Temporal Change of Runoff and Sediment Load and their Differential Response to Human Activities:A Case Study for a Well-vegetated Mountain Watershed of Southern China

This study examined the temporal trends of runoff and sediment load and their differential response to human activities in the Lishui river,a tributary of the Yangtze river in southern China.The long-term observation data at four gauging stations,generally involving two periods from 1954 to 1985 and from 2007 to 2011,were used.We detected no significant temporal trend for both the annual runoff volume(Q) and the annual suspended Sediment Load(SL) over more than 30 years before 1985.The flow duration curves and the Suspended Sediment Concentration(SSC) also hold constant before 1985.Compared with the period before 1985,SL has decreased by about 80% though Q remains unchanged for the period after 2007.Detailed examination shows that the flow duration curves after 2007 have changed with a significant decrease in the high-flow component,which acts as a major cause for the decreasing SL.In addition,SSC has decreased by several times,which also contributes to the decrease in SL after 2007.Both decreases in high-flow discharges and in SSC can be linked with recent human activities,mainly including vegetation establishment and dam constructions.The constant Q and the decreasing SL are also reported for the main stream of the Yangtze River and other major rivers in southern China,although they are orders of magnitude larger than our study area in drainage area size.The present study highlights the importance of high-flow discharges on SL and suggests that the use of SL is more appropriate to reflect environmental change than Q.

Spatio-temporal trends and causes of variations in runoff and sediment load of the Jinsha River in China

The Jinsha River Basin is an important basin for hydropower in China and it is also the main runoff and sediment source area for the Yangtze River,which greatly influence the runoff and sediment in the Three Gorges Reservoir.This study aims to characterize the spatial distribution,inter-annual variation of runoff and sediment load in the Jinsha River Basin,and to analyze the contribution of rainfall and human activities to the runoff and sediment load changes.The monitoring data on runoff,sediment load and precipitation were collected from 11hydrological stations in the Jinsha River Basin from1966 to 2016.The data observed at the outlet of the basin showed that 71.4%of the runoff is from the upper reaches of the Jinsha River Basin and the Yalong River,while 63.3%of the sediment is from the lower reaches(excluding the Yalong River).There is no significant increase in runoff on temporal scale in the Jinsha River Basin,while it has an abrupt change in runoff in both upstream and midstream in 1985,and an abrupt change in downstream in 1980 and2013.The sediment load demonstrated a significantincreasing trend in the upstream,no significant reducing trend in the midstream,but significant reducing trend in the downstream.The sediment load in upstream showed abrupt change in 1987,in midstream in 1978 and 2014,in downstream in 2012.Rainfall dominated runoff variation,contributing more than 59.0%of the total variation,while human activity,including reservoirs construction,the implementation of soil and water conservation projects,is the major factor to sediment load variation,contributing more than 87.0%of the total variation.

Sediment Load in Runoff Under Laboratory and Field Simulated Rainfall

Soil erosion is one of the most important problems in the Loess Plateau of China affectingsustainable agriculture. Near Luoyang (Henan Province, China), field plots were constructed tomeasure soil erosion rates under conventional tillage practices using field-simulated rainfall.Field rainfall experiments were carried out to compare previous results from laboratoryrainfall simulations on the same soil for interrill conditions. Although in the laboratoryexperiments, a strong correlation was found between the stream power of the runoff water andthe unit sediment load, this sediment transport equation overestimated the field rainfallsimulation results. Another sediment transport equation derived by Nearing et al. for rillerosion was in better agreement with the results of the field experiments, although it alsooverestimated these values. The measured sediment load values during the field rainfallsimulations were also lower than those found during field experiments on the same soil but witha loosened surface layer. This difference indicates the importance of soil physical conditionof surfce like soil structure and aggregate size, which may contribute to the discrepancybetween the field and laboratory experiment results.

