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Ezio Todini - One of the best experts on this subject based on the ideXlab platform.
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reply to comment on a dynamic Rating Curve approach to indirect discharge measurement by dottori et al 2009 by koussis 2009
Hydrology and Earth System Sciences, 2010Co-Authors: Francesco Dottori, Ezio TodiniAbstract:In a recent comment, Koussis (2010) moved a number of critiques on the paper by Dottori et al. (2009), which describes a methodology for indirect discharge measurement using simultaneous water stage measurements at two adjacent cross sections in a river reach. The procedure, which requires the geometrical description of the two cross sections, allows for direct computation of water surface slope, and improves accounting for unsteady flow effects through the use of the complete or simplified momentum equation (a reason for calling it DyRaC, the acronym of Dynamic Rating Curve). Among others, Koussis argues that the procedure is not suited for practical use since it is too demanding in terms of data set and flow conditions, and the requirements for its application are generally not met in practice, particularly in rivers with a complex morphology. Then Koussis suggests using an alternative procedure for discharge measurement, based on a modification of the well known Jones Formula he developed several years ago (Koussis, 1975, 1976). Finally, he contends that the procedure proposed by Dottori et al. (2009) is based upon the well known “standard step method” for computing flood depth profiles. The aim of this reply, is to show that the criticisms moved are not really motivated: DyRaC, the proposed approach, may be used for operational measurements in rivers with noticeable advantages with respect to alternative methodologies. As a matter of fact DyRaC has already been installed in Italy and thoroughly tested on-line for estimating unsteady discharges in real-time on the River Parma, as well as successfully applied for flow estimates on several gauging stations along the River Arno course.
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a dynamic Rating Curve approach to indirect discharge measurement
Hydrology and Earth System Sciences, 2009Co-Authors: Francesco Dottori, Mario L V Martina, Ezio TodiniAbstract:Abstract. The operational measurement of discharge in medium and large rivers is mostly based on indirect approaches by converting water stages into discharge on the basis of steady-flow Rating Curves. Unfortunately, under unsteady flow conditions, this approach does not guarantee accurate estimation of the discharge due, on the one hand, to the underlying steady state assumptions and, on the other hand, to the required extrapolation of the Rating Curve beyond the range of actual measurements used for its derivation. Historically, several formulae were proposed to correct the steady-state discharge value and to approximate the unsteady-flow stage-discharge relationship. In the majority of these methods, the correction is made on the basis of water level measurements taken at a single cross section where a steady state Rating Curve is available, while other methods explicitly account for the water surface slope using stage measurements in two reference sections. However, most of the formulae available in literature are either over-simplified or based on approximations that prevent their generalisation. Moreover they have been rarely tested on cases where their use becomes essential, namely under unsteady-flow conditions characterised by wide loop Rating Curves. In the present work, an original approach, based on simultaneous stage measurements at two adjacent cross sections, is introduced and compared to the approaches described in the literature. The most relevant feature is that the proposed procedure allows for the application of the full dynamic flow equations without restrictive hypotheses. The comparison has been carried out on channels with constant or spatially variable geometry under a wide range of flood wave and river bed slope conditions. The results clearly show the improvement in the discharge estimation and the reduction of estimation errors obtainable using the proposed approach.
Trond Reitan - One of the best experts on this subject based on the ideXlab platform.
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propagation of Rating Curve uncertainty in design flood estimation
EGUGA, 2016Co-Authors: Gunnhildur H Steinbakk, Thordis L Thorarinsdottir, Trond Reitan, Lena Schlichting, Sondre Holleland, Kolbjorn EngelandAbstract:Statistical flood frequency analysis is commonly performed based on a set of annual maximum discharge values which are derived from stage measurements via a stage-discharge Rating Curve model. Such design flood estimation techniques often ignore the uncertainty in the underlying Rating Curve model. Using data from eight gauging stations in Norway, we investigate the effect of Curve and sample uncertainty on design flood estimation by combining results from a Bayesian multi-segment Rating Curve model and a Bayesian flood frequency analysis. We find that sample uncertainty is the main contributor to the design flood estimation uncertainty. However, under extrapolation of the Rating Curve, the uncertainty bounds for both the Rating Curve model and the flood frequency analysis are highly skewed and ignoring these features may underestimate the potential risk of flooding. We expect this effect to be even more pronounced in arid and semi-arid climates with a higher variability in floods. This article is protected by copyright. All rights reserved.
