Exploring the 4D scales of eco-geomorphic interactions along a river corridor using repeat UAV Laser Scanning (UAV-LS), multispectral imagery, and a functional traits framework

Vegetation plays a critical role in the modulation of fluvial process and morphological evolution. However, adequately capturing the spatial variability and complexity of vegetation characteristics remains a challenge. Currently, most of the research seeking to address these issues takes place at either the individual plant scale or via larger scale bulk classifications, with the former seeking to characterise vegetation-flow interactions and the latter identifying spatial variation in vegetation types. Herein, we devise a method which extracts functional vegetation traits using UAV laser scanning and multispectral imagery, and upscale these to reach scale guild classifications. Simultaneous monitoring of morphological change is undertaken to identify eco-geomorphic links between different guilds and the geomorphic response of the system in the context of long-term decadal changes. Identification of four guilds from quantitative structural modelling based on analysis of terrestrial and UAV based laser scanning and two further guilds from image analysis was achieved. These were upscaled to reach-scale guild classifications with an overall accuracy of 80 % and links to magnitudes of geomorphic activity explored. We show that different vegetation guilds have a role in influencing morphological change through the stabilisation of banks, but that limits on this influence are evident in the prior long-term analysis. This research reveals that remote sensing offers a solution to the difficulty of scaling traits-based approaches for eco-geomorphic research, and that these methods may be applied to larger areas using airborne laser scanning and satellite imagery datasets.

Assessment of soil erosion, flood risk and groundwater potential of Dhanari watershed using remote sensing and geographic information system, district Uttarkashi, Uttarakhand, India

Quantitative morphometric analysis of Dhanari watershed has been done using remote sensing and Geographical Information System (GIS). The impact of climate, lithology, tectonics, structural antecedents, vegetation cover and land use on hydrological processes is assessed by quantifying geomorphic parameters. The Dhanari River (a tributary of the Bhagirathi River) and its tributaries Dhanpati Gad and Kali Gad forms Dhanari watershed covering 91.8 Km2 area. Several geomorphic aspects viz. linear, areal, relief were computed to comprehend potentials of soil erosion, groundwater, flood vulnerability and the geomorphic response of watershed. LISS-III image is used to generate the Land Use and Land Cover (LULC) map and assess the watershed dynamics. Values of computed hypsometric integral and morphometric parameters viz. drainage density ($$D_{{\text{d}}}$$ D d ), stream frequency ($$F_{{\text{s}}}$$ F s ), stream length ratio ($$L_{{{\text{ur}}}}$$ L ur ), bifurcation ratio ($$R_{{\text{b}}}$$ R b ), rho coefficient (ρ), drainage texture ($$D_{{\text{t}}}$$ D t ), circularity ratio ($$R_{{\text{c}}}$$ R c ), relief ratio ($$R_{{{\text{hl}}}}$$ R hl ), elongation ratio ($$R_{{\text{e}}}$$ R e ), form factor ($$F_{{\text{f}}}$$ F f ), basin shape ($$B_{{\text{s}}}$$ B s ), drainage intensity ($$D_{{\text{i}}}$$ D i ), compactness coefficient ($$C_{{\text{c}}}$$ C c ) and infiltration number ($$I_{{\text{f}}}$$ I f ) have shown a moderate and steady erosion rate, with low groundwater potential and low to moderate flood vulnerability in the watershed. Hypsometry presents a dependable geomorphic parameter to understand the erosion and geomorphic response of a watershed to hydrological processes. Hypsometric integral value (0.51) of Dhanari watershed suggests a mature topography with steady erosion in the watershed.

A data-driven evaluation of post-fire landslide susceptibility

Wildfires change the hydrologic and geomorphic response of watersheds, which has been associated with cascading hazards that include shallow landslides and debris flows. This study evaluates post-wildfire landslide trigger characteristics by comparing precipitation preceding landslides at both burned and unburned locations. Landslide events are selected from the NASA Global Landslide Catalog (GLC) to facilitate regional inter-comparison. Fire and precipitation histories for each site are established using MODIS global burned area and CHIRPS precipitation data, respectively. Analysis of normalized seven-day accumulated precipitation for sites across all regions shows that, globally, landslides at burned sites are preceded by less precipitation than landslides without antecedent burn events. This supports the hypothesis that fire increases rainfall-driven landslide hazards. An analysis of the seasonality of landslides at burned and unburned locations shows that landslide-triggering storms in burned locations tend to exhibit different seasonality from other rainfall-triggered landslides, with a variety of seasonal shifts ranging from approximately six months in the Pacific Northwest of North America to one week in the Himalaya region. Overall, this manuscript offers an exploration of regional differences in the characteristics of rainfall-triggered landslides over a broad spatial scale and encompassing a variety of climates, geographies, and burn conditions.

