Flood Hydrograph (flood + hydrograph)

Distribution by Scientific Domains


Selected Abstracts


Structural patterns in coarse gravelriver beds: typology, survey and assessment of the roles of grain size and river regime

GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 1 2002
Lea Wittenberg
The concept of river-bed stability as indexed by the occurrence of stable bed forms was examined in humid-temperate perennial streams and in Mediterranean ephemeral streams. The study examined the structural patterns of bed forms and their spatial distribution between temperate-humid and Mediterranean streams. Study sites in Northumberland, UK, and Mt. Carmel, Israel, were selected for their morphometric similarity, despite the contrast in climate, vegetation and hydrological regime. Fieldwork was based on a large number of Wolman grain size distributions and structure measurements along cross-sections at seven sites; Differences in mean grain size of bed structures were estimated using the general linear model (GLM) procedure and Duncan's multiple range test. Based on field evidence, river-bed configurations were divided into structural categories, according to the depositional setting of each measured particle on the river bed. Statistical analysis confirmed former qualitative descriptions of small-scale bed forms. The study identified spatial segregation in bed form distribution. In general, 30,40%of the bed material in the surveyed perennial streams was clustered, in contrast to approximately 10%in the ephemeral counterparts. The sorting index revealed higher values for the perennial streams, namely 2.39,3.59 compared with 1.73,2.07 for the ephemeral counterparts. It is suggested that the degree of sediment sorting and the proportion of clusters are strongly related. Sediment sorting, sediment supply and the hydrological regime explain the mechanism of cluster formation. It is assumed that climate shifts or human interference within river basins might affect the regional characteristic flood hydrograph, and consequently alter the sedimentary character of the river bed. In the case where river bed stability is reduced owing to changes in cluster bed form distribution, rivers that normally do not yield a significant amount of sediment might be subject to notable sedimentation problems. [source]


Development of design flood hydrographs using probability density functions

HYDROLOGICAL PROCESSES, Issue 4 2010
Niranjan Pramanik
Abstract Probability density functions (PDFs) are used to fit the shape of hydrographs and have been popularly used for the development of synthetic unit hydrographs by many hydrologists. Nevertheless, modelling the shapes of continuous stream flow hydrographs, which are probabilistic in nature, is rare. In the present study, a novel approach was followed to model the shape of stream flow hydrographs using PDF and subsequently to develop design flood hydrographs for various return periods. Four continuous PDFs, namely, two parameter Beta, Weibull, Gamma and Lognormal, were employed to fit the shape of the hydrographs of 22 years at a site of Brahmani River in eastern India. The shapes of the observed and PDF fitted hydrographs were compared and root mean square errors, error of peak discharge (EQP) and error of time to peak (ETP) were computed. The best-fitted shape and scale parameters of all PDFs were subjected to frequency analysis and the quartiles corresponding to 20-, 50-, 100- and 200-year were estimated. The estimated parameters of each return period were used to develop the flood hydrographs for 20-, 50-, 100- and 200-year return periods. The peak discharges of the developed design flood hydrographs were compared with the design discharges estimated from the frequency analysis of 22 years of annual peak discharges at that site. Lognormal-produced peak discharge was very close to the estimated design discharge in case of 20-year flood hydrograph. On the other hand, peak discharge obtained using the Weibull PDF had close agreement with the estimated design discharge obtained from frequency analysis in case of 50-, 100- and 200-year return periods. The ranking of the PDFs based on estimation of peak of design flood hydrograph for 50-, 100- and 200-year return periods was found to have the following order: Weibull > Beta > Lognormal > Gamma. Copyright © 2009 John Wiley & Sons, Ltd. [source]


High-resolution, monotone solution of the adjoint shallow-water equations

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 2 2002
Brett F. Sanders
Abstract A monotone, second-order accurate numerical scheme is presented for solving the differential form of the adjoint shallow-water equations in generalized two-dimensional coordinates. Fluctuation-splitting is utilized to achieve a high-resolution solution of the equations in primitive form. One-step and two-step schemes are presented and shown to achieve solutions of similarly high accuracy in one dimension. However, the two-step method is shown to yield more accurate solutions to problems in which unsteady wave speeds are present. In two dimensions, the two-step scheme is tested in the context of two parameter identification problems, and it is shown to accurately transmit the information needed to identify unknown forcing parameters based on measurements of the system response. The first problem involves the identification of an upstream flood hydrograph based on downstream depth measurements. The second problem involves the identification of a long wave state in the far-field based on near-field depth measurements. Copyright © 2002 John Wiley & Sons, Ltd. [source]


