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51.
太行山前平原非河道条件下地下调蓄功能实验研究--以滹沱河冲洪积平原为例 总被引:5,自引:0,他引:5
摘要:通过实验研究探讨了太行山前平原地下调蓄能力,实验研究表明,在汇水坑渗、井灌和引水渠渗条件下,太行山前冲洪积平原地下调蓄功能不仅与地表积水深度、入渗时间有关,而且还与汇水总量的多少有关。单位时间渗漏量的大小与地表蓄水深度呈正相关关系。地表蓄水深度愈大,单位时间渗漏量愈大;累计渗漏量随着入渗时间的延长而增加,渗漏速率随着累计渗漏量的增加而减小。采用井灌方式进行地下调蓄的关键,是选择具有强渗透性的层位。 相似文献
52.
The fractional Brownian motion (fBm) and fractional Lévy motion (fLm) can easily describe the geometry and the statistical structure of hydraulic conductivity (K) for real-world. However, the fBm and fLm models have not been systematically evaluated when building the K field for a low-permeability site. In this study, both the fBm and fLm are used to simulate the low-K field at NingCheGu (NCG), Tianjin, China. Groundwater flow and solute transport are then computed using MODFLOW and MT3DMS, respectively, and the influence of the fBm/fLm models for K on groundwater flow and solute transport is discussed. Results show that the fLm fits better the statistics of the low-K medium than fBm, and the random logarithmic K (LnK) field generated by fLm is more stable because the resultant LnK field captures more of the measured properties at the field site than that generated by fBm. In contrast, the LnK generated by fBm is more likely to form both high-K channels and low-K barriers. The fBm therefore predicts more extreme behaviours in flow and transport, including the preferential flow, low-concentration blocks and solute retention. The overall groundwater renewal period and solute travel time for the fLm simulation are slightly shorter than those for fBm. The impacts of the fLm and fBm models on the statistics of the resultant LnK fields and the dynamics of groundwater flow and solute transport revealed by this study shed light on the selection and evaluation of the fractional probability distribution models in capturing the K fields for low-K media. 相似文献
53.
数字遥测地震台网采用无线信道在国内地震界借鉴的经验还非常有限。究竟数字无线遥测,能否在(10^-6)误码率指标下,象模拟无线遥测地震台网一样采用单向传输,尚有不同看法。从三峡无线数字遥测地叶网的成功勘选得一邓许多有益的结果,我们关于鸨线信道和信道设备的探索回答了这个问题。结论是:数字地震台网仍然可以采用无线遥测方式组网,采用传输的信道设备既经济原则,技术上也是可行的。 相似文献
54.
The formation of an anabranching planform in a sandy floodplain by increased flows and sediment load
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Marcin Słowik 《地球表面变化过程与地形》2018,43(3):623-638
Anabranching rivers evolve in various geomorphic settings and various river planforms are present within these multi‐channel systems. In some cases, anabranches develop meandering patterns. Such river courses existed in Europe prior to intensive hydro‐technical works carried out during the last 250 years. Proglacial stream valleys, inherited from the last glaciation, provided a suitable environment for the development of anabranching rivers (wide valleys floors with abundant sand deposits). The main objective of the present study is to reconstruct the formation of an anabranching river planform characterized by meandering anabranches. Based on geophysical and geological data obtained from field research and a reconstruction of palaeodischarges, a model of the evolution of an anabranching river formed in a sandy floodplain is proposed. It is demonstrated that such a river system evolves from a meandering to an anabranching planform in periods of high flows that contribute to the formation of crevasse splays. The splay channels evolve then into new meandering flow paths that form ‘second‐order’ crevasses, avulsions and cutoffs. The efficiency of the flow is maintained by the formation of cutoffs and avulsions preventing the development of high sinuosity channels, and redirecting the flow to newly formed channels during maximum flow events. A comparison with other anabranching systems revealed that increased discharges and sediment loads are capable of forming anabranching planforms both in dryland and temperate climate zones. The sediment type available for transport, often inherited from older sedimentary environments, is an important variable determining whether the channel planform is anabranching, with actively migrating channels, or anastomosing, with stable, straight or sinuous branches. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
55.
