Sediment in Mosul Dam reservoir using the HEC‐RAS model

Mosul Dam, located on the Tigris River north of Iraq, is experiencing sedimentation problems, especially near the Al‐Jazeera pumping station that supplies the irrigation water for the Al‐Jazeera project. The sources of the sediment accumulated within the reservoir are from the Tigris River, as well as ten side valleys on both sides of the reservoir. The sediment inflow rate into the reservoir and the released values are considered on the basis of the operation schedule of the dam for the considered period from 1986 to 2011. The sediment loads were estimated on the basis of available measurements and estimated literature values. The HEC‐RAS 4.1 model was used for flows and sediments in the main river and reservoir. The model was calibrated for flow simulations (coefficient of determination r² = 0.87) and sediment routing based on bed level, (with resultant r² = 0.98 and Mean Absolute Deviation of 0.95). The Ackers–White equation was used in the HEC‐RAS model for sediment routing because of the wide range of sediment sizes in the study case. The resultant total accumulated sediment load volume was 1.13 km³, a value that is very close to the measured values (1.143 km³) obtained from a previous bathymetric survey. Furthermore, the model indicated most of the sediment (80.7%) was deposited during the first five of the dam operation.     

基于水文要素的闹德海水库入库沙量预测模型

针对水库调度需要,以闹德海水库为背景开展入库沙量预报研究。首先分析水库的入库水沙特性,以确定入库沙量的主要影响因素;进而研究建立基于水文要素的BP神经网络入库沙量预测模型,并利用历史场次洪水资料进行训练学习。结果表明所选择的产沙因子基本能够反映流域降雨-产沙-输沙过程的传递关系,模型可用于入库沙量预报,指导水库实时水沙调度决策。     

青狮潭水库大坝安全预报模型

介绍了青狮潭水库大坝安全监控的统计模型、确定模型和混合模型，经优化处理，建立预报模型。     

One‐dimensional sediment transport modeling of pool recovery along a mountain channel after a reservoir sediment release

A reservoir sediment release along the North Fork Cache la Poudre River (North Fork) in northern Colorado resulted in a massive fish kill and channel sedimentation that filled pools critical to fish as overwinter habitat. Recognition of the hazards associated with a large influx of sediment into a riverine ecosystem is critical for a greater understanding of the effects of sediment releases, and hence, future management of sediment within reservoirs. Two one‐dimensional sediment transport models, HEC‐6 and GSTARS 2.0, were evaluated for applicability to predict sediment removal along the steep gradient, bedrock‐controlled pool‐riffle North Fork. The ability of both models to identify flushing discharges that assist channel recovery was also evaluated. Two modeling scenarios representing a low and high flushing discharge were modeled. Within each scenario, two levels of simulations were conducted to represent conditions of data availability, a default simulation for limited data input, and a robust simulation that utilized the entire set of field data, collected over a 1‐year period. The models were calibrated against quantitative measurements of pool bed elevation obtained during field resurveys. Preliminary analyses were conducted to identify the appropriate sediment transport equations. HEC‐6 results indicate that long‐term, robust simulations yield the closest agreement between predicted and measured pool bed elevation change. More than 50% of the actual scour and deposition within three pools was modeled using HEC‐6. Modeling accuracy using GSTARS 2.0 was considerably lower, and it appears that the present construct of the model does not reflect the physical processes operating along the North Fork. Computer models are useful tools in the sediment management decision process, provided adequate data collection and calibration are conducted. In situations where restrictions exist on available flushing discharges, sediment transport modeling can assist management decisions, and modeling is always preferable to uncalibrated estimates. Copyright © 2001 John Wiley & Sons, Ltd.     

平面二维水沙数学模型在永定河滞洪水库设计中的应用

采用平面二维水沙数学模型对滞洪水库修建后永定河主河道和滞洪水库在不同洪水条件下的冲淤演变规律及流态、流势变化进行了计算,掌握了永定河滞洪水库的河势及河道演变规律,验证了3水库联合调度运用方案的合理性,为滞洪水库的设计提供了重要依据.     

