Design Flood Estimation Research Articles

Discussion on “Design Flood Estimation in Western Australia” by D Flavell

Discussion on “Design Flood Estimation in Western Australia” by D Flavell

Investigation into Probabilistic Losses for Design Flood Estimation: A Case Study for The Orara River Catchment, Nsw

Australian Rainfall & Runoff (Pilgrim, 1987) recommends the design event approach (DEA) as the preferred method for estimating design flood hydrographs, in which a single design event is adopted. More recently, Monte Carlo simulation has been used to allow for the probabilistic nature of input variables in flood modelling. This paper adopts a Monte Carlo framework to evaluate the impact of probabilistic losses on design flood estimates for the Orara River catchment in northeastern NSW. A RORB runoff routing model was used to derive loss values for both the initial loss-continuing loss (IL-CL) and initial loss-proportional loss (IL-PL) models. It has been found that the initial, continuing and proportional losses can be approximated by the Gamma, Weibull and Beta distributions, respectively. When these distributions were compared with non-parametric distributions, differences in the flood estimates were found to be minimal. Another finding was that peak floods estimated using the DEA were more biased for the IL-CL model, than for the IL-PL model. In comparison to the at-site flood frequency curve the IL-CL model produced an overall better fit of the shape of the curve, however, the IL-PL model provided a better fit to the observed flood peaks for mid-range events.

A new method for identification of flood seasons using directional statistics

Information on flood seasonality is required in many practical applications, such as estimation of seasonal design floods, flood forecasting and protection, flood-plain management and operation of water resources systems. Directional statistics (DS) and relative frequency (RF) are two of the popular methods for identifying flood seasonality. A new method, which is an improvement over DS, the IDS method, is proposed to identify flood seasonality and partition the flood season into sub-seasons. The performance of the IDS method was evaluated using synthetic data as well as observed data. The RF, DS and IDS methods were applied to the Geheyan and Baishan reservoir basins in China, and their results were compared and analysed. The results of flood seasonality identified by the IDS method were more objective than those of the RF and DS methods. Editor Z.W. Kundzewicz; Associate editor S. Grimaldi Citation Chen, L., Singh, V.P., Guo, S.-L., Fang, B., and Liu, P., 2013. A new method for identification of flood seasons using directional statistics. Hydrological Sciences Journal, 58 (1), 1–13.

Indirect Estimation of Design Flood in Urbanized River Basins Using a Distributed Hydrological Model

AbstractA method for indirect estimation of design flood in poorly gauged urbanized river basins by using distributed hydrological modelling is presented. It is based on the critical flood design criterion that maximizes peak flow for a given return period by transforming precipitation of depth duration frequency curve into runoff. The indirect method is compared against the direct method based on regional approach and index flood estimation. This paper shows that the direct method significantly underestimates design flood in case discharge measurements are strongly affected by artificial alteration of water courses with possible catastrophic consequences in terms of loss of life and damage to property when the cause of alteration would be removed. Moreover, the use of a spatially distributed model allows taking into account the heterogeneity that generally characterizes river basins with an high degree of urbanization. The presented indirect method provides a design hydrograph that is useful for those ca...

