channel responses to declining flow on the rio grande between ft quitman and presidio texas abstract a profound decline in the discharge of the upper rio grande following upstream water development set in motion a chain of responses in channel geometry and sediment budget the case of the rio grande provides a well documented example of the evolution of channel geometry in response to change in a single external variable in a regime of declining flow channel change was driven by an excess of sediment relative to the energy available to do work in the stream channel several different responses can be identified which operated at different rates responses can be ranked according to reaction time to define 3 stages in channel evolution stage i is identified as the shrinking of the channel as excess sediment was deposited within it during stage ii channel capacity began to stabilize as overbank flow carried sediment onto natural levees and floodplain valley wide aggradation began and avulsive migration resumed especially at the mouths of tributaries where stage iii is occurring lag deposits of bedload at tributary mouths are locally regrading the valley initial shrinking of the channel produced positive feedback to the decrease in discharge and sediment transport capacity not until later stages did subordinate responses appear which tended to balance the sediment budget and these involved lateral migration the river approached a balanced sediment budget both by increasing its capacity by shortening and steepening and by decreasing sediment inout by migrating away from tributaries

will river erosion below the three gorges dam stop in the middle yangtze abstract the environmental impact of the three gorges dam has been a subject of vigorous academic political and social debate since its inception this includes the key issue of post dam river channel erosion which was predicted by the feasibility study to extend to the river mouth in this paper we examine the geomorphic response of the channel of the middle yangtze for 660 km downstream of the dam using data on channel characteristics bed material and sediment transport we show that in the decade following the dam closure pre dam seasonal erosion has been replaced by year round erosion a pattern most marked at the upstream end of the study area the sediment carrying capacity of the river channel has been largely reduced below the dam the locus of bed scour has moved progressively downstream ceasing as the bed material became too coarse to be transported e g d 50 0 29 mm pre dam coarsened to 20 mm below the dam by 2008 about 400 km below the dam there is a reduction in channel slope that changes the sediment carrying capacity from 0 25 kg m 3 to only about 0 05 kg m 3 which is insufficient to move bed sediment the new long term hydro morphological equilibrium that will be established in this section of the middle yangtze will prevent the further incision downstream initiated by the three gorges dam the results suggest that the full extent of adverse environmental impact predicted by the pre dam studies will not eventuate

combined effects of multiple large scale hydraulic engineering on water stages in the middle yangtze river abstract investigation of water stages influenced by human projects provides better understanding of riverine geomorphological processes and river management based on hydrological data collected over 60 years an extreme stage extreme discharge analysis and a specific gauge analysis were performed to research the individual and combined effects of multiple engineering projects on a long term time series of water stages in the middle yangtze river conclusions are as follows 1 in accordance with the operation years of the jingjiang cutoff cf the gezhouba dam gd and the three gorges dam tgd the time series 1955 2012 was divided into periods of p1 1955 1970 p2 1971 1980 p3 1981 2002 and p4 2003 2012 water stage changes during p1 p2 p2 p3 and p3 p4 are varied because of the differences in the types and scales of these projects the stage decreased at shashi and increased at luoshan owing to the operation of the cf additionally after the gd was constructed the low flow stage decreased in the upstream reach of chenglingji and increased in its downstream reach whereas the flood stage merely decreased at yichang moreover the tgd resulted in an overall decrease in low flow stages and a limited increase in flood stages because of the differential adjustments of river geometry and resistance between the low flow channel and flood channel 2 although differences existed in the scouring mechanisms between streamwise erosion associated with dams and headward erosion associated with cutoffs particular bed textures in the gravel reach led to a similar adjustment that stage reduction at shashi was the greatest of all stations which caused the flow slope and sediment transport capacity to decrease in the sandy reach 3 these engineering projects caused changes in average low flow and flood stages that varied between yichang 1 58 and 0 08 m respectively shashi 3 54 and 0 12 m and luoshan 1 15 and 0 97 m from p1 to p4 however less influence was observed at hankou owing to its remote location and the short impoundment time of the tgd 4 potentially detrimental decreases in low flow stages and increases in flood stages should be monitored and managed in the future our results are of practical significance for river management and the evaluation of the influences of large scale anthropogenic activities on the hydrological regimes of large rivers

a new interpretation of kinematic stormflow generation the paper reviews a number of possible fast and slow hydrological flow mechanisms to account for rapid runoff generation within a catchment a new interpretation of the kinematic wave process is proposed which develops some of these concepts to explain rapid subsurface flow from a watershed evidence for the process is provided by the results from a laboratory soil core experiment and an investigation of the hydrology of a dartmoor hillslope a tension response was monitored in the soil core in which pressure waves were propagated downwards and expelled water from the base the transmission of the wave down the core was considerably faster than the movement of a chloride tracer the concept of this kinematic wave process and associated water flux was then extended to the dartmoor watershed raindrops reaching the wet soil surface caused pressure waves to travel laterally downslope during large rainstorms the hillslope became hydrologically highly connected and the pressure waves forced existing water from seepage faces into the saturated area adjacent to the stream contributing substantially to the stream discharge a kinematic contributing area was defined as determined by both rainfall runoff ratios and geostatistical analyses of hillslope soil moisture contents which extended over at least 65 of the catchment area this kinematic wave theory is consistent with results of translatory flow and macropore flow models and stable isotope field studies of old new water copyright 2002 john wiley sons ltd

natural and human influence on loess gully catchment evolution a case study from lublin upland e poland abstract this paper presents the functioning of a gully system catchment in the loess area of the lublin upland eastern poland based on investigations of soil and sediment sequences filling the valley floors and correlative sediments on the alluvial fan at the valley outlet stages of the catchment s evolution are proposed from the meso holocene 8400 5100 bp followed by prehistorical and historical stages of human activity to modern times gully erosion varying erosional processes have been identified over a period of about 2800 years bp washing and sediment deposition on the alluvial fan at early stages followed by multi branched gully system development later on land use change of deforestation and agriculture led to dissection of gully edges by a system of badlands this study demonstrates the roll of the human factor as a shifting agent between dominant geomorphic processes in the same catchment area over a long period of time

seasonal variations of sediment discharge from the yangtze river before and after impoundment of the three gorges dam abstract over the past decades 50 000 dams and reforestation on the yangtze river changjiang have had little impact on water discharge but have drastically altered annual and particularly seasonal sediment discharge before impoundment of the three gorges dam tgd in june 2003 annual sediment discharge had decreased by 60 and the hysteresis of seasonal rating curves in the upper reaches at yichang station had shifted from clockwise to counterclockwise in addition the river channel in middle lower reaches had changed from depositional to erosional in 2002 during the four years 2003 2006 after tgd impoundment 60 of sediment entering the three gorges reservoir was trapped primarily during the high discharge months june september although periodic sediment deposition continues downstream of the tgd during most months substantial erosion has occurred supplying 70 million tons per year mt y of channel derived sediment to the lower reaches of the river if sand extraction 40 mt y is taken into consideration the river channel loses a total of 110 mt y during the extreme drought year 2006 sediment discharge in the upper reaches drastically decreased to 9 mt only 2 of its 1950 1960s level because of decreased water discharge and tgd trapping in addition dongting lake in the middle reaches for the first time changed from trapping net sediment from the mainstem to supplying 14 mt net sediment to the mainstem severe channel erosion and drastic sediment decline have put considerable pressure on the yangtze coastal areas and east china sea