Runoff and Sediment Load from the Right Bank Valleys of Mosul Dam Reservoir

Mosul Dam is a Multipurpose Project on the River Tigris in Iraq with 11.11 billion m3 storage capacity. It is used to store the water for irrigation, hydropower generation, and flood control. As in other dams in the world, this dam also have sedimentation problem. Sediment accumulation in its reservoir can effect the dam operation （pumping station, hydropower plants, and bottom outlets） and it will definitely shorten the life span of the dam. In this study, the SWAT （soil and water assessment tool） under （]IS （Geographical Information System） was applied to simulate the yearly surface rtmoff and sediment load for the main three valleys on the right bank of Mosul Dam Reservoir. The simulation considered for the twenty one years begin from the dam operation in 1988 to 2008. The resultant values of the average annual sediment load are 35.6~ 103, 4.9 ~ 103, and 2.2~ 103 ton, while the average values of sediment concentration are 1.73, 1.65, and 2.73 kg/m3 for the considered valleys one, two and three respectively. This implies that significant sediment load enters the reservoir from these valleys. To minimize the sediment load entering the reservoir, a check dam is to be constructed in suitable sites especially for valley one. The check dam can store the runoff water and trap the sediment load, and then the flow can be released to the reservoir.

Impacts of Climate Change on Spatial and Temporal Distribution of Runoff and Sediment Yield in Xixi Watershed of Jinjiang Basin

Based on meteorologic data in Xixi Watershed from 1972 to 1979, the SWAT model was applied to simulate the response of runoff and sediment yield in Xixi Watershed to climate change under 24 kinds of climate change scenarios, and then the spatial and temporal distribution of change rates of the runoff and sediment were analyzed. The results showed that the runoff yield would increase with the increase of precipitation or decrease of temperature, and the sediment yield would increase with the increase of precipitation or increase of temperature; the runoff would be more sensitive to variations in precipitation than to variations in temperature, and precipitation change would lead to more obvious change in the run- off yield; the temporal distribution of change rates of the runoff and sediment yield would be uneven in the 12 months, and the variation trends of the two change rates in the 12 months would be accordant; the spatial distribution of change rates of the runoff and sediment yield would be uneven in the sub-watersheds, and the change rate of the runoff yield would be bigger in the sub-watersheds where the runoff yield in the basic period would be smaller. This study can provide decision-making basis for sustainable development of Jinjiang Basin.

The Intra-Annual Variability of Discharge, Sediment Load and Chemical Flux from the Monitoring: The Yukon River, Alaska

The covered-ice breakup in subarctic to arctic rivers in the early snowmelt season often gives any damage to instruments monitoring physical and chemical factors of water. The serious condition has brought few time series data during the snowmelt runoff except the river stage or discharge. In this study, the contribution of snowmelt runoff to the discharge and sediment load is quantified by monitoring water turbidity and temperature at the lowest gauging station of U. S. Geological Survey in the Yukon River, Alaska, for more than 3 years (June 2006 to September 2009). The turbidity was recorded by a self-recording turbidimeter with a sensor of infrared-ray back-scattering type, of which the window is cleaned by a wiper just before a measurement. The turbidity time series, coupled with frequent river water sampling at mid-channel, produce time series of suspended sediment (SS) concentration, particulate organic carbon (POC) concentration and particulate organic nitrogen (PON) concentration (mg?L–1) by using the high correlation (R2 = 0.747 to 0.790;P 11 to 2.01 × 1011 m3), 8.7% - 22.5% of the annual sediment load (3.94 × 107 to 5.08 × 107 ton), 11.6% - 23.7% of the annual POC flux (4.05 × 105 to 4.77 × 105 ton), and 10.3% - 24.5% of the annual PON flux (2.80 × 104 to 3.44 × 104 ton). In the snowmelt season, the peak suspended sediment concentration preceded the peak discharge by a few days. This probably results from the fluvial sediment erosion in the river channels.

