QGIS ReFH2 to TUFLOW: Difference between revisions

Originally published in 1999, and subject to continuous development, the Flood Estimation Handbook (FEH) comprises the standard methods for estimating flood frequency in the UK. The rainfall-runoff model is one of two core handbook methods. In 2015, the Centre of Ecology and Hydrology (CEH) and Wallingford Hydro Solutions (http://www.hydrosolutions.co.uk) released a new version of the Revitalised Flood Hydrograph rainfall-runoff model (ReFH2) which allows users to generate design flows and hydrographs from given rainfall events for both catchment and development sites. ReFH2 is a rainfall-runoff model that takes inputs from the FEH2013FEH web service (https://fehweb.ceh.ac.uk) and generates design rainfall events and provides a method for calculating design runoff from sites or contributing subcatchments. For a full description of the approaches, the reader is referred to their guidance which can be freely accessed at:- https://www.hydrosolutions.co.uk/support/refh2_faq/refh2_literature/. The ReFH2 method is available within the ReFH2 software. Version 3 of the ReFH2 software was released in 2020 which introduced a new model referred to as '2.3' with some changes to the ReFH2 models as well as support for climate-change adjusted rainfall, new default seasonality based on urban extent and use of the BFIHOST19 descriptor.

=FEH 20132022 Rainfall=

FEH2013FEH2022 is the most up-to-date Depth Duration Frequency (DDF) model for generating design rainfall hyetographs. CEH recommend the use of FEH2013FEH2022, which supersedes the FEH1999FEH2013 DDF model and therefore the 1999 method . In order to generate the design rainfall, the user obtains FEH2013FEH2022 design rainfall depths from the FEH Web Service at https://fehweb.ceh.ac.uk for pre-defined return period/duration combinations. This requires a log on and user credits to purchase the data for the desired location. Data is available at a river catchment scale and as a point value. Both of these provide XML containing the rainfall depths. This is then imported into the ReFH2 software to generate hyetographs based on Flood Studies Report (FSR)/FEH approaches. The ReFH2 2.3 model supports use of both the 2013 and 2022 DDF models. Version 2.2 only supports the 2013 DDF model, an error message will be generated should the user try to use the 2022 DDF rainfall with the 2.2 ReFH2 model.

In order to use the tool, ReFH2 Version 2.27059.19021 or later, must be installed on the local machine which can be downloaded from the following link (https://www.hydrosolutions.co.uk/software/refh-2/refh2_download/). The ReFH2 software requires the relevant local licence. Network licencing may be available in the future.

The first section is where the XML files from the FEH2013 website are loaded into the tool. Both point descriptors and catchment descriptors are supported. The user can then specify whether the location is in England/Wales/Northern Ireland or in Scotland. The ReFH2 software includes Scotland specific algorithms to estimate model parameters from catchment descriptors. More information can be found in the ReFH2 Technical Report. If using the ReFH2.3 engine, the ReFH2.3+ descriptors which contain the BFIHOST19 value should be used. The ReFH2.3+ descriptors were added to the FEH Web Service in November 2019. If the BFIHOST19 parameter is omitted, the 'legacy' 2.2 ReFH2 model used will defaultbe to the 'legacy' 2.2 modelneeded.

When using Catchment Descriptors, the area value from the XML file will be used. For Point Descriptors, there is no area value within the XML file, so the user is prompted to provide an area in km². This can be user specified or can be taken from a GIS polygon specified in a later section. If specifying an urban area, also in km², this is used with Catchment Descriptors for Urban Outputs only. For point descriptors, the urban area is used for both Rural and Urban outputs. The urban area represents the mapped urbanised area within the catchment.

Once the relevant location specific data has been input, then the user should first pick the ReFH2 model that they would like to use. The 'legacy' 2.2 and newer 2.3 ReFH2 models are available. In order to use the ReFH2.3 model ReFH2.3+ descriptor files, containing a new BFIHOST19 parameter, are required. If ReFH2.2 parameters are used with the ReFH2.3 engine, an error message will be flagged. The latest Catchment Descriptors contain information for the 2022 DDF model as well as the 2013 DDF model. The 2022 DDF model is recommended by CEH. However, the 2022 DDF parameters cannot be used with the legacy 2.2 ReFH2 model. Both 2013 and 2022 DDF parameters can be used with the 2.3 ReFH2 model by specifying the desired option in the FEH Rainfall model section. The default options are to use the 2022 DDF model witht he 2.3 ReFH2 model.

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[[File:ReFH2 TEF.png|800px400px]]<br>

•* Choosing ‘no zero padding’ will set the event name to ‘1yr’.

•* Choosing ‘Auto Pad with zeros’ will pad the event names so that all events have the same number of figures. For example if the 100 year event is the highest event, the 1 year event will be named ‘001yr’, if the 1000year event is the largest, the 1 year event will be named ‘0001yr’.

•* Choosing a value will set the padding to that many zeros, for instance 3, will set the name to ‘0001yr’.

These files can then be merged together by the user where multiple boundary conditions are required in the model domain (future developments will allow this to be done automatically, as well as allow global rainfall to be applied) and moved to the relevant TUFLOW model folders to be used within simulations.