Stormwater wetland targeted to treat the rainfall runoff from cow feeding-lot basin has been monitored from May 2010 to
November 2011. Reduction efficiency estimated based on 20 rainfall event monitoring was 88%, 54%, 70%, 31%, and 64%
for TSS, BOD, CODCr, TN, and TP, respectively. Theoretically, as rainfall depth increases, hydraulic exchange ratio has to
be increased. When the exchange ratio approaches to 1 (usually design goal), TSS reduction efficiency was estimated about
55%. Uncertainty in reduction efficiency of the stormwater wetland is normally very high due to the continuous rainfall
activity, its magnitude and intensity, antecedent dry days, and other natural variables which can not be controlled by
experiment conductors. In this study, predominant affecting variables was found to be hydraulics caused by consecutive
rainfall events having different intensity and algal growth during dry days.