The Illinois Transient Model (ITM) is a multipurpose Finite Volume (FV) model to analyze transient flows in circular closed-conduit systems ranging from dry-bed flows to gravity flows, to partly gravity-partly surcharged flows (mixed flows) to fully pressurized flows (waterhammer flows). In the ITM model, ...the free surface region is modeled using the 1D Saint-Venant equations and the pressurized region is modeled using the 1D compressible waterhammer equations. ITM can accurately describe positive and negative mixed flow interfaces, interface reversals, and it can simulate sub-atmospheric pressures in the pressurized flow region. ITM can also simulate transient mixed flows when large pressure wave celerities (~1000 m/s) are used. The latter is very important when pressurized transient flows are of interest. If transients are of no interest, a small pressure wave celerity may be used to speed up the computations. The boundary conditions currently supported include dropshafts, reservoirs, rating curves, closing and opening of gates (open channel or pressurized) as a function of time, and junctions with any number of connecting pipes and any type of horizontal and vertical alignment. The model can also simulate flows in adverse slopes.

The ITM model is a free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

The ITM model was used for several projects. These applications include:

• Impact of gates closure in the formation of transient flows in combined sewer systems
• Potential for surge formations
• Hydraulic transients for the simultaneous occurrence of free surface and pressurized flows in closed-conduit systems
• Analysis of reservoir filling in combined sewer systems ranging from dry-bed flows, to free surface flows, to partly free surface flows-partly pressurized flows, to fully pressurized flows.

The Illinois Transient Model (ITM) was used for the transient analysis of combined sewer systems in the United States of cities such as Chicago, Omaha, San Francisco, Detroit and Dallas, and worlwide in countries such as Switzerland, China, Canada, New Zealand and Mexico. Below is an incomplete list of users:

• Metropolitan Water Reclamation District of Greater Chicago (MWRD), Illinois.
• Metropolitan St. Louis Sewer District, Missouri.
• Dr. Martin Rüdisüli (Martin.Ruedisueli@hunziker-betatech.ch), Hunziker Betatech AG, Switzerland.
• Dr. David H. Axworthy (DAxworthy@nhcweb.com), http://www.nhcweb.com/, Pasadena, California.
• Sam Glovick (sglovick@WadeTrim.com), Wade Trim, Pittsburgh, Pennsylvania.
• Tony Margevicius (Tony.Margevicius@AECOM.com), AECOM, Cleveland, Ohio.

(*) This table presents ITM input files and simulation results for three actual sewer systems, whose geometries and layouts were altered on purpose to maintain confidentiality.

The Illinois Transient Model (ITM) will be posted soon in GitHub. The code can be found at this Github link