Abstract:

Luoshan hydrological station serves as a crucial flood control base in the middle reaches of the Yangtze River as it is located at the confluence of mainstream Yangtze River and the outflow of Dongting Lake with complex stage-discharge relationship. We analyzed the trends and influencing factors of stage-discharge relationship at Luoshan Station under erosion conditions by employing the M-K test method, Theil-Sen Median method, and a comprehensive correction approach for stage-discharge relationship based on measured water level and discharge data from 1990 to 2021 and typical river section data for selected years. Our key findings are as follows: 1) The water levels at Luoshan Station for low and medium discharges significantly decreased, which was consistent with the decline of the centroid elevation of low water-level channel and basic channel. Conversely, the water level at flood discharges exhibited large fluctuation range, yet with a non-significant upward trend. 2) The operation of the Three Gorges Reservoir has narrowed the fluctuation range of water level differences between Luoshan Station and Hankou Station, leading to an overall increase in the average water level difference. However, after 2013, the water level difference within flood flow intervals reduced, potentially exacerbating topwater conditions at Luoshan station during the flood season. During continuous flooding events in 2016 and 2020, contributions from topwater elevation, fluctuation rate, and other influencing factors at Luoshan Station averaged 34.8%, 23.8%, 41.4% and 31.4%, 50.6%, and 18.0% respectively; indicating that topwater elevation and fluctuation rate are primary influencing factors on water levels while other contributing factors may have larger proportions in certain years.

Key words: stage-discharge relationship, downstream jacking, rate of fluctuation, channel geometry adjustment, Luoshan station