A monthly tidal envelope classification for semidiurnal regimes in terms of the relative proportions of the S&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;, N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;, and M&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; constituents

Do-Seong Byun,Deirdre E Hart

doi:10.5194/os-16-965-2020

A monthly tidal envelope classification for semidiurnal regimes in terms of the relative proportions of the S&lt;sub&gt;2&lt;/sub&gt;, N&lt;sub&gt;2&lt;/sub&gt;, and M&lt;sub&gt;2&lt;/sub&gt; constituents

Do-Seong Byun, Deirdre E Hart

Open Access

https://doi.org/10.5194/os-16-965-2020

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Abstract

Abstract. Daily tidal water level variations are a key control on shore ecology, on access to marine environments via ports, jetties, and wharves, on drainage links between the ocean and coastal hydrosystems such as lagoons and estuaries, and on the duration and frequency of opportunities to access the intertidal zone for recreation and food harvesting purposes. Further, high perigean spring tides interact with extreme weather events to produce significant coastal inundations in low-lying coastal settlements such as on deltas. Thus an understanding of daily through monthly tidal envelope characteristics is fundamental for resilient coastal management and development practices. For decades, scientists have described and compared daily tidal forms around the world's coasts based on the four main tidal amplitudes. Our paper builds on this “daily” method by adjusting the constituent analysis to distinguish between the different monthly types of tidal envelopes occurring in the semidiurnal coastal waters around New Zealand. Analyses of tidal records from 27 stations are used alongside data from the FES2014 tide model in order to find the key characteristics and constituent ratios of tides that can be used to classify monthly tidal envelopes. The resulting monthly tidal envelope classification approach described (E) is simple, complementary to the successful and much used daily tidal form factor (F), and of use for coastal flooding and maritime operation management and planning applications in areas with semidiurnal regimes.

Highlights

Successful human–coast interactions in the world’s lowlying areas are predicated upon understanding the temporal and spatial variability of sea levels (Nicholls et al, 2007; Woodworth et al, 2019)
More than 80 years after the development of the ever-useful daily tidal form factors, attention to the regional distinctions between different tidal envelope types within the semidiurnal category forms the motivation for this paper. In this first explicit attempt to classify monthly tidal envelope types, we examined the waters around New Zealand (NZ), a strong semidiurnal regime with relatively weak diurnal tides and little variation in the importance of the S2 and N2 amplitude ratios
The daily water level variations brought about by the tides are a key control on shore ecology and on the accessibility of marine environments via fixed port, jetty, and wharf infrastructure

Summary

Introduction

Successful human–coast interactions in the world’s lowlying areas are predicated upon understanding the temporal and spatial variability of sea levels (Nicholls et al, 2007; Woodworth et al, 2019). This is the case in island nations like New Zealand (NZ), where over 70 % of the population resides in coastal settlements (Stephens, 2015). Developed by van der Stok (1897) and based on three regime types, with a fourth type added by Courtier (1938), this simple and useful daily form factor comprises a ratio between diurnal and semidiurnal tide amplitudes via the equation F = K1 + O1 . The results classify tides into those which roughly experience one high and one low tide per day (diurnal regimes), two approximately equivalent high and low tides per day (semidiurnal regimes), or two unequal high and low tides per day (mixed semidiurnal-dominant or mixed diurnaldominant regimes) (e.g. Defant, 1958).

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