A New Flood Index for Use in Evaluation of Local Flood Severity: A Case Study of Small Ungauged Catchments in Korea1

Ahn, Jae Hyun and Hyun Il Choi, 2013. A New Flood Index for Use in Evaluation of Local Flood Severity: A Case Study of Small Ungauged Catchments in Korea. Journal of the American Water Resources Association (JAWRA) 49(1): 1‐14. DOI: 10.1111/jawr.12025 Abstract: The aim of this article is to develop a new index measuring the severity of floods in small ungauged catchments for initial local flood information by the regression analysis between the new flooding index and rainfall patterns. Although a rapid local flood caused by heavy storm in a short period of time is now one of common natural disasters worldwide, such a sudden and violent hydrologic event is difficult to forecast. As local flooding rises rapidly with little or no advance warning, the key to local flood forecasting is to quickly identify when and where local flooding above a threshold is likely to occur. The new flooding index to characterize local floods is measured by the three normalized relative severity factors for the flood magnitude ratio, the rising curve gradient, and the flooding duration time, quantifying characteristics of flood runoff hydrographs. The new flooding index implemented for the two selected small ungauged catchments in the Korean Peninsula shows a very high correlation with logarithm of the 2‐h maximum rainfall depth. This study proposes 30 mm of rainfall in a 2‐h period as a basin‐specific guidance of precaution for the incipient local flooding in the two study catchments. It is expected that the best‐fit regression equation between the new flooding index and a certain rainfall rate can provide preliminary observations, the flood threshold, and severity information, for use in a local flood alert system in small ungauged catchments. Editor's note: This paper is part of a featured series on Korean Hydrology. The series addresses the need for a new paradigm of river and watershed management for Korea due to climate and land use changes.     

Flooding in Texas: Examination of Temporal Changes and Impacts of Tropical Cyclones

Annual maximum peak discharge measurements from 62 stations with a record of at least 70 years are used to assess extreme flooding in Texas at the regional scale. This work focuses on examination of the validity of the stationarity assumption and on the impact of tropical cyclones (TCs) on the upper tail of the flood peak distribution. We assess the validity of the stationarity assumption by testing the records for abrupt and gradual changes. The presence of abrupt changes in the first two moments of the flood peak distribution is assessed using the Lombard test. We use the Mann‐Kendall test to examine the presence of monotonic trends. Results indicate that violations of the stationarity assumption are most commonly caused by abrupt changes, which are often associated with river regulation. We fit the time series of stationary flood records with the generalized extreme value distribution to investigate whether TCs control the upper tail of the flood peak distribution. Our results indicate that TCs play a diminished role in shaping the upper tail of the flood peak distribution compared with areas of the eastern United States subject to frequent TCs.     

Incorporating low-resolution historic species location data decreases performance of distribution models

Developing robust species distribution models is important as model outputs are increasingly being incorporated into conservation policy and management decisions. A largely overlooked component of model assessment and refinement is whether to include historic species occurrence data in distribution models to increase the data sample size. Data of different temporal provenance often differ in spatial accuracy and precision. We test the effect of inclusion of historic coarse-resolution occurrence data on distribution model outputs for 187 species of birds in Australian tropical savannas. Models using only recent (after 1990), fine-resolution data had significantly higher model performance scores measured with area under the receiver operating characteristic curve (AUC) than models incorporating both fine- and coarse-resolution data. The drop in AUC score is positively correlated with the total area predicted to be suitable for the species (R² = 0.163-0.187, depending on the environmental predictors in the model), as coarser data generally leads to greater predicted areas. The remaining unexplained variation is likely to be due to the covariate errors resulting from resolution mismatch between species records and environmental predictors. We conclude that decisions regarding data use in species distribution models must be conscious of the variation in predictions that mixed-scale datasets might cause.     

Examining Flood Frequency Distributions in the Midwest U.S.1

Villarini, Gabriele, James A. Smith, Mary Lynn Baeck, and Witold F. Krajewski, 2011. Examining Flood Frequency Distributions in the Midwest U.S. Journal of the American Water Resources Association (JAWRA) 47(3):447‐463. DOI: 10.1111/j.1752‐1688.2011.00540.x Abstract: Annual maximum peak discharge time series from 196 stream gage stations with a record of at least 75 years from the Midwest United States is examined to study flood peak distributions from a regional point of view. The focus of this study is to evaluate: (1) “mixtures” of flood peak distributions, (2) upper tail and scaling properties of the flood peak distributions, and (3) presence of temporal nonstationarities in the flood peak records. Warm season convective systems are responsible for some of the largest floods in the area, in particular in Nebraska, Kansas, and Iowa. Spring events associated with snowmelt and rain‐on‐snow are common in the northern part of the study domain. Nonparametric tests are used to investigate the presence of abrupt and slowly varying changes. Change‐points rather than monotonic trends are responsible for most violations of the stationarity assumption. The abrupt changes in flood peaks can be associated with anthropogenic changes, such as changes in land use/land cover, agricultural practice, and construction of dams. The trend analyses do not suggest an increase in the flood peak distribution due to anthropogenic climate change. Examination of the upper tail and scaling properties of the flood peak distributions are examined by means of the location, scale, and shape parameters of the Generalized Extreme Value distribution.     

桃山水库二期工程蓄水对矿井开采的影响评价

桃山水库二期建设工程蓄水后,将对周围矿井开采带来影响.对茄子河区某煤矿的开采现状进行分析,讨论了水库蓄水后,矿井需留设的安全煤岩柱及其安全性,并提出了相应的建议.     

