Wave runup (swash) spectra on natural beaches: morphodynamic controls

TY - CONF

T1 - Wave runup (swash) spectra on natural beaches

T2 - Coasts & Ports 2013 Sydney

AU - Hughes, Michael G.

AU - Aagaard, Troels

AU - Baldock, Tom E.

AU - Power, Hannah E.

PY - 2013

Y1 - 2013

N2 - This paper provides insight into the spectral signatures of wave runup (swash) from contrasting beach types; their nature and range and the morphodynamic controls exerted by beach morphology and wave exposure. An extensive field data set is used covering the full range of micro-tidal beach types (reflective, intermediate and dissipative), and includes beach gradients ranging from approximately 1:6 to 1:60 exposed to offshore significant wave heights of 0.5 m to 3.0 m. The data investigated here consists of 187 individual swash spectra. The ratio of swash energy in the short wave (f>0.05 Hz) to infragravity wave (f>0.05 Hz) frequency bands is found to be significantly different between the three beach types. Swash energy at short wave frequencies is dominant on reflective and intermediate beaches and swash at infragravity wave frequencies is dominant on dissipative beaches; consistent with previously reported spectral signatures for the surf zone on these beach types. The swash spectra were classified using an automated algorithm known as CLARA into five different classes. The ordered classes represent an evolution in the spectrum shape described by a frequency downshifting of the energy peak from the short-wave into the infragravity wave band and an increase in the infragravity swash energy level compared to a consistent short-wave swash energy level. A universally common feature of spectra from all beach-states was an f -4 energy roll-off in the short-wave frequency band. In contrast to the broadly uniform appearance of the short-wave frequency band across all the beach-states, the appearance of the infragravity wave frequency band was highly variable. A conceptual model for the evolution of swash spectra under increasing and decreasing incident wave energy level, with due consideration of beach morphology, is proposed.

AB - This paper provides insight into the spectral signatures of wave runup (swash) from contrasting beach types; their nature and range and the morphodynamic controls exerted by beach morphology and wave exposure. An extensive field data set is used covering the full range of micro-tidal beach types (reflective, intermediate and dissipative), and includes beach gradients ranging from approximately 1:6 to 1:60 exposed to offshore significant wave heights of 0.5 m to 3.0 m. The data investigated here consists of 187 individual swash spectra. The ratio of swash energy in the short wave (f>0.05 Hz) to infragravity wave (f>0.05 Hz) frequency bands is found to be significantly different between the three beach types. Swash energy at short wave frequencies is dominant on reflective and intermediate beaches and swash at infragravity wave frequencies is dominant on dissipative beaches; consistent with previously reported spectral signatures for the surf zone on these beach types. The swash spectra were classified using an automated algorithm known as CLARA into five different classes. The ordered classes represent an evolution in the spectrum shape described by a frequency downshifting of the energy peak from the short-wave into the infragravity wave band and an increase in the infragravity swash energy level compared to a consistent short-wave swash energy level. A universally common feature of spectra from all beach-states was an f -4 energy roll-off in the short-wave frequency band. In contrast to the broadly uniform appearance of the short-wave frequency band across all the beach-states, the appearance of the infragravity wave frequency band was highly variable. A conceptual model for the evolution of swash spectra under increasing and decreasing incident wave energy level, with due consideration of beach morphology, is proposed.

M3 - Paper

Y2 - 11 September 2013 through 13 September 2013

ER -