Regional hydrologic mapping of flows in stream networks

River low flow (LF) is an important hydrological characteristic used in management of the quantity and quality of water resources. A common way to transpose at-station low flow quantiles to ungaged locations involves development of regional multivariate regression models. In site selection studies of water control facilities, need arises to automate the mapping of LF characteristics onto the stream network in a continuous manner. This would allow estimation of LF at any desired ungaged location. A mapping algorithm is introduced that determines the value of regression model's independent variables (input components) over the drainage area of each stream pixel and calculates the flow (output). The mapping algorithm relies mainly on the digital elevation model (DEM) and its derivatives, such as flow direction and flow accumulation. Furthermore, the contribution of each independent variable of the regional model to the total flow may be plotted to represent the flow profiles along the streams. A case study involving LF mapping in rivers of Gilan province, Iran, where LF quantiles are required for issuing water withdrawal permits as well as maintaining water quality standards, is also described in the paper. Overall, the maps and profiles of flow statistics in the region of interest provide convenient visualization and assessment tools for water resource and environmental engineers. The transposition algorithm may also be applied in regional mapping of other flow characteristics such as flood or average flows.     

若尔盖与西秦岭地震反射岩石圈结构和盆山耦合

松潘地块北缘的若尔盖盆地与西秦岭造山带相接触,构成青藏高原东北缘典型的新生代盆山构造.其岩石圈结构与深部构造关系,记录了青藏高原东北缘板块碰撞的深部过程,同时又关联着若尔盖盆地油气远景的评价.2004年秋冬季,我们完成了第一条跨越若尔盖盆地和西秦岭造山带的深地震反射剖面.整个剖面全长254 km,分5段完成,其中第2段剖面（简称SP04_2）横过盆山结合部位.SP04_2剖面首次揭示若尔盖盆地－西秦岭造山带盆山结合部位的岩石圈结构,发现了若尔盖盆地和西秦岭造山带下地壳均以北倾为主的强反射特征,提供出若尔盖盆地下地壳整体向西秦岭造山带俯冲的地震学证据,揭示了若尔盖盆地和西秦岭造山带在挤压构造体系下形成的深部构造关系.而近于平的Moho反射特征又反映出两者在造山后期经历了强烈的伸展作用.     

洱源-江川宽角地震剖面的地壳反射特征

通过对洱源-江川宽角反射地震资料的叠前偏移处理成像,得到了一个类似于近垂直入射多道地震数据的记录剖面.反射剖面图像与地壳速度结构共同揭示出地壳厚度由剖面西北端(约45 km)向东南端(约40 km)减薄.在洱源-楚雄西北附近深度约10 km处存在一组向东南倾斜的强反射震相,其东南约50 km处存在向西北倾斜的强射震相.易门断裂两侧地壳反射属性具有明显的差异,易门断裂之西北方向深度25～40 km处,中下地壳内存在两组强振幅,向东南方向上倾的地震反射同相轴,并被楚雄-建水断裂后期所错断,易门断裂之东南方向上,地壳内反射较为均一,未见特别明显的强间断面反射信息,这个反射结构被解释为印度板块东向俯冲与藏东缘地壳物质东向逃逸综合作用导致下地壳增厚和厚地壳变形的结果.     

天津地区典型土壤剖面饱和烃分布特征及环境意义

分析了天津地区不同环境功能区7 条土壤剖面中饱和烃含量、组成及部分地球化学参数 的变化规律, 比较了不同土壤剖面饱和烃在纵向上的变化特征。结果表明, 市区( 南开区) 及近郊 区( 武清区, 北辰区和宁河县交界处) 表层土饱和烃含量最高, 其他剖面含量较低; 随深度增大, 饱 和烃含量均有所降低, 但不同剖面变化幅度不同, 表层含量较高的剖面随深度增大, 饱和烃含量 降低幅度较大, 反之则较小。根据部分典型地球化学参数的纵向变化特征, 推测表层土壤饱和烃 主要为石油源和植物源的混合源, 且市区和郊区主要受石油源控制。不同土壤剖面表层土污染源 存在差别。同一剖面表层土壤( <30cm) 不同层次的样品的饱和烃污染源较为接近; 剖面深部( > 30cm) 不同层次样品中正构烷烃不同于表层, 且成因复杂, 既受来源于土壤中有机质降解产物的 影响, 又受表层土中饱和烃纵向迁移作用的影响。对于甾、萜类化合物, 表层土壤中饱和烃含量较 高的剖面, 深层土壤受表层土壤甾、萜类污染物迁移作用的影响; 表层土壤中饱和烃含量较低的 剖面, 深层土壤受表层土壤甾、萜类污染物影响较小。     