平面二维溃坝水沙输移动床数学模型研究

为数值模拟溃坝洪水作用下泥沙输移及河床变形,建立了无结构三角形网格的平面二维水沙耦合数学模型。水动力学模型采用浑水流动方程,考虑了泥沙输移及床面冲淤变化对水流动量的影响;泥沙输移采用不平衡泥沙输移模式。模型数值计算格式采用守恒性较好的有限体积法,单元界面的对流通量采用基于近似黎曼解的Roe格式计算,扩散通量采用中心格式,不平衡泥沙输移方程采用坡度限制的二阶空间精度格式离散。模型经经典算例和小尺度瞬间全溃的动床实验资料检验,水面、床面及流速等计算结果与实验资料或解析解等比较吻合,分析了动床与定床水面及洪水传播速度的差异。在上述检验的基础上,采用动床模型对某河道型水库溃坝诱发的水沙运动进行了数值模拟,结果表明溃坝洪水下水流、泥沙及河床变形发生强烈的相互作用,采用水沙及河床变形耦合的数学模型是必要的。     

土石坝沉降的预测灰色模型

本文将灰色系统理论应用到土石坝沉降资料分析中，通过新陈代谢方法与GM（2，1）模型相结合建立了灰色预测模型。该模型的可行性与合理性在铁山水库土坝的实际应用中得到了验证。     

溃坝水流作用下急弯河道泥沙输移数值模拟

将有限元特征分裂算法(CBS)应用于二维浅水控制方程的求解中,建立了模拟溃坝水流泥沙输移的数学模型。CBS算法在计算对流主导的问题时具有很好的稳定性与较高的精度,适用于处理溃坝水流流速大,水位、床面变化剧烈等问题。应用该模型对90°急弯河道全溃所致的水流运动进行了数值计算,并与试验资料进行了比较,证实了该方法的可靠性。最后用该模型模拟了180°弯道中溃坝水流在缓坡、陡坡时的洪水演进与泥沙输移。结果表明:模型能够较好地模拟溃坝水流运动,模拟结果符合水流泥沙运动规律。     

闹德海水库泥沙冲淤数学模型

为了研究水库延长蓄水期后引起的库区泥沙问题,在详细分析了闹德海水库泥沙冲淤演变规律的基础上,研制了闹德海水库泥沙冲淤数学模型,并对模型进行了验证。     

Spatial variation in fine sediment transport in small upland streams: the effects of flow regulation and catchment geology

In cobble‐ and gravel‐bed streams, fine sediments (<4 mm diameter) are an important component of the bed material that can move at a full range of flows, not just during floods and spates. It has been hypothesized that the constant movement of this fine material, as it passes over the coarse bed, is an important ecological disturbance to plants and animals. In this study, I measured baseflow sediment transport rates across a number of regulated and unregulated sites in an upland catchment comprising isolated regions of granite/sandstone and acid volcanics in southern Victoria, southeastern Australia, as a precursor to a study examining the effects of sediment on aquatic biota. Examined on three separate occasions, transport rates for fine sediments were up to 100 times greater in the granite/sandstone streams, but diversion weirs, which greatly reduced downstream sediment loads in the granite/sandstone areas, moderated these differences. Measured transport rates within unregulated sections of the granite/sandstone streams were roughly equivalent to sediment loads found to disturb benthic communities in other experimental studies. On this basis, abrasion by sediment transport in these streams may be sufficient to influence the structure of benthic communities even at baseflow. This hypothesis forms the basis of other research examining the biota at these sites. Copyright © 2004 John Wiley & Sons, Ltd.     

The assessment of suspended sediment inputs to Volta Lake

Information on a river basin's sediment yield is an important requirement for water resources development and management. In the Volta River basin of Ghana, data on suspended sediment yield are limited due to the lack of logistic support for systematic sediment sampling activities. This paper presents the results of a study using the available measurements of suspended sediment transport for eight monitoring stations in order to develop a simple predictive tool for estimating the suspended sediment yields for catchments for which no sediment measurements had been undertaken. Regression analysis was used to establish a relationship between specific suspended sediment yield and both the mean annual run‐off and the drainage basin area. The prediction model was used to estimate the sediment loads of the Volta River and its main tributaries (Black Volta, White Volta and Oti Rivers) in order to estimate the total suspended sediment input to the reservoir and the equivalent specific suspended sediment yield from the catchment surface. Although these sediment yield values are relatively low by world standards, the results obtained provide a basis for assessing future sedimentation problems in Lake Volta and for underpinning the development of sediment control and management strategies for the reservoir.     

