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1.
The operation of large-scale reservoirs have modified water and sediment transport processes, resulting in adjustments to the river topography and water levels. The polynomial fitting method was applied to analyze the variation characteristics of water levels under different water discharge values in the Jingjiang reach of the Yangtze River from 1991–2016. The segregation variable method was used to estimate the contributions of the varied riverbed evaluation, the downstream-controlled water level, and the comprehensive roughness on the altered water level at an identical flow. We find that low water levels in the Jingjiang reach of the Yangtze River from 1991–2016 are characterized by a significant downward trend, which has intensified since 2009. Riverbed scouring has been the dominate factor causing the reduced low water level while increased roughness alleviated this reduction. From 1991–2016, there was first a decrease followed by an increase in the high water level. The variation characteristic in terms of the "high flood discharge at a high water level" before 2003 transformed into a "middle flood discharge at a high water level" since 2009. The increased comprehensive roughness was the main reason for the increased high water level, where river scouring alleviated this rise. For navigation conditions and flood control, intensified riverbed scouring of the sandy reaches downstream from dams enhanced the effects that the downstream water level has on the upstream water level. This has led to an insufficient water depth in the reaches below the dams, which should receive immediate attention. The alteredvariation characteristics of the high water level have also increased the flood pressure in the middle reaches of the Yangtze River.  相似文献   

2.
Deep-water navigation channels in the tidal reaches of the lower Yangtze River are affected by water and sediment fluxes that produce complex shoals and unstable channel conditions. The Fujiangsha reach is particularly difficult to manage, as it has many braided channels within the tidal fluctuation zone. In this study, hydrologic and topographic data from the Fujiangsha reach from 2012 to 2017 were used to examine the variations in deposition and erosion, flow diversion, shoals, and channel conditions. Since the Three Gorges Dam became operational and water storage was initiated, the Fujiangsha reach has shown an overall tendency toward erosion. Channels deeper than 10 m accounted for 83.7% of the total erosion of the Fujiangsha reach during 2012–2017. Moreover, the dominant channel-forming sediments have gradually changed from suspended sediments to a mixed load of suspended and bed-load sediments. Deposition volumes of these sediments has varied significantly among different channels, but has mainly occurred in the Fubei channel. Furthermore, periodic variations in the Jingjiang point bar have followed a deposition-erosion-deposition pattern, and the downstream Shuangjian shoal mid-channel bar has been scoured and shortened. Approximately 44.0% of the bed load from the upstream Fujiangsha reach is deposited within the 12.5-m deep Fubei channel. The increased erosion and river flow from the Jingjiang point bar and the Shuangjian shoal during the flood season constituted 59.3% and 40.7%, respectively, of the total amount of siltation in the Fubei channel.  相似文献   

3.
River basin reservoir construction affects water and sediment transport processes in downstream reaches. The downstream impact of the Three Gorges Projects(TGP) has started to become apparent:(1) reduction in flood duration and discharge, and significant reduction in sediment load. Although there was some restoration in downstream sediment load, the total amount did not exceed the pre-impoundment annual average;(2) in 2003–2014, the d 0.125 mm(coarse sand) load was restored to some degree, and to a maximum at Jianli Station, which was mainly at the pre-impoundment average. After restoration, erosion and deposition characteristics of the sediment was identical to that before impoundment. The degree of restoration during 2008–2014 was less than during 2003–2007;(3) after TGP impoundment, there was some restoration in d 0.125 mm(fine sand) sediment load, however, it was lower than the pre-impoundment average;(4) due to riverbed compensation, the d 0.125 mm sediment load recovered to a certain degree after impoundment, however, the total did not exceed 4400×10~4 t/y. This was mainly limited by flood duration and the average flow rate, and was less affected by upstream main stream, tributaries, or lakes. Restoration of d 0.125 mm suspended sediment was largely controlled by upstream main stream, tributaries, and lakes, as well as by riverbed compensation. Due to bed armoring, riverbed fine suspended sediment compensation capability was weakened;(5) during 2003–2007 and 2008–2014, Yichang to Zhicheng and upper Jingjiang experienced coarse and fine erosion,lower Jingjiang experienced coarse deposition and fine erosion, Hankou to Datong had coarse deposition and fine erosion, and Chenglingji and Hankou was characterized by coarse deposition and fine sand erosion in 2003–2007, and coarse and fine erosion in 2008–2014. This difference was controlled by flood duration and number at Luoshan Station.  相似文献   

