unmanaged channel reaches alternate with short channelized reaches and channel narrowing and incision increases in the downstream direction in june 2010 an 80 year flood occurred on the river and this study aims at determining its effects on physical habitat conditions for river biota channel morphology and valley floor infrastructure surveys of 10 pairs of closely located unmanaged and channelized cross sections performed in 2009 and in the late summer 2010 allowed us to assess the flood induced changes to physical habitat conditions a comparison of channel planforms determined before 2009 and after 2012 the flood provided information on the degree of channel widening as well as changes in the width of particular elements of the river s active zone in eight stretches of the biala the impact of the flood on valley floor infrastructure was confronted with the degree of river widening in unmanaged and channelized river reaches before the flood unmanaged cross sections were typified by finer bed material and greater lateral variability in depth averaged and near bed flow velocity than channelized cross sections the flood tended to equalize habitat conditions in both types of river cross sections obliterating differences in particular physical habitat parameters between channelized and unmanaged channel reaches river widening mostly reflected an increase in the area of channel bars whereas the widening of low flow channels was less pronounced a comparison of channel planform from 2009 and 2012 indicated that intense channel incision typical of downstream sections limited river widening by the flood active channel width increased by half in the unmanaged cross sections and by one third in the channelized cross sections however damage to the valley floor infrastructure was practically limited to the channelized river reaches with reinforced channel banks this indicates incompetent management of riparian areas rather than the degree of river widening as a principal reason for the economic losses during the flood

effects of dam operation and land use on stream channel morphology and riparian vegetation dams are well known for influencing channel and vegetation dynamics downstream but little work has focused on distinguishing effects of land use and channel responses to the impoundment in this paper we examined interacting effects of a dam and land use on downstream changes in channel morphology and riparian vegetation along an agricultural stream system in northern california measurements of planform channel morphology vegetation area and land use were mapped along multiple stream segments based on a chronological sequence of historical aerial photographs over a 34 yr period prior to operation of the dam in 1983 and over a 17 yr period after dam operation and compared to a nearby undammed reference stream a two factor analysis of covariance ancova was used to examine the effect of the dam on changes in bankfull area stream length and riparian vegetation area while accounting for the effect of land use and distance downstream the dammed stream s bankfull area contracted 94 after dam operation prior to dam operation bankfull area decreased when land use area increased but not after operation of the dam stream length varied 64 less after dam operation as a consequence of less frequent episodic channel migration and entrenchment the area of riparian vegetation was decreasing during the pre dam period but then increased 72 after operation of the dam across time periods decreases in the area of riparian vegetation were also associated with increases in land use area in both the dammed and reference stream after operation of the dam reduced peak discharges and sediment reduction likely lead to channel incision and constrained channel migration which allowed vegetation to increase 50 on less accessible abandoned banks rating curve and hydraulic exponent analyses based on stream gauge measurements corroborate statistical analyses of the mapped changes in conclusion we found that operation of the dam and land use patterns together influenced spatial and temporal changes in channel morphology and riparian vegetation use of a nearby undammed reference stream in conjunction with multivariable analysis of spatially and temporally replicated observations provided an effective framework for unraveling interacting effects of dams and land use activities on stream channel and vegetation dynamics

flow hydraulics and geomorphic effects of glacial lake outburst floods in the mount everest region nepal glacial lake outburst floods glofs on 3 september 1977 and 4 august 1985 dramatically modified channels and valleys in the mount everest region of nepal by eroding transporting and depositing large quantities of sediment for tens of kilometres along the flood routes the glof discharges were 7 to 60 times greater than normal floods derived from snowmelt runoff glacier meltwater and monsoonal precipitation referred to as seasonal high flow floods shffs specific stream power values ranged from as low as 1900 w m 2 in wide low gradient valley segments to as high as 51 700 w m 2 in narrow high gradient valley segments bounded by bedrock along the upper 16 km of the glof routes the reach averaged specific stream power of the glofs was 3 2 to 8 0 times greater than the reach averaged specific stream power of the shffs the greatest geomorphic change occurred along the upper 10 to 16 km of the glof routes where the ratio between the glof specific stream power and the shff specific stream power was the greatest there was an abundant supply of sediment and channel valley boundaries consisted primarily of unconsolidated sediment below 11 to 16 km from the source area the geomorphic effects of the glofs were reduced because of the lower specific stream power ratio between the glofs and shffs more resistant bedrock flow boundaries reduced sediment supply and the occurrence of past glofs copyright 2003 john wiley sons ltd

