Rapid Onshore Sand Flux in a High Energy Littoral Cell: Piha Beach, New Zealand

Vast sand deposits have accumulated within headland-bound littoral cells along the west coast of Auckland, New Zealand. Integration of different geomorphological data has been used to quantify and interpret the spatial and temporal variability of interannual to interdecadal and longer-term sand storage within the Piha Beach littoral cell. Survey data indicate highly variable and fluctuating deposits of sand moving on and off the active beach face. However, net changes across the cell inferred from aerial photos show shore line advancement of 0.4 to 1.0 m/year since 1940. This represents some 697,400 m3 of sand (121,350 m2 of beach area) added to the onshore beach system in 60 years. Some 12.7 × 106 m3 of sand is estimated to be stored onshore within the Piha cell. Interpretation of stratigraphy and depositional sequences at Piha using ground penetrating radar indicate fluctuating phases of progradation and episodic-transgressive dune activity in the late Holocene. These general patterns at Piha are analogous to those found at other littoral cells along the west coast.