Stormwater management network effectiveness and implications for urban watershed function: A critical review

Deleterious effects of urban stormwater are widely recognized. In several countries, regulations have been put into place to improve the conditions of receiving water bodies, but planning and engineering of stormwater control is typically carried out at smaller scales. Quantifying cumulative effectiveness of many stormwater control measures on a watershed scale is critical to understanding how small‐scale practices translate to urban river health. We review 100 empirical and modelling studies of stormwater management effectiveness at the watershed scale in diverse physiographic settings. Effects of networks with stormwater control measures (SCMs) that promote infiltration and harvest have been more intensively studied than have detention‐based SCM networks. Studies of peak flows and flow volumes are common, whereas baseflow, groundwater recharge, and evapotranspiration have received comparatively little attention. Export of nutrients and suspended sediments have been the primary water quality focus in the United States, whereas metals, particularly those associated with sediments, have received greater attention in Europe and Australia. Often, quantifying cumulative effects of stormwater management is complicated by needing to separate its signal from the signal of urbanization itself, innate watershed characteristics that lead to a range of hydrologic and water quality responses, and the varying functions of multiple types of SCMs. Biases in geographic distribution of study areas, and size and impervious surface cover of watersheds studied also limit our understanding of responses. We propose hysteretic trajectories for how watershed function responds to increasing imperviousness and stormwater management. Even where impervious area is treated with SCMs, watershed function may not be restored to its predevelopment condition because of the lack of treatment of all stormwater generated from impervious surfaces; non‐additive effects of individual SCMs; and persistence of urban effects beyond impervious surfaces. In most cases, pollutant load decreases largely result from run‐off reductions rather than lowered solute or particulate concentrations. Understanding interactions between natural and built landscapes, including stormwater management strategies, is critical for successfully managing detrimental impacts of stormwater at the watershed scale.     

1976年9月23日巴音木仁Ms 6.2级地震序列分析

本文对１９７６年巴音木仁Ｍｓ６２级地震序列进行了分析,剖析其前震序列的测震学指标异常及余震序列特征,判定了序列类型,得出一些有预报意义的结果。     

Uncertainities in estimation of extrapolated annual occurrence rate of earthquakes using logical tree

The logical tree methods are used for evaluate quantitatively relationship between frequency and magnitude, and deduce uncertainties of annual occurrence rate of earthquakes in the periods of lower magnitude earthquake. The uncertainties include deviations from the self-similarity of frequency-magnitude relations, different fitting methods, different methods obtained the annual occurrence rate, magnitude step used in fitting, start magnitude, error of magnitude and so on. Taking Xianshuihe River source zone as an example, we analyze uncertainties of occurrence rate of earthquakes M ≥ 4, which is needed in risk evaluation extrapolating from frequency-magnitude relations of stronger earthquakes. The annual occurrence rate of M ≥ 4 is usually required for seismic hazard assessment. The sensitivity analysis and examinations indicate that, in the same frequency-magnitude relations fitting method, the most sensitive factor is annual occurrence rate, the second is magnitude step and the following is start magnitude. Effect of magnitude error is rather small. Procedure of estimating the uncertainties is as follows: (1) Establishing a logical tree described uncertainties in frequency-magnitude relations by available data and knowledge about studied region. (2) Calculating frequency-magnitude relations for each end branches. (3) Examining sensitivities of each uncertainty factors, amending structure of logical tree and adjusting original weights. (4) Recalculating frequency-magnitude relations of end branches and complementary cumulative distribution function (CCDF) in each magnitude intervals. (5) Obtaining an annual occurrence rate of M ≥ 4 earthquakes under given fractiles. Taking fractiles as 20% and 80%, annual occurrence rate of M ≥ 4 events in Xianshuihe seismic zone is 0.643 0. The annual occurrence rate is 0.631 8 under fractiles of 50%, which is very close to that under fractiles 20% and 80%.     

Higher-order approximation techniques for estimating stochastic parameter of a sediment transport model

Higher-order approximation techniques for estimating stochastic parameter of the non-homogeneous Poisson (NHP) model are presented. The NHP model is characterized by a two-parameter cumulative probability distribution function (CDF) of sediment displacement. Those two parameters are the temporal and spatial intensity functions, physically representing the inverse of the average rest period and step length of sediment particles, respectively. Difficulty of estimating the parameters has, however, restricted the applications of the NHP model. The approximation techniques are proposed to address such problem. The basic idea of the method is to approximate a model involving stochastic parameters by Taylor series expansion. The expansion preserves certain higher-order terms of interest. Using the experimental (laboratory or field) data, one can determine the model parameters through a system of equations that are simplified by the approximation technique. The parameters so determined are used to predict the cumulative distribution of sediment displacement. The second-order approximation leads to a significant reduction of the CDF error (of the order of 47%) compared to the first-order approximation. Error analysis is performed to evaluate the accuracy of the first- and second-order approximations with respect to the experimental data. The higher-order approximations provide better estimations of the sediment transport and deposition that are critical factors for such environment as spawning gravel-bed.     