Impact of Land Use and Land Cover Changes on Surface Runoff and Sediment Yield in the Little Ruaha River Catchment

Little Ruaha River catchment (6370 Km2) in the Southern Agricultural Growth Corridor of Tanzania (SAGCOT), is one of the country’s most significant waterways due to its ecological composition and economic value. Regardless of its ecological and economical value, the regional hydrologic condition has been tremendously affected due to land uses alteration, influenced by different socio-economic factors. This study aimed to understand the associated impacts of the present Land Use Land Cover (LULC) change on the surface runoff and sediment yield in the Little Ruaha River Catchment. Hydrological modelling using Soil and Water Assessment Tool (SWAT Model) was done to quantify the impact of land use and land cover dynamics on catchment water balance and sediment loads. The calibration and validation of the SWAT model were performed using sequential uncertainty fitting (SUFI-2). The results showed that, for the given LULC change, the average annual surface runoff increased by 2.78 mm while average annual total sediment loading increased by 3.56 t/ha, the average annual base flow decreased by 2.68 mm, ground water shallow aquifer recharge decreased from 2.97 mm and a slight decrease in average annual ground water deep aquifer recharge by 0.14 mm. The model predicts that in the future, there will be a further increase in both surface runoff and sediment load. Such changes, increased runoff generation and sediment yield with decreased base flow have implications on the sustenance flow regimes particularly the observed reduced dry season river flow of the Little Ruaha River, which in turn cause adverse impacts to the biotic component of the ecosystem, reduced water storage and energy production at Mtera Hydroelectrical dam also increasing the chances of flooding at some times of the year. The study recommends land use planning at the village level, and conservation agricultural practices to ameliorate the current situation. Developing multidisciplinary approaches for integrated catchment management is the key to the sustainability of Little Ruaha River catchment.

Applications of AnnAGNPS Model for Sediment and Nutrient Loadings for Funiu Mountain Area, China

The main goal of this study was to evaluate the performance of AnnAGNPS(Annualized AGricultural NonPoint Source)pollution model,in calculating runoff,sediment loading and nutrient loadings for Funiu Mountain area.Most of the model input parameters were sourced from Luanchuan Forest Ecology Station(LFES)in Funiu Mountain area.The data on 23 storms in 2018 was used to calibrate the model and the data on 33 storms in 2019 for validation.The whole evaluation consisted of determining the coefficient of determination(R^(2)),Nash-Sutcliffe coefficient of efficiency(E),and the percentage volume error(VE).Results showed that the runoff volumes were underpredicted by 5.0%with R^(2) of 0.93(P<0.05)during calibration and underpredicted by 5.3%with R^(2) of 0.90(P<0.05)during validation.But sediment loading was able to produce a moderate result.The model underpredicted the daily sediment loading by 15.1%with R^(2) of 0.63(P<0.05)during calibration and 13.5%with R^(2) of 0.66(P<0.05)during validation.Nitrogen loading was overpredicted by 20.3%with R^(2)=0.68(P<0.05),and phosphorus loading performance was slightly poor with R^(2)=0.65(P<0.05)during validation.In general,the model performed well in simulating runoff compared to sediment loading and nutrient loadings.

Vertical distribution of sediment concentration

A simple formula is proposed to predict the vertical distribution of a suspended load concentration in a 2D steady turbulent flow. The proposed formula significantly improves the well-known Rouse formula where sediment concentration has an infinitely large value at the channel bottom and a zero value at the water surface. Based on this formula and the logarithmic ve- locity profile, a theoretical elementary function for the transport rate of a suspended load is developed. This equation improves the Einstein equation in which the unit-width suspended sediment discharge must be solved by numerical integration and a contra- diction between the lower limit of the integral and that of velocity distribution exists.

