Journal of Hydroelectric Engineering

水力发电学报

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2019 Vol. 38, No. 8 Published: 2019-08-25

	1	General rules of dam-valley deformation due to reservoir impoundment
		WU Mingxin, JIANG Hui, ZHANG Chuhan
		DOI: 10.11660/slfdxb.20190801
		This paper presents an investigation on dam-valley deformation responses to reservoir impoundment by analyzing the field data of 11 high concrete dams, including Ertan, Longyangxia, Lijiaxia, Xiaowan, Jinping I, Dagangshan, Xiluodu, Three Gorges, Hoover (USA), Jiangya and Tongjiezi hydropower projects. We collect and analyze the fundamental design parameters, geological and hydrogeological conditions, and field measurements of dam-valley deformation caused by reservoir impoundment, and reveal several general rules of reservoir settlement and downstream valley vertical movements, valley deformation along horizontal direction, and dam structure displacements. The findings can provide valuable references for the design, analysis, and safety monitoring of high dams.
		2019 Vol. 38 (8): 1-14 [Abstract] ( 189 ) PDF (2326 KB) ( 579 )

	15	Dynamic assessments of drought multi-attribute risks and analysis of its driving force
		DAI Meng, HUANG Shengzhi, HUANG Qiang, WANG Lu, GUO Yi
		DOI: 10.11660/slfdxb.20190802
		Most previous studies on drought assessment were limited to static risks, but to practical drought prevention and drought resistance, it is more significant to reveal the dynamic evolution characteristics of drought multi-attribute risks under changing environments. This study calculates the joint return periods of moderate and severe drought events in the Wei River basin using Copula functions, and examines the dynamic characteristics of drought multi-attribute risks based on a sliding window of 31-year time interval. The driving force of drought dynamic evolution is explored using a cross wavelet transform. Results indicate that (1) the drought risk of the Jing River is the highest in the whole basin, and its static joint return period of "and" type is 11.4 and 21.6 years under two drought scenarios, respectively; (2) the drought multi-attribute risk in the basin has become generally higher since 1980s; (3) the drought risk in the basin is closely related to sunspots. The correlation between sunspots and drought index series was subjected to significant phase changes in the 1980s, which could be one of the major reasons for the increased drought risk.
		2019 Vol. 38 (8): 15-26 [Abstract] ( 178 ) PDF (3407 KB) ( 435 )

	27	Joint and optimal impoundment oepration of Jinsha River's cascade reservoirs and Three Gorges Reservoir
		HE Shaokun, GUO Shenglian, LIU Pan, CHEN Kebing, XIONG Feng, ZHANG Jianting
		DOI: 10.11660/slfdxb.20190803
		Based on the hydrologic and meteorological characteristics of the upper Yangtze basin, the timing of reservoir early impoundment is determined in this work. We construct a multi-objective impounding operation model and solve it using a Pareto-archived dynamically dimensioned search (PA-DDS) algorithm to obtain a series of Pareto fronts. The results demonstrate that when an optimal joint impounding scheme is applied, the starting impoundment dates of Wudongde, Baihetan, Xiluodu, Xiangjiaba and Three Gorges reservoirs can be advanced up to Aug. 1, Aug. 1, Sep. 1, Sep. 1 and Sep. 10 respectively, without lowering the design flood control standard. The proposed scheme can generate 3.68 billion kW?h more power (increase 3.12%) annually in comparison with the designed impounding rules and improve the full storage rate to 95.1% (increase 3.38%). For normal and dry years, these starting impoundment dates can be further advanced to Aug. 1, Aug. 1, Aug. 25, Aug. 25 and Sep. 1, which can generate 4.58 billion kW.h extra power (increase 4.1%) and the full storage rate increases from 88.5% to 93.9%.
		2019 Vol. 38 (8): 27-36 [Abstract] ( 241 ) PDF (514 KB) ( 658 )

