Tracking Multi-Decadal Lake Dynamics using Optical Imagery, Digital Elevation Models, and Bathymetric Datasets

The goal of this research is to review the current state of long-term, multi-decadal lake dynamic monitoring and develop novel techniques for scalable analysis at local, regional, and global levels. This dissertation is comprised of three chapters formatted as journal manuscripts with each chapter progressively addressing some key limitation in current lake dynamic monitoring methodologies. Chapter 1 tracks lake dynamics (surface elevation, surface area, volume, and volume change) for a single water body, Lake McConaughy, which is the largest lake and reservoir in the state of Nebraska, using the cloud-based geospatial analysis platform Google Earth Engine. Lake dynamics were estimated using bathymetric survey data, the Shuttle Radar Topography Mission 30-meter digital elevation model, and Landsat 5 image composites for 100 time periods between 1984 and 2009. Water surface elevation was estimated and assessed for 5,994 different combinations of water indices, segmentation thresholds, water boundaries, and statistics and produced elevations as accurate as 0.768 m CI95% [0.657, 0.885] root-mean-square-error. The method also detected seasonal and long-term trends which would have major implications for regional agriculture, recreation, and water quality. Chapter 1 was published as an article in the peer-reviewed journal Water Resources Research in October 2019. Chapter 2 expands and improves upon the techniques explored in Chapter 1 in multiple ways. First, the techniques were improved to remove image contamination sources such as snow, ice, cloud cover, shadow, and sensor error for individual images using the Pixel Quality Assurance (QA) band available as a part of the Landsat 4, 5, 7, and 8 Top-of-Atmosphere Tier-1 Collection-1 archives. Using the Pixel QA band information, image contamination was removed from each image between August 1982 and December 2017 and water surface elevation was estimated with the remaining visible water boundary extents overlaying merged National Elevation Dataset digital elevation model and bathymetric survey data resampled to 30-meters which resulted in enhanced temporal resolution compared to the techniques used in Chapter 1. Second, the analysis was expanded from a single water body to fifty-two lakes/reservoirs to provide a better understanding of how the techniques generalize to imagery and water bodies encompassing a wide range of ecotypes, geologies, climates, and management strategies. A variety of common water indices, such as the Modified Normalized Difference Water Index, naïve and dynamic water indices, water boundary types, and filtering strategies were tested and individual lake accuracies are as low as 0.191m RMSE CI95%[0.129, 0.243], and 45 of the 52 lakes produced sub-meter root-mean-squared-error accuracies. Furthermore, accuracy of surface elevation estimates is highly correlated with the mean slope of surrounding terrain with low-slope shorelines having greater accuracy than high-slope shorelines such as those in canyon-filled reservoirs or in mountainous regions. Overall, the improved techniques extend our ability to track long-term lake dynamics to lakes with bathymetric datasets while lacking in-situ hydrological stations, provide a framework for scale-able analysis in Google Earth Engine, and balance a need between high-accuracy estimates and maximum temporal resolution. Bathymetric survey data, such as that used in Chapters 1 and 2 is, unfortunately, not available for most water bodies at regional and global scales. Chapter 3 introduces a method of tracking long-term lake dynamics without bathymetry data and only using available digital elevation models such as Shuttle Radar Topography Mission, the National Elevation Dataset, and Advanced Land Observing Satellite. In digital elevation models, the water surface is often, but not always, hydroflattened producing a flat surface approximating the surface of the water at the time of the data capture which precludes using water boundaries like those in Chapter 1 and Chapter 2 to estimate water level when it is lower than the hydroflattened surface in the digital elevation model. However, using hypsometric relationships developed from the digital elevation models, subsurface water dynamics can still be estimated by extrapolating the low water levels using regression, albeit with increased uncertainty compared to levels above the hydroflattened surface. Using multiple digital elevation models, the lowest hydroflattened surface can be identified for each water body which reduces uncertainty for low water levels by reducing the extrapolation distance to those values while simultaneously increasing the number of above hydroflattened surface estimates. In addition to low-level uncertainty, hypsometric techniques are highly impacted by image contamination such as cloud, cloud shadow, snow, ice, and sensor error which reduces the observable water surface area resulting in erroneous surface elevation, volume, and volume change estimates. To help alleviate this issue, a technique of using proportional hypsometry was developed to remove contamination effects. Together, using the lowest hydroflattened surface and proportional hypsometry, this research produced 12,680 additional water surface elevation estimates for 46 lakes in comparison to traditional hypsometric techniques, reduced the number of sub-hydroflattened water surface estimates by 549 or more compared to individually using any of the three digital elevation models assessed, and lays the groundwork for regional and global scale surface water dynamic research without bathymetric survey data

