Simple tool to provide green runoff rates

Greenfield runoff rate estimation

The Greenfield runoff rate estimation tool provides users with the ability to estimate runoff rates based on basic site characteristics information.


The Greenfield runoff rate estimation tool has been developed to facilitate easy calculation of greenfield runoff rates for new developments to assist developers, drainage engineers and those involved in assessing planning applications. The methodology is a simple map-based tool which calculates flow rates using currently approved methods as detailed in the document Preliminary rainfall runoff management for developments (SC030219 rev. E 2013).

When to use this tool?

Greenfield runoff rates are usually used as a basis for setting the limiting discharges for surface water runoff for a development site when seeking planning approval. This tool provides greenfield runoff rates based on using the FEH statistical method, or IH124. Both of these techniques are usually approved methods with LLFAs and Planning authorities.

How to use the tool?

The Greenfield runoff rate estimation is an online tool, which is free to use for all registered users. The tool provides users with an interactive map of the United Kingdom. The user simply needs to enter a postcode or click on the map to allow appropriate location-specific data such as soil category and hydrological characteristics to be used by the tool. The user then needs to enter site area and some key characteristics (these will depend on the estimation method selected). All values can be edited by the user. 

Users can choose which estimation method to use:

What values will the tool give?

The Greenfield runoff rate estimation tool gives estimated greenfield runoff rates for a site for the 1:1 year, 1:30 year and 1:100 year return periods. It also provides an estimation of Qbar which is the mean annual maximum flow rate.

The Greenfield runoff rate estimation tool calculates runoff rates for a site based on the correlation formulas used by each method. Parameters are either derived from information embedded in the map, or from information provided by the user. 





HR Wallingford provides training in the use of UK SuDS tools, plus planning and design of SuDS to meet current standards and best practice. 

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