4.
Alluvial channel has always adjusted itself to the equilibrium state of sediment transport after it was artificially or naturally disturbed.How to maintain the equilibrium state of sediment transport and keep the river regime stable has always been the concerns of fluvial geomorphologists.The channel in the middle and lower reaches of the Yangtze River is characterized by the staggered distribution of the bifurcated river and the single-thread river.The change of river regime is more violently in the bifurcated river than in the single-thread river.Whether the adjustment of the river regime in the bifurcated river can pass through the single-thread river and propagate to the downstream reaches affects the stabilities of the overall river regime.Studies show that the barrier river reach can block the upstream channel adjustment from propagating to the downstream reaches;therefore,it plays a key role in stabilizing the river regime.This study investigates 34 single-thread river reaches in the middle and lower reaches of the Yangtze River.On the basis of the systematic summarization of the fluvial process of the middle and lower reaches of the Yangtze River,the control factors of barrier river reach are summarized and extracted:the planar morphology of single-thread and meandering;with no flow deflecting node distributed in the upper or middle part of the river reach;the hydraulic geometric coefficient is less than 4;the longitudinal gradient is greater than 12‰,the clay content of the concave bank is greater than 9.5%,and the median diameter of the bed sediment is greater than 0.158 mm.From the Navier-Stokes equation,the calculation formula of the bending radius of flow dynamic axis is deduced,and then the roles of these control factors on restricting the migration of the flow dynamic axis and the formation of the barrier river reach are analyzed.The barrier river reach is considered as such when the ratio of the migration force of the flow dynamic axis to the constraint force of the channel boundary is less than 1 under different flow levels.The mechanism of the barrier river reach is such that even when the upstream river regime adjusts,the channel boundary of this reach can always constrain the migration amplitude of the flow dynamic axis and centralize the planar position of the main stream line under different upstream river regime conditions,providing a relatively stable incoming flow conditions for the downstream reaches,thereby blocking the upstream river regime adjustment from propagating to the downstream reaches.  相似文献   

5.
长江中游马口-田家镇河段40年来河道演变   总被引：2，自引：1，他引：1  
Quantitative analysis was performed on the filling-scouring process for the river reach within Makou and Tianjiazhen, the middle Yangtze River with the help of GIS and DEM techniques. The research results indicate that the river reach between Makou and Tianjiazhen was dominated by the scouring process, and the magnitude of scouring is increasing over time. The intensity of scouring process is more in the deep and narrower river reach than shallower and wider ones. The river reach in the Makou and Tianjiazhen river knot is in fre-quent scouring and filling process, however the river reach upper to the Makou and lower to the Tianjiazhen river knot is in moderate scouring and filling process. The river reach just upstream or downstream to the river knot (e.g. Makou and Tianjiazhen river knot in this research) is dominated by filling process and the river reach in the river knot is dominated by the scouring process. Research results indicate no changes in the boundary of the river but the scouring and the filling magnitude in specific river channel is strong. The filling and the scouring process of the study river reach is greatly impacted by the sediments and water from the upstream of the study river reach. The construction of the Three Gorges Dam just upstream to Yichang will cause further decrease of the release of the sediment load to the middle and the lower Yangtze River basin, which will further intensify the scouring process of the river channel in the study river reach.  相似文献   

