MULTITEMPORAL SCALE HYDROGRAPH PREDICTION USING ARTIFICIAL NEURAL NETWORKS1

Abstract: An artificial neural network (ANN) provides a mathematically flexible structure to identify complex nonlinear relationship between inputs and outputs. A multilayer perceptron ANN technique with an error back propagation algorithm was applied to a multitime-scale prediction of the stage of a hydro-logically closed lake, Devils Lake (DL), and discharge of the Red River of the North at Grand Forks station (RR-GF) in North Dakota. The modeling exercise used 1 year (2002), 5 years (1998–2002), and 27 years (1975–2002) of data for the daily, weekly, and monthly predictions, respectively. The hydrometeorological data (precipitations P_(t), P_(t-1), P_(t-2), P_(t-3), antecedent runoff/lake stage R_(t-1) and air temperature T_(t) were partitioned for training and for testing to predict the current hydro-graph at the selected DL and RR-GF stations. Performance of ANN was evaluated using three combinations of daily datasets (Input I = P_(t)), P_(t-l), P_(t-2), P_(t-3), T_(t) and R_(t-l); Input II = Input-l less P_(t) P_(t-l), P_(t-2), P_(t-3); and Input III = Input-II less T_(t)). Comparison of the model output using Input I data with the observed values showed average testing prediction efficiency (E) of 86 percent for DL basin and 46 percent for RR-GF basin, and higher efficiency for the daily than monthly simulations.     

WILLINGNESS TO PAY FOR FLOOD RISK REDUCTION AND ITS DETERMINANTS IN JAPAN1

ABSTRACT: This study aimed to clarify public preferences for flood control measures in Japan, willingness to pay (WTP), and the main factors involved in WTP by applying the contingent valuation method. Findings showed that most residents surveyed expected some flood control measures, and revealed a diversity of interest in river management. WTP levels for different measures ranged from a mean of ¥2,887 to ¥4,861 and from a median of ¥1,000 to ¥2,000. However, WTP for additional flood risk reduction beyond initial levels was found to be zero. This was considered to be because WTP for flood risk reduction must be determined within a multi‐risk context. WTP for flood control measures may increase with per capita income, individual preparedness, and/or experience with flooding, but may decrease with distance from a river, acceptability of flood risk, and provision of environmental information. Furthermore, perception of flood risk may increase WTP, while perception of other risks may decrease it. Methods of dealing with environmental risk that were proposed in the survey may have affected WTP levels.     

DOCUMENTATION OF HIGH SUMMER FLOWS ON THE POTOMAC RIVER FROM THE WOOD ANATOMY OF ASH TREES1

ABSTRACT: Ash trees (Fraxinus americana L. and F. Pennsylvanica Marsh.) collected from the flood plain of the Potomac River near Washington, D.C., were studied for evidence of associations between known periods of above-average summer flows and changes in wood-growth anatomy. Concentric bands of latewood fibers with atypically large lumens and thin walls commonly developed in trees growing near the low-water channel. Discharge records indicate that roots of most trees with these “white rings” were flooded temporarily during the latewood-growth interval. Trees apparently were not damaged and a concomitant reduction of internal water stresses seems to have accelerated the rate of radial growth. The intra-ring position of anomalous fibers generally corresponded to the time of increased discharge within the estimated interval of latewood growth. Anomalous fibers occasionally formed in unflooded trees, but their position also coincided with episodes of increased discharge. The results of these studies may have applications for streamflow-reconstruction techniques where hydrologic data are incomplete or lacking.     

NEAR REAL-TIME MAPPING OF THE 1975 MISSISSIPPI RIVER FLOOD IN LOUISIANA USING LANDSAT IMAGERY1

ABSTRACT: The project described in this report was undertaken by the Louisiana State Planning Office to establish the extent of backwater flooding in Louisiana in April 1975. Band 7 Landsat imagery, enlarged to a scale of 1:250,000 was used to visually identify flooded areas. Inundated areas were delineated on overlays keyed to 1:250,000 U.S. Geological Survey topographic quadrangles. Tabular data identifying acres flooded, according to land use type, were derived by merging the flood map overlays with computerized 1972 land use data. Approximately 1.12 million acres of the state were inundated by flood waters. The total acreage and land use types affected by flooding were determined within 72 hours from the time the flood areas were imaged. Flooded maps were prepared for 26 parishes. Field observations were made by Louisiana Cooperative Extension Service county agents in order to determine the accuracy of parish flood maps and flood acreage figures by land use type. Results indicated that this was a fast, accurate, and relatively inexpensive method of compiling flood data for disaster planning and postflood analysis.     

