AERATION PERFORMANCE OF LOW DROP WEIRS

The aeration performance with respect to oxygen transfer of a smooth w eir, 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 0.7 m. A review of existing relationshi ps to predict aeration at weirs indicated that prototype-scale model s tudies and actual prototype data were limited in this range of drop he ights. In addition, most laboratory testing has been conducted at grea ter drop heights and lower unit discharges. To reduce experimental unc ertainty, a procedure was developed which uses an enhanced-oxygen atmo sphere over the flume water surface. The uncertainty in values of the deficit ratio (r) developed from the testing procedure is +/-0.040. Ae ration was greatest with the cobble-faced weir and lowest with the chu te. The superior performance of the cobble-faced weir relative to the smooth weir is attributed to weir surface roughness achieved by overla ying the weir crest with cobbles. A new relationship to predict the de ficit ratio for a cobble-faced weir was developed that is similar to t he relationship of Avery and Novak (1978) and includes a dimensionless term to account for tailwater depth.