1,720,961 research outputs found
A GIS BASED TOOL FOR THE SEDIMENT DELIVERY RATIO COMPARISON
No full textThe note deals with a new tool implementation for evaluating Sediment Delivery Ratio (SDR) in a river basin, through GRASS GIS software. The definition of a spatially distributed value of SDR is a very important task as the sediment routing can affects losses of soil productivity, increase of solid transport in stream channels, and water quality degradation. For such reason the SDR evaluation, coupled with GIS approach, has been extensively used in scientific literature. Geographic information systems provide a fundamental support for a better prediction of SDR, since it can consider the space variability of factors influencing the sediment routing processes. Actually a specific GIS module to estimate the spatial variability of SDR does not exist. We implemented a GRASS GIS module (in python language) called r.sdr where the sediment delivery ratio is evaluated by GIS procedure using several equations available in literature. We applied the tool to the Feo Creek watershed, located in the Apennines area of northeastern Umbria (Italy
A GIS-based tool for automatic bankfull detection from airborne high resolution dem
No full textThe ability to remotely sense bankfull elevations was of particular interest in this study because bankfull mapping depends on topographic indicators. The method proposed here and integrated in a GIS environment combines the hydraulic depth and the flow height for each cross section. The local maxima values indicate a sudden increase in flow width where water spills across the floodplain. Such an approach has been implemented as a GIS tool in the QGIS software, and provides a resulting polygonal map of the bankfull limits. The algorithm was applied on several fluvial reaches in Umbria (central Italy). The source code is available as open source. Preliminary results are presented in Section 4, comparing remotely sensed bankfull limits to those obtained from fields surveys and, more recently, by operator-expert interpretation of aerial orthophotos
Image processing to monitoring morphological changes in river systems: an application to River Paglia (River Tiber basin, central Italy)
No full textRemote sensing is an important tool for risk mitigation and management of natural disasters (Van Westen, 2000). Multispectral images are used in various fields for rapid feature identification over large areas; furthermore, the short time interval in image capturing allows for the temporal analysis and monitoring of feature variations (Sonka et al., 2014). Image processing and classification techniques can also provide interesting applications in fluvial geomorphology, for outlining morpho-sedimentary features (bars, channels, banks and floodplain) at various temporal stages, in order to monitor the evolution of river systems. Monitoring is essential for understanding the dynamics of river systems, particularly in Italian streams that experience rapid channel changes and human disturbance leading to an increase in the risk of flooding in anthropic areas. We show the results of a study aimed at evaluating the planimetric changes which affected the riverbed of the River Paglia (one of the main tributaries of the River Tiber, in central Italy), as a consequence of the flooding event of November 2012. It shows critical characteristics from the morpho-sedimentary dynamic point of view. The riverbed is in a state of sediment-limited non-equilibrium: it is characterized by an intensely active vertical erosion, which led the thalweg to cut through unconsolidated alluvial sediments up and over the bedrock, formed by overconsolidated marine clays. Over time, but especially in the last 50 years, the morphology of the river has changed drastically: the main channel has entrenched and its riverbed has shrunk considerably, leaving most of the bars, which were non-vegetated and active in the past, but now are inactive and covered with dense vegetation of tall trees (abandoned riverbed). Thus, the river has gradually become a “single-channel with low-sinuosity” channel type. An automatic and/or semi-automatic procedure was developed, in order to study the riverbed changes. The procedure starts from the classical photogrammetric techniques, based on multispectral classification, and goes on with post processing operations of pixel aggregation and shadow treatment. The classification also uses the elevation information provided by a Digital Surface Model produced by photogrammetry. The procedure allows for both the identification and classification of the fluvial features in a post flooding condition. Application of the procedure over time permits the evolution of the fluvial dynamics to be monitored in an accurate and inexpensive way, particularly for flood event conditions which lead to major changes in the dynamics of riverbeds
Automatic Web Procedure for Calculating Flood Flow Frequency
No full textThe estimated flood flow frequency in a particular cross-section of a riverbed for a given return period is a topic of great interest for its application in hydrological, geomorphological and hydrogeological fields. Nevertheless, to establish a one-to-one relationship between rainfall and peak flow is a difficult problem to solve, due to the great number of factors involved (intensity and distribution of rainfall, hydromorphological characteristics of the watershed, type and distribution of vegetation, soil saturation conditions, etc.). In Italy, the Tiber River Basin Authority has developed a method to evaluate peak flows in the watersheds within the Tiber Basin. The relationship between rainfall depth with an assigned return period (RP) and the duration of the event was determined using data from 165 gauging stations throughout the Basin and in the neighbourhoods with respect to rainfall from 1 to 24 h and/or from 1 to 5 days. To calculate the peak flow with an assigned RP in small watersheds (area < 100 km 2 ), the Tiber River Basin Authority proposed a methodology that combines the results of regional precipitation analysis of a duration from 1 to 24 h with the Curve Number method, which allows the volume of net rainfall (i.e., the rainfall that contributes to producing the peak flow) to be quantified. Such procedure includes the calculation of various parameters (run-off time, local rainfall and areal rainfall, net rainfall) in order to obtain the value of peak flow. To facilitate the use of this procedure, a WebGIS system has been developed, based on a series of scripts that calculate the values for the above parameters. The user only has to choose the point corresponding to the section of the channel in order to determine the peak flow and the return period. The computational procedure is performed using GRASS GIS that interfaces with the system using the standard WPS; the system returns to output a report with details of the various calculations of parameters and, as a final result, the value of requested peak flow
Seismic-induced rockfalls and landslide dam following the October 30, 2016 earthquake in Central Italy
No full textOn October 30, 2016, a seismic event and its aftershocks produced diffuse landslides along the SP 209 road in the Nera River Gorge (Central Italy). Due to the steep slopes and the outcropping of highly fractured and bedded limestone, several rockfalls were triggered, of which the main event occurred on the slope of Mount Sasso Pizzuto. The seismic shock acted on a rock wedge that, after an initial slide, developed into a rockfall. The debris accumulation blocked the SP 209 road and dammed the Nera River, forming a small lake. The river discharge was around 3.6 m 3 /s; the water overtopped the dam and flooded the road. By a preliminary topographic survey, we estimated that the debris accumulation covers an area of about 16,500 m 2 , while the volume is around 70,000 m 3 . The maximum volume occupied by the pre-existing talus mobilized by the rockfall is about 20% of the total volume. Besides blocking the road, the rockfall damaged a bridge severely, while, downstream of the dam, the water flow caused erosion of a road embankment. A rockfall protection gallery, a few hundred meters downstream of the dam, was damaged during the event. Other elastic nets and rigid barriers were not sufficient to protect the road from single-block rockfalls, with volumes around 1–2 m 3 . Considering the geological and geomorphological conditions, as well as the high seismicity and the socioeconomic importance of the area, a review of the entire rockfall protection systems is required to ensure protection of critical infrastructure and local communities
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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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