Effects of soil conservation practices on soil erosion and the size selectivity of eroded sediment on cultivated slopes

Soil conservation practices can greatly affect the soil erosion process,but limited information is available about its influence on the particle size distribution(PSD)of eroded sediment,especially under natural rainfall.In this study,the runoff,sediment yields,and effective/ultimate PSD were measured under two conventional tillage practices,downhill ridge tillage(DT)and plat tillage(PT)and three soil conservation practices,contour ridge tillage(CT),mulching with downhill ridge tillage(MDT),and mulching with contour ridge tillage(MCT)during 21 natural rainfall events in the lower Jinsha River.The results showed that(1)soil conservation practices had a significant effect on soil erosion.The conventional tillage of DT caused highest runoff depth(0.58 to 29.13 mm)and sediment yield(0.01 to 3.19 t hm^(-2)).Compared with DT,the annual runoff depths and sediment yields of CT,MDT and MCT decreased by 12.24%-49.75%and 40.79%-88.30%,respectively.(2)Soil conservation practices can reduce the decomposition of aggregates in sediments.The ratios of effective and ultimate particle size(E/U)of siltand sand-sized particles of DT and PT plots were close to 1,indicating that they were transported as primary particles,however,values lower/greater than 1 subject to CT,MDT and MCT plots indicated they were transported as aggregates.The ratios of E/U of claysized particles were all less than 1 independently of tillage practices.(3)The sediments of soil conservation practices were more selective than those of conventional tillage practices.For CT,MDT and MCT plots,the average enrichment ratios(ERs)of clay,silt and sand were 1.99,1.93 and 0.42,respectively,with enrichment of clay and silt and depletion of sand in sediments.However,the compositions of the eroded sediments of DT and PT plots were similar to that of the original soil.These findings support the use of both effective and ultimate particle size distributions for studying the size selectivity of eroded sediment,and provide a scientific basis for revealing the erosion mechanism in the purple soil area of China.

Sediment yield and erosion–deposition distribution characteristics in ephemeral gullies in black soil areas under geocell protection

Investigating the effect of geocells on the erosion and deposition distribution of ephemeral gullies in the black soil area of Northeast China can provide a scientific basis for the allocation of soil and water conservation measures in ephemeral gullies.In this study,an artificial simulated confluence test and stereoscopic photogrammetry were used to analyze the distribution characteristics of erosion and deposition in ephemeral gullies protected by geocells and the effect of different confluence flows on the erosion process of ephemeral gullies.Results showed that when the confluence flow was larger,the effect of geocell was more evident,and the protection against ephemeral gully erosion was stronger.When the confluence flow rates were 0.6,1.8,2.4,and 3.0 m^(3)/h,ephemeral gully erosion decreased by 37.84%,26.09%,21.40%,and 35.45%.When the confluence flow rates were 2.4 and 3.0 m^(3)/h,the average sediment yield rate of the ephemeral gully was close to 2.14 kg/(m^(2)•min),and the protective effect of ephemeral gully erosion was enhanced.When the flow rate was higher,the surface fracture of the ephemeral gully was more serious.With an increase in confluence flow rate,the ratio of erosion to deposition increased gradually,the erosion area of ephemeral gullies was expanded,and erosion depth changed minimally.In conclusion,geocell measures changed erosion patterns by altering the rill erosion/deposition ratio,converting erosion from rill erosion to sheet erosion.

The response of sedimentary record to catchment changes induced by human activities in the western intertidal flat of Yalu River Estuary,China

The response to the catchment changes of the sedimentary environment of the western intertidal flat of Yalu River Estuary was investigated by analyzing the vertical variations of the grain size of sediment cores,along with the hydrologic data and human activities in the catchment.The results demonstrated a stepwise decreasing trend for the variations of both the sediment load and water discharge into the sea,which could be divided into three stages as 1958–1970,1971–1990 and 1991–2009.Reservoir construction and the changes of catchment vegetation coverage turned out to be the two predominant contributors to the changes.There are four periods for the variation of the sensitive components of the sediment cores from 1940 to 2010,i.e.,1940–1950,1951–1980,1981–1990 and 1991–2010.The vertical distribution of grain size in the cores mainly varied with the changes of vegetation coverage in the catchment and reservoir construction from 1960 to 1980,whereas it varied depending on the intensity of water and soil erosion in the catchment from 1980 to 1990.Despite the further reduction of the water and sediment input into the sea from 1990 to 2009,this period was characterized by coarsening trends for the grain size of sediment in the estuarine intertidal flat and correspondingly,the significantly increased silt contents of the sensitive component.

