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August 2017
6-5
City of Morgan Hill
Sewer System Master Plan
Sewer loads were developed by combining the flow factors developed in Chapter 3 with the
assessor’s
parcel data for the City, including acreage and land use. The loads calculated were
allocated to the nearest manhole that serves the corresponding parcel.
6.3 MODEL CALIBRATION
Calibration is intended to instill a level of confidence in the flows that are simulated, and it
generally consists of comparing model predictions to the 2014 V&A flow monitoring program, and
making necessary adjustments.
6.3.1
Calibration Plan
Calibration can be performed for steady state conditions, which model the peak hour flows, or for
dynamic conditions (24 hours or more). Dynamic calibration consists of comparing the model
predictions to diurnal operational changes in the wastewater flows. The City’s hydraulic model
was calibrated for dynamic conditions.
In sanitary sewer systems, and when using dynamic hydraulic modeling to evaluate the impact of
wet weather flows, it is common practice to calibrate the model to the following three conditions:
x
Peak dry weather flows.
x
Peak wet weather flows from storm rainfall Event No. 1.
x
Peak wet weather flows from storm rainfall Event No. 2.
After the model is calibrated to these conditions, it is benchmarked and used for evaluating the
capacity adequacy of the sanitary sewer system, under dry and wet weather conditions.
6.3.2
2014 V&A Temporary Flow Monitoring Program
A temporary flow monitoring program was included in this project to validate the existing dry and
wet weather flows from each sewer basin. The program consisted of installing 10 flow meters, for
a period of 20 days, from February 25, 2014 to March 17, 2014. Villalobos and Associates (V&A)
was retained to install the flow meters, monitor rainfall, and perform an Infiltration and Inflow
analysis. The selected flow monitoring sites are listed on
Table 6.2
and shown on
Figure 6.2
.
Additionally,
Table 6.3
provided a calibration result summary for each of the respective sites
monitored.
The 2014 V&A Flow Monitoring Program captured two rainfall events and included a summary
report identifying areas of the City that were most affected by rain dependent infiltration and
inflows. The two rainfall events experienced during the flow monitoring period varied in duration
and intensity (
Table 3.4
), and provided an insight into the sewer system response to storm
conditions.