Technology improvements and management innovations in construction of Xiluodu hydropower station on Jinsha River

Developer and owner:China Three Gorges Corporation(CTG)Engineering management:China Three Gorges Projects Development Corporation(CTGPC)Designer:Chengdu Engineering Corporation Co.,Ltd.,Power

A Novel Hybrid Intelligent Prediction Model for Valley Deformation: A Case Study in Xiluodu Reservoir Region, China

The narrowing deformation of reservoir valley during the initial operation period threatens the long-term safety of the dam,and an accurate prediction of valley deformation(VD)remains a challenging part of risk mitigation.In order to enhance the accuracy of VD prediction,a novel hybrid model combining Ensemble empirical mode decomposition based interval threshold denoising(EEMD-ITD),Differential evolutions—Shuffled frog leaping algorithm(DE-SFLA)and Least squares support vector machine(LSSVM)is proposed.The non-stationary VD series is firstly decomposed into several stationary subseries by EEMD;then,ITD is applied for redundant information denoising on special sub-series,and the denoised deformation is divided into the trend and periodic deformation components.Meanwhile,several relevant triggering factors affecting the VD are considered,from which the input features are extracted by Grey relational analysis(GRA).After that,DE-SFLA-LSSVM is separately performed to predict the trend and periodic deformation with the optimal inputs.Ultimately,the two individual forecast components are reconstructed to obtain the final predicted values.Two VD series monitored in Xiluodu reservoir region are utilized to verify the proposed model.The results demonstrate that:(1)Compared with Discrete wavelet transform(DWT),better denoising performance can be achieved by EEMD-ITD;(2)Using GRA to screen the optimal input features can effectively quantify the deformation response relationship to the triggering factors,and reduce the model complexity;(3)The proposed hybrid model in this study displays superior performance on some compared models(e.g.,LSSVM,Backward Propagation neural network(BPNN),and DE-SFLA-BPNN)in terms of forecast accuracy.

Seismic activities before and after the impoundment of the Xiangjiaba and Xiluodu reservoirs in the lower Jinsha River

The lower Jinsha River basin is located at the junction of Sichuan and Yunnan provinces in Southwest China,a region with intense tectonic movements and frequent moderate to strong seismic activities.Cascade hydropower stations have been constructed along the lower Jinsha River since 2012.However,research on the effect of the impoundment of large-scale cascade reservoirs in a river basin on local seismic activities is currently lacking.Accurately identifying earthquake locations is essential for studying reservoir-induced earthquakes.Analyzing the spatiotemporal migration process of seismic activities based on complete and precise earthquake relocation is fundamental for determining the fluid diffusion coefficient,constructing fault models for reservoir areas,identifying earthquake types,exploring earthquake mechanisms,and evaluating seismic hazards.The seismicity pattern in the Xiangjiaba and Xiluodu reservoir areas,where seismic activities had been weak for a long time,has changed with the successive impoundment of the two reservoirs,showing microseismic events and seismic clusters.We investigated the spatiotemporal characteristics of seismic activities in the Xiangjiaba and Xiluodu reservoir areas using the waveform cross-correlation-based double-difference relocation technique and the b-value analysis method.We discovered that seismic events after the impoundment of these two reservoirs exhibited different characteristics in different regions.The seismic activities at the Xiluodu dam quickly responded to the rising water level,with the seismic intensity decaying rapidly afterward.These events were concentrated in the limestone strata along both sides of the Jinsha River,with a shallow focal depth,generally within 5 km,and a high b-value of approximately 1.2.Such features are close to those of karst-type earthquakes.Microseismic activities frequent occur on the eastern bank of the Yongshan reservoir section downstream of the Xiluodu dam,with two parallel NW-trending earthquake strips visible after precise earthquake relocation.The M_(S)5.2 earthquake near Wuji town on August 17,2014,had prominent foreshocks and aftershocks distributed in a clear NW-trending 20-km-long strip,perpendicular to the riverbank.These seismic events had a low b-value of approximately 0.7.The orientation of the node plane revealed by the strike-slip focal mechanism of the mainshock is consistent with that of the strip formed by the foreshock-mainshock-aftershock sequence,indicating the existence of a NW-striking concealed fault.Seismic activities near the Yanjin-Mabian fault upstream of the Xiangjiaba reservoir area since 2013 were concentrated in a NW-trending strip,with several near EW-trending seismic clusters on its western side,and with the largest event having a magnitude of M_(L)3.7.So far,the impoundment of the Xiangjiaba and Xiluodu reservoirs has not triggered seismic activities on the large Jinyang-Ebian and Yanjin-Mabian faults nearby.