Uncertainty Analysis of a Simple River Quality Model Using Differential Inequalities

SIAM Review, Volume 67, Issue 2, Page 375-398, May 2025.
Abstract.We present and discuss the Streeter–Phelps equations, which were the first river quality model. If the parameters are constants, then the model in its linear formulation can be solved explicitly. This reveals, however, that depending on parameters and initial data, the model might predict negative oxygen concentrations, which marks a breakdown of the model. To address this shortcoming, we introduce a nonlinear modification which, in the case of constant parameters, we can study in the phase plane. In real-world applications, parameters are never constant and are usually known not exactly, but instead with some uncertainty. We show how we can use the solutions for the constant parameter case to obtain estimates for the unknown solutions from estimates of the model parameters, using differential inequalities.