‘Wetlands’ in tidal lagoons and estuaries are among the most valuable ecosystems in the world. Managing these systems requires both a thorough knowledge and validated tools to predict their behavior and development. An important morpho-dynamic process herein is the erosion (‘pick-up’) of the bed, which are in inter-tidal areas often composed of a mixture of sand and mud. Aim of the study was the derivation and calibration of a generic formulation for surface erosion of sand-mud mixtures based on a geotechnical approach. Determining parameters for geotechnical and morphological behavior of sand-mud mixtures have been identified, and a surface erosion formulation is derived and validated. The agreement between calculated and measured erosion values indicates that the physically-derived formulation is an important alternative to present empirical formulations. This is particularly important for applying the formulation for the numerical modeling of the behavior of estuaries and lagoons. Furthermore, two new measuring techniques are developed which enable the in-situ characterization of sedimentological and soil mechanical properties. This data can be used to characterize and compare inter-tidal sediments properties, and to serve as input for the erosion formulation and/or for numerical simulations. Finally, an experimental strategy is presented for the collection of field data which are required to characterize the behavior of sand-mud mixtures.