Character of extreme high tide level variations response to coastline deformation in Taizhou Bay

Abstract

Taizhou Bay, which locates in the southern coast of China, is frequently influenced by human activities, leading coastline changes frequently in coastline changes visible from space. Coastline deformation in this area will obviously affect the character of extreme high tide level variations in Jiaojiang River and Estuary especially during flood and typhoon periods. Statistic data showed that 54.5% of the extreme high tide levels of Jiaojiang River were caused by typhoon and 27.3% by flood in the past twenty-two years. So, a two-dimensional (2-D) hydrodynamic numerical model including Jiaojiang River and East China Sea was established based on the Mike21 FM model. The model was calibrated with field data and then was employed to predict the extreme flood and storm high tide level changes under three different assumption plans of coastline deformation. 100-year return discharge upstream with 2-year return tide level downstream conditions were set in the model to simulate extreme flood level changes, while Typhoon 0414 with actual discharge upstream were considered to simulate extreme storm high tide level variations. According to the flood level changes simulating results, an increase of 0.01∼0.03 m in extreme flood level will happen in river section and estuarine section and a decrease of 0.01∼0.06 m will occur outside estuarine section. Predictions of the typhoon conditions show that an increase of 0.01∼0.15 m in extreme storm high tide level will happen in both river and estuarine sections with a decrease of 0.01∼0.03 m outside of the Jiaojiang Estuary. Further analysis from tide wave point illustrates that propagation direction of nearshore tide wave in Taizhou Bay will be turned by coastline deformation, thus reflection effect of tide wave will be weakened, while distribution of storm tide currents field changes shows that tidal influx of Jiaojiang Estuary increases due to the blocking effect of the seawalls, causing this kind of special extreme high tide level changing formation.