2D Simulations - Rainfall / Infiltration Sub-tab

In addition to flow and stage boundaries, you can also add hydrological inputs to your 2D Solver model. Rainfall/infiltration data for a 2D Solver model can consist of one or more ‘Hydrology Sources’. These enable net rainfall to be applied over a user defined area (within your 2D Solver domain). Equally though a hydrological source could represent evapotranspirition or groundwater infiltration (in these cases your inputs will be negative, i.e. drawing water from your flood flows). Flood Modeller hydrology data files also allow for inbuilt SCS CN and Green-Ampt loss models.

This section details how to define the input data files for your hydrological boundaries. However, it should be noted that hydrology data is optional for a 2D Solver model and does not have to be specified (provided you include some other form of input boundary, e.g. flow time series or linked Flood Modeller 1D model).

Input data formats

The 2D Solver offers a choice of data sources for your hydrological boundary data, which are described as follows:

• You can manually type in time series directly into the 2D Solver New Hydrology Source Form or cut and paste data from a spreadsheet, e.g. MS Excel. In the latter case data must be prepared with dates (or dates and times) and rainfall values in two adjacent columns.
• You can associate a time series data file to your hydrological boundary. This can either be a comma separated text file format (.csv) or a Flood Modeller event file format (.ied text file). Data in a csv file must be prepared with times and rainfall values in two adjacent columns. The format of the csv file is as follows:
  Row 1: header row
  Column 1: time values (real number – date values not permitted – in the units specified in the control file)
  Columns 2-n: rainfall values (in the units specified in the control file)
  If there is more than one column of rainfall data in a file, the header cell (Row 1) for that column must contain the Node name specified in the Node attribute in the corresponding rainfall shapefile (see below).
  You may specify more than one csv file per simulation.
• You can utilise the Flood Modeller 1D hydrology tools to generate a boundary data file (.ied or .dat text files) and link this to your 2D Solver boundary. The Flood Modeller's 1D Build Tab provides a wide variety of tools and options to enable you to build hydrology inputs. These data can then be saved as a separate IED or DAT file, which can then be used as a boundary data input, shared between different 1D or 2D models.

An example of a hydrological time series and associated polygon shapefile defined within the 2D New Hydrology Source Form is shown below:

Hydrology data are added to a 2D Solver model by associating it with one or more polygon shape files that represent the areas over which the data will be applied. You can specify multiple hydrology input areas, i.e. separate polygon shapefiles. Each one of the specified files must then be associated to a separate time series dataset.

These datasets can be produced using any compatible GIS system. For hydrological boundaries defined with time series data no particular attribute fields are required as the 2D Solver uses these shapes only to ascertain which underlying grid cells will receive a hydrological input. The 2D Solver will then apply the same specified input data to all affected grid cells (i.e. there is no dividing of inputs between cells; the full input value is applied to all cells).However, for hydrological boundary inputs defined by a csv file with multiple time series or linked to 1D Solver hydrology units, each polygon within a shape file must contain an attribute field entitled "node". This is used to reference the node names, which then correspond to the node names in the csv header or associated hydrology unit file (*.ied) respectively.

Flood Modeller can be used to construct these polygon shape files as shown in the example below:

2D Solver can accept different units for both the hydrological source data and time data that define your time series input. These units are detailed in the table below:

It is important to take care when preparing your hydrological inputs to ensure your data matches to the units you specify within the 2D Simulation window.

Setting up hydrology inputs

Hydrological inputs to your 2D Solver model are defined by a combination of a polygon shapefile (to define location) and either a time series dataset (pairs of date/time values and corresponding hydrological values) or a Flood Modeller 1D hydrological unit (which provides parameters for 2D Solver to calculate time series values). These data are entered into the 2D Simulation window via the Rainfall/Infiltration tab (a sub tab on the Domains tab). When first accessed this displays as follows:

To enter a new hydrological data input (known as a hydrological source) you should follow the steps detailed as per below:

