The complex interactions between aquatic organisms and physico-chemical processes are fundamental to our understanding and management of both individual biotic communities and the total environment. Of significance are both how organisms modify their environment and how they and their behaviour are, in turn, modified by the environment around them. In marine and freshwater aquatic systems, the interactions between organisms and the prevailing hydraulic conditions are of prime importance. However, the field of experimental and numerical hydraulic modelling frequently reduces the complex consequences of plant and animal interactions with flows to a passive effect on bed roughness. Few experiments in hydraulic facilities have used prototype organisms. Some exceptions are: Statzner et al. (2006, crayfish), Johnson et al. (2011, crayfish), Wilson et al. (2003, vegetation), Fathi-Moghadam & Kouwen (1997, vegetation), Battin (2003, biofilms). This is often because experimental hydraulic facilities are predominantly designed without consideration of the need to keep organisms both alive and behaving as they would in the natural environment. Some ecological experiments have attempted to use experimental hydraulic facilities to model the active responses of organisms to flows. However, many of these experiments are designed with little knowledge of the constraints on model set-up and flow measurement. The results of poorly designed experiments are unlikely to reflect processes in the environments being simulated and in some cases the data may be meaningless.