Boundary condition control of fluvial obstacle mark formation – framework from a geoscientific perspective     

Oliver Schlömer  Jürgen Herget  Thomas Euler 《地球表面变化过程与地形》2020,45(1):189-206

Obstacle marks are sedimentary bedforms, typically composed of an upstream local scour hole and a downstream sediment accumulation in the vicinity of an obstruction that is exposed to a current. However, specific morphologies are variable in fluvial, coastal and submarine environments. Although obstacle marks and the phenomenon of local scouring are subject to different scientific disciplines, the objectives of investigations are rather incoherent and no systematic framework for analysing and evaluating boundary condition control exists yet, especially concerning limited knowledge of the cause and effect relationship of obstacle mark formation at instream boulders or vegetation elements in variable environmental conditions. Thus, a parameter framework is developed which identifies a spectrum of extrinsic and intrinsic boundary conditions that control the major process dynamics of obstacle mark formation. The framework is composed of dimensionless control parameters that are separated by a hierarchical order regarding their significance for obstacle mark formation. Primary control parameters determine the geometrical scale of flow field at the obstacle, and therefore control the potential maximum size of the obstacle. Secondary control parameters affect the dynamics of the flow field in geometrical scale and limit the potential maximum size of the emerging sedimentary structure if thresholds are crossed. The framework is supposed to be a foundation for subsequent quantification and determination of thresholds by systematic laboratory studies. To elucidate this, flume-based research is presented, evaluating the influence of different flow levels at boulder-like obstacles of different shapes. The results show that obstacle mark dimensions were maximized at shallow flow depths compared to obstacle dimensions, while deep flows at submerged boulder-like obstructions caused considerably smaller obstacle marks. In interdependency with a rounded and more streamlined obstacle shape, deep flows even cause a deviation of morphology if the flow depth above an obstacle exceeds 1.6 times the obstacle's dimensions. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

EUV and soft X-ray images of the sun on March 11th, 1971     

H. Bräuninger  H. J. Einighammer  J. V. Feitzinger  H. H. Fink  D. H. Höhn  H. Koops  G. Krämer  U. Mayer  G. Möllenstedt  M. Mozer 《Solar physics》1971,20(1):81-84

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Role of tectonic-sedimentary melange and Permian–Triassic cover units,central southern Turkey in Tethyan continental margin evolution     

Alastair H.F. Robertson  Timur Ustaömer 《Journal of Asian Earth Sciences》2011,40(1):98-120

Melanges play a key role in the interpretation of orogenic belts, including those that have experienced deformation and metamorphism during continental collision. This is exemplified by a Palaeozoic tectonic-sedimentary melange (part of the Konya complex) that is exposed beneath a regionally metamorphosed carbonate platform near the city of Konya in central Anatolia. The Konya complex as a whole comprises three units: a dismembered, latest Silurian–Early Carboniferous carbonate platform, a Carboniferous melange made up of sedimentary and igneous blocks in a sedimentary matrix (also known as the Hal?c? Group or S?zma Group), and an overlying Volcanic-sedimentary Unit (earliest Permian?). The Palaeozoic carbonates accumulated on a subsiding carbonate platform that bordered the northern margin of Gondwana, perhaps as an off-margin unit. The matrix of the melange was mainly deposited as turbidites, debris flows and background terrigenous muds. Petrographic evidence shows that the clastic sediments were mostly derived from granitic and psammitic/pelitic metamorphic rocks, typical of upper continental crust. Both extension- and contraction-related origins of the melange can be considered. However, we interpret the melange as a Carboniferous subduction complex that formed along the northern margin of Gondwana, related to partial closure of Palaeotethys. Blocks and slices of Upper Palaeozoic radiolarian chert, basic igneous rocks and shallow-water carbonates were accreted and locally reworked by gravity processes. Large (up to km-sized) blocks and slices of shallow-water limestone were emplaced in response to collision of the Palaeozoic Carbonate Platform with the subduction zone. The overlying Volcanic-sedimentary Unit (earliest Permian?) comprises alkaline lava flows, interbedded with volcaniclastic debris flows and turbidites, volcanogenic shales and tuff. The complex as a whole is overlain by shallow-water, mixed carbonate–siliciclastic sediments of mainly Late Permian age that accumulated on a regional-scale shelf adjacent to Gondwana. Successions pass transitionally into Lower Triassic rift-related shallow-water carbonates and terrigenous sandstones in the southwest of the area. In contrast, Triassic sediments in the southeast overlie the melange unconformably and pass upwards from non-marine clastic sediments into shallow-marine calcareous sediments of Mid-Triassic age, marking the base of a regional Mesozoic carbonate platform. During the latest Cretaceous–Early Cenozoic the entire assemblage subducted northwards and underwent high pressure/low temperature metamorphism and polyphase folding as a part of the regional Anatolide unit.  相似文献   

