The Calculation Specifications are specified here; a user can select a Force Main Equation from either the Hazen-Williams or Darcy-Weisbach formulae to compute friction losses for pressurised flow.
The Variable Timesteps checkbox will be checked by default. This needs to be unchecked if integrating your urban network with river networks and/or 2D components.
We refer the user to the EPA Manual for further details on this tab of the urban Model Settings window.