Study on Tidal Resonance in Severn Estuary and Bristol Channel

Abstract

A horizontal hydrodynamic model was applied to predict the response characteristics of the Severn Estuary and Bristol Channel to regular long waves, in an effort to gain insight into the tidal behavior of this area. A boundary-fitted curvilinear mesh of high resolution was generated, covering the downstream reach of the River Severn, the Severn Estuary and the Bristol Channel, with the seaward boundary set from Milford Haven to Hartland Point to the west and the riverine boundary at Gloucester towards the east. The simulations were first calibrated against the observed tidal levels and currents at various sites, for typical spring and neap tides. Subsequently, water surface oscillations inside the domain were excited by sinusoidal long waves of different periods at the open boundary to find the fundamental mode of oscillation. The amplitude-frequency relationships were calculated at numerous sites. It was found that the primary resonant mode of oscillation in the Severn Estuary occurred at the tidal period of around 8 h. Although not exactly coinciding with this resonant mode, the M2 tide still observed a relatively high amplification factor, which helps explain why this water body experiences one of the largest tidal ranges in the world.