---
title: "Rainfall Derived Inflow and Infiltration - RDII"
canonical: "https://help.innovyze.com/space/xps/19663367/Rainfall%20Derived%20Inflow%20and%20Infiltration%20-%20RDII"
format: markdown
---
This dialog allows for editing of a Global Database record for the Unit Hydrograph (UH) method for modeling Rainfall Derived Inflow and Infiltration [(RDII)](https://help-innovyze.atlassian.net/wiki/spaces/xps/pages/19662172/Runoff+Sub-Catchment+Data#RunoffSub-CatchmentData-RDII) in combined sewers. This method is also referred to as the RTK method. It is selected in the [Sub-Catchment](https://help-innovyze.atlassian.net/wiki/spaces/xps/pages/19662172) dialog in Runoff Mode.

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![image](media://3004865f-5b58-4c3a-acd8-61b6c197f02b)


The options for months are:

- A default UH for All Months
- Separate UH for any month

If a month is not checked, the All Months UH Method will be used during the simulation in that month.

For each of the three component UHs enter:

- fraction of total rainfall entering the system (R)
- time from the beginning of the rainfall to the hydrograph peak, hr (T)
- ratio of time of recession to time to peak (K)
- initial subcatchment abstractions, in (mm)
- initial subcatchment storage, in (mm)
- recovery rate of storage (initial abstractions) during dry time steps, in/day (mm/day)

In the drop list next to rainfall select a rainfall record from the [Global Database](https://help-innovyze.atlassian.net/wiki/spaces/xps/pages/19663269).

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