The analysis on reservoir sediment deposition and downstream river channel scouring after impoundment and operation of TGP

According to the measured data after impoundment and operation of the Three Gorges Reservoir,the reservoir sediment deposition and downstream river channel scouring are described briefly and compared with the research results achieved in the demonstration stage.It is indicated through analysis that the reservoir sediment deposition and downstream river channel scouring during 8-year impoundment and operation are still within the original forecast,so the original forecasting results are feasible.The further observation and comparison should be conducted because the comparison between the observed data and the original forecast is not so sufficient in time and the prototype observation and related research work should be strengthened in the future.

Experimental Analysis of Sediment Deposition Due to the Effect of an Upstream Reservoir Backwater

The phenomenon of aggradation due to sediment accumulation upstream reservoirs had been studied in this research. For this purpose, groups of experiments were conducted in a laboratory with 25 m long, 0.80 m wide and 0.70 m deep channel. A block was built at the end of the channel to work as a dam to impound water. The channel was supplied with drainage pipes on both sides to release water out in a manner similar to what happens in reservoirs. The bed of the channel was filled with sand of 0.80 mm median sieve diameter and 0.72 geometric standard deviation. The slope was 0.0093 for all experiments. Two sizes of sand were used representing the sediment. The median diameter and geometric standard deviation of the first were 0.365 mm and 0.46 mm, respectively. The second sample had 0.65 mm median diameter and 0.67 standard deviation. A total of 70 experiments were conducted in two groups to examine effects of sediment transport rate, particle size of sediment and flow velocity on aggradation characteristics. The results showed that there was a strong linear direct relationship between aggradation elements （length and depth） with the rate of sediment transport. Groups of dimensionless parameters affecting the aggradation characteristics were used to develop empirical equations to predict the length, maximum depth of aggradation and predict transient bed profile. The results of empirical approach were compared with the measurement data and previous numerical method. The results indicated that the percentage error was 19% to 31% for length of aggradation and -21% to 26% for maximum depth of aggradation. The results also showed that the sediment materials were deposited closer to the body of the dam when the released water from the dam is higher than the inflow.

Using ^(137)Cs Tracing Methods to Estimate Soil Redistribution Rates and to Construct a Sediment Budget for a Small Agricultural Catchment in the Three Gorges Reservoir Region,China

Soil erosion and associated off-site sedimentation are threatening the sustainable use of the Three Gorges Dam. To initiate management intervention to reduce sediment yields, there is an increasing need for reliable information on soil erosion in the Three Gorges Reservoir Region （TGRR）. The purpose of this study is to use 137Cs tracing methods to construct a sediment budget for a small agricultural catchment in the TGRR. Cores were taken from a pond and from paddy fields, for laTCs measurements. The results show that the average sedimentation rate in the pond since 1963 is 1.50 g cm-2 yr-1 and the corresponding amount of sediment deposited is 1,553 t. The surface erosion rate for the sloping cultivated lands and the sedimentation rate in the paddy fields were estimated to be 3,770 t km-2 yr-1 and 2,600 t km-2 yr^1 respectively. Based on the estimated erosion and deposition rates, and the area of each unit, the post 197o sediment budget for the catchment has been constructed. A sediment delivery ratio of 0.5 has been estimated for the past 42 years. The data indicate that the sloping cultivated lands are the primary sediment source areas, and that the paddy fields are deposition zones. The typical land use pattern （with the upper parts characterized by sloping cultivated land and the lower parts by paddy fields） plays an important role in reducing sediment yield from agricultural catchments in the TGRR. A 137Cs profile for the sediment deposited in a pond is shownto provide an effective means of estimating the land surface erosion rate in the upstream catchment.

