Objectives  Due to the joint constraints of boundary conditions, including seabed topography, driven water level at open boundary (DWLOB) and bottom friction coefficient (BFC), the accuracy of the tidal numerical modeling in coastal and offshore waters is relatively low.

  Methods  This paper intends to synchronously optimize the multiple boundary conditions, including seabed topography, DWLOB, and BFC, to improve the accuracy of the tidal numerical modeling in China's coastal and offshore waters for the hydrographic surveying and mapping. This paper simulates the tidal model of Haizhou Bay of the Yellow Sea in China, using a two-dimensional tide numerical model (2D-MIKE21) and based on the synchronously optimized boundary conditions. The water depth with higher resolution and accuracy than the charted depth is used as the seabed topography. The DWLOB is calculated from 12 tidal constituents of the regional tidal model of China seas(CST1). The calculation of the BFC takes into account the spatial variation of water depth.

  Results  For validation, we compare the simulated model with the 1-year tide tables from 6 tide gauges in Haizhou Bay and the CST1 model at 24 randomly selected points, and get the total root sum squares of the 12 tidal constituents of 5.52 cm and 7.10 cm, respectively. The simulated tide model and CST1 are also compared with the 1-month observations at two tide gauges in Haizhou Bay, and the former has a smaller mean square error than the latter.

  Conclusions  The proposed strategy provides a new method for tidal numerical modeling in coastal and offshore waters. This study also shows that it is feasible to obtain the astro-meteorological constituent Sa by tidal numerical modeling. It should be noted that, the wind effect is also not considered in this study due to its strong randomness and the difficulty in obtaining data for one year. We can use the simulated water level heights and the short-term wind velocity and direction as the better open boundary and initial conditions to carry out the short-term tidal modeling in coastal and offshore waters, which can generate the residual water level or storm surge.