Sediment supply dampens the erosive effects of sea-level rise on reef islands

Large uncertainty surrounds the future physical stability of low-lying coral reef islands due to a limited understanding of the geomorphic response of islands to changing environmental conditions. Physical and numerical modelling efforts have improved understanding of the modes and styles of island change in response to increasing wave and water level conditions. However, the impact of sediment supply on island morphodynamics has not been addressed and remains poorly understood. Here we present evidence from the first physical modelling experiments to explore the effect of storm-derived sediment supply on the geomorphic response of islands to changes in sea level and energetic wave conditions. Results demonstrate that a sediment supply has a substantial influence on island adjustments in response to sea-level rise, promoting the increase of the elevation of the island while dampening island migration and subaerial volume reduction. The implications of sediment supply are significant as it improves the potential of islands to offset the impacts of future flood events, increasing the future physical persistence of reef islands. Results emphasize the urgent need to incorporate the physical response of islands to both physical and ecological processes in future flood risk models.

Geomorphic response and paleohydrology of a debris flow event in the upper Ganga River basin, NW Himalaya

<p>Debris flow events are recognized as one of the most prominent mechanisms for landscape evolution in the Himalayan river basins. Triggered by cloud bursts, glacial and landslide lake outburst floods; debris flows can erode, transport and deposit vast amount of sediments with profound landscape changes. The Himalayan river basins frequently experience such debris flow events during the monsoon. However, only a few morphological and hydrological studies are available for such events. Hence, we studied a high-magnitude, low-frequency debris flow event in the Asiganga River basin (a headwater tributary of the Ganga River) on 3<sup>rd</sup> August 2012.</p><p>In the present study, we (i) computed landscape change during the event and (ii) calculated the paleohydrology of the event. The pre and post geomorphic mapping is carried out using satellite imageries (Google Earth), field data, and published literature to analyze landscape modification/change. The paleohydrology of the event is calculated using dimensions of 440 mobilized stream boulders at 11 locations in the Asiganga River basin. Our results suggest that the Asiganaga River’s reaches encountered sediment deposition and erosion on a massive scale; especially in the lower terrace levels. Channel shifting and widening was also a dominating geomorphic response, and it occurred in different magnitude along the course of the Asiganga River. A significant alteration trend is observed in sediment bars, especially in the reaches, which were exceedingly influenced by morphological and hydraulic parameters. The peak discharge is calculated using D95, D90, D85, and D80 of the mobilized stream boulders. Overall, the calculated highest peak discharge is around 4500 m<sup>3</sup>s<sup>-1</sup>. Interestingly, the peak discharge from D90 yielded the value of 2661 m<sup>3</sup>s<sup>-1 </sup>, and it corresponds with the peak discharge (i.e., 2665 m<sup>3</sup>s<sup>-1 </sup>) measured using an instrument based previous study. </p><p>In the Himalayan River basins, documentation of such debris flow events is crucial. Such studies will provide a unique database to study river sensitivity towards future debris flow events.</p>

Vertical distribution of excess ice in icy sediments and its statistical estimation from geotechnical data (Tuktoyaktuk Coastlands, Northwest Territories)

<div>Excess ice can be found in the form of massive ice and within icy sediments and is an important variable to quantify as it strongly influences the geomorphic response of landscapes to permafrost thaw. The melting of excess ice in the Western Canadian Arctic has led to thaw subsidence and an increase in the number and size of thaw slumps observed across the Northwest Territories which cause issues to Northern infrastructure and affect fluvial and lacustrine watersheds. The Inuvik-Tuktoyaktuk Highway (ITH) is the first all-weather road to reach the Canadian Arctic Coast and its planning and construction has resulted in a significant cryostratigraphic dataset of 566 boreholes, which forms the basis of this contribution. Although visible ice is often recorded in boreholes, it is not a reliable measure of excess ice content on its own and there is currently no reliable method to estimate the excess ice content of boreholes based on commonly available geotechnical data. In this study, a 16-borehole subset of the ITH dataset for which samples were processed for volumetric excess ice content is used to train a beta regression model that predicts the excess ice content of stratigraphic intervals in the study area based on interval depth, visible ice content, surficial geology, and material types. The resulting predictions are compared to recorded massive ice intervals in the same boreholes and show that excess ice within icy sediments can significantly contribute to potential thaw strain and should be considered alongside massive ice when making thaw strain estimates.</div>