Evaluating soil erosion and runoff dynamics in a humid subtropic, low stream order, southern plains watershed from cultivation and solar farm development

Much work has been done to understand and improve soil and water conservation where agriculture has driven land use intensification.Less is known about soil-and water-related impacts from intensification driven by solar farming,especially at watershed-scales.Here we employed Hydrologic Engineering Center's Hydrologic Modeling System(HEC-HMS)to model Pond Creek,a rural watershed in Texas,USA.Land use is primarily crop cultivation and secondarily pasture for cattle grazing.Presently,several industrial-scale projects are planned to convert≈15–30%of Pond Creek from agriculture to solar farms.The model was parameterized using public data sources and information from local stakeholders,then calibrated to several historical precipitation events.Experiments were conducted by varying precipitation depth,duration,and land uses:native vegetation pre-cultivation(control),cultivation(current),current conditions with 15%solar farm conversion(solar),and current conditions with 30%solar farm conversion(solar x2).Shifting to solar farming led to significant increases in cumulative sediment load(+12%–30%),with no significant differences in peak discharge rate changes(+0.38%–4%).Comparison to soil loss tolerance values showed current and solar treatment erosion rates exceeded tolerance values between 0.17 and 2.29 tons per hectare and all treatments were significantly different than the native treatment.We discuss high leverage strategies applicable to solar farm development sites as well as watersheds where they reside.Accelerating demand for land for renewable energy such as solar farming warrants greater attention from the soil and water conservation community to anticipate and mitigate impacts across landscapes.

Pollutant concentrations and pollution loads in stormwater runoff from different land uses in Chongqing

To investigate the distribution of pollutant concentrations and pollution loads in stormwater runoff in Chongqing,six typical land use types were selected and studied from August 2009 to September 2011.Statistical analysis on the distribution of pollutant concentrations in all water samples shows that pollutant concentrations fluctuate greatly in rainfall-runoff,and the concentrations of the same pollutant also vary greatly in different rainfall events.In addition,it indicates that the event mean concentrations （EMCs） of total suspended solids （TSS） and chemical oxygen demand （COD） from urban traffic roads （UTR） are significantly higher than those from residential roads （RR）,commercial areas （CA）,concrete roofs （CR）,tile roofs （TRoof）,and campus catchment areas （CCA）;and the EMCs of total phosphorus （TP） and NH3-N from UTR and CA are 2.35-5 and 3 times of the class-III standard values specified in the Environmental Quality Standards for Surface Water （GB 3838-2002）.The EMCs of Fe,Pb and Cd are also much higher than the class-III standard values.The analysis of pollution load producing coefficients （PLPC） reveals that the main pollution source of TSS,COD and TP is UTR.The analysis of correlations between rainfall factors and EMCs/PLPC indicates that rainfall duration is correlated with EMCs/PLPC of TSS for TRoof and TP for UTR,while rainfall intensity is correlated with EMCs/PLPC of TP for both CR and CCA.The results of this study provide a reference for better management of non-point source pollution in urban regions.

