泥石流入汇对河流河床演变的影响

通过对现有文献资料的总结,探讨了泥石流入汇后随主河水流运动的几种可能形态和运动特点,分析了主河河床的演变情况,并提出按主支流水沙相互作用的大小,将主河河床演变分为弯曲、摆动和急流－深潭3种类型;对不同类型河流河床演变进行了分析,为进行泥石流入汇对主河水流运动与河床演变影响的研究奠定了基础。     

论泥石流及其学科性质

目前对泥石流性质的认识还不十分清楚,从而导致对其学科性质的认识还存在着不同的看法,纵观近70年来与泥石流发展有关的学科,通过对50余部代表学科成熟度的中外学术教材和专著的透视可知,地貌学是孕育泥石流的母学科,在泥石流这一学科生长点的发展壮大过程中,新兴的灾害学与其结合得最紧密,从而诞生了一门新的边缘交叉学科－灾害地貌学或称地貌灾害学,泥石流学科性质即定位于此,本文虽是仁者见仁,难免管中窥豹,其目的旨在引起同行的讨论和争鸣,以促进泥石流学科的更快发展。     

Macroinvertebrate Assemblages on Woody Debris and Their Relations with Environmental Variables in the Lower Sacramento and San Joaquin River Drainages, California

Data from 25 sites were used to evaluate associations between macroinvertebrate assemblages on large woody debris (snags) and environmental variables in the lower San Joaquin and Sacramento River drainages in California as part of the U.S. Geological Survey's National Water Quality Assessment Program. Samples were collected from 1993 to 1995 in the San Joaquin River drainage and in 1996 and 1997 in the Sacramento River drainage. Macroinvertebrate taxa were aggregated to the family (or higher) level of taxonomic organization, resulting in 39 taxa for analyses. Only the 31 most common taxa were used for two-way indicator species analysis (TWINSPAN) and canonical correspondence analysis (CCA). TWINSPAN analysis defined four groups of snag samples on the basis of macroinvertebrate assemblages. Analysis of variance identified differences in environmental and biotic characteristics among the groups. These results combined with the results of CCA indicated that mean dominant substrate type, gradient, specific conductance, water temperature, percentage of the basin in agricultural land use, percentage of the basin in combined agricultural and urban land uses, and elevation were important factors in explaining assemblage structure. Macroinvertebrate assemblages on snags may be useful in family level bioassessments of environmental conditions in valley floor habitats.     

Utilization Characteristics and Importance of Woody Biomass Resources on the Rural-Urban Fringe in Botswana

This article examines the utilization characteristics and importance of woody biomass resources in the rural-urban fringe zones of Botswana. In the literature for Africa, attention has been given to the availability and utilization of biomass in either urban or rural environments, but the rural-urban fringe has been neglected. Within southern Africa, this neglect is not justified; the rural-urban fringe, not getting the full benefits available in urban environments in Botswana, has developed problems in woody biomass availability and utilization that require close attention. In this article, socioeconomic data on the importance of woody biomass in the Batlokwa Tribal Territory, on the rural-urban fringe of Gaborone, Botswana, were collected together with ecologic data that reveal the utilization characteristics and potential for regrowth of woody biomass. The analysis of these results show that local woody biomass is very important in the daily lives of communities in the rural-urban fringe zones and that there is a high level of harvesting. However, there is no effort in planning land use in the tribal territory to either conserve this resource or provide alternatives to its utilization. The future of woody biomass resources in Botswana’s rural-urban fringe is uncertain. The investigators recommend that a comprehensive policy for the development of the rural-urban fringe consider the importance of this resource. The neglect of this resource will have far-reaching implications on the livelihoods of residents as well as the environment in this zone.     

A Statistical Sediment Yield Prediction Model Incorporating the Effect of Fires and Subsequent Storm Events1

Abstract: Alluvial fans are continuously being developed for residential, industrial, commercial, and agricultural uses in southern California. Development and alteration of alluvial fans need to consider the possibility of mud and debris flows from upstream mountain watersheds affected by fires. Accurate prediction of sediment yield (or hyper‐concentrated sediment yield) is essential for the design, operation, and maintenance of debris basins to safeguard properly the general populace. This paper presents a model for the prediction of sediment yields that result from a combination of fire and subsequent storm events. The watersheds used in this analysis are located in the foothills of the San Gabriel Mountains in southern California. A multiple regression analysis is first utilized to establish a fundamental statistical relationship for sediment yield as a function of relief ratio, drainage area, maximum 1‐h rainfall intensity and fire factor using 45 years of data (1938‐1983). In addition, a method for multi‐sequence sediment yield prediction under fire conditions was developed and calibrated using 17 years of sediment yield, fire, and precipitation data for the period 1984‐2000. After calibration, this model was verified by applying it to provide a prediction of the sediment yields for the 2001‐2002 fire events in southern California. The findings indicate a strong correlation between the estimated and measured sediment yields. The proposed method for sequence sediment yield prediction following fire events can be a useful tool to schedule cleanout operations for debris basins and to develop an emergency response strategy for the southern California region where plentiful sediment supplies exist and frequent fires occur.     

