Equilibrium sediment transport in lower Yellow River during later sediment-retaining period of Xiaolangdi Reservoir

The Xiaolangdi Reservoir has entered the later sediment-retaining period, and new sediment transport phenomena and channel re-estab- lishing behaviors are appearing. A physical model test was used to forecast the scouring and silting trends of the lower Yellow River. Based on water and sediment data from the lower Yellow River during the period from 1960 to 2012, and using a statistical method, this paper analyzed the sediment transport in sediment-laden flows with different discharges and sediment concentrations in the lower Yellow River. The results show that rational water-sediment regulation is necessary to avoid silting in the later sediment-retaining period. The combination of 3 000 m^3/s 〈 Q 〈 4 000 m^3/s and 20 kg/m^3 〈 S 〈 60 kg/m^3 （where Q is the discharge and S is the sediment concentration） at the Huayuankou section is considered an optimal combination for equilibrium sediment transport in the lower Yellow River over a long period of time.

Attribution analysis of groundwater level fluctuation in the Xinxiang section of the Lower Yellow River's suspended river after the construction of the Xiaolangdi Reservoir

The clear identification and quantification of the factors affecting groundwater systems is crucial for protecting groundwater resources and ensuring safety in agricultural production.The Lower Yellow River(LYR)is a suspended river that replenishes groundwater continuously due to clear differences in the water head,especially in the Xinxiang section.Since its construction,the Xiaolangdi Reservoir has reversed the LYR’s deposition.To accurately determine the factors influencing the groundwater level(GWL),the study area was divided into five subzones based on hydrogeology.A dynamic factor model(DFM),variational mode decomposition(VMD),and a multiple linear regression model were used to identify and quantify the factors influencing the GWL.The impact of the suspended river on the groundwater before and after the construction of the Xiaolangdi Reservoir was examined.The results show that:(1)The rate of decrease in the GWL was 8.53×10^(–4)m/month,and the rate of decrease in the Yellow River water level(RWL)was 4.63×10^(–4)m/month.(2)Mountain front recharge(MFR)(scale=3 months)and precipitation(scale=9 months)were the dominant factors in subzones I and II,accounting for more than 40%of the fluctuation in the GWL.Subzone III was dominated by exploitation(scale=7 months)and precipitation(scale=12months),accounting for 28.43%,and 23.44%of changes in the GWL,respectively.In subzone IV,agricultural irrigation(scale=12 months)was the major factor,accounting for32.47%of GWL changes,while in subzone V,the RWL(scale=12 months)accounted for52.52%of these changes.(3)The Xiaolangdi Reservoir has increased the lateral seepage of the suspended river and altered the inter-annual distribution.The results of this study can provide a valuable reference for controlling groundwater overexploitation and ensuring water supply security.

Adjustment in the main-channel geometry of the lower Yellow River before and after the operation of the Xiaolangdi Reservoir from 1986 to 2015

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.

MATHEMATICAL MODEL OF RIVER BED CHANGE DOWNSTREAM OF XIAOLANGDI RESERVOIR

A mathematical model of river be d change downstream of the Xiaolangdi Reservoir was developed based on the most recent achievement of sediment theory in the Yellow River. The model was verified by the comparison of computed results and measured data from 1986 to 1996. Num erical prediction of the erosion and deposition downstream of the Xiaolangdi Res ervoir in its first operation year was carried out, and a series of suggestions were given for reservoir operation mode in its early operation period.

基于不同评价方法的小浪底水库水质分析及来源解析

水质评价是水生态系统保护和水污染治理的重要基础。为探究小浪底水库不同水期水质特征,于2021年对3个断面的15个水质指标进行监测与分析。采用三种方法对研究区水环境质量进行评价,厘清水质变化规律,确定最佳的评价方法,探讨不同水期影响水质的关键环境因子并解析其来源。研究表明:库区水质总氮浓度超出地表水Ⅴ类标准,其他水质指标均达到Ⅲ类标准及以上;三种方法受指标权重影响,评价结果存在差异,综合比较与分析,确定基于TOPSIS的信息加权和排序法更适用于评价研究区水质状况;相关性分析表明,不同水期影响水质的环境因子及其来源不同,枯水期受人类活动影响,平水期水质变化与上游输入有关,丰水期受降水和水动力条件影响显著。研究结果可为小浪底水库的水环境治理提供科学依据,为库区水质评价提供新的思路。

