1,721,085 research outputs found
Global mapping of river sediment bars
Full text linkRecently, deep learning has been increasingly applied to global mapping of land‐use and land‐cover classes. However, very few studies have addressed the problem of separating lakes from rivers, and to our knowledge, none have addressed the issue of mapping fluvial sediment bars. We present the first global scale inventory of fluvial gravel bars. Our workflow is based on a state‐of‐the‐art fully convolutional neural network which is applied to Sentinel‐2 imagery at a resolution of 10 m. We use Google Earth Engine to access these data for a study site that covers 89% of the Earth's surface. We count 8.9 million gravel bars with an estimated area of 41 000 km2. Crucially, the workflow we present can be executed within a month of highly automated processing and thus allows for global scale, monthly, monitoring of gravel bars and associated rivers
Characterizing physical habitats in rivers using map-derived drivers of fluvial geomorphic processes
No full textNew understanding of fluvial geomorphological processes has successfully informed flood mitigation strategies
and rehabilitation schemes in recent years. However well established geomorphological assessments are
location-specific and demanding in terms of resource and expertise required, and their routine application
for regional or national river characterization, although desirable, is unlikely at present. This paper proposes
a framework based on GIS procedures, empirical relationships and the self organized map for the analysis and
classification of map-derived drivers of fluvial morphological processes. The geomorphic controls analysed
are: channel gradient and hydrology, specific stream power, river order and floodplain extent. The case
study is a gravel bed river in England. Using the self organized map, we analyse patterns of these controls
along the river longitudinal profile and identify clusters of similar configuration. The reciprocal relationships
that emerge amongst the geomorphic controls reflect the hierarchical nature of fluvial systems and are
consistent with the current theoretical understanding of fluvial processes. Field observations from the River
Habitat Survey are used to prove the influence of geomorphic drivers on reach-scale morphological forms.
Six clusters are identified which describe six distinctive channel types. These proved to be characterized by
distinctive configurations of geomorphic drivers and specific sets of physical habitat features. The method
successfully characterizes the notable transitions in channel character along the river course. The framework
is suitable for regional or national scale assessments through automatic GIS and statistical procedures with
moderate effort
Directly assessing uncertainty in designing the optimal operation of water resources systems by batch mode reinforcement learning
No full textNetwork scale sediment connectivity to explore stability andresilience of channel forms and river types in the Vjosa basin
Full text linkSediment connectivity is a fundamental property of river network, which directly influences thegeomorphological processes regulating the formation and development of the different in-channelgeomorphic units and leading to different river types. Alterations of sediment connectivity, e.g.caused by human disturbances such as dam construction or bed mining, are often followed bychanges in channel patterns resulting in potential radical shifts in river types, e.g., from braidedsystems to sinuous single channel, with consequent loss of river ecosystems associated withspecific river types.In this work, we analyze the connections between basin-scale sediment connectivity indices andriver types with the aim of advancing our quantitative ability to inter-relate channel forms andprocesses with type and amount of sediment fluxes available to the river channel. Our studyfocuses on the Vjosa river, Albania, which due to the limited anthropogenic bias still showcases alarge variety of fluvial forms, including ample sections of braided channels, some of the fewremaining in Europe and well renewed as ecological hotspots. The Vjosa river is now interested bylarge scale hydropower development plans, which may threaten the river unique ecological andmorphological value. We estimate sediment transport using the CASCADE model, a modellingframework for basin-scale sediment transport simulation, which generates spatially distributedinformation on sediment movement and connectivity in river networks. The model has beenvalidated using available data on bed load transport in a braided section close to the basin outletand surficial grain size distributions collected across the river network.By integrating CASCADE outputs (i.e., sediment fluxes and size distributions) with availablegeomorphic information at the network scale (e.g., channel slope and water discharge), wesuccessfully tested an empirical formula proposed in literature based on sediment concentration,median grain size, channel slope and bankfull discharge, to disentangle the drivers of braided orsingle channel patterns. We then tested the same threshold for different dam developmentportfolios, showing how even few new dams would alter current conditions in terms of type andamount of sediment availability, leading to multiple channel type shifts from braided to sinuoussingle channel across the network.For the first time, the incorporation of the CASCADE model with more traditional geomorphicanalysis of river system demonstrate how CASCADE sediment connectivity information advances
our ability to interpret existing river system processes, to assess stability of the different channelforms and to evaluate resilience and identify tipping points of fragile system like the Vjosa basin
MODELING CHANGES IN THE FLUX AND GRAIN SIZE DISTRIBUTION OF THE BED SEDIMENT IN A LARGE GRAVEL-BED RIVER
