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S. Orchard, D. R. Schiel
Dune restoration efforts represent decades of progress, but maintenance of restoration sites remains a key requirement due to the continued presence of threats such as invasive species and human disturbance. Climate change may generate even more pervasive threats within relatively short timeframes. Here we describe climate change scenario models of shoreline movement in Christchurch, New Zealand, characterised by a fine-grained marram-invaded dune system. Scenarios were calculated on 900 shore-perpendicular transects across 9km of coastline undergoing restoration and maintenance work that provides the primary protective barrier for nearby residential areas. Uncertainty was addressed through consideration of five independent scenarios, each representing a plausible SLR (sea-level rise) increment (0.25–1.25m) in relation to contemporary climate projections. We also incorporated the continuation of historical (75-year) accretion rates and associated uncertainties. The results demonstrate high vulnerability to climate change in a typical peri-urban setting, with dune elimination across a third of the study area in the 1m SLR scenario. The importance of maintaining at least the minimum foredune space was highlighted. Below a minimum width threshold (c.40 m), foredune depletion occurs from sand loss, with consequent height and volume losses, associated loss of coastal protection services, and biodiversity losses through fragmentation and contraction. Management approaches for maintaining the dune ecosystem include progressive establishment of managed retreat pockets where dune movement is encouraged alongside existing land-uses and hard defences. Through a focus on establishing dunes in locations currently occupied by other land uses, this presents an exciting new dimension for coastal restoration planning.
Conference Presentation, SER2021
Pre-approved for CECs under SER's CERP program