Fuzzy 회귀분석기법을 이용한 평창강 유역의 설계홍수량 산정

선형회귀분석기법은 오랫동안 수공학분야뿐만 아니라 경제학, 통계학 등 여러 분야에서 널리 이용되어 왔다. Fuzzy 회귀분석기법은 자료의 불확실성이 높을 때 이를 정량화하여 회귀분석 모형에 반영할 수 있다. 본 연구에서는 평창강 유역의 임의 지점에서 설계 홍수량을 산정하기 위해 fuzzy 회귀분석모형을 개발하였다. 평창강 유역과 같은 산지하천 유역은 관측소의 부재로 홍수유출해석에 필요한 자료의 습득이 어려운 경우가 많이 있다. 본 연구에서는 지리정보시스템을 이용하여 유역특성인자를 공간적으로 분석하고, 그 결과를 바탕으로 미계측 산지유역에서 설계홍수량을 산정할 수 있는 기법을 검토하였다. Fuzzy 회귀분석기법을 산지하천 유역의 특성을 가지고 있으며 IHP 시험유역 운영을 통하여 비교적 강우와 유량자료가 잘 수집되어 있는 평창강 유역에 적용하였다. 평창강 유역에 대해서 유역특성인자를 이용하여 fuzzy 설계홍수량 산정식을 개발하였고, 유역의 본류를 따라 위치하고 있는 9개의 지점에서 산정된 빈도홍수량과 비교하여 개발된 산정식의 적합성을 검토하였다. Fuzzy 회귀분석을 사용하여 지역회귀분석을 수행한다면 자료 관측에서 발생하는 빈도홍수량의 불확실성을 정량화하고, 불확실성의 전파를 파악할 수 있다. Linear regression technique has been used widely in water resources field as well as various fields such as economics and statistics, and so on. Using fuzzy regression technique, it is possible to quantify uncertainty and reflect them to the regression model. In this study, fuzzy regression model is developed to compute design floods in any place in Pyeongchang River basin. In ungaged basins, it is usually difficult to obtain data required for flood discharge analysis. In this study, basin characteristics elements are analyzed spatially using GIS and the technique of estimating design flood in ungaged mountainous basin is studied based on the result. Fuzzy regression technique is applied to Pyeongchang River basin which has mountainous basin characteristics and well collected rainfall and runoff data through IHP test basin project. Fuzzy design flood estimation equations are developed using the basin characteristics elements for Pyeongchang River basin. The suitability of developed fuzzy equations are examined by comparing the results with design floods computed in 9 locations along the river. Using regional regression method and fuzzy regression analysis, the uncertainties of the design floods occurred from the data monitoring can be quantified.

Assessing Adequacy of a Probability Distribution for Estimation of Design Flood

Estimation of design flood for a desired return period is of prime importance for safe design of hydraulic structures such as dams, spillways, bridges, culverts, urban drainage systems and flood plain zoning. Frequency analysis enables estimation of the probability of occurrence of a certain hydrological event of practical importance by fitting a probability distribution to one that is empirically obtained from recorded annual maximum discharge (AMD) data. This study deals with the fitting of Extreme Value Type-1, Gamma, 2-parameter Lognormal (LN2) and Log Pearson Type-3 (LP3) distributions to the AMD data; and examines the use of goodness-of-fit tests and diagnostic analysis in assessing the adequacy of suitable probability distribution for estimation of design flood. Results of the study showed that LN2 distribution is better suited for modelling flood data for Tapi at Burhanpur, Girna at Dapuri and Bori at Malkheda sites; and LP3 is the best for Purna at Lakhpuri.

Regional flood frequency analysis in arid regions: A case study for Australia

Summary A large part of the world faces the problem of aridity, e.g. in Australia, the semi-arid and arid regions occupy about 50–75% of the country. There is a serious lack of data on many key hydrological processes in the arid regions, which makes it difficult to understand the hydrological processes in these regions. Although arid regions are characterised by a very low mean annual rainfall, it can experience severe flooding causing widespread damage. In hydrological literature, there is a limited presence of the application of regional flood frequency analysis (RFFA) studies for the world arid regions due to limited data availability. This paper presents a RFFA study for the semi-arid and arid regions of Australia using the most up-to-date data set and compares the results with that of the world data. It has been found that arid catchments exhibit a higher loss and lower runoff coefficient values as expected. Based on four model selection criteria and L -moments ratio diagram, it has been found that a Generalised Pareto distribution is preferable to the Exponential distribution to fit the partial duration series flood data in the arid regions of Australia. It has also been found that the arid region exhibits much steeper flood frequency growth curve than that of the humid region and the growth curve gets steeper with the decreasing mean annual rainfall. The developed growth curve for the semi-arid and arid region of Australia is found to be similar to other typical semi-arid and arid regions of the world. The developed prediction equation for the mean annual flood in the semi-arid and arid region of Australia uses two readily obtainable predictor variables (catchment area and design rainfall intensity), which can be used along with the developed growth curve to estimate design floods for the ungauged catchments in these regions with reasonable accuracy. The growth curve developed in this study is primarily applicable to the semi-arid and arid regions of Australia; however, this may be adapted to other similar regions of the world along with the locally developed prediction equation for the scaling factor (i.e. mean annual flood in this case) to derive preliminary design flood estimates.

Methods for design flood estimation in South Africa

The estimation of design floods is necessary for the design of hydraulic structures and to quantify the risk of failure of the structures. Most of the methods used for design flood estimation in South Africa were developed in the late 1960s and early 1970s and are in need of updating with more than 40 years of additional data currently available and with new approaches used internationally. This paper reviews methods used for design flood estimation in South Africa and internationally and highlights research needs in order to update the methods used for design flood estimation in South Africa.

