FLOOD RISK EVOLUTION: EXAMINING CHANGES IN FLOOD BEHAVIOR AND CONSEQUENCES FOR FLOOD RISK ANALYSIS
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Estimates of flood risk involve using the statistical moments of peak flow series data, i.e. mean, standard deviation, to estimate the parameters of a distribution. The fitted distribution relates the probability of exceedance to a peak flow discharge. The fitted distribution, or flood frequency curve, is then used to inform the design of structures and water management and planning. However, flood risk estimation requires key assumptions, some of which have come under scrutiny in recent years. The first, stationarity, assumes that the moments used to fit a probability distribution are time invariant; e.g. the mean is constant throughout the observed record. The second assumption, homogeneity, is defined as the spatial invariance of flood moments. Homogeneity is a critical assumption when using regional information to inform a statistic of interest. In regional flood frequency estimation, commonly employed techniques such as quantile regression, regional skew estimation and the index flood method work under the assumption of homogeneity. Homogeneity assumes that all sites within a defined region will have the same flood frequency curve, indicating that given the same climatic disturbance, all sites will behave similarly. However as climate and landscape change, these assumptions can be violated. Alterations to precipitation and temperature have occurred, producing subsequent changes to associated flood risk. Landscape changes have also altered how runoff is translated through the watershed, ultimately impacting peak flows. This analysis considers several cases under which the assumptions of flood risk are violated. Chapter 1 analyzes the regional water balance, defined by the Baseflow Index (BFI), on the flood frequency curve indexed at key return periods. Chapter 2 assesses how storage in a case study watershed, the Suwannee River Basin, impacts the assumptions of homogeneity. Results from Chapter 2 guide the development of a new regional skew for the Suwannee River Basin which is documented in Chapter 3. Finally, Chapter 4 addresses using hydrological models to assess flood risk. First, different bias correction methods are applied to peak flows modeled using the Soil and Water Assessment Tool (SWAT), and then the impacts of climate and landscape change on these peak flows are compared to determine how each uniquely alter flood risk.Keywords:
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Statistic
ABSTRACT. Summarizing the foregoing discussions in this journal on testing for regional homogeneity the present note shows that in the model of Zellner's seemingly unrelated regressions one test statistic may be used not only to test for overall homogeneity but also to examine for individual coefficient homogeneity. This aim is achieved by varying the linear restrictions in the test statistic according to different problems. To illustrate these tests regional consumption functions for the 11 Bundesläder (States) of the Federal Republic of Germany are used.
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Local communities may experience flood events with devastating damages and economic losses. This work presents the application of an integrated method for flood loss estimation at the watershed level. The one-dimensional hydraulic model MIKE 11 was used to simulate the physical process of a flood event in a river channel and its floodplains. Flood parameters such as flood extent, floodplain water depth and flood duration were estimated. The parameter values obtained from the simulation were used for the estimation of flood loss. A grid-based mathematical model taking into account land use in the study area was used for this purpose. Such an econometric model is capable of determining flood-prone areas as well as estimating the economic losses associated with a flood event. This integrated methodology was applied to the Koiliaris River Basin in Crete, Greece.
Flood forecasting
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The projects of constructing embankment massively on Xijiang River Basin not only lead to flood returning to main channel,but also change the flood channel storage relationship of the original natural river,making that the flood sequences which are used for flood control planning and the risk assessment of flood disaster have lost their consistency.At present,the research of flood retaining to main channel is concentrated on the computation aspect of the flood's return to channel and modification to original state after the flood overflowing the channel,and lacks sufficient consideration of the encounter experience of main and branch flood and the interval flood,and also lacks systematic research of the causes of flood variation and frequency analysis method of inconsistency flood.This article suggested that use the hydrologic variation diagnosis system to carry on variation analysis towards hydrologic features in Xijiang River Basin,and then distinguish its space and time variation rule;Develop conceptive hydrological model of multi-input and single-output(MISOCHM) on the main and branch flood and the interval rainstorm and flood of middle and lower reaches of Xijiang River to simulate its flood forming process;Propose two frequency analysis method of inconsistency flood that one is based on MISOCHM model and another is based on Hilbert-Huang transformation to inquire into the flood frequency distribution of the river cross section under change environment and to appraise the Xijiang River embankment present situation and future flood prevention ability combined the flood prevention plan of Xijiang River Basin.The study results not only has important theoretical significance to water cycle and water environment security research under change environment,but also has important practical applications for river basin flood control planning and flood risk assessment.
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The paper analyses the variability of flood elements and the complexity of flood, puts forward three classification methods of flood grade: standardization value of flood-peak stage exceeding normal stage and probable maximum flood stage exceeding normal stage. Flood return period and standard surface flood flow, analyses 98 flood grade in Changjiang river basin.
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ABSTRACT: Hydraulic modification of flood plains by human activity is the primary cause of rising flood damages throughout the world. As flood‐plain hydraulic roughness increases, so does the water level for a fixed flow rate. This raises the flood damage associated with a flood of given return period, and thus, magnifies the flood risk. This article presents an approach that integrates climatic, hydrologic, and hydraulic principles and presents models to discern the probable causes of flood damage in a basin that undergoes flood‐plain development. The article documents key factors that govern flood damage and presents a case study that illustrates the principles of forensic hydrology in an impacted flood plain. The study demonstrates flood level rise caused by hydraulic alteration of a flood plain between 1969 and 1995 and apportioned the increased water level among agricultural and structural factors located in the study area.
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Currently, there is general concern about the non-stationary behaviour of flood series. Consequently, several studies have been conducted to identify large-scale patterns of change in such flood series. In Spain, a general decreasing trend was found in the period 1959–2009. However, a multi-temporal trend analysis, with varying starting and ending years, showed that trend signs depended on the period considered. Flood oscillations could influence the results, especially when flood-rich and flood-poor periods are located at the beginning or end of the series. In Spain, a flood- rich period in 1950–1970 seemed to lead to the generalised decreasing trend, as it was located at the beginning of the flood series. Nevertheless, the multi-temporal test can only find potential flood- rich and flood-poor periods qualitatively. A methodology has been developed to identify statistically significant flood-rich and flood-poor periods. The expected variability of floods under the stationarity assumption is compared with the variability of floods in observed flood series. The methodology is applied to the longest streamflow series available in Spain. Seven gauging stations located in near-natural catchments, with continuous observations in the period 1942–2014, are selected. Both annual maximum and peak-over-threshold series are considered. Flood-rich and flood-poor periods in terms of flood magnitudes and the annual count of exceedances over a given threshold are identified. A flood-rich period in the beginning of the series and a flood-poor period at its end are identified in most of the selected sites. Accordingly, a flood-rich period placed at the beginning of the series, followed by a flood-poor period, influence the generalised decreasing trend in the flood series previously found in Spain.
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Procedures for estimating recurrence intervals of extreme floods are developed. Estimation procedures proposed in this paper differ from standard procedures in that only the largest 10–20% of flood peaks are explicitly used to estimate flood quantiles. Quantile estimation procedures are developed for both annual peak and seasonal flood frequency distributions. The underlying model of flood peaks is a marked point process , where represents time of occurrence of the j th flood during year i and the mark represents magnitude of the flood peak. Results from extreme value theory are used to parameterize the upper tail of flood peak distributions. Quantile estimation procedures are applied to the 92‐year record of flood peaks from the Potomac River. Results suggest that Potomac flood peaks are bounded above. The estimated upper bound is only 20% larger than the flood of record.
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