1. Click the Add button located at the bottom left corner of the Rainfall/Infiltration tab. This opens a new hydrology source form:
   The window assumes rainfall data is your hydrological input, as this is the most common case. This does not mean you cannot input other data, e.g. evapotranspiration, via this method.
2. Enter the shapefile indicating the area affected in the ‘Hydrology Shapefile’ field. This can be entered directly (including the full path) in the box provided, or browsed to using the button to the right. Note that browsing to your file will result in the filename only (without the path) populating the ‘Hydrology shapefile’ field; if typing directly into the field, the path must be included.
3. Select the relevant option for your timeseries data via the radio buttons. These options are described below. Note that any of these options can be used for entering a hydrology source describing rainfall data only however some are not appropriate for inclusion of a loss model (see below for more details).
   • Use Hydrology Unit File - This option allows you to reference a Flood Modeller 1D hydrology unit, the hydrological parameters of which are then utilised by the 2D solver to calculate the timeseries data. Enter the 1D hydrology (DAT) file and path directly into the field provided or browse via the button to the left of the field. This type of boundary also does not require data units to be specified (these are set by the 1D hydrology unit). However, each polygon within a shape file associated to a hydrological boundary of this type must contain an attribute field entitled "node". This is used to reference Flood Modeller 1D node names, which then correspond to the node names in the associated hydrology unit (IED) file.
   • Use Timeseries File - This option allows you to select a timeseries text file (enter directly into the field provided or browse using the button to the right. A choice of days, hours, minutes and seconds is provided for your time units. Your hydrological data can be specified in units of intensity (mm/hr, in/hr or m/s) or rainfall depth (mm or inches). Take care to ensure your data is converted to a unit that is compatible with 2D Solver before entering it into this interface.
   • User Entered - This option enables a time series table to the right of the screen for the hydrological data. A choice of days, hours, minutes and seconds is provided for your time units. Your hydrological data can be specified in units of intensity (mm/hr, in/hr or m/s) or rainfall depth (mm or inches). Take care to ensure your data is converted to a unit that is compatible with 2D Solver before entering it into this interface. Data values can be added to the table using two methods:
     1. Data added individually by clicking on a cell and typing in a numeric value. After typing each value, press the Enter, Tab or directional arrow keys, or just click on another cell to accept your data entry. As each row is completed (i.e. time and vale entered) a new row is automatically added to the end of the table.
     2. A complete time series can be pasted into the table using functionality provided in a menu accessed by right-clicking on the time series table.
   The right click menu on the time series table provides the following functions:
   • Copy All – copy all rows from the table to the clipboard. Copied rows can then be pasted into another application, e.g. MS Excel spreadsheet to edit further.
   • Copy Selected - copy the highlighted rows in the time series table (to enable pasting elsewhere) Use the Shift and Ctrl keys in conjunction with the mouse to select multiple rows
   • Paste & Append – paste a time series into your table, e.g. a time series created and copied from an Excel spreadsheet. If your table already contains data, then such an operation will append the new data to the existing data.
   • Paste & Replace – paste a time series into your table, e.g. a time series created and copied from an Excel spreadsheet. If your table already contains data, then such an operation will replace the existing data with the new data.
   • Paste & Replace Selected - paste a time series into your table replacing the existing data in selected rows only. Use the Shift and Ctrl keys in conjunction with the mouse to select multiple rows. This operation will append the new data to existing data that has not been selected.
   • Remove Selected Row(s) - removes all selected rows from the table. Use the Shift and Ctrl keys in conjunction with the mouse to select multiple rows. You will be prompted to confirm before deletion.
   If you have a time series prepared in another application, e.g. MS Excel spreadsheet, then you can copy this series to your clipboard (copy two columns of data, first column must be time data). Use the 'Paste & append' command in the above menu to append the new data to existing data in the time series table, or the 'Paste & replace' (or 'Paste & replace selected') commands to replace all (or selected) existing data in the table.
4. A loss model can also be applied to your rainfall. Radial buttons allow choice between ‘Rainfall Only’, ‘Rainfall & Lumped Loss’ and ‘Rainfall & Spatial Loss’. These options are described in further detail below:
   • ‘Rainfall Only’
     This option assumes no loss model is to be applied to the rainfall entered. If you have entered your rainfall via a hydrology unit (DAT) file, any loss procedures setup in the hydrology unit will not be considered: the gross rainfall (rainfall before a loss model has been applied) will be taken from the hydrology unit. Selection of ‘Rainfall Only’ will require no more parameters to be defined for the hydrology source.
   • ‘Rainfall & Lumped Loss’
     This option is available only with the ‘Use Hydrology Unit File’ selected for your timeseries data. Within the 1D hydrology (DAT) file, a Green & Ampt or SCS Curve Number (CN) loss model can be setup. Note these are “lumped” models: a single set of parameters describing your loss model will be applied to the entire catchment area (area set within your hydrology shapefile). Ensure the parameters for the loss model you desire are set in your hydrology file and then select the ‘Rainfall & Lumped Loss’ radial option. The net rainfall (rainfall after the loss model has been applied) will then be taken from the hydrology unit.
   • ‘Rainfall & Spatial Loss’
     Selection of this enables the bottom half of the screen allowing for details of a spatially varying loss model. For any of the above methodologies for entering your timeseries data, a dynamic Green & Ampt loss model can be applied. You must provide a shapefile specifying the location in which to apply the Green & Ampt model. You must define the Green & Ampt parameters to be used for each location, either by providing a look-up file, or by manually entering the values in the table provided. Select the ‘Rainfall & Spatial Loss’ radial option and select the ‘Green-Ampt Infiltration’ method from the drop-down box. Enter the full path and filename of the shapefile in the field provided, and either the look-up file (full path and filename) or the Green & Ampt parameters within the table. Click the button to the right of the field to browse for the files through standard windows file explorer. The shapefile and look-up file need to contain various attributes and parameters – for more details see the ‘Spatially varying rainfall’ section.
     If you have selected to enter your timeseries data by setting up a 1D hydrology (Gerrbdy) unit, the SCS curve number (CN) method is also available as a method to determine the loss. Within the 1D hydrology input form, an initial abstraction and composite curve number can be given (through a number of methodologies, e.g. calculated from published data for different soil types/land uses) to calculate the net rainfall for a given area. The input line this produces in the data file can be repeated to allow different curve numbers and initial abstractions for multiple areas. To apply a spatial loss model of this form, enter the hydrology unit file containing all the parameters and select the ‘Rainfall & Spatial Loss’ radial option. Select the method of ‘SCS Curve Number’ and enter the shapefile specifying the areas for the loss models to be applied (note this could be the hydrology shapefile entered previously). The filename and path can be entered directly into the field given, or the browse button to the right can be used to find the file via standard Windows file explorer. Various attributes must be added to this shapefile to reference the hydrology unit – more details on this are given in the ‘Spatially varying rainfall’ section.
5. Click ‘OK’ to add the information on the source to your 2D model (or click Cancel to discard the new source and return to the main interface). You will be returned to the main 2D Simulation window and your new source information will appear as a new row in the Hydrological Sources table.