factors controlling sediment yield from small intensively cultivated catchments in a temperate humid climate abstract data on sediment yield from 26 small cultivated catchments 10 10 000 ha in central belgium were collected based on sedimentation rates in small flood retention ponds area specific sediment yield varies from 0 4 to 20 6 t ha 1 year 1 for catchments ranging from 7 to 4873 ha various catchment properties were analysed in order to understand this large variation in sediment yield catchment area alone explains 64 of the observed variance in area specific sediment yield although no other parameter could explain more it is concluded that catchment area is not a valid parameter to link with sediment yield overall catchment geomorphology e g presented by the hypsometric integral is much more important in controlling sediment yield the lack of data however made this not very clear a multiple regression model including three morphological catchment properties is a valuable tool to predict total sediment yield t year 1 from catchments in central belgium this model has an efficiency of 0 81 furthermore it was concluded that the within catchment spatial distribution of parameters for instance slope steepness is very important but difficult to obtain one single representative value the use of spatially distributed erosion and sediment delivery models is therefore necessary accurate sediment yield data like the one presented in this study however are needed to validate these models

kinematic wave approximation to infiltration into soils with sorbing macropores infiltration into soils with macropores is treated as two domain flow the first domain is the soil matrix in which water is subjected to capillarity and infiltration is approached by philip s sorptivity concept the second domain is the soil macropore system in which water moves only under gravity and flow is approached by kinematic wave theory a sink function with respect to flow in the macropore system accounts for water sorption by the soil matrix the two domain flow model is then applied to infiltration into a block of undisturbed soil containing macropores

pedological analysis as a key for reconstructing primary loess relief a case study from the magdalenian site in klementowice eastern poland abstract the subject of the study was a gentle and smooth loess slope featuring a magdalenian culture site located near the northern edge of the loess belt in eastern poland based on the probing of 130 soil profiles across a 10 10 m mesh within an area of 1 2 ha the land surface after the deposition of weichselian loess was reconstructed soil mapping indicated the patchwork character of the present soil cover which consists of luvisols of varying degrees of transformation resulting from agricultural use partly eroded and buried soils co occur in the upper part of the ridge flat non eroded soils in the middle part and eroded soils in the lower part in the archaeological site area with buried soils at the foot of the slope the thickness of the primary soil cover was reconstructed by means of geostatistical analyses this was used to reconstruct the primary undulating land relief characterised by numerous small convex forms small hillocks and hummocks and concave forms closed depressions and slope troughs these forms were levelled out by soil erosion in the course of agricultural use the planation of relief caused a decrease of the mean inclination by 25 and elevation difference by 13 the greatest changes occurred on the ridge flat where the denudation of small hillocks and the filling of closed depressions took place local inclinations decreased by up to fourfold and in some places the inversion of slope exposure occurred during the 210 years of agricultural use the eroded surfaces subsided by an average of 0 32 m and at most by 0 92 m which corresponds to an average of 1 5 mm and 4 3 mm per annum respectively less than 50 of the eroded soil material was deposited within the investigated slope most of the material was carried off beyond it the accumulated surface however is 2 5 times smaller than the eroded surface hence the accumulation indicators are slightly higher than the erosion indicators

high resolution gully erosion and sedimentation processes and land use changes since the bronze age and future trajectories in the kazimierz dolny area naleczow plateau se poland abstract this paper presents the results of 40 years of research on the gully system in the doly podmularskie catchment 0 35 km in size which is situated in the south western part of the loess covered naleczow plateau in se poland topographic stratigraphic and pedologic investigations and monitoring of a tributary gully gully area 0 7 ha catchment 2 5 ha were combined with historical archaeological and palaeoecological records the results reveal a long and complex history in terms of the temporal and spatial extent and the impact of land use on gully erosion and the long term feed back mechanisms between land use changes and natural processes since the end of the pleistocene phases of gully erosion and subsequent filling occurred in the bronze age and around the 10th to 11th centuries the most severe deepening and expansion of the gully took place in the 17th century the results also show that field structures and land use intensity had a significant influence on the frequency and magnitude of run off soil erosion piping and landslide events the last significant erosion phase started in the mid 19th century with renewed headward retreat and down cutting within older gully fills today most of the catchment is either forested or the land is covered in berry shrubs in the future the area will continue to produce sediments because of the steep slopes and because there are still areas of bare soil with a low resistance to erosion a legacy from past land uses which will remain a factor affecting soil erosion and sedimentation processes in the future this study is an example of how important it is to observe and understand slow geomorphologic processes and rare extreme events in the light of land use changes when investigating long term human environment interactions

a screening model for nonaqueous phase liquid transport in the vadose zone using green ampt and kinematic wave theory in this paper a screening model for flow of a nonaqueous phase liquid napl and associated chemical transport in the vadose zone is developed the model is based on kinematic approximation of the governing equations for both the napl and a partitionable chemical constituent the resulting governing equation is a first order quasi linear hyperbolic equation to which the generalized method of characteristics can be applied this approach generally neglects the contribution to the napl flux from capillary pressure gradients during infiltration under ponded conditions or when the napl flux exceeds the maximum effective conductivity of the soil the effect of capillary suction is included in the model through the usage of the green ampt model all of the resulting model equations are in the form of ordinary differential equations which are solved numerically by a variable time step runge kutta technique results from a simple column experiment were used to evaluate the vadose zone flow model assumptions independently measured parameters allow simulation without calibration of the model results the match of the model to the data suggests that the model captures the qualitative behavior of the experimental system and is capable of an acceptable degree of quantitative agreement

downstream effects of flaming gorge reservoir on the green river colorado and utah the green river is one of the principal tributaries in the colorado river basin and drains 44 700 m 2 in wyoming colorado and utah since october 1962 flows of the green river have been regulated by flaming gorge reservoir which is located 412 river miles upstream from its confluence with the colorado river mean annual runoff has not been affected by the reservoir the duration of the relatively large discharges that transport most of the annual sediment load however has decreased significantly as a result the mean annual sediment discharge has decreased by 54 to 3 21 10 6 tons from 6 92 10 6 tons at the jensen gage located 105 river miles downstream from the reservoir and by 48 to 8 83 10 6 tons from 17 0 10 6 tons at the green river utah gage located 290 river miles downstream from the reservoir sediment supply to i he channel equals the annual transport within a relatively short distance 68 river miles downstream from the reservoir downstream from river mile 166 the supply of sediment from upstream plus tributary inflow exceeds the transport of sediment by 5 4 10 6 tons per year on an average the quasi equilibrium that appears to have existed prior to the reservoir no longer occurs along a majority of the green river in response to the reduced peak discharges the bankfull channel width of the green river has decreased by 10 adjustment of the channel to decreased peak flows and altered sediment loads is nowhere complete at present it appears that a century or more will be required for the green river to adjust to the effects of flaming gorge reservoir

the use of stream flow routing for direct channel precipitation with isotopically based hydrograph separations the role of new water in stormflow generation abstract understanding the pathways by which event water contributes to stream stormflow provides insight into stormflow generation mechanisms we analyze the impact of storm size on the relative contribution of event water to stormflow by using natural variations in the oxygen isotopic composition of precipitation and stream water to separate multiple stormflow hydrographs from a single fourth order 1212 ha catchment we extend previous isotope based hydrograph separations by independently accounting for the contribution of event water via direct channel precipitation to the stream hydrograph the direct channel precipitation contribution is determined using a numerical model of stream flow routing though the catchment taking precipitation and digital elevation data as input variables for the range of storm sizes sampled having recurrence intervals ranging from less than a week to 4 months essentially all the event water in stream stormflow can be attributed to direct channel precipitation event water not directly falling on the stream channel indirectly contributes to stormflow by increasing the subsurface discharge of pre event water to the stream neither the hydrograph separation data field observations during the precipitation events nor experimental observations of flow in a large scale natural soil column extracted from the watershed are consistent with macropore flow or groundwater ridging as the primary mechanism responsible for increasing subsurface discharge results from a series of artificial rain experiments using the unsaturated natural soil column are consistent with a preferential kinematic flow model and indicate that the discharge of pre event water to the stream during a storm event may be controlled by kinematic flow processes within the watershed soils

