Estimation of Algerian rivers discharges based one Chiu's equation

The introduction of the entropy concept in hydraulics by Chiu gives the possibility to develop a simple method to measure discharges in natural streams. The application of this method on four streams in north Algeria made a possibility to develop a linear mean–max velocity models, deduce the entropy parameters and the cross sectional areas expressions for all streams in order to obtain the water discharges easily with minimum errors. The Chiu’s velocity distribution equation was also checked for a large range of discharges, water levels, and flow pattern, where it proves its efficacy.     

A research on the estimation of coefficient roughness in open channel applying entropy concept

Manning’s roughness coefficient is one of the most important parameters in establishing the plan, design, operation, and maintenance of the water resource projects for hydraulic engineers, and since the worth of this value has a significant effect on the analysis of the water level and flow rate distribution, it is very important to carry out the calculation of flood stage, design of the stream/river structure, and safety assessment of the stream. Due to the importance of these factors, the calculation of objective and quantitative roughness coefficient has long drawn attention from researchers at home and abroad. Many studies have been conducted to estimate the roughness coefficient based on the actual measurements for various types of streams, such as gravel and sand streams, and many others have produced experience equation for various levels of materials and relative depth. Despite many of these efforts, the roughness coefficient uses constant values when applied to the actual model or real design. This application is a major source of error in simulating flood and unsteady flow. To solve these problems, good results were obtained by attempting to calculate the roughness coefficient applied with the entropy concept in open-channel flow. In particular, the proposed roughness coefficient based on the measurements taken from laboratories under conditions showed very similar to the actual stream flow which was found to be about the same as the value from the unsteady flow. Accordingly, the newly developed roughness coefficient equation, which is the result of this study, is a very practical one formula that can be applied to the flood flow of real natural streams. It can also be used as an alternative to make up for the disadvantages of the Manning’s roughness coefficient.     

The subglacial thermal organisation (STO) of ice sheets

This paper examines ice-sheet wide variations in subglacial thermal regime and ice dynamics using the landform record exposed on the beds of former mid-latitude ice sheets (the Laurentide, Cordilleran, Fennoscandian and British-Irish Ice Sheets). We compare the landform patterns beneath these former ice sheets to the flow organisation beneath parts of the contemporary Antarctic Ice Sheet inferred from RADARSAT-1 Antarctic Mapping Project (RAMP) data. The evidence preserved in the landform record and observed on contemporary ice masses can be grouped into four major ice-dynamical components that collectively define the subglacial thermal organisation (STO) of ice sheets. These ice-dynamical components are frozen-bed patches, ice streams, ice-stream tributaries and lateral shear zones. Frozen-bed patches appear at a wide range of spatial scales, spanning four orders of magnitude. In some areas, frozen-bed zones comprise large proportions of the bed (e.g. near the ice divide in continental areas), whilst in other areas they constitute isolated “islands” in areas dominated by thawed-bed conditions. Ice streams, narrow zones of fast flow in ice sheets that are otherwise dominated by slow sheet flow, are also common features of Quaternary ice sheets. Tributaries to ice streams flow at velocities intermediate between full ice-stream and sheet flow, and may divert ice drainage from one primary ice-stream corridor to an adjacent one. Sharp lateral boundaries between landforms indicate sliding and non-sliding conditions, respectively. These lateral boundaries represent important discontinuities in the glacial landscape and mark the location of shear zones between thawed-bed ice streams and intervening frozen-bed areas. We use the landform evidence in the area around Great Bear Lake, Canada to trace the evolution of an ice-stream web through time, demonstrating that frozen-bed patches are integral components of this complex system. We conclude that frozen-bed patches are important for the stability of ice sheets because they laterally constrain and isolate peripheral drainage basins and their ice streams.     