You can repeat the above sequence to add multiple hydrological sources to your 2D Solver model.

The details of a defined hydrological source can be edited within the Sources table. If you double-click on a particular cell in the table, the ‘New Hydrology Source’ window opens. You can also open this window by selecting a row in your Sources Table and clicking ‘Edit/View’ button.

To remove a hydrology source, click on the source you wish to remove and click the ‘Remove’ button (located in the lower left corner of the Rainfall/Infiltration Tab view). You will be asked to confirm the deletion. If you confirm the deletion the hydrology source and its associated time series data will be removed from the display (you need to save your model to commit this change to your model files).

Spatially varying rainfall

Rainfall models

A single rainfall model or multiple SCS rainfall profiles may be specified for a single node label in a Flood Modeller Generic Rainfall Runoff hydrological boundary (GERRBDY) unit. This then enables a 2D model to apply spatially-distributed rainfall, and also optionally to combine with spatially-distributed loss models, either the static SCS CN loss model or the dynamic Green-Ampt infiltration model.
To apply different SCS rainfall profiles to different regions of the 2D model:

• Ensure that the GERRBDY unit is set up in the hydrology data file, with the required number of rainfall models:
  
• Create or edit the rainfall shapefile so that if references:
  
  1. The node label of the corresponding hydrology unit from the data file in the ‘NODE’ attribute
  2. The rainfall sequence number (in the GERRBDY unit) in the ‘RFID’ attribute, for each shape (NB The RFID attribute field may be added using the Shapefile Editor Tool or an alternative GIS package).

In the example given above, note that the first set of rainfall details in the GERRBDY data file (relating to a depth of 21.24) is rainfall sequence number 1. This has been assigned to the third polygon in the shapefile attribute table (the 'RFID' attribute is given as 1 on the third row of the table). The second set of rainfall details (relating to a depth of 18.47) is rainfall sequence 2; this has been assigned to the second polygon. The final set of rainfall details (depth of 23.50) is sequence 3 and relates to the first polygon in the table. Note also the 'NODE' attribute column has been set to 'my_label' - the node label in the GERRBDY unit data file.

To input these data to a 2D simulation via the 'New Hydrology Source' window:

1. Enter your rainfall shapefile in the 'hydrology shapefile' field
2. Ensure the radio button is on 'Use Hydrology Unit File' and enter your hydrology unit file in the field provided
3. Choose 'Rainfall only' to only consider gross rainfall from the hydrology unit.

To apply single or multiple loss models to your simulation, see below.

Loss models

SCS CN loss method

The SCS Curve Number (CN) loss method (for further detail see US SCS Method ) derives a net rainfall based on a design or observed rainfall combined with a loss model based on soil type/land use. This method is extended to the 2D model by allowing multiple CN models representing differing overland regions to be specified in the same Flood Modeller hydrology data file. This can be combined with a single or multiple rainfall input to derive up to m×n different net rainfall inputs, where m and n are the number of rainfall and loss models respectively.

