The unit models transport and decay of coliforms in a river.
Description
The variable representing coliforms is simply a transported substance that can decay according to first order kinetics. It does not interact with any other variable. It therefore behaves in all respects like a decaying pollutant (see DECAY).
The primary use is to model the variation of E-coli or any other bacteria. The only parameter required to model them is their decay rate expressed in terms of a T90 value. T90 (in hours) is the time taken for a population to reduce to 10% of its original density. In this respect it is different from DECAY which uses a decay rate (K) instead of T90. The T90 value can be varied between daytime and night-time. This allows for the increased mortality of the bacteria due to the effect of sunlight.
Equations
The decay of coliforms is simulated by a first order decay equation:
(1)
Where:
K = decay rate (s-1)
C = concentration of coliforms (user defined units)
The first order decay rate constant, K (sec-1) is obtained from T90(hours) by:
(2)
General
The COLIFORMS module may be run independently of the other water quality modules. The COLIFORMS module simulates the transported variable name:
- Coliforms (user-defined units)