Two Referees provided critical, but constructive comments to this manuscript suggesting a revision of the manuscript. The authors replied to them in the online discussion and appear available to revise their article. As such, I suggest a substantial revision that should address all referees' concerns. A systematic point-by-point letter should be submitted along with the revised manuscript. Since one of the Referee suggested a major revision, the revised manuscript will undergo a further review process.

The paper can be accepted subject to minor revisions, i.e. addressing all comments by the referee. In particular, the title should be changed into "Technical Note: Flow velocity and discharge measurement in rivers using terrestrial and UAV imagery".