environmental control on diverse stromatolite morphologies in the 3000 myr pongola supergroup south africa a unique outcrop of partly silicified dolomite in the white umfolozi section of the pongola supergroup south africa indicates that stromatolites were diverse and adapted to a range of shallow tidal depositional settings 3000 myr ago composite columnar stromatolitic bioherms 0 7 1 6m high and 0 4 1 0m in diameter formed along the margins of a tidal channel they were flanked away from the channel by flat stratiform and small domical stromatolites growing in low energy tidal flat environments conical stromatolites 0 05 0 30m high and 0 03 0 10m in diameter accreted in high energy coarse grained carbonate sand along the bottom of the tidal channel the stromatolites probably formed through the activities of filamentous oxygen producing photoautotrophic cyanobacteria

optical observations of the growth and day to day variability of equatorial plasma bubbles 1 a new narrow field ionospheric imaging system the portable ionospheric camera and small scale observatory has been installed at the cerro tololo inter american observatory near la serena chile geographic 30 17 s 289 19 e geomagnetic 16 72 s 0 42 e we present observations of the naturally occurring nightglow emission at 630 0 nm on three consecutive nights demonstrating the day to day variability in the occurrence of equatorial plasma bubbles or depletions on two nights large scale undulations with a wavelength on the order of 300 600 km are observed in the emission regions magnetically connected to the bottomside of the equatorial f layer we demonstrate that at each crest of these large scale waves zero one or multiple depletions may grow thus the presence of a large scale wave on the bottomside alone is not sufficient for irregularity growth this variability is presumably due to the presence or lack of small scale seed waves or some other mechanism needed to increase the instability growth rate past the critical threshold

effects of hydrological events on morphological evolution of a fluvial system abstract this study quantifies morphological evolution of the dez river iran from 1955 to 2016 the approach uses a sequence of landsat images aerial photos and topographic maps in addition the hydrological data including average daily discharge and yearly maximum discharge at the dezful hydrological station for the period 1955 2016 were used the study reach was divided into 48 meander loops from upstream to downstream active channel width w was determined at 10 m intervals and changes assessed along the study reach of the dez river morphological indices including sinuosity index straight meander length centerline flow length erosion area erodible length channel migration centerline elongation and radius of curvature were calculated in the reach results showed that the study reach of the dez river changed dramatically in response to major floods although the general trend is towards a narrowing of active channel width by 38 in the period 1955 2016 results show that most of the meander loops in the study area extended and expanded between 1989 and 1995 all types of meander change were observed there was a direct correlation between the frequency of hydrological events flood days bigger than 2 years return period and elongation of bends

historical changes in channel network extent and channel planform in an intensively managed landscape natural versus human induced effects abstract humans have become major geomorphological agents effecting substantial change in the characteristics of earth s physical landscapes the agricultural midwest of the united states is a region marked by pronounced human influence at the landscape scale humans undoubtedly have strongly influenced critical zone processes including fluvial processes in intensively managed agricultural landscapes yet the exact nature of human alteration of these processes is unknown this study documents historical changes in the extent of the stream channel network and in channel planform within the upper sangamon river basin an intensively managed agricultural watershed in illinois results indicate that the modern channel network is nearly three times more extensive than the channel network in the 1820s most change in drainage density has occurred in headwater portions of the basin where numerous drainage ditches have been added to the network to drain flat uplands no detectable change in channel position is evident between 1940 and 2012 along about 60 of the total length of the sangamon river and its major tributaries nearly 30 of the total length exhibits change related to meander dynamics cutoffs and lateral migration whereas about 8 has changed as a result of channelization channelized sections typically remain straight for decades following human modification supporting the notion that humans produce long lasting catastrophic change in channel planform in this region the findings confirm that humans are effective agents of morphological change in fluvial systems in this intensively managed watershed documenting human induced versus natural changes in fluvial systems is important for evaluating how other critical zone processes in intensively managed landscapes have been affected by these changes human induced changes in channel extent and planform most likely have altered this landscape from one dominated by biogeochemical transformations and storage of water and sediment prior to agricultural development into one now characterized by enhanced fluxes of water sediment and nutrients