Weina Zhang Xiaohe Zhang Huiming Huang Yigang Wang Sergio Fagherazzi 《地球表面变化过程与地形》2020,45(11):2613-2630
We use a hydrodynamic model applied to an idealized fan-shaped basin to explore the morphology and dynamics of radial sand ridges in a convergent coastal system. A positive morphological feedback between channel incision and flow redistribution is responsible for the formation of the channel-ridge pattern. The selection mechanism of bottom wavelength is associated with flow concentration in the deeper part of the channels. Our results are compared to sediment and hydraulic dynamics in the radial sand ridges (RSRs) in China. In a convergent, sloping basin the tangentially averaged tidal velocity peaks at 47 km from the apex. This distance is similar to the arc distance, 62 km, where the RSRs are most incised. An offshore shift in tidal phase results in stronger flows near the north coastline, explaining the presence of asymmetric channel patterns. A numerical stability analysis indicates that small radial oscillations with a wavelength of 10° to 15° maximize the velocity in the troughs. This oscillation wavelength also emerges in the RSRs, which display a peak in spectral energy at a radial wavelength between 25° to 37.5°. High-resolution numerical simulations in the RSRs confirm that flow concentration occurs in the deeper part of the channels, keeping them flushed. We therefore conclude that the RSRs display morphometric characteristics similar to other tidal incisions, like tidal inlets and intertidal channels. This result further supports the dominant role of tidal prism and related peak velocities in incising coastal landscapes. © 2020 John Wiley & Sons, Ltd. 相似文献
56.
Marcus Landschulze 《Geophysical Prospecting》2019,67(6):1571-1581
The presence of geophysical receivers on the seafloor changes the local wave field due to the receiver seafloor interaction. The resulting PP- and PS-wave distortion of the wave field is often referred to as receiver coupling to the seafloor and can make data processing challenging and sometimes impossible. This paper provides an overview of the mathematical approaches to describe receiver coupling, how to estimate receiver coupling and what the difficulties and possible solutions are. The first section shows how the mathematical approach developed from a simple model considering only the vertical receiver component to include all three receiver components and their interactions with the seafloor. In the second section, I show how receiver coupling can be measured and how it can be improved using mathematical and data-driven approaches. 相似文献
57.
What controls submarine channel development and the morphology of deltas entering deep-water fjords?
Jenny A. Gales Peter J. Talling Matthieu J.B. Cartigny John Hughes Clarke Gwyn Lintern Cooper Stacey Michael A. Clare 《地球表面变化过程与地形》2019,44(2):535-551
River deltas and associated turbidity current systems produce some of the largest and most rapid sediment accumulations on our planet. These systems bury globally significant volumes of organic carbon and determine the runout distance of potentially hazardous sediment flows and the shape of their deposits. Here we seek to understand the main factors that determine the morphology of turbidity current systems linked to deltas in fjords, and why some locations have well developed submarine channels while others do not. Deltas and associated turbidity current systems are analysed initially in five fjord systems from British Columbia in Canada, and then more widely. This provides the basis for a general classification of delta and turbidity current system types, where rivers enter relatively deep (>200 m) water. Fjord-delta area is found to be strongly bimodal. Avalanching of coarse-grained bedload delivered by steep mountainous rivers produces small Gilbert-type fan deltas, whose steep gradient (11°–25°) approaches the sediment's angle of repose. Bigger fjord-head deltas are associated with much larger and finer-grained rivers. These deltas have much lower gradients (1.5°–10°) that decrease offshore in a near exponential fashion. The lengths of turbidity current channels are highly variable, even in settings fed by rivers with similar discharges. This may be due to resetting of channel systems by delta-top channel avulsions or major offshore landslides, as well as the amount and rate of sediment supplied to the delta front by rivers. © 2018 John Wiley & Sons, Ltd. 相似文献
58.
