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August 2017
6-2
City of Morgan Hill
Sewer System Master Plan
6.2.1
Skeletonization
Skeletonizing the model refers to the process where pipes not essential to the hydraulic analysis
of the system are stripped from the model. Skeletonizing the model is useful in creating a system
that accurately reflects the hydraulics of the pipes within the system. In addition, skeletonizing the
model will reduce complexities of large models, which will also reduce the time of analysis while
maintaining accuracy, but will also comply with the limitations imposed by the computer program.
The hydraulic model for the City of Morgan Hill was skeletonized to include the major trunk
system. By comparison, the total system includes approximately 160 miles of pipe, whereas the
hydraulic model includes approximately 44 miles of pipelines. The modeled pipes included pipes
10-inches in diameter and larger, in addition to some critical smaller gravity sewer pipes.
Table 6.1
documents the inventory of pipelines included in the hydraulic model by diameter and is
approximately 28 percent of the overall system. The modeled sewer system is shown on
Figure
6.1
.
6.2.2
Digitizing and Quality Control
City staff completed a GIS mapping project for the sanitary sewer system prior to initiating this
master plan project. City staff also conducted manhole field surveys that recorded the rim
elevations, pipe invert elevations, as well as the physical manhole location. This GIS data was
the basis for developing the hydraulic model used in the capacity evaluation of the sewer system.
During the development of the new hydraulic model, the project team consisting of City staff and
Akel Engineering staff implemented a thorough quality control program to resolve discrepancies.
The quality control program included the following:
x
The 2002 Sewer System Master Plan hydraulic model and the subsequent revisions
x
As-Built or construction drawings
x
GIS database provided by City Staff
x
Available closed circuit television (CCTV)
6.2.3
Load Allocation
Load allocation consists of assigning sewer flow to the appropriate manholes (nodes) in the
model. The goal is to distribute the loads throughout the model to best represent actual system
response.
Allocating loads to manholes within the hydraulic model required multiple steps, incorporating the
efficiency and capabilities of GIS and the hydraulic modeling software.