EFFECTS OF FLOW VELOCITY AND DEPTH ON THE RATES OF REAERATION AND BODREMOVAL IN A SHALLOW OPEN-CHANNEL

This study developed an analytical solution of reaeration rate coeffic ient (K-2) and modified the equation of BOD removal in a shallow artif icial open channel. A series of well-controlled batch tests were carri ed out to measure the K-2 and BOD removal rate in the channel at diffe rent flow conditions. The results of these tests indicated that measur ed K-2 within the developing zone of the laminar boundary layer is bet ter described by the analytical solution of this study than by the fiv e semi-empirical formulae mentioned in this paper. On the other hand, a resuspension-sedimentation coefficient, Rs, was added to the BOD rem oval equation to describe the variation in BOD due to varied flow cond itions. Based on the results of the experimental data the following co nclusions in the BOD removal process were reached. It was found that a direct correlation exists between the flow velocity to depth ratio (U /h) and the deoxygenation rate coefficient (K-1), but there is an inve rse correlation between U/h and Rs as well. This modified BOD removal equation can predict BOD removal rate at different travel times or kno wn downstream distances in an open channel under varied flow condition s. (C) 1997 IAWQ. Published by Elsevier Science Ltd.