AZRED v2.0

cameraThe accurate prediction of solute transport in water distribution systems has become a critical component of efforts aimed at delivering clean drinking water safely to large urban populations. One of the central assumptions that water quality models have traditionally relied upon dictates that, in a 4-way junction, two incoming flows of differing quality will mix perfectly to produce two outgoing flows of equal quality, and that such complete mixing occurs irrespective of the specific assemblage.


Figure 1. Flow visualization of incomplete mixing: (a) a simulation result by computational fluid dynamics (CFD) and (b) the corresponding experimental result with a high-speed camera at a cross junction.

In an effort to develop AZRED v2.0, we conducted a series of laboratory experiments and computational simulations in order to characterize solute mixing patterns at double-tee and wye junctions, both of which are commonly found in urban water distribution systems, as shown in the following figures.junction-configs

Figure 2. Junction configurations (a) X1 (Cross), (b) X2 (Cross with opposing flows), (c) N1 (double-Tee), (d) N2 (double-Tee), (e) U1 (double-Tee), (f) U2 (double-Tee), (g) Y1 (one single-Tee and one wye at 45o, E representing YN and E- representing YU), and (h) Y2 (one single-Tee and one wye at 45o, E representing YN and E- representing YU).

setup01setup02Figure 3.  (a) Schematic drawing of experimental setup for mixing at Wye junction, and various configurations, which have been tested: (b) N junction, (c) U junction (c) and (d) YN/YU junction.


This following flow chart outlines the code modifications that were incorporated into the original software tool (EPANET) to give rise to a modified version (AZRED v2.0).


Figure 4. Flowchart of AZRED v2.0 integrated with EPANET 2.00.12

The relevance of the geometric configurations of each junction and their effect on water quality are summarized in the tutorial, and exemplary networks are then simulated using both the complete and incomplete mixing assumptions in order to illustrate the quantifiable difference in tracer concentration as a function of the mixing rate. Beyond the specific upgrade described in this study, the present effort should aid in future examinations of other hydraulic and transport phenomena that are typically modeled by EPANET or similar software tools designed to analyze piping networks.

AZRED v2.0 is an extended version of EPANET, which is the most widely used software for modeling urban water distribution systems. AZRED’s name derives from ‘AZ’, the abbreviation for Arizona (where AZRED v1.0 was originally developed at the University of Arizona, and later completed and documented at the University of Wisconsin-Madison), and ‘RED’, which is a Spanish word for network. AZRED v2.0 adds to the water quality solver of EPANET a module for calculating the effects of incomplete mixing at various types of four-way junctions, such as crosses, double-tees, and wye connectors.

AZRED v2.0 consists of two files: a main core, named ‘epanet2.dll’, which is a Microsoft Dynamic Link Library (DLL) that replaces the simulation engine of EPANET, and a graphic shell, named ‘Epanet2w.exe’, which substitutes the graphical user interface of EPANET. To install AZRED v2.0, first install a copy of EPANET, which can be downloaded from the Environmental Protection Agency website (, and then drop the ‘epanet2.dll’ and ‘Epanet2w.exe’ to the folder where EPANET was installed (‘C:\Program Files\EPANET2\’ or ‘C:\Program Files (x86)\EPANET2\’). A message will appear asking if you want to replace these files.

AZRED v2.0 (0.8 MB zip folder):  Click Here

Tutorial (1.1 MB pdf file):  Click Here

AZRED v2.0 Users Manual (0.2 MB pdf file):  Click Here

Relevant Refereed Journal Articles:

  • Romero-Gomez P, CK Ho, CY Choi (2008) Mixing at cross junctions in water distribution systems – Part I. A numerical study, ASCE Journal of Water Resources Planning and Management. 134:3, 284-294. Click Here
  • Austin RG, B van Bloemen Waanders, S McKenna, CY Choi (2008) Mixing at cross junctions in water distribution systems – Part II. An experimental study, ASCE Journal of Water Resources Planning and Management. 134:3 295-302. Click Here
  • Song I, P Romero-Gomez, CY Choi (2009) Experimental verification of incomplete solute mixing in a pressurized pipe network with multiple cross junctions, ASCE Journal of Hydraulic Engineering. 135:11, 1005-1011Click Here
  • Romero-Gomez P, KE Lansey, CY Choi (2011) Impact of an incomplete solute mixing model on sensor network design, Journal of Hydroinformatics, 13:4, 642-651.  Click Here
  • Romero-Gomez P and CY Choi (2011) Axial dispersion coefficients in laminar flows of water distribution systems, ASCE Journal of Hydraulic Engineering, 137:11, 1500-1508. Click Here
  • Song I, P Romero-Gomez, MA Andrade, M Mondaca, CY Choi (2018) Mixing at junctions in water distribution systems: an experimental study, Urban Water Journal. 15:1, 32-38. Click Here


Professor Christopher Y. Choi
Department of Biological Systems Engineering
460 Henry Mall
University of Wisconsin-Madison
Madison, WI 53706
Phone: (608) 262-0607


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