Modelling morphodynamic responses of a natural embayed beach to Typhoon Lekima encountering different tide types

Abstract

Recent developments in process-based coastal area models such as XBeach provide new opportunities to predict coastal responses to primary forcing mechanisms such as storm hydrodynamic by using 2DH grids. However, due to the lack of measured data, there are few application scenarios of the models. Therefore, more measurement and research are needed. In this paper, the Typhoon Lekima that hitting Zhejiang Province during neap tide period was selected to simulate morphodynamic responses of the Huangcheng Beach by assuming encountering with different tide types. Cross shore measurements with eight cross-shore profiles (named S1 ~ S8 from north to south) of the Huangcheng Beach pre- and post- the Typhoon Lekima respectively were presented. Then a 2DH storm surge and wave coupled model was established with Delft3D Flow/Wave. The model was well calibrated with measured water levels and wave data and provided hydrodynamic boundary conditions of different typhoon and tide types coupling situations for a refined model. The refined model was built using XBeach and simulated the morphological responses of the Huangcheng beach with well verifications. On basis of the numerical results, bed level changes at the eight profiles were analyzed, and the character of erosion and deposition under different tide conditions were illustrated. The net sand volume changes were got smaller under the spring tide condition rather than middle tide and neap tide conditions. Further study of the distribution of wave induced current at different stages of collision, inundation and ebb shown that the stronger current under spring tide condition would increase the sediment transport rate and reduce the deposition volume at profiles S3 and S6 ~ S8, and the total amount of sediment involved in transportation had increased for the whole beach, leading to the reduction of net erosion volume at profiles S1, S2, S4 and S5.

Numerical Simulation of the Beach Response Mechanism under Typhoon Lekima: A Case Study of the Southern Beach of Chudao

“…The elevation differences between the simulated profiles and those measured after the typhoon may be due to sediment particle size. They may also be due to the low-intensity hydrodynamic effects that continuously change the profile elevation before the typhoon, which were not considered in the model [42]. Additionally, compared with post-typhoon measurement analysis, XBeach did not effectively simulate the small amount of deposition at the backshore of the beach shoulder after the typhoon.…”

“…The range of BSS values and the prediction effects they represent are shown in Table 1. The BSS evaluation method is suitable for coastal dynamic simulation and is widely used in current research [28,42]. In this paper, this method is used to evaluate the accuracy of the numerical simulation of beach profile evolution with the following calculation formula:…”