topographic controls on shallow groundwater dynamics implications of hydrologic connectivity between hillslopes and riparian zones in a till mantled catchment hydrologic connectivity is regarded as one of the key controls in determining catchment rainfall run off response and has been linked to the export of solutes from uplands to streams we sought to identify the patterns of hydrologic connectivity within a small forested watershed by monitoring the shallow groundwater fluctuations of simple topographically defined landform sequences footslope backslope shoulder a spatially distributed instrument network was employed to continuously measure hydrometric responses of the shallow subsurface during seasonal wet up from summer through winter in a small till mantled research catchment we demonstrate that the spatial patterns of shallow water table extent and duration and therefore hydrologic connectivity had a strong seasonal signature during the low antecedent soil moisture conditions typically associated with the growing season water tables were patchy discontinuous and only the wettest near stream footslope areas were consistently hydrologically connected with the stream network during the dormant season footslopes and backslopes maintained water tables that persisted between storm events and were almost continuously connected with the stream network in the largest storm events the typically driest landforms shoulder slopes established shallow transient water tables suggesting that nearly the entire catchment was temporarily hydrologically connected with the stream network in addition we found significant differences p 0 05 in the magnitude and duration of groundwater responses to rainfall among landform groups both seasonally and during events these results have implications for using a similarity approach in representing characteristic hydrologic responses of topographically defined watershed elements determining hydrologic connectivity between watershed elements as well as for understanding solute transport in catchments copyright 2010 john wiley sons ltd

the water level fluctuation zone of three gorges reservoir a unique geomorphological unit three gorges reservoir tgr has provoked a series of unprecedented environmental problems many of which are related to the transitional area between the base and capacity water levels of the reservoir commonly referred to as the water level fluctuation zone we proposed here that this zone serves as a unique geomorphological unit playing an important role of influencing the life of the tgr and named it as the tgr disturbance zone because it has been intensively interrupted by various human activities based on its geomorphological characteristics we divided this zone into three types that have hillside profiles with distinct shapes and gradients grain components and sizes and land uses although the three types of the zone have experienced the same set of geomorphological processes under the new annually cyclic hydrological regime their responses and the associated morphologies are distinguishable thus we depicted them separately accompanied with these processes are geochemical and biological processes that bring about exacerbated pollution and destroyed ecosystem in this zone we elaborated these problems and indicated the potential research directions toward fully understanding the complex geomorphological geochemical and biological processes prevalent in the zone c 2015 elsevier b v all rights reserved

surface groundwater interactions in hard rocks in sardon catchment of western spain an integrated modeling approach summary the structural and hydrological complexity of hard rock systems hrss affects dynamics of surface groundwater interactions these complexities are not well described or understood by hydrogeologists because simplified analyses typically are used to study hrss a transient integrated hydrologic model ihm gsflow groundwater and surface water flow was calibrated and post audited using 18 years of daily groundwater head and stream discharge data to evaluate the surface groundwater interactions in semi arid 80 km 2 granitic sardon hilly catchment in spain characterized by shallow water table conditions relatively low storage dense drainage networks and frequent high intensity rainfall the following hydrological observations for the sardon catchment and more generally for hrss were made i significant bi directional vertical flows occur between surface water and groundwater throughout the hrss ii relatively large groundwater recharge represents 16 of precipitation p 562 mm y 1 and large groundwater exfiltration 11 of p results in short groundwater flow paths due to a dense network of streams low permeability and hilly topographic relief deep long groundwater flow paths constitute a smaller component of the water budget 1 of p quite high groundwater evapotranspiration 5 of p and 7 of total evapotranspiration low permeability and shallow soils are the main reasons for relatively large components of hortonian flow and interflow 15 and 11 of p respectively iii the majority of drainage from the catchment leaves as surface water iv declining 18 years trend 4 44 mm y 1 of groundwater storage and v large spatio temporal variability of water fluxes this ihm study of hrss provides greater understanding of these relatively unknown hydrologic systems that are widespread throughout the world and are important for water resources in many regions

modelling water flow and sediment processes in a small gully system on the loess plateau in china abstract a single gully system was selected in a small agricultural watershed on the loess plateau of china with the objective of measuring and then simulating water and sediment transport and defining alternative land uses to reduce discharge and soil loss the gully had a total length of about 40 m and was about 30 m wide the watershed feeding the gully occupied about 1950 m 2 including the gully itself the gully bottom had a slope of about 32 40 whereas the gully walls were from 40 to over 60 soil water content and water and sediment discharge were measured automatically the physically based hydrological and soil erosion model lisem was used to calculate water and sediment discharge calibration has been carried out for one event by adjusting the saturated conductivity values validation was performed for two additional runoff events calibration results show reasonably comparable hydrographs between measured and calculated discharge lisem could be calibrated on the hydrograph quite satisfactorily using the saturated conductivity as a calibration factor also validation of lisem for two other runoff events showed reasonably good results the calibration on total soil loss also shows good results for the validation runs these results are poor probably due to limitations of the measurement equipment and the incapability of the model to simulate small events scenario analyses showed that forest as an alternative land use for the gully bottom will result in significantly lower water and sediment this strongly supports the implementation of the reforestation policy recently suggested and activated by the central government of the p r china

preferential flow and the generation of runoff 1 boundary layer flow theory approaches to soil water flow which are based on the theory of potential flow often overestimate either the volume of flow or the response time at the hillslope scale when their results are compared with observations macropore flow is frequently thought to be the reason for the discrepancy between observations and model performance the expression macropore flow is considered to be too restricting it confines the rapid flow and transport processes to the easily observed channels concealing the more general question as to what degree potential flow theory adequately describes flow in porous media the application of potential flow theory to infiltration leads to the richards equations only when hydrodynamic dispersion of soil water and capillary potential are perfectly correlated in this paper a boundary layer infiltration model is presented which is based on kinematic theory it is also expanded to lateral flow in a sloping soil

phases of alluvial fan development in a loess area lublin upland e poland abstract holocene alluvial fans are a record of the evolution of the environment and human impact over the last 10 000 years the study presents the structure of fans at the mouth of gullies as well as their development in the loess areas of the lublin upland sediment soil sequences of seven alluvial fans and the adjoining flood sediments and dry valley bottom sediments were studied in detail the development of fans occurred in three phases i the eneolithic ii the middle and late bronze age and the hallstatt period and iii the middle ages and the modern times the middle phase consists of two sub phases while last phase consists of three sub phases the early middle ages the little ice age the 19th and first half of the 20th century these phases were interspersed with longer or shorter periods of stabilization of the alluvial fan surface the different course of land use changes in the catchments was the reason for this metachronous development of the alluvial fans our studies indicate that heavy and catastrophic rainfall and rapid thaw had a considerable role in the development of the alluvial fans the establishment of roads along the axes of valleys and across the slopes had a key impact on alluvial fan development the deforestation of the catchment was not an essential condition for the formation of gullies and alluvial fans

