---
title: "Time Area Diagram"
canonical: "https://help.innovyze.com/space/infodrainage2020v2/16416985/Time%20Area%20Diagram"
format: markdown
---
> Macro (anchor)

 Sub-catchments may be entered in the form of a Time/Area spreadsheet. The hydrograph is calculated by combining the rainfall profile with the time area input. The Time / Area diagram accounts for the effect the time of flow into the stormwater control has on the inflow hydrograph. 

> ⚠️ This method may not be available for your region. For more information, refer to the [Regionalisation](https://help-innovyze.atlassian.net/wiki/spaces/infodrainage2020v2/pages/16417436) topic.

**Spreadsheet**

Enter the area that enters the storage structure for each timestep.

- **Time - **The time area diagram may be specified at a user defined set of time steps.
- **Area -  **The area that enters for the given time period, that is from the time entered to the time below.

**Import and Export**

These allow the current Time Area Diagram details to be imported from and export to file so that the details can be reused.

**Clear**

The clear button clears the contents of the table.

**Percent Impervious** 

Pervious portion of the [Inflows](https://help-innovyze.atlassian.net/wiki/spaces/infodrainage2020v2/pages/16417285) area.


### Analysis

The rainfall profile and the time area diagram are combined with the volumetric runoff coefficient in the following way:

**Q**<sub>**1**</sub>** = (I**<sub>**1**</sub>** x A**<sub>**1**</sub>**) x 2.78 x C**<sub>**v**</sub>

**Q**<sub>**2**</sub>** = (I**<sub>**1**</sub>** x A**<sub>**2**</sub>** + I**<sub>**2**</sub>** x A**<sub>**1**</sub>**) x 2.78 x Cv**

**Q**<sub>**3**</sub>** = (I**<sub>**1**</sub>** x A**<sub>**3**</sub>** + I**<sub>**2**</sub>** x A**<sub>**2**</sub>** + I3 x A**<sub>**1**</sub>**) x 2.78 x Cv**

and so on.