A new model for flow in shale-gas reservoirs including natural and hydraulic fractures

In this work, we construct a new coupled Multiscale/Discrete Fracture Model for compressible flow in a multiporosity shale gas reservoir containing networks of natural and hydraulic fractures. The geological formation is characterized by four distinct length scales and levels of porosity. The window of observation of the finest (nanoscale) portraits the nanopores within organic matter containing adsorbed gas. At the microscale, the medium is formed by two solid phases: organic, composed by kerogen aggregates, and inorganic (clay, quartz, calcite). Such phases are separated by the network of partially-saturated interparticle pores where microscopic free gas flow influenced by Knudsen effects along with gas diffusion in the immobile water phase occur simultaneously. The upscaling of the local flow to the mesoscale gives rise to a nonlinear homogenized pressure equation in the shale matrix which lies adjacent to the system of natural fractures. Homogenization of the coupled matrix/preexisting fractures to the macroscale leads to a microstructural model of dual porosity type. Such homogenized model is subsequently coupled with the hydrodynamics in the network of induced fractures which, in the context of the discrete fracture modeling, are treated as (n ? 1), (n = 2, 3) lower dimensional objects. In order to handle numerically the nonlinear interaction between the different flow equations, we adopt a superposition argument, firstly proposed by Arbogast (1996), in each iteration of a fixed-point algorithm. The resultant governing equations are discretized by the finite element method and numerical simulations of gas production in stratified arrangements of the fracture networks are presented to illustrate the potential of the multiscale approach.     

Interaction of multiple ice streams on the Malin Shelf during deglaciation of the last British–Irish Ice Sheet

The Malin Shelf, off north-west Ireland, was an important zone of confluence for marine-based ice streams of the former British–Irish Ice Sheet (BIIS). Legacy geophysical datasets are used to construct models of the seismic character, relative age and distribution of shelf sediments and landforms. Buried and surface landform assemblages provide evidence that during deglaciation of the Late Devensian BIIS, the region was occupied not by a single Hebrides Ice Stream as previously proposed, but by four discrete ice streams, here referred to as the Sea of the Hebrides (SHIS), Inner Hebrides, North Channel and Tory Island ice streams. Our observations of stratigraphic relationships between the deposits of these ice streams indicate physical interactions between them during shelf deglaciation. We interpret an initial dominant cross-shelf flow along the SHIS impeding cross-shelf ice flow from other ice sheet sectors. Following withdrawal of the SHIS grounding line from the shelf edge to mid-shelf bathymetric highs during deglaciation, a reconfiguration of ice sheet flow paths allowed the expansion of smaller cross-shelf ice streams draining central Scotland and north-western Ireland. This internal dynamic behaviour provides a possible physical analogue for time-transgressive flow patterns reported for outlets draining the West Antarctic Ice Sheet.     

Structural control on surface flow in karstic environment

Aquifer hydrodynamical properties, hydrogeological tracing, mapping and piezometric monitoring characterised underground flow in calcareous environments. Surface flow study during low-water season showed water supply spatial heterogeneity due to calcareous aquifer anisotropy. It also underlined the role of structure on water transfer and exchanges between aquifers and rivers. By controlling the hydraulic gradient between the streams network and the saturated zone, structure compartmentalisation moderated considerably the role of fracture on underground flow. Several examples of calcareous basins from eastern France were studied.     

太湖平原圩区河网演变模式探析

以汾湖镇为研究区,采用GIS和RS方法分析了全镇及典型圩区近15年来河网结构的变化特征。结果表明:等级最低的圩内河道的河网结构变化显著,而村级以上的骨干河网结构基本没有变化,河网结构趋于稳定;不同圩区河网结构变化存在明显的时空差异。快速城镇化过程中,经过及时规划和治理的圩区河网结构得到了一定的改善,反之,河网结构受到了较大破坏;根据河网结构演变特征及原因,快速城镇化圩区河网结构演变的主要原因是对水系的保护、整治和破坏等人类活动的影响,据此识别圩区河网演变的几种主要模式为:主动引导型、被动改造型、修复完善型和保护优先型。     

浅谈地下水流模拟中河流的处理方法

本文分析了河水与地下水不同作用形式下的补排关系,给出了河流在地下水流模拟中的两种处理方法.根据河流与地下水的相互作用规律将其概化为四种边界条件,并给出了在不同边界条件中河水与地下水交换量的计算公式,初步建立了河水与地下水的解析耦合模型.     

