Model simulations of tidal changes in a coastal lagoon, the Ria de Aveiro (Portugal)

Tidal changes in the Ria de Aveiro lagoon, Portugal, show an average increase of 0.245 m in M2 amplitude and an average 17.4° decrease in M2 phase, over 16 years (1987–2004). This paper investigates the causes of these changes using: (a) an analytical model and (b) hydrodynamic (vertically integrated) model of the Ria de Aveiro lagoon.The analytical model evaluates the theoretical dampening effect on the surface elevation of a tidal wave propagating into an estuary, through a narrow inlet, as a function of: lagoon area, inlet depth and bottom friction. The hydrodynamic model uses measured changes in channel depth to investigate how these affect M2 amplitude and phase. Both approaches confirm that changes in the bathymetry of the inlet channel are the most significant contribution to the tidal changes. Numerical models, alone, provide detailed information on the tidal response to changes in the parameters representing the complex processes responsible for those responses. However, not always are they the simplest and quickest method to analyse the sensitivity of the tidal responses. Independent results from the analytical model and those of the hydrodynamic model illustrate that these two approaches can complement each other and be applied to other single-inlet systems.