channel arrangements and depositional styles in the sao lourenco fluvial megafan brazilian pantanal wetland abstract the brazilian pantanal is an extensive lowland tropical basin characterized by the presence of fluvial megafans and seasonally inundated savanna floodplain wetlands with an area of about 16 000 km 2 the sao lourenco is the second largest megafan in the pantanal three distinct fluvial channel styles that formed at different times during the late quaternary are found here a geomorphological and sedimentary assessment of these depositional patterns provides valuable insight on the environmental context of their evolution new optically stimulated luminescence data indicate that the upper five meters of sediment in the sao lourenco megafan has been accumulating since the late pleistocene ancient fan lobes located in upper and intermediate fan settings consist of medium and coarse grained fluvial sands and exhibit well preserved distributary braided paleochannels on their surfaces as the megafan evolved through time pleistocene lobes were incised by a prominent valley filled with holocene aged meander belt deposits which consist of silts interbedded with very fine sands and clays currently the incised valley is a zone of sediment bypass modern deposition occurs along the distal toe of the megafan system where lobes characterized by distributary channel levee ridges are widespread these features formed by progradation of avulsion belts into a broad swampy floodbasin which caused the lower portion of the meander belt to be abandoned the significant differences observed in intra fan morphology appear to be linked to the variability in effective precipitation fan lobes deposited with braided distributary channels occurred under relatively dry conditions in the late pleistocene by contrast aggradational meander belt deposits and lobes with distributary channel levee ridges formed during fluctuating precipitation conditions of the holocene when the pantanal emerged from deglacial aridity modern lobes form under heavy seasonal flooding and deposition occurs in response to very rapid and common avulsion events these results have implications for interpreting the complexity of megafan facies in similar continental basins

tectonic and stratigraphic evolution of zagros and makran during the mesozoic cenozoic introduction the zagros fold thrust belt zftb extends for c 2000 km from turkey in the nw to the hormuz strait in the se this belt results from the collision of the arabian and eurasian plates during cenozoic times and constitutes a morphological barrier with some peaks exceeding 4000 m separating the arabian platform from the large plateaux of central iran to the east a pronounced syntaxis marks the transition between the zagros collision belt and the makran accretionary wedge in the zftb the proterozoic to recent stratigraphic succession pile of the southern tethys margin is involved in huge folds detached from the pan african basement and offers the opportunity to study the stratigraphic and tectonic evolution of the palaeo tethyan margin over large time periods few recent data are widely available on the southern tethys margin as preserved in the zagros mountains since the classical works of james wynd 1965 and murris 1980 the most recent synthesis is the palaeogeographical reconstruction of the arabian platform published by ziegler 2001 many petroleum data have been acquired during the last 10 years but few of these have been published the middle east basins evolution mebe programme coordinated by p barrier and m f brunet in close relationship with colleagues of the geological survey of iran was an excellent opportunity to go back to the field and to collect new data to better constrain the evolution of this margin in this volume the structure of the zagros mountains is explored through different scales and using different approaches

modeling flood dynamics along the superelevated channel belt of the yellow river over the last 3000 years the yellow river china experienced 1000 levee breaches during the last 3000 years a reduced complexity model is developed in this study to explore the effects of climate change and human activity on flood levels levee breaches and river avulsions the model integrates yearly morphological change along a channel belt with daily river fluxes and hourly evolution of levee breaches model sensitivity analysis reveals that under natural conditions superelevation of the channel belt dominates flood frequency when there is significant human accelerated basin erosion and breach repair the dominant factors shift to a combination of mean annual precipitation superelevation critical shear stress of weak channel banks and the time interval between breach initiation and its repair the effect of precipitation on flood frequency is amplified by land use changes in the hinterland particularly in the erodible loess plateau uncertainty analysis estimates the most likely values of the dominant factors for six historical periods between 850 b c and a d 1839 which are used to quantitatively reconstruct flood dynamics during 850 b c to a d 1839 when the sediment load increased fourfold the breach recurrence interval was shortened from more than 500 years to less than 6 years and the breach outflow rate increased 27 times river management practices during a d 1579 to a d 1839 focused on levees and triggered a severe positive feedback of increased levee heights and flood hazard exacerbation raising the levee heights proved to be ineffective for sustainable flood management

