Estimating Future Flood Frequency and Magnitude in Basins Affected by Glacier Wastage

INE/AUTC 15.0

Regional Flood Frequency Analysis Using Computer Simulations

Different probability distribution methods were employed to determine the flood frequency analysis using computer simulations. Many probability distributions including Gumbel, lognormal, log-Pearson type iii, General Extreme value have been tried to fit the data. The length of record for most of the stations is over 10 years (chosen from 1956 0nwards). The data was procured from J.R.M.Hosking for various project sites. The common time period of 1956 onwards has been chosen only to avoid the effect of interception of basin due to construction of storage reservoir and was also subject of flood data. The best fitting distribution works out to be General Extreme Value Distribution. Gumbel's distribution ranks poorly among different probability distributions. A trial version of probability software is used to evaluate the best fit distribution and parameters of distribution

Flood Frequency Design in Sparse-data Regions

Project Completion Report OWRT Contract No. 14-31-0001-5217 Grant No. B-030-ALASThis report summarizes work conducted with funds received from the Office of Water Research and Technology (OWRT), Project B-030-ALAS, Flood Frequency in Sparse-Data Regions. The study was conducted from July 1, 1974, to June 30, 1976, plus a one-year extension to June 30, 1977. The technical results are given in a number of publications which are referenced and abstracted here along with a presentation of the overall philosophy of the project and a coherent summary of the work. Alaska may be characterized, as can most northern areas, by a very sparse data collection network of hydrologic variables. In combination with several physical characteristics of northern hydrology, the sparse data network leads to a very difficult design circumstance. The most well known physical aspect of northern hydrology is permafrost. Other factors of importance are large elevation differences, regional inhomogeneity, high latitude, low temperatures, and the very dynamic nature of the spring breakup. These factors, in combination with the short data base in northern regions, cause hydrologic design to have a large degree of uncertainty.The work upon which this completion report is based was supported by funds provided by the U. S. Department of the Interior, Office of Water Research and Technology, as authorized under the Water Resources Research Act of 1964, Public Law 88-379, as amended

Defining the hundred year flood: a Bayesian approach for using historic data to reduce uncertainty in flood frequency estimates

This paper describes a Bayesian statistical model for estimating flood frequency by combining uncertain annual maximum (AMAX) data from a river gauge with estimates of flood peak discharge from various historic sources that predate the period of instrument records. Such historic flood records promise to expand the time series data needed for reducing the uncertainty in return period estimates for extreme events, but the heterogeneity and uncertainty of historic records make them difficult to use alongside Flood Estimation Handbook and other standard methods for generating flood frequency curves from gauge data. Using the flow of the River Eden in Carlisle, Cumbria, UK as a case study, this paper develops a Bayesian model for combining historic flood estimates since 1800 with gauge data since 1967 to estimate the probability of low frequency flood events for the area taking account of uncertainty in the discharge estimates. Results show a reduction in 95% confidence intervals of roughly 50% for annual exceedance probabilities of less than 0.0133 (return periods over 75 years) compared to standard flood frequency estimation methods using solely systematic data. Sensitivity analysis shows the model is sensitive to 2 model parameters both of which are concerned with the historic (pre-systematic) period of the time series. This highlights the importance of adequate consideration of historic channel and floodplain changes or possible bias in estimates of historic flood discharges. The next steps required to roll out this Bayesian approach for operational flood frequency estimation at other sites is also discussed

COST Action ES0901: European procedures for flood frequency estimation (FloodFreq) [Keynote]

The aim of COST Action ES0901 European Procedures for Flood Frequency Estimation (FloodFreq) is to undertake a Pan-European comparison and evaluation of different methods for flood frequency estimation under the various climatologic and geographic conditions found in Europe, and different levels of data availability. A scientific framework for assessing the ability of these methods to predict the impact of environmental change (climate change, land-use and river engineering works) on future flood frequency characteristics (flood occurrence and magnitude) will be developed and tested. The availability of such procedures is crucial for the formulation of robust flood risk management strategies as required by the Directive of the European Parliament on the assessment and management of floods. The outputs from FloodFreq will be disseminated to: academics, professionals involved in operational flood risk management from private and public institutions, and relevant policy makers from national and international regulatory bodies. This Action enable cooperation between researchers involved in nationally funded research projects to, thereby enabling testing of methods free from the constraints of administrative boundaries, and allowing a more efficient use of European flood research funding

