样本窗口中不连续面体积密度的评价与应用

不连续面体积密度是三维网络模拟的基本参数之一,体积密度的取值合理与否直接关系到模拟结果的可信度。对不连续面体积密度的求解已经有一些方法,本文提出了一种较为简捷的求解方法,并应用于实际的模型模拟,得到了预期的效果。      

煤层割理在煤层气开发中的试验研究

根据煤层割理渗透率的各向异性,采用垂直面割理和平行面割理两个方向布置钻孔抽放煤层气。测定研究表明:垂直面割理方向钻孔初始瓦斯抽放百米流量是平行面割理方向钻孔的1.2倍,衰减系数比平行面割理方向钻孔减少了53.7%。垂直面割理方向钻孔的抽放量在任何相应时期都大于平行面割理方向钻孔的抽放量。从而得出:垂直面割理方向钻孔抽放效果明显优于平行面割理方向钻孔,为探索提高煤层气抽放量找到了一条途径。      

塔里木河中游主要植物种群的生态特征分析

根据新疆塔里木河中游植物样地的监测数据,计算了19种主要植物在土壤含水率与土壤盐分资源维上的生态位宽度及生态位重叠值,作出了反映它们相似程度的最小生成树图;探讨了19种植物的生态位特征及各物种在二维环境因子上的相似关系。结果表明:建群种对环境变化的生态适应性较强,在二维生态因子上的生态位宽度值较大,乔灌植物普遍具有较大的生态位宽度(个别物种除外),草本植物除建群种外生态位宽度相应较小,并对个别物种生态位的变化进行了分析。由于环境条件的影响和胁迫,塔里木河中游物种间的生态位重叠值普遍较低。根据最小生成树图分析了19种植物在二维环境因子上的生态相似关系     

金沙峡电站闸坝区渗流场有限体积法数值模拟

为实现泄冲闸、进水闸和土坝结合部位三维渗流场真实区域的数值模拟,采用有限体积法对含排水孔在内的闸坝区三维渗流场进行了网格划分。根据计算结果可知,闸基处防渗墙效果微弱,溢出点垂直坡降大于允许值,对工程不利,并提出了相应的改进措施。     

A hydrological record extension model for reconstructing streamflows from tree‐ring chronologies

Characterizing drought events is an important factor in designing and operating water resource projects, but instrumental hydrologic records are generally short (<100 years). Because estimates of drought statistics can improve when longer records are available, we developed a stochastic model to extend instrumental streamflows based on tree‐ring chronologies. This Record Extension plus Noise (or REXTN) model consists of an autoregressive term to account for the temporal persistence of streamflows, predictor variables with longer records, and a noise term. The noise term was included to avoid underestimating the variability of the flows and to generate multiple extensions, which offer the possibility of quantifying the uncertainty of drought statistics such as the critical drought. For cases where having multiple extensions is not desirable, a statistically based algorithm was developed to select a single extended record. Using a simulation experiment, model REXTN was found to perform better than other existing reconstruction methods. The model was then applied to extend streamflows of the Poudre River, CO, USA, based on tree ring‐chronologies back to the year 1600, and the reconstructions were used to determine drought statistics such as duration and magnitude. When results based on the classical linear regression model were compared with those calculated by model REXTN, the latter was found to better match flow and drought statistics from the instrumental records, as well as to give a broader range of drought duration and magnitude. The REXTN model provides a useful addition to the range of tools available to hydrologists for coping with the uncertainty associated with water resource management under future climate scenarios. Copyright © 2014 John Wiley & Sons, Ltd.     

Watershed‐scale controls on snow accumulation in a small montane watershed,southwestern Alberta,Canada

Snow accumulation in mountain headwater basins is a major water source, particularly in semi‐arid environments such as southern Alberta where water resources are stressed and snowmelt supplies more than 80% of downstream runoff. Relationships between landscape predictor variables and snow water equivalent (SWE) were quantified by combining field and LiDar measurements with classification and regression tree analysis over two winter seasons (2010 and 2011) in a small, montane watershed. 2010 was a below average snow accumulation year, while 2011 was well above normal. In both the field and regression tree data, elevation was the dominant control on snow distribution in both years, although snow distribution was driven by melt processes in 2010 and accumulation processes in 2011. The importance of solar radiation and wind exposure was represented in the regression trees in both years. The regression trees also noted the lower importance of canopy closure, slope, and aspect, which was not observed in the field data. This technique could provide an additional method of forecasting annual water supply from melting snow. However, further research is required to address the lack of data collected above treeline, to provide a full‐basin estimate of SWE. Copyright © 2012 John Wiley & Sons, Ltd.     