characteristics of direct human impacts on the rivers karun and dez in lowland south west iran and their interactions with earth surface movements abstract two of the primary external factors influencing the variability of major river systems over river reach scales are human activities and tectonics based on the rivers karun and dez in south west iran this paper presents an analysis of the geomorphological responses of these major rivers to ancient human modifications and tectonics direct human modifications can be distinguished by both modern constructions and ancient remnants of former constructions that can leave a subtle legacy in a suite of river characteristics for example the ruins of major dams are characterised by a legacy of channel widening to 100 s up to c 1000 m within upstream zones that can stretch to channel distances of many kilometres upstream of former dam sites whilst the legacy of major ancient anthropogenic river channel straightening can also be distinguished by very low channel sinuosities over long lengths of the river course tectonic movements in the region are mainly associated with young and emerging folds with nw se and n s trends and with a long structural lineament oriented e w these earth surface movements can be shown to interact with both modern and ancient human impacts over similar timescales with the types of modification and earth surface motion being distinguishable this paper examines the geomorphological evidence and outlines the processes involved in the evolution of these interactions through time the analysis shows how interactions between earth surface movements and major dams are slight especially after ancient dam collapse by contrast interactions between earth surface movements and major anthropogenic river channel straightening are shown to be a key factor in the persistence of long near straight river courses additionally it is suggested that artificial river development with very limited river channel lateral migration may promote incision across an active fold at unusually long distances from the fold core and may promote markedly increased sinuosity across a structural lineament

morphodynamics of a 1000 year flood in the kamp river austria and impacts on floodplain morphology this paper investigates the impact of a 1000 year flood in august 2002 on floodplains and valley morphology of an austrian mixed alluvial bed rock river discharges with a recurrence interval between 500 and 2000 years caused distinctive overbank scouring and material deposition in the floodplains after the 1000 year flood those morphologically affected areas were at random intervals documented over the whole longitudinal profile in addition to overbank erosion in curved sections cut offs the river bed locally widened floodplain stripping occurred and local overbank scours were documented along straight parts of the river a hydrodynamic numerical model combined with field measurements was used to analyse the cause of these erosional landforms based on the modelled hydraulic conditions for a one year flood 30 78 m3 s 1 and the catastrophic 2002 event 700 800 m3 s 1 the numerical results allowed a cause effect study with 19 parameters deterministic and statistical analysis anova discriminant analysis showed that the morphodynamic effects of the 2002 flood were influenced by the variability of valley morphology of the kamp river which led partially to supercritical flow during flood constriction these processes were in some cases also anthropogenically influenced lateral constriction and expansion of the valley geometry over short distances led to scouring and aggradation within the inundated areas during the event these morphological features were therefore responsible for the elongated scour holes in the floodplains copyright 2009 john wiley sons ltd

changes in morphometric meander parameters identified on the karoon river iran using remote sensing data abstract river meander dynamics and mobility are important indicators of environmental change related to climate changes and anthropogenic activities at local and river basin scales the aim of the present study is to identify morphological changes of the karoon river in iran using high accuracy maps and landsat satellite images by analyses during the time period 1989 2008 in this study 20 meandering reaches were analyzed over a 128 km long river reach located in the middle part of the karoon river iran morphometric indicators such as river width w meander neck length l axis length a radius of curvature r water flow length s and sinuosity of meander c were extracted for the identified meanders the results of a paired t test showed that river width w and meander neck length l have significantly changed during the study period 1989 2008 with an increase of 3 5 m for w and a decrease of 274 m for l spearman correlation analysis has shown that meander parameter changes are highly correlated to each other the parameters that do not have significant correlation together are c with w and l w and l and l with s and a during the period of the study the flow length and river sinuosity decreased for the whole river reach by 4 77 km and 0 11 respectively analysis of land use land cover categories 1989 and 2008 using the support vector machine svm and kernel function method served as one of the tools for interpretation of the meander parameter changes these changes can be attributed not only to lu lc riparian vegetation to agriculture area ratio but also to dam construction in the upstream part of the river that leads to major hydrological regime and sediment transfer alteration sediment extraction may also be an important factor