Rising recreancy: flood control and community relocation in Houston,TX, from an environmental justice perspective

This article looks at issues of recreancy, environmental justice, and relocation as they relate to a flood control infrastructure project in inner city Houston. The main research questions were “What forms would recreancy take?” and “Can a project be environmentally just if recreancy is present?” Through the structural coding of 53 semi-structured interviews, recreancy was found even in a project where the sponsors used community cohesion as a guideline. This article illuminates the difficulties flood control project engineers face when working in local communities and argues that engineering issues are also social issues. Further, the relocatees within this flood control project voice some of the same concerns experienced by people relocated in other involuntary infrastructure development projects. The case outlined in this article could be used to better help those involuntarily relocated for flood control.     

Potential Impact of Climate Change on Hurricane Flooding Inundation,Population Affected and Property Damages in Corpus Christi1

Frey, Ashley E., Francisco Olivera, Jennifer L. Irish, Lauren M. Dunkin, James M. Kaihatu, Celso M. Ferreira, and Billy L. Edge, 2010. Potential Impact of Climate Change on Hurricane Flooding Inundation, Population Affected and Property Damages in Corpus Christi. Journal of the American Water Resources Association (JAWRA) 1–11. DOI: 10.1111/j.1752-1688.2010.00475.x Abstract: The effect of climate change on storm-surge flooding and the implications for population and structural damages on the city of Corpus Christi, Texas, was investigated. The study considered the influence of sea level rise and hurricane intensification, both influenced by climate change. Combinations of future carbon dioxide equivalent emission rates and carbon dioxide doubling sensitivities, based on findings of the Intergovernmental Panel on Climate Change, were considered to define future climate scenarios. A suite of physically based numerical models for hurricane winds and the resulting waves, surge, and morphological change at the coast were used to determine flooded areas, population affected, and property damages for Hurricanes Bret, Beulah, and a version of Carla shifted south from its original track, under present and predicted future climate conditions. A comparison of the economic damages for current climate conditions and for the 2080s climate scenario shows that, for Carla (shifted), there will be an increase in the range of $270-1,100 million; for Beulah, of $100-390 million; and, for Bret, of $30-280 million. A similar analysis was also conducted for 2030s predicted climate scenarios. Overall, the comparison of the results for the different climate conditions indicates what the destructive consequences of climate change could be, even within the somewhat short time frame of 80 years considered here.     

Flood policy reversal in australia

In 1977 the Government of New South Wales introduced a flood prone lands policy which attempted to break with the past emphasis on structural works. Cornerstones of the policy were the preparation of floodplain maps, and use of the 1:100 (100 year or 1%) flood to delineate floodplains and 1:20 flood for floodway definition. The fiscal and regulatory elements of the policy were to be applied more or less uniformly within the two zones. At first there was little effective opposition to the program, but this changed when large areas of Sydney, which had not been inundated since development, were mapped. Local government concern over issues of legal liability led to decisions which in turn prompted opposition to the policy from residents' action groups and property development interests. A perceived drop in property values provided the main motivation for action by residents. This pressure for change, which intensified just before the 1984 state election, saw the policy overturned.
The new policy gives local government greater responsibility for floodplain management. State authorities have withdrawn from floodplain mapping, although technical advice will continue to be provided, and there are no longer any uniform floodplain or floodway definitions. Policy implementation is to be guided by a Manual which attempts to define flood hazard in terms of both physical and social criteria.     

重庆市洪涝灾害的特点、成灾机制成灾背景调查与分析

洪涝灾害是重庆较为严重的一种自然灾害，本文分析重庆市洪涝灾害特征入手，在此基础上，对重庆市洪涝灾害的成灾机制做了阐述，并从影响洪涝灾害夏季降水的主要物理因素、地形地貌背景、地表径流与水系和人为活动等方面对重庆市洪涝灾害的成灾背景进行分析，阐明了各成灾因背景之间的相互联系。     

水盐梯度对闽江河口湿地土壤水稳性团聚体分布及稳定性的影响

为了揭示水盐梯度对河口湿地土壤水稳性团聚体分布及稳定性的影响,对闽江河口不同淹水环境和盐度下短叶茳芏(Cyperus malaccensis)湿地土壤水稳性团聚体进行了测定与分析.结果表明:①闽江河口半咸水湿地和淡水湿地0～30 cm土壤粉+黏团聚体、微团聚体和大团聚体的含量分别为63.12%～77.49%、6.82%～31.64%、4.38%～22.63%.除20～30 cm土层外,高潮滩0～20 cm土壤粉+黏团聚体和大团聚体含量均随盐度的增加而增加,增幅分别为8.74%～9.85%和105.54%～144.40%;0～20 cm土壤微团聚体含量均随盐度的增加而降低,高潮滩降幅为59.56%～65.20%,低潮滩降幅为55.65%～60.92%.②高潮滩土壤团聚体稳定性随盐度的增加而增加,盐度对微团聚体、大团聚体含量(DR_(0.25))和平均重量直径(MWD)的作用力在不同土层均影响显著,盐度和淹水的交互作用对各级土壤水稳性团聚体分布及稳定性的影响均不显著.③土壤团聚体稳定性与土壤TC含量呈倒"U"型关系.综上,淹水环境变化对土壤水稳性团聚体分布及稳定性的影响较小,盐度和有机碳含量是影响闽江河口湿地土壤水稳性团聚体分布及稳定性的重要限制性参数.