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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 12, issue 6
Hydrol. Earth Syst. Sci., 12, 1295–1307, 2008
https://doi.org/10.5194/hess-12-1295-2008
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue: Climate-soil and vegetation interactions in ecological-hydrological...

Hydrol. Earth Syst. Sci., 12, 1295–1307, 2008
https://doi.org/10.5194/hess-12-1295-2008
© Author(s) 2008. This work is distributed under
the Creative Commons Attribution 3.0 License.

  01 Dec 2008

01 Dec 2008

Runoff thresholds in derived flood frequency distributions

A. Gioia1, V. Iacobellis1, S. Manfreda2, and M. Fiorentino2 A. Gioia et al.
  • 1Dipartimento di Ingegneria delle Acque e di Chimica, Politecnico di Bari, Bari, Italy
  • 2Dipartimento di Ingegneria e Fisica dell'Ambiente, Università degli Studi della Basilicata, Potenza, Italy

Abstract. In general, different mechanisms may be identified as responsible of runoff generation during ordinary events or extraordinary events at the basin scale. In a simplified scheme these mechanisms may be represented by different runoff thresholds. In this context, the derived flood frequency model, based on the effect of partial contributing areas on peak flow, proposed by Iacobellis and Fiorentino (2000), was generalized by providing a new formulation of the derived distribution where two runoff components are explicitly considered. The model was tested on a group of basins in Southern Italy characterized by annual maximum flood distributions highly skewed. The application of the proposed model provided good results in terms of descriptive ability. Model parameters were also found to be well correlated with geomorphological basin descriptors. Two different threshold mechanisms, associated respectively to ordinary and extraordinary events, were identified. In fact, we found that ordinary floods are mostly due to rainfall events exceeding a threshold infiltration rate in a small source area, while the so-called outlier events, responsible of the high skewness of flood distributions, are triggered when severe rainfalls exceed a threshold storage in a large portion of the basin.

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