assessment of soil losses by ephemeral gully erosion using high altitude stereo aerial photographs the objective of this study is to explore in a critical way the potential of high altitude stereo aerial photographs for the assessment of ephemeral gully erosion rates on 28 may 1995 an intensive rainfall event 30 mm h 1 during 30 min return period 3 years occurred in central belgium ephemeral gullies formed within an area of 218 ha study area 1 were mapped and measured both in the field and by high altitude aerial photos taken at the same time comparison of these two methods shows that if only one of the two surveying techniques had been used only 75 per cent of the total ephemeral gully length would have been detected so that the combination of aerial and field data leads in fact to the best possible determination of total gully length within the selected area a correction factor c is proposed so that the results of an ephemeral gully erosion survey based on high altitude stereo aerial photos can be adjusted for the undetected gullies next a sequential series of high altitude stereo aerial photographs taken in six different years was analysed in order to determine ephemeral gully erosion rates in three selected study areas study areas 2 3 and 4 selection criteria were chosen so that these three areas were similar to study area 1 and representative for the cultivated areas in central belgium where intense soil erosion regularly occurs ephemeral gullies were mapped and their total length was measured from the aerial photos using a mean gully cross section of 0 2635 m2 determined in study area 1 the average eroded volume is 1 89 m3 ha 1 in six months for study area 1 0 86 m3 ha 1 in six months for area 2 1 44 m3 ha 1 in six months for area 3 and 2 37 m3 ha 1 in six months for area 4 according to the correction factor c these mean ephemeral gully erosion volumes have to be increased by 44 per cent the ephemeral gully erosion rates based on high altitude stereo aerial photos correspond well with the results of other surveys carried out in the belgian loess belt copyright 1999 john wiley sons ltd

geomorphic response of the jingjiang reach to the three gorges project operation upstream damming often causes significant downstream geomorphic adjustments remarkable channel changes have occurred in the jingjiang reach of the middle yangtze river since the onset of the three gorges project tgp therefore it is important to investigate the variations in different fluvial variables for better understanding of the channel evolution characteristics as an example of the jingjiang reach recent geomorphic adjustments in the study reach have been investigated quantitatively including variations in sediment rating curve fluvial erosion intensity channel deformation volume and bankfull channel geometry these fluvial variables adjusted in varying degrees in response to the altered flow and sediment regime caused by the tgp operation a focus of this study has been especially paid on the variation in the bankfull channel geometry calculated bankfull dimensions at section and reach scale indicate that i there were significant bank erosion processes in local regions without bank protection engineering with empirical relations being developed to reproduce the variation in bankfull widths at four typical sections ii the variation in the reach scale channel geometry occurred mainly in the component of bankfull depth owing to the construction of large scale bank revetment works with the depth increasing from 13 7 m in 2002 to 15 0 m in 2014 and with an increase in the corresponding bankfull area of about 11 and iii the reach scale bankfull channel dimensions responded to the previous five year average fluvial erosion intensity during flood seasons at zhicheng with higher correlations for the depth and area being obtained when calibrated by the measurements in 2002 2012 furthermore these developed relations for the section and reach scale bankfull channel geometry were also verified by the observed data in 2013 2014 with encouraging results being obtained this article is protected by copyright all rights reserved

interpretation of the environmental change of dongting lake middle reach of yangtze river china by 210pb measurement and satellite image analysis abstract the present study examined the recent environmental history of the dongting lake located in the middle yangtze river region central china the sediment was recovered by 22 vibrocores in different lake sectors primarily characterizing subaqueous delta and bay subfacies high sedimentation rates revealed by 210pb measurement in different subfacies of the lake ranged from 0 77 to 2 33 cm year these rates equate to deltaic sedimentation associated with mobile channels resulting from yangtze flood events satellite images confirm that the dongting lake does not contain the biggest yangtze floods moreover comparative bathymetric surveys verify that the dongting lake has lost almost two thirds of its total area in the past century due primarily to siltation by yangtze sediment in the late 19th century a major flood induced channel avulsion resulted in the coupling of the four tributary subbasin to the dongting lake causing a massive increase in the sediment supply into the lake since then hydrological data demonstrate that about 83 of the lake s annual sediment influx are derived from the yangtze in addition pressures from a growing population and associated human activities such as reclamation embanking aquaculture slope modification and deforestation are compounding the loss of the lake surface area and associated storage capacity

the value of a physically based model versus an empirical approach in the prediction of ephemeral gully erosion for loess derived soils abstract a data set on soil losses and controlling factors for 58 ephemeral gullies has been collected in the belgian loess belt from march 1997 to march 1999 of the observed ephemeral gullies 32 developed at the end of winter or in early spring winter gullies and 26 ephemeral gullies developed during summer summer gullies the assessed data have been used to test the physically based ephemeral gully erosion model egem and to compare its performance with the value of simple topographical and morphological indices in the prediction of ephemeral gully erosion analysis shows that egem is not capable of predicting ephemeral gully cross sections well although conditions for input parameter assessment were ideal some parameters such as channel erodibility critical flow shear stress and local rainfall depth showed great uncertainty rather than revealing egem s inability of predicting ephemeral gully erosion this analysis stresses the problematic nature of physically based models since they often require input parameters that are not available or can hardly be obtained with respect to the value of simple topographical and morphological indices in predicting ephemeral gully erosion this study shows that for winter gullies and summer gullies respectively over 80 and about 75 of the variation in ephemeral gully volume can be explained when ephemeral gully length is known moreover when previously collected data for ephemeral gullies in two mediterranean study areas and the data for summer gullies formed in the belgian loess belt are pooled it appears that one single length l volume v relation exists v 0 048 l 1 29 r 2 0 91 these findings imply that predicting ephemeral gully length is a valuable alternative for the prediction of ephemeral gully volume a simple procedure to predict ephemeral gully length based on topographical thresholds is presented here secondly the empirical length volume relation can also be used to convert ephemeral gully length data extracted from aerial photos into ephemeral gully volumes

the impact of climate change human interference scale and modeling uncertainties on the estimation of aquifer properties and river flow components summary within the period 1978 2006 climate change and human interferences produced noticeable impacts on the hydrology of a small watershed known as the beca river basin climate change was characterized by a persistent raise in temperature 0 78 c decade 1 and a drop in the annual rainfall 300 mm decade 1 human interferences included the construction of a dam for electric power generation in 1998 and since then the transference of beca river flows from the dam lake to the adjacent t mega river the impacts on catchment hydrology comprised a decline of aquifer hydraulic conductivity and effective porosity by approximately one order of magnitude related to a water table lowering of about 17 m within the bedrock aquifer composed of weathered and fractured hercynian granites and paleozoic metassediments and of saprolite layers derived therefrom aquifer property estimates were compared across spatial scales namely the beca river and the nested sub basins scale sub basin aquifers are more porous and permeable than the basin aquifer because corresponding hydraulic circuits are shallower comparisons were also made between aquifer properties derived from measured and simulated stream flows which revealed effects of modeling uncertainties on the results river flows also suffered a substantial decrease in the course of climate change and human interference especially the overland flows 4 5 decrease and the base flows 2 3 decrease the inter flows were less affected 1 3 decrease because they were partly fed with water from the aquifer storage which in turn underwent depletion the hydrologic changes in the beca river basin anticipate important impacts on the local use of natural water in this context the aforementioned water table lowering may have caused limited access to shallow groundwater for activities such as crop irrigation from dug wells whereas the severe decline in overland flows and base flows had certainly reduced the availability of surface water for the refilling of dam lakes and of groundwater for the supply of public and private boreholes

