Wave Run-Up Analyses Under Dissipative Condition UsingX-Band Radar

Abstract

An X-band nautical radar system was employed to examine wave run-up during a typhoon around the research pier HORS in Hasaki, Japan. Analyses on radar echo images were done to estimate the spatio-temporal variation of water fronts by manually digitizing cross-shore time stack images. Digitized instantaneous water fronts were validated with wave gauge measurements with an acceptable agreement. Longshore distribution of mean shoreline positions and inter-tidal foreshore slopes were then estimated using time-averaged images. Run-up, the height of discrete water level maxima, was estimated from the digitized water fronts with the help of foreshore profile. Run-up variations under dissipative condition were parameterized with surf similarity parameter. Low frequency variances in the run-up motion were observed, which travelled in the longshore direction.

Foreshore Applications of X-band Radar

“…On natural beaches, run-ups at incident frequencies are typically saturated, while run-ups at infra-gravity frequencies are unsaturated and thus increases with offshore wave height (e.g., Guza and Thornton 1982;Holman and Sallenger 1985;Holland et al 1995 etc. ) and also depends on beach morphology (e.g., Hasan and Takewaka 2009). Extensive field evidence supports that energy at infra-gravity frequencies often constitute a large portion of total energy observed at the shoreline during storm events (Holman 1981;Guza and Thornton 1982;Holman and Sallenger 1985;Raubenheimer and Guza 1996).…”

“…Wave run-up is expressed as the set of discrete vertical elevations of seawater, measured on the foreshore from still water level (SWL) consisting of two components: a super elevation of mean water level, commonly known as wave setup, and vertical fluctuations about that mean. Many researchers investigated run-up dynamics on intermediate to reflective beaches (e.g., Holman and Sallenger 1985;Holman 1986;Holland and Holman 1999), low energy and mildly dissipative beaches (e.g., Guza and Thornton 1982;Raubenheimer et al 1995;Raubenheimer and Guza 1996) and highly dissipative beaches (e.g., Ruessink et al 1998;Ruggiero et al 2004;Holman and Boyen 1984;Hasan and Takewaka 2009). Most of the studies parameterized wave run-up with environmental conditions and examined its relation with surf similarity parameter.…”

“…Takewaka and Nishimura (2005) used X-band radar to analyze qualitatively longshore structure of swash motion during an energetic sea state. Recently, Hasan and Takewaka (2009) also analyzed wave run-up using X-band radar images during an energetic sea condition. They could successful in tracing swash variations and its propagation in the longshore direction.…”

“…Foreshore slopes were estimated from the fitted foreshore profiles as the same manner of Hasan and Takewaka (2009). Mean foreshore slope is defined at every longshore position from average of foreshore slopes at three cross-shore locationsswash-up, swash-down and mean swash position (locations are explained in the next section).…”

The Development and Rehabilitation of the Hammamlif Coastline: A Geotechnical Study

“…Wave run-up R is defined as the set of discrete vertical distances of seawater, measured on the foreshore from still water level (SWL). Run-up results from two dynamically different processes: (i) wave setup, a super elevation of mean water level at the shoreline and (ii) vertical fluctuations about that mean [2] (Figure 3). …”