Evolution of river planforms downstream of dams: Effect of dam construction or earlier human‐induced changes?          下载免费PDF全文

Marcin Słowik  József Dezső  Adam Marciniak  Gabriella Tóth  János Kovács 《地球表面变化过程与地形》2018,43(10):2045-2063

When studying the evolution of landscape, it is difficult to discriminate the influence of anthropogenic from natural causes, or recognise changes caused by different sources of human action. This is especially challenging when the influence of certain sources is overprinted. For instance, although dam closure is the most common method of altering river courses, dam construction is often preceded by hydro‐technical works such as channel straightening, embankment construction or sediment mining. Both dam construction and the hydro‐technical works that precede dam closure can result in changes in the balance between sediment supply and transport capacity, and often, changes in river planform. The main objective of this study was to verify whether the works preceding dam closure are an important driver of river planform changes on the lower Drava River (Hungary). The case study is based on geological and geophysical surveys, as well as the analysis of historical maps covering an anabranching, 23 km long valley section. We show that channel straightening conducted prior to dam closure resulted in a transition from a meandering to sinuous planform with channel bars. Dam construction itself then caused enhanced incision, exposure of bar surfaces, vegetation encroachment and the formation of an anabranching planform. Based on this study, we developed models of alluvial island and channel planform evolution downstream of dams. Dam construction enhances channel incision, narrowing, and the reduction of flow caused by earlier hydro‐technical works. Many rivers downstream of dams experience episodes of anabranching or wandering, with a multi‐thread pattern replacing sinuous, braided and meandering courses. When incision continues, river patterns evolve from anabranching to sinuous via the attachment of alluvial islands to floodplains. However, the timing and sequence of these changes depend on hydrological and sediment supply regimes, geomorphic settings and anthropogenic actions accompanying dam construction. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

Tectonic plates parameters estimated in International Terrestrial Reference Frame ITRF2008 based on DORIS stations     

Katarzyna Kraszewska  Marcin Jagoda  Miłosława Rutkowska 《Acta Geophysica》2018,66(4):509-521

This paper concerns an analysis of the accuracy of the estimated parameters Ω (Φ, Λ, ω) which define the tectonic plate motions. The study is based on the velocities of station positions in the IERS (International Earth Rotation and Reference Systems Service) which has published new realization of the International Terrestrial Reference System—ITRF2008 for Doppler Orbitography by Radiopositioning Integrated on Satellite DORIS technique. Eurasian, African, Australian, North American, Australian, Pacific, Antarctic and South American plates were used in the analysis. The influence of the number and localization of stations on the plate surface on the estimation accuracy of the tectonic plate motion parameters were discussed. The results were compared with the APKIM 2005 IGN model and our earlier estimation for the SLR technique. In general, a remarkable concurrent agreement between the present and the APKIM 2005 solutions was found.  相似文献   

Effectiveness of Dynamic Point Symbols in Quantitative Mapping     

Paweł Cybulski  Łukasz Wielebski 《The Cartographic journal》2019,56(2):146-160

The main focus of this paper is the effectiveness of dynamic point symbols in the presentation of quantitative data. Such symbols are of particular use in the design of animated maps and computer games. The authors examine three existing techniques of using dynamic point symbols to present quantitative data: blinking, pulsation, and rotation. The aim of the study is to compare their effectiveness with that of classical cartographic animation techniques. The results of the study show that in animated map design, dynamic point symbols might be used to present not only qualitative but also quantitative data with comparable effectiveness. The results may serve as the basis for designing dynamic point symbols to be as effective as the classical techniques used in animated cartography.  相似文献   

Refined timing and kinematics for Baltica–Avalonia convergence based on the sedimentary record of a foreland basin          下载免费PDF全文

Stanisław Mazur  Szczepan J. Porębski  Artur Kędzior  Mariusz Paszkowski  Teresa Podhalańska  Paweł Poprawa 《地学学报》2018,30(1):8-16

The Caledonian foreland basin of Poland onlaps the SW slope of the East European Craton and is elongated in a NW–SW direction along the margin of the Baltica palaeocontinent. The base of the synorogenic clastic wedge rises in age from Llandovery to Ludlow between NW and SE Poland, respectively. As the initial influx of orogen‐derived detritus can be unequivocally identified, this diachronism documents a southeastward migration of the basin depocentre, parallel to the present‐day Caledonian Deformation Front. Our best‐fit plate model shows an oblique collision of Baltica and Avalonia, the latter initially indenting the Baltica margin in the NW. Afterwards, Baltica was progressively underthrust beneath Avalonia towards the SE in response to the oblique soft‐mode closure of the Tornquist Ocean. The final deformation event within the Caledonian foreland took place in the earliest Devonian as a far‐field effect of sinistral orogen‐parallel displacements along the Iapetus suture.  相似文献   

