The Cause and Statistical Analysis of the River Valley Contractions at the Xiluodu Hydropower Station, China

Abstract

The Xiluodu Dam is a concrete double-curvature arch dam with a crest elevation of 610 m and a height of 285.5 m. Since the impoundment of the Xiluodu reservoir, remarkable river valley contractions (RVCs) have been observed upstream and downstream of the reservoir, potentially threatening the safety of the dam. However, the cause of these RVCs remains unclear. Based on an analysis of hydrogeological conditions, the RVCs were determined a result of the expansion of the aquifer, within which the effective stress decreased due to an increase in the hydraulic head after reservoir impoundment. Referring to the hydrostatic seasonal time (HST) model, a groundwater hydrostatic seasonal (GHS) model is proposed for simulating and predicting the development of the RVCs. Unlike the HST model, the GHS model can provide information on aquifer hydraulic diffusivity. The calibration results illustrate that the GHS model can accurately fit the observed RVCs data. The calculation results revealed that the RVCs were mainly affected by the hydraulic head of the confined aquifer, and that seasonal effects gave rise to less than 10% of the total RVCs. Finally, the development of RVCs were predicted using the GHS model. The prediction results demonstrated that the RVCs of most monitoring lines in the Xiluodu reservoir would gradually approach a convergence condition after 6 February 2021. Until the deadline of the prediction on 1 May 2035, there is still one monitoring line that has not reached a convergence condition (whose RVCs are 157.6 mm, and where the RVC growth rate will decrease to 0.005 mm/d by that time). Considering the large amount of RVCs, we think the safety of the dam requires closer consideration.

Estimation of Hydraulic Diffusivity of a Confined Limestone Aquifer at the Xiluodu Dam

“…Along the downstream direction of the river, the buried depth of limestone gradually increases, and the degree of karst development decreases slowly. Restricted by the upper and lower aquitards, the limestone confined aquifer is only recharged at the basin's edge and discharged into the Jinsha River [23]. Near the bank slope, the AWL is mainly affected 4 Geofluids by the RWL for a short time.…”

Crustal response to water loads and expansion of triggered seismicity around the Xiluodu Reservoir, Southwest China

“…4 For instance, earthquakes following the impoundment of the Koyna Reservoir in India caused 200 deaths and several thousand injuries. 5 Previous reservoir geohazard research mainly focused on 1) the characteristics, monitoring, and preventative countermeasures of surficial geohazards (e.g., slope failures), [6][7][8] 2) the evolution and mechanisms of triggered earthquakes, [9][10][11][12][13] and 3) valley contractions across reservoir dam infrastructure and their associated causes. 14,15 However, due to the complexity of seismic mechanisms and the limitation of data analysis, relatively few studies have systematically evaluated the spatiotemporal distribution of earthquakes and underlying processes, 16,17 and thus their causal mechanisms remain largely uncertain.…”

Surface water–groundwater interactions of Xiluodu Reservoir based on the dynamic evolution of seepage, temperature, and hydrochemistry due to impoundment

“…The maximum valley deformation has exceeded 100 mm with no sign of convergence, which may endanger the safety of the reservoir. The mechanism of valley deformation is directly related to the change of GW level (Jia et al, 2009; Li et al, 2020; Xu et al, 2020); therefore, it is possible to determine the GW movement and evolution by studying the SW–GW interactions in the reservoir area. The results can provide a basis for the mechanism analysis, simulation, and prediction of valley deformation.…”

“…The results can provide a basis for the mechanism analysis, simulation, and prediction of valley deformation. Due to the different hydrogeological conditions of different flow systems in the dam area, including its recharge source, migration route, and water-bearing medium, the GW in the dam area differs greatly in terms of water temperature, hydrochemical characteristics, and quantity (Li et al, 2020;Liang et al, 2002;Zhou & Wang, 2002). The GW quality and distribution characteristics in the dam site have been attributed to the specific location environment (Wang & Zhou, 2000;Zhang et al, 2002;Zhou et al, 2020).…”