mineralogy and geochemistry of the carbonates in the calatayud basin zaragoza spain the calatayud basin is an elongated nw se depression in northeastern spain it is filled with continental miocene sediments resulting from erosion of palaeozoic and mesozoic rocks of the castilian and aragonese branches of the iberian range miocene series consist of lutitic marly carbonate and evaporitic levels characteristic of a short lived salt lake or a low salinity plays lake depositional environment the carbonates detected in the series were calcite dolomite and magnesite the calcites generally how micritic textures anhedral to subhedral morphologies and contain from 0 to 1 mole mgco 3 and so can be considered low mg calcites their mean isotopic values are lso 7 8 0 pdb and 813c 7 7 0 indicating precipitation in isotopic equilibrium with meteoric water and an extensive contribution of co 2 of organic origin to the total dissolved c respectively the calcites present mg ca sr ca and na ca molar ratios that suggest precipitation from na enriched meteoric water dolomites are non stoichiometric 44 5 47 7 mole mgco3 disordered micfitic and anhedral to subhedral their mean isotopic values slso 0 4 0 pdb and 813c 3 8 0 indicate that they precipitated from more evolved water and with a higher contribution of atmospheric co 2 to the total dissolved c respectively than those of the calcites moreover they present mg ca sr ca and na ca molar ratios suggesting precipitation from water with similar composition to seawater the isotopic composition of magnesite 81so 4 6 0 pdb and 513c 4 0 together with the higher concentration in sr and na indicates that this phase probably precipitated from more evolved water the isotopic values and trace element contents of carbonates appear to confirm the mineralogical trend from calcite to dolomite and to magnesite corresponding to the progressive increase of evaporitic concentration as the water in a hydrologically closed system was subjected to more acutely arid conditions

filtering spatial error from dems implications for morphological change estimation abstract scour and fill estimation from digital elevation model dem subtraction or differencing is an increasingly common technique in morphological and sediment transport investigations the technique is commonly used to estimate scour and fill volumes and to produce scour and fill maps that provide process based information to geomorphologists accounting for sources of uncertainty within the dem is of critical importance dem error is spatially variable and has a tendency to be greater at breaks of slope such as bar and bank edges in the past however this has been achieved using a uniform error metric across the dem resulting in over conservative estimates of error in turn this has led to over conservative scour and fill volumes and incorrect process interpretation this paper applies a new approach that permits assessment of spatially distributed error across a dem the method is tested on a sequence of field surveys of the gravel bed river nent cumbria uk the results demonstrate some dramatic differences application of conventional techniques that account for mean error across a dem led to a 15 and 31 underestimation in scour and fill volumes respectively between july and october 1998 whilst for the october 1998 june 1999 subtraction 31 and 13 of scour and fill were underestimated respectively use of a uniform error across a surface captures less change in comparison to a spatially distributed approach furthermore the changes captured using a uniform error are biased toward areas of the channel that have more local topographic variability such as bar and bank edges in contrast the use of a spatially distributed approach provides information on change from flatter surfaces such as bar tops that would otherwise be missed this study also demonstrates that estimates of morphological change can be misleading in the absence of an error filter where the raw survey data is available it is recommended that sediment budgeting studies take account of the spatial variability of error in each dem involved in the subtraction

spatial discontinuity and temporal evolution of channel morphology along a mixed bedrock alluvial river upper drome river southeast france contingent responses to external and internal controls abstract the rehabilitation of degraded river channels is often guided by assumptions of continuity yet in response to spatial and temporal variations in controlling conditions rivers typically display discontinuous response in space and time this study examines the development of a 5 km reach of the drome river s e france characterised by alternating alluvial and bedrock zones that are separated by abrupt downstream transitions this reach is representative of the drome river as a whole and other rivers in the european alps where braided channel planforms have been replaced by more complex discontinuous morphologies the primary aims are to understand how this spatial complexity has developed on the drome evaluate how temporal channel changes have been affected by local factors particularly bedrock exposures and by long term catchment scale changes in sediment supply and the flood activity and consider the implications of this discontinuous geomorphology for reach management the development of geomorphological zonation is examined by documenting sequential changes in channel planform between seven periods using aerial photography 1948 2006 and by analysing change in bed elevation from profiles surveyed in 1928 2003 and 2005 between 1948 and 2001 bedrock exposed in the channel bed and along the floodplain margins defined discontinuities in sediment connectivity that were largely responsible for the configuration of channel zones the impact of floods on this system was not proportional to flood magnitude a modest flood in 1978 was an important event that by incision and avulsion at key locations defined a pattern of zonation that persisted until the end of the study in 2006 during the final 5 years of the study alluvial zones that previously responded to large floods by widening underwent narrowing despite the occurrence of a large flood and led to an overall reduction in width variance this resulted from progressive incision beneath and disconnection from formerly active channel areas in response to long term catchment scale reductions in sediment supply and flood frequency in 2006 the pattern of zonation remains distinct disguising this recent change in channel response and underlining the need for long term and sequential perspectives of channel development to fully understand the processes in operation contemporary snapshots of channel form may be misleading understanding interactions between inherent channel complexity and prevailing flow and sediment conditions and how this shapes channel response to individual floods is essential when interpreting future trajectories of channel change and likely response to management intervention

