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Developing a Main Replacement Prioritization Tool
3. Pipe diameter less than 6 inches — like galvanized steel, another utility goal to phase out.
4. A head loss of more than 10 psi per 1000 feet of pipe. The data was obtained by calibrated hydraulic model
5. A high ratio of repair cost to replacement cost, which reflects part of the evaluation seen in the previous
6. A main located on a street where road paving or reconstruction is scheduled.
Working with the consultant, MAW considered various weightings of these items, choosing one weighting scheme
that seemed to best fit appropriate selection criteria. During this process, additional data errors were identified such as
removing main breaks from pipes that had been retired and replaced.
Step 3 used another element of the GIS based model to schedule a five-year program of main renewal to organize
projects. The model can take the various ranked main segments and using cost estimates for replacement determine
a level of pipe renewal appropriate in terms of budget limitations or a targeted length of main to be replaced over
several years. A final step of the process is to organize annual projects by grouping projects based on proximity of other
mains to be replaced. So a main scheduled in the fifth year of a five-year program might be shifted to the first year if it
is adjacent to a very poor main scheduled in the first year of the program.
This methodology was applied in a system that did not have a fully developed GIS, but the model clearly shows the
value of GIS in such a process. The model also demonstrated the importance of good main break data, which MAW
had provided. The model itself continues to be improved. A next step suggested by the utility is to have the ability to
assign different costs of renewal for same size pipe based on the option to rehabilitate instead of replace or to take
into account different costs of restoration.
Deb, A. F. Grablutz, Y. Hasit, J. Snyder, G.V. Loganathan, and N. Agbenowsi. 2002. Prioritizing Water Main
Replacement and Rehabilitation, order #90898/project #459. Denver: AwwaRF and AWWA.