6.
The lower Yellow River still faces the threat of flood due to the unusual precipitation caused by global environmental change, river channel sedimentation, hidden danger in the dike and unfavorable river regime of ＂hanging river＂. According to the characteristics of the dike-break flood of the Yellow River, this paper has simulated, in six different scenarios, the dike-break flood routing by inputting the terrain data, typical historical flood data and land use data of study area to two-dimensional unsteady flow model. The results show that： firstly, the routing process of flood will occupy other rivers on the way and return to the rivers after reaching the lower reaches; secondly, in the same river reach, flood inundating area of north band is bigger than that at corresponding location of south bank under the same historical flood; thirdly, it is different in the degree of flood inundation in different regions due to different geographical locations in flood plain; fourthly, the area of mainstream where flood is deep and flow velocity is quick is relatively smaller, but the area of non-mainstream, where flood is shallow and flow velocity is slow, is relatively big; and finally, the possible influenced area of the dike-break flood is 141,948 km^2.  相似文献   

7.
The spatial distribution of valley setting （laterally-unconfined, partly-confined, or confined） and fluvial morphology in the source region of the Yangtze and Yellow Rivers is contrasted and analyzed. The source region of the Yangtze River is divided into 3 broad sections （I, II and III） based on valley setting and channel gradient, with the upstream and downstream sections being characterized by confined （some reaches partly-confined） valleys while the middle section is characterized with wide and shallow, laterally-unconfined valleys. Gorges are prominent in sections I and III, while braided channel patterns dominate section II. By contrast, the source region of the Yellow River is divided into 5 broad sections （sections I-V） based on valley characteristics and channel gradient. Sections I, II and IV are alluvial reaches with mainly laterally-unconfined （some short reaches partly-confined） valleys. Sections III and V are mainly confined or partly-confined. Greater morphological diversity is evident in the source region of the Yellow River relative to the upper Yangtze River. This includes braided, anabranching, anastomosing, meandering and straight alluvial patterns, with gorges in confined reaches. The macro-relief （elevation, gradient, aspect, valley alignment and confinement） of the region, linked directly to tectonic movement of the Qinghai-Tibet Plateau, tied to climatic, hydrologic and biotic considerations, are primary controls upon the patterns of river diversity in the region.  相似文献   

8.
近60年黄河水沙变化及其对三角洲沉积的影响   总被引：1，自引：1，他引：0  
In order to find out the variation process of water-sediment and its effect on the Yellow River Delta, the water discharge and sediment load at Lijin from 1950 to 2007 and the decrease of water discharge and sediment load in the Yellow River Basin caused by human disturbances were analyzed by means of statistics. It was shown that the water discharge and sediment load into the sea were decreasing from 1950 to 2007 with serious fluctuation. The human activities were the main cause for decrease of water discharge and sediment load into the sea. From 1950 to 2005, the average annual reduction of water discharge and sediment load by means of water-soil conservation practices were 2.02×109 m3 and 3.41×108 t respectively, and the average annual volume by water abstraction for industry and agriculture were 2.52×1010 m3 and 2.42×108 t respectively. The average sediment trapped by Sanmenxia Reservoir was 1.45×108 t from 1960 to 2007, and the average sediment retention of Xiaolangdi Reservoir was 2.398×108 t from 1997 to 2007. Compared to the data records at Huanyuankou, the water discharge and sediment load into the sea decreased with siltation in the lower reaches and increased with scouring in the lower reaches. The coastline near river mouth extended and the delta area increased when the ratio of accumulative sediment load and accumulative water discharge into the sea (SSCT) is 25.4–26.0 kg/m3 in different time periods. However, the sharp decrease of water discharge and sediment load into the sea in recent years, especially the Yellow River into the sea at Qing 8, the entire Yellow River Delta has turned into erosion from siltation, and the time for a reversal of the state was about 1997.  相似文献   