三维水沙输移模型对深圳深水湾水沙输移的研究

运用三维水沙输移模型研究深圳深水湾的泥沙输移,经过实测资料的验证,计算值能够模拟实际情况,表明波浪对泥沙输移有重要的影响。为进一步研究深圳深水湾泥沙在潮流作用下的输移规律,模拟了1998年7月21日至1998年8月21日涨退潮期间的水沙运动,计算结果表明深水湾属于泥沙淤积区域。     

Channel response to sediment replenishment in a large gravel‐bed river: The case of the Saint‐Sauveur dam in the Buëch River (Southern Alps,France)

The Saint‐Sauveur dam was built in 1992 in the middle section of the Buëch River. Downstream of the dam, a channel incision by several meters was observed. A gravel replenishment operation was planned in order to restore the active channel. An equivalent of two times the mean annual bedload‐transport capacity (43,500 m³) was replenished downstream of the dam in September 2016. The aim of this paper is to quantify morphological change associated with sediment remobilization in order to evaluate the efficiency of the restoration works. The monitoring was based on a combination of (a) change detection using sequential high‐resolution digital elevation models (from airborne LiDAR data), (b) bedload tracing using active ultrahigh‐frequency radio‐frequency identification technology, and (c) complementary field surveys of channel grain‐size distribution and morphology for bedload‐transport computation. Field monitoring allows us to capture a net aggradation along a 2‐km reach after the first post‐replenishment flood. A sediment balance analysis was performed to back‐calculate bedload supply coming from the sluicing operation during the flood. Although the sediment replenishment operation clearly had a positive impact on the morphological conditions of the starved river reach, the effective bedload supply from artificial berms (22,650 m³) was insufficient to initiate substantial channel shifting along the restored reach and a subsequent amplification of the sediment recharge. The combination of high‐resolution topographic resurveys and sediment tracing was successful to evaluate the downstream propagation of sediment replenishment effects.     

Estimating sediment yield risk of reservoirs in northern Ethiopia using expert knowledge and semi‐quantitative approaches

Reservoir siltation is a serious problem that threatens the productivity and sustainability of water‐harvesting schemes. Quantification of sediment deposition in reservoirs and understanding of its major drivers are needed to apply targeted management interventions. Most of the techniques used to estimate sediment deposition in reservoirs require extensive measurements on a frequent time basis, as well as being costly and time‐consuming. Thus, a rapid and relatively economical means of assessing the erosion susceptibility of catchments and predicting their sediment yield potential is necessary. In this study, expert‐based rankings and semi‐quantitative factorial scoring approaches were applied to assess the siltation severity of 25 reservoirs in the Tigray region of northern Ethiopia. The results were then correlated with quantitative sediment yield estimates acquired for representative sites, and a sediment yield predication model was developed for the region. The calibrated model has an efficiency and relative root mean square error (RRMSE) of 79 and 36%, respectively, which is considered adequate to assess erosion susceptibility and siltation risk of reservoirs in similar environments. The study demonstrates that expert knowledge and rapid characterization of catchments, in terms of susceptibility to erosion, are viable options for assessing siltation risks and for analysing controlling factors at a larger number of sites, with minimum costs and acceptable accuracy.     

Experimental and numerical simulations of the hydraulic flushing of reservoir sedimentation for planning and design of a hydropower project

Hydropower projects located on rivers transporting heavy sediment loads require design and operation criteria based on sediment management as a means of sustaining the project life. Sediment management is achieved by designing projects as a run‐of‐the‐river scheme, with provision for drawdown flushing, noting hydraulic model simulations are essential for optimizing the design of these projects. Sediment deposition levels are generally predicted with long‐term simulations using 1‐D numerical models, as well as experiments with scaled physical models that simulate drawdown flushing. The present study presents experiments with scaled model and 3‐D numerical model simulations conducted for hydraulic flushing of a reservoir. Experiments were conducted for various durations and discharges to finalize the intake alignment and optimize the flushing. The results of the 3‐D numerical model simulations are in agreement with the results of the experimental study (4%–6% variation). The results also indicate a combination of a 1‐D numerical model for sedimentation and a 3‐D numerical model for flushing can be effectively used to simulate the sedimentation and flushing of reservoirs during the planning and design stages.     

