Abstract: A methodology to determine the spatial and temporal evolution of stratification in estuaries driven by astronomical tides and river discharges was developed and is presented here. Using a 3D hydrodynamic
model, the variation of estuarine currents, water levels and densities was investigated under different
realistic forcing conditions. These conditions were classified from a long-term period (>30 years) of river
flows and tidal water levels by a K-means clustering approach suggested by Barcena et al. (2015). The
methodology allows computing the location of mixed, partially mixed/stratified and stratified areas in
tidal river estuaries along a continuum by means of Richardson's Layer number and the frequency of
every model scenario. In order to illustrate the power of the method, it was applied to a case study, the
Suances Estuary. In the application case, the Suances Estuary was vertically mixed at its innermost part
due to riverine influence. At the outer part, it was also vertically mixed due to the turbulence caused by
tidal action. At the intermediate section, it was partially mixed in the main channel or stratified in
intertidal areas due to the combined action of forcing, depth gradients between the main channel and
intertidal areas, and salinity variations in the water column.