Abstract: Under tide stress, vertical groundwater flow between aquifer and aquiclude is described based on rock mechanics and groundwater dynamics theory, the amplitude ratio and phase shift are presented for pore pressure generated from tidal force and tidal height under vertical flow. Combined with Hsieh's theory (1987), formulas for calculating amplitude ratio and phase shift for water-level and tide-height is derived under condition of vertical and radial flow. The formulaes are applied to identify the main factors affecting water-level amplitude and phase by comparing their values under M2 and O1 tide stress.

Key words: Tide, Groundwater level, Aquifer, Aquiclude