Two types of design variables are used for the optimal design and rehabilitation of water distribution systems. They are pipe sizes (d) and design actions (e).

Pipe Size

Pipe diameter is treated as a design variable for a new pipe to be sized. A new pipe can be the pipe added to a subdivision, a replacement, or a pipe that is parallel to existing pipes. A modeler can aggregate a number of pipes as one design link. Pipes within one pipe group are sized to the same diameter. Pipe diameter can be selected from a set of discrete and commercially available pipe sizes, given as:

Design Action

Design action is introduced as a design variable for optimizing the rehabilitation alternatives (e.g. cleaning, relining, replacement, parallel pipe, etc.) for existing pipes. A modeler can define a set of possible actions that can be applied to a group of pipes. The pipes within one pipe group will have the same rehabilitation action, given as: