Flood risk index in data-scarce river basins using the AHP and GIS approach

Natural Hazards - The flood risk assessment study is an important factor in order to identify the critical or high-risk zone areas. This research intends to develop a flood risk index map of...     

Uncertainty quantification of overpressure buildup through inverse modeling of compaction processes in sedimentary basins

This study illustrates a procedure conducive to a preliminary risk analysis of overpressure development in sedimentary basins characterized by alternating depositional events of sandstone and shale layers. The approach rests on two key elements: (1) forward modeling of fluid flow and compaction, and (2) application of a model-complexity reduction technique based on a generalized polynomial chaos expansion (gPCE). The forward model considers a one-dimensional vertical compaction processes. The gPCE model is then used in an inverse modeling context to obtain efficient model parameter estimation and uncertainty quantification. The methodology is applied to two field settings considered in previous literature works, i.e. the Venture Field (Scotian Shelf, Canada) and the Navarin Basin (Bering Sea, Alaska, USA), relying on available porosity and pressure information for model calibration. It is found that the best result is obtained when porosity and pressure data are considered jointly in the model calibration procedure. Uncertainty propagation from unknown input parameters to model outputs, such as pore pressure vertical distribution, is investigated and quantified. This modeling strategy enables one to quantify the relative importance of key phenomena governing the feedback between sediment compaction and fluid flow processes and driving the buildup of fluid overpressure in stratified sedimentary basins characterized by the presence of low-permeability layers. The results here illustrated (1) allow for diagnosis of the critical role played by the parameters of quantitative formulations linking porosity and permeability in compacted shales and (2) provide an explicit and detailed quantification of the effects of their uncertainty in field settings.     

中国西北内陆盆地水分垂直循环及其生态学意义

中国西北内陆盆地中的地下水系统,对维系其浅表水分、热量、盐分均衡以及地表的生态平衡、土壤的资源属性和局部地域气候相对稳定性具有不可或缺的调节作用,这种调节作用是通过饱和带水、包气带水(土壤水)、近地表大汽水和植物体内水("四水")之间的垂直循环来实现的.目前的相关研究主要侧重于地下水与地表植被类型间对应关系的统计分析,较少涉及水分运移的机制;而以水分垂直循环的动力学机制为研究对象的SPAC系统(土壤-植物-大气连续体),则对地下水的重视程度不够,且存在着尺度转换的困难,更为完整的应该是GSPAC系统(地下水-土壤-植物-大气连续体).干旱区内陆盆地地下水生态效应的研究需要开展以下的工作:"四水"垂直循环的动力学过程与机制研究,尤其是饱水带-包气带界面水、汽、热转化过程的研究;人类活动影响下地下水系统演化特征的研究,它不仅是实现水分垂直循环研究的最终目的——水资源合理开发利用的中间环节,更是将"四水"垂直循环这一微观水文循环过程与区域水文循环过程相结合,实现尺度转化的关键所在.     

