Geomorphic unit assemblages : from point clouds to consistent unit mapping
Dr. Richard Williams, School of Geographical and Earth Sciences, University of Glasgow
Tuesday 13 November 2018 (11h00 - 12h00) - Géopolis - 3899
Efforts to manage rivers, numerically simulate their morphodynamics, and restore their eomorphological diversity and ecological functioning rest upon understanding the relationships and dynamics between geomorphic units that provide the building blocks of fluvial landscapes. In recent years, considerable advances in geomatics technologies have enabled the generation of high-resolution Digital Elevation Models (DEMs) of river topography, including both dry and wet areas. The proliferation of DEMs across a variety of river styles has created new opportunities to investigate geomorphic unit assemblage using consistent unit mapping approaches based upon topographic data. This seminar will feature three parts. First, the results from a field campaign to verify the accuracy of a wearable laser scanner will be presented, to provide context for the accuracy of DEMs that can be generated using contemporary technologies. A survey of a 500 m long reach of the braided River Feshie, Scotland, was surveyed using a Leica Pegasus Backpack, that integrates Velodyne Puck VLP-16 sensors, and a multi-station static TLS survey using a Riegl VZ-1000 scanner, to produce a DEM and maps of surface sedimentology. Comparison to 107 independent RTK-GNSS check points resulted in a similar Mean Error (ME) and Standard Deviation Error (SDE) for static (ME = -0.025 m; SDE = 0.038 m) and wearable (ME = -0.014 m; SDE = 0.019 m) laser scanning. Absolute errors between the two point clouds were calculated and Chi-square distances for the fitted distribution showing a sharply decreasing Weibull distribution (shape parameter b=0.04, scale parameter a=0.84). Second, the results of applying the Geomorphic Unit Tool (GUT) to consistently map the evolution of geomorphic units on the Allt Lorgy river restoration scheme, Cairngorms, Scotland, will be presented. This software implements topographic definitions to discriminate between a taxonomy of fluvial landforms that have been developed from an extension of the River Styles framework. There are three tiers of processing: (1) differentiation between in-channel deposits & overbank areas; (2) classifying form into one of six categories (mound, bowl, trough, saddle, plane, wall); and (3) mapping GUs based on a range of attributes such as position & orientation. This work demonstrates how high-resolution topography can be used to systematically quantify how geomorphic unit diversity increases when a gravel-bed river is given freedom space. Finally, the scope of a research project titled, “Braided river geomorphic unit assemblage: synthesising global datasets” will be outlined. This project aims to assess whether different braided rivers are characterised by similar geomorphic unit assemblages and includes collaborations with researchers based at Western Ontario, Lausanne, Eastern Finland, Utah, Auckland, Waikato, Lyon, Trento and NIWA.