Water Distribution System Model and Master Plan
City of Grants Pass, Oregon

West Yost developed a water distribution system master plan for the City, a fast-growing community in Southern Oregon with a current population of 21,000. The Grants Pass water distribution system consists of an 18 mgd water treatment plant, nine booster pumping stations, and eight reservoirs, and serves customers in seven separate pressure zones. West Yost refined and expanded an existing hydraulic model of the water distribution system by working closely with the City’s GIS staff and developing routines to export the data, which were required for the hydraulic model.

West Yost was also able to assist the City in creating a database file that assigned the metered information from the City’s Customer Information System (CIS) to a node in the model. We then used this database to link to the model and allocate demands based on real metered data. For allocation of future demands we were able to develop a database that linked the City’s Urban Growth Boundary (UGB) buildout land use polygons to future nodes in the model. We again used the database to link to the model and allocate future demands to their respective nodes. The updated model was calibrated in accordance with field measurements from a set of hydrant flow tests and further confirmed through an extended period simulation of system operation. The model was also used to investigate alternative operational strategies for improving reservoir fill and drain rates in problematic areas of the system.

Based on a comprehensive set of service standards that were also developed as part of the master plan, West Yost reviewed operational data and conducted additional modeling to assess existing system performance. The plan identifies deficiencies and recommends corrective actions for pump station capacities, reservoir storage capacities, service pressures, and fire flow availability. System expansion projects that will be required to expand the service area and satisfy future demand conditions were also identified.