---
title: "Kirpich's Equation"
canonical: "https://help.innovyze.com/space/infodrainage2021v1/16547859/Kirpich's%20Equation"
format: markdown
---
### Parameters

**Flowpath Length - **The length of the Sheet flow path.

**Land Slope - **The slope of the hydraulic grade line.

### Calculation

![image](media://a0a05c80-c5de-45f4-9982-288cb10bdb73)


where:

L  = Length of overland flow (ft)

S = Average catchment slope (ft/ft)

<span style="color: #707070"> </span><span style="color: #707070">t</span><sub>c </sub><span style="color: #707070">= time of concentration (mins)</span>