fluvialcorridor a new arcgis toolbox package for multiscale riverscape exploration abstract both for scientists and river basin managers development of automated geographic information system gis tools is essential today to characterize riverscapes and explore biogeomorphologic processes over large channel networks since the 1990s gis toolboxes and add in programs have been used to characterize catchments however there is currently no equivalent to a planimetric and longitudinal characterization of fluvial corridor networks at multiple scales this paper describes fluvialcorridor a new gis toolbox this package allows the user i to extract a large set of riverscape features such as the main components of fluvial corridors from dem and vector layers e g stream network or valley bottom and ii to aggregate spatial features into homogeneous segments and metrics characterizing each of them the methodological frameworks involved have been previously described by alber and piegay 2011 leviandier et al 2012 and bertrand et al 2013 and this contribution focuses on the gis tools allowing the user to automatically operate them a case study on the drome river france is provided to illustrate the potential of the package both for geomorphologic understanding and target management actions fluvialcorridor has been developed for arcgis with the related native python library named arcpy and tested on arcgis 10 0 and 10 1 obviously each component of the package can be used separately however it also provides a complete workflow for fluvial corridor characterization even as the toolbox is continually under development and revision case study database fluvialcorridor package and guidelines are available online at http umrevs isig fr

a catchment scale evaluation of the siberia and caesar landscape evolution models landscape evolution models provide a way to determine erosion rates and landscape stability over times scales from tens to thousands of years the siberia and caesar landscape evolution models both have the capability to simulate catchment wide erosion and deposition over these time scales they are both cellular operate over a digital elevation model of the landscape and represent fluvial and slope processes however they were initially developed to solve research questions at different time and space scales and subsequently the perspective detail and process representation vary considerably between the models notably caesar simulates individual events with a greater emphasis on fluvial processes whereas siberia averages erosion rates across annual time scales this paper describes how both models are applied to tin camp creek northern territory australia where soil erosion rates have been closely monitored over the last 10 years results simulating 10 000 years of erosion are similar yet also pick up subtle differences that indicate the relative strengths and weaknesses of the two models the results from both the siberia and caesar models compare well with independent field data determined for the site over different time scales representative hillslope cross sections are very similar between the models geomorphologically there was little difference between the modelled catchments after 1000 years but significant differences were revealed at longer simulation times importantly both models show that they are sensitive to input parameters and that hydrology and erosion parameter derivation has long term implications for sediment transport prediction therefore selection of input parameters is critical this study also provides a good example of how different models may be better suited to different applications or research questions copyright 2010 john wiley sons ltd and commonwealth of australia

evolution of the morphology of the river dragonja sw slovenia due to land use changes the effects of increasing agricultural land use on fluvial morphology have received much attention in fluvial research however in several regions in europe a reversing trend of decreasing agricultural activity and land abandonment followed by reforestation is observed the response of fluvial morphology deserves attention because of its large impacts on landscape and riverine habitats with the help of geomorphological mapping multi date aerial photography and a range of dating techniques we reconstructed the evolution of the morphology of the riverbed and the floodplain of the dragonja river in southwestern slovenia the results of this study show that the fluvial morphology in this mediterranean catchment has changed considerably as a result of shifts in agricultural land use in particular large scale land abandonment in the second half of the 20th century until the first half of the 19th century floodplain aggradation prevailed probably around 1870 a large erosion event occurred from which the floodplain did not fully recover a terrace standing 2 5 m above the present floodplain was formed natural reforestation due to depopulation since world war ii caused a reduction in discharge and sediment supply to the river the decreased intensity and frequency of floods allowed invasion of the riverbed by vegetation causing narrowing and incision of the riverbed this resulted in the formation of a terrace which now stands 1 5 m above the present day river this terrace is about 60 years old however the largest increase in forest area occurred since 1975 which intensified this process of riverbed narrowing and incision creating a local terrace at 0 5 m at 0 5 m above the presently meandering river

