Paolo PortoGiovanni CallegariAbid OuadjaErnesto Infusino...
167-177页
查看更多>>摘要：In some areas of southern Italy,the change in land use over the last 4-5 decades has increased pressure on land and water resources and caused different forms of soil degradation.In order to mitigate the magnitude of soil erosion,different strategies that include construction of flood control structures and reforestation programs have been done in several areas.However,quantifying the effectiveness of these strategies is difficult in absence of direct measurements of soil erosion.To cover this information gap,the use of distributed numerical models coupled with measurements of the radionuclide cesium-137(137Cs)offers a good alternative to the classic experimental sites(plot,catchments)that,on the contrary,require long term datasets to produce reliable estimates of soil loss.In this paper,measurements of 137Cs in a floodplain area are firstly described for a representative Calabrian catchment as an example to recon-struct the trend of soil deposition rates during the last six decades.These measurements have been integrated with estimates of soil loss obtained with the Revised Universal Soil Loss Equation(RUSLE)model for which land use maps of different periods are available.The final comparison between esti-mates of soil erosion provided by the RUSLE at catchment scale and sedimentation rates derived from 137Cs measurements on depositional areas allowed interesting information on the trend of soil erosion and deposition rates in these areas to be obtained.
查看更多>>摘要：A model of the channel and catchment components of sediment runoff has been developed.The model makes it possible to estimate the intensity of redistribution of river and bottom sediment in the riverbed,the size distribution of deposited or migrating particles,the mass of particles in the riverbed and catchment components of sediment load,as well as the contribution of the catchment component.The model is based on the assessment of the transport potential of the watercourse and the dynamics of the curves of the granulometric composition of bottom sediment,and products of soil and channel erosion.This approach is focused on the steady flow movement without additional sources of tributary sediment,intensive abrasion of river banks,and products of anthropogenic load.Calculations based on the model applied to the Narva River showed that the contribution of the catchment component to the sediment flow of this watercourse after intense rain is approximately 98％.The obtained results are well confirmed by the weak dynamics of channel deformations in the studied part of the watercourse.
查看更多>>摘要：The Sikkim-Darjeeling Himalaya region receives the highest amount of rainfall along the whole southern Himalayan margin and is known for the occurrence of extreme hydrometeorological and geomorphological events.The massive amounts of water and sediment transported each year through the mountain part of the Teesta River drainage system(～8,150 km2)--the largest river in the region--have been severely impacted by dam construction in recent decades.The aim of the current study was to determine,for the first time in this part of the Himalaya region,the dynamics of suspended sediment transfer at a number of points distributed through the mountainous part of the Teesta River catchment prior to dam construction and preliminarily assess the impact of dam operations on the suspended sediment.Sediment sources were identified using a database of landslide inventories from 1965 to 2019,combined with visual interpretation of satellite imagery from the U.S.Corona programme and Google Earth.Hydrological and sediment data up to the second half of the 1990s were used to reconstruct the discharge and suspended sediment dynamics before direct human intervention in the river channels.The beginning and end of the construction of the reservoirs was determined by analyzing satellite images.The impact of dam operations on the suspended sediment was compiled from the available literature.The results of the current studyindicate that the primary sources of sediment are landslides caused by the interaction of rainfall and road undercutting of slopes as well as channel erosion.During extreme rainfall events,the influence of deforested areas in the mobilization and delivery of sediment to the river network increases.The current analysis reveals that reconstruction of the suspended sediment dynamics should take into account the course of extreme events responsible for supplying material to the river network,as well as the long-term remobilization of already deposited sediment in the river channel.It was found that the mean suspended sediment load(SSL)following extreme rainfall,flooding,and landslides in the Teesta River catchment can be up to four times higher than its average values for the same catchment unaffected by such an event,and the effects can be observed for more than a decade afterwards.Under these conditions,the mean suspended sediment yield can reach 12,000 and up to 20,000 t/(km2·y)in individual years,which is among the highest in the Himalaya region and,indeed,the world.The construction of 13 dams in the last 30 years has disrupted the hydrological regime and sediment transport in the Teesta River catchment along 70％of its main course and largest tributaries,and this has resulted in the selective retention of coarser material in the reservoirs and a reduction in the SSL in the Himalayan piedmont.The high density of the dams suggests that further transport of sus-pended sediment will depend on the efficiency of the water and sediment management at the reservoirs,which may be affected by irregular natural extreme events.