小浪底水库减淤调度模式探讨

小浪底水库在黄河中下游防洪格局中发挥着重要作用,长期保持库区较大库容、延长拦沙运用期,对黄河防洪保安具有重大意义。基于小浪底水库运用以来入库水沙条件变化以及调度实践分析,提出了近期小浪底水库减淤调度模式:前汛期洪水期考虑下游河道淤积和主槽过流能力,尽量利用大流量过程开展降低水位排沙运用,冲刷库区河槽新增淤积物,以恢复河槽过流能力,保持库区高效输沙通道;水库排沙运用过后,运用水位宜不高于库区较大滩地滩面,利用河槽输沙调沙能够有效减缓滩面淤积;后汛期在保证防洪安全的前提下,根据上游来沙情况择机开展水库回蓄,尽早将库水位蓄至HH37断面附近滩面以上,利用HH37断面以上库段临时调沙,减缓滩面淤积。

基于Sentinel-2多光谱遥感影像的小浪底水质反演

多光谱遥感技术可根据遥感波段信息反演水质参数,降低监测成本,提高监测速度和质量,为大范围水环境监测提供了一种新的方法。通过分析小浪底水库的Sentinel-2多光谱影像以及采样点实测水质数据,建立了最佳光谱波段的水质参数反演模型,对小浪底水库的化学需氧量(COD)、总磷(TP)、总氮(TN)和氨氮(NH_3-N)进行了遥感反演,验证了反演模型的精确度和稳定性,并反演了各水质参数的空间分布规律。结果表明:在4种水质参数反演模型中,COD模型精确度和稳定性最高,其次是TP、TN,最低的是NH_3-N,水库出水口和部分边缘COD质量浓度较高,水库中心TN、TP和NH_3-N质量浓度高于边缘处。

小浪底水库汛前调水调沙模拟与综合效益评估

为提高汛前调水调沙期多目标博弈过程中小浪底水库的综合效益,本文构建了调水调沙模拟与综合效益定量评估数学模型。该模型由3个模块构成,其中:水沙计算模块考虑库区明流与异重流输移及干支流倒回灌过程,水库调度模块衔接库区水沙计算和坝下泥沙冲淤计算,效益评价模块采用经济效益指标衡量水库的综合效益。采用2013年和2014年汛前调水调沙过程对该模型开展了参数率定和验证工作,计算结果可模拟异重流潜入、演进、出库的全过程以及水库调度和发电过程。根据历年调水调沙实践经验选取关键调度参数,最终拟定降低对接水位或减小壅水程度的5种方案,采用模型对各方案展开调水调沙过程计算和综合效益评价。结果表明,调度过程中改变对接水位和壅水程度在减淤效益和兴利效益间存在冲突。通过比较综合经济效益指标,最终推荐对接水位为222.57 m并减小库区壅水的方案作为优选方案,可获得最大的综合效益。

洪水期小浪底水库排沙影响因素及规律研究

小浪底水库排沙主要集中在汛前调水调沙期和汛期洪水期。2000—2022年汛前调水调沙期和汛期洪水期小浪底水库累计排沙分别为4.840亿t和21.546亿t,分别占水库运用以来排沙总量的18.3%、81.5%。研究表明,入库水量与回水长度是影响汛前调水调沙期小浪底水库排沙效果的主要因素;入库水量越大,回水长度越短,排沙效果越好。通过多元回归得到了汛前调水调沙期小浪底水库排沙量与影响因素的关系。汛期洪水期小浪底水库排沙主要影响因素为壅水指标和进出库流量比,通过研究量化了汛期洪水期排沙比与影响因素的关系。

小浪底水库运行下花园口河段黄河鲤生态流量研究

【目的】大坝和水库等水利工程的修建在带来防洪减灾效益的同时,也给所在区域的水生生物栖息繁衍带来了一定影响,诊断关键水生生物的生态流量对大坝下游的生态环境修复工作具有重要意义。【方法】以黄河下游花园口河段为例,探讨了小浪底水库运行下不同流量情景下的黄河鲤栖息地质量情况,并由此推求黄河鲤的生态流量。基于栖息地模拟法,通过构建耦合栖息地适宜度模型的二维水动力模型,分析了黄河鲤鱼苗期、亲鱼期的栖息地适宜度指数空间分布,分别建立了黄河鲤两个生命阶段流量与栖息地加权可用面积关系曲线。【结果】结果表明:随着模拟流量的增大,黄河鲤不同生命阶段的栖息地适宜度指数空间分布及栖息地加权可用面积呈现先增加,达到峰值后逐渐减小的变化规律。【结论】黄河下游花园口河段的最小生态流量为1 150 m~3/s,适宜生态流量为1 450 m~3/s,最适宜生态流量为3 000 m~3/s,研究成果加深了对大流量情景下黄河鲤栖息地质量的认识,对黄河下游生态保护与修复具有重要意义。

