Several estimations of the reaeration rate exist, which generally follow the equation
where
*  is a constant.
*  is the flow velocity [m/s].
*  is the depth [m].
*  is a constant.
*  is a constant.
The constants depend on the system to which the equation is applied, i.e. the flow velocity and the size of the stream or river. Different values are available in the literature.
The software "International Hydrological Programme" applies the following equation derived on the basis of values used in published literature
where
* is the average flow velocity [m/s].
* is the average depth of flow in the river [m].