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.
General Hydraulic Geometry