During the last 160 years, land-use changes in the Ozarks have had the potential to cause widespread, low-intensity delivery of excess amounts of gravel-sized sediment to stream channels. Previous studies have indicated that this excess gravel bedload is moving in wave-like forms through Ozarks drainage basins. The longitudinal, areal distribution of gravel bars along 160 km of the Current River, Missouri, was evaluated to determine the relative effects of valley-scale controls, tributary basin characteristics, and lagged sediment transport in creating areas of gravel accumulations. The longitudinal distribution of gravel-bar area shows a broad scale wave-like form with increases in gravel-bar area weakly associated with tributary junctions. Secondary peaks of gravel area with 1·8–4·1 km spacing (disturbance reaches) are superimposed on the broad form. Variations in valley width explain some, but not all, of the short-spacing variation in gravel-bar area. Among variables describing tributary drainage basin morphometry, present-day land use and geologic characteristics, only drainage area and road density relate even weakly to gravel-bar areal inventories. A simple, channel network-based sediment routing model shows that many of the features of the observed longitudinal gravel distribution can be replicated by uniform transport of sediment from widespread disturbances through a channel network. These results indicate that lagged sediment transport may have a dominant effect on the synoptic spatial distribution of gravel in Ozarks streams; present-day land uses are only weakly associated with present-day gravel inventories; and valley-scale characteristics have secondary controls on gravel accumulations in disturbance reaches. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
59.
Seafloor mounds are potential geohazards to offshore rig emplacement and drilling operations and may contain evidence of underlying petroleum systems. Therefore, identifying and mapping them is crucial in de-risking exploration and production activities in offshore domains.A 738 km2 high resolution three-dimensional seismic dataset was used to investigate the occurrence, seismic characteristics and distribution of features interpreted as seafloor and buried sediment mounds, at water-depths of 800–1600 m, on the western Niger Delta slope. Fifteen seafloor mounds and eighteen shallowly buried mounds were identified. The seafloor mounds are characterised by lower seismic amplitude anomalies than the surrounding seabed sediments, and overlie vertical zones of acoustic blanking. The buried mounds in contrast are characterised by high amplitude anomalies; they also directly overlie sub-vertical zones of acoustic blanking. Seismic evidences from the features, their distribution patterns and tectono-stratigraphic associations suggest that their formation was controlled by the juxtaposition of buried channels and structural highs and their formation caused by focused fluid flow and expulsion of entrained sediments at the seabed.Considering the acoustic and geometrical characteristics of the mounds and comparing them with mound-shaped features from around the world, we conclude that the mounds most likely comprise heterolithic seafloor extrusions of muds and sands from the Agbada Formation with gas and possibly oil in some of the pore space giving rise to the acoustic characteristics. 相似文献
60.
Digital outcrop models help to constrain the interactions of stratigraphic and structural heterogeneity on ancient depositional systems. This study uses a stochastic approach that incorporates stratigraphic and structural modeling to interrogate the three-dimensional morphology of deep-water channel strata outcropping on Sierra del Toro in the Magallanes Basin of Chile. This approach considers the relative contributions, and associated uncertainty, of erosional downcutting versus post-depositional structural folding and small-offset faulting on the present-day configuration of the submarine channel complexes. Paleodepositional channel-belt gradients were modeled using a combination of three-dimensional visualization, stochastic surface modeling, palinspastic restoration, and decompaction modeling that are bound with errors constrained by stratigraphic and structural uncertainty. Modeling results indicate that at least 100 m of downcutting occurs over 6 km, and the resultant thalweg gradient of 64–125 m/km (decompacted) suggests that the Cerro Toro axial channel belt is an out-of-grade depositional system. Furthermore, the presence of steeper segments (100–175 m/km decompacted) suggests the preservation of one or more knickpoints that are similar in magnitude to tectonically-induced knickpoints on the modern seafloor. The interpreted knickpoints are correlated with a decreasing channel width-depth ratio and an increase of channel depth. These results indicate that stochastic surface modeling using digital outcrop models can constrain stratigraphic interpretations and post-depositional structural heterogeneity. 相似文献