StreamFlow

Running-StreamFlow

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Table of Content

This page explains how to run a StreamFlow simulation

Introduction

StreamFlow is an extension to the spatially-distributed snow model Alpine3D which allows the user to perform hydrological simulations. Both tools run independently, but Alpine3D needs to be configured in such a way that it outputs a set of files which are expected by StreamFlow as input data (see below). In case you do not know how to run an Alpine3D simulation, please have a look at the Alpine3D documentation.

Once the Alpine3D simulation is run, you can either copy the output data to a new folder or directly perform the StreamFlow simulation in the same folder as Alpine3D (StreamFlow was designed so that no conflict occurs). Similarly to the other tools of the Alpine3D suite, the behavior of StreamFlow is controlled by a configuration file. You can actually use the same one as for Alpine3D, simply adding the keys which are required by StreamFlow (see below).

Additionally to the output data generated by Alpine3D, StreamFlow requires specific files in order to run properly. The latter include the grid delineating the subwatersheds as well as two data files specifying the location and structure of the stream network. All these files can be generated by TauDEM, a tool that was designed to extract various hydrological variables from digital elevation models (see below).

Before being actually run, StreamFlow may need to be calibrated in case it is applied over a new catchment. As for any other hydrological model, this step may be quite computationally intensive since at least a thousand runs are typically required to obtain good parameter estimates. A few guidelines helping you efficiently calibrating the model can be found below.

Once calibrated, the model can eventually be run. The configuration file allows you to control many aspects of the simulation, such as the algorithm which is used to advect water along the stream network, whether stream temperature should be computed or not, or even the rate at which data should be written in the output files.

In summary, the usual procedure for running a StreamFlow simulation is the following:

  1. Configure and run Alpine3D so that it produces the data required by StreamFlow
  2. Create the simulation folder for the StreamFlow simulation, or simply re-use the Alpine3D one
  3. Create the configuration file for the StreamFlow simulation, or simply modify the Alpine3D one by adding the missing keys
  4. Use TauDEM to generate the additional files required by StreamFlow, and copy these files in the simulation folder of StreamFlow
  5. Calibrate StreamFlow
  6. Run the StreamFlow simulation by calling the executable on the command line with the proper options

Each one of these six steps is detailed in a dedicated section below.

Configuration of Alpine3D

Minimum requirements

At the very minimum, StreamFlow requires from Alpine3D the amount of water infiltrating into each subwatershed at every time step. Two possibilities are available for this:

  • In case you already have the grid delineating the subwatersheds (see section about TauDEM below), you can configure Alpine3D so that it directly computes the total amount of water infiltrating into each subwatershed at each time step. The infiltration values will then be written out in SMET files, one for each subwatershed. To this end, you need to copy the grid defining the subwatersheds in folder input\surface-grids of the Alpine3D simulation directory. Please make sure that this grid is in a format which is readable by Alpine3D (TauDEM generates a TIFF grid which needs to be converted; the list of Alpine3D compatible formats can be found in the MeteoIO documentation). You then need to add the following keys in section [INPUT] of the Alpine3D configuration file, with [format] to be replaced with the grid format (e.g. ARC), [folder] with the (absolute or relative) path to the folder in which the grid is located (e.g. ./input/surface-grids), and [file_name] with the grid name (without the path):

        GRID2D              = [format]
        GRID2DPATH          = [folder]
        CATCHMENT           = [file_name]
        CATCHMENT_NUMBERING = TAUDEM
        

    Additionally, the following line has to be added in section [OUTPUT] of the Alpine3D configuration file, where [folder] stands for the (absolute or relative) path to the folder in which the SMET files containing the subwatershed infiltration rates will be generated by Alpine3D:

        CATCHMENTS_PATH = [folder]
        

  • If you do not have the grid delineating the subwatersheds yet, you need to configure Alpine3D so that it outputs the grids containing the water exfiltration rate at the bottom of each soil column. The computation of the total water inflow into each subwatershed will then be performed by StreamFlow itself based on these grids. The writing of the exfiltration grids is triggered by adding the following keys in section [OUTPUT] of the Alpine3D configuration file, with [format] and [folder] to be replaced with the format and the (relative or absolute) path to the folder in which the grids should be written, respectively:

        WRITE_RUNOFF_GRIDS = TRUE
        RUNOFF_GRID2D      = [format]
        RUNOFF_GRID2DPATH  = [folder]
        

    It is recommended that you use the binary NETCDF format for the grids, since it is associated with reduced reading and writing overheads (see section about the NETCDF plugin in the MeteoIO documentation).

