苏南太湖流域地下水过度开采引起的地面沉降及其防治对策

因地下水过量开采而引起的地面沉降是重要的地质灾害和生态环境问题,据最新统计资料,全国96个城市或地区发生了不同程度的地面沉降。苏南太湖流域由于城镇用水和工业用水的迅速增加,大量开采地下水,导致区域内出现了5000km^2的地区地面沉降,有些地区累计沉降量超过2．0m。地面沉降已经影响到区域的供水安全和生态安全,增加了基础设施建设成本,加快区域供水步伐,调整工业结构,加强水资源综合规划和管理是防治地面沉降的重要措施。     

淀山湖水环境质量评价及污染防治研究

从淀山湖环境研究入手。全面考察湖区点源和非点源污染物的分布及其对湖泊的输入,分析湖内污染物的动态变化,采用模糊矩阵复合运算方法对水质进行综合评价,并建立水质污染预测模型,进行水质污染趋势分析。最后,提出了淀山湖水污染防治的对策和措施。     

中国蒙新高原湖区水环境主要问题及控制对策

实施“西部大开发”战略的重大决策,对于平衡中国各区域间的发展位差以及提高整个国家的经济实力具有重要的战略意义.而西部脆弱的生态环境决定了西部大开发中要以生态保护优先的环境保护政策为切入点和立足点,坚持经济大开发与可持续发展有机结合.本文系统地阐述了中国蒙新湖区在气候变化和人类活动的影响下水环境的主要问题及控制对策,并以...     

Effect of combining biogeotextile and vegetation cover on the protection of steep slope of highway in northern China: A runoff plot experiment

Biogeotextiles can be used to facilitate the formation of vegetation cover and to reduce soil erosion.Studies have demonstrated that only biogeotextile or vegetation cover can greatly reduce soil erosion.However, information about the effects of the combination of biogeotextile and vegetation cover on soil erosion is still limited, despite that the combination is the commonly practical form for bare road slope protection. Experimental plots, consisting of a relatively loose surface layer and a c...     

第三次全国国土调查质量控制技术探讨

如何做好第三次全国国土调查(以下简称"三调")的质量控制,保证三调数据成果质量,成为该项工作能否圆满完成的关键所在.笔者根据从事三调工作积累的经验,介绍了实施三调工作的技术路线,提出了市县级"五位一体"的三调质量控制流程,并详细阐述了三调工作全过程质量控制的检查要点和方法.从基础层面保障三调质量管理工作有序高效,确保三...     

海图出版质量检测系统的设计与实现

从目前海图出版的实际出发,分析了数字环境下海图生产质量控制需要解决的具体问题,以用户为最终目标设计,阐述了海图出版质量检测系统的总体结构和实现的技术思路。     

基于扩展关系模型的整体空间数据管理

空间数据模型和数据管理是地理信息系统 (GIS)最重要的研究领域之一。该文介绍一体化的数据模型———扩展关系模型和以此为基础的 ,由作者设计的GIS软件原型系统———GEODBMS。GEODBMS使用统一的数据库管理系统 (DBMS)同时管理图形和属性数据 ;使用改进的四叉树———交叠四叉树索引空间目标 ;使用扩展的SQL语言进行空间查询 ;使用数据恢复和并发控制方法来加强分布式环境下数据的安全性和一致性维护     

Feedback–feedforward control of offshore platforms under random waves

This study investigates the control of jacket‐type offshore platforms. The deck displacement of jacket‐type offshore platforms can be controlled using both passive and active control mechanisms. Among the passive control mechanisms, a tuned mass damper concept is studied in this paper. Active control mechanisms considered here include the active mass damper, the active tendon mechanism and the propeller thruster. An optimal frequency domain approach to active control of wave‐excited platforms is used in which the H₂ norm of the transfer function from the external disturbance to the regulated output is minimized. In this study, the hydrodynamic drag force is evaluated using the JONSWAP wave spectrum. Unlike conventional linearization approaches, the influence of non‐linearity in the drag force is retained in this scheme by expressing the non‐linear force components in terms of higher‐order convolutions of the water‐particle velocities. To demonstrate the effectiveness of this scheme, the platform performance with and without control devices under different sea states is evaluated. It is demonstrated that the control devices are useful in reducing the displacement response of jacket‐type offshore platforms, especially when the wave forces are concentrated at frequencies close to the natural frequencies of the platform. This becomes especially significant in deep waters because the natural frequencies of jacket‐type platforms fall closer to the dominant wave frequencies in deep waters. Adding control devices to deep water platforms will ensure a reduction both in the global response of the platform and in localized effects, such as the fatigue of welded joints. Copyright © 2001 John Wiley & Sons, Ltd.     

