Horizontal mixing is of fundamental importance for both the analysis of the evolution of shallow geophysical flows and also for the related applications (water quality assessment, interfacial transfer processes evaluation, ecosystems description, etc.). The aim of the Colloquium is to bring together researchers with interests in the theoretical description of the mixing dynamics and in its applications to shallow geophysical flows which characterize coastal, estuarine and riverine water bodies. Topics of interest range from the fundamentals of shallow-water turbulence, to the description of mixing in terms of lagrangian/eulerian statistics of tracers, to the implementation of simplified closures for use in solvers of practical application, to the evaluation of the mixing influence on natural ecosystems. Contributions of specialized character and interdisciplinary nature are both welcome.