COMPOSITE VS. DISTRIBUTED CURVE NUMBERS: EFFECTS ON ESTIMATES OF STORM RUNOFF DEPTHS1

ABSTRACT: The U.S. Department of Agriculture Curve Number (CN) method is one of the most common and widely used techniques for estimating surface runoff and has been incorporated into a number of popular hydrologic models. The CN method has traditionally been applied using compositing techniques in which the area weighted average of all curve numbers is calculated for a watershed or a small number of sub-watersheds. CN compositing was originally developed as a time saving procedure, reducing the number of runoff calculations required. However, with the proliferation of high speed computers and geographic information systems, it is now feasible to use distributed CNs when applying the CN method. To determine the effect of using composited versus distributed CNs on runoff estimates, two simulations of idealized watersheds were developed to compare runoff depths using composite and distributed CNs. The results of these simulations were compared to the results of similar analyses performed on an urbanizing watershed located in central Indiana and show that runoff depth estimates using distributed CNs are as much as 100 percent higher than when composited CNs are used. Underestimation of runoff due to CN compositing is a result of the curvilinear relationship between CN and runoff depth and is most severe for wide CN ranges, low CN values, and low precipitation depths. For larger design storms, however, the difference in runoff computed using composite and distributed CNs is minimal.     

重型机动车实际排放特性与影响因素的实测研究

利用美国Sensors公司生产的SEMTECHD车载排放测试仪在上海随机选择了7辆重型柴油车开展实际道路的排放测试,该实验累积测试道路长度为186km,共取得29090个逐秒的有效工况点数据,其中城市主干道12979个,次干道12368个,快速干道3743个.给出了车辆在不同道路上的工况点分布,分析了速度、加速度对燃油消耗、尾气排放的影响.测试结果表明,在选定的城市道路上,车流的平均怠速工况比为17%,加速工况比23.6%,等速工况比为31.0%,减速工况比为28.5%.被测车辆的CO、THC、NOx平均排放因子分别为(4.41±2.46)g·km-1、(1.77±1.17)g·km-1和(6.96±1.93)g·km-1,车辆排放状况因车速、加速度等因素而不同.测试结果基本反映了目前上海道路的交通状况和柴油卡车的排放现状,同时也说明过低的车速和频繁加减速是加重机动车污染的重要原因.     

Physicians' acceptability of termination of pregnancy after prenatal diagnosis in southern france

The acceptability of prenatal diagnosis for Down's syndrome has been extensively studied over the last 15 years but that of other pathologies remains largely unexplored. The main goals of this study were to approach physicians' opinions on six reasons for termination of pregnancy showing different deficiencies, i.e., Down's, Turner and Klinefelter syndromes, cystic fibrosis, spina bifida, and haemophilia, and to identify the origins of reserves. The influence of sociodemographic and professional characteristics of physicians on their opinions and attitudes during the consultation were studied. The data presented are based on information gathered in 1985 by a mailed questionnaire answered by 853 general practitioners, gynaecologists, obstetricians, and pediatricians in the Marseilles Genetic Centre's region. Stepwise logistic regression was used for the multivariate analysis. The results showed that 78 per cent of those answering favour termination of pregnancy for Down's syndrome and that only moral reticences were mentioned by the physicians opposed. Conversely, for haemophilia, only 21 per cent of the physicians considered this indication justified; those opposed were for the most part concerned that severity of illness did not justify termination of pregnancy. Overall, 33 per cent of physicians would voice their personal opinion on termination of pregnancy if so requested by consultees. Results on the influence of age and specialty evidenced their role on physicians' opinions. Indeed, 30 per cent of physicians opposed to pregnancy termination for one of the six fetal anomalies retained herein would modify their positions if diagnosis were possible in the first trimester of pregnancy.     

