Estimation of temporal variation in splash detachment in two Japanese cypress plantations of contrasting age

To elucidate splash erosion processes under natural rainfall conditions, temporal variations in splash detachment were observed using a piezoelectric saltation sensor (H11B; Sensit Co., Portland, ND, USA). Preliminary laboratory tests of Sensit suggested that they were suitable for field observations. Field observations were conducted between July and September 2006 in 21‐ and 36‐year‐old Japanese cypress (Chamaecyparis obtusa) plantations with mean stand heights of 9·2 m and 17·4 m, respectively. Splash detachment (in g m^?2) was measured seven times using splash cups, and raindrop kinetic energy (in J m^?2 mm^?1) in both stands was measured using laser drop‐sizing (LD) gauges. Sensit was installed to record saltation counts, which were converted to temporal data of splash detachment (splash rate; in g m^?2 10 min^?1) using the relationship between splash detachment and saltation counts. Surface runoff was monitored using runoff plots of 0·5 m width and 2·0 m length to obtain temporal data of flow depth (in millimeters). Both total splash detachment and raindrop kinetic energy were larger in the older stand. Increased splash rates per unit throughfall were found in both stands after rainless durations longer than approximately one day in both stands. However, a lower splash rate was found in the 21‐year stand after rainfall events. During extreme rainstorms, the 21‐year stand showed a low runoff rate and a decline in the splash rate, while the 36‐year stand showed a higher splash rate and increased flow depth. The piezoelectric sensor proved to be a useful means to elucidate splash erosion processes in field conditions. Copyright © 2010 John Wiley & Sons, Ltd.     

A comparison of two physics-based numerical models for simulating surface water–groundwater interactions

Problems in hydrology and water management that involve both surface water and groundwater are best addressed with simulation models that can represent the interactions between these two flow regimes. In the current generation of coupled models, a variety of approaches is used to resolve surface–subsurface interactions and other key processes such as surface flow propagation. In this study we compare two physics-based numerical models that use a 3D Richards equation representation of subsurface flow. In one model, surface flow is represented by a fully 2D kinematic approximation to the Saint–Venant equations with a sheet flow conceptualization. In the second model, surface routing is performed via a quasi-2D diffusive formulation and surface runoff follows a rill flow conceptualization. The coupling between the land surface and the subsurface is handled via an explicit exchange term resolved by continuity principles in the first model (a fully-coupled approach) and by special treatment of atmospheric boundary conditions in the second (a sequential approach). Despite the significant differences in formulation between the two models, we found them to be in good agreement for the simulation experiments conducted. In these numerical tests, on a sloping plane and a tilted V-catchment, we examined saturation excess and infiltration excess runoff production under homogeneous and heterogeneous conditions, the dynamics of the return flow process, the differences in hydrologic response under rill flow and sheet flow parameterizations, and the effects of factors such as grid discretization, time step size, and slope angle. Low sensitivity to vertical discretization and time step size was found for the two models under saturation excess and homogeneous conditions. Larger sensitivity and differences in response were observed under infiltration excess and heterogeneous conditions, due to the different coupling approaches and spatial discretization schemes used in the two models. For these cases, the sensitivity to vertical and temporal resolution was greatest for processes such as reinfiltration and ponding, although the differences between the hydrographs of the two models decreased as mesh and step size were progressively refined. In return flow behavior, the models are in general agreement, with the largest discrepancies, during the recession phase, attributable to the different parameterizations of diffusion in the surface water propagation schemes. Our results also show that under equivalent parameterizations, the rill and sheet flow conceptualizations used in the two models produce very similar responses in terms of hydrograph shape and flow depth distribution.     

福建皇山铅锌多金属矿地质特征及成矿标志

文章介绍了福建皇山铅锌矿矿区地层、构造和岩浆岩,通过对矿体地质特征的描述、岩浆岩化学成分组成特征及成矿条件分析,提出矿区找矿标志。     

On the stability of a non-convolutional perfectly matched layer for isotropic elastic media

The multi-axial perfectly matched layer (M-PML) is a material boundary condition for wave propagation problems in unbounded domains. It is obtained by extending the formulation of the split-field perfectly matched layer to a more general absorptive medium, for which damping profiles are specified along all dimensions of the problem. Under the hypothesis of small damping, it has been demonstrated that the stability of the system of partial differential equations of the M-PML can be related to the ratio of the damping profiles, and stable M-PML terminations for isotropic and orthotropic elastic media have been constructed. In the present work, we use the Routh–Horwitz determinants to demonstrate that the conclusions regarding the stability of M-PML for isotropic media for small damping are in fact valid for the more general case of damping coefficients of any (positive) value. The effectiveness of the M-PML is demonstrated by constructing stable terminations for the abovementioned media. The stability analysis is presented for 2-D in-plane (P-SV) wave propagation in elastic isotropic continua.     

