Aeration Performance of Low Drop Weirs
Scott Hogan, Richard Walters, Chester Watson
The aeration performance with respect to oxygen transfer of a smooth weir, a cobble-faced weir, and a cobble-faced chute was investigated in a large laboratory flume. The maximum difference between upstream and downstream water surfaces was 0.7m. A review of existing relationships to predict aeration at weirs indicated that prototype-scale model studies and actual prototype data were limited in this range of drop heights. In addition, most laboratory testing has been conducted at greater drop heights and lower unit discharges. To reduce experimental uncertainty, a procedure was developed which uses an enhanced-oxygen atmosphere over the flume water surface. The uncertainty in values of the deficit ratio (R) developed from the testing procedure is + or - 0.040. Aeration was greatest with the cobble-faced weir and lowest with the chute. The superior performance of the cobble-faced weir relative to the smooth weir is attributed to weir surface roughness achieved by overlaying the weir crest with cobbles. A new relationship to predict the deficit ration for a cobble-faced weir was developed that is similar to the relationship developed by Avery and Novak in 1978 and includes a dimensionless term to account for tailwater depth.
Available upon request at the American Society of Civil Engineer