the impacts of the three gorges dam upon dynamic adjustment mode alterations in the jingjiang reach of the yangtze river china abstract dam operation profoundly modifies downstream flow sediment regimes resulting in a variety of geomorphologic responses without uniform laws the jingjiang reach of the middle yangtze river has undergone significant adjustment mode alterations with intensive channel erosion and major adjustment area changing from the bankfull channel to the medium flow channel at the time boundary of the three gorges dam tgd impoundment while these changes have received some attention little work has been undertaken to reveal the reason in this study based on 172 cross sections measured in the post flood period from 2003 to 2015 different river patterns longitude and reach averaged channel dimensions were assessed to reflect the channel adjustment characteristics of the jingjiang reach an index has been proposed to measure the cumulative water transport capacity of each discharge interval and to assess the relationship with reach scale medium flow channel dimensions the results indicate that the channel adjustment changes are directly driven by the alterations of flow duration and sediment transport capacity with the deficiency of floods medium flow channels respond quite well to small and medium discharges of under approximately 16 500 m3 s a discharge of 16 500 m3 s which can be regarded as a critical threshold corresponds to the average top levels of braided and meandering channel bars which are of morphological significance in constraining the passing flow in the medium flow channel small and medium discharges under the critical threshold associate with relatively larger reductions in sediment loads and hold increased geomorphic impacts qmjp eventually resulting in adjustment mode alterations the results present herein for the jingjiang reach of the yangtze river can provide a better understanding of dam operation and the corresponding impacts on downstream channel morphology

kinematic models for soil moisture and solute transport the kinematic theory of soil moisture and solute transport in the vertical direction for unsaturated groundwater recharge is considered the general theory of kinematic models is reviewed and applied for an isolated wetting event wherein the soil starts at and eventually drains to field capacity analytical expressions are developed for the water content and moisture flux as a function of depth and time the approach is extended for an arbitrary sequence of surface flux or water content boundary conditions the transport of a solute with a general nonlinear sorption isotherm is also considered it is shown that for the general isotherm the vertical displacement of a solute isochore during an arbitrary wetting sequence depends only on the total depth of water infiltrated and not on how the infiltration rate varies with time

effects of three gorges dam operation on spatial distribution and evolution of channel thalweg in the yichang chenglingji reach of the middle yangtze river china abstract the evolution of the channel thalweg and pool riffle sequences is a critical feature of morphological adjustments in fluvial systems and might have important effects on aquatic habitat quality channel stability and navigation based on the 220 cross sectional profiles from 2002 to 2016 residual depths and spatial statistical analyses were used to quantitatively analyse the vertical variations and longitudinal distribution of the pool riffle sequences and channel thalweg in the yichang chenglingji reach ycr of the middle yangtze river which consists of the yizhi zhijiang shashi gongan and shishou jianli sub reaches the results showed that the dramatic reduction in the sediment loads following the construction of the three gorges dam tgd has caused significant adjustments in the size morphological diversity and spatial distribution of pool riffle structures in the ycr the average depth of the pools in the yizhi zhijiang reach and the shishou jianli reach overall exhibited a nonlinear growth trend with the average residual depth increasing by 1 4 m and 1 9 m respectively however the average residual depth in the shashi gongan reach showed a decreasing trend with a reduction of approximately 1 2 m the longitudinal lengths of the riffles in all three reaches contracted to different degrees and the specific percentage of longitudinal river length occupied by riffles total riffle length total sub reach length decreased by 8 9 6 and 5 9 in the three sub reaches from upstream to the downstream in addition the morphological diversity of the thalweg elevation in the shashi gongan reach and shishou jianli reach weakened after the construction of the tgd while the bed topography in the yizhi zhijiang reach became more complex and diverse moreover the pool riffle structures in the ycr were rearranged and distributed regularly following the initiation of the tgd operation although the variation characteristics of the average pool spacing in the three sub reaches were quite different quantitative relationship between the average residual depth and the previous four year hydrological condition was proposed for the three sub reaches based on the delayed response model drm and verified using the measurements from 2013 to 2016

kinematic wave approximation to the transport of escherichia coli in the vadose zone threshold values for macropore flow parameters that are thought to be critical in the transport of microbial suspensions through macroporous soils were established through the application of a kinematic wave approach to bacterial breakthrough curves according to the presented examples moisture content w and conductance b in the macropore systems of four different soils had simultaneously to exceed 0 015 m3 m3 and 0 1 m s respectively before substantial microbial breakthrough was observed at the bottom of undisturbed columns of macroporous soils with lengths ranging from 0 21 to 0 32 m the application of these thresholds in a modeling approach to large scale flow revealed that hardly any microbes can be transported deeper than 2 3 m in soils when durations and intensities of naturally occurring precipitation events were entered into the model it was also shown however that prolonged or intensified water input to the soil surface may efficiently carry microbes deeper than 100 m into the vadose zone

classification of geomorphological effects downstream of dams abstract the effects of dams on downstream geomorphology are reviewed and a typology is devised consisting of nine cases the classification can be seen as a further development of lane s balance between water discharge sediment load grain size and river slope depending on changes in released water flow and changes in released sediment load relative to the transport capacity of the flow it is possible to estimate resulting cross sectional geomorphology the longitudinal extent of changes and their variability with time and the tributary response to altered mainstream cross section changes are also discussed

sediment load responses to climate variation and cascade reservoirs in the yangtze river a case study of the jinsha river abstract climate change and human activities have substantially changed hydrological and geomorphologic processes particularly in upper mountainous catchments the jinsha river basin jrb the uppermost region of the yangtze river and the largest hydropower production region in china was chosen to investigate the sediment load responses to climate variations and human activities the non parametric mann kendall test and double mass curve were used to explore the spatial temporal variations of hydro meteorological variables and quantify the contributions of climate variation and human activities to changes in discharge and sediment load in the jrb from the 1950s to 2015 the results indicate that human activities in particular cascade damming were the governing factor for sediment load changes while climate variations increasing precipitation and snow and glacier melt dominated the discharge changes in the jrb the average annual sediment load at the panzhihua pzh station increased by 42 4 from 1966 1984 to 1985 2010 mainly due to mineral extraction and deforestation followed by a decrease of 75 9 in 2011 2015 because of the operation of the cascade reservoirs in the middle jrb since 2010 the construction of new dams like the xiangjiaba reservoir 2012 and the xiluodu reservoir 2013 in the lower jrb and many other cascade reservoirs since 2010 in the middle jrb further decreased the sediment load by 58 5 bht and 83 8 xjb in the recent five years from 2011 to 2015 although channel erosion downstream of the xjb dam can provide new sediment to the three gorges reservoir tgr the sedimentation rate of the tgr has decreased rapidly and will continue to be reduced due to the construction of more dams in the future

soil loss rates due to piping erosion compared with surface soil erosion by water subsurface erosion piping is generally less studied and harder to quantify however wherever piping occurs it is often a significant or even the main sediment source in this study the significance of soil loss due to piping is demonstrated through an estimation of soil volume lost from pipes and pipe collapses n 560 in 137 parcels under pasture on loess derived soils in a temperate humid climate belgium assuming a period of 5 to 10 years for pipe collapse to occur mean soil loss rates of 2 3 and 4 6 t ha 1 yr 1 are obtained which are at least one order of magnitude higher than surface erosion rates 0 01 0 29 t ha 1 yr 1 by sheet and rill erosion under a similar land use the results obtained for the study area in the flemish ardennes correspond well to other measurements in temperate environments they are however considerably smaller than soil loss rates due to subsurface erosion in semi arid environments although local slope gradient and drainage area largely control the location of collapsed pipes in the study area these topographic parameters do not explain differences in eroded volumes by piping hence incorporation of subsurface erosion in erosion models is not straightforward copyright 2011 john wiley sons ltd

