The Yellow River (YR) is famous for its 'hanging river' due to high sedimentation rate in the lower reach. The reservoir sediment retaining (RSR) and water-sediment regulation (WSR) of the Xiaolangdi Reservoir (XLDR) contribute to mitigating the siltation and adjusting the bankfull channel geometry in the lower Yellow River (LYR). However, few studies have been conducted to quantify the contribution of RSR and WSR to the medium-sized channel shaping. In this paper, we analyzed the temporal and spatial variations of bankfull discharge in the LYR, established empirical expressions between the bankfull discharge and the previous five-year average discharge above 2,000 m(3)/s and the incoming sediment coefficient during flood seasons, and constructed three different water and sediment scenarios to quantify contribution of WSR of the XLDR to the medium-sized channel shaping in the LYR. Calculated results indicated that the contribution of WSR to the recovery of medium-sized channels increased with time and became stabilized eventually. Along the LYR, such contribution also increased and eventually became stabilized in narrow reaches, reaching over 90%. The results will lay a solid technical foundation for the WSR of the XLDR, river regulation downstream of the reservoir, and sediment disposal of the YR.

针对大北干流晋陕河段河道采砂存在的问题,根据防洪、河势、环境敏感区、涉河工程等对河道采砂的要求,进行三区划分,提出禁采区控制性指标和禁采期,充分考虑大北干流河道特点和泥沙补给情况,确定年度采砂控制总量,在充分吸纳各级河道管理部门采砂管理经验的基础上,研究提出采砂实施管理的措施和建议.

Optimizing the flood limit water level (FLWL) of reservoirs in sediment-laden rivers under changing water and sediment conditions is an important research topic that could improve comprehensive utilization benefits. Because reservoir operation has multiple objectives in sediment-laden rivers, this study established a water–sediment mathematical model, a comprehensive benefit evaluation model, and an evaluation index system. Taking the Xiaolangdi Reservoir of the Yellow River as an example, the operation mode of the FLWL under changing water and sediment conditions was studied. Under the scenarios of incoming sediment amounts of 300–800 million tons, when using the operation mode of gradually raising the FLWL, the sediment retention period was 4–13 years longer; the lower average annual siltation of the downstream channel and minimum bank-full discharge of the downstream channel after 50 years was larger by 150–260 m3/s than the operation mode of raising the FLWL at one time. However, with enhanced benefits of sediment blocking and siltation reduction, other benefits such as water resources supply, hydropower generation, and ecological improvement are reduced. The average annual number of days that do not meet the downstream water resources supply requirements, irrigation, and ecological improvement was increased by 0.64–2.16 days, and 91–197 million kW·h reduced average annual hydropower generation. The critical amount of incoming sediment was 350 million for conversion between the two FLWL operation modes, and it will increase to 450 million tons if the incoming runoff of the Yellow River increases by 20%. After constructing the Guxian Reservoir in the middle of the Yellow River, the critical amount of incoming sediment will increase to 600 million tons. This study is of great significance for improving the utilization efficiency of water resources and promoting the socio-economic development of river basins.

Sediment accumulation is severe in the Lower Yellow River. Improving sediment transport efficiency is an important way to save water resources. In this study, we analyzed the sediment transport efficiency at different sediment concentrations and discharge levels using data from 306 non-overbank floods in the lower reaches of the Yellow River from 1960 to 2016. When the sediment concentrations were below 20 kg/m(3), 60 kg/m(3), and greater than 100 kg/m(3), the clear water volumes for transporting sediment were above 50 m(3)/t, approximately 16 m(3)/t, and less than 10 m(3)/t, respectively. Given current scheduling, the Xiaolangdi Reservoir can lower its water level and increase non-overbank large water flows with an outflow discharge of > 3,000 m(3)/s when the incoming water flow has a sediment concentration of > 60 kg/m(3). Mathematical modeling indicates that, for an incoming sediment load of 600 million tons in the Middle Yellow River, the average sediment-transport water volume at the downstream Huayuankou station decreased by 27%, Optimized scheduling at the Xiaolangdi Reservoir could reduce the sedimentation in the downstream channel by 1.1 billion tons more than current scheduling, and extend the reservoir's sediment-trapping period by 10 years. These findings can be applied widely in sandy rivers.

小浪底水库运用以来,为实现下游河道减淤,水库运用方式以蓄水拦沙和调水调沙运用为主,下游河道输沙能力较低.当前,黄河下游河道适宜的中水河槽规模(泄流能力为4000 m3/s)已形成,长期维持该河槽规模,充分发挥黄河下游河道输沙能力输沙入海,成为当前及今后一个时期水库减淤调度的新要求.根据黄河下游1960—2016年306场非漫滩洪水实测资料,分析不同含沙量级、流量级黄河下游河道的冲淤效率和输沙效率,提出含沙量在60 kg/m3以上的大流量洪水过程在下游河道具有较高的输沙效率,但也容易造成河道淤积.进一步提出基于下游河道中水河槽维持的河道输沙对水库运用的要求,即当下游河道中水河槽泄流能力维持在4000 m3/s左右时,为提高河道输沙能力,小浪底水库可适时增加泄放含沙量不超过100 kg/m3的大流量过程;当下游河道中水河槽泄流能力扩大至4500 m3/s以上时,小浪底水库可适时增加泄放含沙量不超过200 kg/m3的大流量过程;若未来下游河道中水河槽泄流能力缩减至4000 m3/s以下时,小浪底水库调度仍以蓄水拦沙和调水调沙运用为主,以重塑河槽规模.数学模型计算结果表明,小浪底水库运用方式调整可提高下游河道输沙能力,同时减缓小浪底水库和下游河道的淤积,且在更长的时间内维持下游河道泄流能力为4000 m3/s左右的中水河槽.