If applying a single set of curve number parameters (i.e. a single (potentially composite) curve number and single initial abstraction value) to the entire area:

• Ensure that the GERRBDY unit is set up in the hydrology data file, with the required number of rainfall models and single loss model:
  
• Create or edit the rainfall shapefile so that if references:
  1. The node label of the corresponding hydrology unit from the data file in the ‘NODE’ attribute
  2. The rainfall sequence number (in the GERRBDY unit) in the ‘RFID’ attribute, for each shape (NB The 'RFID' attribute field may be added using the Shapefile Editor Tool or an alternative GIS package)
  as in the example above.

To input these data to a 2D simulation via the 'New Hydrology Source' window:

1. Enter your rainfall shapefile in the 'hydrology shapefile' field
2. Ensure the radio button is on 'Use Hydrology Unit File' and enter your hydrology unit file in the field provided
3. Choose 'Rainfall and Lumped Loss' to consider net rainfall (amount of rain after the loss through infiltration has been applied) from the hydrology unit

The Generic Event Rainfall Boundary in the Flood Modeller Hydrology tool also allows the modeller to specify multiple loss models associated with the same node label.

To apply multiple loss models to the 2D model:

• Ensure that the GERRBDY unit is set up in the hydrology data file, with the required number of rainfall and loss models:
  
• Create or edit the rainfall shapefile so that if references:
  1. The node label of the corresponding hydrology unit from the data file in the ‘NODE’ attribute
  2. The rainfall sequence number (in the GERRBDY unit) in the ‘RFID’ attribute, for each shape (NB The 'RFID' attribute field may be added using the Shapefile Editor Tool or an alternative GIS package)
  as in the example above.
• Create or edit the loss shapefile so that if references:
  
  1. The node label of the corresponding hydrology unit in the ‘NODE’ attribute
  2. The loss model sequence number (in the GERRBDY unit) in the ‘CNID’ attribute, for each shape (NB The 'CNID' attribute field may be added using the Shapefile Editor Tool or an alternative GIS package).

These are the only two attributes required in the shapefile. Note, as with the multiple rainfall sequences, the first loss model defined in the GERRBDY unit data file, is loss sequence 1. This has been assigned to the third polygon in the shapefile attribute table (the 'CNID' attribute is given as 1 on the third row of the table).

To input these data to a 2D simulation via the 'New Hydrology Source' window:

1. Enter your rainfall shapefile in the 'hydrology shapefile' field
2. Ensure the radio button is on 'Use Hydrology Unit File' and enter your hydrology unit file in the field provided
3. Choose 'Rainfall and Spatial Loss' and ensure 'Method' is set to 'SCS Curve Number'
4. Enter your loss shapefile in the 'Loss Shapefile' field

Green-Ampt infiltration loss

Infiltration can be modelled dynamically using the Green-Ampt infiltration method (for further detail see Green-Ampt Loss model ). Since this is a dynamic method, being related to the water depth and cumulative infiltration, there is no requirement for it to be associated with any rainfall input (although concurrent rainfall input is not precluded).

Since the response will differ for different soil types, it is possible to apply several different parameter sets within the same model. Since each soil type is likely to be repeated for several areas (polygons) within a modelled region, and to make use of similar existing data (e.g. MasterMap), it is more efficient to store the parameter sets in a look-up file, and cross-reference the land/soil type ID in the shapefile and look-up file. Hint: If the loss shapefile is derived from MasterMap or similar data, the index number used should be the ground type ID specified in this.

Although the parameters are specified over an area, since each cell will potentially have a different depth/infiltration, the dynamic Green-Ampt computations are performed on a cell-by-call basis.

When using the Green-Ampt method dynamically, there is no referencing of a hydrology or 1D data file for the Green-Ampt method/parameters (as opposed to modelling a pre-processed net rainfall scenario, in which case this is possible).

Note: It is assumed there is no routing of the infiltrated water.

To apply the Green-Ampt method to the 2D model:

• Create/edit the Green-Ampt parameter look-up file as detailed above.
• Create or edit the loss shapefile so that if references the index number of the look-up table in the ‘GA_INDEX’ attribute for each shape (NB The GA_INDEX attribute field may be added using the Shapefile Editor Tool or an alternative GIS package).

NB This is the only attribute required in the shapefile.

To input these data to a 2D simulation via the 'New Hydrology Source' window:

1. Enter your rainfall shapefile in the 'hydrology shapefile' field. If no rainfall is being simulated, select the loss shape file here, enter a manual time series and set the values to zero.
2. Enter your timeseries rainfall data via hydrology unit file, timeseries file, or user entry as desired. As mentioned above, if no rainfall is being simulated, enter a manual time series and set the values to zero.
3. Choose 'Rainfall and Spatial Loss' and ensure 'Method' is set to 'G & A Infiltration'
4. Enter your loss shapefile in the 'Loss Shapefile' field
5. Enter your look-up file in the 'Look-up File' field, or enter the relevant parameters into the table at the bottom of the window.