PROBLEMS OF RESERVOIR SEDIMENTATION IN CHINA

As there are many heavily sedimentladen rivers in China, with high sediment concentration and a large quantity of sediment load, the sedimentation problems of the reservoirs built on those rivers are so serious that the amount of sediment deposited in the reservoirs is great and the rate of sedimentation is accelerated. According to the statistics, up to the end of 1981, a total amount of 11.5×109m3 of sediment were accumulated in those reservoirs, i.e. 14.2% of the total designed capacity were lost. The average annual loss in storage capacity reached 2.3 percent, being the highest in the world. Silting of impounding lakes not only has an effect on the benefits of the reservoirs and seriously threatens the life of reservoirs, but also results in many environmental problems which were not fully estimated in the planning of the reservoirs. In this paper, the situation of reservoir deposition in China are described from the following aspects: 1) the characteristics of hydrology and sediment of the rivers; 2) the seriousness of reservoir sedimentation in China; 3) problems caused by reservoir deposition; 4) the methods of minimizing sediment deposition, etc.

Analysis of wave clipping effects of plain reservoir artificial islands based on MIKE21 SW model

Plain reservoirs are shallow, and have low dams and widespread water surfaces.Therefore, wind-wave-induced damage to the dam is one of the important factors affecting the safety of the reservoir.To improve upon unsatisfactory plain reservoir wave-clipping schemes, a numerical method is proposed to predict and analyze waves in the reservoir in the presence of artificial islands, constructed from dredged sediment.The MIKE21 SW model is applied to a specific plain reservoir for finding the optimal artificial island parameters.The simulated wave height attenuation results are seen to agree well with empirically predicted values.Thus, the validity and reliability of the numerical model are established.Artificial islands at suitable locations in the reservoir can attenuate the wave heights by approximately 10%e30%, which justifies the efficacy of the clipping scheme making use of dredging and island construction.

Sediment Management of TGP

In this preliminary study, it is shown that for a reservoir on a river of rich runoff like the Yangtze of a rich runoff, an elaborate scheme of sediment management may be devised to substantially reduce the reservoir deposition. The mathematical model applied in this investigation has been fairly well verified with the long term field data on the sediment transport by an unsteady flow in the lower Yellow River. In view of the importance of TGP, however, a further investigation with physical models and mathematical models of other versions is planned. Great financial benefits are involved.

Application of ^(137)Cs fingerprinting technique to interpreting sediment production records from reservoir deposits in a small catchment of the Hilly Loess Plateau,China

According to variations of 137Cs and clay contents, 44 flood couplets were identified in a profile of res- ervoir deposit with a vertical length of 28.12 m in the Yuntaishan Gully. Couplet 27 at the middle of the profile had the highest average 137Cs content of 12.65 Bq·kg?1, which indicated the 1963s' deposits, then 137Cs content decreased both downward and upward in the profile. The second top and bottom couplets had average 137Cs contents of 2.15 Bq·kg?1 and 0.92 Bq·kg?1, respectively. By integrated analysis of reservoir construction and management history, variations of 137Cs contents over the profile, sediment yields of flood couplets and rainfall data during the period of 1958-1970, individual storms related to the flood couplets were identified. 44 floods with a total sediment yield of 2.36×104 m3 occurred and flood events in a year varied between 1 and 10 times during the period of 1960-1970. 7-10 flood events occurred during the wet period of 1961-1964 with very wet autumn, while only 1-2 events during the dry period of 1965-1969. Average annual specific sediment yield was 1.29×104 t·km?2·a?1 for the Yuntaishan Gully during the period of 1960-1970, which was slightly higher than 1.11 ×104 t·km?2·a?1 for the Upper Yanhe River Basin above the Ganguyi Hydrological Station and slightly lower than 1.40 ×104 t·km?2·a?1 for the nearby Zhifang Gully during the same period. Annual specific sediment yields for the Yuntaishan Gully were correlated to the wet season's rainfalls well.

