InfoDrainage can automatically calculate the total greenfield site discharge volume, using either FSR, FEH and ReFH2 calculation method.

This method may not be available for your region. For more information, refer to the Regionalisation topic.

Input for FSR based Discharge Volume

Calculation Method - Select FSR from the drop-down list. Other methods are available (FEH and ReFH2).

Region - Select between England and Wales or Scotland and Ireland from the drop-down list.

M5-60 (mm) - The rainfall depth (specified in mm) for a 60 minute storm with a five year return period.

Ratio R - The ratio of the rainfall depths from the 60 minute storm to the two day storm (both have return period of five years), i.e. M5-60/M5-2day.

Area (ha) - Undeveloped gross area. It is input as hectares in the program for consistency with other data input but the equations express it in square kilometres.

SAAR (mm) - Average annual rainfall (1941-1970) from FSR figure II.3.1 or equivalent. Click the Map button and click the desired area on the map to populate this field.

CWI - Catchment wetness index (CWI) is a function of the average annual rainfall, which can be derived from SAAR.

Urban - Proportion of area urbanised expressed as a decimal 0.000.

Areal Reduction Factor - Reduces the rainfall as it calculated as point rainfall based on time and area. 

SPR - This value can be calculated from Figure I.4.18 (first revision) (Institute of Hydrology, 1978), which shows the various soil types. The soil classifications are also available from the Wallingford Procedure, Volume 3, Maps, “Winter rain acceptance potential”. The equation was first published in FSSR 16, 1985.

where S1 - S2 are the proportions of the catchment covered by soil classes 1-5 respectively.

Where measured flow records are available the SPR may be calculated from the Base Flow Index (BFI) from research published in FSSR 16 and it is not covered here – see also FEH, Volume 4, Chapter 1.

Storm Duration - Storms duration between 15 and 21600 minutes.

There is no option to add Climate Change or select between Winter and Summer storm profiles as these settings have no impact on the pre-development values.

Return Period - Storm return period between 1 and 1000 years.

Input for FEH based Discharge Volume

Most of the FEH input values are imported from the FEH CD-ROM software package or web service via the on-screen Import button. A .csv file containing only FEH 1999 data cannot be loaded as these do not contain all the required information. However, on small catchments, it is particularly important to check the values against a site survey to verify the data where possible.

Calculation Method - Select FEH from the drop-down list. Other methods are available (FSR and ReFH2).

Site Location- This descriptive field allows the site location to be recorded. If the FEH details are imported from a .csv file, then this field is filled in with the grid reference details.

Version - Select either 1999 or 2013. With the 1999 option the six site constants can be typed in. The 2013 data can only be loaded in from a valid csv/.xml file and displays "Point" or "Catchment" based on the data in the file. If a file loaded does not contain 2013 data, then the option is disabled.

Area (ha) - This is the undeveloped gross area. It is input as hectares in the program for consistency with other data input but the equations express it in square kilometres.

SAAR (mm) - The standard average annual rainfall (1961-1990).

CWI - Catchment wetness index (CWI) is a function of the average annual rainfall, which can be derived from SAAR.

URBEXT - The extent of urban and suburban cover. Either select the 1990 or 2000 values, if available, or simply enter a user-defined value. Please note that the year 2000 values are only available if using the FEH CD-ROM Version 2. If values for 1990 or 2000 are zero, please check the values as they may not be available from the FEH data.

Areal Reduction Factor - Reduces the rainfall as it calculated as point rainfall based on time and area. The value may be obtained from FEH Figure 4.3.4.

SPRHOST - SPRHOST is calculated by the FEH CD program and written to the .CSV file. Where measured flow records are available the SPR may be calculated from the Base Flow Index (BFI) from research published in FSSR 16 and it is not covered here – see also FEH, Volume 4, Chapter 1.

Storm Duration - Storms duration between 15 and 21600 minutes.

There is no option to add Climate Change or select between Winter and Summer storm profiles as these settings have no impact on the pre-development values.

Return Period - Storm return period between 1 and 1000 years.


Input for ReFH2 based Discharge Volume

Most of the ReFH2 values are imported from the FEH CD-ROM software package or web service via the on-screen Import button. A .csv files containing only FEH 1999 data cannot be loaded as these do not contain all the required information. However, on small catchments, it is particularly important to check them against a site survey to verify the data where possible.

Calculation Method - Select ReFH2 from the drop-down list. Other methods are available (FSR and FEH).

Site Location - This descriptive field allows the site location to be recorded. If the FEH details are imported from a .csv file, then this field is filled in with the grid reference details.

Version - Select either 1999 or 2013. With the 1999 option, the six site constants can be typed in. The 2013 data can only be loaded in from a valid csv/.xml file and displays "Point" or "Catchment" based on the data in the file. If a file loaded does not contain 2013 data, then the option is disabled.

Season- The season that the rainfall will use to generate the associated profile (this follows the setting on the global variables unless defined peak flows are used). This affects how the loss model is calculated. The recommended seasons are:

  • Winter - November to April
  • Summer - May to October

Country- The country that the gauge data set is taken from to calculate the peak flows. Select between:

  • England, Wales, and Northern Ireland
  • Scotland

Area (ha) - This is the undeveloped gross area.

SAAR - The standard average annual rainfall (1961-1990).

FARL - Index of flood attenuation due to reservoirs and lakes.

URBEXT - The extent of urban and suburban cover. Either select the 1990 or 2000 values if available or simply enter a user-defined value. Please note that the year 2000 values are only available if using the FEH CD-ROM Version 2. If values for 1990 or 2000 are zero, please check the values as they may not be available from the FEH data.

Areal Reduction Factor - Reduces the rainfall as it calculated as point rainfall based on time and area. The value may be obtained from FEH Figure 4.3.4.

SPRHOST - Standard percentage runoff derived from HOST soils data. Where measured flow records are available, the SPR may be calculated from the Base Flow Index (BFI) from research published in FSSR 16 and it is not covered here – see also FEH, Volume 4, Chapter 1.

BFIHOST - Base flow index derived from Hydrology of Soil Types (HOST) soils data.

DPLBAR - The mean drainage path length. This is the mean of the distances between each node (on a 50 m grid) and the catchment outlet. This is not available for FEH Point descriptor files.

DPSBAR - The mean catchment slope. The mean of all inter-nodal slopes. This is not available for FEH Point descriptor files.

PROPWET - The proportion of time when the soil moisture deficit <= 6 mm during 1961-1990 as defined by Met Office Rainfall and Evaporation Calculation System (MORECS).

Max Allowable Volume Calculation Method - The runoff volume from the site is calculated in the following manner.

  • Calculate the total rainfall for the storm details specified (6 hour, 100 year return period by default).
  • Calculate the PR as defined below (this is the same as the unit hydrograph method. Note that the rainfall used in the PR equation is based on the same details as the total rainfall above).

Storm Duration - Storms duration between 15 and 21600 minutes.

There is no option to add Climate Change or select between Winter and Summer storm profiles as these settings have no impact on the pre-development values.

Return Period - Storm return period between 1 and 1000 years.

Output Variables

PR (%)Total percentage run off of the catchment is defined as follows:

FSR

FEH


Discharge Volume (Runoff) (m³)

Runoff = PR * Areal Reduction Factor * Total Rainfall * Area