Conservative Point Source Discharge Effect on Water Quality
The first step that must be taken for modeling conservative point source discharges is
calculating the mass balance at the discharge point. The basic formula is:
Mass rate of substance upstream + Mass rate added by outfall=
Mass of substance Immediately downstream from outfall
Diagram of River with a Discharge
Therefore the mass balance is represented by:
Upstream flows (Qu) and concentration of pollutant (Su) are often known by measurements
or can be estimated by water uses upstream. The elluent flow (Qe) and concentration (Se)
are often know by process dynamics.
A conservative substance is a substance (pollutant) which incures no losses due to
chemical reactions or biochemical degradations, such examples are:
- Total dissolved solids
- Chlorides
- Certain metals during times of the year
When the substance is transported in the dissolved form, the concentration changes only
when new sources of that substance are introduced again into the river or stream. The
concentration can therefore be represented by:
The only assumption made is that the river and discharge are near steady state. This implies
that there are no losses or contributions to the flow due to groundwater.