Effect of contracted river on tidal bore in Qiantang Estuary

Since the late 1960s, the Qiantang Estuary has been narrowed on a large scale, significantly changing the water-sediment dynamics, riverbed evolution and their interaction processes. However, the tidal bore in response to the high-intensity human activities is not fully understood. Based on the measured data of topography, tide and tidal bore, combined with the mathematical model of tidal bore, the effects of large-scale contracted river for regulation on tide, river bed and tidal bore of Qiantang Estuary were studied. The results show that the distribution of shoal and channel was basically stable after the river was narrowed. With the increase of the ratio of river flow to tidal current, roughly bounded by Yanguan, the lower part of the tidal bore reaches was silted, the upper part was scoured, and the sandbar was moved downstream. The high tidal level rose along the estuary, the tidal range increased near the place where the tidal bore occurred and the upper part of the tidal bore reaches from Zhakou to Cangqian reach, and decreased from Cangqian to Yanguan reach. As a result, the occurrence point of the tidal bore and the maximum tidal bore position move downstream, the viewing positions of the tidal bore are fixed, the tidal bore scenery is abundant and stable, the tide bore arrival time is stable, the amplitude of the tidal bore height decreases, and the tidal bore height decreases from Cangqian to Yanguan reach. In order to protect the tidal bore, it is necessary to maintain a large tidal range and appropriate water depth in the tidal bore reach, and it is not suitable to carry out large-scale reclamation.