A stem‐branch topological codification for watershed subdivision and identification to support distributed hydrological modelling at large river basins

Watershed subdivision is a useful discretization method for distributed hydrological models at large river basins. A subwatershed codification method, which is able to identify the subwatershed uniquely and reflect the topological relationship is desired. According to the previous literatures, there are two types of coding methods suitable for the subwatershed codification: the Pfafstetter‐group rules and the modified binary tree codification method. But, both of them have some shortcomings in theory and application. A new coding method named stem‐branch topological codification is developed to overcome these shortcomings, which is based on the stem‐branch topological structure of the drainage networks and capable of reflecting the river hierarchy. The basic coding elements of the method are river reaches in the drainage networks, which are not only generated by the tributary junctions, but also by the splitting points of hydrological factors (e.g. hydrological gauge stations and reservoirs). Also, the method could handle complex confluences (e.g. river reaches with more than two upstream inflows), which are rare under natural conditions, but more frequent in the digital elevation model extracted or artificial drainage networks (e.g. sewage systems or irrigation drainage networks). With the stem‐branch topological codification codes, it is easy to identify the upstream (or downstream) relationship between any two subwatersheds and to calculate the directly connected subwatershed codes. Also, if some changes have occurred in the drainage network, there is no need to recode the whole watershed, but by modifying the existed codes to form the new ones. Copyright © 2013 John Wiley & Sons, Ltd.     

Common temperature signal in four well‐replicated tree growth series from northern Fennoscandia

Four Nordic temperature proxies based on tree growth at the northern timberline – ring‐width from Sweden and Finland, maximum latewood density from Sweden, and height increment from Finland – were compared. Three indexing methods were used to enhance the low (centennial and above), medium (decadal‐to‐multidecadal) and high (decadal‐to‐interannual) frequencies. The proxies are shown to have a strong temperature signal (common variance) at the interannual‐to‐multidecadal scale, while the multidecadal‐to‐centennial trends are less coherent, perhaps reflecting intra‐regional differences in growing conditions but more likely due to the more noisy regional curve standardization method used to retain the longest trends. Various methods of combining the four proxy series were explored and tested by comparison with four long temperature records from northern Fennoscandia. Only relatively high‐frequency, spline‐indexed series produced consistently positive verification statistics as a reconstruction model for summer temperature using all four proxies. Copyright © 2012 John Wiley & Sons, Ltd.     

Paleoclimate studies and natural-resource management in the Murray-Darling Basin II: unravelling human impacts and climate variability

The management of the water resources of the Murray-Darling Basin (MDB) has long been contested, and the effects of the recent Millennium drought and subsequent flooding events have generated acute contests over the appropriate allocation of water supplies to agricultural, domestic and environmental uses. This water-availability crisis has driven demand for improved knowledge of climate change trends, cycles of variability, the range of historical climates experienced by natural systems and the ecological health of the system relative to a past benchmark. A considerable volume of research on the past climates of southeastern Australia has been produced over recent decades, but much of this work has focused on longer geological time-scales, and is of low temporal resolution. Less evidence has been generated of recent climate change at the level of resolution that accesses the cycles of change relevant to management. Intra-decadal and near-annual resolution (high-resolution) records do exist and provide evidence of climate change and variability, and of human impact on systems, relevant to natural-resource management. There exist now many research groups using a range of proxy indicators of climate that will rapidly escalate our knowledge of management-relevant, climate change and variability. This review assembles available climate and catchment change research within, and in the vicinity of, the MDB and portrays the research activities that are responding to the knowledge need. It also discusses how paleoclimate scientists may better integrate their pursuits into the resource-management realm to enhance the utility of the science, the effectiveness of the management measures and the outcomes for the end users.     

Is ‘Centre of Volume’ a robust indicator of changes in snowmelt timing?

The centre of volume (COV), or the hydrograph centroid, is a measure of streamflow timing that is a widely used indicator of the effects of warmer temperatures on the hydrology of snowmelt streams. The COV was originally developed as a measure of land‐use effects, and its response is affected by several factors other than temperature, particularly total run‐off. A ‘toy’ model is used to demonstrate some of these effects, and these effects are also shown for streamflow data from Canada's Reference Hydrologic Basin Network. These deficiencies indicate that COV is neither specific nor robust as an indicator. Although these effects might be overcome by streamflow decomposition, the use of COV as an indicator of snowmelt timing should be avoided. Copyright © 2013 John Wiley & Sons, Ltd.