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City of Morgan Hill
Water System Master Plan
of large systems, which will reduce the time of analysis while maintaining accuracy, but will also
comply with limitations imposed by the computer program.
6.3.2
Pipes and Nodes
Computer modeling requires the compilation of large numerical databases that enable data input
into the model. Detailed physical aspects, such as pipe size, pipe elevation, and pipe lengths,
contribute to the accuracy of the model.
Pipes and nodes represent the physical aspect of the system within the model. A node is a
computer representation of a place where demand may be allocated into the hydraulic system,
while a pipe represents the distribution and transmission aspect of the water demand. In addition,
reservoir dimensions and capacities, and groundwater well capacity and design head, were also
included in the hydraulic model.
6.3.3
Digitizing and Quality Control
The City’s existing domestic water distribution system was digitized in GIS using several sources
of data and various levels of quality control. The data sources included the City’s existing system
as maintained by staff in GIS, as well as the previously developed hydraulic model and
subsequent updates.
After reviewing the available data sources, the hydraulic model was updated and verified by City
staff. Using the existing GIS version of the system, as well as the existing hydraulic model, this
project updated the domestic water system in GIS. Resolving discrepancies in data sources was
accomplished by graphically identifying identified discrepancies and submitting it to engineering
and public works staff for review and comments. City comments were incorporated in the verified
model.
6.3.4
Demand Allocation
Demand allocation consists of assigning water demand values to the appropriate nodes in the
model. The goal is to distribute the demands throughout the model to best represent actual
system response.
The existing demand distribution was obtained from the water billing records. Using GIS, each
customer account was geocoded and spatially joined within its existing pressure zone. The
accounts were then sorted by pressure zone and the total demand in each zone was calculated.
Domestic water demands from each anticipated future development, as presented in a previous
chapter, were also allocated to the model for the purpose of sizing the required future facilities.
The demands from the greater Urban Growth Boundary were allocated based on proposed land
use and the land use acreages. As many of the areas were very large in size, demands were
allocated evenly to the demand nodes within each area. Infill areas, redevelopment areas, and
vacant lands were also included in the future demand allocation.