the rivers of civilization the hydromorphic regimes that underpinned old world river based civilizations are reviewed in light of recent research notable holocene climatic changes varied from region to region whilst the dynamics of floodplain environments were equally diverse with river channel changes significantly affecting human settlement there were longer term trends in holocene hydroclimate and multi centennial length flood rich and flood poor episodes these impacted on five identified flooding and settlement scenarios i alluvial fans and aprons ii laterally mobile rivers iii rivers with well developed levees and flood basins iv river systems characterised by avulsions and floodouts and v large river fed wetlands this gave a range of changes that were either more or less regular or incremental from year to year and thus potentially manageable or catastrophic the latter might be sudden during a flood event or a few seasons acute or over longer periods extending over many decades or even centuries chronic the geomorphic and environmental impacts of these events on riparian societies were very often irreversible contrasts are made between allogenic and autogenic mechanism for imposing environmental stress on riverine communities and a distinction is made between channel avulsion and contraction responses floods droughts and river channel changes can precondition as well as trigger environmental crises and societal collapse the nile system currently offers the best set of independently dated holocene fluvial and archaeological records and the contrasted effects of changing hydromorphological regimes on floodwater farming are examined the persistence of civilizations depended essentially on the societies that maintained them but they were also understandably resilient in some environments pharaonic egypt in the egyptian nile appear to have had more limited windows of opportunity in others the kerma kingdom in the nubian nile or required settlement mobility or exceptional engineering response huang he mesopotamia to accommodate problems such as river avulsion desiccation or local salinization

a framework of holocene and late pleistocene environmental change in eastern iran inferred from the dating of periods of alluvial fan abandonment river terracing and lake deposition abstract we review studies of the holocene and late pleistocene stratigraphy of eastern iran to infer past changes in the environment within this presently arid region we build a scenario of widespread and presumably climatically driven evolution of the landscape through the holocene six sites covering a 10 range in latitude indicate a regional abandonment of alluvial fan surfaces at 10 3 ka with the younger 9 ka end of this age range supported by several of the best constrained studies incision of rivers into the fan surfaces has occurred in discrete stages in the early to mid holocene 9 7 ka leading to the formation of flights of river terraces detailed records of lakebed deposition in the presently arid interior of iran are rare though the available data indicate lake highstand conditions at

anthropocene archaeology of the yellow river china 5000 2000 bp in this paper we use geoarchaeological and paleoenvironmental data from three localities in the yellow river valley china taosi sanyangzhuang and the yiluo valley to argue that human activi

a new model of river dynamics hydroclimatic change and human settlement in the nile valley derived from meta analysis of the holocene fluvial archive in the nile catchment a growing number of site and reach based studies employ radiocarbon and more recently osl dating to reconstruct holocene river histories but there has been no attempt to critically evaluate and synthesise these data at the catchment scale we present the first meta analysis of published and publically available radiocarbon and osl dated holocene fluvial units in the nile catchment including the delta region and relate this to changing climate and river dynamics dated fluvial units are separated both geographically into the nile delta and white blue and desert nile sub regions and into depositional environment floodplain and palaeochannel fills cumulative probability density frequency cpdf plots of floodplain and palaeochannel units show a striking inverse relationship during the holocene reflecting abrupt 100 years climate related changes in flooding regime the cpdf plot of dated floodplain units is interpreted as a record of over bank river flows whilst the cpdf plot of palaeochannel units reflect periods of major flooding associated with channel abandonment and contraction as well as transitions to multi centennial length episodes of greater aridity and low river flow this analysis has identified major changes in river flow and dynamics in the nile catchment with phases of channel and floodplain contraction at c 6150 5750 4400 4150 3700 3450 2700 2250 1350 900 800 550 cal bc and cal ad 1600 timeframes that mark shifts to new hydrological and geomorphological regimes we discuss the impacts of these changing hydromorphological regimes upon riverine civilizations in the nile valley

upstream and downstream controls of recent avulsions on the taquari megafan pantanal south western brazil avulsion the natural relocation of a river is a key process in the evolution of subaerial fans river floodplains and deltas the causes of avulsion are poorly understood which is partly due to the scarcity of field studies of present avulsions at present two avulsions are occurring on the middle and lower taquari megafan pantanal basin south western brazil here we present an analysis of the causes of these avulsions based on field and remote sensing data and show that avulsions on megafans can be controlled by both upstream and downstream processes the middle fan avulsion started in 1997 1998 is a result of upstream control overbank aggradation was caused by the variable input of sandy sediment into the system which caused channel belt superelevation and also created an easily erodible subsurface favouring bank retreat crevassing and scour of deep floodplain channels the sandy subsurface in this area is inferred to have been a major factor in the causation of this avulsion under conditions of little gradient advantage the lower fan avulsion started c 1990 results from interplay of upstream and downstream controls the latter being related to the local base level the paraguay river floodplain at the toe of the fan channel and overbank aggradation on the lower fan was influenced by fan sub lobe progradation and channel backfilling fan sub lobe progradation caused a significant gradient advantage of the avulsion channel over the parent channel avulsions are commonly supposed to be preferentially triggered by high magnitude floods when there is considerable channel belt superelevation however both avulsions studied by us were triggered by small to average floods with modest channel belt superelevation we conclude that flood magnitude and channel belt superelevation have been overrated as causes of avulsion and demonstrate additional causes that influence the growth of crevasses into avulsions

