Dissolved oxygen dynamics in the Whippany river, New Jersey: deterministic/stochastic time-variable model

Water quality criteria for dissolved oxygen (DO) in natural streams generally involves two values: One reflecting the steady-state DO concentration thus defining an average and the second reflecting the dynamic conditions within the system thus defining a minimum. Determination of the dynamic conditions requires a rational consideration of the dynamic effects of net photosynthesis, and oxygen demand (CBOD and NBOD) variability on DO within the system. Therefore, in determining the wasteload allocation for a given system it may be important to include an effluent variability parameter which will assure compliance with the receiving stream's dynamic DO criteria and standards. The modeling methodlogy presented in this paper allows for simulation of DO variability within a stream due to time-variable components of CBOD, NBOD and net photosynthesis. The model was tested by simulating DO variability for the lower Whippany River. In-stream DO deficit concentrations measured over time at Station 15 (4.8 miles down-stream (7.7 km) of the Morristown STP input) averaged 3.6 mg/l with a standard deviation of 0.8 mg/l. Using the actual upper boundary station data and Morristown STP effluent data the model predicted a mean DO deficit of 3.2 mg/l with a standard deviation of 0.8 mg/l at Station 15. The model was able to show that the effluent from the Morristown STP alone created an average dissolved oxygen deficit of 3.3 mg/l with a standard deviation of 0.5 mg/l at Station 15. Deficit variability due to the one-day CBOD and NBOD harmonics were more significant than deficit variability due to the respective seven-day harmonics.