Decay

The unit models transport and decay of a non-conservative pollutant in a river.

Description

The variable simulated by the module is simply a transported substance that can decay according to first order kinetics. It does not interact with any other variable. It therefore behaves like coliforms or bacteria (see COLIFORMS).

The primary use is to model the variation of an organic pollutant as it is discharged and its subsequent decay. The only parameter required to model the decaying pollutant is its decay rate, K (day^-1). In this respect it is different from COLIFORMS which uses a T₉₀ value instead of K. The decay rate can be varied between daytime and night-time. This allows for the increased break-down of the pollutant during daylight hours.

Equations

A decaying pollutant is simulated by a first order decay equation:

                    (1)

Where:
K =       Decay rate (s^-1)
C =       Concentration of coliforms (user defined units)

General

The DECAY module may be run independently of the other water quality modules. The decay module simulates the transported variable name:

• Decaying pollutant (user-defined units)