landform transformation and long term sediment budget for a chernozem dominated lowland agricultural catchment abstract the loess hilly lands of the south west foreland of the west carpathians are characterized by favorable climatic conditions smooth topography fertile soils and a long settlement history for the first time we document changes to human induced landforms in a small zero order dry valley 0 28 km2 with calcic chernozem soils and develop a long term sediment budget the original surface was reconstructed based on interpreting records of erosion and deposition from 185 soil cores and six valley cross sections the topography inherited from the pleistocene was transformed through lowering of hillslope ridges and convexities along with infilling of shallow depressions within the original valley bottom on convex convex landforms had an average net erosion of 0 32 0 01 m while average net accumulation in the valley bottom was estimated at 0 20 0 01 m the correlation between change in soil profile depth with profile curvature 0 51 p

assessing the potential for change in the middle yangtze river channel following impoundment of the three gorges dam abstract the geomorphic impacts of dams on downstream river channels are complex not readily predictable for specific cases but widely reported in the literature for the three gorges dam on the yangtze changjiang river in china no studies of the impact of the changed flow and sediment conditions below the dam on the behaviour of the channel were included in the pre dam feasibility report we have assembled a database of flow and sediment data for the middle yangtze river from yichang to hankou and used this to analyse changes following the closure of the dam while total flow is little affected the operating strategy for the dam that provides for storage of part of the summer high flows to maintain hydroelectric power generation in winter the low flow season is reflected in changes to the seasonal distribution of flow below the dam we calculated potential sediment carrying capacity and compared it with measured sediment concentrations for both pre and post dam conditions while channel sedimentation is indicated along the middle yangtze for pre dam conditions scour is indicated for post dam conditions highest at yichang immediately below the dam and decreasing downstream

yangtze river of china historical analysis of discharge variability and sediment flux hydrological records covering a 100 year period from the upper middle and lower yangtze river were collected to examine the temporal and spatial distribution of discharge and sediment load in the drainage basin the yangtze discharge as expected increases from the upper drainage basin downstream only an estimated 50 of the discharge is derived from the upper yangtze with the rest being derived from the numerous tributaries of the middle and lower course however the distribution of sediment load along the yangtze is the reverse of that observed for discharge with most of the sediment being derived from the upper basin a dramatic reduction in sediment load by 0 8 108 tons year occurs in the middle yangtze because of a marked decrease in slope and the change to a meandering pattern from the upper yangtze rock sections considerable siltation also occurs in the middle yangtze drainage basin as the river cuts through a large interior dongting lake system sediment load in the lower yangtze while significantly less than that of the upper river is somewhat higher than the middle yangtze because of additional load contributed by adjacent tributaries a strong correlation exists between the discharge and sediment load along the yangtze drainage basin during the dry season as lower flows carry lower sediment concentration during the wet season a strong correlation is also present in the upper yangtze owing to the high flow velocity that suspends sand on the bed however a negative to poor correlation occurs in the middle and lower yangtze because the flow velocity in these reaches is unable to keep sand in suspension transporting only fine grained particles downstream hydrological data are treated for 30 years 1950 1980 when numerous dams were constructed in the upper yangtze drainage basin at yichang and hankou hydrological stations records revealed a decreasing trend in annual sediment load along with slightly reduced annual discharge at the same stations this can be interpreted as the result of water diversion primarily for agriculture sediment load at datong further downstream is quite stable and not influenced by slightly reduced discharge furthermore sediment concentration at the three hydrological stations increased which can be attributed to sediment loss in association with intensifying human activity especially in the upper drainage basin such as deforestation and construction of numerous dams mean monthly sediment load of these 30 years pulses about 2 months behind discharge implying dam released sediment transport along the entire river basin during the high water stage

kinematic wave approximations to hillslope hydrological processes in tills this work has been carried out within the framework of nopex a northern hemisphere climate processes land surface experiment its purpose is to describe the spatial variability of groundwater lev

one dimensional modelling of channel evolution in an alluvial river with the effect of large scale regulation engineering abstract in an alluvial river various kinds of river regulation engineering are usually constructed along the reach for the stability of channel regime and the safety of flood control which greatly affects the process of channel evolution therefore a one dimensional 1d morphodynamic model has been improved to simulate the fluvial processes influenced by large scale river regulation works in the refined model each node of a cross section was labeled using a specified point code representing the zones of floodplain and main channel with or without regulation engineering and sediment transport and bed deformation in different zones were treated separately in the zones without regulation engineering both bed deposition and bed erosion were permitted to occur in the zones with regulation works bed deposition was allowed while bed erosion was not permitted to occur owing to the restriction of those engineering unless there was a deposition layer newly formed over the previous simulation period then the improved model was calibrated and verified using field observations through the application to a 347 km long alluvial channel located in the middle yangtze river in china the results for the year 2016 show that the channel scour volume without the effect of river regulation works was 9 greater than the measured value 34 43 106 t while the outcome considering this effect 35 81 106 t was in closer agreement with the measurements moreover the variation in channel geometry obtained from the improved model agreed better with the observed data river regulation works would limit the channel incision and it is likely to scour the other unprotected bed of a cross section or the downstream cross sections as the flow cannot carry enough sediment from the protected bed simulated results indicate that part of the main channel zone at the jing65 section was protected but the riverbed continued to incise by about 0 68 m in the protected area when the effect of bed protection works was not considered in the model which was not in accord with the observed channel geometry therefore this effect of large scale river regulation works on channel evolution needs to be considered for a higher simulation accuracy

colorado river sediment transport 1 natural sediment supply limitation and the influence of glen canyon dam analyses of flow sediment transport bed topographic and sedimentologic data suggest that before the closure of glen canyon dam in 1963 the colorado river in marble and grand canyons was annually supply limited with respect to fine sediment i e sand and finer material furthermore these analyses suggest that the predam river in glen canyon was not supply limited to the same degree and that the degree of annual supply limitation increased near the head of marble canyon the predam colorado river in grand canyon displays evidence of four effects of supply limitation 1 seasonal hysteresis in sediment concentration 2 seasonal hysteresis in sediment grain size coupled to the seasonal hysteresis in sediment concentration 3 production of inversely graded flood deposits and 4 development or modification of a lag between the time of a flood peak and the time of either maximum or minimum depending on reach geometry bed elevation analyses of sediment budgets provide additional support for the interpretation that the predam river was annually supply limited with respect to fine sediment but it was not supply limited with respect to fine sediment during all seasons in the average predam year sand would accumulate and be stored in marble canyon and upper grand canyon for 9 months of the year from july through march when flows were dominantly below 200 300 m3 s this stored sand was then eroded during april through june when flows were typically higher after closure of glen canyon dam because of the large magnitudes of the uncertainties in the sediment budget no season of substantial sand accumulation is evident because most flows in the postdam river exceed 200 300 m3 s substantial sand accumulation in the postdam river is unlikely

