information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

Tidal strength (water flow)

The horizontal movement of water associated with the meteorological, oceanographical and topographical factors. High water flow rates result in areas where water is forced through or over restrictions for example narrows or around protruding offshore rocks. Tidal streams are associated with the rise and fall of the tide where as currents are defined as residual flow after the tidal element is removed (McLeod, 1996).

Very strong > 6 knots ( >3 m/sec.)
Strong 3 to 6 knots (1.5-3 m/sec.)
Moderately strong 1 to 3 knots (0.5-1.5 m/sec.)
Weak < 1 knot (<0.5 m/sec.)
Very weak negligible


  • McLeod, C.R., 1996. Glossary of marine ecological terms, acronyms and abbreviations used in MNCR work. In Marine Nature Conservation Review: rationale and methods, (Ed. K. Hiscock), Appendix 1, pp. 93-110. Peterborough: Joint Nature Conservation Committee. [Coasts and seas of the United Kingdom, MNCR Series].