中国北方盆地大规模铀成矿作用：地层篇

“红黑”耦合沉积建造是中国北方中—新生代盆地（简称北方盆地）砂岩型铀矿的重要控矿要素之一,在勘查实践中得到了广泛证实和应用,指导发现找矿靶区和矿产地300余处,在成矿理论方面取得重要进展。本文系统总结了北方产铀盆地的60万余米铀矿岩芯钻探成果,通过典型矿床赋矿层沉积学、地球化学等对比研究,系统分析了北方盆地侏罗系、白垩系、新近系等赋矿层形成的沉积环境、物质组成等,进一步明确了制约成矿流体运移、铀矿物沉淀的赋矿层条件。结果显示：① 北方盆地自侏罗纪以来,发育了Ⅰ中侏罗世—晚侏罗世早期（Bathonian- Oxfordian）、Ⅱ早白垩世早期（Valanginian）、Ⅲ早白垩世晚期（Aptian）、Ⅳ晚白垩世早期（Cenomanian）、Ⅴ晚白垩世晚期—早古近纪（Campanian- Thanetian）、Ⅵ早新近纪（Aquitanian- Burdigalian）和Ⅶ晚新近纪（Zanclean- Piacenzian）7期红层,与下伏富还原性组分的黑色层构成了典型的对偶沉积建造,为北方盆地大规模成矿奠定了赋矿层基础。② 地球化学指标显示：红层中Fe2+/Fe3+比值介于0. 29~1. 47（n=78）,黑层Fe2+/Fe3+比值介于0. 57~53. 96（n=223）,赋矿层Fe2+/Fe3+比值介于1. 00~26. 45（n=52）。赋矿层、黑层Fe2+/Fe3+比值一般大于1,以发育黄铁矿、炭屑、油斑为特征,为相对较还原的环境。红层Fe2+/Fe3+比值一般小于1,以发育钙质结核为特征,为相对较强氧化的环境。③ 总有机碳含量显示红层为0~0. 16%（n=107）,含矿层为0. 01%~2. 65%（n=137）,黑层为0. 01%~2. 66%（n=339）,含矿层总有机碳含量略低于黑层,与铀矿的富集沉淀有密切关系。④ 砂岩型铀矿体呈“板状”或“楔状”产出于黑层顶部的灰色、灰绿色砂岩和细砂岩,甚至泥岩,红层为含氧含铀流体的运移通道,黑层为含氧含铀流体的富集沉淀的化学屏障。因此,北方盆地红层和黑层对偶沉积、旋回充填是大规模铀成矿必要的地层条件,这些认识打破常规思维,“红黑”旋回叠加导致了北方盆地多层成矿的现象,矿体一般呈板状就位于红层和黑层的过渡带,这对深入理解砂岩型铀矿成矿环境、成矿规律及成矿机理等工作和勘查工作部署具有重要实践意义。     

Catchment scale spatial variability of soil salt content in agricultural oasis,Northwest China

Soil salinization is a serious environmental problem in the world, especially in arid and semi-arid regions. Therefore, estimating spatial variability of soil salinity plays an important role in environmental sciences. Aiming at the problem of soil salinization inside an oasis, a case study was carried out at the Sangong River catchment in Xinjiang province, northwest China. Methods of classical statistics, geostatistics, remote sensing (RS) and geographic information system (GIS) were applied to estimate the spatial variability of soil salt content in the topsoil (0–20 cm) and its relationship with landscape structure at catchment scale. The objective of this study was to provide a scientific basis to understand the heterogeneous of spatial distribution of soil salt content at a large scale. The results revealed that (1) elevation of landform was a key factor for soil salt content’s spatial variability, and soil salt content had a strong spatial autocorrelation, which was mainly induced by structural factors. (2) Mapping of soil salt content by Kriging and comparing it with landscape maps showed that area of soil salinization in old oasis was smaller than that in new oasis, and degree of soil salinization in old oasis was also lower than that in the new one. Among all landscapes, cropland was mostly affected by salinity, with 38.8% of the cropland in new oasis moderately affected by soil salinity, and 8.54% in old oasis.     

Effect of different soil data on hydrological process modeling in Weihe River basin of Northwest China

Hydrological process modeling depends on the soil data spatial resolution of the watershed. Especially, in a large-scale watershed, could a higher resolution of soil data contribute to a more accurate result? In this study, two soil datasets with different classification systems FAO (World Reference Base) and GSCC (the Genetic Soil Classification of China) were used as inputs for the SWAT model to study the effects of soil datasets on hydrological process modeling in Weihe River basin, China. Results show that the discharge simulated using FAO soil data was better than one simulated using GSCC soil data before model calibration, which indicates that FAO soil data needed less effort to calibrate. After model calibration, discharges were simulated better by both of FAO and GSCC soil data but statistical parameters demonstrate that we can make a relatively more accurate estimation of discharge using the GSCC rather than FAO soil data. Soil water content (SW) simulated using GSCC soil data was statistically significantly higher than those simulated using FAO soil data. However, variations in other hydrological components (surface runoff (SURQ), actual evapotranspiration (ET), and water yield (WYLD) were not statistically significant. This might be because SW is more sensitive to soil properties. For studies aiming to simulate or compare SW, merely calibrating and validating models using river discharge observations is not enough. The hydrological modelers need to identify the key hydrological components intrinsic to their study and weigh the advantages and disadvantages before selecting suitable soil data.     

