The role of floodplains in attenuating contaminated sediment fluxes in formerly mined drainage basins

Many upland river catchments in the UK have been historically mined for metals such as lead (Pb) and zinc (Zn), and as part of the mining process large quantities of metal contaminated sediment were released into the river system. The levels of sediment associated heavy metal contamination in river systems are largely controlled by the volumes of contaminated sediment released into the river and fluvial processes (e.g. erosion and deposition). As a consequence, the contamination patterns are often highly variable, which can make it difficult to create accurate assessments of the volumes of contaminated sediment remaining within the system. This paper uses a combination of techniques to establish the volumes of metal contaminated sediment remaining within the River Swale, UK. Firstly, using detailed field sampling and a geographical information system (GIS), it estimates the volumes of sediment remaining within one formerly mined tributary (Gunnerside Beck) which is then extrapolated to represent the contaminant volumes on other tributaries of the River Swale. Secondly, combining fresh field data with a range of existing data, volumes of contaminated sediment on the main stream of the River Swale are established. This two tier approach shows that significant volumes of contaminated sediment remain within the River Swale, with over 32 000 tonnes of Pb within the mined tributaries and 123 000 tonnes within the main channel belt of the River Swale itself. This represents approximately 28% of the Pb produced in the Swale catchment. Given these volumes and present day rates of removal, it may take over 5000 years for all of the metal rich sediment to be removed from the catchment. If the contaminated sediment is used as a tracer, present day rates of reworking of floodplain sediment can be calculated to be 0·02% per year. Copyright © 2008 John Wiley & Sons, Ltd.     

Meso‐scale catchment sediment budgets: combining field surveys and modeling in the Dragonja catchment,southwest Slovenia

In this paper, we present a methodology to construct a sediment budget for meso‐scale catchments. We combine extensive field surveys and expert knowledge of the catchment with a sediment delivery model. The meso‐scale Mediterranean drainage basin of the Dragonja (91 km²), southwest Slovenia, was chosen as case study area. During the field surveys, sheet wash was observed on sloping agricultural fields during numerous rainfall events, which was found to be the main source of sediment. With the sediment yield model WATEM/SEDEM the estimated net erosion on the hillslopes 4·1 t ha^–1 y^–1 (91% of inputs). The second source, bank erosion (4·2%; 0·25 t ha^–1 y^–1) was monitored during several years with erosion pins and photogrammetric techniques. The last source, channel incision, was derived from geomorphological mapping and lichenomery and provided 3·8% (0·17 t ha^–1 y^–1) of the sediment input. The river transports its suspended sediment mainly during high‐flow events (sampled with automated water samplers). About 27% (1·2 t ha^–1 y^–1) of the sediment delivered to the channel is deposited on floodplains and low terraces downstream (estimated with geomorphological mapping, coring and cesium‐137 measurements). The sediment transported as bedload disintegrates during transport to the outlet due to the softness of the bedrock material. As a result, the river carries no bedload when it reaches the sea. The results imply a build‐up of sediment in the valleys catchment. However, extreme flood events may flush large amounts of sediment stored in the lower parts of the system. Geomorphological evidence exists in the catchment that such high magnitude, low frequency events have happened in the past. Copyright © 2009 John Wiley & Sons, Ltd.     

The effect of energy concentration of earthquake ground motions on the nonlinear response of RC structures

Usually different nonlinear time responses due to earthquake ground motion are distinguished by non-localized spectra, such as the response or power spectra. However, these spectra are often not able to explain the large discrepancy among structural responses caused by different earthquake records. The local spectrum, obtained by the wavelet transform, shows the energy distribution in the time-frequency domain, and helps to understand the very different structural responses. By changing the energy distribution in time of several earthquake records, the effect of energy concentration on the structural nonlinear response is demonstrated. This paper proposes the use of the characteristic peak ground acceleration, which is the peak of the signal constructed by only a few special wavelet components of an earthquake record, to quantify the difference between earthquake records, since this measure indicates the magnitude of the energy concentrated around the fundamental period of a structure.     

北极夏季冰面上近地层特征及热量收支问题

应用1999年8月19～24日我国第1次北极考察资料对北极夏季近地层气象要素梯度特征和冰面热量收支问题进行了讨论.北极夏季近地层相对于冰面的相对湿度很大,经常接近于饱和状态,冰温具有明显的日变化,夜间冰面附近冰温梯度较大,白天很小.在冰温垂直分布中20cm冰层温度有时可出现极大值.冰面热量收支计算表明,夜间冰面辐射冷却损失热量主要由冰层向冰面热量输送来补偿.白天冰层的热量主要来源于穿透短波辐射,冰面和以下冰层间的热量交换很低.白天冰面冰雪融化热量是不可忽视的.     

