Integrating multiple lines of evidence to identify erosion hotspots for reducing sediment connectivity and delivery to the Great Barrier Reef, Australia

Abstract

In the Great Barrier Reef (GBR) catchments of northeast Australia, high source to sink sediment connectivity, particularly from gullies and streambanks are adversely impacting the coral ecosystems and millions of dollars are being spent on landscape rehabilitation to help reduce excess sediment delivery. Understanding sediment dynamics and mapping erosion hotspots provides improved data and information to support erosion management practices. There is an urgent need to develop methodologies to help (i) prioritise active gullies for rehabilitation; and (ii) to inform which treatments are most effective at reducing fine sediment yields. Previous research in the highly erosive landscapes of northeast Australia has demonstrated that multiple lines of evidence are needed to support informed management efforts and investment decision making.  Here we discuss the applicability of multi-temporal spatial datasets- differential LiDAR DEMs (Laser Light Detection and Ranging Digital Elevation Models) and Interferometric SAR (InSAR) from Sentinel-1 imagery archives as two lines of evidence for detecting erosion hotspots and assessing gully sediment dynamics within the highly erosive Burdekin catchment. At several case study sites, multi-temporal LiDAR DEMs are used to derive DEMs of Difference (DoDs) to (i) assess the spatial pattern of erosion and deposition within contrasting gully types and (ii) measure sediment yield from control and treatment gullies to analyse rehabilitation efforts. Coherence Change Detection (CCD) from Sentinel-1 archives is used to assess the spatial pattern of geomorphic change (erosion and deposition). Here we will discuss the strengths and limitations of both approaches and how these multiple lines of evidence can be combined to identify erosion hotspots and gully sediment dynamics for better prioritisation of rehabilitation efforts in the GBR catchments.