City of Morgan Hill Sewer System Master Plan 2017

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

Term

Definition

 Pipe Length: The RDI flow rate is divided by the length of pipe (IDM) in the upstream basin. The result is expressed in gallons per day (gpd) per IDM (gpd/IDM).  Basin Area: The RDI flow rate is divided by the geographic area of the upstream basin. The result is expressed in gpd per acre.  ADWF: The RDI flow rate is divided by the average dry weather flow (ADWF). This is a ratio and is expressed without units. The estimated totalized I/I in gallons attributable to a particular storm event is used to identify basins with high total I/I. Because this is a totalized value rather than a rate and can be attributable solely to an individual storm event, the volume of the storm event is also taken into consideration. This allows for a comparison not only between basins but also between storm events:  Pipe Length: Total gallons of I/I is divided by the length of pipe (IDM) in the upstream basin and the rainfall total (inches) of the storm event. The result is expressed in gallons per IDM per inch of rain.  Basin Area (R-Value): Total gallons of I/I is divided by total gallons of rainfall water that fell within the acreage of the basin area. This is a ratio and expressed as a percentage. R-value is described as “the percentage of rainfall that enters the collection system.” Systems with R-values less than 5% 1 are often considered to be performing well.  ADWF: Total gallons of I/I is divided by the ADWF and the rainfall total of the storm event. The result is expressed in million gallons per mgd of ADWF per inch of rain. Ratio of peak measured flow to average dry weather flow. This ratio expresses the degree of fluctuation in flow rate over the monitoring period and is used in capacity analysis. When the flow level is higher than the crown of the pipe, then the pipeline is said to be in a surcharged condition. The pipeline is surcharged when the d / D ratio is greater than 1.0. A set of algorithms developed to approximate the actual I/I hydrograph. The synthetic hydrograph is developed strictly using rainfall data and response parameters representing response time, recession coefficient and soil saturation. The ratio of weekend ADWFs to weekday ADWFs. In residential areas, this ratio is typically slightly higher than 1.0. In business districts, depending on type of service, this ratio can be significantly less than 1.0.

Normalization, total I/I

Peaking factor

Surcharge

Synthetic hydrograph

Weekend/weekday ratio

1 Keefe, P.N. “Test Basins for I/I Reduction and SSO Elimination.” 1998 WEF Wet Weather Specialty Conference, Cleveland.

12-0248 AEG CofMorganHill FM Rpt.docx

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