<Li> D O b (\ displaystyle DO_ (b)) is the background concentration of the dissolved oxygen content in the river (g m 3) (\ displaystyle ((\ tfrac (\ mathrm (g)) (\ mathrm (m) ^ (3))))). </Li> <Li> D O s (\ displaystyle DO_ (s)) is the background concentration of the dissolved oxygen content in the merging river (g m 3) (\ displaystyle ((\ tfrac (\ mathrm (g)) (\ mathrm (m) ^ (3))))). </Li> <Li> Q b (\ displaystyle Q_ (b)) is the flow in the river upstream from the mixing point (m 3 s) (\ displaystyle ((\ tfrac (m ^ (3)) (s)))). </Li> <Li> Q s (\ displaystyle Q_ (s)) is the flow in the merging river upstream from the mixing point (m 3 s) (\ displaystyle ((\ tfrac (m ^ (3)) (s)))). </Li>

In the streeter-phelps model the oxygen deficit is defined as