City of Morgan Hill Sewer System Master Plan 2017

City of Morgan Hill Sanitary Sewer Flow Monitoring and Inflow/Infiltration Study

Flow Monitoring: Peak Measured Flows and Pipeline Capacity Analysis Peak measured flows and the corresponding flow levels (depths) are important to understand the capacity limitations of a collection system. The peak flows and flow levels reported are from the peak measurements as taken across the entirety of the flow monitoring period. Peak flows and levels may not correspond to a rainfall event, but instead may be caused due to blockages, grease or roots that cause a backflow condition.  Peaking Factor: Peaking factor is defined as the peak measured flow divided by the average dry weather flow (ADWF). A peaking factor threshold value of 3.0 is commonly used for sanitary sewer design.  d / D Ratio: The d / D ratio is the peak measured depth of flow ( d ) divided by the pipe diameter ( D ). A d / D ratio of 0.75 is a common maximum threshold value used for pipe design. The d / D ratio for each site was computed based on the maximum depth of flow from the flow monitoring study. Table 9 summarizes the peak recorded flows, levels, d / D ratios, and peaking factors per site during the flow monitoring period. Capacity analysis data is presented on a site-by-site basis and represents the hydraulic conditions only at the site locations; hydraulic conditions in other areas of the collection system will differ. Two key capacity analysis terms are defined as follows:

Table 9. Capacity Analysis Summary

Peak Measured Flow (mgd)

Level Surcharged above Crown (ft)

Peak Level (in)

Peak d / D Ratio

Metering Site

ADWF (mgd)

Peaking Factor

Diameter (in)

Site 1 Site 2 Site 3 Site 4 Site 5 Site 6 Site 7 Site 8 Site 9

0.19 0.36 0.32 0.21 1.15 0.35 0.24 0.16 0.13 0.12

0.56 0.88 0.93 0.53 2.29 0.91 0.77 0.43 0.41 0.31

2.93 2.45 2.95 2.49 1.98 2.60 3.17 2.73 3.03 2.45

18

3.73 7.94

0.21 0.40 0.88 0.50 0.66 0.71 0.32 0.39 0.42 0.39

- - - - - - - - - -

19.75

15 12 24

13.13

6.04

15.95 12.52

17.75

21

6.82 6.76 6.36 4.57

17.5

15

Site 10

11.75

The following capacity analysis results are noted:  Peaking Factor: Sites 7 and 9 had peaking factors that slightly exceeded typical design threshold limits for the ratio of peak flow to average dry weather flow.  d / D Ratio: Only Site 3 had a d / D ratio that exceeded the common design threshold for d / D ratio. None of the flow monitoring sites reached surcharge conditions.

12-0248 AEG CofMorganHill FM Rpt.docx

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