City of Morgan Hill Sewer System Master Plan 2017

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 : x 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). x 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. x 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. x Maximum Month Dry Weather Flow (MMDWF). This maximum month flow occurs during the dry weather season.

August 2017

5-1

City of Morgan Hill Sewer System Master Plan