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Mixed sand and gravel beaches form a wedge of protective sediment at the base of eroding cliffs. In profile these beaches are typically steep with a prominent storm berm. If the volume of beach sediment is insufficient, storms strip beach sediments seaward, exposing the cliff toe to wave attack. The beach volume is thus crucial to the protection of sea cliffs. In this article we describe a method of calculating alongshore variation in the volume of mixed sand and gravel beaches using ground penetrating radar (GPR). Eighteen sites were studied along 50 km of the east coast of South Island, New Zealand. The method was underpinned by an ability to map the boundary between beach sediments and underlying Pleistocene alluvial-fan sediments. This was achieved by studying the radar facies, particularly landward- dipping overwash deposits and seaward-dipping beach erosion surfaces. The method was ground-truthed in three ways: (1) a stream provided a clean section through one site that was imaged by radar; (2) a storm stripped beach sediment from three sites exposing the substrate, which was then surveyed and compared with radar profiles; (3) excavations in a previous study at nine sites were used to combine the stratigraphy with the radar images. GPR proved highly effective in this environment, revealing thin beaches in the south of the study area that thicken northward in the direction of alongshore sediment transport. Cliff height decreases northward such that there is a transition from beaches in front of cliffs, to beaches that overtop low cliffs, to barriers in front of a coastal lagoon. [ABSTRACT FROM AUTHOR]

Modern measurement techniques such as aerial laser scanning allow for rapid determination of the spatial variation of sea surface elevation. Wave fields obtained from such data show spatial inhomogeneity associated with the presence of wave groups. A method based on two-dimensional directional wavelet analysis is described by which such inhomogeneity can be characterized in the spatial and wavenumber domains. The directional wavelet method has been applied to aerial laser scanning measurements of nearshore wave conditions off the east coast of New Zealand’s South Island. A high level of spatial variability was observed, with evidence of ensembles of wave-group envelopes of quasi-Gaussian form. These envelopes occur, with variations in spatial location, across a range of wavelet scales and directions. [ABSTRACT FROM AUTHOR]