the human role in changing river channels abstract direct consequences of the human role where human activity affects river channels through engineering works including channelization dam construction diversion and culverting have been long recognised marsh 1864 thomas 1956 the less obvious indirect effects of point and reach changes occurring downstream and throughout the basin however are much more recently appreciated dating from key contributions by strahler strahler a n 1956 the nature of induced erosion and aggradation in w l thomas ed man s role in changing the face of the earth university of chicago press chicago 621 638 wolman wolman m g 1967 a cycle of sedimentation and erosion in urban river channels geografiska annaler 49a 385 95 schumm schumm s a 1969 river metamorphosis proceedings american society of civil engineers journal hydraulics division 95 255 73 and graf graf w l 1977 the rate law in fluvial geomorphology american journal of science 277 178 191 these are complemented by effects of alterations of land use such as deforestation intensive agriculture and incidence of fire with the most extreme effects produced by building activity and urbanisation changing river channels are most evident in the channel cross section where changes of size shape and composition are now well established with up to tenfold increases or decreases illustrated by results from more than 200 world studies in addition the overall channel planform the network and the ecology have changed specific terms have become associated with changing river channels including enlargement shrinkage and metamorphosis although the scope of adjustment has been established it has not always been possible to predict what will happen in a particular location because of complex response and contingency the ways in which changes in cross section relate to reach and network changes are less clear despite investigations showing the distribution of changes along segmented channels when considering the human role in relation to changing river channels at least five challenges persist first because prediction of the nature and amount of likely change at a particular location is not certain and because the contrasting responses of humid and arid systems needs to be considered modelling is required to reduce uncertainty as was first emphasised by burkham burkham d e 1981 uncertainties resulting from changes in river form american society civil engineers proceedings journal hydraulics division 107 593 610 second feedback effects incorporated within the relationship between changes at channel reach and network scales can have considerable implications especially because changes now evident may have occurred or have been initiated under different environmental conditions third consideration of global climate change is imperative when considering channel sensitivity and responses to threshold conditions fourth channel design involving geomorphology should now be an integral part of restoration procedures this requires fifthly greater awareness of different cultures as a basis for understanding constraints imposed by legislative frameworks better understanding of the ways in which the perception of the human role in changing river channels varies with culture as well as varying over time should enhance application of design for river channel landscapes

geomorphic impacts of a 100 year flood kiwitea stream manawatu catchment new zealand abstract the geomorphic impacts of a 100 year flood are assessed in the kiwitea stream 254 km 2 a tributary within the manawatu river catchment new zealand using sequential aerial photographs and reach based morphological sediment budgeting channel expansion and avulsion eroded in excess of one million cubic metres of sediment over 1 km 2 of floodplain along a 30 km long reach of kiwitea stream channel transformation was spatially discontinuous and predominantly associated with large scale bank erosion in response to a flood over 5 times bigger than the mean annual flood annual recurrence interval ari 100 years total energy expenditure of this flood in the kiwitea was 14 900 10 3 j the spatial discontinuity of channel transformation relates to valley floor and channel configurations high stream powers generated in confined channels at bends produced catastrophic channel transformation where flood flows dissipated overbank stream powers and the extent of channel transformation were reduced hydrologic hydraulic and geomorphic variables can be invoked to thus explain the variability of geomorphic impacts encountered during this event

limestone diagenesis of upper devonian nisku carbonates in the subsurface of central alberta limestone diagenesis of the upper devonian nisku formation in the subsurface of central alberta began syndepositionally most early calcite cements are fibrous bladed and columnar and form isopachous precipitates in primary voids partial syndepositional induration of the lime matrix sand and mud is indicated by angular limestone intraclasts in deposits flanking some buildups hardgrounds and neptunian dikes in the reefal facies some buildups contain intertidal fades possible vadose cements and some early dissolution molds and vugs in their upper parts suggesting shallow influence of meteoric pore waters towards the end of nisku time postdating these features precipitation of fibrous and subequant calcite cements neomorphism mechanical compaction and incipient stylolitization resulted in complete induration and lithification of the buildups and associated marly strata trace element compositions of the various calcites are variable within individual petrographic groups and may have originated from meteoric and or marine phreatic diagenesis however isotopic and petrographic data of most cements suggest marine phreatic diagenesis therefore most cements were probably formed and or recrystallized in pore waters of marine parentage the oxygen isotope data suggest that limestone diagenesis and lithification were essentially completed at a depth of about 300 m this burial depth was achieved near the end of famennian or in early mississippian time

