Characterising sandy beaches into major types and states: Implications for ecologists and managers

Abstract

Sandy beaches are dynamic systems that host a diverse range of fauna whose habitat is controlled by the interactions among sand, waves and tides. In recent decades much of the study of sand beach ecology has focused on community type and structure across the range of beach types, as well as regional variations. In order to compare different studies, accurate information is required on the nature of the environment studied: sand particle size, tide range and wave conditions. Unfortunately this has not always been provided by beach ecologists. Our understanding of sandy beach processes has advanced to the stage where ecologists can no longer omit assessing the role of wave climate, even if this cannot be done precisely, as can be done for sand and tides. In this paper we provide a method to quantify wave conditions and, in combination with sand particle size and tide range, determine the beach type and state. For waves, we first highlight the concepts 'sea' and 'swell' as distinct from the terms 'sheltered' and 'exposed'; we then provide a method to estimate breaker height. We then develop a model with two steps: first, breaker height is combined with tide range to identify whether waves or tides are the primary driver of beach morphology and thereby the define the beach type (wave-dominated, tide-modified or tide-dominated); then, using breaker height, period and sand particle size, the beach state is determined. Seven main beach morphodynamic types-states are defined. At the narrow and steep extreme are wave-dominated reflective beaches and at the wide and low gradient extreme are tide-dominated flats. The physical and ecological features typical of the seven types-states are presented, as well as some management implications.