Evaluating the effect of land development on sediment transport using a probability density function     

T. V. Hromadka II  R. J. Whitely 《Stochastic Environmental Research and Risk Assessment (SERRA)》1993,7(2):102-108

An important problem in sedimentation analysis is the development of a channel section that preserves, as best as possible, the current sedimentation regime even though the flood frequency tendencies have been altered due to land development within the catchment. In order to accomplish this task, a methodology is needed that estimates sediment transport capacity for various channel configurations. Such a procedure is described which allows the computation of the total sediment transport capacity for each of several T-year return frequency runoff hydrographs. This information is used to obtain an approximate probability distribution for the total sediment transport capacity, and the mean and standard deviation of this distribution are computed.Comparing the results for the catchment in its present state with a future developed state, using a selection of new channel parameters, indicates how to improve the channel to control changes in sedimentation due to development. The analysis procedure provides a basis for estimating a new channel configuration such that the new flow conditions retain, as best as possible, the existing condition sedimentation effects, and hence retain the natural sediment supply and transport trends even though runoff flow rates have changed due to land development within the catchment.The results of Wilson Creek are typical of the several sites examined, see Table 3 below. The T=2, T=5, T=25, and T=100 year values for total sediment transport capacity, in kilotons, are 6.9, 39.4, 61.3, and 96.7 with a mean of 17.1 and standard deviation of 19.3. After development with no change in the channel the respective values increase to: 17.9, 84.6, 128.1, and 258.0 with a mean of 39.1 and standard deviation of 44.3. A new channel can be constructed which will reduce these sediment transport capacity values, after development, to 5.2, 41.0, 62.0, and 124.8 with a mean of 17.4 and standard deviation of 22.0.  相似文献   

The role of wind direction in eolian transport on a narrow sandy beach     

Karl F. Nordstrom  Nancy L. Jackson 《地球表面变化过程与地形》1993,18(8):675-685

Comparison of eolian transport during five high-velocity wind events over a 29 day period on a narrow estuarine beach in Delaware Bay, New Jersey, USA, reveals the temporal variability of transport, due to changes in direction of wind approach. Mean wind speed measured 6 m above the dune crest for the five events ranged from 8·5 to 15·9 ms^?1. Mean wind direction was oblique to the shoreline (63° from shore-normal) during one event but was within 14° of shore-normal during the other events. Eolian transport is greatest during low tide and rising tide, when the beach source area is widest and when drying of surface sediments occurs. The quantity of sediment caught in a vertical trap for the five events varied from a total of 0·07 to 113·73 kgm^?1. Differences in temperature, relative humidity and moisture and salt content of surficial sediments were slight. Mean grain sizes ranged from 0·33 to 0·58 mm, causing slight differences in threshold shear velocity, but shear velocities exceeded the threshold required for transport during all events. Beach width, measured normal to the shoreline, varied from 15·5 to 18·0 m; beach slope differed by 0·5°. The oblique wind during one event created a source width nearly double the width during other days. Beach slope, measured in the direction of the wind, was less than half as steep as the slope measured normal to the shoreline. The amount of sand trapped during the oblique wind was over 20 times greater than any other event, even those with higher shear velocities. The ability of the beach surface to supply grains to the air stream is limited on narrow beaches, but increased source width, due to oblique wind approach, can partially overcome limitations of surface conditions on the beach.  相似文献   

Applications of seismic moment tensor inversion in fast response to earthquakes   总被引：1，自引：0，他引：1  

刘瑞丰  陈运泰  周公威  涂毅敏  陈培善 《地震学报(英文版)》1999,12(2):129-136

IntroductionAfteramoderateorstronger(Ms25.0)earthquake,themosturgentworkofthedivisionforearthquakemonitoringandpredictionistodetermineitstimeoforigin,hypocentrallocation(longitude,latitudeanddepth)andmagnitudeandtojudgethetrendofseismicregimedevelopmentassoonaspossible.Ingeneralcases,whenanearthquakewithMS25.0insideChinaoraonewithMS26.0inneighboringareasofChinahasoccurred,theEarthquakeBulletinofChineseSeismologicalNetworkcanprovidedeterminationoftheorigintime,hypocentrallocation(longitude,…  相似文献   

Tempo-spatial rupture process of the 1997 Mani, Xizang (Tibet), China earthquake of MS=7.9   总被引：3，自引：0，他引：3  

许力生  陈运泰 《地震学报(英文版)》1999,12(5)

IntroductionAnearthquakeofMs=7.9occurredinMaul,Xizang(Tibet),Chinaat10:02f55.4(UTC),No')ember8.1997.TheepicenterdeterminedbyChinaNationalSeismographNetwork(CNSN)is87.33"E.3>.26'N,thefocaldepthis40km,andthemagnitudeisMs=7.4.Accordingtothedeterllllnati...  相似文献   

