Rainfall Dependent Infiltration/Inflow (RDII) plays a significant role in sanitary or combined sewer modeling, enabling you to simulate the effects of rainfall events. Innovyze's InfoSewer is a robust platform that allows the modeling of Infiltration/Inflow using RDII parameters or RTK Hydrographs. This short guide will walk you through the process of setting up RDII in InfoSewer Pro.

RDII Parameters (R, T, and K):

The RDII methodology relies on three key parameters, R (ratio of rainfall volume that enters the system as Infiltration/Inflow), T (the average time it takes for rainfall to enter the sewer system), and K (a ratio used to derive the Infiltration/Inflow hydrograph shape).

For RDII, the R parameter gets distributed across three individual R's (R1, R2, and R3) based on a fraction division and the Sewershed Area:

a. R1 = Percent R1 * R / 100

b. R2 = Percent R2 * R / 100

c. R3 = R – R1 – R2

These are expressed as a percentage of the total rainfall converted into Infiltration/Inflow.

RDII Modeling in InfoSewer:

To model RDII in InfoSewer, you need to start by defining the hyetograph or the rainfall data as a curve (Step 1). This is typically represented in Figure 1.

Upon setting the RDII parameters, you can observe the effects of varying the percentage division of R1, R2, or R3 at a specific node. This is typically shown in Figure 2.

The T parameter is expressed in hours, and the product of T*K provides the Time Base for the resulting Unit Hydrograph (UH).

Step 1. Define the hyetograph or rainfall as a curve

Figure 1 Rainfall for RTK in InfoSewer

Step 2. Define the UH as an overall R (percent of Rainfall that turns into Rainfall Dependent Infiltration Inflow)

a. R1 = Percent R1 * R / 100

b. R2 = Percent R2 * R / 100

c. R3 = R – R1 – R2

Figure 2 Define the RTK values. Note R3 is calculated

Figure 3 Define the Rainfall and UH for Each Node

Figure 4 Setup the Storm Tab in the Run Manager

Figure 5 Check to See if there is Storm Flow in the Mass Balance Table

Figure 6 Does the Storm Flow look Reasonable in the Graph

Figure 7 Resultant UH for Nodes with only R1, R2, or R3.