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The Xiaolangdi Dam is a key project for the control and development of the Yellow River. It bears the functions of flood control, controlling water and sediment in the lower reaches, ice prevention, industrial and agricultural water supply, power generation, and so on. Its safety is related to people's life and property safety and local economic and social development. It is of great significance to carry out comprehensive and regular deformation monitoring for dams since the deformation is an important evaluation index for dam safety. Interferometric Synthetic Aperture Radar (InSAR) technology has been a rapidly evolving technology in the field of space geodesy in recent years. It offers advantages such as high monitoring precision, extensive coverage, and high monitoring point density, making it a powerful tool for monitoring deformations in hydraulic engineering projects. Based on Sentinel-1 data covering the Xiaolangdi Dam from September 2020 to November 2022, the PS-InSAR technique was used to obtain the surface deformation of the Xiaolangdi Dam, and reservoir water level data on image acquisition dates were obtained for joint analysis. The results show that there is a large deformation in the center of the dam crest of the Xiaolangdi Dam, while both sides of the slope and downstream dam foot are relatively stable. The time series deformation of the dam body is closely related to the reservoir water level change. When the water level increases, the dam body tends to deform downstream; when the water level decreases, the dam body tends to deform upstream. The deformation and water level of the Xiaolangdi Dam exhibit a clear negative correlation. There is no significant cumulative deformation on the dam slopes or at the base of the dam. However, cumulative deformation occurs over time in the central area of the dam's crest. The deformation process at the central area of the dam's crest follows a continuous and non-disruptive pattern, which is consistent with the typical deformation behavior of the Xiaolangdi earth–rock dam structure. Therefore, it is judged that the current deformation of the Xiaolangdi Dam does not impact the safe operation of the dam. InSAR technology enables the rapid acquisition of high-precision, high-density deformation information on the surfaces of reservoir dams. With an increasing number of radar satellites in various frequency bands, such as Sentinel-1 and TerraSAR-X, there is now an ample supply of available data sources for InSAR applications. Consequently, InSAR technology can be extended to routine monitoring applications for reservoir dam deformations, especially for small and medium-sized reservoirs that may not be equipped with ground measurement tools like GNSS. This holds significant importance and potential for enhancing the safety monitoring of such reservoirs. [ABSTRACT FROM AUTHOR]

Reservoir sedimentation usually occurs in rivers that carry heavy amounts of silt. Setting reasonable schedules for drainage hole operations can balance the reservoir sediment levels and downstream river morphology. China's Yellow River is well known for its abundant sediment supply. The Xiaolangdi Reservoir is the key control project for the main stem of the Yellow River, and its sediment accumulation is especially serious. Preventing sedimentation before the gates is an important issue. The characteristics of the flow and sediment before the intake towers under scheduled drainage hole operations should be thoroughly researched. In this study, a three-dimensional numerical model was established based on MIKE 3. Variations of the flow structure, sediment concentration, and sedimentation elevation were the parameters studied under the scheduled operations. The results showed that the features of the bend flow are developed during the model phase. The velocity distribution in the vertical direction does not follow the general logarithmic distribution law of open channels. Scouring funnels appear during the development of the sedimentation surface before the intake towers. The sedimentation elevation is lower than the permissible value and has no influence on gate operations. This paper can provide a reference for similar research. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 ground-water 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 = 12 months), 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 for 32.47% of GWL changes, while in subzone V, the RWL (scale = 12 months) accounted for 52.52% 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. [ABSTRACT FROM AUTHOR]

Water resources are vital to the development of human society, and mastering the law of runoff changes is the basis for achieving sustainable use of water resources. To study the impact of reservoir construction on the changes of downstream river runoff, this paper decomposes the runoff before and after reservoir construction using the CEEMDAN method based on the runoff data from the Huayuankou hydrological station. The fluctuation characteristics of each decomposition series of runoff before and after reservoir construction and the intra-annual variation pattern of runoff are also analyzed by combining multi-time information entropy and coefficient of variation. The results show that after the operation of the Xiaolangdi Reservoir, the annual runoff variation cycle tends to be flat, and the monthly runoff cycle is significantly reduced. After reservoir construction, the entropy values of each IMF and Res of runoff become larger, the complexity and randomness of runoff changes increase, and predictability decreases. Before and after the operation of the Xiaolangdi Reservoir, the coefficient of variation of runoff were 0.28–1 and 0.38–0.83, the distribution of runoff was more uniform, and the percentage of runoff in the flood season was reduced from 51.51 to 39.89%. HIGHLIGHTS Analysis of runoff data using CEEMDAN and multiscale information entropy.; Analysis from several perspectives, including inter- and intra-year perspectives.; Analysis of monthly runoff using dispersion coefficients and monthly runoff process lines.; The influence of the reservoir on the runoff of the lower Yellow River was studied.;

This paper presents a comprehensive analysis on the ecological benefit and loss of Xiaolangdi reservoir from its completion in 2000 to 2012. We firstly propose a three-step framework of the ecological benefit–loss evaluation for hydropower projects, in accordance with which an index system of riverine wetland ecosystem services valuation was established originally. Then we make a quantitative valuation on the change of riverine wetland ecosystem services caused by this project. Finally, the ecological benefit and loss of the project in the riverine wetland were evaluated in two aspects of positive impacts and negative impacts. The results showed that (1) the positive impacts of Xiaolangdi reservoir mainly included 9 categories of ecosystem services: flood control, ice prevention, sedimentation reduction, energy substitution, emission reduction benefit, water supply, afforestation, shipping and entertainment; the total ecological benefit of the project in the riverine wetland was 26.2058 billion yuan. (2) The negative impacts of Xiaolangdi reservoir mainly included 5 categories: loss due to land submergence, heritage submergence, water and soil erosion, reservoir sedimentation and immigration; the total ecological loss of the project in the riverine wetland was 24.2167 billion yuan. (3) From 2000 to 2012, the net value of ecological benefit–loss for the project was 1.9891 billion yuan. [ABSTRACT FROM AUTHOR]

