Spatiotemporal Distribution Law of Unsteady Flow Induced by Daily Generation of Large-Scale Hydropower Station and Main Driving Factors

After the construction of the large-scale hydropower station,the flow during the dry season downstream will significantly increased.However,the channel downstream the dam will be affected by the unsteady flow induced by daily regulation of the upstream hydropower stations,which directly pose a threat to the safety of ship navigation.It is of great significance to study the spatiotemporal distribution and propagation mechanism of unsteady flow induced by daily regulation of the hydropower stations.This study focuses on the channel between XLD hydropower station and XJB hydropower station in the lower reach of Jinsha river.The data of hourly outflow of XLD hydropower station,water stage downstream of XLD hydropower station and hourly water stage in front of dam of XJB hydropower station during 2015~2020 were adopted.The power generation dispatching rules of XLD hydropower station was revealed by using wavelet analysis.The characteristics and main driving factors of water level fluctuation affected by the unsteady flow induced by daily generation of XLD hydropower station was identified based on the random forest regression.The correlation between maximum water level fluctuation and maximum discharge fluctuation downstream of XLD hydropower station was analyzed.The probability distribution function of maximum water level fluctuation downstream of XLD hydropower station was constructed.The influence area and cumulative frequency of the unsteady flow induced by daily regulation of XLD hydraulic station under the critical threshold condition of the maximum water level variation amplitude for ensuring the safety of ship navigation were analyzed.The study produced some important results:①The main driving factors of the maximum water level fluctuation downstream of XLD hydraulic station are both amplitude variation of discharge from XLD hydropower station and water stage in front of dam of XJB hydropower station,the cumulative contribution rate of which reaches more than 82%;②The maximum amplitude variation of water stage increases with the increasing of maximum amplitude variation of discharge downstream of XLD hydropower station,and there is a significant positive linear correlation between them;③The area with a cumulative frequency of 95% that satisfies the conditions of maximum daily water level variation is less than or equal to 3m and maximum hourly water level variation is less than or equal to 1m is located more than 10.7km downstream from the dam site of XLD hydropower station.