Prediction of tension crack location and riverbank erosion hazards along destabilized channels

Riverbank erosion, associated sedimentation and land loss hazards are a land management problem of global significance and many attempts to predict the onset of riverbank instability have been made. Recently, Osman and Thorne (1988) have presented a Culmann-type analysis of the stability of steep, cohesive riverbanks; this has the potential to be a considerable improvement over previous bank stability theories, which do not account for bank geometry changes due to toe scour and lateral erosion. However, in this paper it is shown that the existing Osman-Thorne model does not properly incorporate the influence of tension cracking on bank stability since the location of the tension crack on the floodplain is indirectly determined via calculation or arbitrary specification of the tension crack depth. Furthermore, accurate determination of tension crack location is essential to the calculation of the geometry of riverbank failure blocks and hence prediction of land loss and bank sediment yield associated with riverbank instability and channel widening. In this paper, a rational, physically based method to predict the location of tension cracks on the floodplain behind the eroding bank face is presented and tested. A case study is used to illustrate the computational procedure required to apply the model. Improved estimates of failure block geometry using the new method may potentially be applied to improve predictions of bank retreat and floodplain land loss along river channels destabilized as a result of environmental change.     

长江三峡地区经济开发条件分析

长江三峡地区区域地理位置重要，区位优势明显，开发意义重大；区内农业、水能、矿产和旅游等优势自然资源丰富，组合配置良好，开发潜力巨大；区域经济开发的交通、能源、出入通道等基础条件已基本具备。     

三峡地区水资源评价

在大量水文资料统计分析的基础上，对三峡地区主要水文要素的时空分布及变化特征、分区水资源的评价和开发利用条件进行了系统分析，可为三峡工程建设提供该地区社会经济发展的科学依据和基本的水文水资源数据。     

试论地震台站监测、科研、预报三结合

本文论述在新形势下地震台站体制、任务改革的必要性与可行性，认为地震台实行地震监测、科研、预报三结合和将单一观测型台站转化成观测－－科研型台站系我国地震台站的发展方向。文中结合牡丹江等地震台的实践对三结合地震台站建设的实施办法和管理体制进行了讨论。     

点源两层大地三维地电模型视电阻率边界元解

本文用两层均匀大地人工点源作用下的空间电位分布作为基本解，导出了下伏基岩中陷含三维地质体情况下，关于电位的边界积分方程组，用边界单元法解积分方程求得地表电位，从而求得了一定装置下的视电阻率。本文方法的独特优点是积分只须在异常体边界面上进行了测线可以沿任意方向。用联剖法计算了均匀半空间下含球形异常体的ρｓ曲线，所得结果与其他学者用解析方法所求得的结果一致。用中间梯度法计算下层基岩中含有一长方体，测线     

Equilibrium bank geometry and the width of shallow sandbed streams

Cross-sections of 16 straight sandbed streams in Minnesota, Iowa, and Nebraska were surveyed. Two stratigraphic horizons were found in the banks at each site, an upper cohesive unit usually composed of silt and clay and a lower unit composed of sand. Bank erosion on these rivers occurs when the upper cohesive unit is undercut by scour at bends. The overhanging cohesive block fails by beam or cantilever failure. As upper bank failure is a direct result of undercutting, the stability and rate of retreat of the bank are largely determined by erosion of the sandy part of the bank. The cohesive layer has little influence on bank retreat and width adjustment on the rivers studied here. A quantitative lateral sediment transport model developed by Parker (1978a) is used to calculate the steady-state geometry of the sandy part of the bank. Results are obtained for the shape, length, and height of the sandy part of the bank. The model predicts the length of the bank fairly well, and the theoretical equation for the height of the bank is of the correct form. The model, however, overestimates the slope of the bank. The height of the sandy part of the bank (D_b) is approximately equal to the depth of the mean annual flow. Since D_b is determined by the lateral sediment transport model, the width (W) may be obtained from the equation of continuity (Q = WD_bV), published flow (Q) data, and a resistance equation for the mean velocity, V. The calculated widths are similar to those measured in the field.     

长江三峡狮子口地区重力滑动构造研究

长江三峡工程坝址西南约１０ｋｍ的狮子口地区，发育一个长约８ｋｍ、宽约３ｋｍ的重力滑动构造系统。它由下伏系统、滑动系统和前缘推挤带构成，是一个典型的多层次滑褶型重力滑动构造。它形成时的温、压条件为１３０．５～１９３．７℃和１８０～２３０ＭＰａ；ｌ；形成深度约５～１０ｋｍ；总体岩层收缩量３２．２％；总滑移距离１０６０ｍ；活动时间上限１２７．６５士３８．２９万年。它是燕山运动期间南北向挤压体制下，在黄陵背斜东、西两侧应力屏蔽区内派生的近东西向拉伸构造应力场的产物。     

新疆钻孔应变异常特征及其与地震三要素关系研究

将新疆高精度钻孔应变仪１０年来观测到的应变异常划分为趋势异常、短期异常、临震异常三类，并对这三种异常的特征进行了分析总结．认为，地震三要素与应变异常参量关系密切，震级与异常量级、震中距有着确定性关系。     

三维地理信息数据在移动通信网络规划和优化系统中的应用

随着移动通信的迅猛发展,网络规模不断扩大,借助数字地图,尤其是三维地理信息数据进行网络规划和优化已变得越来越重要。本文主要介绍三维地理信息数据在建立移动通信网络规划和优化系统中的应用。     

Prediction of surface horizontal displacements, and gravity and tilt changes caused by filling the Three Gorges Reservoir

 Horizontal displacements, and gravity and tilt changes induced by filling the Three Gorges Reservoir are modeled using elastic loading Green functions. When the water surface reaches its highest level, the effects become maximum on the reservoir banks. The longitudinal and latitudinal components of the horizontal displacements reach −8.2 and 7.7 mm respectively, gravity is increased by up to 3.4 mGal, and the prime vertical and meridian components of the tilt changes are −7.8 and −17.5 arcseconds respectively. Accordingly, the filling of the reservoir will influence values observed from global positioning system (GPS), gravimetry and tilt measurements in the area. The results given can be used to provide important corrections for extracting earthquake-related signals from observed data. Received: 19 January 2001 / Accepted: 3 September 2001