疏勒河流域径流量和输沙量变化规律

[目的]探索疏勒河流域水沙变化特性,可为国家实施西部生态安全战略提供科学支撑。[方法]基于疏勒河流域昌马堡、潘家庄、党城湾3个水文站的实测径流量和输沙量序列资料,运用滑动平均、Mann-Kendall突变趋势检验和小波分析法等方法,分析了疏勒河流域径流量和输沙量变化规律。[结果]疏勒河流域年径流量和年输沙量均呈递增趋势,且输沙量增大趋势大于径流量,昌马堡、潘家庄、党城湾3个水文站径流量分别在1999年、2016年、1982年发生突变,昌马堡和潘家庄年输沙量突变均发生在1998年,党城湾输沙量没有突变;疏勒河流域3个代表站的径流量和输沙量都呈现出多时间尺度的演化特征,昌马堡径流量主周期为58 a,31 a,14 a,9 a和5 a,输沙量主周期为48 a,23 a,14 a,7 a和5 a,潘家庄径流量主周期为59 a,32 a,14 a,输沙量主周期为37 a,14 a,8 a和5 a,党城湾径流量主周期为42 a和5 a,输沙量主周期为16 a和8 a。[结论]疏勒河流域水沙总体呈递增趋势,且存在明显的周期变化,除党城湾的输沙量没有突变发生以外,其余站点水沙均有突变发生,同一水文站输沙量的突变的发生滞后于径流量的突变。

北方主要河流水沙变异及其成因

为研究我国北方河流的水沙变异及主要成因,本文利用M-K检验法和水文量累积曲线法,分析了1950—2020年我国北方河流代表站径流量和输沙量的变化特征,探讨了影响北方河流水沙变化的主要因素。结果表明,淮河代表站年径流量没有明显的变化趋势,其他北方河流的年径流量具有减小或显著减小趋势;松花江代表站年输沙量无趋势变化,其他北方河流代表站年输沙量都有显著减少趋势;影响北方河流水沙变化的主要因素包括水土保持、水库拦沙、流域降水变化、引水引沙与泥沙综合利用、工程建设等,其中水土保持是北方河流流域保水减沙的主要措施,水库拦沙在江河水沙态势变异中发挥重要作用,流域降水变化也是北方河流水沙变异的影响因素,引水引沙与泥沙综合利用也对北方平原河流水沙变化发挥一定的作用。

黄河上游近60年水沙变化特征及其影响因素

由于受人类活动及气候变化影响,黄河上游干流水沙特征发生显著变化。为探究黄河上游水沙变化情况,基于黄河上游5个水文站19642019年水沙、遥感影像等数据,利用Mann-Kendall检验法、滑动t检验法、累积距平曲线和双累积曲线等突变检验方法和小波分析法,对黄河上游水沙变化特征进行研究。利用水沙关系曲线及线性回归法等方法估算人类活动和气候对水沙变化的贡献率,并着重讨论梯级水库建设及土地利用变化对水沙的影响。结果表明:1)黄河上游玛曲-小川段流域内降雨量和径流量变化幅度不明显,贵德站、循化站、小川站19862019年年均输沙量分别减至19641985年的9.8%、24.6%、38.8%,输沙量大大减少。黄河上游玛曲-小川段径流量突变多在1986年,输沙量突变多在1969、1986、2004年,径流量存在8、16、22 a周期,输沙量存在4~8、18~21、27 a周期。2)1969年后,河流输沙能力增强,水沙关系显著改变。在不同时段内,人类活动对径流量变化在19872019年贡献率为66.3%,对输沙量变化在19701986、19872004、20052019年的贡献率为72.96%、70.73%、69.7%。人类活动对黄河上游干流水沙影响占据主导因素。3)刘家峡水库淤积最为严重,单库运行期水库淤积量为2.39亿t,排沙比变化范围为1.39%~10.7%。梯级水库联调使得径流量在19642004年间减少47.8%,19642019年间梯级水库减沙94.8%,梯级水库对输沙量影响远大于对径流量的影响。4)19802020年间,草地面积增加了1880.03 km 2,增幅3.1%,有利于减少输沙量,草地拦沙效益大于截流效益。

