Abstract
Abstract. The production of spatially accurate representations of potential inundation is often limited by the lack of available data as well as model complexity. We present in this paper a new approach for rapid inundation mapping, MHYST, which is well adapted for data-scarce areas; it combines hydraulic geometry concepts for channels and DEM data for floodplains. Its originality lies in the fact that it does not work at the cross section scale but computes effective geometrical properties to describe the reach scale. Combining reach-scale geometrical properties with 1-D steady-state flow equations, MHYST computes a topographically coherent relation between the “height above nearest drainage” and streamflow. This relation can then be used on a past or future event to produce inundation maps. The MHYST approach is tested here on an extreme flood event that occurred in France in May–June 2016. The results indicate that it has a tendency to slightly underestimate inundation extents, although efficiency criteria values are clearly encouraging. The spatial distribution of model performance is discussed and it shows that the model can perform very well on most reaches, but has difficulties modelling the more complex, urbanised reaches. MHYST should not be seen as a rival to detailed inundation studies, but as a first approximation able to rapidly provide inundation maps in data-scarce areas.
Highlights
Floods are a recurring phenomenon in France: in September 2014, intense rainfall affected the south of the country, leading to several deaths and about EUR 0.6 billion worth of damage
These scores are presented in detail by Jolliffe and Stephenson (2003) and are defined as a ratio between members of the table where n1 is the number of hits, i.e. the number of flooded cells correctly forecast; n4 is the number of pixels correctly forecast as dry; n2 is the number of false alarms; and n3 the number of observed flooded cells missed by the model
If we look at the “physical” set of parameters we previously identified (Kch = 10 and Kfp = 5 m1/3 s−1), we can see that the critical success index (CSI) reached by the model for this combination varies between the resolutions
Summary
Floods are a recurring phenomenon in France: in September 2014, intense rainfall affected the south of the country, leading to several deaths and about EUR 0.6 billion worth of damage. In June 2016, largescale flooding occurred over the Seine and Loire catchments, mainly affecting their tributaries and resulting in four deaths at a cost of EUR 1.4 billion These are only examples which underline the value of flood inundation mapping to anticipate the impact of such events. Its application on the Mulde catchment in Germany (Falter et al, 2015) showed mixed results concerning inundation extents, correctly predicting only 50 % of the flooded area for the August 2002 event. This underestimation was explained by dike breaches that were not accounted for within the model. A lack of observed data did not allow validation on other events
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