a middle to late holocene avulsion history of the euphrates river a case study from tell ed dēr iraq lower mesopotamia abstract geoarchaeological research was performed to reconstruct the floodplain history in the surroundings of two ancient mesopotamian cities tell ed d r and sippar the mapping of the floodplain is based on facies analyses of the sedimentary succession of 225 hand operated boreholes the archaeological sites tell ed d r and sippar are closely linked to a palaeochannelbelt of the euphrates located in the western part of the study area channel activity started at least in ca 3100 bc 5050 cal bp until ca 1400 1000 bc 3350 2950 cal bp the channel belt was part of an avulsion driven multiple euphrates channel network that gradually became abandoned from the second half of the 2nd millennium bc a second mapped euphrates tigris or joint euphrates tigris palaeochannel belt became abandoned well before 3100 bc examples of natural processes as well as human interactions triggering avulsion are given moreover textual archaeological and geological data show clearly that flood control techniques and the construction of large scale dikes seemed to be a common practice

structural framework of the zagros fold thrust belt iran abstract data gleaned from the literature on the zagros have been compiled and used in conjunction with new interpretations to provide a better picture of the structures sedimentation history and deformation of this hydrocarbon rich mountain belt the belt parallel mountain front the n s trending kazerun izeh and e w trending bala rud fault zones are defined as the master structural elements of the belt these fault zones divide the zagros basin into zones with different stratigraphic successions and different rheological profiles this resulted in different structural styles developing along the belt during the subsequent collision the kazerun and izeh fault zones acted as the depositional system transition zone between the lurestan and fars regions in jurassic cretaceous time and partly controlled the distribution of the kazhdumi formation one of the major source rocks by the end of the cretaceous the nw se trending mountain front fault divided the present folded belt of the zagros into a major foreland basin to the southwest and a piggyback basin to the northeast activity along other major transfer fault zones including the izeh kazerun and bala rud fault zones occurred at this time and controlled the sedimentation and subsidence of the dezful embayment the main target region for hydrocarbon exploration these fault zones controlled the thickness of the asmari formation one of the main reservoirs and also the considerable thickness and facies changes of the gachsaran formation the major seal to the asmari formation the present morphology of the mountain belt is interpreted as being mainly related to the pinning of the mountain front fault to the northwest of the dezful embayment and to the north of the strait of hormuz

river avulsions on the taquari megafan pantanal wetland brazil abstract the pantanal wetland is located in a tectonically active interior sedimentary basin in west central brazil the south flowing paraguay river is the trunk river of an alluvial constructional landform comprising several large alluvial fans the largest one of which is the taquari megafan the taquari river flows in two distinct geomorphologic zones within the megafan entrenched on sediments of pleistocene fan lobes the taquari river flows in a 3 to 5 km wide meander belt in the upper fan where avulsion is hindered by entrenchment downstream of the intersection point stream discharge progressively decreases and the taquari river becomes narrow and shallow toward the paraguay river plain within the distributary fan lobe the channel levee sandy complex is topographically higher than the adjacent floodplains and avulsion is a natural consequence of crevasses in the natural levees many channel avulsions have occurred during the last decades and documented cases show that significant channel changes may take place in a few years beginning with crevassing in 1988 and ending with the abandonment of the former channel in 1998 the river completely changed course in the lower fan presently a major avulsion is occurring in the upper portion of the growing fan lobe where many crevasses have appeared in the natural levees with associated splays onto the floodbasin new anastomosed channels have formed north of the taquari river but downstream of them the flow is unconfined and the water spreads into natural floodbasins this avulsion is still in process and allows observation of channel evolution the geomorphic features produced the sedimentary processes involved and resulting effects if the new channels do not rejoin the main channel the river mouth may abandon its present master channel and shift to a position a hundred kilometers north from its present position a large volume of sediment has been transferred to the floodbasin with progradation of crevasse splay deposits over fine overbank sediments many geomorphic features recognizable in satellite and radar images clearly show that avulsion has occurred many times before in the taquari river avulsion belt deposits and former diverted channels testify to ancient avulsion events within the fan lobe and show that progradation of splays onto the floodbasin is the most important infilling process within the taquari distributary fan lobe the avulsion process in the lower taquari river has accelerated in the last 30 years along with the magnitude of flooding pasture and intensive agriculture in the catchment area has increased the sediment supply to the wetland but larger floods are also a consequence of higher rainfall since 1973 avulsion and floods have been a cause of great concern among the local population and landowners before human intervention in attempting to control floods however a better understanding of the avulsive river system is needed especially because a major navigation project including the channelization of the paraguay river was recently proposed