基于SA-NSGA-Ⅱ算法的水库多目标优化调度研究

针对带精英策略的快速非支配排序遗传算法NSGA-II求解多目标优化问题时存在局部搜索能力较差的缺陷,提出一种基于逐次逼近方法改进的快速非支配排序遗传算法(SA-NSGA-Ⅱ),该算法通过不断调整搜索空间来减小不可行域和支配解占比,从而增强局部搜索能力,快速逼近Pareto真实前沿。以平均出力最大和下游河道适宜生态流量改变度最小为目标,建立小浪底水库多目标优化调度模型,分别采用SA-NSGA-Ⅱ和NSGA-Ⅱ求解模型并比较优化效果。结果表明,在两种算法求解模型生成的混合Pareto前沿中,SANSGA-Ⅱ、NSGA-Ⅱ所生成的Pareto前沿点分别占比80.45%、19.55%;SA-NSGA-Ⅱ、NSGA-Ⅱ生成的Pareto前沿中,分别有86.90%、52.67%的点处于非支配地位,且SA-NSGA-Ⅱ较NSGA-Ⅱ的算法运算时间减少了15.32%。因此,在相同初始条件下,SA-NSGA-Ⅱ的优化效果优于NSGA-Ⅱ,验证了SA-NSGA-Ⅱ在水库多目标优化调度中的适用性。

小浪底水库对接时机与对接水位的库区调控效应

如何运用水库群联合调度发挥最大的排沙效益是水沙调控的关键技术难题。选择2023年汛前黄河调水调沙时期三门峡水库和小浪底水库联合调度运用为对象,分析两库不同对接时机与对接水位的小浪底水库进出库水沙过程,量化两库间不同对接时机与对接水位的水沙调控效应。三门峡水库自身蓄水量较小、调水能力有限,通过改变三门峡泄流出库时机,产生的小浪底库区冲刷效果差异较大。随着对接水位的降低,库区冲刷量逐渐增加。随着三门峡水库相对起泄时间的推迟,库区冲刷量呈现先增加后减少的趋势。

考虑多源入库水出库水的三门峡-小浪底水库汛期联合优化调控

三门峡-小浪底水库联合运用是黄河调水调沙的关键环节。为更好地发掘三门峡和小浪底水库联合优化调控的潜力,提升水沙调控效果,以汛期来水较多的2020年为例,分析了三门峡和小浪底水库库区降雨、蒸发、支流来水、取用水等入库水和出库水过程,以发电和排沙综合效益为目标函数,建立了考虑多源入库水出库水的三门峡-小浪底水库联合优化调度模型,开展了水沙优化调控研究。研究成果表明:1)库区降雨、蒸发、支流来水及取用水等次要入库水出库水对三门峡水库和小浪底水库水量的贡献分别为2.71亿m^(3)和-0.85亿m^(3)。其中,入库水量主要集中于汛期,而出库水量在全年分布相对均匀。2)三门峡库区的次要入库水出库水量占库容的36%左右,将对三门峡-小浪底水库联合优化调控产生影响。3)考虑多源入库水出库水的三门峡-小浪底水库联合优化调控的排沙量有所增加,小浪底水库的汛期发电效益增加约2599.4万元。

小浪底水库水体时空变化特征与驱动因素分析

以2018-2021年Sentinel-2遥感影像为数据源,利用Google Earth Engine (GEE)云平台研究小浪底水库月尺度水体面积的时空变化。结果表明,2018-2021年小浪底水库水体面积月际变化波动较大,每年均呈先降后升的趋势,具有显著的季节性变化规律,夏季汛期防洪降低库容,冬季蓄水增加库容保证生产生活用水;小浪底库区存在约85.29 km2的永久性水体,占总面积的34.84%,出现水陆变化的区域集中于水库边缘区域;气温、降水是水体变化的驱动因素,水体面积与月平均气温、月降水量呈负相关关系。研究结果表明,以GEE云平台为基础的连续时间序列、大范围水体动态变化监测存在可行性。

权衡生态和发电目标的梯级水库强化学习模型及其应用

为更好地发挥经济及生态效益,建立了基于强化学习算法的梯级水库优化调度模型,以周尺度小浪底天然入库流量过程为基础,探讨梯级水库发电与生态目标之间的权衡,并将该模型应用于小浪底-西霞院梯级水库中,分别探讨了不同调度方案下发电最优、生态最优和发电-生态权衡的优化调度策略。结果表明,以发电最优为目标时,梯级水库多年平均发电量比常规调度增加了3.62%~7.92%;以生态最优为目标时,平均生态保证率比常规调度增加了31.68%~33.66%。结果为梯级水库多目标优化调度提供了一种可行方法。

