Comment on "A praxis-oriented perspective of streamflow inference from stage observations – the method of Dottori et al. (2009) and the alternative of the Jones Formula, with the kinematic wave celerity computed on the looped rating curve" by Koussis (2009)

Abstract

Hydrology and Earth System SciencesThis comment addresses issues of the applicability of the DMT method in the field. DMT also advocate their method as a replacement of the widely used Jones Formula. The Jones Formula was modified by Thomas (Henderson, 1966) to include the temporal derivative of the depth, instead of the spatial one, to specifically allow discharge estimation from at-a-section stage observations. The outcome of the comparison is not surprising in view of this approximation. However, this discussion intends to show that, properly evaluated, the praxis-oriented Jones Formula, which did well in the tests, can perform better than DMT imply. It will be also documented that the DMT methodology relates to a known method for computing flood depth profiles.

Reverse flood and pollution routing with the lag-and-route model

“…That aside, with proper parameters, they can treat even pronounced transients on mild slopes, i.e., those generating at a cross-section depth (stage) vs. discharge curves with sizeable loops; the degree of transience can be gauged by the slope ratio SR = -∂y/∂x/S o ≈ ∂y/∂t/c k S o (Koussis and Chang 1982). A conservative limit for storage routing applications is SR ≤ 0.5, but transients with SR ≈ 1 have been handled successfully too (Koussis 2010b)). In such cases the kinematic wave celerity c k = dq/dA| x = const.…”

A methodological approach of estimating resistance to flow under unsteady flow conditions

“…Nonetheless, a number of problematic aspects of this approach have been pointed out. Firstly, Koussis (2010) has stressed the fact that flow depth is highly affected by local geometry. Moreover, Aricó et al (2008) have pointed out that lateral inflow may affect the evaluation of the gradient of flow depth, and for this reason the cross sections should be located close enough to each other to allow for the assumption of negligible lateral inflow.…”

Discharge estimation in a backwater affected meandering river

“…Considering the water level gradient to be a known variable, the terms representing the pressure gradient and spatial acceleration in the momentum equation can be resolved ). The application of formulas using simultaneous stage measurements was criticised by Koussis (2010). Dottori and Todini (2010) refuted most of the criticism by Koussis (2010), but acknowledged that in lowland areas with a small bed level gradient, the occurring water level gradient can drop below the measuring accuracy of the level gauge.…”

“…The application of formulas using simultaneous stage measurements was criticised by Koussis (2010). Dottori and Todini (2010) refuted most of the criticism by Koussis (2010), but acknowledged that in lowland areas with a small bed level gradient, the occurring water level gradient can drop below the measuring accuracy of the level gauge. Dottori and Todini (2010) estimate the minimum distance between the gauges to be in between 2000 and 5000 m when the bed slope is 1 × 10 −5 .…”

“…Dottori and Todini (2010) estimate the minimum distance between the gauges to be in between 2000 and 5000 m when the bed slope is 1 × 10 −5 . Since cross-profiles of the water level are not taken into consideration in one dimensional river hydraulics, neither Koussis (2010) nor Dottori and Todini (2010) considered the drawback that arises from lateral water level gradients, which can be considerable especially in meandering rivers characterised by a high sinuosity. In high-curvature river reaches, level gauges on opposite sides of each of the two cross-section would be needed to infer the longitudinal water surface gradient.…”