Radioactive wastes and sewage discharged into coastal waters may be largely dispersed by tidal streams. Before authorization for sea discharges can be granted by responsible authorities representing public interests, as much information as possible must be obtained on water movement in the chosen area. Comprehensive data on tidal conditions around the British Isles can be found from the Admiralty Tidal Stream Atlases (Hydrographic Department). The method by which these currents are measured is explained in the Admiralty Manual of Hydrographic Surveying (Hydrographic Department, 1948). Further, special surveys using sea surface drifters and current meters are usually necessary to provide additional information in the neighbourhood of a proposed release. The purpose of this note is to point out that further relevant information can be obtained using numerical models and that these results should also be taken into account when decisions have to be made.