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

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.     

一次滇西南秋季暴雨的中尺度分析与诊断

应用大尺度物理量场诊断分析和中尺度带通滤波处理技术,对2001年10月25日发生在云南西南部的一次暴雨过程机制进行了分析。结果表明,在副热带高压(下称副高)外围大尺度西南气流环境场中,中尺度系统是此次暴雨产生的直接原因;大尺度环境场为暴雨的发生提供了充沛的水汽来源,而中尺度系统则在水汽的强烈辐合、向上输送,使对流层中下层达到准饱和状态扮演了十分重要的角色。     

两次岫岩震群的特征及其预报意义研究

本文对1988年1月、1999年11月岫岩两次震群的性质及序列特征作了较系统的分析和研究。结果表明：序列各项特征参数及预测指标都显示出了具有明确意义的预报信息。特别是1999年11月前震序的低b值、低h值及多台小震初动符号和波形特征的高度一致性和稳定性都预示着震源区应力的高度集中和稳定,也为短临预报提供了可靠的信息。此外,前震序列的频度分布的时间结构和能量释放的时间过程也明确显示出“密集－平静－发震”和“增强－减弱－发震”的特点。这种临震预报特征与海域地震前震活动的时空结构和时空过程十分相似。本文还讨论了两震群之间特殊部位发生断层贯通的可能性,并给出震级上限的估计。     

Salt transport on islands in the Okavango Delta: Numerical investigations

This study uses a numerical model to investigate the groundwater flow and salt transport mechanisms below islands in the Okavango Delta. Continuous evapotranspiration on the islands results in accumulation of solutes and the formation of a saline boundary layer, which may eventually become unstable. A novel Lagrangian method is employed in this study and compared to other numerical methods. The numerical results support the geophysical observations of density fingering on Thata Island. However, the process is slow and it takes some hundreds of years until density fingering is triggered. The results are sensitive to changes of the hydraulic gradient and the evapotranspiration rate. Small changes may lead to different plume developments. Results further demonstrate that density effects may be entirely overridden by lateral flow on islands embedded in a sufficiently high regional hydraulic gradient.     

Yielding oscillator subjected to simple pulse waveforms: numerical analysis & closed‐form solutions

Numerical and analytical solutions are presented for the elastic and inelastic response of single‐degree‐of‐freedom yielding oscillators to idealized ground acceleration pulses. These motions are typical of near‐fault earthquake recordings generated by forward rupture directivity and may inflict damage in the absence of substantial structural strength and ductility capacity. Four basic pulse waveforms are examined: (1) triangular; (2) sinusoidal; (3) exponential; and (4) rectangular. In the first part of the article, a numerical study is presented of the effect of oscillator period, strength, damping, post‐yielding stiffness and number of excitation cycles, on inelastic response. Results are presented in the form of dimensionless graphs and regression formulas that elucidate the salient features of the problem. It is shown that conventional R–µ relations may significantly underestimate ductility demand imposed by near‐fault motions. The second part of the article concentrates on elastic‐perfectly plastic oscillators. Closed‐form solutions are derived for post‐yielding response and associated ductility demand. It is shown that all three ground motion histories (i.e. acceleration, velocity, and displacement) control oscillator response—contrary to the widespread view that ground velocity alone is of leading importance. The derived solutions provide insight on the physics of inelastic response, which is often obscured by the complexity of numerical algorithms and actual earthquake motions. The model is evaluated against numerical results from near‐field recordings. A case study is presented. Copyright © 2006 John Wiley & Sons, Ltd.     

高密度电法勘探技术及其应用

简述了高密度电法勘探技术的基本原理。从电极排列、数据预处理及反演处理方法等方面介绍了该技术在应用中应注意的关键技术问题及其处理方法,并通过在长-邵高速公路勘察的应用实例,来说明高密度电法勘探技术在岩溶洞穴、地质灾害等探测领域具有较好的探测效果。     

水文资料在水土保持中的应用研究

本文简要分析了我国水文资料的基本特点及其在水土保持中的应用情况,并结合水文资料在水土保持中的研究实例,探讨了加强水文资料在水土保持中应用范围与价值,在新一轮的站网调整建设中应与水土保持监测站网建设结合起来,避免重复建设,加强水文站网功能,发挥现有水文站网作用。     

对空间数据不确定性研究的思考

对GIS中空间数据不确定性研究中存在的问题进行思考后提出了5点建议.主要包括:1) 要区分GIS中确定性目标和不确定性目标;2) 要区分用离散点逼近曲线/曲面的逼近误差和离散点自身量测误差及其传播;3) 要研究GIS中的几何不确定性,更要重视研究属性和时态不确定性;4) 要研究空间数据质量,更要研究空间信息服务的质量;5) 空间数据不确定性研究要努力向实际应用转化.     

预加载共享动态链接库算法在桌面Linux环境下的设计与实现

针对桌面Linux操作系统在支持桌面交互应用程序上存在着系统响应慢和交互能力差等问题,从内存管理角度提出了旨在缩短系统响应时间、增强系统交互能力的预加载共享动态链接库算法,并在桌面Linux环境下设计和实现了它。该算法从Linux应用程序频繁地调用共享动态链接库这一特点出发,根据共享动态链接库被调用的频率,动态地选择被调用最频繁的一些共享动态链接库,并预先将它们加载到物理内存空间,以加快进程的执行速度,缩短系统的响应时间,最终提升系统的交互能力。     

对空间数据不确定性研究的思考

对GIS中空间数据不确定性研究中存在的问题进行思考后提出了5点建议。主要包括:1)要区分GIS中确定性目标和不确定性目标;2)要区分用离散点逼近曲线/曲面的逼近误差和离散点自身量测误差及其传播;3)要研究GIS中的几何不确定性,更要重视研究属性和时态不确定性;4)要研究空间数据质量,更要研究空间信息服务的质量;5)空间数据不确定性研究要努力向实际应用转化。