The following three sections describe the equations and calibration parameters used for calculating water quality transformations.

Water quality transformations are handled separately from water quality transport. The transport algorithms and parameterizations have been described earlier and are calculated in the HEC-WQ Engine based on hydrological data passed to the WQ Engine from HEC-ResSim. Transformations are calculated in one of three dynamically loaded, native code libraries, written by the USACE Engineering Research and Development Center's Environmental Lab (ERDC-EL). These include libraries for water temperature; nutrients, algae, and dissolved oxygen; and generalized constituents.

The transformation libraries are called as needed from the WQ Engine to update concentrations at the end of each transport time step. Each library is described individually in the sections that follow.