Citic Pacific Mining Management (CPM) has been monitoring the stability of a 7 km section of beach in the northwest of WA since 2009, in accordance with a marine management plan. This has traditionally involved a team of surveyors using real-time kinematic GPS equipment to measure 27 profiles at regular intervals along the beach. Remote sensing techniques have now made this site presence unnecessary, leaving the turtle habitat undisturbed, while providing a much more comprehensive measure of how the beach changes over time.
In order to assess the impact of nearby projects on the coastal ecosystem, it is necessary to measure the amount of erosion and decomposition of sand occurring along the coast to ensure that the process is stable over time. Such coastal processes effect the habitat for turtles in particular, where the appearance of steep escarpments in the sand (“scarps”) may prevent them from reaching their favoured nesting areas.
In order to ensure that the method would match or better the traditional means of satisfying the conditions of the management plan, Astron were commissioned in 2014 to assess the quality of landform measurements derived from aerial imagery, which had been captured in parallel with the ground survey. Linear mixed effects models were used to correlate the aerial data with those of the ground survey at the transect locations, and the results were shown to be accurate to within a few centimetres. This was good news for the client and for the turtles, as it meant that a very accurate measurement of coastal processes could be made, without the need for boots on the ground in the very area in need of protection, and with the added advantage that the whole beach could be surveyed, rather than occasional transects, ensuring that no problem areas were missed.
With this remote sensing technique approved for future surveys with respect to this part of CPM's marine management plan, Astron was engaged once again to analyse the digital elevation model derived from an aerial survey completed in June 2015, to establish any changes to the beach habitat over the year. Erosion and deposition from wave action were calculated and mapped, and any steep slopes formed were mapped and analysed. Results were better than expected, actually showing an improvement for the turtles. The two comprehensive digital surfaces now established will form the basis for ongoing monitoring of this important coastal ecosystem using remote sensing methods.