The optimal control problem of reservoir group flood control is a complex, nonlinear, high-dimensional, multi-peak extremum problem with many complex constraints and interdependent decision variables. The traditional algorithm is slow and easily falls into the local optimum when solving the problem of the flood control optimization of reservoir groups. The intelligent algorithm has the characteristics of fast computing speed and strong searching ability, which can make up for the shortcomings of the traditional algorithm. In this study, the improved sparrow algorithm (ISSA) combining Cauchy mutation and reverse learning strategy is used to solve the flood control optimization problem of reservoir groups. This study takes Sanmenxia Reservoir and Xiaolangdi Reservoir on the mainstream of the Yellow River as the research object and Huayuankou as the downstream control point to establish a joint flood control optimization operation model of cascade reservoirs. The results of the improved sparrow algorithm (ISSA), particle swarm optimization (POS) and sparrow algorithm (SSA) are compared and analyzed. The results show that when the improved ISSA algorithm is used to solve the problem, the maximum flood peak flow of the garden entrance control point is 11,676.3 m3, and the peak cutting rate is 48%. The optimization effect is obviously better than the other two algorithms. This study provides a new and effective way to solve the problem of flood control optimization of reservoir groups. [ABSTRACT FROM AUTHOR]

The construction of water conservancy projects not only brings benefits such as flood control and disaster reduction but also has many effects on the habitat and reproduction of local aquatic organisms. Taking the reach from Xuzhuang Station to Gaocun Station in the lower Yellow River as an example, this paper discusses the effect of the Xiaolangdi Reservoir on the habitat of Yellow River carp (Cyprinus carpio). By constructing a two-dimensional hydrodynamic model, coupled with a habitat suitability model of the spawning ground of Yellow River carp, the weighted usable area (WUA) of the Yellow River carp habitat was calculated, and the spatial distribution of the habitat suitability index (HSI) in the reach was analyzed to evaluate habitat quality before and after the construction of the Xiaolangdi Reservoir. The results showed that the Xiaolangdi Reservoir had a negative effect on the habitat of Yellow River carp, resulting in the reduction of the spatial distribution of HSI, a decrease in WUA by 45.53%, and a decrease in habitat quality. The construction of the Xiaolangdi Reservoir reduced or even eliminated flow pulses in the downstream reach, but had little effect on the suitability index of water depth and velocity. However, the suitability index of water level rise was significantly reduced, which is not conducive to the spawning activities of aquatic organisms and has a negative effect on habitat. The results of this study will provide a reference for ecological restoration in this region.

Abstract: This paper studies relations between bankfull discharge, lateral cross section variation and the incoming flow and sediment condition in the Lower Yellow River using measured data from 1950 to 2003. Since 1950 the bankfull discharge has obviously decreased and the ratio of channel width to flow depth has increased. The critical annual average incoming sediment coefficient (defined as the ratio of sediment concentration to discharge) and discharge at the Huayuankou station are approximately 0.012 and 1,850 m3 s−1, respectively, for no accumulative deposition occurring in the reach from Huayuankou to Lijin. On this basis, a mathematical model is used to study the scale of the main channel in the Lower Yellow River and its corresponding bankfull discharge under possible incoming flow and sediment conditions in the near future. The main factors influencing the scale of the main channel are analyzed, and measures to shape and maintain a medium-sized channel are discussed. The results show the effect of various water and sediment combinations released from the Xiaolangdi Reservoir on the shaping of the main channel and suggest that under recent incoming flow and sediment conditions, it is possible to shape and maintain a medium-sized channel with a bankfull discharge of approximate 4,000 m3 s−1. [Copyright &y& Elsevier]

The Xiaolangdi Reservoir has entered the later sediment-retaining period, and new sediment transport phenomena and channel re-establishing 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 m3/s

The Yellow River is the most hyperconcentrated sediment-laden river in the world. Throughout recorded history, the Lower Yellow River (LYR) experienced many catastrophic flood and drought events. To regulate the LYR, a reservoir was constructed at Xiaolangdi that became operational in the early 2000s. An annual water-sediment regulation scheme (WSRS) was then implemented, aimed at flood control, sediment reduction, regulated water supply, and power generation. This study examines the eco-environmental and socioenvironmental impacts of Xiaolangdi Reservoir. In retrospect, it is found that the reservoir construction phase incurred huge financial cost and required large-scale human resettlement. Subsequent reservoir operations affected the local geological environment, downstream riverbed erosion, evolution of the Yellow River delta, water quality, and aquatic biodiversity. Lessons from the impact assessment of the Xiaolangdi Reservoir are summarized as follows: (1) The construction of large reservoirs is not merely an engineering challenge but must also be viewed in terms of resource exploitation, environmental protection, and social development; (2) long-term systems for monitoring large reservoirs should be established, and decision makers involved at national policy and planning levels must be prepared to react quickly to the changing impact of large reservoirs; and (3) the key to solving sedimentation in the LYR is not Xiaolangdi Reservoir but instead soil conservation in the middle reaches of the Yellow River basin. Proper assessment of the impacts of large reservoirs will help promote development strategies that enhance the long-term sustainability of dam projects. [ABSTRACT FROM AUTHOR]