Anthropogenic influences on Hong Kong streams

The Hong Kong countryside has experienced centuries of intense human impact, and none of the native climax forest remains. Anthropogenic influences upon Hong Kong freshwaters reflect, on the one hand, pollution and degradation of rivers and wetlands as a consequence of urbanization of rural lowlands. On the other hand, the need to preserve pristine catchments for the supply of water for human consumption has ensured the protection of upland streams which are typically unpolluted. Hong Kong has no natural lakes, limited ground-water reserves, and marked seasonal and inter-year rainfall variation. Most upland streams are impounded, and water is transferred from them into reservoirs by underground tunnels. Hong Kong's 17 reservoirs collect insufficient water from local catchments to meet the territory's needs. To satisfy the shortfall, large amounts of water (1.1 billion m³ in 1994) are piped each year from the Dongjiang (a tributary of the Zhujiang or Pearl River) in Guangdong Province (southern China) into reservoirs in Hong Kong where it mixes with water from local streams. The natural seasonality of flow in Hong Kong streams is heightened by aggressive water extraction during the dry season. No consideration is given to maintenance of the minimum in-stream flows necessary to conserve ecosystem integrity below extraction points and, in extreme cases, surface flow ceases during the dry season. Water extraction also causes dry-season increases in pollution load as flows are reduced and the ability of streams to dilute pollution is diminished. The cumulative impact of such modifications is severe, and lowland freshwaters now support a depauperate flora and fauna of adaptable generalists, including a significant proportion of exotic or alien species.     

An automatic ordering method for streams in surface-water/groundwater interaction modeling

The widely used groundwater flow model MODFLOW offers a range of software packages to simulate the interaction between streams and groundwater in aquifer systems. However, these existing packages lack a general method to address the chaotic simulation sequences of stream segments and require these segments to be ordered by modelers as input to the code. Therefore, it is challenging to simulate a stream network divided into a large number of segments such as a canal irrigation system. In this study, the Streamflow Automatic Routing (SAR) package was developed, and an effective method is proposed to automatically determine the segment simulation sequence. The stream segment order in the SAR input file is arbitrary, which allows modifications of the stream network by removing segments directly and adding segments at the end of the segment group. This mainly includes two processes: scanning all the outlet channels of the water system and calling the recursive algorithm for each outlet channel of the water system. The SAR package was tested using a hypothetical stream–aquifer system and applied to a complex flow field in Aiding Lake of Turpan Basin, China. In the results, a close fitting between the simulation and observations shows that the SAR package precisely simulated the exchange flux between the steams and aquifer. The SAR package can significantly improve the efficiency of simulations in a complex stream network, and it can be widely used as a subroutine package of MODFLOW in agricultural irrigation areas where rivers and canals are interlaced.

     

Ice stream sticky spots: A review of their identification and influence beneath contemporary and palaeo-ice streams

Rapidly-flowing ice streams are the arterial drainage routes in continental ice sheets and exert a major influence on ice sheet mass balance. Recent observations have revealed that ice stream flow exhibits considerable variability, with relatively rapid changes taking place in speed and direction. This spatial and temporal variability is intimately linked to the conditions at the base of the ice streams and the distribution of localised patches of basal friction, known as ‘sticky spots’. In this paper, we provide a detailed review of sticky spot observations from both contemporary and palaeo-ice stream beds in order to better understand their nature and influence. Observations and theoretical considerations reveal four primary causes of ‘stickiness’: (i), bedrock bumps; (ii), till-free areas; (iii), areas of ‘strong’ (well drained) till; and (iv), freeze-on of subglacial meltwater. These may act together in one location, or in isolation; and a progressive increase in their distribution could lead to ice stream shut-down. Bedrock bumps are influential under active ice streams, where they provide form drag and can create thinner ice which increases the likelihood of basal freeze-on. Increased bed roughness may prevent the lateral migration of some ice streams but bedrock bumps are unlikely to cause ice stream shut-down because, over long time-scales, ice stream erosion might be expected to reduce their amplitude. The influence of till-free areas beneath an ice stream will depend critically on the amount of water that might be drawn out of the surrounding till to lubricate such areas. They are likely to be most important in ice stream onset zones but their identification has proved difficult beneath active ice streams. If an ice stream operates solely by till deformation, it is conceivable that a progressive increase in the exposure of till-free areas could lead to shut-down through a process of sediment exhaustion. Areas of strong, well drained till have been identified beneath both active and ancient ice streams and are most likely to result from the reorganisation of subglacial meltwater. The collapse of an inefficient ‘cannalised’ system to a more efficient ‘channelised’ system can occur rapidly and this mechanism has been hypothesised as a candidate for ice stream shut-down in both contemporary and palaeo-settings. Basal freeze-on has also been observed and inferred from beneath modern and palaeo-ice streams, and a reduction in basal meltwater supply coupled with ice stream drawdown and the advection of cold ice increases the likelihood of switching off an ice stream. A paucity of data from ice stream sticky spots limits a better understanding of their nature, distribution and evolution beneath ice streams. Future technological advances are likely to improve the resolution of the data collected from the beds of modern ice streams but well-preserved palaeo-ice stream beds also hold potential for investigating their influence on ice stream flow and we present simple landsystems models to aid their identification. Such data will considerably enhance the basal boundary condition in ice stream models which will, ultimately, refine our predictions of the response of contemporary ice sheets to future changes in climate.     

