The purpose of this study was to identify problems that may be encountered when placing prefabricated barrage caisson units close to existing caissons during the construction of tidal barrages. The potential for serious damage to occur is greatly increased when manoeuvring caissons into place next to units that are already in position. The specific aims of the study were to: (a) Determine the forces required to hold a caisson in position in a range of constant tidal flows when ballasted to different draughts and restrained by moorings of varying stiffnesses. (b) define the motion of the caisson under the conditions in (a) above and (c) establish the same quantities over the same range of variables in (a) and (b) above when the unit is moored close to caissons that have already been positioned. The study employed conventional hydraulic modelling techniques using a generic caisson model built to a scale of 1:100. The use of a generic model enables the results to be applied to caissons of similar proportions, but different overall dimensions, by the use of simple scaling techniques. (author).