黑河高山草甸冻土带水热传输过程

以黑河源区高山草甸冻土带的基本气象参数、植被参数和土壤水热性质参数为输入条件,利用CoupModel模型计算了试验点两个完整年度日尺度上的各种基本水热状况,计算结果较符合实测值(7层地温和土壤液态含水量平均R2分别为0.95和0.83).利用模型输出的土壤热通量和土壤水迁移分析了试验点季节性冻土区的水热传输过程:在土壤层开始冻结期,下层土壤液态水向冻结锋面集结,集结期向上的地热通量急剧增加;在冻结期,土壤热传导主要与上下层的土壤温度有关,土壤水迁移基本处于零通量状态;在融化期,在融化锋面未出现液态水分集结现象,融化层土壤水热传输过程迅速改变并与非冻结土壤一致,向下的地热通量急剧增加.     

GIS morphometric indicators for the analysis of sediment dynamics in mountain basins

Watershed management and headwater reconstruction programs require a reliable knowledge of sediment dynamics. Geographical Information Systems (GIS) provide the framework for the implementation of different complex techniques for the assessment of shallow landsliding and erosion processes in mountain basins. This paper presents some morphometric indicators aimed at erosion and sediment delivery analysis. The proposed indicators can be easily derived from medium to fine resolution Digital Elevation Models (DEM). Applications conducted in Eastern Italian Alps have shown the adequateness of the proposed approach to address erosion and sediment-related problems. The analysis considered the classification of sediment source areas with regard to their activity, the comparison between drainage basins having different morphological characteristics and the topographic control on sediment transport capacity, with a particular attention to the identification of channel reaches characterised by a low sediment transport capacity.     

Application of the WRF model rainfall product for the localized flood hazard modeling in a data-scarce environment

Natural Hazards - Urban flood hazard model needs rainfall with high spatial and temporal resolutions for flood hazard analysis to better simulate flood dynamics in complex urban...     

Impact of anthropogenic and natural processes on the chemical compositions of precipitation at a rapidly urbanized city in Northwest China

In this study, the chemical composition of precipitation was applied as an indicator to study the influence of urbanization on the atmosphere in Qilian County, a northwest city in China. The results showed that the annual mean pH calculated from the concentration of H⁺ was 7.35 due to alkaline ion neutralization, and Ca²⁺ had the largest contribution. Ca²⁺ and SO₄ ^2? were the most abundant ions, accounting for 45 and 17%, respectively, of the total ion mass. The correlation coefficient between SO₄ ^2? and NO₃ ^? reaching 0.85 in the urban area indicated the same source. The highest concentration of sulfate in spring was probably related to the strong wind in Northwest China, while the concentration of nitrate was the highest in winter suggesting that most of the nitrate originated from coal combustion, not vehicle emission. The application of factor and cluster analysis indicated that 38.43% of the SO₄ ^2? and 16.97% of the NO₃ ^? in Qilian County were from crustal sources, while 61.5% of the SO₄ ^2? and 83.03% of the NO₃ ^? originated from the human activities. The back trajectory analysis indicated that the pollution emitted from the surrounding areas also made a great contribution to the local atmospheric quality. Thus the communication and cooperation mechanisms with surrounding cities and improvement of energy consumption efficiency should be strengthened in the next few years.     

Designs of medium scale hazard maps of mountain slopes in Japan

Conclusion The ultimate hill-slope hazard map may be a map showing the degree of hazard risk of each geomorphic units, but no such a quadangle sheet has been drawn yet. For the present, the exact distribution of the concave type hillslope, that is the slope of landslide or of talus, is still important for a practical use. And so, how to express the slope topography clearly is the first problem in making the medium scale geomorphic hazard sheet and then how to draw rapidly is the second. Some part of the two problems are solved by the computer mapping method using the finer degital elevation model.     

中国西北地区的生态足迹

可持续发展指标体系的研究是可持续发展研究领域的一个重点问题 .在介绍生态足迹理论的基础上 ,应用中国西北五省区的截面统计资料对该区域 1999年的发展状况进行了评价 .结果发现 ,陕、甘、宁、青、新的生态足迹都呈现赤字 (分别为 0 .1119、0 .3995、0 .42 42、0 .0 6 1、0 .886 3hm2 ·人 -1) ,这表明我国西北五省区的消费模式是不可持续的 ;还发现各省区的人均生态足迹需求的GDP产出系数呈现出陕 >宁 >青 >甘 >新 ,这反映出五省区的资源消耗产出效率的差异 .最后对生态足迹理论尚待进一步深入研究的几个方面进行了简要的评述 .     