Identification of the deposited layers in landslides reservoir and investigation of the sediment yields during the later sixteenth century on the Hill Loess Plateau,China

There are many sediment trapping reservoirs in the Hill Loess Plateau.The Huangtuwa small catchment is selected as a research field where samples were collected in a sediment deposit profile with a vertical length of 12.73 m.By the variation of fine particle content and pollen concentration,54 flood couples were identified.Taking the freeze-thawing disturbed texture as the sign of the latest flood couple in a year,it is ascertained that those 54 floods should happen in 31 years.Using pyramid volume calculation formula,the sediment yields of flood ranged between 716―30376 t·km-2.The average sediment yield was 7106 t·km-2.The annual sediment yields varied between 968―55579 t·(km2·a) -1,and the average value is 12629 t·(km2·a) -1.Compared with the modern annual sediment discharge of the Huaining River,the erosion rate in the Huangtuwa region 450 years ago was similar to the modern erosion rate.In the period from the 27th year to the 31st year,the average annual sediment yield increased sharply to 31309 t·(km2·a) -1.It implied that re-reclamation of the abandoned land in the catchment since the landslide disaster,where vegetation had rehabilitated already,caused very severe soil erosion in the catchment.

三门峡水库控制运用方式的优化探讨

三门峡水库“蓄清排浑”运用为多沙河流的治理提供了宝贵经验,随着来水来沙情况的变化及对水库功能需求和对水库泥沙冲淤规律认识的深化,该运行方式亦在实践中不断调整和完善。为此,针对不同的典型年份设定集中敞泄与分段敞泄的敞泄排沙方案,采用一维非恒定水沙数学模型,对选取的2018~2019年丰水少沙年和2014~2016年枯水少沙年设定12种控制运用方案进行模拟,比较各方案下库区冲淤变化的优劣,据此选取适合三门峡水库的控制运用方式。结果表明,2018~2019年分段敞泄方案的冲刷效果优于集中敞泄方案,即使在后汛期的控制水位抬高至310 m,也能达到较好的冲刷效果;2014~2016年分段敞泄方案虽优于集中敞泄方案,但其冲刷主要集中于2014年汛期,2015、2016年整体呈淤积状态,综合考虑建议枯水少沙年份水库采用“泥沙年际调节”运用模式。

金盆水库上游降雨径流二维泥沙输移沉积模拟

为了探究降雨径流在不同流量、含沙量下对西安市金盆水库水体的影响规律,基于湍流流动模型,对2022年10月降雨径流时期西安市金盆水库上游的泥沙输移和沉积进行了数值模拟,并对所建立模型的可靠性进行了验证。通过对不同流量、含沙量下的径流进行模拟计算,表明在沿程前部断面处,流速越大底部含沙量越小;在沿程后部断面处,流速越大断面含沙量越高;径流含沙量越大,断面含沙量越大,泥沙分布厚度越大。因此,可以根据降雨径流时期来水的流量及含沙量分析泥沙输移沉积的过程,为水库的运行维护提供参考。

高洪水期运行水位对三峡水库泥沙淤积的影响

三峡水库泥沙问题直接关系到水库库容的长效保持。选取典型高洪水期,基于数值模型探究入库水沙量级、水沙异步及运行水位对三峡库区沙峰输移和淤积排沙的影响。结果表明:入库洪峰的增大抑制了涪陵沙峰比的衰减,并导致更多泥沙输运至坝前,使得坝前沙峰降幅受运行水位的抬升更为显著;变动回水区较常年回水区更易受到入库水沙异步影响,且随着来沙系数的增大,由低水位抬升时淤积占比更高;水库排沙比受入库水沙异步影响有限,且随着入库洪峰、沙峰的增大,排沙比增加的同时对运行水位抬升导致的衰减更为敏感。研究成果初步揭示了入库水沙异步及运行水位对库区沙峰运动与淤积的影响,可为三峡水库汛期优化沙峰排沙调度提供参考。