	37	Short-term optimal operation of cascade reservoirs considering dynamic water flow hysteresis
		JI Changming, LIU Yuan, ZHANG Yanke, LIANG Xiaoqing
		DOI: 10.11660/slfdxb.20190804
		In short-term optimal operation of a cascade hydropower system, the influence of water flow hysteresis between cascade reservoirs is usually neglected or the time delay considered as a constant. However, water flow hysteresis changes dynamically with upstream reservoir outflow, river channel storage, interval inflow and other factors. It is difficult to accurately predict downstream reservoir inflow in the cases of dynamic water flows. In this study, we screen out main factors affecting the inflow of lower reservoirs using a variety of methods, and develop a prediction model of the lower reservoir inflow by employing artificial neural networks with these factors as inputs. In a case study of the Jindong and Guandi hydropower stations, a daily optimization scheduling model of cascade reservoirs is constructed considering the dynamic time delay and solved with a progressive optimization algorithm. The results show that compared with the constant time delay models, a dynamic time delay model of a cascade reservoir system is more accurate in modeling the water flow connection between the reservoirs and can give an optimized scheme that increases the system’s power generation efficiency to a certain degree.
		2019 Vol. 38 (8): 37-47 [Abstract] ( 202 ) PDF (640 KB) ( 347 )

	48	Circulation characteristics of inlet/outlet open channel sections under asymmetric terrain
		GAO Xueping, ZHU Hongtao, SUN Bowen, ZHANG Han
		DOI: 10.11660/slfdxb.20190805
		This study simulates the details of the flow in a diversion open channel at a pumped storage power station to study its circulation characteristics under asymmetric terrain. It has been found that a large-size circulation is generated in the channel due to unfavorable terrain conditions, such as the asymmetric terrain boundaries in front and on both sides of the channel. This not only affects the flow pattern in the open channel, but reduces flow uniformity in the trash rack section at the inlet/outlet, thereby producing unfavorable effects. To improve the flow, we suggest two measures ? increasing the length of connection to the channel and expanding the excavation at one side of the channel. Numerical simulations show that these measures can shift the circulation to locations far away from the inlet/outlet, thus improving the flow pattern to a certain extent and reducing flow non-uniformity and other adverse effects. This study provides engineering measures to adjust the intake/outlet location and avoid large-scale excavation for the design of diversion channels of pumped storage power stations.
		2019 Vol. 38 (8): 48-60 [Abstract] ( 115 ) PDF (7546 KB) ( 66 )

	61	River pattern discriminace based on river energy consumption against flow resistance
		YANG Shuqing, BAI Yuchuan, XU Haijue
		DOI: 10.11660/slfdxb.20190806
		River flow is governed by resistance laws and its energy consumption against flow resistance is affected by various factors including flow and sediment conditions and riverbed morphology. The macro morphology of a river is a consequence of flow resistance, and its channel adapts to different boundary conditions of flow and sediment through adjusting morphology. Based on a dialectical relationship between energy consumption by resistance and river morphology, this paper introduces a river morphological parameter for simple discriminance of river patterns. We conduct statistical analysis on this new parameter using the data of several natural rivers of sandy and gravel beds and make correction for the influence of riparian vegetation factors on river patterns. And then we derive its empirical expression through data fitting and obtain the standard curves of different river patterns. Verification against the classical measurements reported previously and analysis of natural river data show that our method is simple to calculate and effective in classifying river patterns.
		2019 Vol. 38 (8): 61-74 [Abstract] ( 193 ) PDF (2529 KB) ( 490 )

	75	Effects of calculation methods of stormwater outlet discharges on simulations of urban flooding
		ZHU Chenghao, XIA Junqiang, ZHOU Meirong, HOU Jingming
		DOI: 10.11660/slfdxb.20190807
		Stormwater outlets transfer surface runoff to the sewer network, playing a key role in urban flood control. To understand the stormwater discharging mechanism of the outlets, this paper summarizes the outlet discharging capacity in previous experimental studies and compares the pros and cons of different calculation methods and their application scopes. Then, we modify the source code of SWMM to create a dynamic link library (DLL), develop an urban flood model, and improve the calculations of stormwater outlet discharge. Through application in a case study of the Fengxi new town in Xi’an, different calculation methods are evaluated quantitatively in terms of the accuracy in the outlet discharge volume and the depth of depression storage over a catchment. Results show that for a typical catchment under a typical rainfall event, the total outlet discharge volume is 38% - 48% of the rainfall volume, as predicted by different methods. An 18% difference in discharge coefficient among the different formulas is amplified up to a 55% difference in the simulated depth of depression storage, and the maximum depth over the study area is in a range of 0.1-0.6 m due to insufficient capacity of the outlets.
		2019 Vol. 38 (8): 75-86 [Abstract] ( 211 ) PDF (2664 KB) ( 475 )