西北某放射性废物处置预选区地下水水化学特征及地球化学模拟

在放射性废物处置库的选址过程中,地下水水化学特征是最重要的因素之一。为了查明西北某放射性废物处置预选区地下水水化学特征及其演化机制,对该区地下水水样进行了水质测试,综合运用Piper三线图法、相关性分析、饱和指数模拟和质量平衡反应模拟,全面分析了该预选区地下水水化学类型的空间分布和地下水水演化的主要水文化学过程。结果表明:研究区地下水在北部山区接受补给,并向南运移,地下水类型随径流由SO4.Cl—Na型转变为Cl.SO4—Na型。地下水在径流过程中主要经历了溶滤作用、蒸发浓缩作用和阳离子交换作用等水文化学过程,它们是控制该区地下水水化学组分演化的关键。     

西北地区水资源再生利用研究

水资源是西北地区社会经济发展和生态环境建设的重要制约因素,水资源的高效利用是推进西北地区发展过程中必须解决的问题。文章根据西北地区水资源短缺的现状,分析该地区水资源的特点及其利用中存在的主要问题,并以西安为研究案例,提出西北地区水资源再生利用的途径。     

西北地区生态环境需水估算的几个问题研讨

西北地区生态环境需水研究是生态环境建设的重要基础。但是,目前区域生态需水研究仍处在初期阶段,面临许多问题与挑战。研讨了西北地区生态环境需水估算的几个问题,目的是为西北地区水资源合理配置、生态环境建设和可持续发展问题研究,探讨一些基本的研究思路和方法论。     

Helium isotope compositions in sedimentary basins in China

The abundance and isotopic composition of He have been determined for a variety of natural gases (oil-field gases) in sedimentary basins in the continent of China. The³He/⁴He and⁴He/²⁰Ne ratios range from 0.004 to 4.99 Ra (where Ra denotes atmospheric³He/⁴He ratio = 1.4 × 10⁻⁶), and from 100-39,000, respectively. Helium in the gas sample is composed of mantle-derived He and crustal radiogenic He.The high³He/⁴He ratios were observed in the sedimentary basins which underwent Cenozoic extension in the eastern domain, such as the Songliao, Liaohe, North China, Subei, Sanshui and South China Sea basins. The basins where mantle-derived He is recognized are characterized by the presence of surface and subsurface volcanic rocks, high terrestrial heat flow, deep faults and thinned crust. On the other hand, regions which underwent pre-Tertiary extension such as the Jungar, Tarim, Tuba, Caidam and Yumen basins in the NW and tectonic loading such as the Ordos and Sichuan basins in the central domain are marked by almost pure radiogenic⁴He of crustal origin and thus by an apparent absence of mantle-derived He, which coincides with complete lack of Cenozoic volcanics, low terrestrial heat flow and thickened crust. Such a³He/⁴He distribution pattern clearly indicates that tectonic environment control the distribution of He isotopes in the continent of China.     

山区河流平面二维流场的数值模拟

针对山区河流边界地形复杂、水位及流速变化剧烈的特点,用"混合五对角法"建立平面二维数学模型并求解,进行水位和流速的数值模拟.利用嘉陵江重庆金刚碑-朝阳桥河段地形及5个横断面的水位和水深平均流速资料对此模型进行了验证,模型快速、准确地再现了该河段的水位和水深平均流速情况.     

Finite-element method in modeling geologic transport processes

Deterministic mathematical modeling of complex geologic transport processes may require the use of odd boundary shapes, time dependency, and two or three dimensions. Under these circumstances the governing transport equations must be solved by numerical methods. For a number of transport phenomena a general form of the convective-dispersion equation can be employed. The solution of this equation for complicated problems can be solved readily by the finite-element method. Using quadrilateral isoparametric elements or triangular elements and a computational algorithm based on Galerkin's procedure, solutions to unsteady heat flux from a dike and seawater intrusion in an aquifer have been obtained. These examples illustrate that the finite-element numerical procedure is well suited for solving boundary-value problems resulting from modeling of complex physical phenomena.