Waikato Regional Council

1006425 Waikato Peatland Subsidence Monitoring Lidar

The Waikato region has about 65,000 ha of peatlands which are subsiding due to land drainage. Peat subsidence can damage infrastructure, reduce drainage efficiency, and impact on how the land can be used. Waikato Regional Council (WRC) monitors peat subsidence as part of its state of the environment monitoring programme and historic surveys using peat depth probing have estimated that land subsidence in drained peatlands is about 19 mm per year. However, in 2019, recognising the limitations of peat depth probing, WRC reviewed the range of methods to monitor subsidence and subsequently developed a method using high specification helicopter-based lidar. In the selected method, hard ground surface models (HGSMs) developed from lidar survey point clouds, collected within representative transects at 5-yearly intervals, are compared to estimate regional-scale peat subsidence. Uncertainty associated with each change measure at each sampling point on hard ground (beneath vegetation and thatch) needs to be low enough to detect change in hard ground of at least 100 mm (at 95% confidence level) between the 5-yearly surveys, where ‘sampling point’ could be a 1 m or greater voxel (voxel size to be recommended in proposal). Therefore, an uncertainty of less than 50 mm at 95% confidence, (in terms of random stratified test on hard-ground locations) on sampling points beneath the vegetated surfaces for each surface model, is needed.

The first lidar survey was flown on 28 April 2021 over 12 transects covering 14,755 ha, and within that, about 13,000 ha of peatland. Waikato Regional Council wants to repeat that survey and are therefore seeking quotes from vendors to undertake the lidar survey (including appropriate ground control checks), provide post processed point clouds, hard ground surface models (HGSMs), and associated uncertainty estimates, to be used for ground surface elevation change analysis.

While we are seeking quotes from all vendors capable of meeting our specifications, if all other criteria are equal then lidar affixed to a helicopter platform will be preferred, to maintain consistency with the 2021 survey.