Segmentation of topographic change by geomorphic units to assess physical habitat transitions in a restored river

Abstract

River restoration schemes that utilise natural processes need to be monitored post-implementation to inform adaptive management, to assess their success at delivering sustained ecological improvements and to contribute to the design of other schemes. All three of these monitoring objectives require an understanding of the geomorphic mechanisms that cause channel adjustment and how they shape the mosaic of geomorphic units that make up physical habitat. In the last decade repeat, high-resolution topographic surveys of river restoration schemes have become commonplace through the application of a range of geomatics technologies including echo-sounders, laser scanners and Structure from Motion photogrammetry. Such datasets offer opportunities to map geomorphic change and geomorphic unit evolution to quantitatively analyse the relative roles of different processes in generating physical habitat. Here, we present results from an investigation into the morphodynamics of the Whit Beck river restoration scheme, implemented by the West Cumbria Rivers Trust, UK. We use repeat Digital Elevation Models (DEMs) to quantify patterns of erosion and deposition using the Geomorphic Change Detection (GCD) toolbox and to map geomorphic units, using the Geomorphic Unit Tool (GUT). The segmentation of maps of erosion and deposition with maps of geomorphic units quantifies physical habitat transitions. The resulting analysis indicates the different mechanisms of adjustment that generate physical habitat throughout the restoration scheme and how they are linked to different initial conditions.