山区卵砾石河道水流阻力计算

卵砾石河道广泛存在于山区河流中,在卵砾石河床近底层的水流流速低于上方流速,速度剖面出现拐点,类似于自由剪切流动,传统的指数型和对数型水流阻力公式计算误差偏大。将自由剪切流理论类比到山区卵砾石河道,并考虑山区河流特殊流态、流场和剪切力的影响,引入雷诺数(Re)、弗劳德数(Fr)和摩阻流速利用水槽数据进一步修正了该类水流阻力公式。筛选位于意大利南部的亚平宁山脉140条山区河流野外数据对新公式进行验证,并检验对比了已发表的多个山区河流阻力公式。结果表明:修正后的水流阻力公式Nash-Sutcliffe效率指数最接近1、均方根误差最小、相对误差最小。自由剪切流动的类比是从湍流结构角度推导河道水流阻力,能更好地阐释特殊水流结构,进而提高计算精度。     

山区卵砾石河道水流阻力计算

卵砾石河道广泛存在于山区河流中，在卵砾石河床近底层的水流流速低于上方流速，速度剖面出现拐点，类似于自由剪切流动，传统的指数型和对数型水流阻力公式计算误差偏大。将自由剪切流理论类比到山区卵砾石河道，并考虑山区河流特殊流态、流场和剪切力的影响，引入雷诺数（Re）、弗劳德数（Fr）和摩阻流速利用水槽数据进一步修正了该类水流阻力公式。筛选位于意大利南部的亚平宁山脉140条山区河流野外数据对新公式进行验证，并检验对比了已发表的多个山区河流阻力公式。结果表明：修正后的水流阻力公式Nash-Sutcliffe效率指数最接近1、均方根误差最小、相对误差最小。自由剪切流动的类比是从湍流结构角度推导河道水流阻力，能更好地阐释特殊水流结构，进而提高计算精度。     

Development of a coupled surface-groundwater-pipe network model for the sustainable management of karstic groundwater

This paper considers the hydrogeological simulation of groundwater movement in karstic regions using a hydrological modelling system (SHETRAN) which has been adapted for modelling flow in karstic aquifers. Flow and transport through karstic aquifers remains poorly understood, yet quantitative hydrogeological models are essential for developing and implementing groundwater protection policies. The new model has been developed and used within the STALAGMITE (Sustainable Management of Groundwater in Karstic Environments) project, funded by the European Commission. The SHETRAN model is physically based insofar as most of the parameters have some physical meaning. The SHETRAN model represents all of the key processes in the hydrological cycle, including subsurface flow in the saturated and unsaturated zones, surface flow over the ground surface and in channels, rainfall interception by vegetation canopies, evapotranspiration, snow-pack development and snowmelt. The modifications made to SHETRAN to simulate karstic aquifers are (1) the coupling of a pipe network model to a variably saturated, three-dimensional groundwater component (the VSS-NET component), to simulate flow under pressure in saturated conduits; (2) the coupling of surface water features (e.g. sinking streams or "ponors", and spring discharges) to the conduit system; (3) the addition of a preferential "bypass" flow mechanism to represent vertical infiltration through a high-conductivity epikarst zone. Lastly, a forward particle tracking routine has been developed to trace the path of hypothetical particles with matrix and pipe flow to springs or other discharge points. This component allows the definition of groundwater protection zones around a source for areas of the catchment (watershed) which are vulnerable to pollution from non-point sources (agriculture and forestry).     

