City of Morgan Hill Sewer System Master Plan 2017

City of Morgan Hill

Sanitary Sewer Flow Monitoring and Inflow/Infiltration Study

12-0248 AEG CofMorganHill FM Rpt.docx

Page 10 of 46

INTRODUCTION

Scope and Purpose

V&A was retained by Akel Engineering Group to perform sanitary sewer flow monitoring and inflow

and infiltration (I/I) analysis within the City of Morgan Hill, California (City). Flow monitoring was

performed over a 20-day period at ten open-channel flow monitoring sites within the City. The flow

monitoring period began on February 25, 2014, and ended on March 17, 2014. The purpose of this

study was to measure sanitary sewer flows at the flow monitoring sites and estimate available sewer

capacity and infiltration and inflow (I/I) occurring in the basins upstream from the flow monitoring

sites.

Flow Monitoring Sites

Flow monitoring sites are the manholes where the flow monitors were placed. Flow monitoring site

data may include the flows of one or many drainage basins. To isolate a flow monitoring basin, an

addition or subtraction of flows may be require

d 2 .

Capacity and flow rate information is presented on

a site-by-site basis. The locations and other information for the flow monitoring sites are shown in

Table 3

and illustrated i

n Figure 7.

Flow Monitoring Basins

Flow monitoring basins are localized areas of a sanitary sewer collection system upstream of a given

location (often a flow meter), including all pipelines, inlets, and appurtenances. The basin refers to the

ground surface area near and enclosed by the pipelines

3 .

A basin may refer to the entire collection

system upstream from a flow meter or may exclude separately monitored basins upstream. I/I

analysis in this report will be conducted on a basin-by-basin basis. The isolated basins of this project

are illustrated in

Figure 8.

Due to potential cross-connections between basins, the I/I results for

Basins 7 and 8 are shown together, labelled “Basin 7/8”. The individual results for Basin 7 and 8 will

be presented in future analyses tables as sub-headers and for informational purposes only.

For this study subtraction of flows was required to isolate the drainage areas of some flow monitoring

basins. Shown in

Table 4 a re the equations (in which Q refers to

flow rate) used to calculate the flow

rate results for each basin from the flow rates recorded at the monitoring sites. Detailed descriptions

of the individual flow monitoring sites, including photographs, are included in

Appendix A

Harding Flow Meter

V&A had access to flow monitoring data from the Harding Avenue Flow Meter. This meter measures

the total flow from the City of Morgan Hill through a single 21-inch transmission sewer line sewer prior

to entering into the City of Gilroy collection system. Flows from this meter during the flow monitoring

period are also presented in this report and used to establish system totals.

There is error inherent in flow monitoring. Adding and subtracting flows increases error on an additive basis. For example, if

Site A has an error of ±10% and Site B has an error of ±10%, then the resulting flow when subtracting Site A from Site B would

have an error of up to ±20%.

The basin areas (in acres) were provided by Akel Engineering Group.