Study of overland flow phenomenon using experimental and modelling approaches

Rainfall-runoff analysis of a watershed is needed for the purposes of water resources planning, design flood estimation, flood forecasting, study of movement of pollutants, and many other applications. For a mathematical simulation of this phenomenon, controlled rainfall-runoff experimental runs were conducted on the V-catchment system placed over the advanced hydrologic system to obtain runoff hydrograph data. The approximate convection–diffusion (ACD) equation–based overland flow model was used for simulation of these observed hydrographs. Considering various combinations of runoff simulation scenarios, a total of 111 laboratory experiments were conducted on two types of overland flow and channel flow roughness conditions generated (1) on a V-catchment model made up of acrylic sheet surface and (2) with artificial roughness surface generated with the help of sand paper pasted on the acrylic V-catchment model. These 111 experimental runs were made corresponding to six rainfall intensity inputs, that is, varying from 54 to 84 mm/hour, and for four overland plane slope conditions varying from 0.22% to 1.54%, for each of the three channel slopes used. Overall, it is demonstrated that the ACD equation–based overland flow model is able to reproduce the observed hydrographs closely, in many cases with Nash–Sutcliffe efficiency greater than 90%. But in all the experiments, the recession limb of the observed hydrographs could not be reproduced very closely because of prolonged flow of water. The reason behind this behaviour could be attributed to the retention of runoff of the recession limb because of surface water tension prevailing over the overland flow bed, channel bed and even over the weir model used for flow measurement. Except for this problem, the experimental set-up established in the laboratory reasonably generates overland flow hydrographs which could be reproduced by the overland flow model developed based on the ACD equation, including those cases of diffusion behaviour of the V-catchment experimental hydrographs.

Runoff models and flood frequency statistics for design flood estimation in Austria – Do they tell a consistent story?

► We compare design flood estimates from flood frequency statistics and rainfall runoff models. ► Statistical estimates can be too low when a step change in the flood frequency curve occurs. ► Runoff model estimates are too high when chosen design storms are too large. ► Design flood dominating runoff components have to be represented correctly. Design floods for a given location at a stream can be estimated by a number of approaches including flood frequency statistics and the design storm method. If applied to the same catchment the two methods often yield quite different results. The aim of this paper is to contribute to understanding the reasons for these differences. A case study is performed for 10 alpine catchments in Tyrol, Austria, where the 100-year floods are estimated by (a) flood frequency statistics and (b) an event based runoff model. To identify the sources of the differences of the two methods, the 100-year floods are also estimated by (c) Monte Carlo simulations using a continuous runoff model. The results show that, in most catchments, the event based model gives larger flood estimates than flood frequency statistics. The reasons for the differences depend on the catchment characteristics and different rainfall inputs that were applied. For catchments with a high storage capacity the Monte Carlo simulations indicate a step change in the flood frequency curve when a storage threshold is exceeded which is not captured by flood frequency statistics. Flood frequency statistics therefore tends to underestimate the floods in these catchments. For catchments with a low storage capacity or significant surface runoff, no step change occurs, but in three catchments the design storms used were larger than those read from the IDF (intensity duration frequency) curve leading to an overestimation of the design floods. Finally, also the correct representation of flood dominating runoff components was shown to influence design flood results. Geologic information on the catchments was essential for identifying the reasons for the mismatch of the flood estimates.

Why continuous simulation? The role of antecedent moisture in design flood estimation

Continuous simulation for design flood estimation is increasingly becoming a viable alternative to traditional event‐based methods. The advantage of continuous simulation approaches is that the catchment moisture state prior to the flood‐producing rainfall event is implicitly incorporated within the modeling framework, provided the model has been calibrated and validated to produce reasonable simulations. This contrasts with event‐based models in which both information about the expected sequence of rainfall and evaporation preceding the flood‐producing rainfall event, as well as catchment storage and infiltration properties, are commonly pooled together into a single set of “loss” parameters which require adjustment through the process of calibration. To identify the importance of accounting for antecedent moisture in flood modeling, this paper uses a continuous rainfall‐runoff model calibrated to 45 catchments in the Murray‐Darling Basin in Australia. Flood peaks derived using the historical daily rainfall record are compared with those derived using resampled daily rainfall, for which the sequencing of wet and dry days preceding the heavy rainfall event is removed. The analysis shows that there is a consistent underestimation of the design flood events when antecedent moisture is not properly simulated, which can be as much as 30% when only 1 or 2 days of antecedent rainfall are considered, compared to 5% when this is extended to 60 days of prior rainfall. These results show that, in general, it is necessary to consider both short‐term memory in rainfall associated with synoptic scale dependence, as well as longer‐term memory at seasonal or longer time scale variability in order to obtain accurate design flood estimates.