Removing coarse sediment by sorting of reservoirs

Reservoir sedimentation is an unsolved problem.In this paper,based on measured data,theoretical analysis and numerical computations,we prove that a proportion of the sediment coarser than 0.1 mm(CS) is sorted and deposited in specific reaches in the upper backwaters or in run-of-river reservoirs.The ratio of CS is usually small but it impacts the slope of deposition delta greatly and raises the backwater in later stages for a river shaped reservoir(RSR).Based on these facts,we propose to remove such CS from a fixed basin(FB) in the upper backwater by dredging and we prove that the removal of CS is effective in reducing sediment deposition and in preserving the long-term capacity of reservoirs.A numerical model computation of the Three Gorges Project(TGP) reservoir indicates that dredging 30×106-50×106 t/a of CS could reduce 20% total deposition by the end of 100th year,so that the slope of deposition can be slowed down by 25%-30%.This would be remarkable for a long extended RSR.This method of removing CS can also be applied to the Xiaolangdi reservoir(XLD) on the Yellow River(YR) to not only limit reservoir deposition but also filter out the CS from entering the Lower Yellow River(LYR) to slow down the rise of the perched LYR.It provides a new alternative to postpone the continuous siltation of the LYR.

三峡水库汛期沙峰预报技术及排沙调度实践

水库排沙调度是三峡水库安全运行和发挥综合效益的关键技术问题。基于长序列实测水沙资料和水库调度运行情况,系统阐述了三峡水库汛期水沙特性、沙峰预报技术体系和水库汛期沙峰排沙调度试验效果。2012年以后三峡水库汛期径流占全年总径流量的45%,但汛期输沙占比达到84%,场次洪水输沙占比明显增大,且存在明显的水沙输移异步现象。基于泥沙实时报汛数据,构建多形式边界预报模型和库区水沙输移模型相耦合的水库泥沙实时预报系统,能够预报沙峰传播至坝前的时间和相应的含沙量,为水库汛期的沙峰调度提供必要的技术支撑。目前三峡水库已成功开展多次沙峰排沙调度试验,取得了预期效果,经调度后水库排沙比显著增大,场次洪水排沙比在27%~39%范围内。

2022年“汛期反枯”对三峡库区泥沙冲淤的影响

为深入分析2022年“汛期反枯”这一水文情势对三峡库区泥沙冲淤的影响,采用输沙量法评估三峡库区泥沙淤积总量变化,以断面法分析水库淤积的沿程分布情况。2022年汛期三峡水库入库径流量的大幅减少,致使库区的泥沙淤积规律较往年发生较大变化,主要表现为库区干流泥沙淤积量显著减少,仅淤积1097万t,为蓄水运用以来最低值。断面法计算结果表明库区河床冲刷0.157亿m^(3),且变动回水区和常年回水区均冲刷明显,出现“伪冲刷”现象。分析发现,汛期来沙大幅减少,无法补足淤积泥沙密实沉降造成的河床断面变化是造成库区出现“伪冲刷”的主要原因。建议加强库区淤积泥沙密实规律及影响机制研究,关注特殊水情下库区河床冲淤演变规律,以支撑三峡工程科学调度需要。

三峡水库秋汛期水沙特点及秋汛洪水对库区冲淤的影响

长江上游秋汛洪水是三峡水库重要水沙事件,对三峡库区冲淤特性有直接影响。基于1954-2022年实测资料分析表明,近70年来长江上游秋汛期来水量变化不大,来沙量均值在2013年前后减幅达到87%。2013年以后,三峡库区秋汛洪水的来沙高度集中于嘉陵江流域,占寸滩沙量的70%以上,秋汛洪水通过影响嘉陵江的水沙条件,进而间接影响三峡水库秋汛期的入库水沙条件。与汛期洪水相比,秋汛洪水的泥沙90%以上在库区淤积,且库尾淤积更加突出。实测资料分析结果表明,秋汛洪水期间适时加大水库下泄流量,可显著增大排沙量,减轻库区淤积。研究成果对加深三峡水库淤积特性认识、优化三峡水库秋汛洪水调度具有重要意义。

