---
title: "ADAS 345 Method"
canonical: "https://help.innovyze.com/space/infodrainage2020v2/16417517/ADAS%20345%20Method"
format: markdown
---
This method is based on ADAS 345 and originally intended for land drainage design. See ADAS reference book 345 (The design of field drainage pipe systems), ADAS.

> ⚠️ 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.

**The Peak Flood Flow Q0 for catchments under 30 ha**

The ADAS 345 document does not refer to any return period but yields a “Peak Flood Flow”. However, the ADAS 345 method is a simplified form of a more comprehensive ADAS method within report number 5, which is no longer in print. In Report Number 5 return periods were listed rather than the crop types shown in ADAS 345. Crop types were intended to imply a selected risk category and therefore give a different return period depending on the value of the crop. ADAS has confirmed that selecting “Grass” from the chart you are actually selecting the return period of 2 years. Therefore, growth curves can be applied to the two-year return period event. This in confirmed in the Environment Agency Flood Estimation Guidelines.

A two-year peak runoff may be converted to a Mean Annual Flood using Table 1 of FSR No 2, 1977. The Mean Annual Flood may then be converted to other return periods using the method described for IH 124.

Q<sub>0</sub> = ST.F.A

where

ST: Soil type factor

A: Area in hectares

F: Number derived from a lookup process outlined below:

Catchment Characteristic C

![image](media://26cf046a-2502-4a3b-ad72-8db8870f4125)

This is then used along with the selected crop type and average annual rainfall to determine the image from the graph below:

![image](media://1028bf36-79cd-4b5c-a9cd-70227611781c)

*The image above has been copied from 'The design of field drainage pipe systems' ADAS Reference Book 345.*


![image](media://a1a05305-d583-446f-9dd5-060c4fc96d04)

### Input Variables

**Area - **Catchment area.

**Length - **The maximum length of the catchment.

**Average Slope - **Average slope of catchment (height/length).

**Region - **Region number of the catchment based on FSR Figure I.2.4. This can be selected from the [Region Picker](https://help-innovyze.atlassian.net/wiki/spaces/infodrainage2020v2/pages/16417462).

**AAR - **The average rainfall.

**Soil Type - **Determine the soil type factor ST.

| **Permeability class** | **St** |
| --- | --- |
| Very slow | 1 |
| Slow to Moderate | 0.8 |
| Moderate | 0.5 |
| Very Rapid | 0.1 |

*There are more details available from the above reference.

**Paved Area - **Percentage paved but not exceeding 10%.

**Additional Options**

**Return Period - **Rainfall return period between 1 and 1000 years.

**Growth Curve - **Click the Growth Curve Details icon to open the [Growth Curve Editor](https://help-innovyze.atlassian.net/wiki/display/infodrainage2020v2/Growth+Curve+Editor).

### Output Variables

**Q0 - **Peak flood flow for 2 year return period.

**Total Q - **Peak flood flow including Paved area for 2 year return period.