Hydrodynamics of the Qiantang Tidal Bore and Its Responses to Embankment, Morphology, and River Discharge

The Qiantang tidal bore is globally renowned for its spectacular landscape and its strong impacts on the Qiantang riverbed erosion/deposition process. However, due to the extremely high spatial gradient of its water level along the propagation direction around the bore front, as well as the very swift movement of this front, the numerical reproduction of the bore formation and propagation has been a challenge for several decades. Here, using GPU acceleration and Local Time Stepping (LTS), we present a high-resolution simulation of the Qiantang tidal bore formation and propagation, achieving a 10 m resolution across 1169 km2, which captures the bore dynamics and the full formation-to-decay processes while simulating 2-day tidal bore phenomena in 1.2 h. The formation mechanisms of three typical tidal bores (cross-shape bore, thread-shape bore, and returned bore) are revealed numerically. The cross-shape bore appears first and is generated by flow division around the mid-channel bars; further upstream, the thread-shape bore is formed due to the increasingly narrow river along a straight reach; and its reflection results in the returned bores at the YC bending reach. This study also highlights how variations in flow discharge affect the tidal bore. When the discharge increases to the annual mean discharge, the intensity of the tidal bore is increased, whereas extremely high flood peak discharge inhibits bore propagation. This study provides a scientific basis for conserving tidal bore landscapes and offers decision support for sustainable estuarine governance.