基于BP神经网络模型的水库塌岸预测研究

考虑水库塌岸预测的非线性,构建基于BP神经网络模型的水库塌岸非线性预测模型,以漳河流域内岳城水库为研究对象,结合野外实地勘察数据,对岳城水库塌岸进行预测。研究结果表明:所建水库塌岸非线性预测模型预测结果与实际情况较为吻合,预测的左右岸水库塌岸和实地调查塌岸相对误差分别为1.92%和2.15%,岳城水库左右岸塌岸宽度预测平均值分别为31.8m和36.9m;水库下游预测塌岸速度小于1m/a,中上游塌岸速度大于1m/a,下游库岸态势较为稳定,中上游塌岸趋势将加剧。研究成果对于水库塌岸非线性预测及岳城水库塌岸防治和岸坡加固设计提供参考价值。     

嘉陵江流域北碚站年输沙量的变化规律及预测研究

首先利用小波变换对北碚站年输沙量的变化规律进行了研究,结果表明:年输沙量呈现出明显的减少趋势;其次,将小波变换结合BP神经网络建立小波网络模型,并利用该模型对北碚站的年输沙量进行预测,同时将预测结果与BP神经网络模型的预测结果进行了比较。认为在缺乏其它相关资料的情况下,单从输沙量和径流量资料出发,小波网络模型的预测效果明显优于BP神经网络模型。由此表明,小波网络模型不仅能对年输沙量的趋势进行预测,还能对年输沙量的大小进行较为准确的预测,从而为在资料较少的情况下进行输沙量的定量分析提供了一种新的方法。     

河流泥沙水文学模型边界条件参数化方法探讨

针对河流泥沙水文学模型,在对基础方程(考虑上站来水含沙量的幂律函数公式)基本内涵(不平衡输沙理念、相对空间概念及自动调整作用)综合分析的基础上,从河道边界条件(河段长度、宽度、比降等)参数化角度出发,提出根据河道边界条件确定模型参数的方法。边界条件参数化方法途径主要包括:统计分析方法与理论比较途径。其中,统计分析方法宜先对同一河段选用同一进口断面,分别选取下游不同距离出口断面,通过实测资料统计回归,研究参数随距离的变化规律;理论比较途径主要基于对水文学、水动力学模型方程的理论比较分析,探求参数的计算方法。从断面质点系统跟踪角度来看,河流泥沙水文学与水动力学模型关于空间变化的基础方程,经过空—时变量变换均可表示为关于时间变化的滞后响应模型方程形式,两者区别在于对描述系统水沙组合的特征变量选择不同。河流泥沙水文学模型边界条件参数化最终结果转化为了水沙质点系统的调整时间与泥沙沉降时间,这从另一角度提供了对河流泥沙水文学模型方程物理意义的理解。     

黄河下游灌渠水流泥沙数学模型

本文结合灌渠的结构特点及水流泥沙特性，对一维非耦合，非均匀、不平衡沙基本方程组进行了合理的简化，根据实体模型试验实测资料，确定了自流与提灌时干，支渠分流的不同分沙分水比。     

Reducing reservoir impacts and improving outcomes for dam‐forced resettlement: experiences in central Vietnam

The present study focuses on the growing problem of the impacts of human displacement resulting from hydropower dam construction, within the context of the integrated lake basin management of dam reservoirs. Dam‐forced displacement and resettlement can pose severe challenges to the environmental, economic and social sustainability of a reservoir basin. A case study in Quang Nam Province, central Vietnam, suggests that many resettled communities experience impoverishment due to the lack of adequate replacement land, declines in supplemental food sources and reduced access to natural resources. In response to such situations, resettled residents may (i) destroy lake catchment forests for the purpose of converting them to farmland or engage in illegal logging; (ii) increase agrichemical inputs on reduced land, thereby polluting run‐off and groundwater; and (iii) place increased pressure on fish stocks and wildlife. Examples are provided from central Vietnam to illustrate the need for applying management approaches that allows the affected people to become beneficiaries of dam projects and for including civil society organisations in resettlement planning. The hydropower authority can fund benefit‐sharing mechanisms, including village‐level electrification and payment for environmental services schemes, in which resettled populations are paid for forest maintenance and protection to prevent erosion and deforestation, and reservoir access can be provided for fishing, aquaculture and agriculture. Civil society organizations can advocate for residents’ interests and for reallocation of protected forest land for community forestry. These approaches can be supported by an inclusive reservoir management board working to achieve environmental sustainability, economic growth and social equity.