A model of equilibrium bed topography for meander bends with erodible banks     

Stephen E. Darby  Ivana Delbono 《地球表面变化过程与地形》2002,27(10):1057-1085

Channel curvature produces secondary currents and a transverse sloping channel bed, along which the depth increases towards the outer bank. As a result deep pools tend to form adjacent to the outer bank, promoting bank collapse. The interaction of sediment grains with the primary and secondary flow and the transverse sloping bed also causes meanders to move different grain sizes in different proportions and directions, resulting in a consistent sorting pattern. Several models have been developed to describe this process, but they all have the potential to over‐predict pool depth because they cannot account for the influence of erodible banks. In reality, bank collapse might lead to the development of a wider, shallower cross‐section and any resulting flow depth discrepancy can bias associated predictions of flow, sediment transport, and grain‐size sorting. While bed topography, sediment transport and grain sorting in bends will partly be controlled by the sedimentary characteristics of the bank materials, the magnitude of this effect has not previously been explored. This paper reports the development of a model of flow, sediment transport, grain‐size sorting, and bed topography for river bends with erodible banks. The model is tested via intercomparison of predicted and observed bed topography in one low‐energy (5·3 W m^?2 specific stream power) and one high‐energy (43·4 W m^?2) study reach, namely the River South Esk in Scotland and Goodwin Creek in Mississippi, respectively. Model predictions of bed topography are found to be satisfactory, at least close to the apices of bends. Finally, the model is used in sensitivity analyses that provide insight into the influence of bank erodibility on equilibrium meander morphology and associated patterns of grain‐size sorting. The sensitivity of meander response to bank cohesion is found to increase as a function of the available stream power within the two study bends. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

流动成像测井研究进展   总被引：2，自引：3，他引：2  

吴锡令 《地球物理学进展》2002,17(2):272-276

流动成像测井属于对非均匀介质动态的非线性测量，通过对油气井内多相流体信息的投影扫描和反演处理，实时成像显示流体分布及流动状况，国外研制的电导法，电容法仪器采用电导探针或电容元件构成阵列测量探头，分别利用油气与水的导电特性和介电特性差异辨识井内流体，对流动截面的测量局限于个别点上，已在水平井中见到应用效果，但对物场信息投影测量的数据量和分辨率未能满足成像要求。我国提出的电磁法采用环状阵列电极构成测量探头，综合利用油气与水的导电和介电特性差异辨识井内流体，可以测量获得多相流体流动截面的清晰图像，为研究开发全新的流动成像测井系统奠定了良好基础。  相似文献   

Efficient methods for solving water flow in variably saturated soils under prescribed flux infiltration     

Xiaoxian Zhang  A. Glyn Bengough  John W. Crawford  Iain M. Young 《Journal of Hydrology》2002,260(1-4):75-87

The non-linear solvers in numerical solutions of water flow in variably saturated soils are prone to convergence difficulties. Many aspects can give rise to such difficulties and in this paper we address the gravity term and the prescribed-flux boundary in the Picard iteration. The problem of the gravity term in the Picard iteration is iteration-to-iteration oscillation as the gravity term is treated, by analogy with the time-step advance technique, ‘explicitly’ in the iteration. The proposed method for the gravity term is an improvement of the ‘implicit’ approach of Zhang and Ewen [Water Resour. Res. 36 (2000) 2777] by extending it to heterogeneous soil and approximating the inter-nodal hydraulic conductivity in the diffusive term and the gravity term with the same scheme. The prescribed-flux boundary in traditional methods also gives rise to iteration-to-iteration oscillation because there is no feedback to the flux in the solution at the new iteration. To reduce such oscillation, a new method is proposed to provide such a feedback to the flux. Comparison with traditional Picard and Newton iteration methods for a wide range of problems show that a combination of these two proposed methods greatly improves the stability and consequently the computational efficiency, making the use of small time step and/or under-relaxation solely for convergence unnecessary.  相似文献   

不同损失条件下的泥石流预报模型   总被引：14，自引：2，他引：14  

韦方强  胡凯衡  崔鹏  杨坤 《山地学报》2002,20(1):97-102

泥石流预报是泥石流减灾的重要手段之一，然而泥石流形成的复杂性使泥石流预报准确度低，误报和漏报率较高。泥石流误报和漏报都会造成损失，但二者造成的损失有很大的差别。为了减少泥石流误报或漏报造成的损失，应当考虑两种错报造成损失的不同。根据使总平均损失达到最小的原则，建立了不同损失条件下的泥石流预报模型，并将该模型应用到云南东川蒋家沟。  相似文献   

