A bed‐load transport model for rough turbulent open‐channel flows on plane beds

Data from flume studies are used to develop a model for predicting bed‐load transport rates in rough turbulent two‐dimensional open‐channel flows moving well sorted non‐cohesive sediments over plane mobile beds. The object is not to predict transport rates in natural channel flows but rather to provide a standard against which measured bed‐load transport rates influenced by factors such as bed forms, bed armouring, or limited sediment availability may be compared in order to assess the impact of these factors on bed‐load transport rates. The model is based on a revised version of Bagnold's basic energy equation i_bs_b = e_bω, where i_b is the immersed bed‐load transport rate, ω is flow power per unit area, e_b is the efficiency coefficient, and s_b is the stress coefficient defined as the ratio of the tangential bed shear stress caused by grain collisions and fluid drag to the immersed weight of the bed load. Expressions are developed for s_b and e_b in terms of G, a normalized measure of sediment transport stage, and these expressions are substituted into the revised energy equation to obtain the bed‐load transport equation i_b = ω G ^3·4. This equation applies regardless of the mode of bed‐load transport (i.e. saltation or sheet flow) and reduces to i_b = ω where G approaches 1 in the sheet‐flow regime. That i_b = ω does not mean that all the available power is dissipated in transporting the bed load. Rather, it reflects the fact that i_b is a transport rate that must be multiplied by s_b to become a work rate before it can be compared with ω. It follows that the proportion of ω that is dissipated in the transport of bed load is i_bs_b/ω, which is approximately 0·6 when i_b = ω. It is suggested that this remarkably high transport efficiency is achieved in sheet flow (1) because the ratio of grain‐to‐grain to grain‐to‐bed collisions increases with bed shear stress, and (2) because on average much more momentum is lost in a grain‐to‐bed collision than in a grain‐to‐grain one. Copyright © 2006 John Wiley & Sons, Ltd.     

Bed waves at the basin scale: implications for river management and restoration

An extensive literature about fluvial sediment waves, slugs or pulses has emerged in the past 20 years. The concept has been useful in many respects, but has been applied to diverse phenomena using a variety of definitions. Moreover, inferred linkages between channel‐bed changes and sediment loads are often not justifiable. This paper reviews concepts of large fluvial sediment waves at scales extending to several tens of kilometres. It points out constraints on the inferences that can be made about sediment loads based on changes in channel‐bed elevation at this scale where channel sediment interacts with storage in floodplain and terrace deposits. The type area of G. K. Gilbert's initial sediment‐wave concept is re‐examined to show that neither wave translation nor dispersion occurred in the simple manner commonly assumed. Channel aggradation and return to graded conditions provide an alternative theory explaining Gilbert's observed bed‐elevation changes. Recognizing the evidence and implications of the former passage of a large‐scale bed wave is essential to the accurate diagnosis of catchment conditions and the adoption of appropriate river restoration goals or methods. Sediment loads, water quality, channel morphologic stability and aquatic ecosystems often reflect changes in sediment storage long after the channel bed has returned to grade. Copyright © 2006 John Wiley & Sons, Ltd.     

The use of riparian vegetated filter strips to reduce river sediment loads: an overestimated control measure?

The spatially distributed soil erosion and sediment delivery model WATEM/SEDEM was used to simulate the impact of riparian vegetated filter strips (RVFSs) on river sediment delivery at different spatial scales. For a field plot with a straight slope, sediment reduction by the RVFSs is comparable to results obtained through experimental set‐ups elsewhere (i.e. >70%). However, at the scale of an entire catchment, sediment reduction is much less (i.e. ±20%) due to (1) overland flow convergence, which reduces the sediment trapping efficiency of an RVFS, and (2) because part of the sediment bypasses the RVFSs through ditches, sewers and road surfaces. These results suggest that, at the catchment scale, RVFSs should be accompanied with other conservation techniques that are more appropriate for reducing river sediment loads, and that also reduce on‐site soil erosion. Copyright © 2006 John Wiley & Sons, Ltd.     

基于图像处理技术的岩心裂缝图像提取

基于数字图像处理技术,利用油田大量现场岩心纵向(或平面)劈开面图像资料,可直接分离出岩心剖面上裂缝信息.最大类间方差法的二值化算法是基于类间方差达到最大为准则,采用该法获得了理想的二值化效果,较准确地从岩心剖面中提取出裂缝图像信息.     

白河黄石板铅锌矿的热水沉积岩及找矿潜力

经过对黄石板铅锌矿含矿层展布、产态、矿化富集规律等基本特征的总结,以及对含矿层中典型热水沉积岩岩石学特征、岩石化学特征、含矿物质来源初步分析,通过热水沉积岩和盆地正常水沉积围岩的稀土元素地球化学等与南秦岭泥盆纪热水沉积岩的对比、研究,初步认为白河县黄石板铅锌矿为一较典型的热水沉积矿床。提出黄石板矿区西段高家沟一带深部仍存在隐伏矿体的可能性较大,并通过钻探验证发现较富隐伏铅锌矿体。运用热水沉积成岩成矿理论指出该地区找矿方向。     

考虑泥沙冲淤对水流控制方程的改进与模拟

以一维数学模型为例,通过数值实验及渭河实际资料的验证,发现在含沙量较大的情况下,水流连续方程里的浑水与床面的交换项对流量影响是明显的,计算中应予考虑.解释了在像黄河这样的多沙河流中存在的“水变沙”、“沙变水”的现象.由此可见,在模拟含沙量较大河流的水沙数学模型中,应完整考虑水流连续方程的微元河段的水量变化率、进出通量变化及浑水与床面的交换通量这三项.     

洞庭湖泥沙淤积数值模拟模式

在确保沙量守恒的非恒定流、非均匀沙的二维水沙数学模型的基础上,通过洞庭湖水沙输运和河床变形计算实践,比较了两种冲泻质与床沙质的转化模式,提出了包括冲泻质在内的泥沙淤积模式和水沙动边界计算模式.从洞庭湖泥沙输运和河床变形计算的结果看,洞庭湖泥沙淤积数值模式具有较好的稳定性和较高的模拟精度,说明所建湖泊泥沙模型的良好性能和具有推广运用的前景.     

Geophysical survey on the tectonic and sediment distribution of Qinghai Lake basin

1 Introduction in China, with an area of 4400 km2 and a drainage area With the advancement of global change study, peo- of nearly 29,660 km2[2]. Occurring at a “climatic triple ple are paying more and more attention to the conti- junction” among the East Asian monsoon, Indian nental environment (in which we reside), its evolution Monsoon and the Westerly Jet Stream, it lies in the and its future tendency. As a component of the global transitional belt of the east monsoonal humid areas sys…     

CHANNEL SHRINKAGE AND ITS INSTABILITY IN THE LOWER YELLOW RIVER1

From the mid 1980s through the late 1990s, the channel of the lower Yellow River experienced serious shrinkage, which has decreased the flood conveyance of the channel and the sediment carrying capacity of the flow, raised the water levels of floods, and, thus, severely threatened the safety of flood control along the river. The completion of Xiaolangdi Dam in 1999 could help mitigate the channel shrinkage problem, but the situation has not changed yet. This paper analyses the characteristics, mechanisms, and conditions resulting in channel shrinkage, points out channel instabilities, and puts forward approaches of channel rehabilitation.