QGIS ReFH2 to TUFLOW: Difference between revisions

 

Once the ‘Extract ReFH2 for TUFLOW (beta)’ tool has been selected, the ReFH2 to TUFLOW Dialog will appear.

 

The tool has a number of data input sections with the following headings associated with them:-

 

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.

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.

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Once the relevant location specific data has been input, then the user should pick the events that they are interested in. The user can select from a number of pre-determined return periods or specify their own. All return period boundary conditions will be output in a single csv file for use as a TUFLOW boundary condition.

The user can also specify a duration and a timestep. If no duration is specified, then the ReFH2 to TUFLOW tool will use the recommended duration determined by the ReFH2 software. The recommended duration is a function of the time to peak parameter (Tp) and the catchment average annual rainfall (SAAR). Once the duration is specified, an appropriate timestep is required that meets the requirement that the duration must be an odd multiple of the timestep. Table 1 below shows some common timesteps for some common durations. Where possible it is recommended a timestep between 10% and 20% of the duration should be used.

 

A GIS layer can be used to help specify an area when using point descriptors, or to specify a TUFLOW boundary to a particular region, point or line.

The user must specify the ‘Input Catchment Layer’ which is the GIS layer which the feature exists in, specify the ID field and the specific feature that the user is wanting to use to calculate the area or output to.

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Rainfall outputs can be applied as 2d_rf or 2d_sa_rf TUFLOW boundaries. The user selects whether they want to use the Gross Design Rainfall, or the Net Design Rainfall where the ReFH2 losses have been applied. The former would usually be applied to TUFLOW with some allowance for losses within TUFLOW, most commonly via 2D Infiltration. The latter will have ReFH2 losses already accounted for so additional losses would not usually be required.

As well as the option to specify Gross or Net rainfall, the user can also select the rainfall type. The options are rural and urban. The rural rainfall is the default option which would represent the situation were the subcatchment 100% rural whereas the urban rainfall allows the representation of the URBEXT2000 parameter. Further control over the impact of urbanisation can be carried out within the ReFH2 software. Note, that this option will only affect the Net Design Rainfall, it will have no impact on the Gross Design Rainfall.

 

The other option is to output an inflow hydrograph which can be output to TUFLOW 1D_bc, 2D_bc and 2d_sa boundaries. The user can again select the rural and urban boundary types. There is also the option to select the inflow, ReFH2 calculates the total runoff as the sum of direct runoff and base flow. The direct runoff is obtained via a soil moisture accounting approach to convert rainfall to direct runoff. The base flow model is based on the linear reservoir concept.

Splitting up the runoff hydrographs allows the user to apply the direct runoff as a 2d_sa boundary to apply the flow over a region and then add the base flow as a point or line source elsewhere within the model domain.

When the tool is run, three csv files are output. The first is the raw output from ReFH2. This contains the timeseries of all the result parameters for the selected return periods of interest. This will have the same name as the XML file which is loaded into the ReFH2 to TUFLOW tool unless the ReFH2 Output File option is used to specify a different name and location for the file (for example, a TUFLOW bc_dbase folder).

A second csv file is the processed data for the output of interest (ie, net rainfall or direct runoff) for the return periods of interest. This file is named as the above raw file but has the suffix ‘_TUFLOW’. As well as only included the selected output time-series, the time format is converted from HH:MM:SS to hours which is the format used by TUFLOW. The first value in the time series is also set to Zero to be valid within a TUFLOW simulation.

The third csv output is a bc_dbase.csv file which links the boundary name to the source csv. An optional Boundary name can be specified to specify the boundary ID which the hyetograph or hydrograph is applied to. When a GIS layer has been used as an input, the input feature will override this setting. This value, or the GIS layer feature, will provide the name for the boundary within the bc_dbase.csv file.

Column 1 references the ‘Time (hr)’ data in the processed time series csv file whereas column 2 will reflect the chosen output. Column 2 will contain the ~ARI~ wildcard, such that the column used will depend on the event simulated and specified in the batch file.

A fourth file is also generated which is the TUFLOW Event File (TEF). This defines the event names together with the ~ARI~ wild card value which would be used in the bc_dbase.csv file to link the correct event with the boundary conditions. The use of TUFLOW event is described in a later section.

The zero padding option in the ReFH2 to TUFLOW tool determines how many zeros are added to the event name. For instance:-

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