the role of human interference on the channel shifting of the karkheh river in the lower khuzestan plain mesopotamia sw iran abstract this study is concerned with the late holocene floodplain history of the karkheh river in lower khuzestan and in particular with the role of human action upon its channel shifts the research was conducted in a multidisciplinary way in which resources and approaches from different research fields were combined 1 geomorphological mapping based on the interpretation of landsat and corona satellite imagery 2 analyses of geological sequences including the identification of sedimentary facies and radiocarbon dating of organic material 3 an archaeological field survey of ancient settlements and 4 consultation of historical documents mainly arabic texts from the 9th 14th century and european travel literature from the 16th early 20th century three main channel belts of the karkheh were identified labelled kh1 kh2 and kh3 corresponding to successive stages in the evolution of the floodplain two river shifts are documented in the datasets both taking place within the last 2000 years the first avulsion regards a shift from channel belt kh1 once a tributary of the karun to the straight river bed of kh2 taking place at least after 1240 1310 cal bp 710 640 ad the second avulsion from kh2 to kh3 is clearly documented in historical sources and happened in a single night event in the year 1837 113 cal bp reactivation of the kh2 river bed and its irrigation canals can be attributed to the recent construction of an artificial canal bypassing the second avulsion point both river shifts were strongly influenced by human interference whereby an artificial irrigation canal took over the entire river flow from the main channel belt most likely a combination of human induced factors such as weakening of the river levees high sedimentation rates and disadvantageous channel gradients led to a situation prone to avulsion

estimation of pumpage and recharge in alluvial fan topography under multiple irrigation practices summary in this study we estimate small scale temporal variations in groundwater pumpage and recharge in alluvial fan topography we study these variations on a monthly scale using groundwater storage hydrograph and isotope analysis along with area rainfall hydrographs and data of historical irrigation pumpage variations we consider multiple irrigation practices whose effect was measured only on an annual basis in mostly previous studies in previous studies pumpage for non irrigation or irrigation purposes was regarded as known but illegal pumping was not accounted for also recharge sources include rainfall rivers boundary inflow and groundwater irrigation which have not been individually accounted for in previous studies pumpage can be estimated from the pumping rate and the number of pumping days in alluvial fan topography the actual pumping rate including that because of illegal wells can be deduced from the recession slope of the groundwater hydrograph the annual pumping rate of non irrigation pumping is assumed to be constant and can be estimated as the slope of the groundwater hydrograph over consecutive non rainy days during the non irrigation periods of the dry season for cases where there are multiple irrigation practices the temporal distribution of the irrigation pumping rate can be estimated from the slope of the groundwater hydrograph and also from records provided by the irrigation association in this study we regard recharge as the difference between inflow and loss different types of inflow can be inferred from the storage hydrograph in rainy or non rainy days and the loss can then be obtained by using the groundwater balance equation the isotope mass balance equation is then used to quantify various sources of recharge in this study we apply the proposed methodology to the cho shui river alluvial fan taiwan the results show that the proposed methodology can overcome previous restrictions of groundwater hydrograph and isotope analyses to effectively and rationally estimate monthly variations in pumpage and recharge thus making it possible to research fine flow mechanisms within a multi layer groundwater system

geochemistry and mineralogy of late quaternary loess in the upper mississippi river valley usa provenance and correlation with laurentide ice sheet history abstract the midcontinent of north america contains some of the thickest and most extensive last glacial loess deposits in the world known as peoria loess peoria loess of the upper mississippi river valley region is thought to have had temporally varying glaciogenic sources resulting from inputs of sediment to the mississippi river from different lobes of the laurentide ice sheet here we explore a new method of determining loess provenance using k rb and k ba values in k feldspars and micas in loess from a number of different regions in north america results indicate that k rb and k ba values can distinguish loess originating from diverse geologic terrains in north america further different loess bodies that are known to have had the same source sediments using other criteria have similar k rb and k ba values we also studied three thick loess sections in the upper mississippi river valley region at each site the primary composition of the loess changed over the course of the last glacial period and k rb and k ba values parallel changes in carbonate mineral content and clay mineralogy we thus confirm conclusions of earlier investigators that loess composition changed as a result of the shifting dominance of different lobes of the laurentide ice sheet and the changing course of the mississippi river we conclude that k rb and k ba values are effective robust and rapid indicators of loess provenance that can be applied to many regions of the world