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dynamic Rating Curve assessment in unstable rivers using ornstein uhlenbeck processes
Water Resources Research, 2011Co-Authors: Trond Reitan, Asgeir PetersenoverleirAbstract:[1] The procedure of fitting Rating Curves in channels where the stage-discharge relationship is subject to changes driven by morphological processes remains one of the major unsolved problems in hydrometry. This paper addresses this issue by formulating the stage-discharge relationship as a steady flow, one-segmented power law model with parameters that are viewed as stochastic processes with characteristics associated with the temporal instabilities of the channel elements governing the stage-discharge relationship. A Bayesian analysis with informative priors and time-stage-discharge measurements as forcing data is used to determine the most plausible model and its posterior parameter distributions using Markov chain Monte Carlo simulation techniques and particle filtering. The proposed framework is applied to data from gauging stations in two unstable rivers and one stable river in Norway.
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Bayesian Rating Curve Inference as a Streamflow Data Quality Assessment Tool
Water Resources Management, 2009Co-Authors: Asgeir Petersen-Øverleir, André Soot, Trond ReitanAbstract:A streamflow time-series is normally obtained by transforming a time-series of recorded stage to discharge using an estimated Rating Curve. The accuracy of this streamflow time-series depends on the characteristics of the available stage-discharge measurements used to fit the Rating Curve. The Norwegian Water Resources and Energy Directorate (NVE) has developed a method based on Rating Curve uncertainty for performing objective quality assessment of streamflow time-series. The method, which is based on a Bayesian statistical framework, uses the available stage-discharge measurements and the corresponding stage time-series to derive statistics utilised for a quality assurance of the streamflow time-series. Nearly one thousand streamflow time-series periods have been classified using the method. This paper presents the results.
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accounting for Rating Curve imprecision in flood frequency analysis using likelihood based methods
Journal of Hydrology, 2009Co-Authors: Asgeir Petersenoverleir, Trond ReitanAbstract:This paper examines the joint impact of sample variability and Rating Curve imprecision in at-site flood frequency analysis. A novel likelihood-based framework is developed for this purpose, assuming a power-law model for the stage-discharge measurements and a generalised extreme value (GEV) model for the annual maximum discharges. It is shown that the two models can be pooled into one likelihood function. This allows for simultaneous estimation of the Rating Curve and GEV parameters, and the assessment of the uncertainty of a T-year flood estimate due to both sample variability and Rating Curve imprecision. Sampling experiments show that (1) the novel method is computationally feasible and little affected by estimation bias, and (2) the chief effect of Rating Curve imprecision is to inflate the estimation variability of the GEV quantile estimates. The application of the method to data from 12 Norwegian gauging stations illustrates that (3) the novel and traditional methods give very similar Rating Curve and GEV parameter estimates and (4) the net effect of sample variability and Rating Curve imprecision can give rise to significant wide confidence intervals for the estimated T-year flood.
Francesco Dottori - One of the best experts on this subject based on the ideXlab platform.
