PML Applications supported South Devon Area of Outstanding Natural Beauty (AONB) to quantify changes in sediment levels and erosion rates at Sharpham Marsh on the River Dart south of Totnes, Devon. Two surveys were undertaken, one in February 2019 and another 16 months later in June 2020.
The two surveys were carried out during low tides to ensure comparable river levels and as much of the marsh was exposed as possible. Orthomosaics and Digital Elevation Models (DEMs) were derived from aerial photographs using Structure from Motion (SfM) techniques. The elevation difference between the two datasets was computed to quantify erosion in the area.
The image shows the elevation difference between the 2019 and 2020 data collected over Sharpham. Seasonal changes in vegetation are clearly visible as the 2020 survey was taken in summer while 2019 was collected during winter. The plot shown on A highlights the cross section sample of the edge of the Marsh with its main connection to the river Dart. Please note that changes in elevation are very minor and therefore the impact of erosion was estimated to be insignificant in the area. Plot B shows how the vegetation has clearly grown over the course of the year and how a tree was removed in the area.