variations in downstream grain sizes to interpret sediment transport in the middle lower yangtze river china a pre study of three gorges dam abstract in 2000 and 2003 before the closure of 3 gorges dam numerous sediment samples were taken from the middle lower yangtze river channel to examine sediment transport processes and associated hydromorphological nature of the river analytical results show that the riverbeds consist mostly of medium to coarse sands and gravelly sands and fine sand occurs locally especially near the river coast the results further indicate a downstream fining trend in riverbed sediment from yichang to the river mouth totaling about 1900 km long with 12 sediment zones i xii these were identified as alternate coarse and fine grained sediment on the riverbed although the zonation of i iii below three gorges dam site is weaker the mode of sediment transport in the river is dominated by saltation 20 80 followed by bed load transport with 3 15 transport by suspension is quite low grain sizes associated with hydrological parameters have greater values in the jingjiang reaches from yichang to chenglingji unit stream power 5 18 n m 1 s 1 boundary shear stress 14 nm 2 and mean flow velocity 2 3 2 ms 1 whereas the values obtained from chenglingji downstream are considerably low 1 s 1 1 4 nm 2 and 1 these values when compared with on site measured velocity of the adp flow column revealed the erosive riverbed sediment transport in the jingjiang reaches and the accumulative riverbed transport downstream from wuhan to the river coast hydrological parameters together with distribution of grain sizes indicate a coarsening riverbed in the jingjiang river largely because damming peaked since the last half century this corroborates the weakening sediment zonation in the jingjiang reaches which is expected to extend further downstream towards the river coast in response to the potential impact of 3 gorges dam in the coming decades

temporal and spatial variations of sediment rating curves in the changjiang yangtze river basin and their implications the natural hydrologic regime of the changjiang yangtze river in china has been disturbed considerably by intensified human activities over the past five decades in this study sediment rating curves were analyzed based on monthly data of water discharge and suspended sediment concentration at stations in the upper yichang station middle hankou station and lower datong station reaches of the changjiang in different periods from 1955 to 2007 temporal and spatial variations of the sediment rating curves were analyzed with respect to the impact of human activities and watershed characteristics results indicate that human disturbances have had a substantial impact on sediment rating parameters with the magnitude of the impact related to the scale of the river sections as indicated by the sediment rating parameters the sediment transport regimes between the upper and the mid lower reaches differ significantly in particular the impoundment of the three gorges dam in 2003 changed the sediment transport regimes in the upper and mid lower reaches of changjiang into similar regimes characterized by a decrease in the sediment transport capacity of high water discharge furthermore the sediment rating curve at the datong station in 1955 1968 was applied to estimate the potential sediment load 1969 2007 in the absence of human influences the mean annual sediment deficit caused by human activities has increased from 80 mt yr 1969 1985 to 250 mt yr 2003 2007 this indicates that intensified human activities in the changjiang basin especially the construction of the three gorges dam have altered the natural sediment transport process and have thus become a dominant force in changjiang sediment delivery to the sea

the impact of snowmelt and heavy rainfall runoff on erosion rates in a gully system lublin upland poland the study examines water runoff and geomorphic processes within a permanent gully located in an agricultural catchment of the lublin upland southeast poland the studies were conducted in the period 2003 to 2006 during which time the volume and intensity of precipitation were recorded and water runoff and sediment concentration at the outlet of the main gully were measured after large surface runoff events that resulted in geomorphic effects erosion and accumulation forms were examined the role of snowmelt and heavy rains in the runoff of water and suspended solids from the catchment as well as their effect on the dynamics of certain processes such as rill erosion piping and accumulation within the gully all were evaluated it was observed that the gully developed spatially through piping and headcut processes during snowmelt while the main gully form became shallower as a result of accumulation processes headcut erosion at the gully bottom and transport of the material out of the catchment predominantly during pluvial runoff events were much less intensive it was estimated that the intensity of snowmelt runoff in the years 2003 to 2006 was similar to the multi annual average while the intensity of pluvial runoff was significantly lower an attempt was made to describe the dynamics of gully erosion and the direction of gully system evolution on a medium term time scale 50 to 100 years it was found that the roles of snowmelt and heavy rains in such catchments are in opposition snowmelt runoff events lead to the spatial development of the gullies and make them shallower while pluvial runoff events add to the deepening of the gully and result in transporting the material outward these two processes keep the gully system in relative balance copyright 2009 john wiley sons ltd

heavy metals in the slope deposits of loess areas of the lublin upland e poland abstract the concentration of heavy metals cd cu pb zn has been analyzed in holocene slope deposits of the loess agricultural area in the eastern poland five profiles were examined in general low concentrations of the examined metals were determined on average 50 of the samples exceeded the designated regional geochemical background the average concentrations were cadmium

gully erosion impacts factors and control gully erosion attracts increasing attention from scientists as reflected by two recent international meetings poesen and valentin eds catena 50 2 4 87 564 li et al 2004 gully erosion under global change sichuan science technology press chengu china 354 pp this growing interest is associated with the increasing concern over off site impacts caused by soil erosion at larger spatial scales than the cultivated plots the objective of this paper is to review recent studies on impacts factors and control of gully erosion and update the review on dgully erosion and environmental change importance and research needst poesen et al 2003 catena 50 2 4 91 134 for the farmers the development of gullies leads to a loss of crop yields and available land as well as an increase of workload i e labour necessary to cultivate the land gullies can also change the mosaic patterns between fallow and cultivated fields enhancing hillslope erosion in a feedback loop in addition gullies tend to enhance drainage and accelerate aridification processes in the semi arid zones fingerprinting the origin of sediments within catchments to determine the relative contributions of potential sediment sources has become essential to identify sources of potential pollution and to develop management strategies to combat soil erosion in this respect tracers such as carbon nitrogen the nuclear bomb derived radionuclide 137 cs magnetics and the strontium isotopic ratio are increasingly used to fingerprint sediment recent studies conducted in australia china ethiopia and usa showed that the major part of the sediment in reservoirs might have come from gully erosion gullies not only occur in marly badlands and mountainous or hilly regions but also more globally in soils subjected to soil crusting such as loess european belt chinese loess plateau north america and sandy soils sahelian zone north east thailand or in soils prone to piping and tunnelling such as dispersive soils most of the time the gullying processes are triggered by

intensive water content and discharge measurement system in a hillslope gully in china abstract an automatic monitoring system was constructed to intensively study the water profile runoff interactions during rain events of a hillslope gully the system was installed on the loess plateau in the shaanxi province in northern china the primary goal was to obtain a better understanding of soil erosion processes in this district to aid in better management to accomplish this infiltration and runoff data for running calibrating and validating the lisem erosion model was needed the system presented here consisted of 29 time domain reflectometry tdr water content sensors that monitored the water content variation in time sensors were installed in different subsystems throughout the gully geometry such as in the cropland surrounding the gully in some gully slopes and in the gully floor at the outflow point of the gully an h flume was installed in order to measure the actual discharge of the gully system and to measure directly the sediment concentration in the discharge the monitoring system was programmed in this way so that more measurements were recorded when a rainstorm occurred installation took place in april 1998 and it was used until september 2000 in 1998 five major rain events were recorded which generated runoff and erosion in 1999 and 2000 only one cropland measurements showed high water contents and high infiltration rates all through the measuring period and also showed a strong reaction to precipitation the sidewalls of the gully showed much lower water contents where only very shallow parts showed some infiltration during rain showers while steep parts of the gully such as pipes and vertical walls showed an extremely low water content and practically no water content variation with time simulation results confirmed the suspicion that these areas are an important source for hortanian overland flow within the gully system model simulations further showed that most of the sediment being eroded from the gully system was coming from rills and smaller gullies being cut into the main gully bottom saturation excess overland flow proved to be dependent on the characteristic of the rain event as well as on the water content of the soil at the beginning of the event