simulating river meandering processes using stochastic bank erosion coefficient this study first compares the first order analytical solutions for flow field by ikeda et al 1981 and johanesson and parker 1989b ikeda et al s 1981 linear model of bank erosion was implemented to predict the rate of bank erosion in which the bank erosion coefficient is treated as a stochastic variable that varies with physical properties of the bank e g cohesiveness stratigraphy vegetation density the developed model was used to predict the evolution of meandering planforms then the modeling results were analyzed and compared to the observed data because the migration of meandering channels consists of downstream translation lateral expansion and downstream or upstream rotations several measures are formulated to determine which of the resulting planform is closest to the experimental measured one results from the deterministic model highly depend on the calibrated erosion coefficient because field measurements are always limited the stochastic model yielded more realistic predictions of meandering planform evolutions because the coefficient of bank erosion is a random variable the meandering planform evolution is a stochastic process that can only be accurately predicted by a stochastic model

the geomorphic effectiveness of a large flood on the rio grande in the big bend region insights on geomorphic controls and post flood geomorphic response abstract since the 1940s the rio grande in the big bend region has undergone long periods of channel narrowing which have been occasionally interrupted by rare large floods that widen the channel termed a channel reset the most recent channel reset occurred in 2008 following a 17 year period of extremely low stream flow and rapid channel narrowing flooding was caused by precipitation associated with the remnants of tropical depression lowell in the rio conchos watershed the largest tributary to the rio grande floodwaters approached 1500 m 3 s between a 13 and 15 year recurrence interval and breached levees inundated communities and flooded the alluvial valley of the rio grande the wetted width exceeding 2 5 km in some locations the 2008 flood had the 7th largest magnitude of record however conveyed the largest volume of water than any other flood because of the narrow pre flood channel conditions record flood stages occurred we used pre and post flood aerial photographs channel and floodplain surveys and 1 dimensional hydraulic models to quantify the magnitude of channel change investigate the controls of flood induced geomorphic changes and measure the post flood response of the widened channel these analyses show that geomorphic changes included channel widening meander migration avulsions extensive bar formation and vertical floodplain accretion reach averaged channel widening between 26 and 52 occurred but in some localities exceeded 500 the degree and style of channel response was related but not limited to three factors 1 bed load supply and transport 2 pre flood channel plan form and 3 rapid declines in specific stream power downstream of constrictions and areas of high channel bed slope the post flood channel response has consisted of channel contraction through the aggradation of the channel bed and the formation of fine grained benches inset within the widened channel margins the most significant post flood geomorphic changes have occurred at and downstream from ephemeral tributaries that contribute large volumes of sediment

application of reservoir geology to enhanced oil recovery from upper devonian nisku reefs alberta canada the upper devonian west pembina reef trend of west central alberta contains recoverable reserves of over 79 106 m3 500 million bbl of oil and 1 4 1010 m3 500 billion ft3 of gas within approximately 50 pinnacle reefs in the nisku formation although the oil is saturated with gas at original reservoir pressure primary depletion would soon lower the reservoir pressure below the bubble point decreasing recovery thus pressure maintenance is applied early in the producing life of the pools through waterflood or miscible flood schemes selection of the appropriate enhanced recovery scheme depends upon the internal flow unit geometry of the reefs the bigoray nisku c pool and the pembina nisku l pool for end members of the reservoir spectrum they can be used as flow unit models in the geological input for reservoir simulation studies the bigoray nisku c pool is dominantly limestone the primary textures well preserved in this reef provide the key to interpreting the relict textures in fully dolomitized reefs a well displayed ecological zonation of rugose corals passes vertically upward into laminar stromatoporoids which in turn pass into solenoporacean algae the coral and stromatoporoid zones each contain two generic flow unit types depending upon the presence or absence of dolomitization the incipient reef facies and the algal cap with associated tidal flat sediments represent two additional flow units due to the presence of horizontal permeability barriers associated with the limestone lithology the pool is developed with a waterflood displacement scheme ultimate recovery is estimated to be on the or er of 0 55 106 m3 3 5 million bbl or 46 of original oil in place ooip the pembina nisku l pool is a completely dolomitized reef representative of the majority of the reefs in the nisku fairway in contrast to the bigoray nisku c pool the complete dolomitization reduces the number of generic reservoir flow units observed in the l pool reef from six to three due to the excellent reservoir quality and absence of horizontal permeability barriers it is being exploited by a vertical miscible flood the nisku l pool is one of the largest pinnacle reefs discovered in the nisku reef fairway and contains an estimated 5 106 m3 31 million bbl ooip ultimate recovery is estimated to be approximately 4 1 106 m3 25 8 million bbl or 82 of ooip

