Reply to Comment on {"}a dynamic rating curve approach to indirect discharge measurement by Dottori et al. (2009){"} by Koussis (2009)

In a recent comment, Koussis (2010) moved a number of critiques on the paper by Dottori et al. (2009), which describes a methodology for indirect discharge measurement using simultaneous water stage measurements at two adjacent cross sections in a river reach. The procedure, which requires the geometrical description of the two cross sections, allows for direct computation of water surface slope, and improves accounting for unsteady flow effects through the use of the complete or simplified momentum equation (a reason for calling it DyRaC, the acronym of Dynamic Rating Curve). Among others, Koussis argues that the procedure is not suited for practical use since it is too demanding in terms of data set and flow conditions, and the requirements for its application are generally not met in practice, particularly in rivers with a complex morphology. Then Koussis suggests using an alternative procedure for discharge measurement, based on a modification of the well known Jones Formula he developed several years ago (Koussis, 1975, 1976). Finally, he contends that the procedure proposed by Dottori et al. (2009) is based upon the well known “standard step method” for computing flood depth profiles. The aim of this reply, is to show that the criticisms moved are not really motivated: DyRaC, the proposed approach, may be used for operational measurements in rivers with noticeable advantages with respect to alternative methodologies. As a matter of fact DyRaC has already been installed in Italy and thoroughly tested on-line for estimating unsteady discharges in real-time on the River Parma, as well as successfully applied for flow estimates on several gauging stations along the River Arno course.