延长小浪底水库拦沙运用年限对黄河防洪保安的重大意义

小浪底水库是黄河下游防洪保安的核心工程,水库拦沙期是防洪减淤效益发挥最为显著的时期。分析新形势下黄河下游防洪保安对小浪底水库运用的新要求,指出尽可能延长小浪底水库拦沙运用年限,使水库长时期保持较大的有效库容,尤其是防洪库容,具有重大战略意义。研究表明,较大的库容处理大洪水的能力强,有利于预防“黑天鹅”降雨事件;水库防洪运用后滩库容损失小,有利于水库长期保持较强的防洪能力;水库拦沙库容与调水调沙库容结合利用,可明显增强调水调沙活力,为古贤水库投入运用后发挥水沙调控体系整体合力创造库容条件;拦沙库容用于下游滩区防洪,有利于提升滩区防洪标准,降低滩区中常洪水漫滩损失。优化水库调度运用方式、实施水库清淤、尽快建设古贤水利枢纽工程等是延长小浪底水库拦沙年限的重要措施。

大型水库运用对河口尾闾河道出汊的影响研究

为定量研究大型水库运用对河口尾闾河道出汊的影响,以黄河口尾闾段为研究对象提出了一种基于改进熵权法的河道出汊阈值确定方法,根据实测水沙资料确定了尾闾河道出汊指标计算公式及相应的河道出汊阈值,在还原无小浪底工程时尾闾段水沙及河槽形态调整过程的基础上,结合出汊阈值对比分析了有、无小浪底工程时尾闾段发生河道出汊概率的差异。结果表明:河段河相系数和汛期平均水流冲刷强度分别为边界和水沙条件中对河道出汊贡献最大的两个指标;黄河口尾闾段河道出汊阈值为38.16,当出汊指标大于38.16时尾闾段发生河道出汊;小浪底工程运用约束了进入尾闾段的沙量,河道出汊概率明显减小。

遗传算法在黄河水沙监测中的应用

为了及时掌握黄河水沙通量的动态变化情况,最大程度地减少黄河水沙监测成本,本文基于黄河小浪底水库下游的某水文站水沙通量的实时监测数据,首先建立了决策树模型预测该水文站未来两年水沙通量的变化趋势,然后利用遗传算法制订了未来两年的最优监测方案。研究结果表明,运用遗传算法求解制定的监测方案能在减少监测次数的同时有效监测水沙通量的突变点和变化趋势,平均降低69.77%的监测成本。

小浪底水库调控后黄河下游冲淤规律与水沙调控指标

为科学指导黄河调水调沙调度实践,根据小浪底水库调控后黄河下游冲淤规律对水沙调控指标进行优化。选取2011—2022年黄河下游实测121场不同含沙量级水沙过程,分析黄河下游水沙特点及其冲淤效率与水沙条件的响应关系,以黄河下游不淤积以及主槽过流能力不降低为总体目标提出水沙调控指标。结果表明:①小浪底水库对黄河下游水沙过程具有两极分化的调控作用,高含沙量水流(平均含沙量S av>10 kg/m^(3))的沙量全年占比为94%,清水水流(S av<1 kg/m^(3))的水量全年占比为85%。②高含沙量水流的淤积效率与平均含沙量呈正相关线性关系。③清水水流的冲刷效率与平均流量呈正相关对数关系。④对于高含沙量水流,丰水年调控水量为80亿m^(3),平均流量为2000~4600 m^(3)/s,平均含沙量为50 kg/m^(3);平水年调控水量为10亿m^(3),平均流量为2000~4600 m^(3)/s,平均含沙量为150 kg/m^(3);枯水年水库不排沙。对于清水水流,需要避免下泄平均流量在800~1800 m^(3)/s范围内的水流过程。

生态文明视角下小浪底水库漂浮物管控探析

漂浮物的存在影响小浪底水库水生态、水环境和水质,同时影响泄洪和发电设备安全运行,管控好漂浮物是水库安全稳定运行的现实需求。研究小组通过分析漂浮物种类和运移特性,借鉴国内外大中型水库漂浮物管控治理经验,按照黄河流域生态保护和高质量发展的要求,结合小浪底水库实际情况,提出了“管、捞、拦、排、用”的漂浮物优化管控建议。