Causes and consequences of woody plant encroachment into western North American grasslands

As woody plants encroach into grasslands, grass biomass, density and cover decline as wood plant biomass, density and cover increase. There is also a shift in location of the biomass from mostly belowground in the grasslands to aboveground in the woodlands. In addition, species richness and diversity change as herbaceous species are replaced by woody species. This is not a new phenomenon, but has been going on continually as the climate of the Planet has changed. However, in the past 160 years the changes have been unparalleled. The process is encroachment not invasion because woody species that have been increasing in density are native species and have been present in these communities for thousands of years. These indigenous or native woody species have increased in density, cover and biomass because of changes in one or more abiotic or biotic factors or conditions. Woody species that have increased in density and cover are not the cause of the encroachment, but the result of changes of other factors. Globally, the orbit of the Earth is becoming more circular and less elliptical, causing moderation of the climate. Additional global climate changing factors including elevated levels of CO₂ and parallel increases in temperature are background factors and probably not the principal causes directing the current wave of encroachment. There is probably not a single reason for encroachment, but a combination of factors that are difficult to disentangle. The prime cause of the current and recent encroachment appears to be high and constant levels of grass herbivory by domestic animals. This herbivory reduces fine fuel with a concomitant reduction in fire frequency or in some cases a complete elimination of fire from these communities. Conditions would now favor the woody plants over the grasses. Reduced grass competition, woody plant seed dispersal and changes in animal populations seem to modify the rate of encroachment rather than being the cause. High concentrations of atmospheric CO₂ are not required to explain current woody plant encroachment. Changes in these grassland communities will continue into the future but the specifics are difficult to predict. Density, cover and species composition will fluctuate and will probably continue to change. Increased levels of anthropogenic soil nitrogen suggest replacement of many legumes by other woody species. Modification and perhaps reversal of the changes in these former grassland communities will be an arduous, continuing and perhaps impossible management task.     

Science guides search and rescue after the 2006 Philippine landslide

A rockslide-debris avalanche destroyed the remote village of Guinsaugon in Southern Leyte, Philippines, on 17 February 2006. Although search and rescue procedures were implemented immediately, the scale of the landslide and a lack of information about its nature resulted in unfocused and imprecise efforts in the early days of the operation. Technical support was only introduced five days after the event, provided by a team of volunteer geologists, geophysicists, and meteorologists. By the time search and rescue operations were transferred to specific target sites, however, the chances of finding survivors trapped under the rubble had diminished. In such critical situations, speed, accuracy, and the maximum appropriation of resources are crucial. We emphasise here the need for a systematic and technically informed approach to search and rescue missions in large-scale landslide disaster contexts, and the formulation of better disaster management policies in general. Standard procedures must be developed and enforced to improve how civil authorities respond to natural calamities.     

舟曲＂8.7＂泥石流的特征及其防治措施初探

2010年8月7日晚,舟曲县城发生特大泥石流灾害,导致了巨大的人员伤亡和财产损失.文章从地质构造、地形地貌、新构造运动与地震、气象和水系水文条件等五方面阐述了舟曲县自然环境整体背景,并分析了此次＂8.7＂泥石流形成的地形、物源和水源条件,总结了＂8.7＂泥石流的特征.在此基础上,为舟曲灾后重建提出了工程措施与生态措施相结合的防治建议.     

多层冲击防护结构研究进展

介绍了一种先进的空间碎片防护结构——多层冲击防护结构,以及多层冲击防护结构防护性能与结构参数的关系。从工程应用角度,总结了适合于多层冲击防护结构的弹道极限方程、设计方程和应用技术。     

粘性泥石流阵性运动对沟床冲淤演变的影响--以云南东川蒋家沟为例

粘性泥石流沟床的冲淤具有其特殊的机理,年内及一场泥石流的沟床冲淤主要受泥石流体性质、流型、规模的控制,阵性运动中沟床演变主要反映在残留层厚度的变化。对云南东川蒋家沟进行野外现场泥石流及沟床冲淤的定位观测,应用观测资料对阵性粘性泥石流泥深、流速、拖曳力与沟床冲淤值的关系进行分析,认为在泥深<2.0m,流速<8m/s,流量<1500m3/s情况下,阵性泥石流运动前后沟床冲淤值与三者没有明显线性关系,沟床冲淤幅度较小,一般在-0.8~1.0m之间。通过分析,求得粘性泥石流沟床冲刷深度极限值的表达式。