The parameters used for pressure loss calculation in pipe flow are not unique

[fwitte]

They should be. At the moment, it is possible to specify the method for the parameter group "hydro_group" by choosing "HW" for the Hazen-Williams equation and any other parameter (or no parameter at all) for the Darcy-Weisbach equation. The roughness parameter (ks) is entirely different for both methods. Therefore, the implementation should be changed in the following way:

• ks and hydro_group will refer to the default implementation (Darcy-Weisbach), therefore no API change.
• ks_hw and hydro_group_hw refer to the Hazen-Williams equation, therefore API change.