BIVARIATE FREQUENCY ANALYSIS OF FLOODS USING COPULAS1

Abstract: Bivariate flood frequency analysis offers improved understanding of the complex flood process and useful information in preparing flood mitigation measures. However, difficulties arise from limited bivariate distribution functions available to jointly model the correlated flood peak and volume that have different univariate marginal distributions. Copulas are functions that link univariate distribution functions to form bivariate distribution functions, which can overcome such difficulties. The objective of this study was to analyze bivariate frequency of flood peak and volume using copulas. Separate univariate distributions of flood peak and volume are first fitted from observed data. Copulas are then employed to model the dependence between flood peak and volume and join the predetermined univariate marginal distributions to construct the bivariate distribution. The bivariate probabilities and associated return periods are calculated in terms of univariate marginal distributions and copulas. The advantage of using copulas is that they can separate the effect of dependence from the effects of the marginal distributions. In addition, explicit relationships between joint and univariate return periods are made possible when copulas are employed to construct bivariate distribution of floods. The annual floods of Tongtou flow gauge station in the Jhuoshuei River, Taiwan, are used to illustrate bivariate flood frequency analysis.     

基于人工社会模型的退田还湖生态补偿机制实例研究

基于补偿者和受偿者意愿的研究方法是建立切实可行的生态补偿机制的有效手段。为探讨在我国许多地区开展退田还湖生态补偿政策的有效实施机制,减少洪涝灾害与生态环境退化负面效应,研究构建了基于农户、政府和企业三类主体及其相互作用的生态补偿模型,并重点分析生态补偿标准、洪灾风险、生态环境保护、劳动力本地转移政策等因素对农户主体土地利用决策的影响。以鄱阳湖区莲湖乡为实例,以农户和企业从事生产活动的行为特征和政府宏观调控方式为基本准则,利用构建的多主体模型模拟了不同补偿机制下退田还湖政策可能产生的土地利用长期效应。结果表明,政府给予农户的经济补偿可以使农户自愿实施退田,但在不同情景下,政府实施退田还湖的代价和达到预期目标的时限差距显著。企业参与不仅能减轻政府的经济负担,同时也有利于剩余农村劳动力的转移。政府发展壮大当地经济,提高农业劳动力向非农产业转移的速度和质量,均有助于推进退田还湖政策的有效实施。     

Influence of flooding and vegetation on carbon, nitrogen, and phosphorus dynamics in the pore water of a Spartina alterniflora salt marsh

Four sites were selected in a salt marsh in the Bah′?a Blanca Estuary (Argentina): (1) low marsh (flooded by the tide twice daily) vegetated by S. alterniflora; (2) non-vegetated low marsh; (3) high marsh (flooded only in spring tides) vegetated by S. alterniflora; (4) non-vegetated high marsh. The pH and Eh were measured in sediments, while dissolved nutrients (ammonium, nitrate, nitrite and phosphate) and particulate organic matter (POM) were determined in pore water. pH (6.2–8.7) was only a ected by vegetation in low areas. Eh (from –300 to 250 mV) was lower at low sites than at high ones; in the latter, the values were higher in the non-vegetated sediments. The POM concentration was greater in the high marsh than in the low marsh, with no e ect of vegetation. Ammonium was the most abundant nitrogen nutrient species in pore water, except in the non-vegetated high marsh where nitrate concentration was higher. All nitrogen nutrients were a ected by both flooding and vegetation. Phosphate was always present in pore water at all sites throughout the year and its concentration varied within narrow limits, with no e ect of flooding and greater values always at non-vegetated sites. Our results showed that the variability of the pore water composition within the marsh is greater than the temporal variation, meaning that both tidal flooding and vegetation are important in the dynamics of nutrients and organic matter in the sediment pore water.     

某聚合物驱油先导实验职业卫生调查

对某采油厂聚合物驱油先导试验项目进行了职业卫生调查,以明确有害因素存在的岗位部位、种类、危害程度,并对职业病危害控制措施及效果进行调查分析。     

Nonstationarity: Flood Magnification and Recurrence Reduction Factors in the United States1

Vogel, Richard M., Chad Yaindl, and Meghan Walter, 2011. Nonstationarity: Flood Magnification and Recurrence Reduction Factors in the United States. Journal of the American Water Resources Association (JAWRA) 47(3):464‐474. DOI: 10.1111/j.1752‐1688.2011.00541.x Abstract: It may no longer be reasonable to model streamflow as a stationary process, yet nearly all existing water resource planning methods assume that historical streamflows will remain unchanged in the future. In the few instances when trends in extreme events have been considered, most recent work has focused on the influence of climate change, alone. This study takes a different approach by exploring trends in floods in watersheds which are subject to a very broad range of anthropogenic influences, not limited to climate change. A simple statistical model is developed which can both mimic observed flood trends as well as the frequency of floods in a nonstationary world. This model is used to explore a range of flood planning issues in a nonstationary world. A decadal flood magnification factor is defined as the ratio of the T‐year flood in a decade to the T‐year flood today. Using historical flood data across the United States we obtain flood magnification factors in excess of 2‐5 for many regions of the United States, particularly those regions with higher population densities. Similarly, we compute recurrence reduction factors which indicate that what is now considered the 100‐year flood, may become much more common in many watersheds. Nonstationarity in floods can result from a variety of anthropogenic processes including changes in land use, climate, and water use, with likely interactions among those processes making it very difficult to attribute trends to a particular cause.     