Assessment of chlorophyll-a as a criterion for establishing nutrient standards in the streams and rivers of Illinois

Nutrient enrichment is a frequently cited cause for biotic impairment of streams and rivers in the USA. Efforts are underway to develop nutrient standards in many states, but defensible nutrient standards require an empirical relationship between nitrogen (N) or phosphorus (P) concentrations and some criterion that relates nutrient levels to the attainment of designated uses. Algal biomass, measured as chlorophyll-a (chl-a), is a commonly proposed criterion, yet nutrient-chl-a relationships have not been well documented in Illinois at a state-wide scale. We used state-wide surveys of >100 stream and river sites to assess the applicability of chl-a as a criterion for establishing nutrient standards for Illinois. Among all sites, the median total P and total N concentrations were 0.185 and 5.6 mg L(-1), respectively, during high-discharge conditions. During low-discharge conditions, median total P concentration was 0.168 mg L(-1), with 25% of sites having a total P of > or =0.326 mg L(-1). Across the state, 90% of the sites had sestonic chl-a values of < or =35 microg L(-1), and watershed area was the best predictor of sestonic chl-a. During low discharge there was a significant correlation between sestonic chl-a and total P for those sites that had canopy cover < or =25% and total P of < or =0.2 mg L(-1). Results suggest sestonic chl-a may be an appropriate criterion for the larger rivers in Illinois but is inappropriate for small rivers and streams. Coarse substrate to support benthic chl-a occurred in <50% of the sites we examined; a study using artificial substrates did not reveal a relationship between chl-a accrual and N or P concentrations. For many streams and rivers in Illinois, nutrients may not be the limiting factor for algal biomass due to the generally high nutrient concentrations and the effects of other factors, such as substrate conditions and turbidity.     

自然气候老化测试及应用

描述自然气候条件对材料老化的影响以及对预测材料不同应用方向等方面的影响。通过对不同地点,不同老化方法的比较,重点介绍了目前国际上使用的老化方法－直接曝晒,黑板箱曝晒,间接曝晒,自然加速老化等多种标准方法的特点,使用的局限性以及对材料老化结果的影响,并详细介绍了适用于自然老化地点的选择,主要影响因素等等。文章在分析多种老化方法的同时,指出了各种方法的适用性,这对材料老化方面的研究有很大的参考价值和指导意义。     

Stable isotopic evidence for trophic groupings and bio-regionalization of predators and their prey in oceanic waters off eastern Australia

Muscle tissue was collected for stable isotope analysis (SIA) from the main fish predators and their fish and cephalopod prey from oceanic waters off eastern Australia between 2004 and 2006. SIA of δ¹⁵N and δ¹³C revealed that the species examined could be divided into three main trophic groups. A “top predator” group consisted mainly of large billfish (Xiphias gladius and Tetrapturus audax), yellowfin (Thunnus albacares), bigeye (T. obesus) and southern bluefin (T. maccoyii) tunas and sharks; with mako (Isurus oxyrinchus) the highest. Below this tier was a second group composed of mid-trophic level fishes including albacore tuna (Thunnus alalunga), lancet fish (Alepisaurus ferox), mahi mahi (Coryphaena hippuris) and ommastrephid squid. Underlying both groups was a grouping of small fishes including myctophids, small scombrids and nomeids as well as surface fishes including macrorhamphosids. These groupings were based largely on mean animal size which showed a positive linear relation to δ¹⁵N (r ² = 0.58). Some species showed significant ontogenetic variation in either δ¹⁵N (swordfish, lancet fish, yellowfin and albacore tuna) or δ¹³C (mako shark). We also noted a consistent latitudinal change in δ¹⁵N and δ¹³C at ~28°S for the top predator species, particularly albacore and yellowfin tuna. The differences were consistent with a change from oligotrophic Coral Sea to nutrient rich Tasman Sea waters. These differences suggest that predatory fishes may have extended residence time in distinct regions off eastern Australia.     

Stakeholder perspectives on the value proposition of enterprise-level natural capital accounting for three primary industries

Environment Systems and Decisions - Globally we are experiencing a decline in aggregate natural capital. Many primary industries and enterprises are highly dependent on renewable and non-renewable...