Additional requirements

The above configuration of Alpine3D is sufficient in case you intend to compute only discharge and water depth in the stream network. The computation of stream temperature requires additional output from Alpine3D:

  1. Depending on the configuration of StreamFlow, the computation of the temperature of water exfiltrating out of the subwatersheds into the stream network may require soil or air temperature averaged over each subwatershed. It should be mentioned that the value of soil temperature which is expected by StreamFlow corresponds to the average temperature between the soil surface and a given depth (see below). Two cases might occur:
    • In case you have the grid delineating the subwatersheds (see previous section), you can simply proceed as explained in the first bullet point of the above section and add the following lines in section [INPUT] of the Alpine3D configuration file:

          RUNOFF_FILES_EXTRA_DATA = TA TSOIL
          SOIL_TEMPERATURE_DEPTH  = [depth]
          

      [depth] should be replaced with the depth (in meters) down to which soil temperature should be averaged. The first line tells Alpine3D to add the average air and soil temperature to the SMET files which are created for each subwatershed and contain the water infiltration rates.
    • If you have not generated the grid delineating the subwatersheds yet, you should simply follow the steps indicated in point 2 below. In this case, StreamFlow will itself average soil temperature over each subwatershed based on the corresponding grids generated by Alpine3D. It will also average air temperature based on the same meteorological input data as used by Alpine3D.
  2. Additionally, StreamFlow expects soil temperature grids in order to compute the diffusive thermal exchange between the water and the stream bed in each stream cell. Similarly to point 1 above, soil temperature should be understood here as a vertical profile average between the soil surface and a given depth. In order for Alpine3D to output soil temperature grids, the following keys should be added in the Alpine3D configuration file:

        [INPUT]
        SOIL_TEMPERATURE_DEPTH = [depth]
    
        [OUTPUT]
        GRID2D             = [format]
        GRID2DPATH         = [folder]
        GRIDS_WRITE        = TRUE
        GRIDS_START        = 0
        GRIDS_DAYS_BETWEEN = 0.125
        

    In the above lines, [depth] should be replaced with the depth down to which the soil temperature profile must be averaged. Similarly, [format] and [folder] should be replaced by the format and folder in which the soil temperature grids should be written out. The NETCDF format is highly recommended in order to reduce the size and generation time of the output grids. Key GRIDS_DAYS_BETWEEN controls the simulation time interval at which the output grids are generated; it is usually sufficient to have only one grid produced every 3 hours (= 0.125 days) since soil temperature does not evolve very rapidly in time.

Simulation folder

Although not strictly required, it is recommended that you create a new folder for each StreamFlow simulation with the same structure as recommended for Alpine3D. Alternatively, you can simply use the same folder as the one in which the Alpine3D simulation was run.

Configuration file

  • In order to compute stream temperature, StreamFlow requires the values of a selection of meteorological variables (air temperature, wind velocity, relative humidity, and incoming short and long wave radiations) over each stream cell. These values are spatially interpolated by StreamFlow based on the same station measurements or meteo grids than in Alpine3D (see Alpine3D documentation). As such, the same keys are required by StreamFlow that are also expected by Alpine3D to specify the location and format of the meteorological input data. For example, the interpolation of meteorological station measurements in the SMET format and located in folder ./input/meteo can be specified using the following keys:

        [INPUT]
        METEO     = SMET
        METEOPATH = ./input/meteo
        STATION1  = WFJ
        STATION2  = DAV
        STATION3  = SBG
        

Generation of the stream network with TauDEM

Calibration

Calling the executable