City of Morgan Hill Sewer System Master Plan 2017

August 2017

5-1

City of Morgan Hill

Sewer System Master Plan

2017

City of Morgan Hill

5.0

CHAPTER 5 – SANITARY SEWER FLOWS

This chapter summarizes historical wastewater flows experienced at the South Country Regional

Wastewater Authority (SCRWA) WWTP and defines flow terminologies relevant to this evaluation.

This chapter discusses the wastewater flow distribution within the ten flow monitored basins, and

identifies the design flows used in the hydraulic modeling effort and capacity evaluation. The

design flows include the existing condition (existing customers) and the projected ultimate buildout

scenario.

5.1 FLOWS AT THE SCRWA WWTP

The wastewater flows collected and treated at the SCRWA WWTP vary monthly, daily, and

hourly. While the dry weather flows are influenced by customer uses, the wet weather flows are

influenced by the severity of storm events and the condition of the system.

Figure 5.1

shows the

monthly flows versus rainfall at the SCRWA WWTP for 2012. April and December were the

maximum months during 2012, with December also being higher than average due to the

considerable amount of rain received that month.

Flow data influent to the SCRWA WWTP was obtained from City operation staff. The flow data

covered a period from 2010 to 2015. From this data monthly, daily, peak daily flows, and peak

hourly flows (if available), were determined as summarized on

Table 5.1

The following definitions are intended to document relevant terminologies shown on

Table 5.1

Average Annual Flow (AAF).

The average annual flow is the total annual flow, or

average monthly flow, for a given year, expressed in daily or other time units. This flow

includes the combined average of the average dry weather flow (ADWF) and average wet

weather flow (AWWF).

Average Dry Weather Flow (ADWF).

The average dry weather flow occurs on a daily

basis during the dry weather season, with no evident reaction to rainfall. The ADWF also

includes the Base Wastewater Flow (BWF). The base wastewater flow is the average flow

that is generated by residential, commercial, and industrial users. The flow pattern from

these users varies depending on land use types.

Average Wet Weather Flow (AWWF).

This average wet weather flow occurs on a daily

basis during the wet weather season. In addition to the flow components in the ADWF, the

AWWF includes infiltration and inflow from storm rainfall events.

Maximum Month Dry Weather Flow (MMDWF).

This maximum month flow occurs during

the dry weather season.