Reliability of recharge rates estimated from groundwater age with a simplified analytical approach

Groundwater age is often used to estimate groundwater recharge through a simplified analytical approach. This estimated recharge is thought to be representative of the mean recharge between the point of entry and the sampling point. However, given the complexity in actual recharge, whether the mean recharge is reasonable is still unclear. This study examined the validity of the method to estimate long-term average groundwater recharge and the possibility of obtaining reasonable spatial recharge pattern. We first validated our model in producing reasonable age distributions using a constant flux boundary condition. We then generated different flow fields and age patterns by using various spatially varying flux boundary conditions with different magnitudes and wavelengths. Groundwater recharge was estimated and analysed afterwards using the method at the spatial scale. We illustrated the main findings with a field example in the end. Our results suggest that we can estimate long-term average groundwater recharge with 10% error in many parts of an aquifer. The size of these areas decreases with the increase in both the amplitude and the wavelength. The chance of obtaining a reasonable groundwater recharge is higher if an age sample is collected from the middle of an aquifer and at downstream areas. Our study also indicates that the method can also be used to estimate local groundwater recharge if age samples are collected close to the water table. However, care must be taken to determine groundwater age regardless of conditions.     

Sublimation over seasonal snowpack at the southeastern edge of a desert in central Eurasia

The Gurbantonggut Desert, China, is an ideal site for study of sublimation from the snowpack because there are sparse vegetation and simple topography, and the wind speed is not large enough to blow snow into the atmosphere from the snowpack. Daily sublimation was measured by manual snow lysimeters at 8:00, and an automatic weather station was deployed at the top of a stout longitudinal dune chain at the southeastern edge of the desert. It is shown that on a daily scale, there was an extremely significant no‐intercept linear relationship between the measured sublimation and that calculated by the bulk aerodynamic method, although the former was only 83.8% of the latter. It is also demonstrated that ?10°C and 2 m/s were the thresholds where the sublimation varied with the air temperature and the wind speed. When these two thresholds were exceeded, the sublimation accelerated. However, the air temperature and the wind speed at 2 m above the ground averaged ?17.2°C and 1.3 m/s, respectively, and the percentages of the time when the air temperature was below ?10 °C and the wind speed was below 2 m/s were 76.9% and 85.1%, respectively. As a result, the rate of sublimation was quite low most of the time, and the thin snowpack remained in a quasi‐static state until the melt stage started. Copyright © 2011 John Wiley & Sons, Ltd.     

Meta‐analysis of flow modeling performances—to build a matching system between catchment complexity and model types

Hydrological models play a significant role in modelling river flow for decision making support in water resource management. In the past decades, many researchers have made a great deal of efforts in calibrating and validating various models, with each study being focused on one or two models. As a result, there is a lack of comparative analysis on the performance of those models to guide hydrologists to choose appropriate models for the individual climate and physical conditions. This paper describes a two‐level meta‐analysis to develop a matching system between catchment complexity (based on catchment significant features (CSFs)) and model types. The intention is to use the available CSF information for choosing the most suitable model type for a given catchment. In this study, the CSFs include the elements of climate, soil type, land cover and catchment scale. Specific choices of model types in small and medium catchments are further explored with all CSF information obtained. In particular, it is interesting to find that semi‐distributed models are the most suitable model type for catchments with the area over 3000 km², regardless of other CSFs. The potential methodology for expanding the matching system between catchment complexity and model complexity is discussed. Copyright © 2014 John Wiley & Sons, Ltd.     

超前帷幕注浆技术在蔡园煤矿导水断层治理中的应用

蔡园煤矿中部发育一条走向近NW向的正断层,对开采12煤层有影响,在分析断层特征及水文地质条件基础上,采用超前帷幕注浆技术对断层破碎带进行了加固,并对影响断层富水性的灰岩含水层进行了预注浆封堵,实现了对断层破碎带加固、堵水的双重效果,达到了巷道围岩加固及含水层改造的双重目的,保证了巷道的安全通过。     

内蒙古中心屯地区晚侏罗世火山岩岩石地球化学特征及其成因意义

中心屯地区位于大兴安岭火山岩带中南段,区内岩浆活动强烈,发育有中生代不同时期的基性-酸性火山岩。在野外地质调查的基础上,通过研究晚侏罗世火山岩岩石学特征及岩石化学数据,发现区内晚侏罗世火山岩主要为中性-酸性岩石,属于钙碱性系列;稀土元素大都具有铕负异常,配分曲右倾,显示轻稀土元素富集、重稀土元素亏损的特点;微量元素的过渡元素Cr、Co、Ni含量较低,富集大离子亲石元素Rb、Ba、K等,亏损大离子亲石元素Sr,亏损Nb、Th、Ti、P等高场强元素。综合分析表明,晚侏罗世火山岩岩浆来源于地壳。其形成环境处于亚洲大陆边缘断陷带,受太平洋板块俯冲作用的影响。     

