Preprints
https://doi.org/10.5194/hess-2020-597
https://doi.org/10.5194/hess-2020-597

  04 Dec 2020

04 Dec 2020

Review status: a revised version of this preprint is currently under review for the journal HESS.

Performance of automated flood inundation mapping methods in a context of flash floods: a comparison of three methods based either on the Height Above Nearest Drainage (HAND) concept, or on 1D/2D shallow water equations

Nabil Hocini1,, Olivier Payrastre1,, François Bourgin1,2, Eric Gaume1, Philippe Davy3, Dimitri Lague3, Lea Poinsignon4, and Frederic Pons4 Nabil Hocini et al.
  • 1GERS-LEE, Univ Gustave Eiffel, IFSTTAR, F-44344 Bouguenais, France
  • 2Université Paris-Saclay, INRAE, UR HYCAR, 92160 Antony, France
  • 3Géosciences Rennes, 35042 Rennes, France
  • 4Cerema Méditerranée, 13290 Aix-en-Provence, France
  • These authors contributed equally to this work.

Abstract. Flash floods observed in headwater catchments often cause catastrophic material and human damage worldwide. Considering the large number of small watercourses possibly affected, the use of automated methods for flood inundation mapping at a regional scale can be of great help for the identification of threatened areas and the prediction of potential impacts of these floods. An application of three mapping methods of increasing level of complexity (HAND/MS, caRtino 1D, and Floodos 2D) is presented herein. These methods are used to estimate the flooded areas of three major flash floods observed during the last ten years in South-Eastern France: the 15th of June 2010 flood on the Argens river and its tributaries (585 km of river reaches), the 3rd of October 2015 flood on small coastal rivers of the French Riviera (131 km of river reaches) and the 15th of October 2018 floods on the Aude river and its tributaries (561 km of river reaches). The common features of the three mapping approaches are their high level of automation, their application based on a high-resolution (5 m) DTM, and their reasonable computation times. Hydraulic simulations are run in steady-state regime, based on peak discharges estimated using a rainfall-runoff model preliminary adjusted for each event. The simulation results are compared with the reported flood extent maps and the high water level marks. A clear grading of the tested methods is revealed, illustrating some limits of the HAND/MS approach and an overall better performance of hydraulic models solving the shallow water equations. With these methods, the inundated areas are overall well retrieved, and the errors on water levels remain mostly below 80 cm for the 2D Floodos approach. The most important remaining errors are related to limits of the digital elevation model such as the lack of bathymetric information, uncertainties on embankment elevation and to possible bridge blockages not accounted for in the models.

Nabil Hocini et al.

 
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Nabil Hocini et al.

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Comparison of three automated flood inundation mapping methods in a context of flash floods Nabil Hocini and Olivier Payrastre https://doi.org/10.6096/mistrals-hymex.1598

Nabil Hocini et al.

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Short summary
Automated flood inundation mapping methods can be of great help for a comprehensive identification of flash-flood related risks spread over large territories, and mainly caused by small upstream watercourses. A comparison of three mapping methods of increasing level of complexity is presented here, based on three actually observed flash-floods. The results illustrate the overall satisfactory performance of these methods, and the added value of using a 2D hydraulic approach (2D Floodos model).