Dear Authors,

The paper “hess-2018-146: Inundation mapping based on reach-scale effective geometry” (by Rebolho et al.) introduces the development of a novel conceptual inundation mapping procedure called MHYST, based on the DEM-based HAND concept coupled with 1-D steady-state flow equations. Applications were conducted on the French river Loing.

Three referees evaluated the paper. Referees #1 and #2 have sent their comments during the discussion period, and the authors have given responses to both referees’ comments. Referee #3 has sent her/his comments after the closure of the discussion, and you find her/his comments at the end of this message.

All three referees state that the paper is novel, useful for applied hydrology/hydraulics, and is a valuable contribution to Hydrology and Earth System Sciences. Referees #1 and #3 ask for “Minor revisions”. Referee #2 asks for “Major revisions” and raises important questions concerning the need: i) to conduct sensitivity and uncertainty analyses; ii) to include a comparison between an actual and a predicted inundation mapping of several continuous reaches. The authors have given detailed and convincing responses to the comments of Referees #1 and #2 available during the discussion period.

The paper will be reconsidered after “Major revisions”. In the revised version, authors are invited to respond point by point to each comment of each referee, giving convincing proofs to all questions raised by referees. Please highlight clearly what you changed in the revised manuscript, so the referees are able to assess your changes.

With kind regards,

Roger Moussa


Referee #3

The authors aim at providing a new forecasting tool able to provide flooding map rapidly.

They give a very good overview of the existing tools, discussing about advantages and limitations of these approaches based mostly based on 1d and 2d shallow water equations and their simplifications (diffusive wave and kinematic wave). The main limitation encountered with these methods is the lack of data.

The authors with their new tool: MHYST aim at tackling this issue.

Alternative techniques have been used before the authors’ work: based on DEM analysis (EXZECO and HAND).

In HAND, the DEM study allows determining the flowpath. Then a relation between a threshold height and discharge allows generating floodmap.

The tool presented by the authors (MHYST) is based on an improvement of HAND’s method. Hydraulics équations are used at reach scale. A strong assumption is made: flow constant in space and time. Thus a relation between the threshold height and discharge is generated. DEM analysis provides geometrical variables (cross section area, bankfull water level, ...). With use of boundary conditions, this allows to generate flood map.

The methodology is applied on an event which occurred in France in 2016 with the river Loing.

The results are not perfect as recognized by the authors. But as they mention they are not so bad. As this methodology is fast to apply, it can provide first answer when needed in case of urgent situations.

I think this is an efficient tool; the article is well written and deserves to be published.

Dear Authors,

The revised version takes into account all comments of the referees. Minor revisions are required (please see the attached file of the referee).

Kind regards,

Roger Moussa

Dear Authors,

The revised version of the manuscript takes into account all reviewer's minor comments. The paper can be consiered now for publication in Hydrology and Earth System Sciences.

Kind regards,

Roger Moussa