9.
The Yangtze River is the third largest river in the world and the longest and largest river in China.China has adopted a national strategy to protect the Yangtze River.A better understanding of the ecosystem services value along the Yangtze River would provide support for the Yangtze River protection strategy.Using Costanza’s method to estimate the ecosystem services value,the value of 10 ecosystem services was estimated within 1 km and 2 km from the Yangtze River in 2017.These 10 services were derived from the four established groupings of provisioning,regulating,supporting,and cultural services.This study compared and analyzed the changes in the ecosystem services value in the upper,middle,and lower reaches of the river,and in provinces,cities,and villages along the Yangtze River.The total ecosystem services value within 1 km and 2 km from the river was 37.208 and 43.769 billion yuan,respectively.Within 1 km,the ecosystem services value in the middle reaches was 12.93 billion yuan,while the next highest value was in the upper reaches at 12.45 billion yuan,and the downstream area had the smallest value of 11.855 billion yuan.Within 2 km,the value of upstream ecosystem services was the highest at 16.31 billion yuan,while the second highest value was in the middle reaches at 14.376 billion yuan,and the smallest value was in the downstream area at 13.083 billion yuan.In the Yangtze River Basin,regulating services played a leading role,accounting for 81.6%and 78.9%of the ecosystem services value within 1 km and 2 km from the river,respectively.Among the 10 ecosystem services,hydrological regulation was the most important,while the value of raw material production made the smallest contribution.Among the provinces and cities along the Yangtze River,the highest ecosystem services value was in Hubei Province,while the lowest values were in Shanghai and the Qinghai-Tibet Plateau.If villages within 1 km and 2 km from the river were to be relocated,the total regional ecological value would increase by 527 and 975 million yuan,respectively.  相似文献   

10.
Based on the measured discharge,sediment load,and cross-sectional data from 1986 to 2015 for the lower Yellow River,changes in the morphological parameters(width,depth,and cross-sectional geomorphic coefficient)of the main channel are analyzed in this paper.The results show that before the operation of the Xiaolangdi Reservoir(XLDR)from 1986 to 1999,the main channel shrunk continually,with decreasing width and depth.The rate of reduction in its width decreased along the river whereas that of depth increased in the downstream direction.Because the rate of decrease in the width of the main channel was greater than that in channel depth,the cross-sectional geomorphic coefficient decreased in the sub-reach above Gaocun.By contrast,for the sub-reach below Gaocun,the rate of decrease in channel width was smaller than that in channel depth,and the cross-sectional geomorphic coefficient increased.Once the XLDR had begun operation,the main channel eroded continually,and both its width and depth increased from 2000 to 2015.The rate of increase in channel width decreased in the longitudinal direction,and the depth of the main channel in all sub-reaches increased by more than 2 m.Because the rate of increase in the depth of the main channel was clearly larger than that of its width,the cross-sectional geomorphic coefficient decreased in all sub-reaches.The cross-sectional geometry of the main-channel of the lower Yellow River exhibited different adjustment patterns before and after the XLDR began operation.Before its operation,the main channel mainly narrowed in the transverse direction and silted in the vertical direction in the sub-reach above Aishan;in the sub-reach below Aishan,it primarily silted in the vertical direction.After the XLDR began operation,the main channel adjusted by widening in the transverse direction and deepening in the vertical direction in the sub-reach above Aishan;in the sub-reach below it,the main channel adjusted mainly by deepening in the vertical direction.Compared with the rates of decrease in the width and depth of the main channel during the siltation period,the rate of increase in channel width during the scouring period was clearly smaller while the rate of increase in channel depth was larger.After continual siltation and scouring from 1986 to 2015,the cross-sectional geometry of the main-channel changed from wide and shallow to relatively narrow and deep.The pattern of adjustment in the main channel was closely related to the water and sediment conditions.For the braided reach,the cross-sectional geomorphic coefficient was negatively correlated with discharge and positively correlated with suspended sediment concentration(SSC)during the siltation period.By contrast,the cross-sectional geomorphic coefficient was positively correlated with discharge and negatively correlated with SSC during the scouring period.For the transitional and meandering reaches,the cross-sectional geomorphic coefficient was negatively correlated with discharge and positively correlated with SSC.  相似文献   

