A simple model to calculate the residual flows in a Spanish ria. Hydrographic consequences in the ria of Vigo

Abstract

In this article a stationary model for the calculation of residual flow and mixing of water in a ria, on the basis of contribution of fresh water and salinity as a tracer, is presented. The model is applied to the ria of Vigo, whose circulation is similar to that of a partially stratified estuary. This ria is divided into five boxes and a system of 20 equations is proposed whose solutions are the residual outflows and inflows, and the rise and mixing fluxes, which occur in the ria. In the winter the velocities of the residual currents are from 4 to 8 cm s −1 , and the exit of fresh water is high for the northern mouth of the ria. The flows diminish and the mixing of water increases in the ria (2–3 m day −1 in box 2) as the contribution of fresh water decreases in the spring and summer. The presence of northerly winds increases the residual circulation threefold in the summer, there being an out-flow of 10 6 kg s −1 to the ocean. However, southerly winds retain the water in the ria and the proposed model can only be applied to the ria's inner and middle sections.