Stream Reaeration in Nonuniform Flow: Macroroughness Enhancement

Abstract

The authors presented two papers which are a welcome addition to the topic of water quality and stream re-aeration. The renewal theory and small eddy model provides interesting results for smooth and smallroughness channels. The discussers feel however that the second paper highlights some limits of the method, particularly when free-surface aeration takes place.The present discussion provides additional material on the problem of stream re-aeration in presence of 'white waters' (i.e. air bubble entrainment). It complement the original paper and some references are added including large-scale data. MASS TRANSFER EQUATION AND AIR-WATER INTERFACE AREAThe mass transfer rate of a chemical across an interface varies directly as the coefficient of molecular diffusion and the negative gradient of gas concentration. If the chemical of interest is volatile (e.g. oxygen), the transfer is controlled by the liquid phase and the gas transfer of the dissolved chemical across an air-water interface is rewritten usually as : a by MOOG, D

Temperature dependence of stream aeration coefficients and the effect of water turbulence: A critical review

“…An alternative theoretical model for bubble mediated gas transfer velocity was suggested by Kawase and Moo-Young (1992) and was repeatedly used in the meticulous experimental studies of Hubert Chanson quantifying the airewater interfacial area in self-aerated flows (e.g. Chanson, 1995;Chanson and Toombes, 2000;Toombes and Chanson, 2005;Felder and Chanson, 2009). A unique property of this model is that K L is almost constant regardless of bubble size and flow situations (K L increases with temperature from 1.8 to 3.5 cm min À1 within 0e35 C).…”

Hydraulic Structures in Water Aeration Processes

“…Novak (1994) compared a cascade as investigated by Essery et al (1978) with a cascade of pools and a single jet/pool configuration. Toombes and Chanson (2000) and Chanson and Toombes (2000) considered aeration in small-slope stepped cascades. Chanson and Toombes (2002) conducted gas-liquid interface measurements in stepped cascade.…”

An experimental investigation of aeration performance in stepped spillways

“…Essery et al (1978) studied nappe flow in pooled stepped chutes. Toombes & Chanson (2000) and Chanson & Toombes (2000) considered aeration in small‐slope stepped chutes. Chanson & Toombes (2002c) conducted gas–liquid interface measurements in a stepped cascade.…”