查看更多>>摘要：Spur dikes are structures built along riverbanks that serve two purposes:stabilizing the banks and minimizing erosion risk by controlling water flow in the river channel.The current study used L-shaped spur dikes in an alluvial channel to analyze the bed morphology and flow pattern in the spur dikes zone with the influence of no-seepage and two distinct seepage velocities,VS1=0.075 mm/s and VS2=0.15 mm/s near the channel bed z/h＜0.2.The experimental study was also done to examine and compare the transformation in the local scour depth for the seepage condition.According to the study results,downward seepage movement causes significant modification in the channel's bed elevation and the development of scour depth.Observations indicate that the maximum local scour occurs at the first spur dike's leading edge.Seepage velocity VS1 results in a 16.1％increase in the maximum scour depth compared to the no-seepage scenario.In comparison,seepage velocity VS2 causes an increase of 252％in the maximum scour depth.Due to downward seepage,the flow distribution is shifted down near the channel's boundary.With an increase in the seepage rate,the magnitude of velocity,Reynold shear stress,turbulent kinetic energy,and bed shear stress also rise close to the channel's boundary.The current study also examined bursting events near the channel's bed under seepage and no-seepage conditions.These events included outward interaction,inward interaction,ejection,and sweep.Quad-rant analysis of velocimeter data revealed that ejection and sweep were the dominant events contrib-uting to the production of Reynolds shear stress in seepage and no-seepage flows.Meanwhile,outward interactions and inward interactions made minor contributions compared to ejection and sweep events to the Reynolds shear stress.
查看更多>>摘要：The current paper deals with the navigable section of the Volga River tailwater of the Nizhny Novgorod Hydropower Plant.To ensure navigation in this area,the existing navigation structures are being reconstructed and an additional chamber of the Gorodets Navigation Lock is to be constructed,and an extended navigable channel in the Volga River is to be created.To assess the impact of the planned measures on hydrological and riverbed regimes,the hydromorphological situation has been analyzed,and the flow parameters and the water level regime in the tailwater pool of the hydro system have been studied.An analysis of the changes in the riverbed along the design channel path was done and the kinematics of the flow and sediment transport parameters were studied under conditions of unsteady water movement resulting from the daily regulation of the river flow.Numerical experi-ments have revealed the peculiarities of river sediment movement under conditions of unsteady water movement,and recommendations for modeling river bed deformation under such conditions have been developed.It was found that with daily and weekly regulation of river,discharge bedload transport becomes more active at the moment when a wave of daily release from the upper reaches of the hydrosystem passes through.The basic characteristics of bedload transport,i.e.,dune velocity and bedload rate,increase in comparison with a steady water flow.Under the conditions of unsteady water movement due to the daily regulation of the river flow,there are no strong changes in the size of the bottom dunes,while their velocity,and,consequently,the bedload rate increases significantly during periods when the wave of daily water releases from upstream passes.The results obtained indicate that for hydraulic calculations of the characteristics of water movement and sediment transport,it is necessary to use data from hourly observations of flow rates and water levels.It was found that during the passage of release waves under daily flow regulation,there are short periods of increase in Froude number values.Similarly,the bedload rate increased during these periods compared to the average daily values.The result of this comparison ultimately led to the recommendation that daily flow regulation should be abandoned in order to reduce the intensity of bedload transport rate and channel erosion in the tailwater of the hydrosystem.
查看更多>>摘要：Sediment leads to problems with navigation,agricultural productivity,and water pollution.The study of sediment flow in river reaches,which is a non-linear and complex process,is,thus,essential to addressing these issues.The application of artificial neural networks(ANN)to such problems needs to be investigated.For unsteady flow in a river system,river reach storage is an important variable that needs to be considered in data-driven models.However,previous research on sediment modeling did not involve the explicit use of storage variables in such models as is investigated in the current study.In the current study,storage variables have been explicitly(Model 2)used to predict the output state of the system at time't+1'from the input state at time't'using ANNs.Sediment discharge at six gaging stations on the Mississippi River system,USA,has been considered as the state variable.The model has been compared with a model considering implicit variation of the storage parameter in the river system(Model 1).Dynamic ANNs are used for time-series datasets,which are more suitable for incorporating the sequential information within the dataset.Focussed gamma memory neural networks have been used in the current study.The numbers of hidden layers and hidden nodes,activation function,and learning rate have been varied step by step to obtain the optimal ANN configurations.The best selected input-output variables are those used in Model 2 as it performed slightly better than the other model in terms of Nash-Sutcliffe efficiency coefficient(CE)values.Model performance evaluated using normal-ized root mean square error(NRMSE)and CE shows satisfactory results.NRMSE was＜10％for all the outputs except for the Venedy and Murphysboro locations and CE values for sediment loads were＞0.45 for all locations except Murphysboro indicating acceptable performance by both the models.The models proved highly efficient(CE＞0.80,i.e.,very good predictions)for predicting sediment discharge at lo-cations along the main river channel with acceptable accuracy(CE＞0.45)for other locations and the storage change for the river system.These models can be used for real-time forecasting and management of sediment-related problems.