tripod measured residual currents and sediment flux impacts on the silting of the deepwater navigation channel in the changjiang estuary four bottom mounted instrument equipped tripods were deployed at two sections spanning the region characterized by severe sedimentation rates in the deepwater navigation channel dnc along the north passage of changjiang estuary in order to observe currents near bed suspended sediment and salinity seaward residual currents predominated in the up estuary section in contrast a classical two layered estuarine circulation pattern occurred in the down estuary section flow moved seaward in the upper layer and a heavier inflow driven by the salinity gradient moved landward in the lower layer the near bed residual currents in the up estuary section and the down estuary section acted in opposing directions which implies that the region is a convergence zone of near bed residual currents that trap sediment at the bottom the maximum salinity gradient at the maximum flood current indicates the presence of a strong front that induces sediment trapping and associated near bottom convergence of sediment which explains the high sedimentation rates in this section of the estuary

qualitative and quantitative applications of lidar imagery in fluvial geomorphology the potential for geomorphological mapping and quantitative calculations of light detection and ranging lidar data within fluvial geomorphology was studied for two river catchments within belgium dijle and ambleve which differ in physical settings and floodplain morphology two commercial of the shelf lidar datasets with different specifications horizontal resolution and vertical accuracy were available for parts of the floodplains of both catchments real time kinematic rtk global positioning system gps data were used as ground truth for error calculations qualitative analysis of lidar data allowed the identification of former channel patterns levees colluvial hillslope and fan deposits these results were confirmed by field data topographic surveys and historical maps the pixel resolution proved to be an important factor in the identification of small landforms only features with a width equal to or larger than lidar resolution can be detected this poses limits on the usability of regionally available lidar data which often have a horizontal resolution of several metres the lidar data were also used in a quantitative analysis of channel dynamics in the study area the width of the dijle river channel increased 3 m on average between 1969 and 2003 a sediment budget of channel processes for the period 1969 2003 indicated a total river bank erosion of 16 1 103 m3 and a total within channel deposition of 7 1 103 m3 resulting in a net river erosion of 9 0 103 m3 or c 0 4 mg year 1 per metre river length sequential lidar data can in theory be used to calculate vertical sedimentation rates as long as there is control on the error of the reference levels used copyright 2008 john wiley and sons ltd

hydrological controls on the morphogenesis of low energy meanders cher river france summary river restoration is a key issue for european hydrosystems that were modified over centuries by human activities this is particularly true for numerous low energy rivers flowing in the plateaus of western europe because of this limited energy their potential in terms of autogenic restoration a priori appears strongly restricted this study examines the conditions under which the morphogenesis on one of these systems occurs in relation to various hydrologic conditions two complementary approaches are combined on three reaches of the meandering cher river france firstly we examine at a pluri decadal scale the control of duration frequency and intensity of floods on the planimetric erosion bank retreat mainly secondly we estimate the range of effective discharge for bedload transport the results show that the morphogenesis is controlled by low magnitude hydrological events two major controlling factors are suggested low differential of energy between small and large floods peculiar to low energy rivers of mid latitude and low critical discharges for lateral erosion and bedload mobilization for these reasons the ability of the alluvial cher river to self restore its fluvial dynamics seems to be relatively high

nighttime medium scale traveling ionospheric disturbances at low geomagnetic latitudes 1 nighttime medium scale traveling ionospheric disturbances mstids are a commonly observed structure in the middle latitude ionosphere during the months surrounding the solstices and low solar flux conditions mstids consist of one or more narrow bands exhibiting uplift in f region electron density which are elongated from northwest to southeast in the northern hemisphere and southwest to northeast in the southern hemisphere these electrified structures propagate westward and toward the equator in a direction perpendicular to their long dimension previously this type of mstid was not thought to occur at magnetic latitudes equatorward of the equatorial anomalies or approximately 15 geomagnetic latitude here we present observational evidence from a field aligned narrowfield imaging system of mstids existing very close to the magnetic equator we discuss the implications of this observation in terms of the development and propagation of mstids