渭河径流输沙变化及其对降水和人类活动的响应

[目的]探究渭河径流量与输沙量的变化特征及其驱动因素,为渭河流域水资源管理和生态环境建设提供科学依据。[方法]利用渭河流域降水量数据以及华县和状头两个控制水文站1957—2019年实测径流量及输沙量资料,采用现代数理统计方法,分析渭河流域年降水量、径流量和输沙量的变化趋势,检测水文要素的突变年份,计算了渭河径流量和输沙量变化的驱动因素贡献率,最后探讨了人类活动对渭河径流、输沙变化的主要影响因素。[结果]渭河1957—2019年径流量和输沙量都呈现出极显著的减少趋势(p<0.01);年降水量随机波动,没有明显的变化趋势。年径流量在1990年发生突变(p<0.01),年输沙量在1996年发生突变(p<0.01)。降水因素对渭河流域径流量减少贡献率为19%,对输沙量减少贡献率为17%;人类活动对径流量减少的贡献率为81%,对输沙量减少的贡献率为83%。[结论]人类活动在渭河径流和输沙的变化过程中具有决定性的影响,是导致渭河径流、输沙减少的主要原因。

窟野河流域水沙变化及其驱动因素

[目的]探究窟野河流域径流和输沙变化特征,量化气候变化及人类活动对流域水沙变化的贡献,以期为窟野河流域水资源合理利用和水土保持措施的优化配置提供科学依据。[方法]基于窟野河流域新庙、王道恒塔、神木和温家川水文站1960—2020年径流、输沙及降雨资料,采用线性趋势法、Mann-Kendall趋势检验和Pettitt突变检验法分析了流域径流输沙时空变化特征,结合双累积曲线法定量分析了不同时期气候变化与人类活动对河流水沙变化的贡献。[结果]窟野河流域1960—2020年径流输沙均呈现极显著减少趋势(p<0.01),新庙、王道恒塔、神木和温家川4站径流量减少速率分别为0.024亿m^(3)/a,0.034亿m^(3)/a,0.081亿m^(3)/a,0.106亿m^(3)/a,输沙量减少速率分别为43.8万t/a,69.3万t/a,160.3万t/a,272.1万t/a,且各水文站年径流量和输沙量均在1979年、1996年发生突变,由此可将径流输沙序列划分为基准期(1960—1979年,P 1期)和变化期(1980—1996年,P 2期;1997—2020年,P 3期)。研究时段内不同子流域多年平均径流深和输沙模数均呈减小趋势,但在空间上存在差异。[结论]流域不断增强的人类活动(水利水保措施与煤矿开采等)是窟野河流域水沙变化的主导因素,相较基准期,各水文站径流输沙量在P 2期、P 3期均减少,且P 3期减少幅度更剧烈,不同水文站在P 2和P 3期内,人类活动对径流输沙减少的贡献高于降雨变化。

基于Copula函数的嘉陵江流域水沙丰枯遭遇关系探究

为了深入了解嘉陵江水沙关系的变化规律。基于嘉陵江出口北碚水文站1965-2022年的年径流量和年输沙量资料,利用Mann-Kendall检验法、双累积曲线法并结合物理成因法诊断水沙关系的变异点,通过AIC、BIC、RMSE对径流量和输沙量的边缘分布函数和Copula函数进行优选,确定最优Copula函数并建立嘉陵江流域水沙联合分布模型,运用模型对流域内水沙丰枯遭遇概率、联合和同现重现期进行计算,进而对比分析水沙单变量和联合变量设计值。结果表明:①水沙关系在1989年发生突变,变异前的水沙相关性强于变异后的水沙相关性;②1965-1989年阶段水沙序列最优边缘分布都为Logn,最优水沙联合分布模型为Gumbel Copula模型。1990-2022年阶段径流量和输沙量的最优边缘分布分别为Gamma、GP,最优水沙联合分布模型为Frank Copula模型;③2个阶段水沙序列同步概率分别是59.77%、61.14%,均大于异步概率,且出现极端情况“水丰沙枯”、“水枯沙丰”类型的概率极低,表明水沙概率存在较大的相关性,来水来沙条件相对稳定;④联合变量设计值大于单变量设计值,通过两变量联合分布计算的径流量和输沙量设计值更加可靠。水沙联合重现期集中在2年附近,同现重现期绝大部分小于50年。通过探讨嘉陵江流域来水来沙联合变化特征,可为流域的水沙调控、防灾减灾等工作提供参考。