The effects of urbanization on floods in the Austin metropolitan area, Texas

This report looks at compiled data from 1956-1980 to "provide a technique for estimating the magnitude and frequency of flood-peak discharges at ungaged sites and to estimate the effects of changes in urbanization on flood peaks."The effects of urbanization on flood peaks in streams in the Austin metropolitan area were studied in two separate analyses. In the first analysis, annual peak discharge records at 13 streamflow-gaging sites were used to compute a recorded flood frequency relation for each site. Rainfall and streamflow data for 10 to 20 storms for each of these sites were used to calibrate a rainfall-runoff model in which a 55-year rainfall record was used to simulate 55 annual peak discharges. These simulated discharges also were used to develop a flood-frequency relation at each site. The flood-frequency relations from recorded and generated data were then combined by weighting the recorded flood frequency by the years of record at each site to produce a combined (or weighted) flood frequency at each site. Flood frequencies for all 13 sites were subsequently regressed against basin characteristics at each site to determine possible effects of urbanization. The regression analysis of the combined flood-frequency data for the 13 sites yielded an equation for estimating floods of a given recurrence interval at ungaged sites in the Austin area as a function of the contributing drainage area, the total impervious area percentage, and basin shape. The regression equation estimates that a near fully developed hypothetical drainage basin (impervious area percentage, 45) would have discharges for the 2- and 100-year recurrence interval that are 99 percent and 73 percent greater, respectively, than discharges for those frequencies from a rural drainage basin (impervious percentage, 0). In the second analysis, records at one streamflow-gaging site on Waller Creek were analyzed for changes in rainfall-runoff and flood-frequency relations due to urbanization. Annual peak discharges from 1956 to 1980 and data from a total of 80 storms at the Waller Creek site were analyzed. Both analyses showed increases comparable to those predicted using the equations developed from the 13-station analysis. The last 14 years of record (the near fully developed land-use stage for the Waller Creek analysis) at the two sites on Waller Creek were part of the 13-station analysis. The U.S. Geological Survey, in cooperation with the Texas Department of Water Resources began limited investigations of urban watersheds in Austin in 1954, with the installation of two streamflow-gaging stations and three recording rain gages in the Waller Creek watershed. In 1963, a streamflow gage and three recording rain gages were installed at Wilbarger Creek watershed, a rural area just north of Austin. In cooperation with the City of Austin, the urban study was expanded in 1975 to include additional streamflow and rainfall gaging stations and the collection of surface water-quality data. The number of streamflow-gaging stations increased from 2 to 25 and the number of recording rain gages increased from 3 to 31.Waller Creek Working Grou

Theoretical investigation of process controls upon flood frequency: role of thresholds

International audienceTraditional statistical approaches to flood frequency inherently assume homogeneity and stationarity in the flood generation process. This study illustrates the impact of heterogeneity associated with threshold non-linearities in the storage-discharge relationship associated with the rainfall-runoff process upon flood frequency behaviour. For a simplified, non-threshold (i.e. homogeneous) scenario, flood frequency can be characterised in terms of rainfall frequency, the characteristic response time of the catchment, and storm intermittency, modified by the relative strength of evaporation. The flood frequency curve is then a consistent transformation of the rainfall frequency curve, and could be readily described by traditional statistical methods. The introduction of storage thresholds, namely a field capacity storage and a catchment storage capacity, however, results in different flood frequency "regions" associated with distinctly different rainfall-runoff response behaviour and different process controls. The return period associated with the transition between these regions is directly related to the frequency of threshold exceedence. Where threshold exceedence is relatively rare, statistical extrapolation of flood frequency on the basis of short historical flood records risks ignoring this heterogeneity, and therefore significantly underestimating the magnitude of extreme flood peaks

A joint probability approach for the confluence flood frequency analysis

The flood frequency analysis at or nearby the confluence of two tributaries is of interest because it is necessary for the design of the highway drainage structures. However, The shortage of the hydrological data at the confluence point makes the flood estimation challenging. This thesis presents a practical procedure for the flood frequency analysis at the confluence of two streams by multivariate simulation of the annual peak flow of the tributaries based on joint probability and Monte Carlo simulation. Copulas are introduced to identify the joint probability. The results of two case studies are compared with the flood estimated by the univariate flood frequency analysis based on the observation data. The results are also compared with the ones by the National Flood Frequency program developed by United State Geological Survey. The results by the proposed model are very close to ones by the unvariate flood frequency analysis

Flood Frequency Estimation in Northern Sparse Data Regions: Completion Report

The primary objective of this project was to complete development of an arctic hydrologic model and to evaluate its usefulness in generating information useful for a design tool in estimation of peak flow discharges. The peak flow discharges studied were those generally analyzed and evaluated in the design of facilities for stream crossings.The work upon which this report is based was supported by funds (Project B-021 ALAS) provided by the United States Department of the Interior, Office of Water Resources Research, as authorized by Water Resources Research Act of 1964, Public Law 88-379, as amended