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reply to comment on a dynamic Rating Curve approach to indirect discharge measurement by dottori et al 2009 by koussis 2009
Hydrology and Earth System Sciences, 2010Co-Authors: Francesco Dottori, Ezio TodiniAbstract:In a recent comment, Koussis (2010) moved a number of critiques on the paper by Dottori et al. (2009), which describes a methodology for indirect discharge measurement using simultaneous water stage measurements at two adjacent cross sections in a river reach. The procedure, which requires the geometrical description of the two cross sections, allows for direct computation of water surface slope, and improves accounting for unsteady flow effects through the use of the complete or simplified momentum equation (a reason for calling it DyRaC, the acronym of Dynamic Rating Curve). Among others, Koussis argues that the procedure is not suited for practical use since it is too demanding in terms of data set and flow conditions, and the requirements for its application are generally not met in practice, particularly in rivers with a complex morphology. Then Koussis suggests using an alternative procedure for discharge measurement, based on a modification of the well known Jones Formula he developed several years ago (Koussis, 1975, 1976). Finally, he contends that the procedure proposed by Dottori et al. (2009) is based upon the well known “standard step method” for computing flood depth profiles. The aim of this reply, is to show that the criticisms moved are not really motivated: DyRaC, the proposed approach, may be used for operational measurements in rivers with noticeable advantages with respect to alternative methodologies. As a matter of fact DyRaC has already been installed in Italy and thoroughly tested on-line for estimating unsteady discharges in real-time on the River Parma, as well as successfully applied for flow estimates on several gauging stations along the River Arno course.
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a dynamic Rating Curve approach to indirect discharge measurement
Hydrology and Earth System Sciences, 2009Co-Authors: Francesco Dottori, Mario L V Martina, Ezio TodiniAbstract:Abstract. The operational measurement of discharge in medium and large rivers is mostly based on indirect approaches by converting water stages into discharge on the basis of steady-flow Rating Curves. Unfortunately, under unsteady flow conditions, this approach does not guarantee accurate estimation of the discharge due, on the one hand, to the underlying steady state assumptions and, on the other hand, to the required extrapolation of the Rating Curve beyond the range of actual measurements used for its derivation. Historically, several formulae were proposed to correct the steady-state discharge value and to approximate the unsteady-flow stage-discharge relationship. In the majority of these methods, the correction is made on the basis of water level measurements taken at a single cross section where a steady state Rating Curve is available, while other methods explicitly account for the water surface slope using stage measurements in two reference sections. However, most of the formulae available in literature are either over-simplified or based on approximations that prevent their generalisation. Moreover they have been rarely tested on cases where their use becomes essential, namely under unsteady-flow conditions characterised by wide loop Rating Curves. In the present work, an original approach, based on simultaneous stage measurements at two adjacent cross sections, is introduced and compared to the approaches described in the literature. The most relevant feature is that the proposed procedure allows for the application of the full dynamic flow equations without restrictive hypotheses. The comparison has been carried out on channels with constant or spatially variable geometry under a wide range of flood wave and river bed slope conditions. The results clearly show the improvement in the discharge estimation and the reduction of estimation errors obtainable using the proposed approach.
Asgeir Petersenoverleir - One of the best experts on this subject based on the ideXlab platform.
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dynamic Rating Curve assessment in unstable rivers using ornstein uhlenbeck processes
Water Resources Research, 2011Co-Authors: Trond Reitan, Asgeir PetersenoverleirAbstract:[1] The procedure of fitting Rating Curves in channels where the stage-discharge relationship is subject to changes driven by morphological processes remains one of the major unsolved problems in hydrometry. This paper addresses this issue by formulating the stage-discharge relationship as a steady flow, one-segmented power law model with parameters that are viewed as stochastic processes with characteristics associated with the temporal instabilities of the channel elements governing the stage-discharge relationship. A Bayesian analysis with informative priors and time-stage-discharge measurements as forcing data is used to determine the most plausible model and its posterior parameter distributions using Markov chain Monte Carlo simulation techniques and particle filtering. The proposed framework is applied to data from gauging stations in two unstable rivers and one stable river in Norway.