鲜水河断裂带古构造残余应力随深度分布及带中残余能量

本文介绍了测量岩体中三维区域残余应力和嵌镶残余应力及其弹性应变能密度的方法,并给出了鲜水河断裂带上的5个大口径深钻孔岩芯的具体测量结果,分析了鲜水河断裂带古构造残余应力及残余应变能密度沿深度的分布规律。结果表明,残余应力及残余弹性应变能密度均随深度的增加而增大。本文还估算了该断裂带岩体中储存的残余弹性应变能的量级。     

孟加拉湾南部冷池的极端事件及其机理初析

本研究利用多源卫星遥感数据对比分析了2018年和2015年孟加拉湾南部冷池的极端异常事件。孟加拉湾南部冷池早期出现在5月,8月和 9月强度达到最大,10月开始减弱,随后逐渐消失。数据显示2018年和2015年冷池海表温度距平值分别为-0.55 ℃和0.43 ℃,是1993—2018年26 年中冷池降温最强和最弱的年份。2018年孟加拉湾南部冷池风应力距平值为0.02 N/m2,而2015年距平值为-0.01 N/m2。2018年Ekman抽吸速度距平在冷池区域为正,2015年为负。经混合层热收支计算得到,造成冷池产生的主要原因是平流效应,且2018年与2015年的夏季（6—8月）降温平流项分别占49.2%和80.7%。冷池极端事件主要发生在6月,2018年6月冷池降温是2015年的2.76倍,并且海表净热通量项和平流项的异常对冷池极端事件的产生起了重要作用。     

测绘生产成本费用与财政预算科目的比较

介绍了国家测绘局编制的《测绘生产成本费用定额》与湖北省财政厅编制的“财政预算科目”之间的差异。通过两者的比较,阐述了如何使项目预算文本和日常业务处理规范化。这将有益于测绘项目的立项申报及管理。     

Nitrate-nitrogen isotopic patterns in surface waters of the western and central equatorial pacific

To understand the processes transporting nitrate to the surface layer of the western and central equatorial Pacific, we measured the nitrogen isotopic ratio of nitrate (δ ¹⁵NO ₃ ⁻ ), which is a very useful tracer of the source of nitrate, above 200 m depth in this region in December 1999. δ ¹⁵NO ₃ ⁻ is higher (about 13.0‰) in the surface water than in the subsurface water (where it is about 6.5‰) due to isotopic fractionation during nitrate uptake by phytoplankton. The δ ¹⁵NO ₃ ⁻ value has a roughly linear relationship with the natural logarithm of nitrate concentration (ln[NO ₃ ⁻ ]). However, for values above 150 m depth, the intercept of this linear relationship varies with position from east to west. On the other hand, the data at 200 m depth at all observation stations are concentrated around a single point (ln[NO ₃ ⁻ ] = 2.5 and δ ¹⁵NO ₃ ⁻ = 6.5‰) and do not fit the linear relationships for the shallower values. To examine the meaning of the observed distributions of δ ¹⁵NO ₃ ⁻ and nitrate concentration we developed a box model including nitrogen and nitrogen isotopic cycles. By reproducing the observed relationship between δ ¹⁵NO ₃ ⁻ and nitrate concentration using this model we found that most nitrate is transported horizontally from the eastern equatorial Pacific. We also conducted case studies and investigated the effects of differences in pathways of nitrate transport on the distributions of δ ¹⁵NO ₃ ⁻ and nitrate concentration. From these studies we concluded that the observed linear relationships between δ ¹⁵NO ₃ ⁻ and ln[NO ₃ ⁻ ], having a common slope around 6‰ but different intercepts at each station, are evidence of the significant horizontal transport of nitrate to the surface water in this area.     

基于虚拟激励法的消能减震结构随机响应分析

基于虚拟激励法推导了用于具有非比例阻尼特征的消能减震结构在随机地震激励下计算其响应功率谱的一般解答.该法避免了复模态方法的复数运算,可高效地求出响应功率谱和均方响应.算例验证分析说明该方法符合工程经验,具有很高的计算效率.     

Suspended sediment transport in the Gulf of Lions (NW Mediterranean): Impact of extreme storms and floods

In situ observations were combined with 3D modeling to gain understanding of and to quantify the suspended sediment transport in the Gulf of Lions (NW Mediterranean Sea). The outputs of a hydrodynamic–sediment transport coupled model were compared to near-bottom current and suspended sediment concentration measurements collected at the head of seven submarine canyons and at a shallow shelf site, over a 6-month period (November 2003–May 2004). The comparisons provide a reasonable validation of the model that reproduces the observed spatial and time variations. The study period was marked by an unusual occurrence of marine storms and high river inputs. The major water and sediment discharges were supplied by the Rhone, the largest Mediterranean river, during an exceptional flood accompanying a severe marine storm in early December 2003. A second major storm, with moderate flooding, occurred in February 2004. The estimate of river input during the studied period was 5.9 Mt. Our study reveals (i) that most of the particulate matter delivered by the Rhone was entrapped on the prodelta, and (ii) that marine storms played a crucial role on the sediment dispersal on the shelf and the off-shelf export. The marine storms occurring in early December 2003 and late February 2004 resuspended a very large amount of shelf sediment (>8 Mt). Erosion was controlled by waves on the inner shelf and by energetic currents on the outer shelf. Sediment deposition took place in the middle part of the shelf, between 50 and 100 m depth. Resuspended sediments and river-borne particles were transported to the southwestern end of the shelf by a cyclonic circulation induced by these onshore winds and exported towards the Catalan shelf and into the Cap de Creus Canyon which incises the slope close to the shore. Export taking place mostly during marine storms was estimated to reach 9.1 Mt during the study period.