Modeling Hydrologic Benefits of Low Impact Development: A Distributed Hydrologic Model of The Woodlands,Texas

Low Impact Development (LID) is alternative design approach to land development that conserves and utilizes natural resources to minimize the potential negative environmental impacts of development, such as flooding. The Woodlands near Houston, Texas is one of the premier master‐planned communities in the United States. Unlike in a typical urban development where riparian corridors are often replaced with concrete channels, pervious surfaces, vegetation, and natural drainage pathways were preserved as much as possible during development. In addition, a number of detention ponds were strategically located to manage runoff on site. This article uses a unique distributed hydrologic model, Vflo?, combined with historical (1974) and recent (2008 and 2009) rainfall events to evaluate the long‐term effectiveness of The Woodlands natural drainage design as a stormwater management technique. This study analyzed the influence of LID in The Woodlands by comparing the hydrologic response of the watershed under undeveloped, developed, and highly urbanized conditions. The results show that The Woodlands drainage design successfully reflects predeveloped hydrologic conditions and produces peak flows two to three times lower than highly urbanized development. Furthermore, results indicate that the LID practices employed in The Woodlands successfully attenuate the peak flow from a 100‐year design event, resulting in flows comparable to undeveloped hydrologic conditions.     

电化学脱稳技术处理油田含聚污水

采用"电化学除油器—斜板除油器—核桃壳过滤器"模拟装置处理模拟含聚采油污水,考察了有/无清水剂加入条件下含聚污水的处理效果,并对电化学除油机理进行了分析。实验结果表明:各级处理单元的除油率与电化学处理时间成正比,不加入清水剂、电化学处理40 min时,各级处理单元的除油率均超过92%;在电化学除油器前加入清水剂100 mg/L、电化学处理20 min时,各级处理单元的除油率分别为98.8%~99.4%,处理后污水含油量小于30 mg/L,处理效果优于在斜板除油器前加入清水剂;电化学处理与清水剂处理有良好的协同除油效果,可大幅降低清水剂用量。机理分析结果表明,电化学作用主要使吸附于油-水界面的产出聚合物降解、脱稳,实现了对油-水界面膜强度和界面电荷的有效破坏,除油效果优异且处理后的絮体松散、无黏附性。     

双亲型清水剂处理油田含聚污水

考察了双亲型清水剂QS-03对油田含聚污水处理效果的影响因素,并对其作用机理进行了分析。实验结果表明:当清水剂QS-03的亲水性与亲油性功能基团的摩尔比为2∶1、清水剂加入量大于等于200 mg/L时,处理后污水澄清透明,污水含油量由4 540 mg/L大幅降至26~45 mg/L;在处理温度为50~80℃和污水含油量为3 200~5 800 mg/L的范围内,清水剂QS-03均表现出良好的清水效果,生成的絮体呈松散状,具有良好的流动性。机理分析结果表明,双亲型清水剂QS-03可有效破坏油-水界面双电层、降低界面膜强度,并且与污水中阴离子聚合物的相互作用大幅减弱,因而在高效清水除油的同时可有效避免含聚污水处理中的黏性"含聚油泥"问题。     

Methane Fluxes from a Wetland using the Flux-Gradient Technique The Measurement of Methane Flux from a Natural Wetland Pond and Adjacent Vegetated Wetlands using a TDL-Based Flux-Gradient Technique

Methane emissions were measured from a bog andlake in the Experimental Lakes Area in Northern Ontario in 1992and 1993, prior to and following flooding. Bog fluxes were smallin 1992 (0.27 mg m^-2 d^-1) but increased 5-fold in 1993 afterflooding. Over the bog, there was a diel cycle of nighttimeemission and daytime uptake in 1992 in contrast to constantemission in 1993. Lake emissions decreased after flooding butwere much greater than bog emissions in both years (average = 7.3 mg m^-2 d^-1). Seasonally, the bog flux was correlated withground temperatures after flooding. In 1992, lake fluxes werecorrelated with air temperature on a daily basis. In contrast,seasonal lake fluxes were correlated with water and sedimenttemperatures in 1992, but only with sediment temperatures in1993. These results are explained with respect to the effects offlooding on lake and bog dynamics.     

Upstream Addicks–Barker reservoir damages during Hurricane Harvey: A case study of urban hydrology and policy failure in Houston,TX

Addicks and Barker reservoirs were built in the 1940s to protect downtown Houston from flooding and have generally worked very well until 2017 when Hurricane Harvey devastated much of Houston and surroundings with up to 40 inches (102 cm) of rainfall causing flooding of 154,000 homes in over 22 watersheds in Houston/Harris County alone. However, the story of how Addicks and Barker flooded upstream residential areas from a hydrologic standpoint is a harsh lesson in flood infrastructure policy and funding. This failure to protect both downstream properties in Buffalo Bayou and upstream areas behind the dams ended up with tens of thousands of flooded homes and properties, with many having flood waters for over 10 days. This paper explores the main causes for the flooding and addresses the hydrologic issues upstream in both reservoirs. The main causes of flooding were not just related to a massive rainfall event, but also explosive urban expansion of land use upstream of reservoirs, altered and updated reservoir design issues, and lack of governmental action in the years leading up to the disaster. Potential long-term solutions to the flooding and design problems are addressed in this article as well.