Journal cover Journal topic
Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Technical note
02 Dec 2016
Review status
A revision of this discussion paper is under review for the journal Hydrology and Earth System Sciences (HESS).
Technical Note: Design flood under hydrological uncertainty
Anna Botto1,a, Daniele Ganora1, Pierluigi Claps1, and Francesco Laio1 1Department of Environment, Land and Infrastructure Engineering – Politecnico di Torino – Corso Duca degli Abruzzi, 24 – 10129 Torino, Italy
anow at: the Department of Civil, Environmental and Architectural engineering РUniversità di Padova РVia Marzolo, 9 РPadova, Italy
Abstract. Planning and verification of hydraulic infrastructures demands for a design estimate of hydrologic variables, usually provided by frequency analysis, neglecting hydrologic uncertainty. However, when hydrologic uncertainty is accounted for, the design flood value is no longer a deterministic value, but should be treated as a random variable itself. As a consequence, the design flood is no longer univocally defined, making the design process undetermined.

Both et al. (2014), with the development of the Uncertainty Compliant Design Flood Estimation (UNCODE) procedure, have shown that it is possible to fix the ambiguity in the selection of the design flood under uncertainty by considering an additional constraint based on a cost-benefit criterion. This paper contributes with an easy-to-use framework to implement the UNCODE procedure without resorting to numerical computation, but using a correction coefficient that modifies the standard (i.e., uncertainty-free) design value on the basis of sample length and return period only. The procedure is robust and parsimonious, as it does not require additional parameters with respect to the traditional uncertainty-free analysis.

Simple equations to compute the correction term to the standard estimate are provided for a number of probability distributions commonly used to represent the flood frequency curve. This new design tool provides a robust way to manage the hydrologic uncertainty and to go beyond the use of traditional safety factors. With all the other parameters being equal, an increase of the sample length reduces the correction factor, and thus the construction costs, still keeping the same safety level. This improvement is shown to be more effective when short samples are extended.

Citation: Botto, A., Ganora, D., Claps, P., and Laio, F.: Technical Note: Design flood under hydrological uncertainty, Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2016-637, in review, 2016.
Anna Botto et al.
Anna Botto et al.
Anna Botto et al.


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Short summary
The paper provides a simplified solution of the UNCODE model, which allows one to directly account for hydrological uncertainty in the estimation of the design flood. With this methodology it is possible to easily quantify the "value" of data in the design process.
The paper provides a simplified solution of the UNCODE model, which allows one to directly...