11.
The sand dredging and its impacts on riverbed evolution and tidal dynamic change in the lower reaches and delta of the Dongjiang River are examined in this paper. The large amount of sand, totally 3.32 billion m^3 from 1980 to 2002, was mined from the riverbeds of the lower reaches and delta of the Dongjiang River. Increasing of the channel capacity, lowering of the average riverbed elevation, deepening of the water depth and decreasing of the longitudinal riverbed gradient are the main effects on the riverbed evolution brought by the large amount of sand dredging. Under the strong sand dredging and associated significant riverbed deformation, the notable changes of the tidal dynamic in the lower reaches and delta of the Dongjiang River occurred, including： （1）in the upper reaches of the Dongjiang River delta and lower reaches of the Dongjiang River, tidal level dropped apparently, tidal range widened, flood tidal duration became longer, amplitudes for major tidal components became bigger and tidal dynamics intensified; （2） tidal wave spread faster; and （3） the limits of the tidal level, tidal current and salt water moved upstream.  相似文献   

12.
Given the importance of waterway depths in river development, the effects of the evolution of bars and troughs on waterway expansion play an important role in river management and water depth conservation. This study aims to expand the waterway dimensions of the Jingjiang Reach of the Yangtze River. To achieve this objective, determining the relationship between river evolution processes and the potential for waterway depth improvement and navigation hindrances is vital. Therefore, the sedimenta...  相似文献   

13.
The mouth bar in the Yangtze estuarine waterways has a significant influence on navigational transport within the estuary,flood discharge and construction of the Shanghai Port.In this paper the morphological evolution and mechanisms of mouth bar formation of the Yangtze estuarine waterways are studied by analyzing hundreds of years of historical data and the latest profile maps of some or the main mouth bar channels in the Yangtze Estuary.The results are shown as follows:The mouth bars in the North Branch have moved gradually from outside the mouth to the inside and formed a huge sand bar.In the North Channel,the head of the mouth bar has migrated about 30 kilometers downstream,and a channel bar has been developing since 2001.Two mouth bar tops,which always existed in the North Passage,disappeared in 2010.The head of the mouth bar in the South Passage has migrated downstream about 14 km and the number of tops increased at first but is reduced to only one now.According to the results,we can conclude that the evolution of the mouth bars differs depending on their location.In the North Branch it is directly related to large-scale reclamation in Chongming Island,but in the North Passage it has a close relationship with regulation of the Yangtze Estuary Deepwater Channel.However,the evolution of mouth bars in the North Channel and South Passage is not only connected with the Yangtze Estuary Deepwater Channel Regulation Project,but also with the reclamation in the East Hengsha Shoal and the closure of the Qingcaosha Reservoir.  相似文献   

14.
It is of necessity to investigate the adjustment of flood discharge capacity in the Lower Yellow River(LYR) because of its profound importance in sediment transport and flood control decision-making, and additionally its magnitude is influenced by the channel and upstream boundary conditions, which have significantly varied with the ongoing implementation of soil and water conservation measures in the Loess Plateau and the operation of the Xiaolangdi Reservoir. The braided reach between two hydrometric stations of Huayuankou and Gaocun in the LYR was selected as the study area. Different parameters in the study reach during the period 1986–2015 were calculated, covering bankfull discharge(the indicator of flood discharge capacity), the pre-flood geomorphic coefficient(the indicator of channel boundary condition), and the previous five-year average fluvial erosion intensity during flood seasons(the indicator of incoming flow and sediment regime). Functional linkages at scales of section and reach were then developed respectively to quantitatively demonstrate the integrated effects of channel and upstream boundary conditions on the flood discharge capacity.Results show that:(1) the reach-scale bankfull discharge in the pre-dam stage(1986–1999)decreased rapidly by 50%, accompanied with severe channel aggradation and main-channel shrinkage. It recovered gradually as the geometry of main channel became narrower and deeper in the post-dam stage, with the geomorphic coefficient continuously reducing to less than 15 m-1/2.(2) The response of bankfull discharge to the channel and upstream boundary conditions varied at scales of section and reach, and consequently the determination coefficients differed for the comprehensive equations, with a smallest value at the Jiahetan station and a highest value(0.91) at reach scale. Generally, the verified results calculated using the comprehensive equations agreed well with the corresponding measured values in 2014–2015.(3) The effect of channel boundary condition was more prominent than that of upstream boundary condition on the adjustment of bankfull discharge at the Jiahetan station and the braided reach, which was proved by a larger improvement in determination coefficients for the comprehensive equations and a better performance of geomorphic coefficient on the increase of bankfull discharge.  相似文献   

