TR(BR)-5/96-97 : Assessment of probability distribution of dissolved oxygen

Abstract

It has been recognized that processes in natural stream environments are inherently random. The ability to quantify the probabilistic status of stream environments is of vital importance in water quality management decision making. This report presents a methodology to assess the probability distribution of dissolved oxygen based Streeter-Phelp equation. The methodology involves the use of First-order analysis and Monte Carlo simulation to analyze the uncertainty associated with dissolved oxygen. The mean and standard deviation of the parameters have been assumed same for studied probability distributions.

The critical DO is found to be approximately normally distributed. The mean value of DO at the critical location is found to be more or less same, irrespective of the method used. But the level of uncertainty associated with the DO is found to be considerably different. The Monte Carlo simulations with log-normally distributed input is found to give the lower uncertainty in the DO levels.

For estimation of travel time, Monte Carlo simulation with lognormally distributed input variables is found to be a preferable method. For the over all DO profile in the stream, First order analysis predicting the same DO level as given by Monte Carlo simulation and lower level of uncertainty, is found to be more justified