Formation Mechanism and Stability Analysis of the Hejia Landslide

The existing research data show that, after reservoir impoundment, due to the repeated rise and fall of water level and water-rock interaction, the mechanical parameters of landslide are reduced, which will have an adverse effect on the stability of landslide. Therefore, sufficient attention must be paid to the stability of slope after reservoir impoundment. Hejia landslide is the largest landslide near the bank of Miaojiaba hydropower station, and its stability plays an important role in the normal operation of the hydropower station. Through field investigation and analysis of regional geological conditions, it is concluded that Hejia landslide is a large-scale landslide, through long-term sliding-bending deformation; it is generated from the external hard rock with thick layers and sliding zone for layered soft rock; the formation mechanism of landslide is as follows: (1) high-steep and hard-soft layered slope is the slope structure condition that caused the large landslide; (2) the existence of thick soft rock belt provides material conditions for the formation of slip surface; (3) certain air conditions provide displacement space for the separation and disintegration of the sliding body, and the landslide is stable at present. Numerical analysis results show that reservoir impoundment will adversely affect the stability of landslide. In order to ensure the normal operation of power station, certain engineering measures must be taken to treat Hejia landslide. After taking measures, years of monitoring data show that the deformation of Hejia landslide tends to be stable, and the current operation is normal, indicating that the engineering treatment measures are reasonable and feasible.

The Dynamics of Hongjian Nur, the Largest Desert Freshwater Lake in China, during 1990–2017

China’s largest desert freshwater lake, Hongjian Nur (HN), which is the largest habitat of relict gull (Larus relictus), has rapidly changed in recent years. However, it is difficult to quantitatively monitor the dynamics of the lake and determine the causes of its changes due to the lack of in situ observation. In this study, a remote sensing-based approach was utilized to overcome these limitations. The monthly water areas during 1990–2017 were first extracted from Landsat multispectral images via an improved method based on the floating algae index (FAI). Then, lake surface elevations measured by real-time kinematics (RTK) were used to calculate the variations in the water storage of HN. Finally, the driving factors of the rapidly changed HN in different periods were investigated by correlation analysis. The result indicated that the drivers affecting the water storage of HN in different periods were not the same. Climate change was the main driving factor of lake level fluctuation during the HN relatively stable stage (1990–1998). Drought and the intensification of human activities were the main factors for the rapid shrinkage of the HN during 1999–2010. Human activities, especially coal-related industries and reservoir impoundment, likely was the primary factors driving the decrease in the water storage of HN from 2010 to 2015. After 2015, the policies that decreased the water consumed by human activities formulated by the government and humid climate were the main factor for the expansion of HN.

Projected climate impacts of large artificial reservoir impoundment in Yalong River Basin of southwestern China

Cascade reservoirs were designed for Yalong River Basin, which ranks the 3rd largest hydropower base in China. Reservoir impoundment has certain impacts on local climate, but few researches focus on this field. This paper integrates the spatiotemporal analysis techniques and geostatistical methods to identify the reservoir projected meteorological indices (MIs) variations as well as the impact scope under different circumstances. Results show: The reservoir projected variations of moisture indexes were much more significant than temperatures. Anthropogenic disturbance has led to dramatic decrease of relative humidity in the past decade, far beyond its periodic amplitude range. Moreover, dry valley faced more serious drought risk but reservoir impoundment of this region alleviated the local drought risk. The daily minimum temperature, relative to the maximum temperature, was more sensitive to catchment changes with an earlier appearance of temperature zone variation. Since impounding, the MIs internal relationships in non-dry valley varied significantly more than that in dry valley, with the positive correlation of 0.7 between the relative humidity and precipitation weakened greatly. The severe warming hotspots distributed in the upper reach and had the probability of 0.95- 1 to exceed 1.5℃ IPCC control target. This study provides references for the disturbance of reservoir impoundment to local climate at multiple temporal-spatial scales under different circumstances and contributes to the MIs variation pattern identification and quantitative risk assessment.

A Comprehensive Investigation on Abnormal Impoundment of Reservoirs—A Case Study of Qionglin Reservoir in Kinmen Island

Leakage is the most serious problem in reservoir operation, because heavy leakage influences reservoir impoundment efficiency and even leads to a complete loss of reservoir functions. Since its completion in 1982, Qionglin Reservoir has never been fully filled with water except in the spring of 1983 when there was heavy rain. The reservoir management unit suspected that its side slopes, bottom or dam might leak and carried out a number of leakage prevention and improvement works, but all of them failed to fulfill the impoundment function of the reservoir. Hence, this study attempts to find out the reasons why the reservoir cannot impound water. A series of tests and investigations are carried out in this study, including electrical resistivity tomography of dam, tracer test, geological drilling test, reservoir water level observation, investigation of reservoir catchment area and field investigation of dam. The test results and investigation results show that no leakage path and leakage are found. According to the analysis, there is no serious leakage of this reservoir. The main reason for the failure of impoundment is that massive improper development in the catchment area influences the runoff into the reservoir.

