Direct determination of tidal levels for engineering applications based on biological observations

• Published in: Coastal engineering (Amsterdam) 2008-06, Vol.55 (6), p.459-467
• Main Authors: Stiros, S.C., Pirazzoli, P.A.
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Biological Mean Sea Level; Datum; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Engineering geology; Environmental Sciences; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Humanities and Social Sciences; Marine; Marine and continental quaternary; Sea level; Sea water ecosystems; Surficial geology; Synecology; Tide; Tide gauge; Vertical zonation
• ISSN: 0378-3839; 1872-7379
• DOI: 10.1016/j.coastaleng.2008.01.005

The scarcity of tide gauges in a global scale and the variability of the tidal levels along contiguous coasts mainly due to changing hydrographic conditions make the determination of tidal levels, especially of the Mean Sea Level, not an easy task. Determination of such levels with a precision of about 10 cm, necessary for most coastal engineering works, is usually based on records of temporary tide gauges or on geomorphological techniques. In this paper we present an alternative approach permitting to accurately identify tidal levels with a precision suitable for civil engineering applications based on biological observations on rocky shores, including breakwaters and quays. More specifically, we present evidence that the biological zonation, i.e. the distribution of coastal species in well-defined sub-horizontal belts, is practically insensitive to seasonal and other small-scale fluctuations of the sea level and is clearly related to certain levels, mostly the Mean Low Water (MLW). This approach, somewhat similar to what has been used in the past (for instance for the determination of the geodetic vertical datum in the Republic of Venice, Italy, till approximately AD 1800), permits direct determination of the Mean Sea Level or of other tidal levels on the basis of biological observations without statistical analyses of tide-gauge records with an accuracy of 5–10 cm, especially in microtidal, low-energy coasts.