Runoff generative process and runoff yield from arid talus mantled slopes

Previous works dealing with the influence of a stone cover on runoff yield showed that runoff, attributed to the sealing effect of the topsoil by raindrops impact, was negatively related to the per cent of stone cover and stone size. These works were conducted on gentle slopes (3–11·5 degree) with a per cent of stone cover generally lower than 50 per cent, and composed of gravels. The present study deals with the runoff yield of steep talus slopes (26–36 degree) whose per cent of stone cover is very high (90–100 per cent), composed of cobbles and boulders. Three stimulated rainstorms were performed at various rainfall. intensities and durations on each one of six plots representative of the North eastern sector of Sinai. Although the contiguous stony cover prevented surface sealing by raindrops impact, runoff developed quite quickly on most slopes, and reached at peak discharge, after approximately ten minutes, up to 56 per cent of the rainfall. Differences between plots, in time lag, peak discharge and other hydrological variables, could be attributed mainly to the properties of the upper stony layer, with stone size as the most influential factor. Contrary to previous works, a positive relationship, was obtained between stone size to runoff yield. The result is explained by the process of water concentration. Each cobble and boulder behaves, on a smaller scale, like a bare rocky surface and yields per unit area water amounts beyond the infiltration rate of the limited uncovered areas. For a given stony cover the effect of water concentration is quicker with the big blocks than with gravels. A series of graphs trying to relate theoretically the relative importance of sealing and water concentration processes in runoff generation, at various conditions of stone cover and stone size, is proposed. The graphs enable to reconcile the results of the present study with those of previous works.     

Analysing topographical changes in open cast coal-mining region of Patratu,Jharkhand using CARTOSAT-I Stereopair satellite images

This study provides an assessment of changes in the terrain topography due to opencast coal mining in the Patratu region of Jharkhand state during the period of 1962–2007. It demonstrated the potential of digital elevation model (DEM) differencing technique using Cartosat-I satellite (2007) derived DEM with reference to DEM derived from contours obtained from Survey of India topographical map (1962). The topographical changes through DEM differencing revealed positive relief changes (up to 49 m) due to coal-mining overburden dumps. The dumping of overburden near the banks of perennial Damodar River also caused positive topographic changes (up to 20 m) indicating adverse effects on its hydrological regime. Negative relief changes are represents by deep depressions (up to 66 m) created within coal mines due to the extraction of coal. These depression areas within the abundant mines generally become the zones of water accumulation causing wastage of surface and ground water resources.     

On the use of mean monthly runoff to predict the flow–duration curve in ungauged catchments

ABSTRACT

We examine the applicability of predicting the daily flow–duration curve (FDC) using mean monthly runoff represented in its stochastic form (MM_FDC) to aid in predictions in ungauged basins, using long-term hydroclimatic data at 73 catchments of humid climate, in the eastern USA. The analysis uses soil hydrological properties, soil moisture storage capacity and the predominant runoff generation mechanism. The results show that MM_FDC did not distinguish the shapes of the upper and lower thirds of the FDC. The upper third is where the precipitation pattern and the antecedent moisture conditions are dominant, while the lower third is where drought-induced low flows and the evapotranspiration effect are prevalent. It is possible to use the MM_FDC to predict the middle third of the FDC (exceedence probabilities between 33% and 66%). The method is constrained by the catchment flow variability (slope of FDC), which changes in accordance with landscape properties and the predominant runoff generation mechanism.     

Saturated area dynamics and streamflow generation from coupled surface–subsurface simulations and field observations

A distributed physically-based model describing coupled surface–subsurface flows is applied to an instrumented catchment to investigate the links between runoff generation processes and the dynamics of saturated areas. The spatial characterization of the system is obtained through geophysical measurements and in situ observations. The model is able to reproduce the dynamics of the system through the calibration of only few parameters with a clear physical interpretation, providing a solid basis for our numerical investigations. Such investigations demonstrate the important control exerted by surface topography on the time evolution of saturated area patterns, mainly mediated by topographic curvature, that dictates both the dominant streamflow generation process at the local scale and the connection-disconnection dynamics of saturated areas. The relation between hillslope water storage and streamflow, Q = f(V), is shown to be highly hysteretical and dependent on the mean saturation of the catchment: higher degrees of saturation tend to yield one-to-one relationships between streamflow and water storage. On the contrary, streamflow-water storage relations are importantly affected by the specific configuration of saturated areas connected to the outlet when the system is far from complete saturation. This observation contradicts common assumptions of a one-to-one relationship Q = f(V) often used to justify widely observed power-law Q vs. dQ/dt recession curves. Furthermore, even when Q = f(V) becomes unique at high degrees of saturation, no power-law form emerged in our runs, speculatively because of the small size of the catchment formed by a single incision and the corresponding hillslope.     

基于离散粒子理论地震波传播数值模拟网格剖分计算方法

介绍一种基于离散粒子理论地震波传播数值模拟的网格剖分计算方法.根据离散粒子理论,将研究区域划分为由一系列相互作用的粒子组成的正六边形网格,这些粒子在它们的接触点处发生相互作用,并用Hooke定律和Newton定律描述.为解决六边形网格带来的网格交错而难以计算以及波场输出问题,将横向网格进行加密,加密处赋予假想的粒子,输出波场时选取偶数行偶数列点或奇数行奇数列点的波场值.均匀介质和层状介质模型的数值模拟结果表明,该网格剖分计算方法能够将离散粒子理论用于模拟弹性波在非均匀各向同性介质中地震波的传播.     