shallow subsurface stratigraphy and alluvial architecture of the kosi and gandak megafans in the himalayan foreland basin india abstract the kosi and the gandak are two major himalayan tributaries of the ganga river in the north bihar plains india with a large hinterland in the nepal himalaya both these rivers have generated megafans in the plains over the quaternary time scale both these rivers are known to be highly dynamic and sediment charged a few conceptual models and limited field data suggested that these megafans have produced thick sand sheets over late quaternary period but these ideas have remained speculative and there is no data on the size and dimension of these sand bodies this paper attempts to reconstruct the subsurface stratigraphy and alluvial architecture for the upper 100 m of the megafans based on electrical resistivity soundings borehole data and drill cores alluvial architecture of the kosi megafan shows significant variability from proximal to medial parts of the fan in terms of sediment grain size and layer thicknesses while the medial part shows 20 30 m thick medium to coarse sand sheets which are laterally stacked the proximal part of the fan has a dominantly gravel unit below 15 m depth that is underlain and overlain by medium to coarse sand units further the medial fan also shows significant vertical and lateral variability in alluvial stratigraphy the near surface

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

archaeology of the anthropocene in the yellow river region china 8000 2000 cal bp although archaeological analysis emphasizes the importance of climatic events as a driver of historical processes we use a variety of environmental and archaeological data to show that human modif

evidence of hydrocarbon and metalliferous fluid migration in the palaeoproterozoic earaheedy basin of western australia dolomitized limestones of the earaheedy basin contain solid bitumen and metal sulphides sulpharsenides and arsenides within a network of fractures which acted as pathways for migrating fluids the solid bitumen formed from residual oil that was thermally altered within those fractures immobilization of oil was postdated by precipitation of fracture filling calcite and later replacive dolomite and quartz cements as well as of magnesian chlorite solid bitumen has high concentrations of fe zn pb ni and fecu bearing sulphides sulpharsenides and arsenides in minute inclusions that are randomly distributed throughout its groundmass galena and pyrite also fill cracks in the bitumen whereas pyrite arsenopyrite galena gersdorffite enargite and chalcopyrite fill contraction vugs small crystals of cassiterite are associated with cavity filling magnesian chlorite multiple phases of base metal precipitation are apparent the first indicated by the inclusions probably formed during mixing of hydrocarbon and metal rich fluids later phases resulted from the filling of bitumen contraction structures that formed during and after thermal alteration and degassing processes and which imply the migration of metal rich fluids after oil immobilization the association of metal rich minerals and fracture filling bitumen in this non ore setting is a guide to the possible existence of ore grade mineralization elsewhere in the basin

irrigation agriculture and the sedimentary record in the palpa valley southern peru abstract irrigation agriculture is an ancient and widespread feature in regions where allogenic rivers flow through arid landscapes this paper reports the results of sedimentological pedological investigations in the palpa valley in the coastal desert of southern peru where sediment laden river water is used for irrigation an adapted facies classification is used to deduce a generalised stratigraphical sequence of the valley bottom sediments chronological constraints from radiocarbon dating and archaeological finds are used to reconstruct sedimentation rates for fossil to recent irragric anthrosols actualistic case studies are used to quantify present day irrigation sedimentation the investigations result in a clarification of the sedimentological and geomorphic history of this valley and a quantification of irrigation related sedimentation irragric anthrosols date back more than 3500 years and provide direct evidence for the beginning of irrigation agriculture in this region it is concluded that i the up to approximately 4 m thick fine grained sediments in the palpa valley bottom totaling a volume of 21 4 mio m3 are a result of long lasting human impact and have to be considered as artefacts of prehistoric and historic irrigation agriculture in the hyperarid coastal desert ii the fine grained sediments represent a geoarchive which holds information on the history of irrigation agriculture as well as information on possible natural disturbance by extreme fluvial events iii the identification of irragric anthrosols has implications for archaeological and paleoenvironmental reconstructions