15.
Based on the analysis of suspended sediment elements at estuaries,influence of human activities and estuarine regulation projects on the turbidity maximum zone was studied according to the measurement data between 1959 and 2011.It was found that human activities had little effect on the seaward water while the sharp decrease of sediment volume and concentration in runoff led to the sharp decrease of turbidity maximum zone in the estuary.The concentration at outside sea and Hangzhou Bay did not change,and that along the Subei coast also decreased a little,which had no influence on the turbidity maximum zone.Compared with the concentration between 1959 and 1999,the peak of concentration moved upstream in the estuary,and the concentration in 2000–2009 decreased by about 24.73% with a narrower variation range along the river to the sea.The suspended sediment concentration in North Passage was low in upstream and downstream because of the decrease of seaward sediment and coarsening of bed material,while it was relatively high in the middle due to the influence of sediment cross the north jetty.  相似文献   

16.
Lateral migration of the Bhagirathi River temporally creates unavoidable geomorphic hazards in West Bengal, India. The Bhagirathi River flows SW for ～67.30 km between the confluence point of Ajay and Jalangi rivers in East Burdwan and Nadia districts of West Bengal. The course of Bhagirathi is notably migration prone and cultivates problematic changes along its course over time. In the study, we have looked into its migration tendency and unpredictability for past 238 years and then predicted the lateral shifting of river centerline using temporal satellite imageries – Landsat-5(TM) of 1987(8, December), 1995(28, January), 2005(7, January) and LISS-IV satellite imagery(2017, 5 January);SOI Toposheet – 1968–1969(79 A/2, 79 A/3, 79 A/6 and 79 A/7) and Rennell's map of 1779. Other highlights are the quest of fluvial features, oxbow lakes, mid-channel bars, channel migration rate, meander geometry, channel sinuosity in different parts of river course and the parts that experience intensive bank erosion. The entire river course has been subdivided into three segments; viz. reaches A, B and C. Investigation displays that degree of sinuosity decreases from its anterior course(1968) to the existing course(2017). Reach-specific outputs display that reach B is highly sinuous(SI value 1.94 in 2017) and SI increases temporarily, whereas for reaches A and C it decreases with time. The rate of migration is higher in reach B than that in reaches C and A. The study displays a notably decreasing trend of migration in comparison with its previous lateral migration and shows that the migration nature over time is intensively inconsistent and unpredictable except very few portions of the river course. The nature of deposition within the river channel shows an unstable behavior during the entire period of the study. Meander geometry depicts a rapid change of river course innate to meander bends and shows a higher rate of migration by meander loop cut-off rather than lateral migration that reflects the inconsistency, erosion vulnerability and unpredictable nature of migration. The present work offers a valuable source to comprehend channel changes in Bhagirathi River and serve as an efficacious base for river-bank migration and erosion hazard planning and management.  相似文献   

