CalGIS2016

Historical methods of selecting water mains for replacement were centered on anecdotal knowledge of field staff and were poorly supported by objective data. A common practice to select a replacement candidate was: The main on Maple St is leaky lets replace that one. These methods are outdated and insufficient to meet system performance needs, given budget constraints and labor resources, now and in the future.
A new approach utilizing GIS analysis and lifecycle cost calculations in Excel was piloted in 2014. Spatial analysis was performed to aggregate disparate pipe segments into analytical units, which were then analyzed for historical leaks and proximity to risk factors such as sensitive watersheds and freeways, and approximately 15 other factors. The result of this spatial analysis was a short list of replacement candidates.
The short list was then processed in Excel to apply a lifecycle cost model considering replacement cost and operations and maintenance costs to further narrow the list of replacement candidates. The results of the Excel analysis were applied to the GIS data and the final pipe replacement projects were selected.
Map books were created showcasing each proposed project and an ArcGIS Online web map was created to provide system-wide context to engineers.
The final outcome of the analysis being a strong list of data-driven pipe replacement candidates, supported by objective analysis, submitted to the California Public Utilities Commission for the Company’s 2015 General Rate Case.
The spatial analysis processes will be of particular interest to a GIS-centric audience. The entire workflow was coded in Python and several unique data challenges had to be overcome to achieve the desired, accurate results.

Presenter: Nathaniel Mirin, GISP, GIS Analyst, California Water Service, San Jose, CA