Flood loss analysis and quantitative risk assessment in China

Risk assessment is a prerequisite for flood risk management. Practically, most of the decision making requires that the risks and costs of all risk mitigation options are evaluated in quantified terms. Therefore, a quantitative assessment of possible flood loss is very important, especially for emergency planning and pre-disaster preparedness. This paper presents a preliminary methodology and an operational approach for assessing the risk of flood loss to the population, crops, housing, and the economy at county level in China. The present work assesses the risk of loss for each element (people, crops, and so on) under low-, moderate-, and high-intensity flood using intensity-loss curves and loss rates based on historical flood data from 1990 to 2008. Results show that the counties with high flood risk are primarily located in North, East, Central, and South China, particularly in the lower reaches of rivers. On the other hand, the risk of most counties in the western region is generally lower than that of counties in the eastern region. However, for the entire country, the high-risk regions have both a substantial amount of rainfall and low terrain, making such regions highly prone to flooding. Moreover, these high-risk regions present both high population and wealth density.     

Multiband fitting to three long GRBs with Fermi/LAT data:structured ejecta sweeping up a density-jump medium

We present broadband (radio,optical,X-ray and GeV) fits to the afterglow light curves and spectra of three long-duration gamma-ray bursts (GRBs 080916C,090902B,and 090926A) detected by the Gamma-Ray Burst Monitor and Large Area Telescope (LAT) instruments on the Fermi satellite.Using the observed broadband data,we study the origin of the high energy emission,and suggest that the early-time GeV emission and the late-time radio,optical,and X-ray afterglows can be understood as being due to synchrotron emissio...     

长江河口近底层悬沙和沉积物的交换过程研究

大河河口的动力沉积过程一直是陆海相互作用研究的核心内容,其中水体泥沙的垂向交换是河口动力-沉积机制分析中的关键环节。基于2011年12月对长江河口及其邻近海湾采集的大范围、高密度的近底层悬沙、海床表层1~2cm(表层沉积物)和垂向向下约2~10cm的沉积物(次表层沉积物)同步3组303个样品,利用经验正交函数方法,对河口地区的悬沙和沉积物交换过程进行研究。结果表明:近底层水体悬沙的空间分布模式主要以粉砂粒级为主,空间分布差异性不大;表层及次表层沉积物的空间分布模式相似,但较近底层水体悬沙的分布复杂,存在明显的区域性特征,其中南汇边滩水域中部辐散区的沉积物表现为粗粉砂-细砂模式,其他区域由粉砂组分模式组成。近底层水体悬沙、表层和次表层沉积物的第一模态主要反映了粒径较细的泥沙运动,第二模态主要反映了粒径较粗的泥沙运动。在近底层水体悬沙与表层沉积物的垂向交换中,主要交换粒级为粉砂组分粒级。在表层沉积物与次表层沉积物的垂向交换中,南汇边滩中部辐散区的主要交换粒级为粗粉砂-细砂组分粒级,其他区域主要为粉砂组分粒级。     

条带状铁建造（BIF）的形成时代及其研究方法

对条带状铁建造（BIF）进行精确的年代学约束,具有非常重要的科学意义,可以获得BIF的时间分布趋势,反映对应时代的大气和海洋环境,准确建立与重大地质事件的对应关系,为铁建造的成因提供依据。本文在综合前人资料的基础上,重新绘制了全球BIF形成时代的分布图,结果表明BIF在3.6～1.6 Ga连续分布,在2.8～2.7 Ga、 2.5～2.4 Ga、 1.9～1.8 Ga的3个区间范围内形成高峰;Algoma型BIF主要集中于中-晚太古代,而Superior型BIF主要出现在古元古代。本文重点对前人关于BIF年代学的测试方法及其应用进行了介绍和评述,结果表明目前锆石U-Pb测年法依然为主要手段,而Sm-Nd等时线法和Re-Os等时线法尽管有效,但直接测定BIF条带的Sm-Nd等时线和磁铁矿的Re-Os等时线年龄仍存在较大问题,但可用来反映物质的来源以及后期构造热事件的改造等问题,而采取BIF相关单元的年龄来间接代表BIF的形成年龄是目前较为成熟的方法,其中测定铁建造火山岩夹层锆石U-Pb年龄是国际上测定BIF时代常用的手段。