The physical characteristics of sediments were measured from transects in the Minho, Lima, Cávado, and Ave estuaries in the northern part of Portugal. The variables investigated were: chemical composition, particle size, water content, salinity, temperature, and pH. In a miniflume used to measure erodibility, erosion tests were filmed with a high speed camera and the rheological characteristics of overlaying fluid layer were measured using a rheometer. Because the physical sediment characteristics are related to its erosion, the physical characterization and the erodability were correlated. The influence of the season and sampling site on the sediment properties were assessed for the Cávado estuary.

Large differences were found in the physical characterization between the four estuaries, namely in particle size, water content, and chemical composition, and these were important in determining the stability of sediments. Short-term changes in weather conditions prior to sampling and site-to-site variability were found to have more significant effects on the sediment physical properties than seasonal changes.