tributary distributary and other fluvial patterns what really represents the norm in the continental rock record abstract this paper evaluates the recent claim made by weissmann et al 2010 that deposits of distributive fluvial systems dfs may form the bulk of the continental fluvial record weissmann et al 2010 define dfs as a pattern of channel and floodplain deposits that radiate outward from an apex that is located where the river enters the sedimentary basin as such dfs are fan like systems on which multiple channels coexist and distribute water and sediment across the fan published criteria for the recognition of dfs weissmann et al 2010 are 1 a radial pattern of channels from the dfs apex 2 downslope decreases in channel size 3 down dfs grain size decreases and 4 a lack of lateral channel confinement however in weissmann et al 2010 and subsequent papers only the first of these criteria is applied rigorously thus allowing a variety of types of fluvial system including avulsive incised anabranching and coastal plain distributary systems to potentially be classified uncritically as dfs an ancient succession formed by dfs should preserve mostly small channel bodies with a limited range of dimensions and no outsized channel bodies channel bodies in dfs dominated successions should also decrease in size in a down palaeoslope direction and show palaeocurrent relationships indicative of radial dispersal in order for the term dfs to be applied these characteristics should also be established within stratigraphic bodies that formed coevally however very few examples have yet been published that satisfy these criteria if the claim that dfs dominate the alluvial stratigraphic record is valid then few if any sedimentary bodies formed by large channels should be preserved a review of published research demonstrates however that the alluvial stratigraphic record contains a broad diversity of fluvial network styles including abundant representatives of tributary avulsive anabranching and incised in addition to distributary types it is also clear that the deposits of large main stem rivers that are comparable to the big rivers of the modern world are abundantly preserved in the stratigraphic record an analysis of the planimetric area of modern tributary and distributary fluvial systems is presented demonstrating that tributary systems are also likely to represent a far larger proportion of the ancient sedimentary record than dfs the body of evidence presented herein from modern and ancient alluvial systems thus suggests that the hypothesis of weissmann et al 2010 should be wholly rejected dfs do not dominate the continental stratigraphic record

fluvial fans myths misconceptions and the end of the terminal fan model we propose that the so called terminal fan facies model should be abandoned since it is flawed on several counts and it is leading to misunderstanding and poor communication rivers in drylands may experience excessive down stream discharge reduction such that they terminate subaerially rather than reach the sea or a lake the facies model predicts that the distal reaches of such rivers form a network of bifurcating distributary channels producing a fan shaped sediment body with downstream thinning and fining of sedimentary units ending in sand filled ribbons encased in mud extensive review of modern rivers has failed to turn up convincing examples that fit the model rivers in drylands do not ubiquitously end in fans fan shaped fluvial bodies are common wherever rivers are released from confinement and the discharge conditions promote frequent avulsion channels on such fans generally do not repeatedly bifurcate downstream where they are seen to do so it can usually be shown they are lacustrine deltas inherited from wetter times the term distributary is being used carelessly and is conveying incorrect understanding of sediment geometry and architecture the proposed synonym of fluvial distributary systems is unsatisfactory as it perpetuates the same misunderstandings reliance on planform alone in analogue selection is highly risky the fluvial fan is a composite sediment body resulting from frequent nodal avulsions in a setting without horizontal constraints channels on fans range in planform as much as any other river the resultant sedimentary record differs little from that expected from non fan fluvial systems except having a regionally radiating orientation when viewed over geological time scales contrary to the implications of the facies model there is no distinctive terminal fan sedimentary succession

late cenozoic reorganization of the arabia eurasia collision and the comparison of short term and long term deformation rates the arabia eurasia collision deforms an area of 3 000 000 km2 of continental crust making it one of the largest regions of convergent deformation on earth there are now estimates for the active slip rates total convergence and timing of collision related deformation of regions from western turkey to eastern iran this paper shows that extrapolating the present day slip rates of many active fault systems for 3 7 million years accounts for their total displacement this result means that the present kinematics of the arabia eurasia collision are unlikely be the same as at its start which was probably in the early miocene 16 23 ma or earlier in some but not all active fault systems short term 10 year and long term 5 million year average deformation rates are consistent there is little active thickening across the turkish iranian plateau and possibly the interior of the greater caucasus these are two areas where present shortening rates would need more than 7 million years to account for the total crustal thickening and where there are structural and or stratigraphic data for pre late miocene deformation we suggest that once thick crust up to 60 km built up in the turkish iranian plateau and the greater caucasus convergence took place more easily by crustal shortening in less elevated regions such as the zagros simple folded zone the south caspian region and foothills of the greater caucasus or in other ways such as westward transport of turkey between the north and east anatolian faults the time and duration of this changeover are not known for certain and are likely be diachronous although deformation started or intensified in many of the currently active fault systems at 5 2 ma

