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

TOC - vi

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.

Normalization,

total I/I

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%

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.

Peaking factor

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.

Surcharge

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

ratio

is greater than 1.0.

Synthetic

hydrograph

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.

Weekend/weekday

ratio

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.

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