岩溶山区聚落格局演变等级效应及其与交通条件的关系——以贵州省后寨河、王家寨、茂兰地区为例

运用1963年、80年代2004年三期高分辩率影像数据源和GIS分析方法,以贵州省后寨河、王家寨、茂兰地区为例,按空间规模将聚落分为五级,并探讨其分布格局演变规律与交通条件的关系。结果表明:(1)1963年,高等级聚落个数较少,低等级聚落较多;高等级聚落多分布在水源条件好、耕地资源多而优的峰林-平原地带;(2)1963年到80年代期间,岩溶山区聚落发展主要集中于中等级聚落,高、低等级聚落变化不大;(3)到2004年,各等级聚落的数量和规模均得到了较大发展,但发展的强度主要出现在两极(1级、5级);(4)岩溶山区聚落等级变化受交通条件影响较大,同时也受制于区域经济发展水平、自然地理因素影响;(5)今后聚落优化建设、交通条件改善应以4级聚落作为重点对象,5级聚落的重构应重点考虑空间迁移,方向为公路两侧,以改善对外通达度。      

煤与瓦斯突出能量条件及突出强度影响因素分析

针对煤与瓦斯突出机制尚不明确的问题,在前人研究的基础上对煤与瓦斯突出强度的影响因素做进一步分析。通过三维突出模型的构建和不规则突出孔洞体积的求解,得出了突出煤体释放的弹性势能,结合突出过程中瓦斯内能和突出后能量的分析,得到煤与瓦斯突出发生的能量条件模型与突出强度预测模型。在统计10次瓦斯突出事故的基础上,运用能量条件模型与强度预测模型进行计算分析,得出突出前、后能量基本相等,突出强度预测值与统计值相差无几的结论,从而验证了该模型的合理性,为从能量角度进行煤与瓦斯突出的研究提供了量化手段。利用该能量条件模型进行了中梁山煤矿和化处煤矿突出实例的突出强度影响因素分析,结果表明,煤层的地应力和瓦斯含量是突出强度的主要影响因素,坚固性系数和进尺对突出强度的影响程度相对较小;突出强度对瓦斯含量变化的敏感度大于对地应力变化的敏感度。     

石家庄一次秋季罕见暴雪天气过程物理诊断分析

利用NCEP再分析资料,采用天气学诊断方法,对2009年11月10—12日石家庄地区出现的一次历史同期罕见区域性暴雪天气过程的环流特征和物理量场进行了探讨。结果表明：此次暴雪天气过程属典型的东北回流型降雪,地面从贝加尔湖南下冷高压与河套低压倒槽、700 hPa暖式切变线、500 hPa高空槽是主要影响系统。低空西南急流与超低空东北急流耦合,在为暴雪提供水汽和热量输送的同时加强了抬升运动。水汽的垂直输送导致局地比湿显著增大,深厚的湿层和强烈的水汽辐合为暴雪提供了充沛的水汽条件。“高空辐散、低空辐合”以及强劲的上升运动是暴雪的动力条件,降雪强度最大时段对应上升运动的强盛发展阶段。暴雪开始阶段云水含量的时空演变特征,一方面显示了水汽的迅速增加与爬升,另一方面也说明了地形的强迫抬升作用不容忽视。850 hPa温度低于700 hPa,有利于水汽经过此层时被凝华成固态。逆温层提前24 h出现,而且暴雪最强时段内两层温差均为5 ℃以上,这对暴雪预报具有指示意义。     

单层土模型场地地震反应分析中土层参数随机性的影响

土体的地震反应与结构震害密切相关,是地震工程中的一个重要问题,也是抗震设计的基础之一.然而目前的工程场地地震反应分析中存在着诸多不确定性因素,如何估计这些不确定的影响是一个亟待解决的问题.本文采用泰勒级数展开估计土层参数随机性对场地传递函数的影响,对单层土模型在土层参数服从独立高斯分布假定下进行公式推导和实例计算,比较了不同的泰勒级数阶次、土层参数变异系数以及阻尼比对传递函数随机性的综合效应,从而探讨了研究土层传递函数不确定性时采用各阶泰勒级数展开的精度和使用范围.     

青海木里地区天然气水合物形成条件分析

我国的青藏高原地区有大面积的多年冻土分布,其适宜的温压条件为天然气水合物的形成创造了有利的环境。在青藏高原北部祁连山区木里煤田多年冻土层煤炭地质勘查施工中,发现天然气水合物存在的证据。通过分析木里地区多年冻土带天然气水合物的形成条件,对天然气水合物烃类气体的来源进行了探讨,提出煤层和煤系分散有机质热演化过程中形成的烃类气体是木里煤田天然气水合物主要来源的观点,将并其称之为“煤型气源”天然气水合物。     

浅析含硫化氢地质环境对钻井作业的影响

在高含硫地质环境钻井作业中,硫化氢溢流给安全钻井带来极大的挑战。本文介绍了硫化氢的成因以及含硫地质环境的特点,并重点对含硫化氢地质环境对钻井作业的影响进行了分析和研究。