The 24th IAHR-APD Congress (24th IAHR-APD Congress)

187 / 2024-02-27 10:54:23

Seiche oscillations in an impounded river due to flow regulation of cascade reservoirs

seiche oscillations; impounded river; numerical model; flow regulation;

The primary method of managing water resources in medium- and large-sized rivers worldwide today is joint scheduling of cascade reservoirs; outflow regulation operation of cascade hydropower stations increases the non-constancy of river flow, and dam barriers foster large-scale reciprocal oscillations of river flow. Based on measured water-level and 1D-RKDG hydrodynamic numerical model, the existence of multi-modal high-frequency seiche oscillations is confirmed in the impounded river between Three Gorges Dam and Gezhouba Dam (D2D) in this paper, and they are excited by the rapid outflow regulation of hydropower stations. Measured water-level indicates that the first four modal periods of seiche oscillations are approximately 1.65, 1.0, 0.68, and 0.53 h. The simulated frequency of the fundamental seiche mode is about 10 cpd (periodicity 2.4 h), and the amplitudes of simulated water-level and discharge are in the order of cm and 10² m³/s, respectively. This study also discusses the generation mechanism of seiche based on the gravity wave theory, specifically, it shows how the outflow joint regulation causes the anomalous inclination of channel's water surface as well as oscillation back and forth. Additionally, the decay time of seiche is calculated to be about 3 h based on the standing wave exponential decay theory, and the decay process is regulated by friction attenuation of channel itself and the radiation attenuation from hydropower station outflow process. For the operation of hydropower stations, faster regulation time and larger regulation amplitude will significantly strengthen the intensity of the seiche oscillations in D2D.