WWRC 88-12
Assessing the Risk of Violating Stream Water Quality Standards
Abstract
For many years, managing agencies have enacted and enforced water quality
standards based on a deterministic evaluation of the stream environment under
their control. Given the random nature of the processes occurring within a
stream system, the deterministic approach to water quality regulation is subject
to obvious shortcomings. In an attempt to improve water quality regulation, a
method is presented for quantifying the joint risk associated with dissolved
oxygen deficits exceeding a specified standard and the length of such violations
within a stream environment. Techniques are employed utilizing the
Streeter-Phelps equation in conjunction with Monte Carlo simulation. In
addition, flexibility is provided in the formulation by allowing several
probability distributions to be assigned to each parameter in the model. A
sensitivity analysis is also performed on the joint risk for the various probability
distributions and statistical properties assumed for each parameter. Implied in
the methods and results presented is the development of improved water quality
standards incorporating the inherent stochastic nature of stream environments.
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