Observations of the swash zone on a gravel beach during a storm using a laser-scanner (Lidar)

ABSTRACT Almeida, L.P., Masselink, G., Russell, P.E., Davidson, M.A., Poate, T.G., McCall, R.T., Blenkinsopp, C.E. and Turner, I.L. 2013. Observations of the swash zone on a gravel beach during a storm using a laser-scanner The collection of detailed field measurements from the swash zone during storms is an extremely challenging task which is difficult to execute with traditional in-situ deployments (e.g., scaffold rigs with instruments). The levels of difficulty increase for gravel beaches where the wave energy reaches the beach face with almost no loss of energy, leading to violent plunging wave breaking on the beach face that can produce large vertical morphological changes and extremely strong uprushes that can easily and rapidly damage, bury or detach instrumentation. Remote-sensing techniques emerge as the most appropriate solution to perform field measurements under such adverse conditions since they have the ability to perform measurements without being deployed in-situ. A mid-range (~ 50 m) Laser-scanner mounted on a tower (~ 7 m high) in the mid beach face of a gravel beach (Loe Bar - SW England) was used to measure bed-level changes and runup at a sampling rate of 2 Hz along one beach profile during a storm. The results from the comparison of this system with other state-of-the-art instruments (e.g., ultrasonic bed level sensors, GPS and video cameras) indicate that the quality of the measurements obtained is within the accuracy of the standard methods. The advantages of this system is the reduced logistical infrastructure required for the deployment, the capability to perform surveys with high spatial and vertical resolution, during day and night, and to reach areas of the swash zone where no other instrument can be deployed safely. Measurements performed with a laser-scanner on a gravel beach (Loe Bar) show complex and fast-changing morphology on the gravel beach, which appears to be a form of negative morphodynamic feedback to controls the hydrodynamic evolution in the swash zone.