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Generate rainfall data variable in time and space from multiple rain gauges

Product(s):	OpenFlows FLOOD
Version(s):	10.xx.xx.xx

Problem

When simulating a hydrologic simulation (rainfall/infiltration/runoff) over a large watershed using only data from a single rainfall gauge, i.e. assuming homogeneous rainfall rate distribution over the catchment area) can be unrealistic. For larger watersheds, spanning over hundreds or thousands of km2, considering spatial and time variable rainfall data is more valid approach.

This article describes the workflow to create a HDF5 file containing rainfall data variable in time and space from multiple rain gauges using OpenFlows FLOOD.

Solution

The first step to generate the spatially variable rainfall data is to create a rainfall time series file for each of the rain gauges. You can learn more on how to create this data in this wiki article: Imposing time variable rainfall depth.

Then create a folder in your project's "General Data" folder (e.g. "Boundary Conditions\Rainfall"). Copy the rainfall time series files to the folder.

Then select the created folder, right-click and select Create File -> Empty file.

Save the file in the folder as FillMatrix.dat.

Copy the following contents into the file:

PROPERTY_NAME : precipitation
PROPERTY_UNITS : mm

OUTPUT_FILE : Rainfall.hdf5

GRID_DATA_FILE : DTM.dat

VARIABLE_IN_TIME : 1
START : 2020 3 1 0 0 0
END : 2020 3 2 0 0 0
MAX_TIME_SPAN : 864000
OUTPUT_TIME : 0 3600
SKIP_NULLVALUES : 0
INTERPOLATION_METHOD : 2

IWD_N : 2
MAX_DISTANCE : 100000

The options: PROPERTY_NAME, PROPERTY_UNITS, VARIABLE_IN_TIME, SKIP_NULLVALUES, INTERPOLATION_METHOD, should not be changed. These are defaults for rainfall data in OpenFlows FLOOD. The default interpolation method is Inverse Weighted Distance, which should be used for rainfall data.

In OUTPUT_FILE please define the path to the HDF5 output file that will be generated. In GRID_DATA_FILE please define the path to your simulation gridded Terrain Model File (Grid Data format). See more information in this article.

In START and END please set the initial and end dates (year, month, day, hour, minute, second) that the rainfall HDF5 will contain. The period needs to be the same or contain the period of the simulation.

MAX_TIME_SPAN refers to the maximum time interval (in the rain gauge time series data) for a rainfall rate value to be considered.

OUTPUT_TIME sets the output frequency (time interval between 2 rainfall maps in the HDF5 file).

IWD_N sets the Inverse Weighted Distance power parameter (i.e. the weight of a rainfall gauge for a specific location is given by 1/R where R is the D^n, where D is the distance between the gauge and the grid cell and n is the power parameter.

The for each rainfall gauge add a block like the one shown below:

<begin_station>
NAME : PT-0251
X : -9.1308
Y : 38.9831
VALUE_TYPE : TIMESERIE
FILENAME : PT-0251.srm
DATA_COLUMN : 2
<end_station>

Where X and Y refer to the coordinates of the meteorological station (the same coordinate system as the one defined in the gridded Terrain Model Grid Data file must be used).

FILENAME refers to the time series file containing rainfall data for that gauge, and DATA_COLUMN is the number of the column where the rainfall data is placed.

The rainfall gauge positions don't have to be inside the computational grid area and should cover as much area as possible.

Here is an example of 3 rain gauges over a catchment.

Once the configuration file (FillMatrix.dat) is ready, save it. Then in the same folder, right click and select "Open in Explorer" to open it in Windows Explorer. Then create a simple text file using notepad and copy the following commands inside:

SET EXE="C:\Program Files\Bentley\OpenFlows FLOOD\MohidExe\x86\FillMatrix_release_double_x86.exe"

%EXE%

del Error_and_Messages_1.log
del UsedKeyWords_1.dat

pause

Save the file as RUN.BAT. The file will then be recognized as a batch command file. Double click the file to execute it. A command line dialog as the one below will appear.

At the end a message "Finished..." will appear. Click any key to close the dialog. A HDF5 file will appear on your HDF Files list.

Double click the file to open it in the Map Window. Here is an example of a time frame of the spatially variable rainfall data. The red markers indicate the position of the rainfall gauges.