Estuary/Tide Decay Modeling*

Introduction

Understanding and predicting the impact of various sources are essential components of a typical course on Analysis of Stream and Estuary Pollution in an engineering curriculum. Dispersal and decay of contaminants in lakes, streams, estuaries, and oceans. Effects of pollutants on chemical quality and ecology of receiving waters.

Point Source

--- Nonconservative Substances

Under some assumptions, the mass balance equations can be derived for an infinitely long, constant parameters:

for S = S0 at x = 0; S = 0 at x = . If the derivative is expanded and assumptions are made, then the solution is:
--- Conservative Substances

For conservative substances, K = 0,  the mass balance is:

for S = S0 at x = 0; S = 0 at x = -. If the derivative is expanded and assumptions are made, then the solution is:
Figure 1 shows the distribution of concentration for idealized estuary.
Distributed Sources

For a reactive water quality constituent distributed along the length of a constant parameter estuary, the differential equation is:

Consequently, there are three solution regions, the solutions are summarized in Table 1
Multiple Sources

An example of this principle is found in Figure 2 where two points sources discharge a given substance into an estuary which has a constant flow and dispersion coefficient.

Model Examples * Contents and Pictures are from "Principles of Surface Water Quality Modeling and Control" by Robert V. Thomann and John A. Mueller, Harper-Collins, 1988