morphological adjustments in a meandering reach of the middle yangtze river caused by severe human activities abstract in the past 50 years the shishou reach in the middle yangtze river underwent significant channel evolution owing to the implementation of an artificial cutoff the construction of bank revetment works and the operation of the three gorges project tgp based on the measured hydrological data and topographic data the processes of channel evolution in this reach were investigated mainly from the adjustments in planform and cross sectional geometries the variation in planform geometry obtained in this study indicates that i the artificial cutoff at zhongzhouzi caused the river regime to adjust drastically with the mean rate of thalweg migration at reach scale of 42 0 m a over the period 1966 1975 ii then the effect of this artificial cutoff reduced gradually with the mean migration rate decreasing to 40 m a owing to the occurrence of high water levels in 1993 1998 and iii the average annual rate of thalweg migration decreased to 29 3 m a because of the impacts of various bank protection engineering and the tgp operation during the period 2002 2015 however remarkable thalweg migration processes still occurred in local regions after the tgp operation which resulted in significant bankline migration in local reaches of beimenkou shijiatai and tiaoxiankou in addition the adjustments of bankfull channel geometry were investigated at section and reach scales after the tgp operation calculated results show that lateral channel migration in this reach was restricted by various river regulation works and that channel evolution was mainly characterized by an increase in bankfull depth and cross sectional area empirical relationships were developed between the reach scale bankfull dimensions depth and area the bankfull widths at specified sections and the previous 5 year average fluvial erosion intensity during flood seasons with high correlation degrees between them being obtained

extraordinary flood events and the response to monsoonal climatic change during the last 3000 years along the middle yangtze river valley china abstract well dated long term flood data series is very important in studying of hydrological response to past climatic change along the mainstream of the yangtze river five palaeoflood events recorded by slackwater deposits were identified by the sedimentological criteria and analytical results a detailed chronological framework of palaeoflood events during the late holocene was established by optically stimulated luminescence dating in combination with anthropogenic remains and with pedo stratigraphic correlations with well dated holocene loess soil profiles within the middle yangtze river basin the five palaeoflood events were dated to 2 43 0 18 ka 1 82 0 17 ka 0 94 0 07 ka 0 72 0 06 ka and 0 59 0 05 ka respectively these results are consistent with geological records at other palaeoflood sites and historical flood records along the middle yangtze river valley a regional synthesis of the palaeoflood chronology over the last 3000 years was compiled along the middle yangtze river extraordinary flood events generally seem to be correlated with late holocene climatic variability i e neoglacial cooling roman warm period dark ages cold period medieval climate anomaly and little ice age the high resolution climatic proxies from stalagmites of the dongge cave and heshang cave ice cores of the grip the total solar irradiance variations and sunspot number and enso activities suggest that these hydroclimatic events are possibly related to the weaker asia summer monsoon and the cooling climatic events as well as the stronger enso activities during the late holocene in the yangtze river valley these results provide insights into the response of hydroclimatic system to global change in the large rivers of asia

morphodynamic adjustments in the yichang chenglingji reach of the middle yangtze river since the operation of the three gorges project abstract to investigate the evolution characteristics of the yichang chenglingji reach ycr of the middle yangtze river and develop simulation methods the temporal and spatial morphodynamic adjustments of the ycr were analysed comprehensively on the basis of runoff sediment load and cross sectional profiles data at 220 cross sections from 2002 to 2016 results showed that significant channel degradation has occurred in the ycr especially in the low flow channels due to a drastic reduction in sediment yield since the operation of the three gorges project tgp the variations of upstream flow and sediment regimes would drive equilibrium channels to become increasingly narrow and deep and the current bankfull width and depth were less than their equilibrium counterparts in the recent period however the recent channel evolution was mainly characterized by the prominent channel deepening via a one way deformation due to the large scale bank revetments within the ycr where the reach scale bankfull depth increased by 1 6 m in the span of 15 years a semi empirical method for determining the equilibrium values of channel degradation and aggradation volume at the ycr was proposed on the basis of a comprehensive analysis of the effects of flow sediment concentration sediment gradation and water depth moreover the equilibrium values of the channel width and depth were estimated with the least action principle method the calculation methods for the equilibrium width depth width depth ratio and aggradation degradation volume were combined with the delayed response model drm then the methods for calculating the variations in channel geometry and aggradation degradation volume were derived results showed that the proposed methods effectively simulated the channel geometry and cumulative erosion volume in the ycr from 2002 to 2016 in addition the response of the channel evolution in the ycr was closely related to the previous four year hydrological conditions implying that channel evolution may lag behind the variations of flow and sediment discharges

analysis of topographic and climatic control on rainfall triggered shallow landsliding using a quasi dynamic wetness index abstract a model for the prediction of both topographic and climatic control on shallow landslide initiation processes in hilly mountainous terrain is proposed the model develops upon a theory for coupled shallow subsurface flow and landsliding of the soil mantle previously proposed by montgomery and dietrich water resour res 30 1994 1153 the model uses a quasi dynamic wetness index to predict the spatial distribution of soil saturation in response to a rainfall of specified duration the rainfall predicted to cause instability in each topographic element is characterised by duration and frequency of occurrence the incorporation of a rainfall frequency duration relationship into assessment of landslide hazard provides a practical way to include climate information into estimation of the relative potential for shallow landsliding the model is applied to a mountain experimental basin where high resolution digital elevation data are available the cordon catchment 5 km2 in north eastern italy an inventory of landslide scars is used to document sites of instability and to provide a test of model performance by comparing observed landslide locations with model predictions the model reasonably reproduces the observed distribution of landslides although spatial variability of soil properties and hydrologic complexities not accounted for by the model complicate prediction of where landslides occur within areas of similar topographic climatic control model predictions from the quasi dynamic model are compared with those provided by the steady state model water resour res 30 1994 1153 these results suggest that the quasi dynamic model offers significant improvement over the steady state model in predicting existing landslides as represented in the considered landslide inventory

a method for dendrochronological assessment of medium term gully erosion rates abstract a method based on dendrochronology to estimate gully erosion rates was developed as an alternative of traditional methods for assessing medium term gully retreat rates such as field monitoring of headcuts or aerial photo interpretation of gully retreat the method makes use of trees or parts of a tree affected by gully erosion revealing information on the history of the erosion process by datable deviations of their normal growth pattern hence defined as datable objects these include roots exposed by erosion browsing scars made by ungulates on exposed roots or on above ground parts of fallen trees exposed and dead root ends root suckers stems branches and leading shoots of fallen trees and a sequence of trees within a gully the method is based on the differentiation between three main conditions depending on the relation between the dynamics of the datable object part of the tree and the development of the gully the first condition implies that the datable object was created before erosion of the gully volume to be dated e g exposed tree roots according to the second condition the datable object developed as an immediate consequence of the erosion event e g growth reactions of a fallen tree the third condition implies that the datable object was created some time after the erosion event took place e g trees colonising the gully bed each principle has consequences for the accuracy and the correct interpretation of the estimated erosion rate i e whether the true erosion rate is underestimated exact or overestimated in spite of methodological limitations and dendrochronological dating problems the method was successfully applied in southeast spain conservative estimations of gully head retreat rate resulted in an average medium term 3 46 years value of 6 m3 year 1 n 9 for gully sidewall processes the average minimum erosion rate per unit sidewall length amounted 0 1 m3 year 1 m 1 n 9 a strong correlation was found between the headcut retreat rate vm ortho m3 year 1 and the drainage basin area a m2 of the gullies expressed by vm ortho 0 02a0 57 r2 0 93 n 9 comparing the findings from this study with those obtained by short term headcut retreat monitoring suggests a high reliability of the estimated retreat rates supporting the applicability of the developed dendrochronological method