土壤剖面的磁学特征及其对交通污染的指示意义——以北京首都机场高速公路为例

对北京首都机场高速公路旁采集的土壤柱状T01剖面的磁学参数和金属元素分析,探讨了研究区内现代交通导致的土壤磁学性质的变化及其对环境污染的响应.结果表明,磁参数(χ,ARM和SIRM)与重金属含量呈同步垂向变化趋势.来源于交通运输排放的污染物是土壤剖面上部(0～8 cm)磁性和金属含量增强的主要原因,8cm以下,土壤基本未受到污染,磁性矿物和重金属含量较低,磁性颗粒变化稳定,基本代表了该地区土壤的自然背景.尽管土壤岩石磁学分析表明剖面上下部受污染和未受污染样品的磁载体均是粒度较粗的多畴磁铁矿,但是结合磁参数比值曲线,说明底部样品的磁颗粒的粒度较顶部偏细.磁性矿物的含量变化没有影响磁颗粒的粒度特征.指标聚类等相关分析表明,土壤磁参数(χ,ARM和SIRM)与重金属元素(Pb,Zn和Cu)含量显著相关;结合模糊聚类分析,磁参数可用于追踪、识别交通污染物质在土壤剖面中的富集、迁移状态,揭示不同深度土壤的污染程度.     

FY-4A数据在2021年1月6—8日寒潮监测中应用

基于静止气象卫星图像解译理论和位涡理论,应用FY-4A水汽图像、干涉式大气垂直探测仪（GIIRS）产品和欧洲中心第五代大气再分析资料（ERA5）对2021年1月6—8日我国中东部地区寒潮天气进行分析。结果表明：高空冷涡和地面冷高压是影响此次寒潮天气的主要影响系统,冷空气5日08:00从贝加尔湖南部向东、向南加强发展,8日20:00 减弱;对比FY-4A/GIIRS与ERA5 850 hPa 24 h变温数据发现：两种数据反映的对流层低层冷空气东移南下特征和正负变温区域分布特征基本一致,FY-4A/GIIRS 850 hPa 24 h负变温中心和0℃等变温线的位置与ERA5数据接近,FY-4A/GIIRS 850 hPa 24 h变温中心值强度略大于ERA5。水汽图像暗区变暗附近的高层位涡的增加激发高层气旋性环流后侧下沉运动增强,干空气下沉造成了地面高压增强;500 hPa冷涡中心附近绝对涡度增加是引起冷空气增强的原因之一;冷空气急剧增强时段,中低层位涡的加大引起地面冷空气堆积,寒潮增强。FY-4A/GIIRS温度产品反映的冷空气移动特征与位涡理论对冷空气增强原因分析结果一致,说明应用FY-4A/GIIRS温度产品能够有效监测分析寒潮冷空气演变特征。     

Engineering characteristics and uses of duricrusts in Australia

The uses and shortcomings of duricrusts (ferricrete, calcrete and silcrete) in engineering construction (as used for road‐base, aggregate, foundation materials and aquifers) are reviewed. Australian production of these materials represents about one‐third of all unprocessed road‐base and they are especially important as pavement courses for lightly trafficked, low‐cost rural and outback roads. However, duricrusts are regarded as marginal materials at best because of their typically poor grading, particle unsoundness, high fines plasticity, and absorption of water and bitumen. These materials are used because they are available locally in areas that are otherwise lacking in hard rock materials, such as deeply weathered and sedimentary rock terrains. The weathering profiles of which they form part are characterized by high permeability (despite being clay‐rich), variable cementation, low compressibility and a tendency to become weaker with depth. Although the more indurated layers are unrippable, they are also difficult to blast. Pedogenic (nodular) duricrusts were formerly sought for natural road‐base, because they occur widely and require only rudimentary processing. However, well‐cemented groundwater (vadose) duricrusts are now the preferred deposits, even though they require crushing and screening. Ferricrete is the most widely exploited of the duricrusts for engineering purposes, especially in northern and southwestern Australia, although calcrete is important in South Australia and in the Murray Basin. Silcrete is only a minor source of aggregate and road‐base, mainly in western Queensland.     