Light variation of LX persei between eclipses     

C. Ibanoĝlu  S. Evren  O. Tümer  A. Y. Ertan  Z. Tunca 《Astrophysics and Space Science》1983,95(2):409-416

Two-colour photoelectric observations of LX Per carried out at Ege University Observatory in 1981 and 1982 observing seasons are presented. The light curve of the system has a wave-like distortion which migrates towards the decreasing orbital phase. The period of the retrograde migration of the wave-like distortion has been determined as 475 days. The amplitude of the wave appears to change with time periodically.  相似文献   

Photoelectric photometry of AR Lac in 1982     

S. Evren  C. Ibanoglu  O. Tümer  Z. Tunca  A. Y. Ertan 《Astrophysics and Space Science》1983,95(2):401-408

In this paper we present the observations of AR Lac, which were obtained in 1982. The variations in the light curves, occurred in the time interval as short as two months, indicated that the system was very active in 1982 like in 1979. The times of the minima obtained in this study indicate that the orbital period of the system continues to decrease. The decrease in the period was recalculated using all the times of minima obtained photoelectrically between 1961 and 1982 and found to be 17.0±1.4 s century^?1.  相似文献   

Updated UBV Light-Curve and Period Analysis of Eclipsing Binary HS Herculis     

Zeynep Bozkurt  Ömer Lütfi Değirmenci 《Astrophysics and Space Science》2006,304(1-4):29-33

UBV light-curves of the eclipsing binary HS Herculis, obtained in 2002–2003 observational seasons, were analysed with Wilson-Devinney computer code. New absolute dimensions of the system were calculated using the results of the light-curve analysis. Period variation of the system was also investigated. Several new times of minima have been secured for this problematic system. An apsidal motion with a period of 80.7 years was confirmed and a third body in a pretty eccentric orbit (e ₃ = 0.90 ± 0.08) with a period of 85.4 years was found. The corresponding internal structure constants of the binary system, log k ₂, and the mass of the third body were derived.  相似文献   

The Inference of Geo-Mechanical Properties of Soft Rocks and their Degradation from Needle Penetration Tests   总被引：2，自引：1，他引：1  

Ömer Aydan  Akira Sato  Masatoshi Yagi 《Rock Mechanics and Rock Engineering》2014,47(5):1867-1890

Needle penetration tests (NPTs) are used for inferring the uniaxial compressive strength of soft rocks, particularly in tunneling through squeezing rocks and foundations on weathered rocks in Japan. The device measures the applied load and the penetration depth of its needle. The ratio of applied load to penetration depth was originally called the needle penetration index (NPI). In this study, this device has been used to infer the geo-mechanical properties of soft rocks from Japan, Turkey, Indonesia, and Egypt. Various equations are presented to infer the geo-mechanical properties in terms of the NPI and compared with the experimental results. The possibility of evaluating the anisotropy of geo-mechanical properties is shown. Furthermore, the characterization of geo-mechanical properties of fault/fracture and slip (shear) surfaces is explained. Some additional equations are given to consider the degradation of geo-mechanical properties as a function of water content, weathering state, and number of cycles of freezing–thawing. Furthermore, the possibility of evaluating the time-dependency characteristics of soft rocks by needle penetration testing is discussed through experiments. It is shown that the effects of water content, weathering state, and number of cycles of freezing–thawing and time-dependency can be evaluated using the NPT technique.  相似文献   