Pedestrian network map generation approaches and recommendation

With the advanced capabilities of mobile devices and the success of car navigation systems, interest in pedestrian navigation systems is on the rise. A critical component of any navigation system is a map database, which represents a network (e.g., road networks for car navigation) and supports key functionality such as map display, geocoding, and routing. Road networks, mainly due to the popularity of car navigation systems, are well defined and publicly available. However, in pedestrian navigation systems, as well as other applications including urban planning and physical activity studies, road networks do not adequately represent the paths that pedestrians usually travel. Currently, there is a void in literatures discussing the challenges, methods, and best practices for pedestrian network map generation. This coupled with the increased demand for pedestrian networks is the prime motivation for development of new approaches and algorithms to automatically generating pedestrian networks. Three approaches, network buffering, using existing road networks, collaborative mapping, using Global Positioning System (GPS) traces collected by volunteers, and image processing, using high-resolution satellite and laser imageries, were implemented and evaluated with a pedestrian network baseline as a ground truth. The results of the experiments indicate that these three approaches, while differing in complexity and outcome, are viable for automatic pedestrian network map generation. The recommendation of a suitable approach for generating pedestrian networks for a given set of sources and requirements is provided.     

海相烃源岩二次生烃潜力定量评价新方法

烃源岩二次生烃的演化过程是残余干酪根热解演化与残留油热裂解转化两个既相互联系又完全不同的物理化学反应过程的叠加。本文利用自制高压釜热压生烃模拟实验装置,采取分阶段连续递进模拟实验方式,以海相烃源岩样品为例分别评价了残余干酪根的生烃潜力与残留可溶有机质转化油气潜力,建立了一套不同起始与终止成熟度海相烃源岩二次生烃潜力的定量评价方法,并首次明确提出了干酪根生油指数KIo、干酪根生气指数KIg、干酪根生烃指数KIh等评价烃源岩生烃潜力的参数,弥补了ROCK EVAL热解评价方法无法分别评价烃源岩在不同生烃演化阶段所生成的“油”或“烃气”潜力的不足。     

中国古生界海相烃源岩生烃潜力评价标准与方法

中国古生界海相高、过成熟烃源岩原始生烃潜力评价问题是一个没有解决的老问题,至今没有可靠的评价方法与统一评价标准。低成熟元古宇—古生界海相泥岩/页岩与碳酸盐岩地球化学分析揭示,由于有机质组成不同,不同时代烃源岩的有机碳含量与热解生烃潜力之间存在着不同的线性关系。按照岩石热解生烃潜力来衡量,泥岩/页岩与碳酸盐岩作为有效烃源岩的有机质丰度下限没有本质区别,其有机碳含量必须大于0.5%;对于元古宇-下古生界海相烃源岩,达到中等生烃潜力的有机碳含量必须大于0.75%,好烃源岩的有机碳含量必须大于1.5%,很好烃源岩的有机碳含量大于2%,有机碳含量大于4%的属于极好的烃源岩;上古生界海相泥岩各级烃源岩相应的有机碳界线值高于下古生界泥岩。按照低成熟元古宇—古生界烃源岩有机碳含量与热解生烃潜力之间的关系方程,由有机碳含量基本上可以定量评价高、过成熟的元古宇—古生界烃源岩的原始生烃潜力。     

铀对(Ⅱ型)低熟烃源岩生烃演化的影响Ⅱ

在油、气、煤、铀多种能源矿产形成演化富集成藏(矿)过程中,有机-无机相互作用是普遍存在的,在有机质的强大吸附作用及其所提供的还原环境为铀的富集成矿起促进作用的同时,铀也改变了烃源岩的生烃演化进程。本文在Ⅱ型低熟烃源岩中加入碳酸铀酰溶液的条件下进行了生烃模拟实验,对比无铀-加铀样品生烃模拟实验产物的相关参数,以探讨油气生成过程中无机铀所起的作用。从实验结果可以看出,铀可以使产物中不饱和烃向饱和烃转化;促进长链烃的裂解,促进低分子量烃类的产生,从而使CH4的含量提高,使生成的烃类的干气化程度增加。铀可以在低温阶段促进有机质的成熟度,降低烃源岩的生烃门限,使低熟烃源岩早期生成烃类;同时在高温阶段阻止有机质过度成熟,利于所生成烃的保存。因而铀可能是未熟-低熟油气生成可能的无机促进因素之一。     

下扬子区印支期后构造演化与有利勘探区预测

通过恢复下扬子区白垩纪末期与古近纪末期的剥蚀厚度及分析印支不整合面Tg0的最大埋深,结合古地温条件得出下扬子区中生界、古生界均发生过晚期生烃和成藏。白垩纪末期,黄桥、句容和无为地区最大剥蚀厚度分别为1 000m、1 500 m和800 m。古近纪末期,黄桥地区最大剥蚀厚度约450 m,句容和无为地区无剥蚀。在3.3℃/100 m～4℃/100 m的古地温梯度下,白垩纪末期,无为地区约70%面积的二叠系—下三叠统烃源岩埋深达到2 000～4 000 m,进入生油阶段,但未进入生气阶段;句容地区二叠系—下三叠统烃源岩几乎全部进入生油阶段,次凹区进入了4 000 m以下的生气阶段;黄桥地区约70%面积的二叠系—下三叠统烃源岩进入生油阶段,主要位于北部深凹区和西部次凹区,凹陷深处烃源岩进入生气阶段。印支不整合面Tg0自白垩纪末期油气生成以来的多个古鼻凸轴线指示了油气运移路径、方向和聚集区,从喜山期至今的迁移变化指示了有利勘探区。