Anticipating the effects of groundwater withdrawal on seawater intrusion and soil settlement in urban coastal areas

Intensive pumping in urban coastal areas is a common threat to water resource quality due to seawater intrusion. In those areas where subsurface water resources are not usually used for human consumption or irrigation, intensive pumping is associated with other activities like the lowering of the water table necessary to support underground structures and building foundations. This activity also increases the likelihood of soil settlement that affects building stability and the corrosion of concrete structures due to groundwater salinity. Under these circumstances, the awareness of a certain municipality (Calonge, NE Spain) of the potential effects of groundwater withdrawal upon foundations has led to an integrated approach to anticipate seawater intrusion related to urban development. Geological mapping and correlation of borehole logs, electrical resistivity tomography, and hydrochemical data provide comprehensive knowledge of the geology and hydrogeology of the area and act as screening tools necessary to discern the influence of hydrological processes in coastal areas. Developing Strack's analytical solution, new comprehensive, dimensionless expressions are herein derived to determine the critical pumping rate necessary to prevent seawater intrusion, as well as to reproduce the evolution of the wedge toe and the water table stagnation point under different withdrawal rates. Furthermore, the Dupuit–Forchheimer well discharge formula allows the estimation of the effects of the water table lowering due to such critical pumping in the surrounding building foundations. Field data from the Calonge coastal plain illustrate this approach and provide assessment criteria for future urban development and planning. Copyright © 2012 John Wiley & Sons, Ltd.     

Modelling combined open channel flow by artificial neural networks

Combined open channel flow is encountered in many hydraulic engineering structures and processes, such as irrigation ditches and wastewater treatment facilities. Extensive experimental studies have conducted to investigate combined flow characteristics. Nevertheless, there is no simple relationship that can fully describe the velocity profiles in a turbulent flow. The artificial neural network (ANN) has great computational capability for solving various complex problems, such as function approximation. The main objective of this study is to evaluate the applicability of the ANN for simulating velocity profiles, velocity contours and estimating the discharges accordingly. The velocity profiles measured by an acoustic doppler velocimeter in the open channel of the Chihtan purification plant, Taipei, with different discharges at fixed measuring section and different depths are presented. The total number of data sets is 640 and the data sets are split into two subsets, i.e. training and validation sets. The backpropagation algorithm is used to construct the neural network. The results demonstrate that the velocity profiles can be modelled by the ANN, and the ANN constructed can nicely fit the velocity profiles and can precisely predict the discharges for the conditions investigated. Copyright © 2005 John Wiley & Sons, Ltd.     

Rate and historical change of direct recharge from precipitation constrained by unsaturated zone profiles of chloride and oxygen‐18 in dry river bed of North China Plain

Quantifying of direct recharge derived from precipitation is crucial for assessing sustainability of well‐irrigated agriculture. In the North China Plain, the land use is dominated by groundwater‐irrigated farmland where the direct recharge derived from precipitation and irrigation. To characterize the mean rate and historical variance of direct recharge derived from precipitation, unsaturated zone profiles of chloride and δ¹⁸O in the dry river bed of the Beiyishui River were employed. The results show that archival time scale of the profile covers the duration from 1980 to 2002 (corresponding to depths from 5 to 2 m) which is indicated by matching the δ¹⁸O peaks in the isotope profile with the aridity indexes gained by instrumental records of annual precipitation and annual potential evaporation. Using the chloride mass balance method, the mean rate of the direct recharge corresponding to the archival time scale is estimated to be 3·8 ± 0·8 mm year^?1, which accounts for about 0·7% of the long‐term average annual precipitation. Further, the direct recharge rates vary from 2·1 to 6·8 mm year^?1 since 1980. Despite the subhumid climate, the estimate of recharge rates is in line with other findings in semiarid regions. The low rate of direct recharge is considered as a result of the relative dry climate in recent decades. In dry river bed, unsaturated zone profiles of chloride and δ¹⁸O combined with instrumental records could offer valuable information about the direct recharge derived from precipitation during droughts. Copyright © 2011 John Wiley & Sons, Ltd.