Properties of a Diffusive Hydrograph and the Interpretation of Its Single Parameter

The mathematical properties of the normalized diffusive hydrograph allow for easy determination of intrinsic basin characteristics. These include lag times between storm events and peak flow, recession rate, and the total, temporally integrated flow volume, all in terms of a single parameter, the basin time constant “b”. This simple function displays surprising fidelity to measured hydrographs of springs and hundreds of streams and small rivers. We explain this fidelity by showing that the curvature of the theoretical hydrograph matches that of the natural hydrographs better than several alternate models, and by demonstrating that the simple hydrograph function can be integrated over a range of time constants (0 to b _max) to represent the hierarchy of flow paths of varying lengths that exist in real watersheds. Surprisingly, the unwieldy analytical results from this integration are almost numerically indistinguishable from a simple hydrograph using a single, suitably-weighted average for the time constant. The peak flow times are shifted slightly. The accuracy with which the simple hydrograph approximates the integrated results for hierarchies of hydrographs representing individual flow paths explains why the former can realistically describe the discharge behaviors of complex natural watersheds.     

Untersuchungen zur kreislaufmahlung in einer aufbereitung für komplexe sulfidische erze

Circuit grinding was investigated in the Rammelsberg ore dressing plant. From short-interval sampling it was possible to make a statement about the non-stationary and stationary state of grinding. The objective of these investigations was to establish the distribution curves of the quantitative flow, of the grain sizes and of the mineralogical components in the individual streams of the circuit grinding.     

Cubic law with aperture-length correlation: implications for network scale fluid flow

Previous studies have computed and modeled fluid flow through fractured rock with the parallel plate approach where the volumetric flow per unit width normal to the direction of flow is proportional to the cubed aperture between the plates, referred to as the traditional cubic law. When combined with the square root relationship of displacement to length scaling of opening-mode fractures, total flow rates through natural opening-mode fractures are found to be proportional to apertures to the fifth power. This new relationship was explored by examining a suite of flow simulations through fracture networks using the discrete fracture network model (DFN). Flow was modeled through fracture networks with the same spatial distribution of fractures for both correlated and uncorrelated fracture length-to-aperture relationships. Results indicate that flow rates are significantly higher for correlated DFNs. Furthermore, the length-to-aperture relations lead to power-law distributions of network hydraulic conductivity which greatly influence equivalent permeability tensor values. These results confirm the importance of the correlated square root relationship of displacement to length scaling for total flow through natural opening-mode fractures and, hence, emphasize the role of these correlations for flow modeling.     

岩溶地区地下河系统水资源定量评价的问题与出路

岩溶地区含水介质的多重性和高度复杂性,给地下河系统的水资源量评价带来许多难题。在分析地下河系统水资源形成、分布和运移特征基础上,认为目前用于地下水评价的主要方法都不太适用来解决地下河系统水资源量的评价和预测问题。作者在比较地下河与地表水多方面的相似性后,建议引入现代水文学的理论方法和模型来解决岩溶地区地下河系统水资源评价问题,并分析了可能需要解决的若干关键问题。针对岩溶水资源的特征,作者认为,改变传统定量评价的思维、引进现代水文学理论方法和充分利用3S技术,是解决地下河系统水资源定量评价的主要出路。      

Risk analysis of tripping accidents of power grid caused by typical natural hazards based on FTA-BN model

As the scale of the power grid becomes larger, the requirements for transmission reliability are getting higher. Due to the large geographical span and the harsh environment of the power transmission line, it has become the most severely affected equipment of the power grid by natural factors. However, the quantitative assessment of transmission line tripping accidents caused by multiple natural hazards has rarely been investigated. In this study, a risk analysis method to probabilistically analyze the tripping accidents of power transmission lines caused by wildfire, lightning, strong wind and ice storm was proposed. The analysis process consists of comprehensively identifying the risk of tripping accidents based on fault tree analysis and dynamically performing the predictive analysis of tripping accident evolution process in transmission line from causes to consequences based on Bayesian network. Critical risk evolution paths corresponding to four natural hazards are determined through a 72-node BN. The source risks of the four critical risk evolution paths are artificial ignition source from the wildfire path, aging from the lightning path, thoughtless of surrounding environment from the strong wind path and wind effect from the ice storm path. The countermeasures of tripping accidents are derived through the source risks and synergy between risks in three scenario analysis. This study is expected to examine the key challenges of risk management in power grid tripping accidents, which provides technical supports for accident preventing, handling and recovering of tripping accidents of the power transmission line according to “scenario–response”-based hazard response strategy.