Runup estimations on a macrotidal sandy beach

This paper presents a methodological approach to calculate runup from the analysis of morphodynamic conditions on a macrotidal sandy beach. The method is based on measurements of the elevation of high-tide deposits and on the analysis of morphological and hydrodynamic changes. A series of measurements has been carried out on the beach of Vougot (Brittany, France) under different wave conditions. This allowed to assess runup formula effectiveness on a macrotidal sandy beach and to determine the best slope parameters to estimate runup. The results suggest that on that macrotidal sandy beach the slope of the active section of the upper beach should be used instead of the entire slope of the foreshore, the latter resulting in an underestimation of runup elevations when used in predictive equations from the literature. Results obtained with widely used equations are relatively well correlated with observed values (r2 = 0.63). An analysis of the relationship between observed runup elevations and various variables has enabled the establishment of a runup estimation formula with a relatively good fit to the study site (r2 = 0.86).

► This paper presents the first analysis of runup processes on a macrotidal sandy beach from in situ measurement.
► The method developed is practical and relatively easy to carry out to measure in situ runup on macrotidal sandy beach.
► Results highlight the importance of the choice of the slope when using equations on macrotidal sandy beaches.