考虑黄河未来可能的水资源条件,以及生态保护、经济社会发展多目标对水量年内过程分布需求,根据黄河下游水沙资料、河道冲淤资料,采用实测资料分析、公式计算、数学模型模拟等多种方法研究了有利于黄河下游河流生态良性维持的平衡输沙的沙量阈值.未来进入黄河下游的年来水量为250亿m3左右,实测资料分析和公式计算表明,未来较小的平衡输沙阈值为2.0～2.2亿t.数学模型计算在小浪底水库等现有工程联合调控作用下黄河下游平衡输沙的临界沙量为2.5亿t.中游古贤水库建成后和小浪底水库联合调度,可以进一步提高汛期的输沙效率,平衡输沙的沙量阈值可进一步提高.研究成果对黄河下游治理具有重要意义,可为黄河泥沙处置措施优化提供技术支撑.

There are large differences in the grain sizes of incoming sediments in different source areas of aggrading rivers in desert areas. The scour-deposition characteristics of sediment fractions affect river governance decision-making. Based on a large number of prototype observation datasets, this study has systematically sorted and analysed the data of water and sediment (particularly, the sediment fractions) in the Ningxia-Inner Mongolia Reach (Ning-Meng Reach) of the Yellow River since the 1960s, specifically to determine the sources of coarse sediment. It has been clarified that the channel sediments are mainly composed of incoming sediments from the main stream and tributaries and that the corresponding coarse sediments mainly come from seasonal tributaries and aeolian sand that is transported into the Yellow River in the reach. It has been considered that the sediment in the reach has a low incipient velocity-when the discharge exceeds 1500 m(3)/s, the sediment in the riverbed generally meets the incipient velocity and transportation conditions. Meanwhile, the study has revealed the characteristics of sediment scour deposition during different floods in the Ning-Meng Reach. The results have shown that the sediments of aggrading rivers in desert areas come from the main stream and seasonal tributaries, along with aeolian sand that is transported into the Yellow River. The grain sizes of the majority of the sediments are smaller than 0.05 mm, but there is still a certain proportion of coarse sediment with grain sizes larger than 0.05 mm. Both the median and mean grain sizes of the riverbed sediment vary between approximately 0.12 and 0.22 mm, and almost all of the sediment grains have low incipient velocities. Furthermore, the scour deposition process of the channel mainly depends on the river sediment transportation capacity. The entire reach can evolve into scour deposition, or the deposition efficiency can decrease due to the increasing discharge during non-floodplain floods, while the conducive discharges are 2500-3000 m(3)/s for the transportation of each sediment fraction.

黄河小北干流放淤试验工程建成以后,按照来水含沙量、流量、粗颗粒泥沙含量及水沙相同历时等调度运行指标要求,先后在2004-2007年、2010年、2012年共计进行了15轮无坝自流放淤试验.原型观测资料分析表明:放淤试验工程总计引水11 603.4万m3,引沙899.6万t,淤区淤积泥沙622.1万t,粗沙淤积比明显大于细沙淤积比,实现了较好的淤粗排细效果;由于黄河水沙变化和引水口门处河势变化等原因,导致放淤频次降低,放淤闸引水含沙量降低、引沙中粗沙比重减小,使得淤积量和淤积物中粗沙比重减小.总结分析认为小北干流无坝放淤在有利的水沙条件、河势条件及精细的调度管理情况下,可以实现多引泥沙,尤其是多引粗沙,淤粗排细.由于无坝自流放淤影响因素多,很难全面控制,放淤效果持续保障的难度大.

Aeolian sand into the Ningxia-Inner Mongolia reach of the Yellow River is redefined on the basis of the summary of previous study findings of the reach, as the Aeolian sand directly blown into the river by wind force from the areas along both banks of the river reach from Xiaheyan to Toudaoguai in the main stream of the Ningxia-Inner Mongolia reach. Moreover, methods to indirectly estimate the amount of Aeolian sand into the Yellow River are put forward after analysis of the contribution of the Aeolian sand into the Yellow River to the evolution of channel scouring and deposition as well as the form of sediment deposition in the river. After collection and analysis of the data such as water and sediment data and cross-section data measured at the Ningxia-Inner Mongolia reach, among the amount of Aeolian sand calculation methods, one is based on the principle of sediment balance, the other is based on deducting the sediment deposition brought by overbank flood from the sediment deposition on floodplain. Based on comprehensive results of the two methods, the quantities of and variation in the Aeolian sand into the Ningxia-Inner Mongolia reach of the Yellow River since the 1990s are put forward, which indicates a downtrend of the Aeolian sand into the Ningxia-Inner Mongolia reach of the Yellow River since the 1990s, i.e., from approximately 21 million tons in the 1990s to approximately 11 million tons at present, with an annual average approximating 16 million tons.

This paper introduced the modes and application scheme of floodplain warping and lowland regulation on channel deposition reduction in the lower Yellow River,and analyzed the effect of flood diversion warping and mechanical silting on sedimentation reduction of the downstream channels using measured data and current achievements.The results show that the sediment disposal ability of floodplain warping and lowland regulation can reach to 2.452 billion tons,which will reduce sedimentation deposition of 3.190 ~ 3.854 billion tons in the Lower Yellow River channels.Meanwhile,dredging riverbed can enlarge the flood carrying capacity.If the dredging is conducted at the bottle-neck reaches,better effect of the flood carrying capacity in the main channel can be achieved.