2002年6月陕西佛坪山洪灾害成因及特征

陕西省佛坪县位于秦岭中部南坡。2002年6月9日,该县山洪暴发,造成数百人死亡和失踪及巨大财产损失。15小时250.3mm的特大暴雨,是本次洪灾形成的根本原因。防灾意识不强,在山洪危险区建房等人为因素增大了洪灾损失。由于县境内主河支流短小,洪峰快速形成,具有很大破坏性。针对洪灾的成因和特征,提出了洪灾对策。     

"05728"小兴安岭致洪暴雨中尺度分析

为了加强对黑龙江省暴雨中尺度系统的认识，有利于暴雨灾害的预报和防御，对2005年7月28-29日发生在小兴安岭的暴洪中尺度系统，从大尺度环流形势、环流演变特征、云图和雷达回波上观测到的中尺度云团的发生发展、水汽来源、产生的热力和动力条件等几方面进行了比较深入的分析。分析表明：暴雨中尺度系统是在高空槽和新生东北低涡的环境中诱发出来的；卫星和雷达图像也观测到了中-β尺度和中-α尺度的中尺度对流复合体（Mesoscale Convective complex，MCC）的发生发展；中尺度系统的水汽通道主要有两支：西南气流和偏东气流；中层冷空气的推动、风场垂直和水平切变及地形强迫抬升是这次暴洪过程中尺度系统的动力因子和触发条件。     

MANAGEMENT OF FLOOD CONTROL SUMPS AND POLLUTANT TRANSPORT1

ABSTRACT: Levee sump systems are used by many riverine communities for temporary storage of urban wet weather flows. The hydrologic performance and transport of stormwater pollutants in sump systems, however, have not been systematically studied. The objective of this paper is to present a case study to demonstrate development and application of a procedure for assessing the hydraulic performance of flood control sumps in an urban watershed. Two sumps of highly variable physical and hydraulic characteristics were selected for analysis. A hydrologic modeling package was used to estimate the flow hydrograph for each outfall as part of the flow balance for the sump. To validate these results, a water balance was used to estimate the total runoff using sump operational data. The hydrologic model calculations provide a satisfactory estimate of the total runoff and its time‐distribution to the sump. The model was then used to estimate pollutant loads to the sump and to the river. Although flow of stormwater through a sump system is regulated solely by flood‐control requirements, these sumps may function as sedimentation basins that provide purification of stormwater. A sample calculation of removals of several conventional pollutants in the target sumps using a mass balance approach is presented.     

Assessment of Flood Vulnerability Based on CMIP5 Climate Projections in South Korea

The objective of this article was to assess flood vulnerability based on the representative concentration pathways (RCP) scenarios at city and county levels. A quantile mapping method was adopted to correct bias that is inherent in climate change scenarios. A series of proxy variables related to climate exposure, sensitivity, and adaptive capacity were chosen to assess flood vulnerability. Proxy variables were standardized using the Z‐score method. Principal component analysis was carried out to calculate the weighting of proxy variables. The study area was the Korean peninsula. The spatial resolution was on a city and county basis and the temporal resolution was 1990s, 2025s, 2055s, and 2085s (divided into 1976‐2005, 2011‐2040, 2041‐2070, and 2071‐2100). In the spatial comparison, we found that the areas with high‐level flood vulnerability increased over time in the central region, including metropolitan areas, and near the southern coast. In the temporal comparison, we found that the RCP4.5 scenario showed a tendency to increase steadily and the RCP8.5 scenario showed a tendency to decrease in the 2055s slightly and increase again in the 2085s. The study findings may provide useful data for the determination of priority for countermeasure development, though robustness of these findings with additional future projections should be established.     

基于情景分析的区域洪涝灾害风险评价——以巢湖流域为例

洪涝灾害是制约区域粮食安全和社会可持续发展的主要因子之一。在风险识别的基础上,从致灾因子、孕灾环境、承灾体等方面选取评价指标,建立评价指标体系。运用层次分析法确定指标权重,通过情景分析技术从降水、土地利用、人口、GDP等方面构建复合情景;应用GIS空间分析技术构建洪涝灾害风险评价模型,对巢湖流域洪涝灾害风险进行评价。研究结果表明:2020年巢湖流域洪涝灾害危险性由东南部向西北部减小;合肥市区的洪涝灾害易损性最大,和县的易损性最小。巢湖流域东南部洪涝灾害风险最大,西南部的大别山区风险较小,随着重现期的增大,流域的洪涝灾害风险也逐渐增大。模拟灾害发生的情景,并分析不同情景下的洪涝灾害风险,更能体现洪涝灾害的不确定性和变化性,为流域防洪战略决策研究提供科学依据。     

四川省不同类型山洪灾害与主要影响因素的关系

以四川省为例,在明确溪河洪水及其引发的滑坡、泥石流三类山洪灾害分布格局的基础上,构建概念模型,分析降雨、地形、人口资产易损性等引发山洪灾害的基本因子和土壤、河网密度、土地利用等一般因子对不同类型山洪灾害的影响程度,并比较它们的异同。结果表明:(1)四川省山洪灾害主要分布在盆周山区、川西高原和横断山脉一带;(2)如果3项基本因子可以解释山洪灾害空间分布100%的变化,则它们对三类灾害的影响程度分别为:溪河洪水,降雨59%、地形28%、人口资产13%;泥石流,降雨15%、地形73%、人口资产12%;滑坡,降雨48%、地形34%、人口资产18%;(3)总体上,泥石流灾害对地形、岩性、土地利用等下垫面因子的依赖更高,而溪河洪水和滑坡灾害受降雨要素的影响更大。