No full textSediment budgets developed for high gradient rivers are subject to large uncertainties in the quantification of source-area and storage terms. Fluxes of the coarse fraction of the supply (bed load) can be constrained from measurements, but the time and effort required to measure these fluxes is prohibitive in most cases. In this presentation, we discuss the development of a sediment routing model that tracks downstream changes in the flux and grain size distribution of the bed load through a 250 km reach of the Colorado River in western Colorado and eastern Utah. The model is formulated for nine reaches where values of discharge, width, reach-average slope and roughness have been measured or verified. The reaches are defined geographically by changes in lithology which affect valley confinement. Bed surface grain size distributions (GSDs) have been measured at 78 locations across the study area, but these distributions are used as a test of the model, not as input, except at the upstream boundary. The model is formulated under the assumption that the coarse sediment load is derived from the bed surface, and transport capacity is determined by local hydraulic conditions and grain size. Estimates of the bankfull bed load transport capacity for each reach are computed for 14 size fractions of the surface sediment, and fractional transport rates are summed to get the bed load transport capacity of that reach. In the adjacent reach, the GSD and fluxes of each size fraction from upstream are used to determine the mean grain size, and fractional transport capacity of that reach. Calculations proceed downstream from one reach to the next, and illustrate linked changes in (1) bed load transport capacity, and (2) grain size distributions of the bed surface. Results show that the model-derived GSDs match the measured GSDs very closely, except for the two most distal reaches where the slope is affected by uplift associated with salt diapirs. The mismatch between modeled and observed GSDs in these reaches occurs because the slope is not self-formed, consequently the model overestimates the local transport capacity in relation to supply. Except for these two reaches, the modeled bed load fluxes seem very reasonable (Qb ~ 0.5-1.0 kg/m/s at bankfull discharge), and exhibit downstream trends that are consistent with trends reported in two previous studies
Characterizing fluvial systems at basin scale by fuzzy signatures of hydromorphological drivers in data scarce environments
Full text linkAnalyzing tradeoffs between hydropower production and hydrological alteration to support water resources planning in large river systems
No full textIn many countries water is a key renewable resource to complement carbon-emitting energy production in the face of demand pressure from fast-growing industrial production and urbanization. In this study, we analyze the case of the Red River Vietnam, a large basin of 169.000 kmq where the storing capacity, mainly targeted at hydropower production, has steadily increased since from the Eighties through the construction of a number of reservoirs (Hoa Binh completed in 1994, Tuyen Quang in 2008, Son La in 2012), which nowadays account for the 15% of the national electric power production. On the other hand, reservoir operation dramatically alters downstream river hydrology, geomorphological processes and riverine ecosystems.
In this work, we focus in particular on the alteration of the hydrological regime downstream of the Hoa Binh reservoir and explore re-operation options to mitigate the hydrological alteration while guaranteeing reasonable hydropower production. To reach this goal we (i) define an index of hydrological alteration starting from the well established set of Indicators of Hydrological Alteration and applying a novel selection and aggregation procedure; (ii) embed such an index into a multi-objective optimization process, to design reservoir operating policies that represent Pareto-optimal solutions between maximization of hydropower production and minimization of hydrological alteration.
This work demonstrates the potential of multi-objective optimization and simulation tools to analyze tradeoffs between conflicting needs and thus support the evaluation and planning of sustainable energy production programs
PROCESS BASED CLASSIFICATION OF SEDIMENT CONNECTIVITY AT THE RIVER BASIN SCALE.
Full text linkNovel modelling approaches allow to trace the fate of sediment contributions from individual river reaches throughout the river network and to assess the resulting sediment connectivity at the basin scale. The derived information is an unprecedented source of information to assess from where and over which times a downstream river reach recruits its sediment. This information links strongly to the reach sensitivity to anthropic disturbance or restoration efforts. In this paper, we demonstrate how to make the complex data-sets resulting from basin scale connectivity models accessible for river basin management applications. We introduce the concept of “connectivity signatures” that epitomizes the timing, magnitude, and quality (grain size) domain of connectivity at the reach scale. We use data driven classification techniques to identify a reduced set of typical connectivity classes. Spatial distribution of connectivity classes reveals that these classes represent specific, functional “connectivity styles” with specific locations and functions for sediment routing in the river network. Results concretize the interpretation of sediment connectivity from an operational perspective and open the way for its application to large river basins
Data mining of external and internal forcing of fluvial systems for catchment management: A case study on the Red River (Song Hong), Vietnam
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