1,721,033 research outputs found
The Use of Stream Power as an Indicator of Channel Sensitivity to Erosion and Deposition Processes
Full text linkStream power is a measure of the main driving forces acting in a channel and determines a river's capacity to transport sediment and perform geomorphic work. Recent digital elevation models allow the calculation of channel gradient and consequently stream power at unprecedented spatial resolution, opening promising and novel opportunities to investigate river geomorphic processes and forms. The present paper investigates the suitability of map-derived information on total and specific stream power (SSP) to identify dominant processes within the channel (i.e. erosion, transport or deposition). SSP has been already used to identify a threshold for channel stability. This paper tests this knowledge and investigates whether or not attributes of stream power profiles are statistically correlated with distinctive field morphological forms. Two gravel bed single-thread English rivers are used as case studies, the Lune and the Wye. Available deposition and erosion features surveyed in the field from 124 different locations are used to classify channel reaches as erosion, transport or deposition dominated. Meaningful patterns emerge between the stream power attributes and the field-based channel classification. An SSP threshold, which erosion is triggered, compares favourably with the ones in the literature. Information about upstream stream power profiles helps to determine the dominant processes. The joint configuration of local and upstream stream power information uniquely classifies reaches into four classes of different sensitivity to erosion and deposition
Characterizing physical habitats in rivers using map-derived drivers of fluvial geomorphic processes
No full textBalancing Sediment Connectivity and Energy Production via Optimized Reservoir Sediment Management Strategies
Full text linkSediment connectivity plays a fundamental role in sustaining ecosystem goods and services in fluvial systems, including hydropower production. Dams alter the natural processes of sediment transport by trapping sediment and reshaping downstream hydrology and geomorphology. Due to these processes' interconnected nature, dams' impacts extend in time and space beyond the dam site to the entire river system. System-scale approaches to reduce dam impacts commonly only consider dam siting, overlooking the potential of sediment management strategies integrated into the dam operations to offer more flexible solutions for mitigation. Herein, we contribute a sediment routing model (D-CASCADE) to assess the impacts of reservoirs and their management strategies on river sediment connectivity. D-CASCADE is applied to the 3S river system, a tributary of the Mekong River, a hotspot of potential dams in the Lower Mekong. We analyze three dam development portfolios. The effect of reservoir management is examined by assessing daily sediment delivery with specific dam release strategies. Model results predict sediment yield to the Mekong to reduce by 31%-60%. Finally, we explore trade-offs between hydropower generation and sediment connectivity across cascades of multiple reservoirs. Results show that repeated flushing operations during the early wet season could significantly increase sediment delivery with minimal (max 6%) hydropower losses. While poor trade-offs between sediment and hydropower have been locked-in in the Mekong, our results highlight the potential of including sediment connectivity models in multi-objective decision-making frameworks to devise integrated water and sediment management strategies that mitigate connectivity disruptions while minimizing losses in other sectors
Quantifying earth surface processes via remote sensing technologies
No full textIn this chapter, we discuss how available remote sensing technology such as satellites and piloted or unpiloted aerial vehicles provide an unprecedented capacity to map and quantify contemporary earth surface processes affecting landscape evolution. These tools enable the quantification of topographic changes and of dynamic shifts of geomorphic units over time, supporting the monitoring of landslides, glaciers, riverine and coastal dynamics. Their increasing spatiotemporal resolution and spatial extent also contribute to the generation of sediment budgets and the estimate of water and sediment fluxes from slopes to river systems and coastal areas. The chapter highlights technologies and methods available to monitor landscape evolution with a focus on fluvial systems and slope dynamics. It also discusses the limitations of remote sensing technologies in terms of data availability, accuracy, demand of computational power, and spatial and temporal resolutions. Integrated approaches of technologies and data analyses must be adopted to link processes and disciplines toward a large-scale mapping and monitoring of contemporary earth surface processes
The CASCADE toolbox for analyzing river sediment connectivity and management
No full textSediment connectivity in rivers directly links to fluvial processes and eco-system services. Modelling network-scale sediment connectivity and its response to anthropic alterations, such as dams or land-use changes, is key to better understanding river processes and to inform river basin management. This paper contributes a Matlab (TM) toolbox for network-scale sediment connectivity based on an implementation of the CASCADE (CAtchment Sediment Connectivity And DElivery) model. CASCADE combines concepts of graph theory with empirical sediment transport formulas to quantify sediment transfers between many connected sediment sources and sinks in a river network. Greater numerical efficiency compared to common hydrodynamic models enables application to large river networks, stochastic simulations of sediment connectivity, and screening impacts of many infrastructure portfolios. Input data requirements are flexible and basic functionality is available with globally available datasets to ensure applicability to data-scarce basins. The toolbox offers options for customization and interactive output visualization tools
The Growing Hierarchical Self-Organizing Map (GHSOM) for analysing multi-dimensional stream habitat datasets
No full textA Dynamic, Network Scale Sediment (Dis)Connectivity Model to Reconstruct Historical Sediment Transfer and River Reach Sediment Budgets
Full text linkModeling network-scale sediment (dis)connectivity and its response to anthropic pressures provides a baseline understanding of river processes and sediment dynamics that can be used to forecast future hydro-morphological changes in river basins. However, this requires a solid understanding of how a system is currently operating, and how it operated in the past. We present the basin-scale, dynamic sediment connectivity model D-CASCADE, which combines concepts of network modeling with empirical sediment transport formulas to quantify spatiotemporal sediment (dis)connectivity in river networks. D-CASCADE accounts for multiple factors affecting sediment transport, such as spatiotemporal variations in hydrological regime, different sediment grain sizes, sediment entrainment and deposition. Add-ons are included in D-CASCADE to model local changes in river geomorphology driven by sediment-induced variations in features such as channel width. We apply D-CASCADE to the well-documented Bega River catchment, NSW, Australia, where significant geomorphic changes to rivers have occurred post European colonization (after 1850s), including widespread channel erosion and sediment mobilization. The Bega catchment provides a useful case study to test D-CASCADE, as original source data on the historical sediment budget are available. By introducing historic drivers of change in the correct chronological sequence, the D-CASCADE model successfully reproduced the timing and magnitude of major phases of sediment transport and associated channel adjustments over the last two centuries. With this confidence, we then ran the model to test how well it performs at estimating future trajectories of basin-scale sediment transport and sediment budgets at the river reach scale
Robotic photosieving from low-cost multirotor sUAS: A proof-of-concept
Full text linkMeasurement of riverbed material grain sizes is now a routine part of fieldwork in fluvial geomorphology and lotic ecology. In the last decade, several authors have proposed remote sensing approaches of grain size measurements based on terrestrial and aerial imagery. Given the current rise of small unmanned aerial system (sUAS) applications in geomorphology, there is now increasing interest in the application of these remotely sensed grain size mapping methods to sUAS imagery. However, success in this area has been limited owing to two fundamental problems: lack of constraint of image scale for sUAS imagery and blurring effects in sUAS images and resulting orthomosaics. In this work, we solve the former by showing that SfM-photogrammetry can be used in a direct georeferencing (DG) workflow (i.e. with no ground validation) in order to predict image scale within margins of 3%. We then propose a novel approach of robotic photosieving of dry exposed riverbed grains that relies on near-ground images acquired from a low-cost sUAS and which does not require the presence of ground control points or visible scale objects. We demonstrate that this absence of scale objects does not affect photosieving outputs thus resulting in a low-cost and efficient sampling method for surficial grains
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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