Abstract
Beach foredunes following introduction of Ammophila arenaria have been shown to promote accretion and progradation, but after a few decades, large steep-faced foredunes develop that subsequently erode. Beach profile measurement combined with spatial change techniques have not been applied to investigation of A. arenaria foredune change before. This study investigated two adjacent beaches in Tasmania along 3.4km of coastline, one infested by A. arenaria and the other retaining native vegetation. Dune profile surveys were derived from topographic measurement and LiDAR data, and recent aerial imagery was analysed using the Digital Shoreline Analysis System to quantify net shoreline movement and rates of change. Results showed lack of progradation on the A. arenaria infested beach, with tall, steep-faced, concave foredunes that retreated up to 15m in 10 years. By contrast, the native vegetated beach showed continued progradation, with smaller convex-faced foredunes. The A. arenaria foredunes retreated particularly where the dune toe was lower in elevation. Sediment supply is likely reduced by the tall foredunes with dense vegetation-holding sand, causing storm erosion not to be replaced, hence a lowering beach and dune toe. Future erosion is likely to be a greater risk with sand supply locked into high volume A. arenaria-infested dunes, relative to native vegetated dunes.
Highlights
Countries with long shorelines, such as Australia, with a coastal length of 29,900km comprising 49% of sandy beach systems,[1] are expected to experience the greatest loss of coastal land and the largest costs associated with sea-level rise.[2]
Tasmania has the largest ratio of coastal length to land area of all Australian States and Territories, with 2,237km of coastal length of the main island, of which 39% is sandy beaches and dunes.[1]
By contrast the west beach showed little change, with sections of small progradation and small regression shown by the Net Shoreline Movement (NSM) results, with rates of change of mostly less than 0.5ma-1 (Figure 4B)
Summary
Countries with long shorelines, such as Australia, with a coastal length of 29,900km comprising 49% of sandy beach systems,[1] are expected to experience the greatest loss of coastal land and the largest costs associated with sea-level rise.[2]. Increased storminess caused by climate change[8] will likely result in dune erosion, accelerated beach erosion, and coastal recession.[9,10,11] Where the invasive marram grass (Ammophila arenaria) has been introduced, problems may be exacerbated by locking sediment into over-steepened foredunes
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