查看更多>>摘要：Identifying organic carbon(OC)sources in lake sediment is essential for elucidating biogeochemical cycling processes and effectively supporting watershed management.However,the complexity of sources as well as environments in the land-river-lake continuum makes it challenging to accurately identify OC sources.Accordingly,the current study utilized a systematic approach to identify and validate OC sources in a typical land-river-lake continuum.Two tracer groups(group 1∶δ13C and 815N;group 2:fluorescence index and biotic index,respectively(where C is carbon and N is nitrogen))and one model(MixSIAR)were eventually selected from five tracer groups and two models to identify the OC sources in a land-river-lake continuum according to a consistency evaluation and virtual mixing test.The results showed that the distribution of OC sources in lake sediment was spatially heterogeneous.Closer to the lake center(from sampling site S1 to S3),the autochthonous contributions increased while the allochthonous contributions decreased.Downstream of the inlet river(site S1)was dominated by allochthonous contributions(78.6％),especially cropland(28.7％±0.5％,where±indicates a standard deviation range)and urban land(30.5％±2.5％).From site S1 to S2,the allochthonous contribution decreased 11.4％.Autochthonous OC gradually became the major source closer to the lake center(site S3:phragmites:48％±4.5％).This distribution of OC sources in the land-river-lake system was attributed to the mixing effect of the autochthonous sources,selective transport of sediment,and human activities.The current findings may aid in validating the ability of different tracers and models to identify OC sources in complex ecosystems and also provide a theoretical basis for watershed management.
Zeeshan AkbarGhufran Ahmed PashaNorio TanakaUsman Ghani...
243-256页
查看更多>>摘要：A river's planform pattern changes due to erosion of banks and the bed near the outer bend.The primary cause of these planform changes is the formation of helical flow patterns in response to centrifugal forces.Uncontrolled bed scouring can have a negative impact on the river's geometry,aquatic habitat,and floodplains.To alleviate this scouring,various structures,such as spur dikes,can be placed at any accessible location along the bend.The current research was accomplished by installing two meandering models with different sinuosities of 1.3 and 1.5,in a flume.For both sinuosities,the maximum bed scour was observed at an approximate angle of 45° relative to the bend apex.Thus,the main objective was to control this maximum scour by installing spur dikes with varying porosities,ranging from 0％to 75％,at five locations along the outer bend.The spur dikes were found to divert the helical flow regime away from the outer bend and protect the riverbed from severe scouring.However,the results show that the effectiveness of spur dikes decreases as sinuosity increases.Furthermore,for both meandering models,a 50％permeable spur dike installed at the+30° location yielded the best performance.Finally,a regression-based predictive equation is proposed to determine the proportion of scouring around a spur dike in a meandering channel.
查看更多>>摘要：Total arsenic(TAs)contamination is a serious health issue that affects many parts of the world.The sources of TAs in the Himalayas and Hindu Kush Mountains are rocks containing sulfide minerals and coal.The current study investigated the concentrations of TAs in soil,vegetables,and fruits collected from the Chitral Valley in the Hindukush Mountains of Pakistan.Vegetables consisted of Solanum tuberosum(potatoes),Mentha spicata(mint),Chenopodium album(goosefoot),Coriandrum sativum(coriander),Cucumis sativus(cucumber),Amaranthus viridis(green amaranth),and Medicago sativa(alfalfa);and fruits consisted of Prunus armeniaca(apricot),Morus alba(mulberry),Juglans regia(nut),Malus domestica(apple),and Vitis vinifera(grapes).The average concentration of TAs was the highest in the Gabur soils and lowest in the Bamborait soils.In vegetables,the highest TAs concentration was found in goosefoot(11.11±1.9 mg·kg-1)and the lowest in cucumbers(1.38±0.3 mg·kg-1).In fruits,the highest TAs concentration was found in grapes(4.3±0.5 mg·kg-1),while no TAs concentration was detected in nuts(±indicates the one standard deviation range).The transfer factor(TF)values were high only in Bomborait soils(TF＞1).Leafy vegetables and juicy fruits(possessing high water content)were found to be more susceptible to TAs contamination.The daily intake of metals(DIA),human health risk index(HRI),and cancer risk demonstrated that the Chitral Valley is at high risk due to TAs contamination,which may pose a threat to the concerned community and ecosystem.The current findings suggest that leafy vegetables and juicy fruits in the study area should be carefully consumed.
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