Predicting Oxygen Content Downstream of Weirs, Spillways and Waterways.

Abstract

At hydraulic structures (e.g. weirs, spillways), air-water transfer of atmospheric gases (e.g. oxygen) occurs by self-aeration along the chute and by flow aeration in the hydraulic jump at the downstream end of the structure. In this paper, experimental data are re-analysed and compared with a numerical method to predict the free-surface aeration. Aeration at hydraulic jumps is also examined and compared with existing correlations. Calculations of free-surface aeration and empirical correlations for hydraulic jump aeration are combined to predict the DO content downstream of weirs and spillways. Good agreement between calculations and prototype data is obtained. The results indicate that self-aeration might contribute to a large part of the oxygenation taking place at hydraulic structures for small water discharges. For large discharges, the reduction or the disappearance of free-surface aeration affects substantially the aeration efficiency.

Efficiency of the Nam Theun 2 hydraulic structures on water aeration and methane degassing

“…This result is consistent with previous studies (Chanson, 1995;Richard et al, 2005) that demonstrated that low flows had higher waterfall, facilitating the flow to plunge into the water body. At low discharges, breakup of the jet is observed as drop height increases.…”

“…time of the air-water exchange (Chanson, 1995;EPRI, 2002;Emiroglu & Baylar, 2006). Moreover, to obtain an unbiased estimate of the intrinsic efficiency of the devices, an assessment of the contribution of flow stretches between the devices and the downstream measurement points should have been made and it would have been better to test the structure under the entire range of upstream conditions (0 to 100% of upstream DO saturations and low to very high CH 4 saturations); which has not been possible to test for the Aeration Weir for instance.…”

“…Solutions range from hypolimnetic oxygen injection, reservoir clearing and selective withdrawal to the construction of dedicated hydraulic structures like weirs or baffle blocks. Creation of turbulence by hydraulic structures and subsequent aeration is a principle utilized by aeration weirs and seems to be the most efficient solution for aeration (Chanson, 1995;EPRI, 2002;Emiroglu & Baylar, 2003). DO transfer occurs when air is entrained into the flow in the form of a large number of bubbles.…”

Measuring air-water interface area in supercritical open channel flow

“…Equation (4) is reported on figure 4. Although equation (4) is a very crude approximation, it is interesting to note the similarity of shape between the data and equation (4) Altogether the present study suggests that previous calculations of air-water interface area and air-water gas transfer (CHANSON 1994(CHANSON ,1995 are some form of reasonable approximation. H.…”

“…WOOD 1991, CHANSON 1994, there is little information on the air-water interface area and bubble size distributions within the flow. WILHELMS and GULLIVER (1989) and CHANSON (1995) discussed the air-water gas transfer process. GULLIVER et al (1990) and CHANSON (1994) attempted to derive bubble size predictions.…”