Abstract: Yaojiang River, Fenghua River and Yongjiang River are known as “Three Rivers of Ningbo”. According to hydrological data measured for seven times during 2013-2016, together with measured hydrological data in 1987 and tide data for many years, the characteristics and causes of flow and sediment change in the Three Rivers were analyzed. Results revealed that runoff had large effect on slowing down sediment transport from estuaries to upstream, and sediment concentration gradually decreased from estuaries to the upstream in Yongjiang River. The average high tide level displayed a rising trend since the 1980s on account of sea level rise, river regime change and human activities. In 2010-2016, the average high tide level at Zhenhai station was 0.33 m higher than that in the 1980s. In the past three decades, under the same tidal range, the mean velocity of rising tide in Yongjiang River estuary experienced no significant change; while influx showed a trend of decrease, yet sediment concentration and sediment discharge showed a trend of increase. The research findings offer scientific basis for riverbed evolution research and technical support for the regulation of Yongjiang river drainage basin.

Key words: Three Rivers of Ningbo, characteristics of flow and sediment change, tidal characteristic, sediment concentration, sediment discharge