Issue link: https://read.dmtmag.com/i/78956
It's the Data LVVWD has more than 6,350 miles of pipeline and 117,000 valves providing service to more than 375,350 accounts. The system adheres to a logical design that was optimized for supporting a wide range of business processes: engineering needs, operations, finance, risk management and customer service. When GIS staff investigated expanding the use of built-in VI functions, they discovered conflicts with the existing database design. The first issue was ensuring the physical and logical connectivity among networked features. Physical connectivity is the shared space (within tolerances) of pipelines, valves, meters, hydrants, reservoirs, wells, etc. Logical connectivity is an internal map, maintained by the GIS, that's used to "traverse" networked fea- tures. Internal processes ensure physical connectivity, but the logical connectivity needed to be rebuilt and maintained using the GIS software's toolset. Reviewing and rebuilding the logical network was a lengthy pro- cess that had to account for hundreds of thousands of connections. LVVWD's water data model also was problematic, as Figure 3. Valves that isolate a main break are quickly identified and highlighted on a map. it wasn't optimized for VI. The water data model con- tained a mixture of features that conflict with modeling water flow. For example, blow offs, air-release valves and sample ports can interrupt modeling water flow using GIS software, but in "real life," they have no impact on water flow. Redesigning the GIS database so it's optimized for VI would be a significant undertaking that would nega- tively impact ongoing GIS products and services. Automation was developed to build and maintain The Las Vegas Water District Manages Service Outages Before they Happen Figure 4. A VI module allows users to exclude a valve and re-run the analysis. 24 GEO W ORLD / AUGUST 2O12 a secondary database specifically tuned for VI. The Oracle Spatial Network Data Model was adopted for this approach, allowing control of which water- distribution-system elements would be used for modeling flow. The automation supported incremen- tal updates that facilitated correction of topological errors as the network underwent tuning. Registering these tables with the GIS allowed display and map- ping of the network and trace results. Custom VI Staff designed a custom solution to better manage VI issues and provide additional functionality not readily available in the commercial GIS. The system logic is based on a simple "A-Start" algorithm used in most network analysis. The code processes nodes (i.e., valves) in all directions from the incident location until all "first-return" valves are identified. It then identifies a valve as a shutdown by performing an is-reachable analysis to its potential water source in the direction away from the incident. Benefits of this approach include easy identification of network elements that caused a VI to "fail" or report unusual results. Such uncovered data anomalies, specific Infrastructure