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accounting for Rating Curve imprecision in flood frequency analysis using likelihood based methods
Journal of Hydrology, 2009Co-Authors: Asgeir Petersenoverleir, Trond ReitanAbstract:This paper examines the joint impact of sample variability and Rating Curve imprecision in at-site flood frequency analysis. A novel likelihood-based framework is developed for this purpose, assuming a power-law model for the stage-discharge measurements and a generalised extreme value (GEV) model for the annual maximum discharges. It is shown that the two models can be pooled into one likelihood function. This allows for simultaneous estimation of the Rating Curve and GEV parameters, and the assessment of the uncertainty of a T-year flood estimate due to both sample variability and Rating Curve imprecision. Sampling experiments show that (1) the novel method is computationally feasible and little affected by estimation bias, and (2) the chief effect of Rating Curve imprecision is to inflate the estimation variability of the GEV quantile estimates. The application of the method to data from 12 Norwegian gauging stations illustrates that (3) the novel and traditional methods give very similar Rating Curve and GEV parameter estimates and (4) the net effect of sample variability and Rating Curve imprecision can give rise to significant wide confidence intervals for the estimated T-year flood.
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modelling stage discharge relationships affected by hysteresis using the jones formula and nonlinear regression
Hydrological Sciences Journal-journal Des Sciences Hydrologiques, 2006Co-Authors: Asgeir PetersenoverleirAbstract:Abstract Gauging stations where the stage—discharge relationship is affected by hysteresis due to unsteady flow represent a challenge in hydrometry. In such situations, the standard hydrometric practice of fitting a single-valued Rating Curve to the available stage—discharge measurements is inappropriate. As a solution to this problem, this study provides a method based on the Jones formula and nonlinear regression, which requires no further data beyond the available stage—discharge measurements, given that either the stages before and after each measurement are known along with the duration of each measurement, or a stage hydrograph is available. The regression model based on the Jones formula Rating Curve is developed by applying the monoclinal rising wave approximation and the generalized friction law for uniform flow, along with simplifying assumptions about the hydraulic and geometric properties of the river channel in conjunction with the gauging station. Methods for obtaining the nonlinear least-sq...
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accounting for heteroscedasticity in Rating Curve estimates
Journal of Hydrology, 2004Co-Authors: Asgeir PetersenoverleirAbstract:Abstract The non-linear least squares (NLS) method has long been the standard technique used by hydrologists for constructing Rating Curves. The reasons for its adaptation are vague, and its appropriateness as a method of describing discharge measurement uncertainty has not been well investigated. It is shown in this paper that the classical method of NLS can model only a very limited class of variance heterogeneity. Furthermore, this lack of flexibility often leads to unaccounted heteroscedasticity, resulting in dubious values for the Rating Curve parameters and estimated discharge. By introducing a heteroscedastic maximum likelihood model, the variance heterogeneity is treated more generally. The maximum likelihood model stabilises the variance better than the NLS approach, and thus is a more robust and appropriate way to fit a Rating Curve to a set of discharge measurements. Finally, it is shown that an extreme value analysis of the discharge can be affected by the model used to construct the Rating Curve.
P Di Giammarco - One of the best experts on this subject based on the ideXlab platform.
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Rating Curve estimation using local stages upstream discharge data and a simplified hydraulic model
Hydrology and Earth System Sciences, 1999Co-Authors: Marco Franchini, P Lamberti, P Di GiammarcoAbstract:Abstract. This article proposes a methodology for synthesising the Rating Curve in one or more cross-sections of a watercourse provided with stage data, when a reliable Rating Curve and stage data are also available in the upstream cross-section; the synthesised Rating Curves are consistent with each other. The proposed methodology uses a variable parameter Muskingum-Cunge model whose parameters take express account of travel times and attenuation of the flood wave, and are expressed in such a way that allows for an integration in the time-space domain even when a topographic survey of the river is not available. Furthermore, the methodology proposed implicitly provides a ready-calibrated simulation model whose ease of application suggests that it could also be useful in real time stage forecasting. The paper includes a description of a numerical application to a reach of the Po River (Italy).
