Managing the Great Barrier Reef catchments using LiDAR

MANAGING GREAT BARRIER REEF CATCHMENTS CASE STUDY

USING LIDAR TO MAP THE GREAT BARRIER REEF CATCHMENTS Quick Facts The Great Barrier Reef is a unique ecosystem; home to thousands of species of marine life, including fish, whales, dolphins, and six of the world’s seven species of marine turtle.

1 of 7 Natural wonders of the world.

Largest Living structure on the planet, so big it’s visible from space.

348,000 km2 Of World Heritage Listed area, which is slightly more than the 344,400 km2 Great Barrier Reef Marine Park area including some 980 islands, internal waters, intertidal areas and other state waters.

1975 The Great Barrier Reef Marine Park was created.

Project Background The condition of the Great Barrier Reef is deteriorating and while climate change is considered the most serious risk to coral reefs, agricultural pollution has also had a major impact on their health. Fine sediment and associated particulate nutrients reduce water clarity, slow down coral growth and increase their vulnerability. Locating the major sources of sediment (and nutrients) and understanding how to remediate these landscapes is crucial for the coral reefs long term health. The area draining into the Great Barrier Reef is vast and hence managing its condition requires prioritisation of funds.

Project Outline As part of a project funded by the Australian Government’s Reef Trust, there was a requirement to acquire LiDAR and Orthophotography to improve the government’s investment prioritisation in the management of erosion and fine sediment losses to the reef. This was to be done through the establishment of a new baseline of extent of gully and streambank erosion and this 2019 acquisition was the second of a planned multi-year acquisition project.

Aerometrex was brought on board for this project to provide aerial LiDAR data, orthophotography and a ground checkpoint survey of gullied and eroded areas within nominated catchment areas in the following two Great Barrier Reef Natural Resource Management Regions of Queensland: - Normanby River catchment west of Cooktown (~900 sq. km) - Lower Burdekin River, including Bowen-Bogie and Don catchments (~300 sq. km)

3000 Individual reefs.

150

Inshore mangrove islands.

Project Brief This project was conducted by Aerometrex as a part of the Australian Government’s Reef Trust investment program. The Reef Trust is an initiative designed to improve Reef health and resilience by utilizing the best available science to deliver the Reef 2050 Long-Term Sustainability Plan – the Australian and Queensland Government’s framework for protecting and managing the Great Barrier Reef.

This DSM (Digital Surface Model) otherwise known as first reflective surface shows a good example of the sort of features targeted in the study i.e., the small gullies that feed into major watercourses.

Visualisation of the Type 2 classified LIDAR data used in this study to isolate the bare ground surface (brown) from above ground features (in this case vegetation shown in green) to map small gullies that may contribute fine sediments to major tributaries.

Aerometrex Approach The nature of the gully features being captured required higher than usual point density and accuracy to delineate near-vertical gully edges and allow calculation of gully volumes. The gully features commonly have near-vertical walls (1-3 m high), low relief near drainage lines, and trees and low vegetation are common, making LiDAR the ideal approach.

Eight outbound pulses per square metre and a swath overlap of at least 50% (producing an effective sixteen pulses per square metre) would ensure all areas were illuminated in two different directions and increase the likelihood of capturing gully sidewall positions and heights. Additionally, a vertical accuracy of +/- 20cm for 95% of points was planned.

Our VQ-780i LiDAR sensor from RIEGL was ideal to achieve the point density and accuracy requirements of this project. The VQ-780i can capture 8 points per square metre in a single swath from an altitude of 1000 metres. Using 55% side overlap we could achieve the required 16 points per square metre. This high-density point capture minimised the number of runs needed to complete the work and provided an efficient, accurate

A close-up example of a small gully, mapped in three dimensions, that feeds into the main channel

and cost-effective solution. LiDAR and imagery were captured simultaneously using the digital camera built into the LiDAR sensor.

Project Deliverables: - Unclassified Point Cloud – Fully compliant LAS with all returns, all collected points, fully calibrated, and adjusted to specified vertical datum - Classified Point Cloud – Classified based on a modified ASPRS classification scheme and to Level 3 Standard (with Ground Correction) - Orthophotography with ground resolution of 20 cm or better - Orthometric DSM and bare earth DEM from the LiDAR mass point data, with hydro-flattening undertaken for water bodies About the Reef Trust:

The Reef Trust is the Australian Government’s flagship investment program to support the delivery of the Reef 2050 Long-Term Sustainability Plan – the Australian and Queensland Government’s long-term framework for protecting and managing the Great Barrier Reef.

The Reef Trust provides cost effective and strategic investment to address key threats to the Great Barrier Reef and conserve the outstanding universal value of this World Heritage-listed icon. The Reef Trust has a strong focus on adaptive management and is committed to provide innovative, targeted investment in improving water quality, restoring coastal ecosystem health, controlling crown-of-thorns starfish, and protecting threatened and migratory species in the Great Barrier Reef region.

51-53 Glynburn Rd, Glynde SA 5070 08 8362 9911 info@aerometrex.com.au www.aerometrex.com.au