Effects Of Spring-neap Tides In Regional Coastal Groundwater Flow Modeling

The coastal boundary condition is commonly set to be the mean sea level in existing models of regional coastal groundwater flow, neglecting the influence of tides. When the beach angle is small, the over-height caused by tides is very profound. The regional groundwater simulation is based on large scales, but the tidal movement occurs at a relative small scale. Direct coupling of tides with regional groundwater models has a great difficulty since it would increase the computation cost significantly. Therefore, it is of great theoretical and applied value to convert the dynamic effect of tides to an equivalent static effect (over-height) and to develop an equivalent input boundary condition that can replace the original dynamic boundary condition at the coastline.In this paper, we first examine the mechanism of the spring-neap tidal water table fluctuations (SNWTF) and analyze the features of the groundwater table fluctuation due to spring-neap tides. Then we quantitatively analyze the over-height and establish a relationship between the over-height and each physical parameter. Finally we derive the equivalent seaward boundary condition incorporating the tidal effects. The paper includes several novel aspects as follows:(1) A model of spring-neap tidal water table fluctuations including the seepage face is established.(2) The mechanism of the spring-neap tidal water table fluctuations is examined.(3) The features of the groundwater table fluctuation due to spring-neap tides are studied based on a theoretic analysis and numerical simulations.(4) The factors influencing the over-height are determined through a dimensionless analysis of the mathematical model.(5) The experiential formula of over-height and each influencing factor is derived based on the results of model simulations.(6) The equivalent seaward boundary condition is established according to the experiential formula of over-height.(7) Based on a large scale physical model combined with an intelligent data collection and control system, the features of SNWTF are investigated.