Wave runup and overwash on a prototype-scale sand barrier

• Prototype-scale laboratory measurements of wave runup for a range of conditions
• Runup equations performed optimally using beach face gradient
• Wave rundown is consistently below SWL and is a function of Irribarren number.
• Runup extent can be accurately predicted if bore height at collapse is known.

Accurate methods to predict wave runup are of critical importance to coastal engineers. Extreme runup during storm conditions can present a danger to coastal infrastructure and lead to dune overtopping and erosion, overwash of barrier beaches and is an essential design parameter for certain coastal protection works.This paper uses data obtained during the unique BARDEX II prototype-scale laboratory experiment on a reflective sand barrier to investigate wave runup and overwash. Runup measurements were acquired using ultrasonic altimeters, 2D scanning Lidar and camera systems under controlled wave and water level conditions.It was found that extreme runup (R2%) scaled well with the deepwater Irribarren number where the beach slope was taken to be the beach face gradient. The lower limit of the swash zone, defined by the 2% wave rundown limit was also found to be a function of the Irribarren number and was consistently below the SWL in all tests.The high resolution free-surface measurements obtained using the ultrasonic altimeters and Lidar enabled an analysis of the dynamics of individual swash events. It was found that the vertical runup excursion of each swash correlated strongly with the height of the bore at collapse, and could be predicted based on the assumption of a conversion of potential to kinetic energy at bore collapse.