A MODIFIED RATIONAL FORMULA FOR FLOOD DESIGN IN SMALL BASINS,

JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2003
Jiapeng Hua
ABSTRACT: New formulas and procedures under the framework of the Rational Formula are presented that are applicable to flood design problems for a small basin if the geometry of the basin can be approximated as an ellipse or a rhombus. Instead of making the assumption in the traditional rational formula that the rainfall is uniformly distributed in the whole duration (Dw) of a design storm, the new method modifies that assumption as: the rainfall is uniformly distributed only in each time interval CD) of the design storm hyetograph, thus extending the rational formula applicable to the case that the rainfall duration is less than the basin concentration time (Tc). The new method can be applied to estimate the flood design peak discharge, and to generate the flood hydrograph simultaneously. The derivation of the formulas is provided in detail in this paper, and an example is also included to illustrate how to apply the new formulas to the flood design problems in small basins. [source]


Development of design flood hydrographs using probability density functions

HYDROLOGICAL PROCESSES, Issue 4 2010
Niranjan Pramanik
Abstract Probability density functions (PDFs) are used to fit the shape of hydrographs and have been popularly used for the development of synthetic unit hydrographs by many hydrologists. Nevertheless, modelling the shapes of continuous stream flow hydrographs, which are probabilistic in nature, is rare. In the present study, a novel approach was followed to model the shape of stream flow hydrographs using PDF and subsequently to develop design flood hydrographs for various return periods. Four continuous PDFs, namely, two parameter Beta, Weibull, Gamma and Lognormal, were employed to fit the shape of the hydrographs of 22 years at a site of Brahmani River in eastern India. The shapes of the observed and PDF fitted hydrographs were compared and root mean square errors, error of peak discharge (EQP) and error of time to peak (ETP) were computed. The best-fitted shape and scale parameters of all PDFs were subjected to frequency analysis and the quartiles corresponding to 20-, 50-, 100- and 200-year were estimated. The estimated parameters of each return period were used to develop the flood hydrographs for 20-, 50-, 100- and 200-year return periods. The peak discharges of the developed design flood hydrographs were compared with the design discharges estimated from the frequency analysis of 22 years of annual peak discharges at that site. Lognormal-produced peak discharge was very close to the estimated design discharge in case of 20-year flood hydrograph. On the other hand, peak discharge obtained using the Weibull PDF had close agreement with the estimated design discharge obtained from frequency analysis in case of 50-, 100- and 200-year return periods. The ranking of the PDFs based on estimation of peak of design flood hydrograph for 50-, 100- and 200-year return periods was found to have the following order: Weibull > Beta > Lognormal > Gamma. Copyright © 2009 John Wiley & Sons, Ltd. [source]


Effect of growing watershed imperviousness on hydrograph parameters and peak discharge

HYDROLOGICAL PROCESSES, Issue 13 2008
Huang-jia Huang
Abstract An increasing impervious area is quickly extending over the Wu-Tu watershed due to the endless demands of the people. Generally, impervious paving is a major result of urbanization and more recently has had the potential to produce more enormous flood disasters than those of the past. In this study, 40 available rainfall,runoff events were chosen to calibrate the applicable parameters of the models and to determine the relationships between the impervious surfaces and the calibrated parameters. Model inputs came from the outcomes of the block kriging method and the non-linear programming method. In the optimal process, the shuffled complex evolution method and three criteria were applied to compare the observed and simulated hydrographs. The tendencies of the variations of the parameters with their corresponding imperviousness were established through regression analysis. Ten cases were used to examine the established equations of the parameters and impervious covers. Finally, the design flood routines of various return periods were furnished through use of approaches containing a design storm, block kriging, the SCS model, and a rainfall-runoff model with established functional relationships. These simulated flood hydrographs were used to compare and understand the past, present, and future hydrological conditions of the watershed studied. In the research results, the time to peak of flood hydrographs for various storms was diminished approximately from 11 h to 6 h in different decrements, whereas peak flow increased respectively from 127 m3 s,1 to 629 m3 s,1 for different storm intensities. In addition, this study provides a design diagram for the peak flow ratio to help engineers and designers to construct hydraulic structures efficiently and prevent possible damage to human life and property. Copyright © 2007 John Wiley & Sons, Ltd. [source]