Dynamic Characteristics of Granite Subjected to Intermediate Loading Rate

Summary A large diameter split Hopkinson pressure bar (SHPB) has been developed. This equipment is briefly described, together with a shaped striker that initiates a half-sine incident waveform to obtain the complete stress-strain relationship of the Bukit Timah granite at medium strain rate. Good constant strain rate was derived, and the dynamic complete stress-strain curves and energy absorption of the granite were measured at a strain rate between 20 and 60 per second. Repeated impact between 60–90% of the static strength of the granite was also conducted. Results from the tests show that the cumulative damage of the granite depends on the peak stress of the dynamic loads with a fixed duration. The dynamic fracture strength of the granite loaded at medium strain rate is directly proportional to the cube root of the strain rate. For the granite loaded at this strain rate, Youngs modulus is unchanged. Energy absorption of the samples loading to fragmentation determined its fragmented size distribution. At high strain rate, the rock possesses large energy absorption and the particle size of the fragments is much smaller.     

三门湾多个围垦工程的整体影响数学模型研究

海湾内的围垦工程对潮流及冲淤都将产生影响.以三门湾蛇蟠和下洋涂围垦工程为例,设计了3组试验对比的数值模拟计算方案,对比计算结果表明,预测三门湾内2个围垦工程对水动力环境产生的影响,当讨论单一围垦工程时,应把工程前的海湾状态设置为湾内没有任何其它工程,这样才能得出单个围垦工程对湾内环境的真实影响;当讨论2个围垦工程对水动力环境产生影响时,应进行2个围垦工程整体数学模拟计算,考虑2个围垦工程的叠加累积影响,并与海湾原始状态(即假定海湾在围垦前湾内没有任何其它围垦工程)进行比较,才能得出较为科学的预测结果.     

中国高等教育经费投入空间格局及形成机理研究

利用Cartogram专题地图分析1995~2011年中国省际高等教育经费支出空间分布差异的基础上,采用Wolfson极化指数与循环累积因果原理分析高等教育经费投入空间差异化的形成机理,得出结论：① 中国高等教育经费投入总体呈“东、中、西”阶梯状递减的非均衡空间格局,空间极化日益显著;生均教育经费虽然比较均衡,但仍呈“东西两大地带隆起而中部塌陷”的特征;部属院校教育经费非均衡性与地方院校相比更为突出。②中国高等教育经费投入区域差异是受国家政策主导,在人口分布、地理环境、经济发展水平及资金收益率等多因素的影响下形成的复杂循环累积效应所致。     

小秦岭金矿区西峪河底泥重金属元素污染的潜在生态危害评价

重金属元素易于累积,生态效应影响强烈。分析了陕豫接壤的西峪河水系沉积物中Hg、Pb、Cd、As、Cr、Cu、Zn 7种重金属元素的含量,根据地区参比值,评价了金矿活动对西峪河底泥的污染。结果显示Hg、Pb是主要的污染元素;进而用潜在生态危害指数法探讨了重金属元素污染的潜在生态危害性,认为整个西峪河流域的Hg、Pb潜在生态危害很强,Cd具有强的潜在生态危害,而Cr、As、Zn的潜在生态危害性轻微。     

基于Origin的概率累积曲线的计算与绘制

图解法计算沉积物粒度参数在沉积学研究中被广泛应用,但需要通过手工作图求累积曲线,是一项相当繁杂的劳动。通用计算软件Origin拥有很强的函数计算和绘图功能,不仅可以批量计算图解粒度参数,同时还可以直接绘制（分段）概率累积曲线图;其实施过程操作简单,仅需点击菜单命令,无需编写任何语句,有利于不懂编程的沉积分析人员进行数据分析,有很大的应用价值。文章随机选取10个不同沉积环境下形成的松散沉积物样本,利用Origin求解各样本粒度累积曲线的百分位数,在其内嵌的Excel表格中计算粒度参数,并用Origin的制图功能绘制粒度概率累积曲线与沉积组分分段直线图。Origin与手工作图计算的结果之间的差值（绝对值平均）及方差都很小（0.004 2~0.018 6）。计算结果表明Origin在粒度参数计算方面完全可以代替手工作图,不仅操作简单,而且精度非常高。     

科尔沁沙地自然与人为因素对沙漠化影响的累加效应分析

采用滑动平均法分析了科尔沁沙地年平均温度、年降水量(代表自然因素)和耕地指数、草场载畜量(代表人为因素)对沙漠化影响的累加效应。结果表明,年平均温度和年降水量的累加作用持续的时间较短(在4a之内),其中年平均温度对沙漠化影响的累加效应作用在2a最大,但作用不明显;年降水量对沙漠化的影响以4a最高,累加效应最明显,关联系数为0.801,而且二者之间有较显著的回归关系。年降水量和年平均温度的波动特点是决定累加作用时间和影响强度的关键。代表人为因素的耕地指数和草场载畜量对沙漠化影响的累加效应都比较明显、作用持续的时间较长(大于8a),其中耕地指数对沙漠化的影响以7a的累加效应最明显;草场载畜量对沙漠化的影响以10a的累加效应最明显,耕地指数和草场载畜量与沙漠化之间存在着较显著的回归关系。人口持续增长导致的对资源环境压力的增大是耕地指数和草场载畜量对沙漠化影响产生累加效应的根本原因。