平行走滑断层相互作用的粘弹模型和减震作用   总被引：6，自引：0，他引：6  

傅征祥  刘桂萍 《地震》1999,19(2):127-134

研究了二维粘弹性介质中平行走滑断层的相互力学作用及其地震活动性的影响。当一条断层发生滑动,将导致平行断层面上剪切应力减小,因此,可能推迟平行断层发生滑动,推迟时间在几年至几百年的范围内,这取决于发生滑动的断层与平行断层之间的距离,以及平行断层自身应力积累孕育地震过程经历的时间。  相似文献   

论川西炉霍裂谷微细浸染型金矿的矿质来源     

王小春 《大地构造与成矿学》1999,23(3):254-261

扼要介绍了川西炉霍裂谷微细浸染型金矿的地质特征, 通过地层和岩石中元素丰度特征,稀土元素、同位素、微量金的可化性实验等系统分析, 提出炉霍裂谷微细浸染型金矿的成矿物质来自三叠纪地层中的细碎屑质浊积岩建造和裂谷海底火山作用提供的深源物质。并讨论了矿质初始富集的机制。  相似文献   

碧口群铜矿床的成矿时限及其意义   总被引：4，自引：0，他引：4  

丁振举  刘丛强  姚书振  周宗桂 《大地构造与成矿学》1999,23(4):368-372

碧口群铜矿床作为早期同生喷流,后期受变质改造的沉积一变质改造型矿床,其保留有同生沉积的纹层构造和后生叠加改造的脉状构造。脉状硫化物Sr同位素及含矿石英脉的Ar同位素定年分别给出329Ma和211．3Ma,说明脉状硫化物的成矿时限在329－211Ma左右。由于该年龄明显小于矿体围岩的Sin－Nd、Rb－Sr年龄,所以该年龄反映了碧口群矿床的后期叠加成矿的时间。  相似文献   

长庆气田奥陶系风化壳气藏、气源研究   总被引：22，自引：4，他引：18  

戴金星  夏新宇 《地学前缘》1999,6(Z1):195-203

对10年来长庆气田奥陶系风化充气藏气源问题存在的不同观点（上古生界煤成气和奥陶系海相碳酸盐岩气何者为主）及相应的证据进行了总结和讨论,认为“奥陶系自生自储为主”的观点对地质和地球化学现象的解释存在疑问,包括用次要组分来判别混源天然气的主要来源,用不确切的端员气地球化学特征来计算混源比,对本溪组底部岩石的封盖性和下奥陶统碳酸盐岩的原始生烃潜力评价偏高,忽略了石炭系存在能够生成油型气的海相源岩。因此,长庆气田不能作为海相贫有机质的碳酸盐岩生成的大、中型油气田的实例。根据天然气及气源岩的地球化学特征,提出长庆气田奥陶系风化壳气藏气是以上古生界煤成气为主、石炭系海相源岩生成的油型气为辅的混合气。  相似文献   

变质作用矿床概述   总被引：8，自引：0，他引：8  

董申保 《地学前缘》1999,6(2):231-232

近代矿床学研究已初步摆脱经典和相对立的内生及外生作用矿床的研究范围,走向一个以整体地质环境为背景,以各种地质作用相互联系为基础的动力学研究方向,并从矿床的源区和源岩出发,在不同的地质作用下特别是与挥发组分的参与相结合,追溯其矿床的形成过程。变质作用矿床是一类中间型的矿床,属于近源迁移型。在原有地壳中含矿建造和矿源层的基础上,经历了变质作用和它的后期混合岩作用过程,并通过变质作用传导体制的不同阶段中出现的流体的参与,形成一系列由前变质矿床直至混合岩化期后矿床。文中对影响变质作用矿床的控制因素及其地位作了扼要的叙述,进行了变质作用分类的探讨,并从其传导体制中出现的热流及其形成环境上,与岩浆型花岗岩期后热液型进行对比和讨论。  相似文献   

Bjerhammar球面单层密度时间变化的实用解算理论   总被引：1，自引：1，他引：0  

申重阳 《大地测量与地球动力学》1999,19(2):9-16

研究了Ｂｊｅｒｈａｍｍａｒ球面单层密度时变实用解算理论和稳定算法。从利用重复大地测量数据联合确定Ｂｊｅｒｈａｍｍａｒ球面单层密度时变基本理论出发,推导了不同Ｂｊｅｒｈａｍｍａｒ球面上ｑ＊ｔ和δＷ＊ｔ之间的一般解式;分析研究了ｑ＊ｔ的迭代求解过程和收敛特性,得出其收敛稳定性很大程度上取决于Ｒ值的结论,同时给出了界限Ｒ的关系式;提出了解求ｑ＊ｔ的分步迭代算法,该算法从理论上解决了以前算法存在的收敛稳定问题（Ｒ较小时）,并指出：地表观测点ｑｔ的确定应遵循匹配处理准则,即各观测点数据应蕴含相同物理过程。最后给出了ｑ＊ｔ的精度评估公式。  相似文献