Robust dual‐sensor data sea‐surface ghost attenuation for quality control purposes

Three‐dimensional receiver ghost attenuation (deghosting) of dual‐sensor towed‐streamer data is straightforward, in principle. In its simplest form, it requires applying a three‐dimensional frequency–wavenumber filter to the vertical component of the particle motion data to correct for the amplitude reduction on the vertical component of non‐normal incidence plane waves before combining with the pressure data. More elaborate techniques use three‐dimensional filters to both components before summation, for example, for ghost wavelet dephasing and mitigation of noise of different strengths on the individual components in optimum deghosting. The problem with all these techniques is, of course, that it is usually impossible to transform the data into the crossline wavenumber domain because of aliasing. Hence, usually, a two‐dimensional version of deghosting is applied to the data in the frequency–inline wavenumber domain. We investigate going down the “dimensionality ladder” one more step to a one‐dimensional weighted summation of the records of the collocated sensors to create an approximate deghosting procedure. We specifically consider amplitude‐balancing weights computed via a standard automatic gain control before summation, reminiscent of a diversity stack of the dual‐sensor recordings. This technique is independent of the actual streamer depth and insensitive to variations in the sea‐surface reflection coefficient. The automatic gain control weights serve two purposes: (i) to approximately correct for the geometric amplitude loss of the Z data and (ii) to mitigate noise strength variations on the two components. Here, Z denotes the vertical component of the velocity of particle motion scaled by the seismic impedance of the near‐sensor water volume. The weights are time‐varying and can also be made frequency‐band dependent, adapting better to frequency variations of the noise. The investigated process is a very robust, almost fully hands‐off, approximate three‐dimensional deghosting step for dual‐sensor data, requiring no spatial filtering and no explicit estimates of noise power. We argue that this technique performs well in terms of ghost attenuation (albeit, not exact ghost removal) and balancing the signal‐to‐noise ratio in the output data. For instances where full three‐dimensional receiver deghosting is the final product, the proposed technique is appropriate for efficient quality control of the data acquired and in aiding the parameterisation of the subsequent deghosting processing.     

Limnology of the neotropical high elevation shallow lake Yahuarcocha (Ecuador) and challenges for managing eutrophication using biomanipulation

Temperate and tropical shallow lakes differ in several fundamental aspects with respect to management of eutrophication. High altitude tropical shallow lakes are a special case, showing similarities with temperate and tropical lakes. We studied the ecology of the eutrophic high-altitude tropical lake Yahuarcocha in the Ecuadorian Andes and evaluated the potential of biomanipulation to control eutrophication. With a toxin-producing Cylindrospermopsis bloom, low Secchi depth and low submerged macrophyte cover, Yahuarcocha is clearly in a turbid ecosystem state. Relatively low nutrient concentrations should theoretically allow for a shift to a clear water state through biomanipulation. Top-down control of phytoplankton by zooplankton, however, is complicated by the (1) absence of predatory fish, (2) fish community dominated by small poecelid species, (3) lack of a refuge for zooplankton from fish predation within the macrophytes, and (4) persistent, grazing resistant bloom of the cyanobacterium Cylindrospermopsis. In these aspects, lake Yahuarcocha is more similar to tropical shallow lakes, probably because water temperature is high relative to the mean air temperature and because of the absence of a cold season. The fish and macrophyte communities consisted almost entirely of exotic species. The exotic fish species probably stabilized the turbid state in the lake.