Characterisation and Analysis of Catastrophic Landslides and Related Processes using Digital Topographic Data

This thesis represents a large body of work that seeks to describe, quantify, and simulate the behaviour of large rock slope failures (> 1 Mm³), in the form of landslides and rock avalanches, and their secondary processes, such as landslide-dammed lakes, utilizing remotely sensed data. Remotely sensed data includes aerial photography, high resolution satellite imagery from various platforms (e.g. LANDSAT, ASTER, EO-1, SPOT), and digital topographic elevation models of the Earth’s surface (e.g. SRTM-3, ASTER GDEM2, LiDAR). This thesis focused on regions in northwest North America (British Columbia, Yukon Territory, and Alaska), and on regions in the Himalaya and Pamirs Mountain chains (Tajikistan, Afghanistan, Pakistan, Tibet, and India). These study regions are each highly dynamic landscapes, where the occurrence of rock slope failures per area is higher than non-mountainous regions, and these events are aiding to the shape and profile of the landscapes and surfaces found today. This thesis focuses on: 1) the ability to accurately calculate geometrics (e.g. areas, volumes, runouts, debris depths) for large scale landslides and their associated landslide dammed lakes (e.g. areas, volumes, outbursts), utilizing data from remotely sensed sources; 2) the attempt to successfully simulate the observed dynamics for both landslide emplacement and their resulting debris deposits (DAN-W, DAN3D), and possible outburst flood scenarios (FLO2D); and, 3) attempt to quantify the kinetic and specific energy involved in rock avalanches, and how these energetics relate to fragmentation, as well as the lateral spreading and thinning of debris sheets. The river valleys of the northwest Himalayas (Pakistan and India) and the adjacent Pamirs Mountains of Afghanistan and Tajikistan contain in excess of two hundred known rockslide deposits of unknown age that have interrupted surface drainage and previously dammed major rivers in the region in recent and prehistoric time. Some prehistoric rockslide dams in the northwest Himalayas have impounded massive lakes with volumes in excess of 20 Gm³. The region contains: 1) the highest rockslide dam in the world (the 1911 Usoi rockslide, Tajikistan), which impounds the current largest rockslide-dammed lake (Lake Sarez) on Earth (est. volume 17 Gm³); 2) the largest documented outburst flood (6.5 Gm³) associated with a historical rockslide dam outburst (the 1841 Indus Flood, Pakistan); and, 3) the world’s most recent rockslide-dammed lake emergency, the 2010 Attabad rockslide dam on the Hunza River, in the Upper Indus basin, including the newly created Lake Gojal. By accurately quantifying the volume of an impoundment, and the downstream valley topography (DEM), floodwave scenarios can be created for various breaching situations, allowing for the delineation of downstream inundation areas, or the creation of hazard and risk scenarios. Two methods are used to attempt to quantify the volumes of landslide-dammed lakes: 1) a contour interpolation method, focusing on the creation of contours to represent lake levels in the DEM data; and, 2) a new technique using digitized shorelines and statistical methods to obtain lake elevations on specific dates. A new technique has also been developed to quantify the larger block fragmentation from rock avalanches in the glacial environment, and a credible grain-size curve for the largest blocks can be obtained, aiding in the creation of a more complete grain-size curve for a particular event. The combination of landslides and their associated landslide dammed lakes are an important geomorphic process to study, as these events have a direct relationship to the hazard and risk faced by local communities living and working in these regions. By understanding the emplacement and deposit dynamics of large landslides and/or the outburst flood scenarios from naturally impounded reservoirs, we can attempt to reduce the direct impacts these events have to local communities.4 month

Spatial and temporal variations of inundation and their influence on ecosystem services from a shallow coastal lake. A case study of Soetendalsvlei in the Nuwejaars catchment, South Africa

Philosophiae Doctor - PhDEnhancing our understanding of wetland properties and the ecosystem services provided by wetlands within a dynamic landscape, is fundamental to ensuring appropriate management strategies for enhanced biodiversity and ecosystem benefits. With increased anthropogenic activities and the impacts of climatic variability, a better understanding of the factors influencing the water balance dynamics of wetlands can provide insight into how wetlands respond to change. The main aim of the research was to improve the understanding of the spatial and temporal availability of water and storage of a depression wetland in a semi-arid climate, and to relate these to ecosystem functions. As ecosystems are intricately connected to society, a secondary aim of the research was to gain insight to how wetland ecosystems, within a changing climate and landscape, provide benefits to society, and add value to human-wellbeing. Soetendalsvlei, a shallow freshwater depression, and one of the few coastal freshwater lakes of South Africa, was the focus of the research