Numerical Study On Coastal Tide And Tidal Current Off Qinhuangdao

The coastal waters off Qinhuangdao is located in the west of Bohai Sea.It is an important port and breeding base in the northern coastal area of China.The coastal current system is an important part of the Bohai Sea circulation system,It plays a decisive role in aquaculture industry,pollutant distribution and self-purification capacity,and ecological environment protection.The current is dominated by tidal current in the coastal waters off Qinhuangdao.Due to the limitation of observation conditions,most of the current researches for tide and tidal current in the coastal waters are based on the water level data of coastal tide gauge stations and a small amount of measured current data,and lack of refined understanding of the tide and tidal current in the whole coastal waters off Qinhuangdao.In addition,the existing research results also show that there is a phenomenon that the tide type is not consistent with the tidal current type in the coastal waters off Qinhuangdao,and there is no systematic research on this phenomenon.This paper is based on ROMS ocean dynamics model,a high-resolution tide and tidal current model is established in the coastal waters off Qinhuangdao.And the tide and tidal current in the coastal waters are simulated in detail,and the simulation results are verified.The verification results show that the value of the total relative error pairs of the amplitude and the lag angle of M₂ are within 3%.The value of the total relative error of K₁ component amplitude is about 9%.the lag angle is about 5%.the numerical simulation results are in good agreement with the measured data.Based on the analysis of numerical simulation results of tide and tidal current in the coastal waters off Qinhuangdao,it is found that there is a semidiurnal tidal non-tidal point in the study waters,which is located at 120.08^°E and 39.9175^°N.There are some regular diurnal tides around this non-tidal point,surrounded by irregular diurnal tides,and other areas are irregular semidiurnal tides.The main tide is diurnal tide in the coastal waters off Qinhuangdao,and K1 is the main dominant tide.The average value of K1 amplitude is28cm,and value of O1 is 22cm.And the average values of M₂ and S₂ amplitude are17cm and 7cm respectively.In the coastal waters off Qinhuangdao,the residual water level is positive in most of the sea areas from Luanhe estuary to dog estuary,and negative in most of the sea areas from dog estuary to Xingcheng estuary.Among them,the sea area near erhekou is the largest sea level drop area.It is dominated by regular semidiurnal tidal current in the coastal waters off Qinhuangdao,which is distributed in most of the coastal waters from Qinhuangdao to Xingcheng estuary.There is a part of irregular semidiurnal tidal current in the south of the study area.There are no current-amphidromic points in the coastal waters off Qinhuangdao.In the study area,the semidiurnal tidal current mainly rotates clockwise,while the diurnal tidal current mainly rotates anti-clockwise.In the coastal waters off Qinhuangdao,the main is NE-SW complex flow in the near shore sea area,the flow direction is roughly parallel to the shoreline.And the main is rotary flow in the open waters off Qinhuangdao.In the coastal waters off Qinhuangdao,the velocity of tidal residual current from surface to bottom decreases gradually.The maximum velocity of the surface,middle and bottom tidal residual currents is 25cm/s,22cm/s and 17cm/s respectively.The velocity of tidal residual current in most of the coastal waters from Luanhe estuary to dog estuary is small,while that in the north of the coastal waters off Qinhuangdao is relatively large,and the velocity of tidal residual current reaches the maximum in the sea area near the erhekou.In addition,a clockwise eddy circulation system is formed in the sea area near the erhekou.Based on the numerical simulation results of tide and tidal current,this paper analyzes the spatial distribution characteristics of tide and tidal current types in the coastal waters off Qinhuangdao.The results show that in the coastal waters off Qinhuangdao,the types of tide and tidal current are inconsistent in most of the coastal waters from Qilihai to Xingcheng estuary.And the types of tide and tidal current are basically the same in the waters near Luanhe estuary.In addition,there is a small area with the same types of tide and tidal current in the southeast of the coastal waters off Qinhuangdao and the waters near Taili East Port.When the tide is diurnal tide,the type of tidal current and tide are not consistent,and the tidal current shows regular semidiurnal and irregular semidiurnal tidal current.In the coastal waters which tidal and tidal current types are consistent,the tide and tidal current show irregular semidiurnal tide and irregular semidiurnal tidal current.