Step changes in the flood frequency curve: Process controls

Empirical distribution functions of flood peaks in small catchments sometimes show discontinuities in the slope; that is, the largest flood peaks are significantly larger than the rest of the record. The aim of this paper is to understand whether these discontinuities, or step changes, can be a consistent effect of hydrological processes. We conducted field surveys in two Austrian alpine catchments 73 km2in size to map the spatial patterns of surface runoff generation and hydrogeologic storage. On the basis of this information, we selected the parameters of a distributed continuous runoff model, which is designed to simulate well the point when the storage capacity of the catchment is exhausted. Then we calibrated a stochastic rainfall model and performed Monte Carlo simulations of runoff to generate flood frequency curves for the two catchments. The curves exhibit a step change around a return period of 30 years. An analysis of the storage capacities suggests that this step change is due to a threshold of storage capacity being exceeded, which causes fast surface runoff in large parts of the catchments. The threshold occurs when the storage within the catchment is spatially rather uniform. To identify step changes, reliable estimates of the catchment storage capacity are needed on the basis of detailed hydrogeological information. The occurrence of a step change is of importance for estimating low‐probability floods since the flood estimates with the step change accounted for can be significantly different from those based on commonly used distribution functions. We therefore suggest that step changes in the flood frequency curve of small catchments can be real and their possible presence should be taken into account in design flood estimation.

A Hydrologic Model of Kemptville Basin—Calibration and Extended Validation

An integrated hydrologic/hydraulic model of the Kemptville Creek basin has been built using the Mike11 modeling system of the Danish Hydraulic Institute and available GIS-based watershed data. This watershed system is complex, comprising of channels, local drainage areas, lateral inflows, wetlands, and a regulated dam. The model was calibrated using measured streamflow data for five years and then validated for another five years. A wide range of methods—both qualitative and quantitative—were used to evaluate the model performance. It was found that the model can simulate high flows with a high degree of accuracy, and the low flows less satisfactorily. Additional (split-sample) validation tests were conducted for another two five-year periods, which revealed that the model is capable of performing equally well for time periods beyond those used for calibration and validation. This model is now being used for various watershed management purposes, including synthetic hydrograph generation, flood forecasting, design flood estimation, wetland function analysis, etc.

Performance of flood frequency pooling analysis in a low CV context

Pooling of flood data is widely used to provide a framework to estimate design floods by the Index Flood method. Design flood estimation with this approach involves derivation of a growth curve which shows the relationship between XT and the return period T, where XT = QT /QI and QI is the index flood at the site of interest. An implicit assumption with the Index Flood procedure of pooling analysis is that the XT –T relationship is the same at all sites in a homogeneous pooling group, although this assumption would generally be violated to some extent in practical cases, i.e. some degree of heterogeneity exists. In fact, in only some cases is the homogeneity criterion effectively satisfied for Irish conditions. In this paper, the performance of the index-flood pooling analysis is assessed in the Irish low CV (coefficient of variation) hydrology context considering that heterogeneity is taken into account. It is found that the performance of the pooling method is satisfactory provided there are at least 350 station years of data included. Also it is found that, in a highly heterogeneous group, it is more desirable to have many sites with short record lengths than a smaller number of sites with long record lengths. Increased heterogeneity decreases the advantage of pooling group-based estimation over at-site estimation. Only a heterogeneity measure (H1) less than 4.0 can render the pooled estimation preferable to that obtained for at-site estimation for the estimation of 100-year flood. In moderately to highly heterogeneous regions it is preferable to conduct at-site analysis for the estimation of 100-year flood if the record length at the site concerned exceeds 50. Editor Z.W. Kundzewicz; Associate editor A. Carsteanu Citation Das, S. and Cunnane, C., 2012. Performance of flood frequency pooling analysis in a low CV context. Hydrological Sciences Journal, 57 (3), 433–444.