Impact of the 2010 tsunami on an endangered insular soil–plant system     

Ingo J. Hahn  Pablo M. Vergara  Julia Baumeister  Gerardo E. Soto  Uwe Römer 《Natural Hazards》2014,71(1):987-993

Natural catastrophes could damage island biodiversity and ecosystems, and their effects could become devastating if combined with human disturbances. In this study, we determined the effects of the tsunami occurred in Robinson Crusoe Island (Chile) on 27 February 2010 on an endangered soil–plant system. Using data of endemic Cabbage Trees (Dendroseris litoralis Skottsb.) and soil attributes taken before and after the 2010 event, we developed thematic maps to assess the changes in population size and soil substrate of Cabbage Trees caused by the tsunami. We determined that from 153 pre-tsunami (2009) standing Cabbage Trees, only 66 (43 %) survived in 2011, mostly in elevations above 25 m a.s.l. Before the tsunami, 86 (56 %) of Cabbage Trees were established in humus-rich soil sites whereas after the tsunami, this number declined to 53 (35 %). These results represent the first report of a severe population decline after a tsunami and indicate that tsunamis are an important source of species extinction in small oceanic islands not only by reducing the population size but also by reducing the quality of sites for plant growth.  相似文献   

Geotechnical evaluation of slope and ground failures during the 8 October 2005 Muzaffarabad earthquake, Pakistan   总被引：4，自引：0，他引：4  

Ömer Aydan  Yoshimi Ohta  Masanori Hamada 《Journal of Seismology》2009,13(3):399-413

A large devastating earthquake with a magnitude of 7.6 struck in Kashmir on Oct. 8, 2005. The largest city influenced by the earthquake was Muzaffarabad. Balakot town was the nearest settlement to the epicenter, and it was the most heavily damaged. The earthquake caused extensive damage to housing and structures founded on loose deposits or weathered/sheared rock masses. Furthermore, extensive slope failures occurred along Neelum and Jhelum valleys, which obstructed both river flow and roadways. In this article, failures of natural and cut slopes as well as other ground failures induced by the earthquake and their geotechnical evaluation are presented, and their implications on civil infrastructures and site selection for reconstruction and rehabilitation are discussed. It is suggested that if housing and constructions on soil slopes containing boulders as observed in Balakot and Muzaffarabad are allowed, there should be a safety zone between the slope crest and allowable construction boundary.  相似文献   

Comparing quantitative precipitation forecast methods for prediction of sewer flows in a small urban area     

Alma Schellart  Sara Liguori  Stefan Krämer  Adrian Saul  Miguel A. Rico-Ramirez 《水文科学杂志》2014,59(7):1418-1436

Abstract

Due to the relatively small spatial scale, as well as rapid response, of urban drainage systems, the use of quantitative rainfall forecasts for providing quantitative flow and depth predictions is a challenging task. Such predictions are important when consideration is given to urban pluvial flooding and receiving water quality, and it is worthwhile to investigate the potential for improved forecasting. In this study, three quantitative precipitation forecast methods of increasing complexity were compared and used to create quantitative forecasts of sewer flows 0–3 h ahead in the centre of a small town in the north of England. The HyRaTrac radar nowcast model was employed, as well as two different versions of the more complex STEPS model. The STEPS model was used as a deterministic nowcasting system, and was also blended with the Numerical Weather Prediction (NWP) model MM5 to investigate the potential of increasing forecast lead-times (LTs) using high-resolution NWP. Predictive LTs between 15 and 90 min gave acceptable results, but were a function of the event type. It was concluded that higher resolution rainfall estimation as well as nowcasts are needed for prediction of both local pluvial flooding and combined sewer overflow spill events.