Beach Hardness Variation-New Moisture Related Phenomenon and a Case Study from Byron Bay, Australia


  • A. W. Sam Smith
  • Arthur C. Trembanis


Sand hardness, moisture, age-hardening, beach scarps, slope failure, angle of repose.


Sand hardening has direct relevance for beach erosion, sediment transport modeling, sea turtle nesting, recreational beach use, and property loss mitigation. One quantified measure of sand hardness is the angle of repose. A study of granular media kinematics identified the phenomenon of age-hardening responsible for increasing the angle of repose. The concept of age-hardening is applied to an explanation of the ubiquitous occurrence of scarps on beaches during storms. Scarp formation and maintenance within the swash, the subaerial beach, and the dunes are discussed. Field observations from Byron Bay in New South Wales, Australia illustrate the interaction of sand hardening processes to form variations in scarp angle along a single beach. Age-hardening helps explain some but not all of the observed scarp variation. Fine silt and clay soils formed in the dunes are theorized to contribute to the observed scarp slope variation. Further research should be devoted to understanding how various physical, chemical, geological, and biological factors promote sand hardening.