泥石流多发干旱河谷区植被恢复研究   总被引：10，自引：2，他引：10  

沈有信  张彦东  刘文耀 《山地学报》2002,20(2):188-193

云南东北部东川小江流域的干旱河谷土地退化十分严重，土地表层的砾石含量已超过60％，有机质含量、全氮、有效氮、有效磷、有效钾的含量相对于残存燥红土明显下降。草坡是当地的主要植被类型，并未起到防治土地退化的应有作用。以合欢（Leucaena glauca)、马桑（Coriaria sinica)种植为主的恢复方式对土地的恢复有明显的改善作用。高密度的乔木树种合欢的种植使林下的草本物种的数量和组成发生了极大变化，较耐荫的植物占据了林分下层，且物种数量较草坡减少，群落多样性指数降低。三种马桑种植方式下，不但原有的草坡群落的物种仍有大量的生存空间，而且为一些新物种创造了生存环境，从而使物种的种类较原有草坡地增加，提高了群落的多样性指数。合欢种植的生物量最高，对解决当地薪柴严重短缺意义重大，马桑种植在增加灌木层生物量的同时，并未改变草坡的物种组成，还可兼顾解决当地的饲草和放牧，应大力推广。  相似文献   

A New Model for Heat Flow in Extensional Basins: Estimating Radiogenic Heat Production   总被引：1，自引：0，他引：1  

Waples  Douglas W. 《Natural Resources Research》2002,11(2):125-133

Radiogenic heat production (RHP) represents a significant fraction of surface heat flow, both on cratons and in sedimentary basins. RHP within continental crust—especially the upper crust—is high. RHP at any depth within the crust can be estimated as a function of crustal age. Mantle RHP, in contrast, is always low, contributing at most 1 to 2 mW/m² to total heat flow. Radiogenic heat from any noncrystalline basement that may be present also contributes to total heat flow. RHP from metamorphic rocks is similar to or slightly lower than that from their precursor sedimentary rocks. When extension of the lithosphere occurs—as for example during rifting—the radiogenic contribution of each layer of the lithosphere and noncrystalline basement diminishes in direct proportion to the degree of extension of that layer. Lithospheric RHP today is somewhat less than in the distant past, as a result of radioactive decay. In modeling, RHP can be varied through time by considering the half lives of uranium, thorium, and potassium, and the proportional contribution of each of those elements to total RHP from basement. RHP from sedimentary rocks ranges from low for most evaporites to high for some shales, especially those rich in organic matter. The contribution to total heat flow of radiogenic heat from sediments depends strongly on total sediment thickness, and thus differs through time as subsidence and basin filling occur. RHP can be high for thick clastic sections. RHP in sediments can be calculated using ordinary or spectral gamma-ray logs, or it can be estimated from the lithology.  相似文献   

Deterministic non-linear source processes of volcanic tremor signals accompanying the 1996 Vatnajökull eruption, central Iceland     

Konstantinos I. Konstantinou 《Geophysical Journal International》2002,148(3):663-675

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Determination of thermal conductivity and formation temperature from cooling history of friction-heated probes   总被引：1，自引：0，他引：1  

Tien-Chang Lee  A. D. Duchkov  S. G. Morozov 《Geophysical Journal International》2003,152(2):433-442

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粘性泥石流残留层的形成及减阻作用--以云南蒋家沟泥石流为例   总被引：1，自引：0，他引：1  

张军  吴积善  游勇  程尊兰 《山地学报》2003,21(2):223-227

通过对云南蒋家沟粘性泥石流的野外观测 ,讨论了粘性泥石流残留层的定义特征 ,在大量实测数据基础上 ,分析了残留层易形成时段的特性 ;分别对一次泥石流过程、若干阵泥石流和一阵泥石流残留层的变化进行了相关分析 ;最后用观测数据分析了泥石流残留层的减阻作用  相似文献   

云南兰坪北部铜多金属矿化区成矿流体流动与矿化分带——流体包裹体和稳定同位素依据   总被引：13，自引：7，他引：13       下载免费PDF全文

徐启东  李建威 《矿床地质》2003,22(4):365-376

滇西兰坪盆地北部发育了一类受逆冲推覆构造控制的浅成热液Cu—Ag—Pb-Zn矿化，形成了白秧坪、富隆厂、吴底厂、麻栗坪及金满、科登涧等大-中型矿床和矿点，并存在矿化分带。文章利用这些矿化脉体的流体包裹体和热液方解石的碳氧同位素组成资料，研究成矿流体与矿化分带的关系。结果表明，成矿流体主要属于NaCl-H2O成分体系，盐度ω(NaCleq)为2％～11％，形成温度为170～300℃，形成于1．8～3．8km深度内，这些相似性说明这类矿化的发生具有相似的流体性质和沉淀机制。热液方解石在δ^13C-δ^18O图解中呈近水平线展布的型式，指示流体源自地壳浅部的地下水系统，与海相灰岩等围岩作用形成了溶解碳以[HCO3^]-为主的成矿流体，流体与岩石的相互作用可能是成矿流体沉淀的主要机理。从西到东，流体包裹体的盐度-温度由高到低变化与矿化分带和逆冲推覆构造的根带→中带→锋带相配套，显示重力驱动流动可能是主要的流体流动机制。成矿流体在不同构造部位流动的通畅及流体．岩石系统的封闭-开放程度等流体流动性质与矿化发生的强度和规模有关，兰坪北部逆冲推覆构造中带的流体通畅地流动及沉淀时处于相对开放状态，有利于该区形成较大规模的浅成热液多金属矿化。  相似文献