spatial variation of overbank aggradation rate and its influence on avulsion frequency river avulsions are commonly considered to be driven by the aggradation and growth of alluvial ridges and the associated increase in cross valley slope relative to either the down channel slope or the down valley slope the latter is termed the slope ratio in the present paper therefore spatial patterns of overbank aggradation rate over stratigraphically relevant time scales are critical in avulsion dominated models of alluvial architecture detailed evidence on centennial to millennial scale floodplain deposition has to date been largely unavailable new data on such long term overbank aggradation rates from the rhine meuse and mississippi deltas demonstrate that the rate of decrease of overbank deposition away from the channel belt is much larger than has been supposed hitherto and can be similar to observations for single overbank floods this leads to more rapid growth of alluvial ridges and more rapid increase in slope ratios potentially resulting in increased avulsion frequencies a revised input parameter for overbank aggradation rate was used in a three dimensional model of alluvial architecture to study its effect on avulsion frequency realistic patterns of avulsion and interavulsion periods 1000 years were simulated with input data from the holocene rhine river with avulsions occurring when the slope ratio is in the range 3 5 however caution should be practised with respect to uncritical use of these numbers in different settings evidence from the two study areas suggests that the avulsion threshold cannot be represented by one single value irrespective of whether critical slope ratios are used as in the present study or superelevation as has been proposed by other investigators

the role of long term human impact on avulsion and fan development this study aims to understand mainly qualitatively the long term role of human impact on avulsion processes and the development of fluvial mega fans in semi arid environments in this paper we refer to human impact as the direct influences of actions on the river s hydraulics i e flow regulation flow diversion and channel engineering in five case studies drawn from the khuzestan plains in southwest iran we have analysed the setup and triggering conditions of specific avulsions that occurred in the past timescale of millennia and identified the role of human interference in their causation our analysis is based on the integration of historical archaeological geomorphological and geological data through this study we demonstrate that avulsions in the khuzestan plains are the result of long term and complex interplay between multiple human induced and natural causes in similar ways human induced actions may play important roles during different phases of avulsion development the success of an avulsion in the post triggering phase may be defined by human induced setup causes as well as morphodynamic processes we suggest that present day flood events may be partly inherited from long term human alterations of the natural processes these finding could have implications for any fluvial system e g distributive fluvial systems deltas where avulsion plays a major role in their development and research tends to emphasize on natural mechanisms copyright 2016 john wiley sons ltd

magnitude and frequency in proglacial rivers a geomorphological and sedimentological perspective abstract proglacial fluvial sedimentary systems receive water from a variety of sources and have variable discharges with a range of magnitudes and frequencies little attention has been paid to how these various magnitude and frequency regimes interact to produce a distinctive sedimentary record in modern and ancient proglacial environments this paper reviews the concept of magnitude and frequency in relation to proglacial fluvial systems from a geomorphic and sedimentary perspective rather than a hydrological or statistical perspective the nature of the meltwater inputs can be characterised as low magnitude high frequency primarily controlled by ablation inputs from the source glacier or high magnitude low frequency primarily controlled by exceptional inputs the most important high magnitude low frequency inputs are catastrophic outburst floods often referred to by the term jokulhlaup icelandic for glacier burst glacier surges are an additional form of cyclical variation impacting the proglacial environment which briefly alter the volumes and patterns of meltwater input the sedimentary consequences of low magnitude high frequency discharges are related to frequent variations in stage the greater directional variability that sediment will record and the increased significance of channel confluence sedimentation in contrast the most significant characteristics of high magnitude low frequency flooding include the presence of large flood bars and mid channel jokulhlaup bars hyperconcentrated flows large gravel dunes and the formation of ice block kettle hole structures and rip up clasts glacier surges result in a redistribution of low magnitude high frequency processes and products across the glacier margin and small floods may occur at the surge termination criteria for distinguishing magnitude and frequency regimes in the proglacial environment are identified based on these major characteristics studies of quaternary proglacial fluvial sediments are used to determine how the interaction of the various magnitude and frequency regimes might produce a distinctive sedimentary record consideration of sandur architecture and stratigraphy shows that the main controls on the sedimentary record of proglacial regions are the discharge magnitude and frequency regime sediment supply the pattern of glacier advance or retreat and proglacial topography a model of sandur development is suggested which shows how discharge magnitude and frequency in combination with sandur incision and aggradation controlled by glacier advance and retreat can control sandur stratigraphy