Slow slip-driven seismic signature triggered by water-reservoir impoundment

One of the most important and widely used renewable energy sources is hydroelectric energy produced via Water Reservoir Impoundment (WRI). WRI can trigger strong earthquakes under favourable geological conditions. Thus, the socio-economic impact of reservoir triggered seismicity is very significant. Although many studies have investigated the relationship between the pore pressure changes due to WRI and the observed seismicity, hydromechanical models that explain the observed processes are rare. Here, we investigate the role of hydromechanical interactions during fault deformation to understand earthquake swarm bursts under pore pressure changes due to WRI. As a natural laboratory, we selected the Song Tranh 2 Reservoir in Vietnam. Because the analysed triggered seismicity has swarm characteristics, our work contributes to the further investigation of the physical mechanisms responsible for earthquake swarms and their relationship to slow slip. We conclude that the small high-frequency seismic swarms accompanying WRI are driven by slow slip along a fault; they occur due to the temperature-controlled frictional fault heterogeneity, and their rate and magnitude depend on the sizes of these heterogeneities. Swarm earthquakes are the effect of slip acceleration on the seismic radiation level. The nucleation fronts expand the nucleation regime and may transition into stronger earthquakes. These results provide insights into the physical mechanisms of seismic processes triggered by WRI, which may have implications for assessing the seismic hazards associated with hydroelectric energy production.

Remote Sensing Investigation of the Offset Effect between Reservoir Impoundment and Glacier Meltwater Supply in Tibetan Highland Catchment

This article presents multi-source remote sensing measurements to quantify the water impoundment and regulation of the Zhikong Reservoir (ZKR) and Pangduo Reservoir (PDR), together with the estimation of the glacier mass balance to explore whether the increased glacier meltwater supply can buffer the influences of the reservoir impoundment to some degree in the Tibetan highland catchment. The ZKR and PDR are two reservoirs constructed on the upper Lhasa River that originate from the Nyainqentanglha glaciers in the remote headwater in the Tibetan Plateau (TP) and lacks historical in situ hydrological observations in the long term. Therefore, the Joint Research Center (JRC) Global Surface Water dataset (GSW), and the Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM) data were used for estimating the total amount of water storage of the two reservoirs, and the SRTM and TanDEM-X DEMs were used for estimating the glacier mass balance. The result shows that the total amount of water impounded by reservoirs is 0.76 Gt, roughly 54% of their design capacities. The mass balance of the glaciers is estimated by comparing the elevation changes between the SRTM and TanDEM-X DEMs. The glaciers in this region melt at an average rate of 0.09 ± 0.02 Gt·year−1 from 2000 to circa 2013, and the impounded water of these reservoirs is comparable to the amount of glacier-fed meltwater in eight years.

Predicting the effects of reservoir impoundment on phytoplankton and shoreline vegetation communities using the space-time substitution method

The prediction of the influence of reservoir impoundment on water quality and phytoplankton community is the basis of ecological compensation or restoration. The aim of the current study was to predict the effects of reservoir impoundment on phytoplankton and shoreline vegetation communities using the space-time substitution method. The Huangjinxia Reservoir under construction on the Han River was selected as the research object. The space-time substitution method indicated that the average values of the total phosphorus (TP) and ammonia (NH4+-N) increased from 0.049 and 0.279 mg L−1 to 0.139 and 1.132 mg L−1, respectively, after reservoir impoundment. The percentage of diatom biomass exceeded 95% before the reservoir impoundment. However, it was gradually decreased to 75% after the reservoir impoundment. Meanwhile, the biomass of Chlorophyta, Cryptophyta and Pyrrophyta increased significantly, accounting for 32, 20 and 13% of the total biomass, respectively, after reservoir impoundment. Cynodon dactylon (65.3%), Polygonum hydropiper (51.7%) and Aster subulatus (50.3%) were the dominant shoreline vegetation before the reservoir impoundment, whereas after the reservoir impoundment, the dominant species shifted to Alternanthera philoxeroides (62.3%), Lobelia chinensis (55.7%) and C. dactylon (53.9%). Our results suggested that the percentage of bloom-forming phytoplankton would gradually increase after the reservoir impoundment. In addition, A. philoxeroides, C. dactylon and L. chinensis would be the plants suitable for living in the shoreline of reservoirs in this area.