Uncertainty Analysis of Dissolved Oxygen Model

First-order uncertainty analysis was applied to 258 stream segments to determine the relative contributions to scatter, or uncertainty, in dissolved oxygen predictions by each of the parameters of the Streeter-Phelps equation. For very sluggish streams with reaeration rates less than about 0.1 per day (base e), the most important parameters for dissolved oxygen predictions were the initial deficit and the deoxygenation rate constant. For streams having reaeration coefficients greater than 0.1 per day the most important parameter corresponded to the predominant aspect of the oxygen balancing mechanism for the stream segment. On the depletion portion of the dissolved oxygen sag curve, where deoxygenation exceeds reaeration, the deoxygenation rate constant contributed most of the uncertainty in D. O. predictions. However, on the recovery portion of the D. O. sag curve, where reaeration exceeds deoxygenation, the reaeration rate constant contributed most of the uncertainty in D. O. predictions. Application of the uncertainty analysis to identify critical water quality parameters for a given stream would lead to more efficient data collection efforts.