In Bluelink 2 the development of the Littoral Ocean Modelling System (LOMS) provided a platform to run the littoral zone hydrodynamic model, XBeach. LOMS provides predictions of nearshore waves and currents on the assumption that the bathymetry is immobile. Mean currents are driven by wind and breaking waves and, since wave breaking is a depth-dependent process, bathymetry influences the spatial variability of the mean currents. The mean currents transport sediment stirred into suspension by the waves, modifying the bathymetry which, in turn, alters the distribution of wave breaking and the associated mean current field. In Bluelink 3 LOMS was extended by including morphological changes in responses to time varying waves and currents. Morphodynamic time scales are typically much longer than hydrodynamic time scales, except perhaps through extreme events, and measuring morphological change under breaking waves is a challenge with conventional hydrographic surveying methods. Long-term, continuous monitoring of morphological change and the nearshore wave field is most effectively done with remote techniques such as video and radar. Video is sensitive to optical properties, for example white water associated with wave breaking, while radar is sensitive to surface roughness associated with breaking waves and surface waves. Both provide slightly different measures of the distribution of wave breaking which in turn serves as a proxy for water depth. Nearshore currents such as rip currents are often associated with an increase in surface roughness due to short waves steepening on the opposing current and are more easily discerned in radar images. CSIRO has developed the Nearshore Research Facility (NRF) as part of a measurement program using both in-water and shore-based equipment. X-Band radar has proved to be a useful tool for measuring the surface wave field to a range of a few kilometres and can provide continuous data collection during storm events. The X-band radar can also be used to infer bathymetry in a couple of ways; (i) by measuring the distribution of depth induced wave breaking which then provides a proxy for the underlying bathymetry and (ii) by directly measuring the wave speed which is a known function of water depth. An Argus video system has also been included to compliment the capabilities of the radar system. The radar and video data are used to ground truth numerical model hindcasts of morphological evolution on a natural beach.
Collection(s) and Series: CAWCR technical report- No. 65
Format: Digital (Free)