Quantification of landscape evolution on multiple time-scales

Essential information about the activity or even the mechanics of tectonic and erosional processes can be extracted from their surface expression. For this purpose, it is necessary to appropriately constrain the temporal as well as the spatial framework, in which to consider a specific process. While recently developed dating techniques, such as thermochronology or radiocarbon dating, allow to assess the age of landforms and therefore rates of tectonic and erosional processes, detailed spatial information is also required to assess these rates correctly. Due to a lack of appropriate topographic data in the past it was sometimes challenging to reliably approximate the spatial framework, because the size of a particular landform can often cover a wide range of spatial scales. Recently available, conventional topographic data, such as those of the Shuttle Radar Topography Mission, substantially improved the definition of an appropriate spatial framework due to their spatial coverage and resolution of down to less than 1 m. However, to constrain this framework at a detail beyond the resolution of several decimeter terrestrial laser scanning provides a highly efficient approach. This technique permits the rapid acquisition (within minutes) of tremendous amounts of topographic data with both, a high resolution of a few centimeters and a high accuracy of a few millimeters. High-resolution topographic maps of a certain area of the surface of the Earth are derived from individual laser-scanner measurements, that in turn allow to characterize the in-situ geomorphic setting at great detail. Moreover, repeated measurements of this area allow to quantify morphological changes thereby supporting the survey of surface processes on short-term scales ranging from days up to several years. The former approach is best suited for tectono- and the latter one for fluvial-geomorphic studies, and we present results from two case studies that are either based on single or repeated laser-scanner measurements. In the first case, we combined field mapping and high-resolution digital elevation model (DEM) analysis to evaluate the detailed meter- to hundred meter-scale structure and surface expression of one flank of the Rex Hills pressure ridge in the western United States. Based on terrestrial laser scanning (Riegl LMS-Z420i) we derived a DEM with cm-scale resolution and extracted high-resolution topographic cross-sections. This enabled us to identify fault scarps and determine their relative ages and geometry. In the second case, we carried out a detailed field mapping of erosion and sedimentation patterns in the Alp Valley, central Switzerland, to assess its Holocene evolution. Simultaneously, we conducted repeated high-resolution (less than 1 cm locally) laser-scanning surveys (Topcon TLS-1000) along two tributaries, the Erlenbach and Vogelbach, to determine channel-morphology changes and the nature of shortest-term sediment transport by comparing the individual DEMs derived from these measurements, as well as to evaluate the context to the longer-term evolution of the Alp Valley. Both case studies, however, highlight the potential of medium-range laser scanners with measurement distances of up to hundreds of meters. Such scanners are most appropriate to efficiently analyze closely-spaced fault scarps across a broad range of spatial scales, and to document complex morphologic changes in small mountainous torrents due to sediment transport. Moreover, terrestrial laser scanning is a key tool to monitor surface processes, but the insights gained from this method are generally evaluated best in the context of further data sets including geochronological, structural, subsurface, or climate data. Surface processes, in particular erosion, sediment transport, and deposition in sedimentary basins are intermittent in space and time challenging both, the appropriate definition of a spatiotemporal framework addressed above and a comprehensive process understanding. A major objective of this thesis is to contribute to a better understanding of scale linkage concerning these processes. We therefore first carried out a comprehensive comparison of short- to long-term erosion measurements from the Alps based on an approach originally established to evaluate the significance of geologic and geodetic measurements along intra-continental faults on time scales of millions to tens of years. In a second step, we re-assessed the sediment budget of the Alps, a data set that is usually considered to be an appropriate measure of long-term erosion in the Alps. The two major results of both studies indicate that: short- and medium-term erosion in the Alps over years to ten thousands of years is dominantly influenced by climate and weather variability, e.g., due to seasonal differences in the amount of precipitation; whereas long-term erosion over millions of years is controlled by tectonic processes

High Resolution Bathymetric Lidar Data To Hydraulic - Modelling A Mountain Stream By Bathymetric Lidar Data

Knowledge about the hydraulic situation in a mountain torrent is relevant to quantify flood risks, to study sediment transport and to assess the waterbodies’ ecology. To conduct reliable calculations, high-quality terrain data of riverbeds, riverbanks and floodplains are required. Typically, digital terrain models (DTMs) of floodplains are derived from classical airborne laserscanning (red wavelength) together with terrestrial surveys along riverbeds and riverbanks. Usually these are restricted to a limited number of cross sections. The terrestrial surveys are necessary because those laser systems cannot penetrate through the water column of the observed waterbodies. Consequently, data for the geometry of riverbeds and bank structures are hardly available at a high spatial resolution and extent, comparable to the airborne-laser scanning derived data for river floodplains. In this study, a newly available, water-penetrating airborne laser system (green wavelength, FFG research project between the University of Innsbruck and Riegl LMS) was used to survey a mountain torrent. Detailed and extensive data (~30 points/m² on topobathy side) of the riverbed, the riverbanks and the neighboring floodplains were acquired with this single sensor. The general applicability of such hydromapping data as a base for 2D- and 3D numerical simulations was investigated. For this, a detailed analysis was carried out by comparing results of 2D-calculations based on the new hydromapping data and 2D- calculations based on traditional terrestrially measured cross-sections. For example, the morphologic boundary conditions are significantly better defined when using the hydromapping data than they are when using cross-sections. This is already due to the original high spatial resolution and spatial data coverage of the hydromapping data, which saves the need of any interpolation, required when using cross-sections that can be tens to hundreds of meters apart from each other. Hydromapping delivers the entire structure of a riverbed and therefore a geometrical information about its friction

Das Potential der Full-Waveform-Prozessierung topo-bathymetrischer LiDARDaten

Aufsatz veröffentlicht in: "Wasserbau-Symposium 2021: Wasserbau in Zeiten von Energiewende, Gewässerschutz und Klimawandel, Zurich, Switzerland, September 15-17, 2021, Band 2" veröffentlicht unter: https://doi.org/10.3929/ethz-b-00049975