Temperature

The unit models temperature in a river or other channel.

Description

Most of the biochemical and biological processes included in the 1D Water Quality Solver are temperature dependent. The simulation of water temperature is therefore integral to any water quality simulation. Temperature may be included in the 1D Water Quality Solver in one of three forms.

If it can be assumed that the mean water temperature does not vary greatly during the period of the simulation then a constant value may be set using the keyword, CONSTANT.

In cases where the temperature changes with time, for instance due to seasonal variations, but not spatially then the keyword, PRESCRIBED, may be used. PRESCRIBED data is entered in the form of a time-history where time is set either by dates or uses units of days, weeks, lunar months, months, years, decades or a user defined multiplier.

It may be necessary to consider variations of temperature both spatially and temporally then the keyword, VARIABLE, should be used. This may be of use in an estuary model where the sea and river temperatures differ significantly. This feature may also be used to investigate the effects of thermal discharges on the river. When the keyword, VARIABLE, is used, heat transfer to and from the atmosphere is included. The model simulates the excess temperature above a user specified base temperature.

Equations

When VARIABLE temperature is being simulated then heat transfer to and from the atmosphere is represented by the following equation:
                                                                                 (1)

Where:

KT = heat transfer coefficient (s^-1)

T_base = equilibrium water temperature (°C)

When the water temperature is T_base then there is no heat transfer between the air and the water. When the water temperature exceeds T_base then the water will cool, otherwise the water heats up.

General

The TEMPERATURE module may be run independently of the other water quality modules. If the simulation of the DISSOLVED OXYGEN module is required then the TEMPERATURE module must be included in the simulation. The TEMPERATURE module simulates the following variable name:

• Temperature (^oC)

This is a transported variable when the keyword VARIABLE is used.