17.
This paper describes valley bottom troughs of the Changjiang River and infers the geomorphologic development of troughs. Based on the morphology of the troughs, the following conclusions are drawn. (1) The deep troughs on the Three Gorges valley bottom are formed by river downcutting along the structural zones on the background of regional tectonic uplift at about 40-30 ka BP. (2) When river downcutting occurred in the river bed of Changjiang, the jets current (particularly eddy current) with a large number of pebbles ground and eroded the valley bottom, resulting in trough formation and deepening. Meanwhile, water currents with gravels and pebbles eroded the bank and the left wall of No.76 trough as well as the right wall of No.77 trough by striking, scouring, horizontal and vertical grinding. (3) The depth of the trough is mainly determined by the intensity of the water current and the consistency of bedrock against erosion, and is not controlled hv the altihlde of the sea level as the base level of erosion.  相似文献   

18.
Based on the analysis of suspended sediment elements at estuaries, influence of human activities and estuarine regulation projects on the turbidity maximum zone was studied according to the measurement data between 1959 and 2011. It was found that human activi- ties had little effect on the seaward water while the sharp decrease of sediment volume and concentration in runoff led to the sharp decrease of turbidity maximum zone in the estuary. The concentration at outside sea and Hangzhou Bay did not change, and that along the Subei coast also decreased a little, which had no influence on the turbidity maximum zone. Com- pared with the concentration between 1959 and 1999, the peak of concentration moved up- stream in the estuary, and the concentration in 2000-2009 decreased by about 24.73% with a narrower variation range along the river to the sea. The suspended sediment concentration in North Passage was low in upstream and downstream because of the decrease of seaward sediment and coarsening of bed material, while it was relatively high in the middle due to the influence of sediment cross the north jetty.  相似文献   

19.
1951-2002年长江流域降水特征   总被引：2，自引：0，他引：2  
The monthly, seasonal, and annual precipitation trends in the Yangtze river catchment have been detected through analysis of 51 meteorological stations‘ data between 1950-2002 provided by National Meteorological Administration. Results reveal that: 1) Summer precipitation in the Yangtze river catchment shows significant increasing tendency. The Poyanghu lake basin, Dongtinghu lake basin and Taihu lake basin in the middle and lower reaches are the places showing significant positive trends. Summer precipitation in the middle and lower reaches experienced an abrupt change in the year 1992; 2) The monthly precipitation in months just adjoining to summer shows decreasing tendency in the Yangtze river catchment. The upper and middle reaches in Jialingjiang river basin and Hanshui river basin are the places showing significant negative trends; 3) Extreme precipitation events show an increasing tendency in most places, especially in the middle and lower reaches of the Yangtze river catchment.  相似文献   

20.
The capacity of soil and water conservation measures, defined as the maximum quantity of suitable soil and water conservation measures contained in a region, were determined for the Loess Plateau based on zones suitable for establishing terraced fields, forestland and grassland with the support of geographic information system(GIS) software. The minimum possible soil erosion modulus and actual soil erosion modulus in 2010 were calculated using the revised universal soil loss equation(RUSLE), and the ratio of the minimum possible soil erosion modulus under the capacity of soil and water conservation measures to the actual soil erosion modulus was defined as the soil erosion control degree. The control potential of soil erosion and water loss in the Loess Plateau was studied using this concept. Results showed that the actual soil erosion modulus was 3355 t·km~(–2)·a~(–1), the minimum possible soil erosion modulus was 1921 t·km~(–2)·a~(–1), and the soil erosion control degree was 0.57(medium level) in the Loess Plateau in 2010. In terms of zoning, the control degree was relatively high in the river valley-plain area, soil-rocky mountainous area, and windy-sandy area, but relatively low in the soil-rocky hilly-forested area, hilly-gully area and plateau-gully area. The rate of erosion areas with a soil erosion modulus of less than 1000 t·km~(–2)·a~(–1) increased from 50.48% to 57.71%, forest and grass coverage rose from 56.74% to 69.15%, rate of terraced fields increased from 4.36% to 19.03%, and per capita grain available rose from 418 kg·a~(–1) to 459 kg·a~(–1) under the capacity of soil and water conservation measures compared with actual conditions. These research results are of some guiding significance for soil and water loss control in the Loess Plateau.  相似文献   

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