	87	Hydrologic-hydrodynamic model and its application in flood risk analysis
		YU Wangyang, JIANG Chunbo, LIU Jian, ZHOU Qi
		DOI: 10.11660/slfdxb.20190808
		Watershed flood simulation is a focus of flood analysis and prediction and a fundamental issue in flood control and disaster reduction. In this study, flood propagation process in a small basin is calculated by coupling a distributed hydrological model and a hydrodynamic model on the platform of SWAT and HEC-RAS. In a case study of the Longxi River basin in Chongqing, different scenarios of rainstorms over a small watershed are predicted through runoff generation, confluence calculation, and two-dimensional numerical simulation of floods, considering meteorological, topographic, and underlying surface conditions. The calculations show that this coupling model can simulate effectively the confluence process over the basin under complicated conditions and it is useful to the decision of disaster reduction when combined with disaster loss assessment and flood risk analysis.
		2019 Vol. 38 (8): 87-97 [Abstract] ( 342 ) PDF (1800 KB) ( 803 )

	98	Surface flooding in urban areas under heavy downpours: Case study of Tsinghua University campus
		LIU Lu, SUN Jian, YUAN Bing, LIN Binliang
		DOI: 10.11660/slfdxb.20190809
		Along with rapid urbanization, imperious ground surfaces are expanding dramatically in China, resulting in a higher risk of urban flooding. This study focuses on accurate high-resolution simulations of rainfall-runoff process over an urban area featured with buildings, roads, grass lands and street outlets, and examines the performance of its surface drainage system. A two-dimensional hydrodynamic model is used in a case study of the Tsinghua University campus in Beijing, and it is calibrated and validated against the pressure gauge measurements of water depth at two waterlogging sites under two heavy downpour events. The results show accurate predictions of the surface flooding water depth and the necessity of using atmospheric pressure data recorded during the downpours to reduce the errors in water depth calculations that are otherwise significant. A detailed examination on overland flow patterns under a downpour of July 21st, 2012 reveals significant variations in the total runoff drainage into all the street outlets with different rainfall processes. Most of the surface impoundment was drained into rainwater outlets and 70.0% of the total rainfall volume released through surface runoff into the drainage system, while only 11.1% was through surface infiltration.
		2019 Vol. 38 (8): 98-109 [Abstract] ( 240 ) PDF (9480 KB) ( 113 )

	110	Ultra-low frequency oscillation attenuation and stability margin region of hydropower units
		HOU Liangyu, YANG Jiandong, YANG Weijia, MA Anting, ZHAO Zhigao
		DOI: 10.11660/slfdxb.20190810
		Recent years have seen frequent problems of ultra-low frequency oscillations in power systems caused by hydropower units. Understanding the characteristics of such oscillations at hydropower stations is key to the stable operation of power systems, and an in-depth study is necessary in engineering practice on how to ensure the stability margin of a system along with a quantitative analysis of its oscillation attenuation characteristics. Aiming at this problem, this paper develops a mathematical model of hydraulic unit regulation based on the concept of a stability margin. By comparing theoretical analysis with numerical simulation, we discuss attenuation characteristics of the ultra-low frequency oscillations of the units in different stability margin regions, and reveal a relationship of the parameters of the regulating system versus the attenuation coefficient, together with a brief example of engineering application for demonstration. The results show that a stability margin can represent the attenuation of system responses in time domain. It is the power coefficient of the response envelope expressed in an exponential form, and equals the product of the response frequency and damping ratio of the system. When the parameters in a regulating system change, the attenuation characteristics of its ultra-low frequency oscillations can be obtained by deriving theoretically the variation in its stability margin region.
		2019 Vol. 38 (8): 110-120 [Abstract] ( 195 ) PDF (1199 KB) ( 375 )