THE EFFECT OF TIDE RANGE ON BEACH MORPHODYNAMICS AND MORPHOLOGY - A CONCEPTUAL BEACH MODEL

Natural beaches may be grouped into several beach types on the basis o f breaker height (H(b)), wave period (T), high tide sediment fall velo city (w(s)) and tide range (TR). These four variables are quantified b y two dimensionless parameters: the dimensionless fall velocity (OMEGA = H(b)/w(s)T) used by WRIGHT and SHORT (1984) to classify micro-tidal beaches, and the relative tide range (RTR = TR/H(b)) introduced in th is paper. The value of the dimensionless fall velocity indicates wheth er reflective, intermediate or dissipative surf zone conditions will p revail. The relative tide range reflects the relative importance of sw ash, surf zone and shoaling wave processes. A conceptual model is pres ented in which beach morphology (beach type) may be predicted using th e dimensionless fall velocity and the relative tide range, whereby the mean spring tide range (MSR) is used to calculate the relative tide r ange. The model consists of the existing micro-tidal beach types, whic h as RTR increases, shift from reflective to low tide terrace with and finally without rips; from intermediate to low tide bar and rips and finally ultra-dissipative; and from barred dissipative to non-barred d issipative and finally ultra-dissipative. Using this model, all wave-d ominated beaches in all tidal ranges can be classified.