Assessment and optimisation of runup formulae for beaches fronted by fringing reefs based on physical experiments

Abstract

An extensive new set of laboratory measurements have been performed with random and monochromatic waves to study runup on fringing reef-fronted beaches. The experiments were conducted with an idealised fringing reef profile and tested with different forcing conditions (waves and water levels) and reef geometries. Experimental physical data are compared with empirical models developed on open coasts to predict runup. The results show that runup predictions are scattered and are overestimated by existing empirical models when using the off-reef wave conditions. Predictions based on the wave and water level conditions at the beach toe show much less scatter, with the run-up scaling remaining consistent with that proposed by Hunt (1959). Two revised optimizations of Hunt (1959) formula were derived from the experimental data. The results showed that these formulations and the existing runup scaling laws are useful to characterize runup on fringing reef-fronted beaches if the appropriate wave and water level conditions are adopted. Consequently, existing runup models can be combined with the results from phase-averaging wave models to estimate runup on beaches landward of fringing reefs.