Lake Annan (Case Study)
By way of a case study for this innovative new service, we created a sediment map using a 2010 bathymetry survey for our as built baseline map. This was georeferenced and digitized to create a baseline survey and overlayed with a 2017 bathymetry survey using our acoustic sounding device. We created a sediment or difference map by subtracting the baseline map from the current mapped data. The “Sediment Accumulated” statistic is calculated by totaling the volume of the three classes greater than zero. This assessment allows managers make observations that can help design improvement works. Our case study showed that:
- There has been 5,870m3 of sediment accumulated in the 2.57ha lake since 2010. This rate of sedimentation is equivalent to 978m3 per annum and, if evenly distributed, would provide uniform coverage of 2.6cm per annum.
- A major contribution of this sediment is the eroding island, where sediment accumulation has been at least 0.5m
- The eastern side is where there is greater sedimentation. This indicates the main flow from the inlet passes along the western side of the island.
- Apart from sedimentation, areas of sediment loss has occurred near the outlet (northern end) indicating scouring in high flows.