factors controlling the holocene avulsion history of the rhine meuse delta the netherlands abstract the avulsion history of the holocene rhine meuse delta the netherlands was reconstructed on a timescale of millenia using detailed paleogeographic maps based on approximately 200 000 lithological borehole descriptions over 1150 14c ages and 36 000 archaeological artifacts gradient lines were constructed for all channel belts these allowed determination of gradients paleo flow direction relative age of channel belts and time correlation of undated channel belt fragments avulsion sites were inferred from the paleogeographic reconstruction at least 91 avulsions occurred over the past 10 000 years of which 82 could be dated with an accuracy of 200 14c years the location and shifting of holocene avulsion sites in the rhine meuse delta in space and time are related to 1 relative sealevel rise in the early holocene avulsions could not take place because rivers were still incised around 7500 yr bp avulsions occurred in the western part of the present delta as a result of backfilling of the late weichselian valley between 7500 and 3700 yr bp the zone where avulsions occurred shifted inland as a result of relative sealevel rise 2 neotectonics between 4900 and 1700 yr bp the location of avulsion sites seems to have been influenced by neotectonic movements of the upthrown peel horst four out of six avulsion nodes in the rhine meuse delta were located in the peel horst fault zones 3 increased discharge and or within channel sedimentation from 2800 until about 1500 yr bp avulsion sites were located all over the delta during this time the number of channels was high and avulsion frequency reached a maximum at a time when aggradation rate decreased with a reduction in the rate of sealevel rise after 2000 yr bp meander wavelength of alluvial channels increased considerably the increased meander wavelength and the high avulsion frequency are attributed to increased bankfull discharge or within channel sedimentation leading to channel widening or both 4 human influence between 1000 and 650 yr bp all the rivers were embanked and avulsions could no longer take place the few that occurred were induced by humans

avulsions channel evolution and floodplain sedimentation rates of the anastomosing upper columbia river british columbia canada ages of channels of the anastomosing upper columbia river south eastern british columbia canada were investigated in a cross valley transect by c 14 dating of subsurface floodplain organic material from beneath levees the avulsion history within the transect was deduced from these data and morphological stages in channel development were recognized additionally floodplain sedimentation rates were established the new data demonstrate that the upper columbia river is a long lived dynamic anastomosing system results show that anastomosis at the study location has persisted since at least 2700 cal years bp with avulsions occurring frequently at least nine channels have formed in the studied cross valley transect within the past 3000 years channel lifetimes from formation to abandonment appear to be highly variable ranging from approximately 800 to 3000 years log jams provoking avulsions and or silting up of old channels are proposed as reasons for this variability long term average floodplain sedimentation rates appear to be significantly lower than previously proposed by smith 1983 int assoc sedimentol spec publ 6 155 168 a long term 4550 years average of 1 75 mm per year after compaction was based on c 14 dates whilea short term sedimentation rate of 0 8 mm was determined for a single relatively small seasonal flood in 1994 using sediment traps however short term sedimentation rates vary considerably over the floodplain with levees aggrading up to four times faster than floodbasins channels of the upper columbia river anastomosed reach follow a consistent pattern in their development with each stage being characterized by different morphology and processes channel evolution comprises the following succession 1 avulsion stage in which a crevasse splay channel deepens by scour and levee sedimentation 2 widening and deepening stage in which bank slumping and bed scouring dominates 3 infilling stage in which either channel narrowing bank accretion or channel shallowing bed accretion takes place and 4 abandonment stage in which the residual remnant channel is filled exclusively by silt clay and organic material vertical stacking super imposition of active channels on recent channel fill sand bodies is a notable feature of the upper columbia river which suggests that reoccupation of residual channels is a common process

distributary channels and their impact on sediment dispersal a global analysis of world deltas with details from a natural and an anthropogenic influenced delta demonstrates how distributary channels control the flux of sediment into the coastal ocean the study addresses the range in the number of distributary channels across world deltas using remote sensing techniques a power law relationship is found between the number of distributary channels and the length of river and separately the delta gradient these relationships hold for all types of deltas whether controlled or strongly influenced by waves river discharge tides or ice permafrost or sea ice nature controlled deltas such as the klinaklini delta have distributary channels that act as overflow conduits that become active during flooding events anthropogenic controlled deltas like the po delta have distributary channels that are controlled for flood mitigation or low flow maintenance anthropogenic influences greatly impact the natural rate of delta progradation through changes in sediment supply controlling the position of distributary channels and impacting subsidence from gas and groundwater extraction even with flood controls the po delta traps 16 of the sediment load in its channels that are becoming super elevated at rates of 4 to 10 cm yr with respect to the delta plain a new model is formulated and shown to predict accurately the sediment flux through each channel along with their hydraulic properties deltas with high numbers of distributary channels produce hypopycnal plumes with reduced transport capacity as a result sediment diffuses out of the multi channel deltas as a buoyantly driven plume rather than as a momentum driven jet