Internal structure and sources of selected ice jams on the lower Vistula River          下载免费PDF全文

Bogusław Pawłowski 《水文研究》2016,30(24):4543-4555

The lower stretch of the Vistula is the most ice‐jammed river section on the North European Plain. Since 1982, the structure of hanging dams has been studied by means of a mechanical non‐core sampler. In this article, a selected of field research results of the hanging dams' structure and the degree of filling of the cross section with ice obtained during surface ice‐jam events in the years 1995–2014 are presented, along with an explanation of their causes. Surface ice jams occurred during spring snowmelt surges and ice breakups and also during freeze‐up and ice‐covered periods. Their main cause was changes in the river flow and was also those affected by anthropogenic sources. A characteristic feature of the analysed cross sections was the considerable share of the underhanging ice dam's firm accumulation with ice floes, when the cross section would be filled with ice in excess of 70%. In most cases, due to low river discharge, there was no substantial flooding damage. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Pinched between the plates: Armenia's voluminous record of volcanic activity     

Ralf Halama  Khachatur Meliksetian  Ivan P. Savov  Patrick J. Sugden  Krzysztof Sokół 《Geology Today》2020,36(3):101-108

Located in the heart of the Lesser Caucasus mountains, where the Arabian and Eurasian tectonic plates collide, Armenia occupies an exceptional geological position shaped through millions of years of subduction and collision. It is a unique place on the Earth recording extensive intrusive and volcanic activity related to the long-standing continental convergence. The volcanoes of Armenia provide a rare opportunity to study the sources and processes involved in this unusual type of magmatism. More than 500 Quaternary volcanoes have been mapped in Armenia, most of them formed from single eruptive episodes. Among several large composite volcanoes, the mighty Aragats stands out as the largest volcano in Armenia and the region altogether. Volcanic deposits testify to the range of eruptive styles—from the ignimbrites formed in eruptions as explosive and voluminous as any seen globally in the modern era to the enormous fissure-fed lava flows that form the Southern Caucasus flood basalt province, the smallest and youngest Large Igneous Province in the world. Several pre-historical and historical eruptions have been documented, highlighting the potential for future volcanic activity in the region. In recent years, research has focused on the volcanic hazards associated with the Armenian Nuclear Power Plant, located in the foothills of Aragats volcano. This article highlights some of the extraordinary volcanic and intrusive features observed in Armenia and summarizes aspects of recent volcanological and petrological research.  相似文献   

Deep Electrical Resistivity Structure of the European Lithosphere in Poland Derived from 3-D Inversion of Magnetotelluric Data     

Jóźwiak  Waldemar  Nowożyński  Krzysztof  Mazur  Stanisław  Jeż  Maciej 《Surveys in Geophysics》2022,43(5):1563-1586

Surveys in Geophysics - This paper presents a three-dimensional (3-D) model of the resistivity distribution in the European lithosphere at the junction between the East European Craton, the...  相似文献   

Effectiveness of Random Field Approach in Serviceability Limit State Analysis of Strip Foundation     

Winkelmann  Karol  Żyliński  Kamil  Korzec  Aleksandra  Górski  Jarosław 《Geotechnical and Geological Engineering》2022,40(9):4705-4720

Geotechnical and Geological Engineering - This work conducts a probabilistic inquiry on how the variability of the parameter defining soil deformability affects the settlement of the foundation...  相似文献   

Effect of partial mining of shaft protection pillar in terms of reliability index     

J. Bauer  W. Puła 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2015,9(4):242-249

ABSTRACT

The work presents calculations of shaft support reliability index during partial extraction of protection pillar deposit and the related seismic phenomena. It has been assumed that the probability of failure caused by seismic phenomena depends on the velocity random variable of the shaft support vibrations. The random vibration velocity is a function of random variables of energy, shock distance and vibration frequency. Estimations of probability distributions for energy and frequency have been based on the actual measurement data from a mine. Failure probability has been estimated by means of methods based on so-called Hasofer-Lind reliability index β.  相似文献   

Phytoplankton response to the environmental and climatic variability in a temperate lake over the last 14,500 years in eastern Latvia     

N. Stivrins  P. Kołaczek  T. Reitalu  H. Seppä  S. Veski 《Journal of Paleolimnology》2015,54(1):103-119

  相似文献