Design flood estimation in ungauged catchments and statistical characterization using principal components analysis: application of Gradex method in Upper Moulouya

AbstractDesign flood estimation in ungauged catchments is of great importance in hydrologic practice especially where there is no available data about streamflow. Except the watershed of Anseghmir who is equipped with a gauge station, all the other watersheds are ungauged catchments. The use of frequency analysis of series of rainfall and streamflow is very important for the characterization of the hydrologic resources of the Upper Moulouya. The region has a semiarid climate that requires a good knowledge of the watershed's potential water to assist policy makers in forecasting extreme events, managing water resources and decision making. The frequency analysis was used to determine the design flood of different return periods. The results obtained are used in Gradex method to estimate the hydrologic variables of each subcatchment of the Upper Moulouya. Once the hydrologic study is completed, a principal components analysis was made to highlight the affinities between the different subcatchments and to deduce the hydrologic and hydrographic parameters that better characterize them. Copyright © 2012 John Wiley & Sons, Ltd.

Uncertainty in design flood profiles derived by hydraulic modelling

The scientific literature has widely shown that hydraulic modelling is affected by many sources of uncertainty (e.g. model structure, input data, model parameters). However, when hydraulic models are used for engineering purposes (e.g. flood defense design), there is still a tendency to make a deterministic use of them. More specifically, the prediction of flood design profiles is often based on the outcomes of a calibrated hydraulic model. Despite the good results in model calibration, this prediction is affected by significant uncertainty, which is commonly considered by adding a freeboard to the simulated flood profile. A more accurate approach would require an explicit analysis of the sources of uncertainty affecting hydraulic modelling and design flood estimation. This paper proposes an alternative approach, which is based on the use of uncertain flood profiles, where the most significant sources of uncertainty are explicitly analyzed. An application to the Po river reach between Cremona and Borgoforte (Italy) is used to illustrate the proposed framework and compare it to the traditional approach. This paper shows that the deterministic approach underestimates the design flood profile and questions whether the freeboard, often arbitrarily defined, might lead to a false perception of additional safety levels.

Design flood estimation in Western Australia

This paper provides details of flood frequency procedures developed for the Pilbara, Kimberley, Wheatbelt and Goldfields regions of Western Australia, which should provide better estimates of design floods than the methods recommended in the 1987 version of Australian Rainfall and Runoff. The first section of the paper discusses the adequacy of the stream flow data on which the regional flood frequency procedures (RFFPs) are based and identifies the large extrapolation of the gauging station rating curves and the general underestimation of the magnitude of larger flood events. This leads to the conclusion that a conservative approach is required when developing a RFFP. A description of the general approach taken in developing the RFFPs is then given. Details of the RFFPs developed for each region follow and finally a comparison is made between the magnitudes of the floods in each region.

Design flood estimation in Western Australia

This paper provides details of food frequency procedures developed for the Pilbara, Kimberley, Wheatbelt and Goldf elds regions of Western Australia, which should provide better estimates of design foods than the methods recommended in the 1987 version of Australian Rainfall and Runoff. The first section of the paper discusses the adequacy of the stream flow data on which the regional food frequency procedures (RFFPs) are based and identif es the large extrapolation of the gauging station rating curves and the general underestimation of the magnitude of larger food events. This leads to the conclusion that a conservative approach is required when developing a RFFP. A description of the general approach taken in developing the RFFPs is then given. Details of the RFFPs developed for each region follow and finally a comparison is made between the magnitudes of the foods in each region.

考虑水库调蓄影响的设计洪水计算方法<br>Design Flood Estimation at Downstream Section by Considering the Impact of Upstream Reservoir Regulation

考虑水库调蓄影响的设计洪水计算方法<br>Design Flood Estimation at Downstream Section by Considering the Impact of Upstream Reservoir Regulation

梯级水库设计洪水方法及研究进展

流域上游修建水库后将改变下游河道的洪水特性，直接影响下游断面的设计洪水，因此应该考虑上游水库的调洪影响及设计断面以上各部分洪水的地区组成。针对我国目前主要采用同频率组成法和典型年组成法来拟定设计洪水地区组成的现状，综述梯级水库设计洪水的研究进展，分析现有方法的优缺点，探讨推求梯级水库设计洪水的新途径，并提出进一步开展研究工作的建议。 The construction of upstream reservoirs will certainly change the flood characteristics and affect the design floods in the downstream river. As a result, the reservoir operation and regional composition of upstream and inter-basin inflows should be considered when estimating design flood in the downstream controlled sections. The equivalent frequency and typical year synthesis are the most frequently used regional composition analysis methods in China, the research advancement of design flood estimation methods for cascade reservoirs are summarized and reviewed. New approaches of design flood derivation for cascade reservoir are also discussed by assessing the advantage and disadvantage of these methods. The research directions of design flood for cascade reservoir are also suggested.