基于ArcGIS 9.0的DEM的生成及坡度分析

介绍了利用地理信息系统软件ArcGIS 9.0来构建DEM的方法,并对生成的荆江分洪区DEM进行了坡度分析。DEM还可应用于区域规划、城镇规划和土地评估等工作中。实验证明,这种方法除了地形图的扫描外,其他过程都在ArcGIS 9.0软件中完成,不需要投入大量设备,成本低,速度快,容易更新,并可按工程的规模实时组织进行。     

A marching in space and time (MAST) solver of the shallow water equations. Part I: The 1D model

A new approach is presented for the numerical solution of the complete 1D Saint-Venant equations. At each time step, the governing system of partial differential equations (PDEs) is split, using a fractional time step methodology, into a convective prediction system and a diffusive correction system. Convective prediction system is further split into a convective prediction and a convective correction system, according to a specified approximated potential. If a scalar exact potential of the flow field exists, correction vanishes and the solution of the convective correction system is the same solution of the prediction system. Both convective prediction and correction systems are shown to have at each x − t point a single characteristic line, and a corresponding eigenvalue equal to the local velocity. A marching in space and time (MAST) technique is used for the solution of the two systems. MAST solves a system of two ordinary differential equations (ODEs) in each computational cell, using for the time discretization a self-adjusting fraction of the original time step. The computational cells are ordered and solved according to the decreasing value of the potential in the convective prediction step and to the increasing value of the same potential in the convective correction step. The diffusive correction system is solved using an implicit scheme, that leads to the solution of a large linear system, with the same order of the cell number, but sparse, symmetric and well conditioned. The numerical model shows unconditional stability with regard of the Courant–Friedrichs–Levi (CFL) number, requires no special treatment of the source terms and a computational effort almost proportional to the cell number. Several tests have been carried out and results of the proposed scheme are in good agreement with analytical solutions, as well as with experimental data.     

Distribution and geochronology of Oregon Plateau (U.S.A.) flood basalt volcanism: The Steens Basalt revisited

The timing and petrogenesis of mid-Miocene flood basalt volcanism in the northwest United States has been extensively addressed, yet the chemical characteristics and temporal details of the Steens Basalt, exposed on the Oregon Plateau, are poorly defined. Steens Basalt volcanism has generally been accepted to have occurred at ∼ 16.6 Ma, coeval and/or just prior to the onset of Columbia River Basalt Group volcanism to the north. New major and trace element analyses and nine ⁴⁰Ar/³⁹Ar ages ranging from 15.51 ± 0.28 to 16.58 ± 0.18 Ma were obtained on Oregon Plateau flood basalt lava flows from stratigraphic sections in close proximity to Steens Mountain. Additionally, new ⁴⁰Ar/³⁹Ar ages were obtained on the uppermost and thirty-first lava flow down from the top of the ∼ 1 km section of Steens Basalt exposed at Steens Mountain and yield eruption ages of 16.59 ± 0.10 and 16.55 ±0.10 Ma, respectively. Field relations between these basalt sections suggest that multiple eruptive centers were present in the vicinity of Steens Mountain.     

Sub-grid scale parameterisation of 2D hydrodynamic models of inundation in the urban area

This paper presents preliminary results from a study considering the parameterisation of coarse-grid 2D flood models to take into account sub-grid scale flow patterns occurring in the urban area. A simulation of a severe flood in an urbanized coastal floodplain is first run using a fine grid that can resolve the flow around and between buildings. Next, the same model is run again using the same underlying topography, although stripped from any buildings, and a set of 7 values of the roughness parameter (Manning’s n), all larger than (or equal to) the value used in the original run. A further set of simulations is carried out using a five-fold increased grid cell size. It is found that while it may be possible to model the overall effects of the buildings using strongly increased roughness parameter values, using a coarse grid otherwise has implications related to the loss of information about the site topography that results in flood flow routes being incorrectly modelled.     

Characteristics of Two General Circulation Patterns During Floods over the Changjiang-Huaihe River Valley

Characteristics of the atmospheric general circulation during the catastrophic floods over the Changjiang- Huaihe River Valley(CHRV)are investigated.There are two precipitation patterns over China in the CHRV flood years:the CHRV flood-whole country-wet(P1)pattern and the CHRV flood-south(north)side-dry (P2)pattern.The circulation analysis results show that there are obvious differences between the NH 500- hPa geopotential height fields of P1 and P2 precipitation patterns.The establishment of East Asia-Atlantic (EAA)correlation chain(the South China Sea(SCS)high-the Meiyu trough-the Okhotsk Sea high over East Asia)is a critical condition for excessive summer precipitation over the CHRV,while the European blocking high plays an important role in determining the precipitation pattern over China in the CHRV flood years.Besides,the relation between the EAA correlation chain and the sea surface temperature anomaly (SSTA)in the North Pacific is also studied.     

21世纪前期新疆洪旱灾害防灾减灾对策研究

洪旱灾害是我国内陆干旱区最主要的自然灾害。本文归纳总结了新疆洪旱灾害的基本特征、近期变化和形成机理;阐述了洪旱灾害近期研究动态和灾害防治的新进展,对新疆洪旱灾防治能力作了简要评估;在以人为本的科学发展观指导下,根据"治水"的新理念和新疆的实际,提出21世纪前期新疆洪旱灾害减灾对策建议。     

上海市近百年来夏季降水时空分布特征及影响因素

依据前人的研究和上海1949-2005年气象资料,研究了上海地区夏季降水特征,结果显示:上海夏季降水在时间分布上具有周期性变化,在100多年中有3个多雨湿润期和3个少雨偏干期;在空间分布上,因城市"雨岛"效应影响,城市和郊区差异明显。太阳活动周期对降水存在周期性的影响,ENSO事件对降水多寡有影响,火山爆发使降水出现1~2 a的较短的周期波动。     

洪涝统计方法探讨

利用深圳气象台1953-2005年的雨量资料,对洪涝的两种统计方法进行了对比分析,并引出了更为科学和合理的"任意连续10 d/20 d雨量统计洪涝的方法"。通过检验,该方法能够较准确地反映洪涝灾害的实际情况。     

一种基于数字伴潮海岸线的潮滩淹没区仿真算法

提出了一种基于数字伴潮海岸线（digital tide-coordinated shoreline，DTS）的潮滩淹没区仿真算法。此算法在建立数字潮滩模型和瞬时水位模型的基础上实时提取DTS。根据DTS的类型确定不连通的洼地，并快速计算其影响域，同时合理地确定潮滩与水面模型的表达方式，正确构建和显示淹没区。实验结果证明，本文算法在表达的准确性和计算的速度上明显优于传统算法。