Timing the time of concentration: shedding light on a paradox

Michailidi, Eleni Maria; Antoniadi, Sylvia; Koukouvinos, Antonis; Bacchi, Baldassare; Efstratiadis, Andreas

doi:10.1080/02626667.2018.1450985

Cited by 56 publications

(53 citation statements)

References 24 publications

(41 reference statements)

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“…In the case of complex river networks, i.e., with confluences, we considered the longest flow path across each corresponding area. Theoretical proof and empirical evidence imply that t c is definitely not a constant property of the basin, but it varies significantly with the flow [13,48]. In fact, the variability of t c is explained by the dependence of the kinematic wave celerity on the flow rate.…”

Section: Hydrological Model Assumptions and Representation Of Uncertamentioning

confidence: 97%

An Operational Method for Flood Directive Implementation in Ungauged Urban Areas

et al. 2018

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An operational framework for flood risk assessment in ungauged urban areas is developed within the implementation of the EU Floods Directive in Greece, and demonstrated for Volos metropolitan area, central Greece, which is frequently affected by intense storms causing fluvial flash floods. A scenario-based approach is applied, accounting for uncertainties of key modeling aspects. This comprises extreme rainfall analysis, resulting in spatially-distributed Intensity-Duration-Frequency (IDF) relationships and their confidence intervals, and flood simulations, through the SCS-CN method and the unit hydrograph theory, producing design hydrographs at the sub-watershed scale, for several soil moisture conditions. The propagation of flood hydrographs and the mapping of inundated areas are employed by the HEC-RAS 2D model, with flexible mesh size, by representing the resistance caused by buildings through the local elevation rise method. For all hydrographs, upper and lower estimates on water depths, flow velocities and inundation areas are estimated, for varying roughness coefficient values. The methodology is validated against the flood event of the 9th October 2006, using observed flood inundation data. Our analyses indicate that although typical engineering practices for ungauged basins are subject to major uncertainties, the hydrological experience may counterbalance the missing information, thus ensuring quite realistic outcomes.

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Section: Hydrological Model Assumptions and Representation Of Uncertamentioning

confidence: 97%

An Operational Method for Flood Directive Implementation in Ungauged Urban Areas

et al. 2018

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“…(2) Copula-based rainfall analysis considers the joint distribution of rainfall amounts with different critical durations, which enables the generation of different types of rainfalls rather than a deterministic type of rainfall for a certain return period. In addition, since copula-based design rainfall uses joint probability and IDF-curve-based design rainfall uses only marginal probability, according to the copula's Frechet-Hoeffding bounds [30], given a return period, copula-based design rainfall will always be larger than IDF-curve-based design rainfall, as illustrated in Figure 12. With regard to this study, this phenomenon can also be interpreted such that flooding from multiple sources will always be more dangerous than flooding from only a single source.…”

Section: Discussionmentioning

confidence: 99%

“…The relationship between the response characteristics of flooding and inundation from different sources can therefore be treated as the correlation between rainfall amounts and different critical rainfall durations. Many empirical formulas have been proposed to estimate the time of concentration based on the natural characteristics of a basin (e.g., path length, basin slope, land use), including the Kraven's formula, Izzard's formula, Kodoya and Fukushima's formula, Loukas and Quick's formula, and Michailidi's formula [21,30]. Predetermining the time of concentration from different flood sources and using them as critical rainfall durations to analyze rainfall data and generate rainfall events is likely to be an efficient way to assess spatial flood risk considering multiple flood sources.…”

Section: Introductionmentioning

confidence: 99%

Assessing Spatial Flood Risk from Multiple Flood Sources in a Small River Basin: A Method Based on Multivariate Design Rainfall

Jiang

Yang

Tatano

2019

Water

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A key issue in assessing the spatial distribution of flood risk is considering risk information derived from multiple flood sources (river flooding, drainage inundation, etc.) that may affect the risk assessment area. This study proposes a method for assessing spatial flood risk that includes flooding and inundation in small-basin areas through multivariate design rainfall. The concept of critical rainfall duration, determined by the time of concentration of flooding, is used to represent the characteristics of flooding from different sources. A copula method is adopted to capture the correlation of rainfall amounts in different critical rainfall durations to reflect the correlation of potential flooding from multiple flood sources. Rainfalls for different return periods are designed based on the copula multivariate analysis. Using the design rainfalls as input, flood risk is assessed following the rainfall–runoff–inundation–loss estimation procedure. A case study of the Otsu River Basin, Osaka Prefecture, Japan, was conducted to demonstrate the feasibility and advantages of this method. Compared to conventional rainfall design, this method considers the response characteristics of multiple flood sources, and solves the problem of flood risk assessment from multiple flood sources. It can be applied to generate a precise flood risk assessment to support integrated flood risk management.

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“…Haan et al (1984), Viessman and Lewis, (1995) and Musy and Higy (2004), in contrast, still refer to time of concentration in the glossary definition. This has also continued in the recent papers of, for example, Li et al (2018) and Michailidi et al (2018). More embarrassingly, Shaw et al (2011) following earlier editions, treat time of concentration as the longest travel time based on velocities on both a catchment and in a pipe network while more correctly discussing celerities elsewhere.…”

Section: Mathematical Celerities and Natural Hillslopesmentioning

confidence: 96%

A history of the concept of time of concentration

Beven¹

2020

Preprint

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Abstract. The concept of time of concentration in the analysis of catchment responses dates back over 150 years to the introduction of the Rational Method. Since then it has been used in a variety of ways in the formulation of both unit hydrograph and distributed catchment models. It is normally discussed The concept of time of concentration in the analysis of catchment responses dates back over 150 years to the introduction of the Rational Method. Since then it has been used in a variety of ways in the formulation of both unit hydrograph and distributed catchment models. It is normally discussed in terms of the velocity of flow of a water particle from the furthest part of a catchment to the outlet. This is also the basis for the definition in the International Glossary of Hydrology. While conceptually simple, this definition is, however, wrong when applied to catchment responses where, in terms of how surface and subsurface flows produce hydrographs, it is more correct to discuss and teach the concept based on celerities and time to equilibrium. While this has been recognized since the 1960s, some recent papers and text remain confused over the definition and use of time of concentration. The paper sets out the history of its use and clarifies its relationship to time to equilibrium but suggests that both terms are not really useful in explaining hydrological responses. An appendix is included that quantifies the differences between the definitions of response times for subsurface and surface flows under simple assumptions that might be useful in teaching.

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Timing the time of concentration: shedding light on a paradox

Cited by 56 publications

References 24 publications

An Operational Method for Flood Directive Implementation in Ungauged Urban Areas

An Operational Method for Flood Directive Implementation in Ungauged Urban Areas

Assessing Spatial Flood Risk from Multiple Flood Sources in a Small River Basin: A Method Based on Multivariate Design Rainfall

A history of the concept of time of concentration

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