Infiltration

Both infiltration and inflow affect the operation of a sanitary sewer system and pumping, treatment, and overflow regulators facilities.  The infiltration load in the pipe is listed as an external load into the upstream manhole.  The load is a point load and is not distributed over the length of the link.  Infiltration occurs in gravity pipes while inflow occurs at manholes and wet wells. Infiltration loads refer to the volume of groundwater entering the sewer system from the soil through defective joints, broken or cracked pipes, improper connections, or manhole walls. It can be derived by subtracting base flow from total metered flow during dry weather or by compiling flow isolation measurements. Infiltration can be defined as proportional to the pipe length; proportional to the pipe length and to the pipe diameter; proportional to the pipe surface area (pipe length multiplied by its perimeter); proportional to the number of defects in the pipe (count-based); or as a pattern load/hydrograph (flow vs. time) as shown below:

Creating Infiltration

A gravity main needs to be first selected by the user.  The user can then click on the Infiltration icon located on the Attribute Browser to launch the following dialog box. The different methods to assign infiltration is explained as below:

• Pipe Length: The infiltration is defined as an infiltration rate per unit of pipe length. The amount of infiltration is proportional to the pipe length. If the pipe is 200 feet long and I enter a 1 then the infiltration flow is 200 MGD which mean the infiltration rate unit is mgd/foot/day

• Pipe Diameter-Length: The infiltration is defined by an infiltration rate per unit of pipe diameter times pipe length.  The amount of infiltration is proportional to the pipe length and to the pipe diameter.

• Pipe Surface Area: The infiltration is specified by an infiltration rate per unit of pipe surface area. The pipe surface area is calculated as its length multiplied by its full perimeter. The amount of infiltration is proportional to the pipe length and to the pipe diameter.

• Count-Based: The infiltration is specified by an infiltration unit count value (for example, this may be the number of defects in the pipe) and the infiltration rate per unit of count.

• Pattern-Based: The infiltration is specified by an infiltration rate and a pattern. A pattern consists of a collection of multipliers (multiplication factors) that are applied to a base infiltration rate to allow it to vary over time during an EPS/Dynamic simulations.

Infiltration Load

The pipe infiltration enters the network as a load at the upstream node of the link.  The infiltration load in the pipe is listed as an external load into the upstream manhole.  The load is a point load and is not distributed over the length of the link.