基于泥沙淤积的水库灌溉库容分析

水库库容主要受泥沙淤积、蒸发和渗漏制约,而这些又受入库洪水影响。为了科学确定府谷县某水库灌溉库容能力,基于支沟和水库基本情况,采用铁一院法、推理公式法、经验公式法,在分析河道入库洪水的基础上,对水库的淤积、蒸发和渗漏情况进行探讨。结果显示,水库设计库容满足工程灌溉用水量需求,目前库死水位为1614 m,现状库容只有86万m^(3),需通过库区开挖清淤平整处理扩大灌溉库容,以满足灌溉用水需求,可为水库防洪灌溉和效益发挥提供科学依据。

老鹰岩一级水电站水库泥沙淤积及汛期运行调度方式研究

老鹰岩一级水库与上游龙头石水电站尾水相衔接,其水库汛期坝前运行水位将直接影响龙头石电站厂房的防洪安全。文章结合工程特点,拟定了老鹰岩一级水库的汛期运行调度方式,采用一维水沙数学模型针对各汛期排沙运行控制水位方案开展水库泥沙淤积计算及衔接回水计算,综合考虑防洪安全、库区淹没影响、发电效益等因素,推荐汛期排沙运行控制水位为903.00 m。

三峡水库运行初期的泥沙淤积特点

针对三峡蓄水运行后的泥沙淤积问题,基于实测资料,采用输沙率法和断面法分析了三峡水库运行初期的泥沙淤积特点。结果表明:三峡水库2003—2013年泥沙淤积总量为15.31亿t,平均排沙比为24.5%,均较论证阶段降低;库区泥沙淤积主要分布在常年回水区的宽谷和弯道河段,宽谷段全断面发生淤积、弯道断面流速较小一侧淤积、峡谷无累积性淤积;常年库区近坝段泥沙淤积速度逐年减小,而上段泥沙淤积速度则呈增大趋势;淤积物粒径沿程分选不明显,常年回水区淤积物中值粒径多在0.01 mm以下。库区峡谷段深泓线无明显变化、尚未出现泥沙淤积三角洲、库尾泥沙淤积上延和尾水抬高不明显,据此初步推断峡谷河段存在富余挟沙力而成为局部侵蚀基准面,整个库区将无统一平衡比降的趋势。

小浪底水库运用以来库区泥沙淤积分析

为了提高小浪底水库排沙效果,延长水库拦沙寿命,对水库运用以来库区的淤积情况进行了分析。结果表明:(1)小浪底库区干流仍为三角洲淤积形态,三角洲顶点距坝16.39 km,高程为222.59 m。远离大坝的支流沟口淤积面均高于支流内部,支流畛水出现明显的拦门沙坎,高度为9.9 m。(2)汛期库区年均淤积2.117亿t,占总淤积量的92%。高程235 m以下淤积泥沙33.983亿m3,是淤积的主体。大坝—HH20、HH20—HH38库段是淤积的主要库段,分别淤积19.972亿m3、11.101亿m3,占总淤积量的61%、34%。干流淤积量为26.136亿m3,占总淤积量的80%。(3)淤积物中,细沙、中沙、粗沙分别占总量的39.7%、28.9%、31.4%。中细泥沙,尤其是不会造成下游大量淤积的细沙淤积在水库中,减少了拦沙库容,降低了水库的拦沙效益,缩短了水库的拦沙寿命。

潼关高程及三门峡水库运用方式问题探讨

作者对潼关高程从三门峡水库“蓄清排浑”运用以来的变化进行了分析 ,指出潼关高程近年来不断上升的主要原因是由于汛期来水量大幅度减少所致。要控制和降低潼关高程 ,必须调整三门峡水库的运用方式来适应新的来水来沙条件。建议非汛期最高运用水位控制在 3 1 6～ 3 1 8m ,汛期敞泄排沙流量减小到 1 0 0 0～1 5 0 0m3 s,桃汛起调水位 3 1 3m ,6月上旬运用水位降至 3 1 0m。